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Speaker 1: Get in touch with technology with tech Stuff from how

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Speaker 1: stuff works dot com. Hey there, and welcome to tech Stuff.

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Speaker 1: I'm your host, Jonathan Strickland. I'm an executive producer with

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Speaker 1: how Stuff Works and I love all things tech, and

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Speaker 1: today we are going to continue our episodes about how

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Speaker 1: speakers work and how they are able to take electricity

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Speaker 1: and make those sweet, sweet sounds for your ear holes.

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Speaker 1: So let us jump back with a quick explanation of

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Speaker 1: electro magnetism. So electricity and magnetism are very closely related,

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Speaker 1: and you've likely done the simple physics exercise of creating

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Speaker 1: a basic electro magnet. So you'll take something like an

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Speaker 1: iron nail and you'll wrap insulated copper wire in a

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Speaker 1: coil around the nails several times. The nail acts as

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Speaker 1: a ferromagnetic core. The copper wire coil is a conductor,

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Speaker 1: so connecting the ends of the copper wire to a

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Speaker 1: battery will then allow current to flow through the wire.

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Speaker 1: It'll flow from one end of the battery through the

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Speaker 1: wire down into the other end of the battery. As

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Speaker 1: it goes around this coil, the flow of electricity creates

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Speaker 1: a magnetic field. The nail and coil will behave like

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Speaker 1: a permanent magnet. Would it's an electro magnet, but it

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Speaker 1: will behave like a permanent magnet with a north pole

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Speaker 1: and a south pole. And if you brought it close

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Speaker 1: to a permanent magnet, then the opposite poles would attract

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Speaker 1: each other and the similar poles would repel each other.

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Speaker 1: So if you brought the electro magnets north pole next

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Speaker 1: to a permanent magnets north pole, it would push that

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Speaker 1: other magnet away and the polls will not change. Because

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Speaker 1: the source of electricity is a battery, and batteries provide

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Speaker 1: direct current, which means the current is always going to

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Speaker 1: flow in the same direction. It's never going to reverse.

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Speaker 1: But if you hooked the same nail and coil up

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Speaker 1: to a source of alternation current, things would be very different.

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Speaker 1: With alternating current, the direction of the flow of electricity

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Speaker 1: changes rapidly every second, and as the direction of electricity changes,

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Speaker 1: it affects the magnetic field. With electricity flowing in one direction,

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Speaker 1: the head of the nail might represent the north pole

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Speaker 1: of the magnet, and when the electricity switches to the

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Speaker 1: other direction, the head of the nail will become the

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Speaker 1: south pole of the magnet. And vice versa. You have

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Speaker 1: created a fluctuating magnetic field by running an alternating current

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Speaker 1: through an electro magnet, and you can do some pretty

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Speaker 1: cool stuff with a fluctuating magnetic field. For example, if

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Speaker 1: you bring this apparatus close to a conductive material, you'll

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Speaker 1: induce a change of voltage in that material even without

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Speaker 1: making physical contact between the two. So if you do

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Speaker 1: this with a stable magnetic field, all you'll do is

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Speaker 1: see a very short spike, but then it stops because

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Speaker 1: the magnetic field is not fluctuating. To induce electricity to

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Speaker 1: flow by changing voltage in this other conductor, the magnetic

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Speaker 1: field has to be fluctuating, or the conductor has to

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Speaker 1: be moving in and out of the magnetic field constantly.

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Speaker 1: If you get two coils of copper wire and you

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Speaker 1: make sure the second copper wire has twice as many

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Speaker 1: coils as the first one, you can create a transformer.

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Speaker 1: So imagine you've got your first coil of wire. Let's

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Speaker 1: say it's got ten coils ten ten loops around its core,

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Speaker 1: and you've got a second core with copper wire, but

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Speaker 1: there are twenty loops around the second core. If you

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Speaker 1: run a current through the first coil, it will induce

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Speaker 1: current to flow through the second coil. Moreover, the voltage

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Speaker 1: in the second coil will be higher than the voltage

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Speaker 1: in the first coil because the second coil has twice

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Speaker 1: as many coils as the first one. So the more

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Speaker 1: times you loop a wire around a or the greater

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Speaker 1: the change of voltage is going to be between coil

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Speaker 1: number one and coil number two. This particular version of

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Speaker 1: a transformer would be called a step up transformer because

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Speaker 1: the secondary coil has more turns than the primary coil

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Speaker 1: and steps up the voltage. If the opposite were true,

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Speaker 1: if coil number one had ten coils or ten loops

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Speaker 1: and coil number two had five loops, then that would

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Speaker 1: be a step down transformer. You would lower the voltage

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Speaker 1: from primary to secondary. Transformers are what made alternating current

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Speaker 1: the more viable solution to supplying electricity to homes and

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Speaker 1: businesses back in the early days, because transmitting electricity was

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Speaker 1: all about efficiency. How could you efficiently get electricity from

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Speaker 1: a power plant to where it needed to be? Well?

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Speaker 1: If you used alternating current, you could create transformers and

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Speaker 1: you could step up the voltage two very high levels,

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Speaker 1: and that meant that you could transmit power across power

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Speaker 1: lines much more efficiently. If you didn't do that, you

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Speaker 1: had so much power loss that you would have to

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Speaker 1: have lots of different power generators throughout the region in

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Speaker 1: order to supply all the power needs of your area,

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Speaker 1: at least back in the old days of direct current,

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Speaker 1: because it wasn't easy to step up the voltage. And again,

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Speaker 1: high voltage makes it more efficient to transmit power across

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Speaker 1: long distances, So in the early days, that's why a

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Speaker 1: C went out over d C. These days, you could

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Speaker 1: actually do things a little differently if you wanted to,

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Speaker 1: and you could go with direct DC power if you

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Speaker 1: really wanted to, but it would require a big overhaul

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Speaker 1: of the infrastructure. But transformers made a C much more

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Speaker 1: practical anyway. Electromagnets are pretty awesome now. With speakers, it's

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Speaker 1: not so much about voltage and current as it is

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Speaker 1: about making the diaphragm of the speaker move in precise ways.

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Speaker 1: With speakers, the electrical current acts as both the carrier

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Speaker 1: of information and the means to make the diaphragm move.

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Speaker 1: So you start with a steady magnetic field inside the basket.

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Speaker 1: You can create that steady magnetic field either with permanent

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Speaker 1: magnets like I mentioned before, or with electro magnets, but

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Speaker 1: it remains the same no matter what. The north pole

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Speaker 1: is always going to be the north pole. The south

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Speaker 1: pole is always going to be the south pole. Inside

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Speaker 1: the frame, that field does not change. The voice coil

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Speaker 1: on the cone ends up receiving the variable current that

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Speaker 1: came from the transmitter that represents the recorded sound. Now,

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Speaker 1: remember the way we record sound as we typically will

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Speaker 1: use something like a microphone, and a microphone is essentially

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Speaker 1: a speaker in reverse. A microphone has a diaphragm in

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Speaker 1: it that vibrates in the presence of sound waves. Those

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Speaker 1: vibrations cause fluctuations inside an electric current. You might vary

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Speaker 1: the resistance of the circuit, as we talked about with

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Speaker 1: the the old Johan Philip Rice approach, and by varying

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Speaker 1: those that electric resistance within the circuit, you can fluctuate

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Speaker 1: the electric current and then you can send that to

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Speaker 1: a speaker, though you would typically send it to an

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Speaker 1: amplifier first, but we'll talk about that in a minute.

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Speaker 1: The speaker then essentially reverses this process. It takes those

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Speaker 1: fluctuations sends them through an electro magnet. Which will generate

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Speaker 1: a variable magnetic field in response, which then makes the

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Speaker 1: cone vibrate within the speaker and essentially do the opposite

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Speaker 1: of what the microphones diaphragm was doing and recreate the

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Speaker 1: recorded sound. It's pretty cool and pretty elegant, really. So

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Speaker 1: the electrical signal representing the recorded sound comes into the speaker,

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Speaker 1: feeds into the voice coil creates this fluctuating magnetic field.

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Speaker 1: The field interacts with the permanent magnetic field inside the basket,

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Speaker 1: either pulling the diaphragm forward in the basket and thus

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Speaker 1: pushing air outward, or pulling the cone back towards the

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Speaker 1: back of the basket and allowing air to come further

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Speaker 1: in by creating that lower pressure. And these fluctuations happen

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Speaker 1: at high frequencies, so the I fragm is moving very

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Speaker 1: rapidly inside the basket. It's not just pushing out then

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Speaker 1: pulling in. It's doing this hundreds or thousands of times

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Speaker 1: per second, and it increases or decreases the air pressure

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Speaker 1: as the cone pushes those air molecules or suddenly moves away,

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Speaker 1: creating more space for them. And because sound is vibration,

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Speaker 1: those air molecules carry the sound up to our ears

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Speaker 1: and then we rock out to a C d C

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Speaker 1: or whatever band you happen to like. That isn't nearly

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Speaker 1: as cool as a C d C. Now, keep in

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Speaker 1: mind what I have described is how a driver works.

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Speaker 1: A speaker can and often does have more than one driver,

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Speaker 1: and drivers come in different shapes, sizes, and purposes. So

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Speaker 1: let's talk a little bit about what those are and

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Speaker 1: what they do, and why you need to have different

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Speaker 1: ones in the first place. Actually, that last question is

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Speaker 1: the easiest answer right away. Remember again, sound is vibration,

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Speaker 1: and low frequency sounds have longer wave forms. The points

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Speaker 1: of high and low pressure are further apart from each

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Speaker 1: other than with high frequency sounds. If you could actually

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Speaker 1: see the changes in air pressure due to sound, you

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Speaker 1: would see that the low frequency sounds have these larger

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Speaker 1: gaps between the high and low pressure points in the

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Speaker 1: waves as they move out from the source of sound.

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Speaker 1: So you need a cone diaphragm that can vibrate at

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Speaker 1: a slower frequency and push air effectively at that speed.

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Speaker 1: For that reason, you would typically go with a heavier,

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Speaker 1: larger diaphragm, both because the wavelengths of sound are longer.

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Speaker 1: If you're looking at the lower frequencies, and because making

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Speaker 1: the material heavy gives it greater inertia, it takes more

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Speaker 1: force to move the diaphragm, and it will move at

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Speaker 1: a pace that will reproduce those low frequency sounds you want.

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Speaker 1: This type of speaker falls into the whiffer or subwhiffer categories.

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Speaker 1: These are the speakers that create the base sounds. A

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Speaker 1: subwhiffer tends to handle frequencies from around twenty hurts to

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Speaker 1: two hurts. Think of a hurts as how long it

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Speaker 1: takes a wave to pass through a given point in

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Speaker 1: one se end, or how many waves can pass through

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Speaker 1: a given point in one second. Al Right, guys, we

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Speaker 1: got some more to chat about with speakers. Before I

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Speaker 1: jump into that, Let's take a quick break to thank

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Speaker 1: our sponsor. Human hearing ranges from twenty hurts, which is

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Speaker 1: twenty waves passing a given point in one second, to

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Speaker 1: twenty killer hurts or twenty thousand waves passing through a

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Speaker 1: point in one second. This really tells you more about

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Speaker 1: the wavelength of the wave itself and thus the frequency

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Speaker 1: and then the pitch. Remember, the lower frequencies are the

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Speaker 1: lower pitches. The higher frequencies are the higher pitches, and

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Speaker 1: that's the frequency range for typical human hearing twenty hurts

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Speaker 1: to twenty thousand hurts. Now, I can tell you from

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Speaker 1: my experience using a frequency sweeper which will slowly go

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Speaker 1: through a selection of frequencies that is all set at

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Speaker 1: the same volume, so you get a standard volume across

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Speaker 1: us all of them, that while I can technically hear

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Speaker 1: stuff at twenty hurts, it's not until you hit a

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Speaker 1: frequency of about fifty hurts that it quote unquote sounds

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Speaker 1: loud to me, even though actual volume of the two

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Speaker 1: tones remains the same, so the amplitude is exactly the same,

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Speaker 1: But until you get to a frequency of about fifty hurts,

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Speaker 1: it just doesn't sound loud to me because my ears

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Speaker 1: are not great at picking up those lower, super low frequencies. Also,

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Speaker 1: I should mention that while sound waves come in different frequencies,

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Speaker 1: sound itself travels at a speed that is dependent upon

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Speaker 1: the medium through which it travels. So, in other words,

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Speaker 1: low frequency sounds and high frequency sounds travel at the

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Speaker 1: same speed through the same medium. Otherwise you would have

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Speaker 1: all the high pitched sounds hitting your ears before the

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Speaker 1: low pitched ones and conducting an orchestra would drive you crazy.

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Speaker 1: The speed of sound is defined as the distance traveled

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Speaker 1: by a sound wave in a certain unit of time.

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Speaker 1: But hey, Jonathan, some of you might be saying you

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Speaker 1: were just talking about frequencies. If a high frequency sound

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Speaker 1: has twenty sound waves pass a certain point in the second,

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Speaker 1: and a low frequency sound has twenty waves passing that

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Speaker 1: same point in the second, are they traveling at different speeds? No,

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Speaker 1: they're not. This is easier to imagine if we take

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Speaker 1: an analogy. So let's say you're standing on the side

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Speaker 1: of the road. Every single vehicle going past you on

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Speaker 1: this one way road is traveling at a smooth twenty

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Speaker 1: miles per hour or about thirty two kilometers per hour

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Speaker 1: if you prefer. But they're all going that speed. Doesn't

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Speaker 1: matter what kind of car it is, they're all going

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Speaker 1: exactly twenty miles or thirty two kilometers per hour. Some

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Speaker 1: of these vehicles are very tiny, little smart cars. Some

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Speaker 1: of them are super long extended buses, but they're all

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Speaker 1: traveling at that same speed. So even though they're going

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Speaker 1: at the same speed, the buses take more time to

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Speaker 1: pass you than the smart cars do because the buses

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Speaker 1: are longer in the time it takes one super long

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Speaker 1: bus to go buy you, like the front passes you

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Speaker 1: and you time it out. Maybe four smart cars could

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Speaker 1: go buy you and that same amount of time, even

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Speaker 1: though they're all going at twenty miles per hour. The

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Speaker 1: same is true with sound waves, so we're not just

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Speaker 1: talking about speed but wavelength. So low frequency sounds and

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Speaker 1: high frequency sounds are traveling at the same speed. It's

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Speaker 1: just you can fit more of the waves in at

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Speaker 1: that time than others because of the length. All right

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Speaker 1: back to the speed of sound. Now, I cannot give

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Speaker 1: you a standard speed of sound for all occasions because

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Speaker 1: the speed of sound depends on a lot of little things,

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Speaker 1: For example, how much moisture is in the air or

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Speaker 1: how cold is the air. Sound passes through the air,

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Speaker 1: and air is made up of gases, and gases are

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Speaker 1: made up of molecules. So as you heat up a gas,

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Speaker 1: the molecules move apart from each other and they bounce

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Speaker 1: around more. They're more able to move. As gas is cool,

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Speaker 1: the molecules pack around together and they move around less,

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Speaker 1: so they get more tightly packed. So a cold gas

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Speaker 1: will transmit sound at a slightly slower speed than a

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Speaker 1: warm gas will if the temperature outside is sixty eight

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Speaker 1: degrees fahrenheit or about twenties celsius and the air is dry,

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Speaker 1: sound will travel at one thousand one per second or

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Speaker 1: three forty three meters per second. And it doesn't matter

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Speaker 1: what frequency sound waves you're working with, that's the speed

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Speaker 1: they're going to travel at. And again, at different temperatures

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Speaker 1: and there are different media, sound will travel at a

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Speaker 1: different speed. All right. Now, let's go back to the

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Speaker 1: different types of drivers. After you handled the sub whoffers

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Speaker 1: and the whoofers, well, the whoffers will still handle lower frequencies,

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Speaker 1: but sub whoffers are are specialized whoffers, largely because they

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Speaker 1: will frequently be paired with special circuits and cabinets dedicated

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Speaker 1: to creating those very very low frequencies in an effort

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Speaker 1: to produce a specific quality of sound, such as let's

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Speaker 1: say you're watching an action film and something done blowed

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Speaker 1: up real good. You want to have that rumbly low

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Speaker 1: base for those moments, you know, the kind where you

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Speaker 1: can actually feel it because it's vibrating the chair and

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Speaker 1: the air around you, and so it's it's that kind

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Speaker 1: of rumble you can feel in your chest well. That

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Speaker 1: frequently means you need a dedicated subwhiffer unit that has

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Speaker 1: its own power supply to generate the vibrations with enough

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Speaker 1: force necessary to create that effect. So it's not just

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Speaker 1: the speed but how hard it's pushing. After subwhiffers and whoffers,

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Speaker 1: you've got mid range drivers or mid range speakers, and

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Speaker 1: as the name suggests, these drivers are responsible for producing

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Speaker 1: sounds in the middle range frequencies of human hearing. A

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Speaker 1: typical range might include two fifty hurts to two thousand hurts.

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Speaker 1: You may have also heard the term squawker when referencing

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Speaker 1: mid range speakers. They're made of lighter materials and they

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Speaker 1: can vibrate at higher frequencies than whoffers and subwhiffers, which

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Speaker 1: is necessary to create those mid range tones. And then

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Speaker 1: you have tweeter speakers. These are made of the lightest

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Speaker 1: weight material and they vibrate the fastest in an effort

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Speaker 1: to reproduce frequencies on the upper levels of human hearing,

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Speaker 1: which tends to be between two thousand and twenty thou

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Speaker 1: hurts at least for consumer speakers. There are tweeters that

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Speaker 1: can be made for special purposes that can generate sound

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Speaker 1: frequencies well above the range of human hearing, some of

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Speaker 1: them as high up as a hundred killer hurts or

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Speaker 1: one hundred thousand hurts. That's five times higher than the

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Speaker 1: highest frequency the average human is capable of perceiving. So

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Speaker 1: why would you want a tweeter that could go beyond

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Speaker 1: the range of human hearing. Well, you might use it

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Speaker 1: for scientific research purposes, like finding out what high high

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Speaker 1: high pitches the ultrasonic pitches might due to affect animal behavior.

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Speaker 1: So you might be able to do that to learn

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Speaker 1: how high a pitch a dog might be able to hear,

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Speaker 1: for example, because dogs can hear at a different range

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Speaker 1: than humans can. Or you might want to do experiments

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Speaker 1: to see if those imperceptible frequencies have an effect on

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Speaker 1: the sounds we can here. So there are audio files

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Speaker 1: who insist that frequencies beyond the human range of hearing

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Speaker 1: can change the quality of the sounds that we do here,

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Speaker 1: and thus it's imperative to get a sound system and

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Speaker 1: a type of media capable of reproducing sound frequencies at

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Speaker 1: every level if you want a true reproduction of an

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Speaker 1: original sounds quality. Uh this falls into the realm of

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Speaker 1: psychoacoustics the study of sound perception. Because hearing involves processes

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Speaker 1: in the brain, there is a subjective component to it

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Speaker 1: that cannot be easily described through physics. We can talk

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Speaker 1: all about the physics of sound waves and sound propagation,

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Speaker 1: but ultimately, when it comes to the way we experience sound,

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Speaker 1: we have to take gray matter into account, and that

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Speaker 1: gets tricky since our experience of perceiving sound can depend

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Speaker 1: upon other things unrelated to the actual physics of the

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Speaker 1: sound itself. For example, if I were to tell you

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Speaker 1: that I have a sound system, and I've set it

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Speaker 1: up and it consists of the most expensive and most

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Speaker 1: technologically advanced components, and the media that was going to

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Speaker 1: play represented the most true reproduction of an actual sound,

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Speaker 1: that might be an enough to influence your perception of

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Speaker 1: the sound. Even if what I was really using was

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Speaker 1: just good equipment, not the best, but just good stuff.

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Speaker 1: Even if all all that stuff I told you wasn't true,

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Speaker 1: your perception of sound might make it seem like you're

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Speaker 1: listening to the most perfect reproduction of the original performance

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Speaker 1: as could be attained. Or if I did play a

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Speaker 1: sound back on what really was an amazing sound system,

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Speaker 1: but before I did it, I made a whole bunch

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Speaker 1: of apologies for how the system I was using could

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Speaker 1: not faithfully represent high tones, or had a very weak

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Speaker 1: base output, or something like that. You might perceive the

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Speaker 1: playback as following these trends that I had mentioned, even

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Speaker 1: if scientific recording instruments were to show that the playback

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Speaker 1: didn't suffer from those problems at all. All that being said,

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Speaker 1: the psychological aspect of how we perceive sound does have limitations.

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Speaker 1: No amount of snake oil salesmanship is going to convince

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Speaker 1: you that a truly subpar stereo system is capable of

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Speaker 1: reproducing the glory of the Philharmonic Orchestra, for example. But

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Speaker 1: because there is the subjective element and how we perceive sound,

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Speaker 1: there's the opportunity to exploit that element and make a

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Speaker 1: lot of money in the process. I've talked before about

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Speaker 1: how certain manufacturers have used this to market high end

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Speaker 1: audio equipment, and some of that has little to no

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Speaker 1: scientific evidence to back up the claims that they make

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Speaker 1: about those gadgets, and yet they're able to set exorbitant

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Speaker 1: prices for components that audio files will cover it because

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Speaker 1: they're always in a quest to get that perfect representation

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Speaker 1: of a sound. Uh so this stuff does happen. I

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Speaker 1: also covered this when I talked about MP three compression,

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Speaker 1: because if you remember an m P three's part of

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Speaker 1: the compression strategy is to take all the different parts

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Speaker 1: of a sound that we humans typically don't notice, and

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Speaker 1: you just cut them. You get rid of them, because

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Speaker 1: that way you cut down on the size of the

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Speaker 1: sound file. The strategy is, if you can't perceive it,

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Speaker 1: then we don't need it in the information. We can

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Speaker 1: just cut it that. Audio files say no, if you

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Speaker 1: do that, it affects the off that we can here,

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Speaker 1: and thus you are changing the nature of the audio recording.

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Speaker 1: Just because you couldn't hear the thing doesn't mean the

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Speaker 1: thing wasn't doing something else. I think the jury is

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Speaker 1: still out on that in a large part. I mean,

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Speaker 1: there are some legitimate arguments to make about harmonics and

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Speaker 1: things that do come into play, but I'm not sure

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Speaker 1: it gets to the level of subtlety that a lot

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Speaker 1: of audio files argue. At least I don't see the

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Speaker 1: scientific evidence supporting it. That doesn't mean it's wrong, It

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Speaker 1: just means I haven't seen the evidence supporting it. Anyway.

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Speaker 1: As soon as we come back. I'm gonna go into

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Speaker 1: talking about amplification and why that's important, but first let's

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Speaker 1: take another quick break to thank our sponsor. All right. Now,

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Speaker 1: Back when I was talking about the development of the loudspeaker,

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Speaker 1: I mentioned that Rice and Kellogg observed there needed to

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Speaker 1: be advancements and amplification, and by that they meant there

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Speaker 1: needed to be a way to boost the electrical signal

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Speaker 1: from the risk the transmitter the microphone in order to

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Speaker 1: give a speaker enough oomph to vibrate at a force

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Speaker 1: strong enough to play back the sounds at a suitable volume.

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Speaker 1: Without amplifiers, the signal strength might only allow a speaker

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Speaker 1: to play back a sound at a low volume, or

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Speaker 1: if the signal is very weak, it might not even

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Speaker 1: move the speaker significantly enough at all to create any

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Speaker 1: real sound. The reason the signal tends to be weak

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Speaker 1: goes back to the limitations we face when we record

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Speaker 1: sound in the first place. So using the microphone effect,

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Speaker 1: we transform sound into electrical signals by making the microphones

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Speaker 1: diaphragm vibrate, mimicking the way our ear drums work. Right,

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Speaker 1: So it's like we're speaking into someone's ear when we

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Speaker 1: talk into a microphone. Then we transform sound into electrical

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Speaker 1: signals by making that microphone diaphone vibrate, and those small

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Speaker 1: vibrations introduced fluctuations into an electrical signal in some way.

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Speaker 1: But for sound to affect the diaphragm at all, the

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Speaker 1: diaphragm has to be very lightweight, very sensitive, and it

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Speaker 1: has to make very small movements. Otherwise we'd have to

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Speaker 1: make sound an enormous amplitudes or volume in order to

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Speaker 1: generate the force necessary to vibrate the diaphragm. So it

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Speaker 1: has to be very lightweight, very very sensitive, and it's

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Speaker 1: moving in a very small distance, so it can only

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Speaker 1: make tiny changes in electrical current or generate a very

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Speaker 1: tiny electrical current. Now that's good enough for the purposes

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Speaker 1: of recording the sound. You can do that. You can

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Speaker 1: use that to record sound. It's fine because it can

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Speaker 1: record at those tiny details. But if you want to

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Speaker 1: play the sound back on a speaker, you have to

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Speaker 1: boost that signal in order to drive the speakers to

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Speaker 1: physically move them. You want to make the signal more powerful,

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00:22:48,320 --> 00:22:51,119
Speaker 1: but you also want to keep all the fluctuations of

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Speaker 1: the signal, all the dynamics of the signal so that

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00:22:54,840 --> 00:22:58,960
Speaker 1: way you can represent when a song gets louder or

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Speaker 1: more quiet, or when one element is taking over over

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Speaker 1: another element. All of these things are very subtle, and

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Speaker 1: you have to preserve that. So you want the signal

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Speaker 1: not just to be boosted, but for all the different

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Speaker 1: fluctuations of that signal to be represented in that boost.

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Speaker 1: You want it all to be at the same relative

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Speaker 1: strength as they were in the weaker signal. Now, an

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Speaker 1: amplifier does this through the use of two separate circuits.

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Speaker 1: The first circuit is the input circuit. That's the weaker

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Speaker 1: of the two signals, that's the one that's coming from

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Speaker 1: the microphone. The second circuit is your output circuit, which

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Speaker 1: sends a stronger signal out to the speakers, and it

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Speaker 1: draws upon the amplifier's power supply to boost the signal.

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Speaker 1: So you have an amplifier, it has its own power supply.

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Speaker 1: It's generating the signal that's going through this output circuit.

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Speaker 1: The power going through the output circuit is a direct current,

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Speaker 1: so it's flowing in a set direction. It does not change.

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00:23:55,680 --> 00:23:58,160
Speaker 1: If you have an amplifier and you've hooked it directly

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Speaker 1: up to your house is ultra nating current. There's a

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Speaker 1: power supply element inside the amplifier that converts it from

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Speaker 1: alternating current to direct current. Now, think of the output

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Speaker 1: circuit as always pushing a strong signal out towards the speakers.

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Speaker 1: It's just most of the time this signal is not

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Speaker 1: carrying any information. But when the amplifiers on, that's what

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Speaker 1: it's doing. It's pushing the strong signal out to the speakers.

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00:24:23,200 --> 00:24:26,680
Speaker 1: The input circuit's job is to use the original weak

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Speaker 1: electrical signal as a way to vary the resistance in

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00:24:30,400 --> 00:24:35,160
Speaker 1: the output circuit, so the variable resistance recreates the voltage

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00:24:35,160 --> 00:24:38,560
Speaker 1: fluctuations in the original signal. So what you're doing is

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Speaker 1: you've got this strong signal going out, use the weak

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Speaker 1: signal to introduce the same fluctuations into the strong signal,

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Speaker 1: and then the strong signal will reflect the weaker one.

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Speaker 1: It will be exactly the same, except stronger. In the

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00:24:54,119 --> 00:24:57,800
Speaker 1: good old days, amplifiers relied upon vacuum tubes as an

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00:24:57,800 --> 00:25:02,119
Speaker 1: integral component, and in fact, i'm amplifiers still do, particularly

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00:25:02,160 --> 00:25:07,080
Speaker 1: for stuff like professional electric guitar amplifiers. There are professional

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00:25:07,160 --> 00:25:10,760
Speaker 1: musicians who swear by vacuum tube amplifiers and they will

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00:25:10,800 --> 00:25:14,840
Speaker 1: not use anything else. Vacuum tubes are pretty interesting technology

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00:25:14,880 --> 00:25:17,160
Speaker 1: and they date back to the early twentieth century. So

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00:25:17,400 --> 00:25:20,479
Speaker 1: let's talk about how they work for just a second. First,

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00:25:20,920 --> 00:25:23,280
Speaker 1: they look a lot like light bulbs, and in fact,

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00:25:23,280 --> 00:25:27,320
Speaker 1: they operate very similar to light bulbs. They are glass tubes.

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00:25:27,640 --> 00:25:31,160
Speaker 1: Inside this glass tube is a filament like a light bulb.

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00:25:31,160 --> 00:25:34,639
Speaker 1: The filament inside uses electrical resistance to heat up. The

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00:25:34,720 --> 00:25:38,480
Speaker 1: filament either contains or is somehow wrapped around a material

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00:25:38,600 --> 00:25:42,240
Speaker 1: like tungsten, which, when it's heated to very high temperatures,

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00:25:42,480 --> 00:25:46,440
Speaker 1: starts to boil off electrons. That would be the cathode

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00:25:46,880 --> 00:25:50,040
Speaker 1: of the vacuum tube. It's the source of electrons. The

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00:25:50,040 --> 00:25:53,359
Speaker 1: electrons accept only so much energy, and then after that

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00:25:53,400 --> 00:25:56,879
Speaker 1: they effectively jump ship. They're ready to burst off of

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00:25:56,960 --> 00:26:00,359
Speaker 1: the atoms that they were previously connected to. Now, also

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00:26:00,400 --> 00:26:03,320
Speaker 1: inside the vacuum tube is a plate that has a

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00:26:03,359 --> 00:26:07,240
Speaker 1: relative positive charge to it compared to the cathode. That's

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00:26:07,320 --> 00:26:11,280
Speaker 1: called the anode. The electrons are negatively charged, and so

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00:26:11,320 --> 00:26:15,440
Speaker 1: they're attracted to the positively charged anode, and the negative

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00:26:15,520 --> 00:26:20,040
Speaker 1: charged electrons flow towards the positively charged anode. Now, if

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00:26:20,040 --> 00:26:22,399
Speaker 1: this were all there were to a vacuum tube, it

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00:26:22,400 --> 00:26:25,280
Speaker 1: would just be a diode. That means it would be

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00:26:25,280 --> 00:26:27,879
Speaker 1: an element in a circuit that would allow electricity to

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00:26:27,920 --> 00:26:31,159
Speaker 1: pass one way from the cathode to anode, but not

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00:26:31,359 --> 00:26:34,479
Speaker 1: back the other way. However, there's a third element, and

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00:26:34,560 --> 00:26:38,080
Speaker 1: that's what creates the amplification effect. That element is a

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00:26:38,119 --> 00:26:42,000
Speaker 1: grid of spiral wires or a mesh material. The acts

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00:26:42,000 --> 00:26:45,199
Speaker 1: as a sort of control grid or cage between the

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00:26:45,280 --> 00:26:50,080
Speaker 1: cathode and the anode, so it essentially surrounds the cathode. Now,

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00:26:50,080 --> 00:26:53,000
Speaker 1: if you apply a voltage to this control grid that

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00:26:53,160 --> 00:26:56,560
Speaker 1: is lower than the cathode itself, it reduces the amount

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00:26:56,560 --> 00:26:59,800
Speaker 1: of current passing from cathode to anode. By placing a

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00:27:00,040 --> 00:27:03,680
Speaker 1: large positive voltage on the plate and then feeding a

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00:27:03,720 --> 00:27:07,160
Speaker 1: signal to the control grid, you can affect the voltage

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00:27:07,200 --> 00:27:10,320
Speaker 1: across the load on the circuit. So you make tiny

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00:27:10,440 --> 00:27:13,000
Speaker 1: changes in the control grid's voltage and you get a

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00:27:13,080 --> 00:27:16,240
Speaker 1: much larger change across the load of the circuit amplifying

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00:27:16,280 --> 00:27:19,680
Speaker 1: the signal. So again, you you put a large positive

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00:27:19,720 --> 00:27:24,000
Speaker 1: voltage on this plate, you feed the input signal into

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00:27:24,320 --> 00:27:29,680
Speaker 1: the the control grid, and then you amplify that signal

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00:27:30,400 --> 00:27:33,880
Speaker 1: across the entire load, and that load would typically involve

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00:27:34,560 --> 00:27:38,399
Speaker 1: speakers or an amplifier. These days, most amplifiers do not

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00:27:38,640 --> 00:27:42,919
Speaker 1: use vacuum tubes. Instead, we use solid state transistors. To

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00:27:43,000 --> 00:27:46,919
Speaker 1: describe how those transistors work gets a little complicated, but

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00:27:47,000 --> 00:27:49,840
Speaker 1: in general, a basic transistor has three components. You've got

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00:27:49,880 --> 00:27:53,800
Speaker 1: an emitter, a base, and a collector. The emitter and

486
00:27:53,840 --> 00:27:58,439
Speaker 1: the collector are both in type UH semiconductors, meaning that

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00:27:58,480 --> 00:28:02,119
Speaker 1: they have more elect trons. They have a surplus of

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00:28:02,119 --> 00:28:04,040
Speaker 1: electrons there. You can think of it almost like a

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00:28:04,080 --> 00:28:07,919
Speaker 1: negative charge. The base is a P type semiconductor. It's

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00:28:07,960 --> 00:28:11,480
Speaker 1: sandwiched between the emitter and the collector. It has what

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00:28:11,600 --> 00:28:15,160
Speaker 1: would we would call a positive charge or holes for electrons.

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00:28:15,720 --> 00:28:18,760
Speaker 1: Feeding the input current between the emitter and the base

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00:28:19,200 --> 00:28:21,960
Speaker 1: creates a much larger output current between the emitter and

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00:28:22,000 --> 00:28:25,720
Speaker 1: the collector, thus amplifying the signal. Now, the output signal

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00:28:25,800 --> 00:28:30,600
Speaker 1: should ideally match the input signal exactly, except again, everything

496
00:28:30,720 --> 00:28:34,320
Speaker 1: is just bigger as an amplified and that signal would

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00:28:34,320 --> 00:28:36,480
Speaker 1: be strong enough to do the work of moving those

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00:28:36,520 --> 00:28:41,400
Speaker 1: speaker diaphragms and generating the sounds we enjoy now. In

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00:28:41,440 --> 00:28:44,600
Speaker 1: a future episode I'm going to cover headphones. Headphones are

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00:28:44,680 --> 00:28:48,440
Speaker 1: very much closely related to speakers. Obviously they are essentially

501
00:28:48,600 --> 00:28:51,440
Speaker 1: very small speakers that fit on your ears. But the

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00:28:51,520 --> 00:28:54,760
Speaker 1: history of headphones has its own story that we need

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00:28:54,760 --> 00:28:57,640
Speaker 1: to cover, and it's very fascinating. But it's too much

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00:28:57,680 --> 00:28:59,840
Speaker 1: to cover in just one episode. But I hope you

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00:28:59,880 --> 00:29:02,400
Speaker 1: and joined this episode, MICHAELA. And if you guys have

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00:29:02,480 --> 00:29:05,960
Speaker 1: episode ideas for future tech Stuff shows, then send me

507
00:29:06,000 --> 00:29:09,000
Speaker 1: a message. The email address for tech Stuff is tech

508
00:29:09,040 --> 00:29:11,800
Speaker 1: Stuff at how stuff works dot com, or you can

509
00:29:11,880 --> 00:29:14,640
Speaker 1: drop me a line on Facebook or Twitter. The handle

510
00:29:14,680 --> 00:29:17,320
Speaker 1: for both of those is text stuff h s W.

511
00:29:18,000 --> 00:29:20,000
Speaker 1: Let me know what you think. Maybe there's a topic

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00:29:20,040 --> 00:29:21,840
Speaker 1: you want me to cover. It could be a technology,

513
00:29:22,080 --> 00:29:24,480
Speaker 1: could be a company, it could be an important person

514
00:29:24,520 --> 00:29:26,840
Speaker 1: in tech. Maybe there's an interview you would like me

515
00:29:26,880 --> 00:29:28,760
Speaker 1: to conduct, or a guest you would like me to

516
00:29:28,800 --> 00:29:31,360
Speaker 1: have on the show as a guest host. I would

517
00:29:31,360 --> 00:29:34,000
Speaker 1: be happy to hear all of those suggestions. Again, write

518
00:29:34,000 --> 00:29:37,320
Speaker 1: me at tech stuff at how stuff works dot com. Also,

519
00:29:37,400 --> 00:29:39,840
Speaker 1: remember we have an Instagram account. Go make sure you're

520
00:29:39,880 --> 00:29:43,080
Speaker 1: following that and you can watch me record this show

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00:29:43,160 --> 00:29:46,680
Speaker 1: live on Wednesdays and Friday's just go to twitch dot

522
00:29:46,760 --> 00:29:50,000
Speaker 1: tv slash tech Stuff. You'll see the schedule there. I

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00:29:50,040 --> 00:29:51,720
Speaker 1: hope to see you there. You can join in, be

524
00:29:51,800 --> 00:29:54,680
Speaker 1: in the chat room, make jokes at my expense. I'm

525
00:29:54,720 --> 00:29:57,560
Speaker 1: getting used to it. The keyword there's getting used to it.

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00:29:58,240 --> 00:30:07,000
Speaker 1: And I'll talk to you again really soon for more

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00:30:07,000 --> 00:30:09,280
Speaker 1: on this and thousands of other topics because at how

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00:30:09,360 --> 00:30:20,200
Speaker 1: stuff Works dot com