Speaker 1: Get in touch with technology with tech Stuff from how
Speaker 1: stuff works dot com. Hey there, and welcome to tech Stuff.
Speaker 1: I'm your host, Jonathan Strickland. I'm an executive producer with
Speaker 1: how Stuff Works and I love all things tech, and
Speaker 1: today we are going to continue our episodes about how
Speaker 1: speakers work and how they are able to take electricity
Speaker 1: and make those sweet, sweet sounds for your ear holes.
Speaker 1: So let us jump back with a quick explanation of
Speaker 1: electro magnetism. So electricity and magnetism are very closely related,
Speaker 1: and you've likely done the simple physics exercise of creating
Speaker 1: a basic electro magnet. So you'll take something like an
Speaker 1: iron nail and you'll wrap insulated copper wire in a
Speaker 1: coil around the nails several times. The nail acts as
Speaker 1: a ferromagnetic core. The copper wire coil is a conductor,
Speaker 1: so connecting the ends of the copper wire to a
Speaker 1: battery will then allow current to flow through the wire.
Speaker 1: It'll flow from one end of the battery through the
Speaker 1: wire down into the other end of the battery. As
Speaker 1: it goes around this coil, the flow of electricity creates
Speaker 1: a magnetic field. The nail and coil will behave like
Speaker 1: a permanent magnet. Would it's an electro magnet, but it
Speaker 1: will behave like a permanent magnet with a north pole
Speaker 1: and a south pole. And if you brought it close
Speaker 1: to a permanent magnet, then the opposite poles would attract
Speaker 1: each other and the similar poles would repel each other.
Speaker 1: So if you brought the electro magnets north pole next
Speaker 1: to a permanent magnets north pole, it would push that
Speaker 1: other magnet away and the polls will not change. Because
Speaker 1: the source of electricity is a battery, and batteries provide
Speaker 1: direct current, which means the current is always going to
Speaker 1: flow in the same direction. It's never going to reverse.
Speaker 1: But if you hooked the same nail and coil up
Speaker 1: to a source of alternation current, things would be very different.
Speaker 1: With alternating current, the direction of the flow of electricity
Speaker 1: changes rapidly every second, and as the direction of electricity changes,
Speaker 1: it affects the magnetic field. With electricity flowing in one direction,
Speaker 1: the head of the nail might represent the north pole
Speaker 1: of the magnet, and when the electricity switches to the
Speaker 1: other direction, the head of the nail will become the
Speaker 1: south pole of the magnet. And vice versa. You have
Speaker 1: created a fluctuating magnetic field by running an alternating current
Speaker 1: through an electro magnet, and you can do some pretty
Speaker 1: cool stuff with a fluctuating magnetic field. For example, if
Speaker 1: you bring this apparatus close to a conductive material, you'll
Speaker 1: induce a change of voltage in that material even without
Speaker 1: making physical contact between the two. So if you do
Speaker 1: this with a stable magnetic field, all you'll do is
Speaker 1: see a very short spike, but then it stops because
Speaker 1: the magnetic field is not fluctuating. To induce electricity to
Speaker 1: flow by changing voltage in this other conductor, the magnetic
Speaker 1: field has to be fluctuating, or the conductor has to
Speaker 1: be moving in and out of the magnetic field constantly.
Speaker 1: If you get two coils of copper wire and you
Speaker 1: make sure the second copper wire has twice as many
Speaker 1: coils as the first one, you can create a transformer.
Speaker 1: So imagine you've got your first coil of wire. Let's
Speaker 1: say it's got ten coils ten ten loops around its core,
Speaker 1: and you've got a second core with copper wire, but
Speaker 1: there are twenty loops around the second core. If you
Speaker 1: run a current through the first coil, it will induce
Speaker 1: current to flow through the second coil. Moreover, the voltage
Speaker 1: in the second coil will be higher than the voltage
Speaker 1: in the first coil because the second coil has twice
Speaker 1: as many coils as the first one. So the more
Speaker 1: times you loop a wire around a or the greater
Speaker 1: the change of voltage is going to be between coil
Speaker 1: number one and coil number two. This particular version of
Speaker 1: a transformer would be called a step up transformer because
Speaker 1: the secondary coil has more turns than the primary coil
Speaker 1: and steps up the voltage. If the opposite were true,
Speaker 1: if coil number one had ten coils or ten loops
Speaker 1: and coil number two had five loops, then that would
Speaker 1: be a step down transformer. You would lower the voltage
Speaker 1: from primary to secondary. Transformers are what made alternating current
Speaker 1: the more viable solution to supplying electricity to homes and
Speaker 1: businesses back in the early days, because transmitting electricity was
Speaker 1: all about efficiency. How could you efficiently get electricity from
Speaker 1: a power plant to where it needed to be? Well?
Speaker 1: If you used alternating current, you could create transformers and
Speaker 1: you could step up the voltage two very high levels,
Speaker 1: and that meant that you could transmit power across power
Speaker 1: lines much more efficiently. If you didn't do that, you
Speaker 1: had so much power loss that you would have to
Speaker 1: have lots of different power generators throughout the region in
Speaker 1: order to supply all the power needs of your area,
Speaker 1: at least back in the old days of direct current,
Speaker 1: because it wasn't easy to step up the voltage. And again,
Speaker 1: high voltage makes it more efficient to transmit power across
Speaker 1: long distances, So in the early days, that's why a
Speaker 1: C went out over d C. These days, you could
Speaker 1: actually do things a little differently if you wanted to,
Speaker 1: and you could go with direct DC power if you
Speaker 1: really wanted to, but it would require a big overhaul
Speaker 1: of the infrastructure. But transformers made a C much more
Speaker 1: practical anyway. Electromagnets are pretty awesome now. With speakers, it's
Speaker 1: not so much about voltage and current as it is
Speaker 1: about making the diaphragm of the speaker move in precise ways.
Speaker 1: With speakers, the electrical current acts as both the carrier
Speaker 1: of information and the means to make the diaphragm move.
Speaker 1: So you start with a steady magnetic field inside the basket.
Speaker 1: You can create that steady magnetic field either with permanent
Speaker 1: magnets like I mentioned before, or with electro magnets, but
Speaker 1: it remains the same no matter what. The north pole
Speaker 1: is always going to be the north pole. The south
Speaker 1: pole is always going to be the south pole. Inside
Speaker 1: the frame, that field does not change. The voice coil
Speaker 1: on the cone ends up receiving the variable current that
Speaker 1: came from the transmitter that represents the recorded sound. Now,
Speaker 1: remember the way we record sound as we typically will
Speaker 1: use something like a microphone, and a microphone is essentially
Speaker 1: a speaker in reverse. A microphone has a diaphragm in
Speaker 1: it that vibrates in the presence of sound waves. Those
Speaker 1: vibrations cause fluctuations inside an electric current. You might vary
Speaker 1: the resistance of the circuit, as we talked about with
Speaker 1: the the old Johan Philip Rice approach, and by varying
Speaker 1: those that electric resistance within the circuit, you can fluctuate
Speaker 1: the electric current and then you can send that to
Speaker 1: a speaker, though you would typically send it to an
Speaker 1: amplifier first, but we'll talk about that in a minute.
Speaker 1: The speaker then essentially reverses this process. It takes those
Speaker 1: fluctuations sends them through an electro magnet. Which will generate
Speaker 1: a variable magnetic field in response, which then makes the
Speaker 1: cone vibrate within the speaker and essentially do the opposite
Speaker 1: of what the microphones diaphragm was doing and recreate the
Speaker 1: recorded sound. It's pretty cool and pretty elegant, really. So
Speaker 1: the electrical signal representing the recorded sound comes into the speaker,
Speaker 1: feeds into the voice coil creates this fluctuating magnetic field.
Speaker 1: The field interacts with the permanent magnetic field inside the basket,
Speaker 1: either pulling the diaphragm forward in the basket and thus
Speaker 1: pushing air outward, or pulling the cone back towards the
Speaker 1: back of the basket and allowing air to come further
Speaker 1: in by creating that lower pressure. And these fluctuations happen
Speaker 1: at high frequencies, so the I fragm is moving very
Speaker 1: rapidly inside the basket. It's not just pushing out then
Speaker 1: pulling in. It's doing this hundreds or thousands of times
Speaker 1: per second, and it increases or decreases the air pressure
Speaker 1: as the cone pushes those air molecules or suddenly moves away,
Speaker 1: creating more space for them. And because sound is vibration,
Speaker 1: those air molecules carry the sound up to our ears
Speaker 1: and then we rock out to a C d C
Speaker 1: or whatever band you happen to like. That isn't nearly
Speaker 1: as cool as a C d C. Now, keep in
Speaker 1: mind what I have described is how a driver works.
Speaker 1: A speaker can and often does have more than one driver,
Speaker 1: and drivers come in different shapes, sizes, and purposes. So
Speaker 1: let's talk a little bit about what those are and
Speaker 1: what they do, and why you need to have different
Speaker 1: ones in the first place. Actually, that last question is
Speaker 1: the easiest answer right away. Remember again, sound is vibration,
Speaker 1: and low frequency sounds have longer wave forms. The points
Speaker 1: of high and low pressure are further apart from each
Speaker 1: other than with high frequency sounds. If you could actually
Speaker 1: see the changes in air pressure due to sound, you
Speaker 1: would see that the low frequency sounds have these larger
Speaker 1: gaps between the high and low pressure points in the
Speaker 1: waves as they move out from the source of sound.
Speaker 1: So you need a cone diaphragm that can vibrate at
Speaker 1: a slower frequency and push air effectively at that speed.
Speaker 1: For that reason, you would typically go with a heavier,
Speaker 1: larger diaphragm, both because the wavelengths of sound are longer.
Speaker 1: If you're looking at the lower frequencies, and because making
Speaker 1: the material heavy gives it greater inertia, it takes more
Speaker 1: force to move the diaphragm, and it will move at
Speaker 1: a pace that will reproduce those low frequency sounds you want.
Speaker 1: This type of speaker falls into the whiffer or subwhiffer categories.
Speaker 1: These are the speakers that create the base sounds. A
Speaker 1: subwhiffer tends to handle frequencies from around twenty hurts to
Speaker 1: two hurts. Think of a hurts as how long it
Speaker 1: takes a wave to pass through a given point in
Speaker 1: one se end, or how many waves can pass through
Speaker 1: a given point in one second. Al Right, guys, we
Speaker 1: got some more to chat about with speakers. Before I
Speaker 1: jump into that, Let's take a quick break to thank
Speaker 1: our sponsor. Human hearing ranges from twenty hurts, which is
Speaker 1: twenty waves passing a given point in one second, to
Speaker 1: twenty killer hurts or twenty thousand waves passing through a
Speaker 1: point in one second. This really tells you more about
Speaker 1: the wavelength of the wave itself and thus the frequency
Speaker 1: and then the pitch. Remember, the lower frequencies are the
Speaker 1: lower pitches. The higher frequencies are the higher pitches, and
Speaker 1: that's the frequency range for typical human hearing twenty hurts
Speaker 1: to twenty thousand hurts. Now, I can tell you from
Speaker 1: my experience using a frequency sweeper which will slowly go
Speaker 1: through a selection of frequencies that is all set at
Speaker 1: the same volume, so you get a standard volume across
Speaker 1: us all of them, that while I can technically hear
Speaker 1: stuff at twenty hurts, it's not until you hit a
Speaker 1: frequency of about fifty hurts that it quote unquote sounds
Speaker 1: loud to me, even though actual volume of the two
Speaker 1: tones remains the same, so the amplitude is exactly the same,
Speaker 1: But until you get to a frequency of about fifty hurts,
Speaker 1: it just doesn't sound loud to me because my ears
Speaker 1: are not great at picking up those lower, super low frequencies. Also,
Speaker 1: I should mention that while sound waves come in different frequencies,
Speaker 1: sound itself travels at a speed that is dependent upon
Speaker 1: the medium through which it travels. So, in other words,
Speaker 1: low frequency sounds and high frequency sounds travel at the
Speaker 1: same speed through the same medium. Otherwise you would have
Speaker 1: all the high pitched sounds hitting your ears before the
Speaker 1: low pitched ones and conducting an orchestra would drive you crazy.
Speaker 1: The speed of sound is defined as the distance traveled
Speaker 1: by a sound wave in a certain unit of time.
Speaker 1: But hey, Jonathan, some of you might be saying you
Speaker 1: were just talking about frequencies. If a high frequency sound
Speaker 1: has twenty sound waves pass a certain point in the second,
Speaker 1: and a low frequency sound has twenty waves passing that
Speaker 1: same point in the second, are they traveling at different speeds? No,
Speaker 1: they're not. This is easier to imagine if we take
Speaker 1: an analogy. So let's say you're standing on the side
Speaker 1: of the road. Every single vehicle going past you on
Speaker 1: this one way road is traveling at a smooth twenty
Speaker 1: miles per hour or about thirty two kilometers per hour
Speaker 1: if you prefer. But they're all going that speed. Doesn't
Speaker 1: matter what kind of car it is, they're all going
Speaker 1: exactly twenty miles or thirty two kilometers per hour. Some
Speaker 1: of these vehicles are very tiny, little smart cars. Some
Speaker 1: of them are super long extended buses, but they're all
Speaker 1: traveling at that same speed. So even though they're going
Speaker 1: at the same speed, the buses take more time to
Speaker 1: pass you than the smart cars do because the buses
Speaker 1: are longer in the time it takes one super long
Speaker 1: bus to go buy you, like the front passes you
Speaker 1: and you time it out. Maybe four smart cars could
Speaker 1: go buy you and that same amount of time, even
Speaker 1: though they're all going at twenty miles per hour. The
Speaker 1: same is true with sound waves, so we're not just
Speaker 1: talking about speed but wavelength. So low frequency sounds and
Speaker 1: high frequency sounds are traveling at the same speed. It's
Speaker 1: just you can fit more of the waves in at
Speaker 1: that time than others because of the length. All right
Speaker 1: back to the speed of sound. Now, I cannot give
Speaker 1: you a standard speed of sound for all occasions because
Speaker 1: the speed of sound depends on a lot of little things,
Speaker 1: For example, how much moisture is in the air or
Speaker 1: how cold is the air. Sound passes through the air,
Speaker 1: and air is made up of gases, and gases are
Speaker 1: made up of molecules. So as you heat up a gas,
Speaker 1: the molecules move apart from each other and they bounce
Speaker 1: around more. They're more able to move. As gas is cool,
Speaker 1: the molecules pack around together and they move around less,
Speaker 1: so they get more tightly packed. So a cold gas
Speaker 1: will transmit sound at a slightly slower speed than a
Speaker 1: warm gas will if the temperature outside is sixty eight
Speaker 1: degrees fahrenheit or about twenties celsius and the air is dry,
Speaker 1: sound will travel at one thousand one per second or
Speaker 1: three forty three meters per second. And it doesn't matter
Speaker 1: what frequency sound waves you're working with, that's the speed
Speaker 1: they're going to travel at. And again, at different temperatures
Speaker 1: and there are different media, sound will travel at a
Speaker 1: different speed. All right. Now, let's go back to the
Speaker 1: different types of drivers. After you handled the sub whoffers
Speaker 1: and the whoofers, well, the whoffers will still handle lower frequencies,
Speaker 1: but sub whoffers are are specialized whoffers, largely because they
Speaker 1: will frequently be paired with special circuits and cabinets dedicated
Speaker 1: to creating those very very low frequencies in an effort
Speaker 1: to produce a specific quality of sound, such as let's
Speaker 1: say you're watching an action film and something done blowed
Speaker 1: up real good. You want to have that rumbly low
Speaker 1: base for those moments, you know, the kind where you
Speaker 1: can actually feel it because it's vibrating the chair and
Speaker 1: the air around you, and so it's it's that kind
Speaker 1: of rumble you can feel in your chest well. That
Speaker 1: frequently means you need a dedicated subwhiffer unit that has
Speaker 1: its own power supply to generate the vibrations with enough
Speaker 1: force necessary to create that effect. So it's not just
Speaker 1: the speed but how hard it's pushing. After subwhiffers and whoffers,
Speaker 1: you've got mid range drivers or mid range speakers, and
Speaker 1: as the name suggests, these drivers are responsible for producing
Speaker 1: sounds in the middle range frequencies of human hearing. A
Speaker 1: typical range might include two fifty hurts to two thousand hurts.
Speaker 1: You may have also heard the term squawker when referencing
Speaker 1: mid range speakers. They're made of lighter materials and they
Speaker 1: can vibrate at higher frequencies than whoffers and subwhiffers, which
Speaker 1: is necessary to create those mid range tones. And then
Speaker 1: you have tweeter speakers. These are made of the lightest
Speaker 1: weight material and they vibrate the fastest in an effort
Speaker 1: to reproduce frequencies on the upper levels of human hearing,
Speaker 1: which tends to be between two thousand and twenty thou
Speaker 1: hurts at least for consumer speakers. There are tweeters that
Speaker 1: can be made for special purposes that can generate sound
Speaker 1: frequencies well above the range of human hearing, some of
Speaker 1: them as high up as a hundred killer hurts or
Speaker 1: one hundred thousand hurts. That's five times higher than the
Speaker 1: highest frequency the average human is capable of perceiving. So
Speaker 1: why would you want a tweeter that could go beyond
Speaker 1: the range of human hearing. Well, you might use it
Speaker 1: for scientific research purposes, like finding out what high high
Speaker 1: high pitches the ultrasonic pitches might due to affect animal behavior.
Speaker 1: So you might be able to do that to learn
Speaker 1: how high a pitch a dog might be able to hear,
Speaker 1: for example, because dogs can hear at a different range
Speaker 1: than humans can. Or you might want to do experiments
Speaker 1: to see if those imperceptible frequencies have an effect on
Speaker 1: the sounds we can here. So there are audio files
Speaker 1: who insist that frequencies beyond the human range of hearing
Speaker 1: can change the quality of the sounds that we do here,
Speaker 1: and thus it's imperative to get a sound system and
Speaker 1: a type of media capable of reproducing sound frequencies at
Speaker 1: every level if you want a true reproduction of an
Speaker 1: original sounds quality. Uh this falls into the realm of
Speaker 1: psychoacoustics the study of sound perception. Because hearing involves processes
Speaker 1: in the brain, there is a subjective component to it
Speaker 1: that cannot be easily described through physics. We can talk
Speaker 1: all about the physics of sound waves and sound propagation,
Speaker 1: but ultimately, when it comes to the way we experience sound,
Speaker 1: we have to take gray matter into account, and that
Speaker 1: gets tricky since our experience of perceiving sound can depend
Speaker 1: upon other things unrelated to the actual physics of the
Speaker 1: sound itself. For example, if I were to tell you
Speaker 1: that I have a sound system, and I've set it
Speaker 1: up and it consists of the most expensive and most
Speaker 1: technologically advanced components, and the media that was going to
Speaker 1: play represented the most true reproduction of an actual sound,
Speaker 1: that might be an enough to influence your perception of
Speaker 1: the sound. Even if what I was really using was
Speaker 1: just good equipment, not the best, but just good stuff.
Speaker 1: Even if all all that stuff I told you wasn't true,
Speaker 1: your perception of sound might make it seem like you're
Speaker 1: listening to the most perfect reproduction of the original performance
Speaker 1: as could be attained. Or if I did play a
Speaker 1: sound back on what really was an amazing sound system,
Speaker 1: but before I did it, I made a whole bunch
Speaker 1: of apologies for how the system I was using could
Speaker 1: not faithfully represent high tones, or had a very weak
Speaker 1: base output, or something like that. You might perceive the
Speaker 1: playback as following these trends that I had mentioned, even
Speaker 1: if scientific recording instruments were to show that the playback
Speaker 1: didn't suffer from those problems at all. All that being said,
Speaker 1: the psychological aspect of how we perceive sound does have limitations.
Speaker 1: No amount of snake oil salesmanship is going to convince
Speaker 1: you that a truly subpar stereo system is capable of
Speaker 1: reproducing the glory of the Philharmonic Orchestra, for example. But
Speaker 1: because there is the subjective element and how we perceive sound,
Speaker 1: there's the opportunity to exploit that element and make a
Speaker 1: lot of money in the process. I've talked before about
Speaker 1: how certain manufacturers have used this to market high end
Speaker 1: audio equipment, and some of that has little to no
Speaker 1: scientific evidence to back up the claims that they make
Speaker 1: about those gadgets, and yet they're able to set exorbitant
Speaker 1: prices for components that audio files will cover it because
Speaker 1: they're always in a quest to get that perfect representation
Speaker 1: of a sound. Uh so this stuff does happen. I
Speaker 1: also covered this when I talked about MP three compression,
Speaker 1: because if you remember an m P three's part of
Speaker 1: the compression strategy is to take all the different parts
Speaker 1: of a sound that we humans typically don't notice, and
Speaker 1: you just cut them. You get rid of them, because
Speaker 1: that way you cut down on the size of the
Speaker 1: sound file. The strategy is, if you can't perceive it,
Speaker 1: then we don't need it in the information. We can
Speaker 1: just cut it that. Audio files say no, if you
Speaker 1: do that, it affects the off that we can here,
Speaker 1: and thus you are changing the nature of the audio recording.
Speaker 1: Just because you couldn't hear the thing doesn't mean the
Speaker 1: thing wasn't doing something else. I think the jury is
Speaker 1: still out on that in a large part. I mean,
Speaker 1: there are some legitimate arguments to make about harmonics and
Speaker 1: things that do come into play, but I'm not sure
Speaker 1: it gets to the level of subtlety that a lot
Speaker 1: of audio files argue. At least I don't see the
Speaker 1: scientific evidence supporting it. That doesn't mean it's wrong, It
Speaker 1: just means I haven't seen the evidence supporting it. Anyway.
Speaker 1: As soon as we come back. I'm gonna go into
Speaker 1: talking about amplification and why that's important, but first let's
Speaker 1: take another quick break to thank our sponsor. All right. Now,
Speaker 1: Back when I was talking about the development of the loudspeaker,
Speaker 1: I mentioned that Rice and Kellogg observed there needed to
Speaker 1: be advancements and amplification, and by that they meant there
Speaker 1: needed to be a way to boost the electrical signal
Speaker 1: from the risk the transmitter the microphone in order to
Speaker 1: give a speaker enough oomph to vibrate at a force
Speaker 1: strong enough to play back the sounds at a suitable volume.
Speaker 1: Without amplifiers, the signal strength might only allow a speaker
Speaker 1: to play back a sound at a low volume, or
Speaker 1: if the signal is very weak, it might not even
Speaker 1: move the speaker significantly enough at all to create any
Speaker 1: real sound. The reason the signal tends to be weak
Speaker 1: goes back to the limitations we face when we record
Speaker 1: sound in the first place. So using the microphone effect,
Speaker 1: we transform sound into electrical signals by making the microphones
Speaker 1: diaphragm vibrate, mimicking the way our ear drums work. Right,
Speaker 1: So it's like we're speaking into someone's ear when we
Speaker 1: talk into a microphone. Then we transform sound into electrical
Speaker 1: signals by making that microphone diaphone vibrate, and those small
Speaker 1: vibrations introduced fluctuations into an electrical signal in some way.
Speaker 1: But for sound to affect the diaphragm at all, the
Speaker 1: diaphragm has to be very lightweight, very sensitive, and it
Speaker 1: has to make very small movements. Otherwise we'd have to
Speaker 1: make sound an enormous amplitudes or volume in order to
Speaker 1: generate the force necessary to vibrate the diaphragm. So it
Speaker 1: has to be very lightweight, very very sensitive, and it's
Speaker 1: moving in a very small distance, so it can only
Speaker 1: make tiny changes in electrical current or generate a very
Speaker 1: tiny electrical current. Now that's good enough for the purposes
Speaker 1: of recording the sound. You can do that. You can
Speaker 1: use that to record sound. It's fine because it can
Speaker 1: record at those tiny details. But if you want to
Speaker 1: play the sound back on a speaker, you have to
Speaker 1: boost that signal in order to drive the speakers to
Speaker 1: physically move them. You want to make the signal more powerful,
Speaker 1: but you also want to keep all the fluctuations of
Speaker 1: the signal, all the dynamics of the signal so that
Speaker 1: way you can represent when a song gets louder or
Speaker 1: more quiet, or when one element is taking over over
Speaker 1: another element. All of these things are very subtle, and
Speaker 1: you have to preserve that. So you want the signal
Speaker 1: not just to be boosted, but for all the different
Speaker 1: fluctuations of that signal to be represented in that boost.
Speaker 1: You want it all to be at the same relative
Speaker 1: strength as they were in the weaker signal. Now, an
Speaker 1: amplifier does this through the use of two separate circuits.
Speaker 1: The first circuit is the input circuit. That's the weaker
Speaker 1: of the two signals, that's the one that's coming from
Speaker 1: the microphone. The second circuit is your output circuit, which
Speaker 1: sends a stronger signal out to the speakers, and it
Speaker 1: draws upon the amplifier's power supply to boost the signal.
Speaker 1: So you have an amplifier, it has its own power supply.
Speaker 1: It's generating the signal that's going through this output circuit.
Speaker 1: The power going through the output circuit is a direct current,
Speaker 1: so it's flowing in a set direction. It does not change.
Speaker 1: If you have an amplifier and you've hooked it directly
Speaker 1: up to your house is ultra nating current. There's a
Speaker 1: power supply element inside the amplifier that converts it from
Speaker 1: alternating current to direct current. Now, think of the output
Speaker 1: circuit as always pushing a strong signal out towards the speakers.
Speaker 1: It's just most of the time this signal is not
Speaker 1: carrying any information. But when the amplifiers on, that's what
Speaker 1: it's doing. It's pushing the strong signal out to the speakers.
Speaker 1: The input circuit's job is to use the original weak
Speaker 1: electrical signal as a way to vary the resistance in
Speaker 1: the output circuit, so the variable resistance recreates the voltage
Speaker 1: fluctuations in the original signal. So what you're doing is
Speaker 1: you've got this strong signal going out, use the weak
Speaker 1: signal to introduce the same fluctuations into the strong signal,
Speaker 1: and then the strong signal will reflect the weaker one.
Speaker 1: It will be exactly the same, except stronger. In the
Speaker 1: good old days, amplifiers relied upon vacuum tubes as an
Speaker 1: integral component, and in fact, i'm amplifiers still do, particularly
Speaker 1: for stuff like professional electric guitar amplifiers. There are professional
Speaker 1: musicians who swear by vacuum tube amplifiers and they will
Speaker 1: not use anything else. Vacuum tubes are pretty interesting technology
Speaker 1: and they date back to the early twentieth century. So
Speaker 1: let's talk about how they work for just a second. First,
Speaker 1: they look a lot like light bulbs, and in fact,
Speaker 1: they operate very similar to light bulbs. They are glass tubes.
Speaker 1: Inside this glass tube is a filament like a light bulb.
Speaker 1: The filament inside uses electrical resistance to heat up. The
Speaker 1: filament either contains or is somehow wrapped around a material
Speaker 1: like tungsten, which, when it's heated to very high temperatures,
Speaker 1: starts to boil off electrons. That would be the cathode
Speaker 1: of the vacuum tube. It's the source of electrons. The
Speaker 1: electrons accept only so much energy, and then after that
Speaker 1: they effectively jump ship. They're ready to burst off of
Speaker 1: the atoms that they were previously connected to. Now, also
Speaker 1: inside the vacuum tube is a plate that has a
Speaker 1: relative positive charge to it compared to the cathode. That's
Speaker 1: called the anode. The electrons are negatively charged, and so
Speaker 1: they're attracted to the positively charged anode, and the negative
Speaker 1: charged electrons flow towards the positively charged anode. Now, if
Speaker 1: this were all there were to a vacuum tube, it
Speaker 1: would just be a diode. That means it would be
Speaker 1: an element in a circuit that would allow electricity to
Speaker 1: pass one way from the cathode to anode, but not
Speaker 1: back the other way. However, there's a third element, and
Speaker 1: that's what creates the amplification effect. That element is a
Speaker 1: grid of spiral wires or a mesh material. The acts
Speaker 1: as a sort of control grid or cage between the
Speaker 1: cathode and the anode, so it essentially surrounds the cathode. Now,
Speaker 1: if you apply a voltage to this control grid that
Speaker 1: is lower than the cathode itself, it reduces the amount
Speaker 1: of current passing from cathode to anode. By placing a
Speaker 1: large positive voltage on the plate and then feeding a
Speaker 1: signal to the control grid, you can affect the voltage
Speaker 1: across the load on the circuit. So you make tiny
Speaker 1: changes in the control grid's voltage and you get a
Speaker 1: much larger change across the load of the circuit amplifying
Speaker 1: the signal. So again, you you put a large positive
Speaker 1: voltage on this plate, you feed the input signal into
Speaker 1: the the control grid, and then you amplify that signal
Speaker 1: across the entire load, and that load would typically involve
Speaker 1: speakers or an amplifier. These days, most amplifiers do not
Speaker 1: use vacuum tubes. Instead, we use solid state transistors. To
Speaker 1: describe how those transistors work gets a little complicated, but
Speaker 1: in general, a basic transistor has three components. You've got
Speaker 1: an emitter, a base, and a collector. The emitter and
Speaker 1: the collector are both in type UH semiconductors, meaning that
Speaker 1: they have more elect trons. They have a surplus of
Speaker 1: electrons there. You can think of it almost like a
Speaker 1: negative charge. The base is a P type semiconductor. It's
Speaker 1: sandwiched between the emitter and the collector. It has what
Speaker 1: would we would call a positive charge or holes for electrons.
Speaker 1: Feeding the input current between the emitter and the base
Speaker 1: creates a much larger output current between the emitter and
Speaker 1: the collector, thus amplifying the signal. Now, the output signal
Speaker 1: should ideally match the input signal exactly, except again, everything
Speaker 1: is just bigger as an amplified and that signal would
Speaker 1: be strong enough to do the work of moving those
Speaker 1: speaker diaphragms and generating the sounds we enjoy now. In
Speaker 1: a future episode I'm going to cover headphones. Headphones are
Speaker 1: very much closely related to speakers. Obviously they are essentially
Speaker 1: very small speakers that fit on your ears. But the
Speaker 1: history of headphones has its own story that we need
Speaker 1: to cover, and it's very fascinating. But it's too much
Speaker 1: to cover in just one episode. But I hope you
Speaker 1: and joined this episode, MICHAELA. And if you guys have
Speaker 1: episode ideas for future tech Stuff shows, then send me
Speaker 1: a message. The email address for tech Stuff is tech
Speaker 1: Stuff at how stuff works dot com, or you can
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Speaker 1: in the chat room, make jokes at my expense. I'm
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