WEBVTT - How Speakers and Amplifiers Work 0:00:04.280 --> 0:00:07.320 Get in touch with technology with tech Stuff from how 0:00:07.360 --> 0:00:13.600 stuff works dot com. Hey there, and welcome to tech Stuff. 0:00:13.640 --> 0:00:16.319 I'm your host, Jonathan Strickland. I'm an executive producer with 0:00:16.360 --> 0:00:19.600 how Stuff Works and I love all things tech, and 0:00:19.640 --> 0:00:23.279 today we are going to continue our episodes about how 0:00:23.360 --> 0:00:27.240 speakers work and how they are able to take electricity 0:00:27.440 --> 0:00:30.880 and make those sweet, sweet sounds for your ear holes. 0:00:31.280 --> 0:00:34.839 So let us jump back with a quick explanation of 0:00:34.920 --> 0:00:39.960 electro magnetism. So electricity and magnetism are very closely related, 0:00:40.240 --> 0:00:43.479 and you've likely done the simple physics exercise of creating 0:00:43.560 --> 0:00:46.800 a basic electro magnet. So you'll take something like an 0:00:46.840 --> 0:00:50.680 iron nail and you'll wrap insulated copper wire in a 0:00:50.760 --> 0:00:54.440 coil around the nails several times. The nail acts as 0:00:54.480 --> 0:00:59.320 a ferromagnetic core. The copper wire coil is a conductor, 0:00:59.480 --> 0:01:01.600 so connecting the ends of the copper wire to a 0:01:01.640 --> 0:01:05.479 battery will then allow current to flow through the wire. 0:01:05.680 --> 0:01:08.760 It'll flow from one end of the battery through the 0:01:08.800 --> 0:01:12.240 wire down into the other end of the battery. As 0:01:12.240 --> 0:01:15.400 it goes around this coil, the flow of electricity creates 0:01:15.400 --> 0:01:19.520 a magnetic field. The nail and coil will behave like 0:01:19.680 --> 0:01:22.200 a permanent magnet. Would it's an electro magnet, but it 0:01:22.240 --> 0:01:25.039 will behave like a permanent magnet with a north pole 0:01:25.280 --> 0:01:27.200 and a south pole. And if you brought it close 0:01:27.240 --> 0:01:30.959 to a permanent magnet, then the opposite poles would attract 0:01:31.000 --> 0:01:33.920 each other and the similar poles would repel each other. 0:01:34.160 --> 0:01:36.520 So if you brought the electro magnets north pole next 0:01:36.520 --> 0:01:38.720 to a permanent magnets north pole, it would push that 0:01:38.800 --> 0:01:43.240 other magnet away and the polls will not change. Because 0:01:43.680 --> 0:01:47.600 the source of electricity is a battery, and batteries provide 0:01:47.800 --> 0:01:50.800 direct current, which means the current is always going to 0:01:50.800 --> 0:01:54.320 flow in the same direction. It's never going to reverse. 0:01:54.600 --> 0:01:58.520 But if you hooked the same nail and coil up 0:01:58.560 --> 0:02:02.360 to a source of alternation current, things would be very different. 0:02:02.600 --> 0:02:07.200 With alternating current, the direction of the flow of electricity 0:02:07.320 --> 0:02:12.240 changes rapidly every second, and as the direction of electricity changes, 0:02:12.480 --> 0:02:16.359 it affects the magnetic field. With electricity flowing in one direction, 0:02:16.520 --> 0:02:19.160 the head of the nail might represent the north pole 0:02:19.240 --> 0:02:21.960 of the magnet, and when the electricity switches to the 0:02:22.000 --> 0:02:24.280 other direction, the head of the nail will become the 0:02:24.360 --> 0:02:27.360 south pole of the magnet. And vice versa. You have 0:02:27.560 --> 0:02:32.000 created a fluctuating magnetic field by running an alternating current 0:02:32.240 --> 0:02:35.040 through an electro magnet, and you can do some pretty 0:02:35.040 --> 0:02:39.079 cool stuff with a fluctuating magnetic field. For example, if 0:02:39.080 --> 0:02:43.200 you bring this apparatus close to a conductive material, you'll 0:02:43.280 --> 0:02:47.680 induce a change of voltage in that material even without 0:02:47.720 --> 0:02:51.080 making physical contact between the two. So if you do 0:02:51.160 --> 0:02:54.360 this with a stable magnetic field, all you'll do is 0:02:54.360 --> 0:02:57.600 see a very short spike, but then it stops because 0:02:57.720 --> 0:03:01.480 the magnetic field is not fluctuating. To induce electricity to 0:03:01.520 --> 0:03:06.239 flow by changing voltage in this other conductor, the magnetic 0:03:06.240 --> 0:03:09.000 field has to be fluctuating, or the conductor has to 0:03:09.000 --> 0:03:11.360 be moving in and out of the magnetic field constantly. 0:03:11.960 --> 0:03:15.120 If you get two coils of copper wire and you 0:03:15.160 --> 0:03:18.359 make sure the second copper wire has twice as many 0:03:18.400 --> 0:03:22.200 coils as the first one, you can create a transformer. 0:03:22.600 --> 0:03:25.720 So imagine you've got your first coil of wire. Let's 0:03:25.720 --> 0:03:29.840 say it's got ten coils ten ten loops around its core, 0:03:30.560 --> 0:03:34.280 and you've got a second core with copper wire, but 0:03:34.320 --> 0:03:38.000 there are twenty loops around the second core. If you 0:03:38.080 --> 0:03:42.120 run a current through the first coil, it will induce 0:03:42.160 --> 0:03:46.800 current to flow through the second coil. Moreover, the voltage 0:03:46.960 --> 0:03:50.080 in the second coil will be higher than the voltage 0:03:50.120 --> 0:03:53.440 in the first coil because the second coil has twice 0:03:53.600 --> 0:03:57.040 as many coils as the first one. So the more 0:03:57.360 --> 0:04:02.200 times you loop a wire around a or the greater 0:04:02.320 --> 0:04:05.960 the change of voltage is going to be between coil 0:04:06.040 --> 0:04:10.000 number one and coil number two. This particular version of 0:04:10.000 --> 0:04:13.480 a transformer would be called a step up transformer because 0:04:13.560 --> 0:04:17.040 the secondary coil has more turns than the primary coil 0:04:17.240 --> 0:04:20.359 and steps up the voltage. If the opposite were true, 0:04:20.760 --> 0:04:23.880 if coil number one had ten coils or ten loops 0:04:24.279 --> 0:04:27.080 and coil number two had five loops, then that would 0:04:27.080 --> 0:04:30.880 be a step down transformer. You would lower the voltage 0:04:30.880 --> 0:04:35.599 from primary to secondary. Transformers are what made alternating current 0:04:35.880 --> 0:04:39.400 the more viable solution to supplying electricity to homes and 0:04:39.440 --> 0:04:44.120 businesses back in the early days, because transmitting electricity was 0:04:44.160 --> 0:04:48.080 all about efficiency. How could you efficiently get electricity from 0:04:48.080 --> 0:04:50.600 a power plant to where it needed to be? Well? 0:04:50.640 --> 0:04:54.760 If you used alternating current, you could create transformers and 0:04:54.800 --> 0:04:57.719 you could step up the voltage two very high levels, 0:04:58.240 --> 0:05:02.159 and that meant that you could transmit power across power 0:05:02.240 --> 0:05:06.320 lines much more efficiently. If you didn't do that, you 0:05:06.360 --> 0:05:09.080 had so much power loss that you would have to 0:05:09.120 --> 0:05:13.599 have lots of different power generators throughout the region in 0:05:13.720 --> 0:05:16.720 order to supply all the power needs of your area, 0:05:16.920 --> 0:05:18.760 at least back in the old days of direct current, 0:05:18.800 --> 0:05:22.119 because it wasn't easy to step up the voltage. And again, 0:05:22.240 --> 0:05:25.560 high voltage makes it more efficient to transmit power across 0:05:25.640 --> 0:05:28.880 long distances, So in the early days, that's why a 0:05:29.000 --> 0:05:31.520 C went out over d C. These days, you could 0:05:31.560 --> 0:05:33.440 actually do things a little differently if you wanted to, 0:05:33.520 --> 0:05:37.520 and you could go with direct DC power if you 0:05:37.560 --> 0:05:39.960 really wanted to, but it would require a big overhaul 0:05:40.000 --> 0:05:43.320 of the infrastructure. But transformers made a C much more 0:05:43.320 --> 0:05:47.880 practical anyway. Electromagnets are pretty awesome now. With speakers, it's 0:05:47.920 --> 0:05:51.040 not so much about voltage and current as it is 0:05:51.080 --> 0:05:54.640 about making the diaphragm of the speaker move in precise ways. 0:05:55.120 --> 0:05:58.400 With speakers, the electrical current acts as both the carrier 0:05:58.480 --> 0:06:01.400 of information and the means to make the diaphragm move. 0:06:01.920 --> 0:06:06.000 So you start with a steady magnetic field inside the basket. 0:06:06.400 --> 0:06:10.640 You can create that steady magnetic field either with permanent 0:06:10.640 --> 0:06:14.120 magnets like I mentioned before, or with electro magnets, but 0:06:14.640 --> 0:06:17.159 it remains the same no matter what. The north pole 0:06:17.200 --> 0:06:18.599 is always going to be the north pole. The south 0:06:18.600 --> 0:06:20.640 pole is always going to be the south pole. Inside 0:06:20.640 --> 0:06:24.279 the frame, that field does not change. The voice coil 0:06:24.520 --> 0:06:28.320 on the cone ends up receiving the variable current that 0:06:28.400 --> 0:06:32.400 came from the transmitter that represents the recorded sound. Now, 0:06:32.440 --> 0:06:35.760 remember the way we record sound as we typically will 0:06:35.839 --> 0:06:38.599 use something like a microphone, and a microphone is essentially 0:06:38.640 --> 0:06:41.800 a speaker in reverse. A microphone has a diaphragm in 0:06:41.880 --> 0:06:45.200 it that vibrates in the presence of sound waves. Those 0:06:45.279 --> 0:06:50.400 vibrations cause fluctuations inside an electric current. You might vary 0:06:50.480 --> 0:06:54.000 the resistance of the circuit, as we talked about with 0:06:54.160 --> 0:06:59.680 the the old Johan Philip Rice approach, and by varying 0:06:59.720 --> 0:07:03.680 those that electric resistance within the circuit, you can fluctuate 0:07:03.720 --> 0:07:05.760 the electric current and then you can send that to 0:07:05.800 --> 0:07:08.120 a speaker, though you would typically send it to an 0:07:08.120 --> 0:07:10.400 amplifier first, but we'll talk about that in a minute. 0:07:10.800 --> 0:07:14.040 The speaker then essentially reverses this process. It takes those 0:07:14.040 --> 0:07:17.320 fluctuations sends them through an electro magnet. Which will generate 0:07:17.320 --> 0:07:20.360 a variable magnetic field in response, which then makes the 0:07:20.400 --> 0:07:24.160 cone vibrate within the speaker and essentially do the opposite 0:07:24.200 --> 0:07:27.160 of what the microphones diaphragm was doing and recreate the 0:07:27.240 --> 0:07:31.280 recorded sound. It's pretty cool and pretty elegant, really. So 0:07:31.440 --> 0:07:35.560 the electrical signal representing the recorded sound comes into the speaker, 0:07:35.880 --> 0:07:39.120 feeds into the voice coil creates this fluctuating magnetic field. 0:07:39.160 --> 0:07:42.440 The field interacts with the permanent magnetic field inside the basket, 0:07:42.760 --> 0:07:45.960 either pulling the diaphragm forward in the basket and thus 0:07:46.280 --> 0:07:50.720 pushing air outward, or pulling the cone back towards the 0:07:50.720 --> 0:07:53.800 back of the basket and allowing air to come further 0:07:53.920 --> 0:07:58.080 in by creating that lower pressure. And these fluctuations happen 0:07:58.160 --> 0:08:01.240 at high frequencies, so the I fragm is moving very 0:08:01.320 --> 0:08:04.640 rapidly inside the basket. It's not just pushing out then 0:08:04.640 --> 0:08:07.720 pulling in. It's doing this hundreds or thousands of times 0:08:07.720 --> 0:08:11.120 per second, and it increases or decreases the air pressure 0:08:11.240 --> 0:08:14.239 as the cone pushes those air molecules or suddenly moves away, 0:08:14.520 --> 0:08:17.800 creating more space for them. And because sound is vibration, 0:08:18.160 --> 0:08:21.000 those air molecules carry the sound up to our ears 0:08:21.320 --> 0:08:23.400 and then we rock out to a C d C 0:08:24.240 --> 0:08:26.679 or whatever band you happen to like. That isn't nearly 0:08:26.720 --> 0:08:30.000 as cool as a C d C. Now, keep in 0:08:30.080 --> 0:08:33.000 mind what I have described is how a driver works. 0:08:33.440 --> 0:08:36.640 A speaker can and often does have more than one driver, 0:08:37.080 --> 0:08:40.800 and drivers come in different shapes, sizes, and purposes. So 0:08:41.160 --> 0:08:43.440 let's talk a little bit about what those are and 0:08:43.480 --> 0:08:45.200 what they do, and why you need to have different 0:08:45.200 --> 0:08:48.040 ones in the first place. Actually, that last question is 0:08:48.080 --> 0:08:52.280 the easiest answer right away. Remember again, sound is vibration, 0:08:52.600 --> 0:08:56.640 and low frequency sounds have longer wave forms. The points 0:08:56.679 --> 0:08:59.920 of high and low pressure are further apart from each 0:09:00.000 --> 0:09:02.960 other than with high frequency sounds. If you could actually 0:09:02.960 --> 0:09:05.280 see the changes in air pressure due to sound, you 0:09:05.320 --> 0:09:07.960 would see that the low frequency sounds have these larger 0:09:08.000 --> 0:09:10.640 gaps between the high and low pressure points in the 0:09:10.640 --> 0:09:13.000 waves as they move out from the source of sound. 0:09:13.320 --> 0:09:16.360 So you need a cone diaphragm that can vibrate at 0:09:16.400 --> 0:09:20.680 a slower frequency and push air effectively at that speed. 0:09:21.040 --> 0:09:24.000 For that reason, you would typically go with a heavier, 0:09:24.520 --> 0:09:28.959 larger diaphragm, both because the wavelengths of sound are longer. 0:09:29.280 --> 0:09:32.200 If you're looking at the lower frequencies, and because making 0:09:32.240 --> 0:09:35.199 the material heavy gives it greater inertia, it takes more 0:09:35.280 --> 0:09:37.600 force to move the diaphragm, and it will move at 0:09:37.600 --> 0:09:40.800 a pace that will reproduce those low frequency sounds you want. 0:09:40.840 --> 0:09:45.120 This type of speaker falls into the whiffer or subwhiffer categories. 0:09:45.720 --> 0:09:48.920 These are the speakers that create the base sounds. A 0:09:48.960 --> 0:09:53.000 subwhiffer tends to handle frequencies from around twenty hurts to 0:09:53.120 --> 0:09:56.240 two hurts. Think of a hurts as how long it 0:09:56.360 --> 0:09:59.320 takes a wave to pass through a given point in 0:09:59.440 --> 0:10:02.400 one se end, or how many waves can pass through 0:10:02.440 --> 0:10:05.160 a given point in one second. Al Right, guys, we 0:10:05.240 --> 0:10:07.559 got some more to chat about with speakers. Before I 0:10:07.679 --> 0:10:10.120 jump into that, Let's take a quick break to thank 0:10:10.160 --> 0:10:20.400 our sponsor. Human hearing ranges from twenty hurts, which is 0:10:20.600 --> 0:10:24.280 twenty waves passing a given point in one second, to 0:10:24.440 --> 0:10:28.720 twenty killer hurts or twenty thousand waves passing through a 0:10:28.800 --> 0:10:31.680 point in one second. This really tells you more about 0:10:31.720 --> 0:10:35.439 the wavelength of the wave itself and thus the frequency 0:10:35.559 --> 0:10:39.360 and then the pitch. Remember, the lower frequencies are the 0:10:39.440 --> 0:10:42.480 lower pitches. The higher frequencies are the higher pitches, and 0:10:42.520 --> 0:10:45.760 that's the frequency range for typical human hearing twenty hurts 0:10:45.760 --> 0:10:48.319 to twenty thousand hurts. Now, I can tell you from 0:10:48.360 --> 0:10:52.800 my experience using a frequency sweeper which will slowly go 0:10:53.000 --> 0:10:56.920 through a selection of frequencies that is all set at 0:10:56.960 --> 0:11:00.000 the same volume, so you get a standard volume across 0:11:00.040 --> 0:11:02.400 us all of them, that while I can technically hear 0:11:02.520 --> 0:11:04.719 stuff at twenty hurts, it's not until you hit a 0:11:04.800 --> 0:11:08.520 frequency of about fifty hurts that it quote unquote sounds 0:11:08.800 --> 0:11:11.440 loud to me, even though actual volume of the two 0:11:11.480 --> 0:11:15.520 tones remains the same, so the amplitude is exactly the same, 0:11:16.080 --> 0:11:19.040 But until you get to a frequency of about fifty hurts, 0:11:19.040 --> 0:11:21.560 it just doesn't sound loud to me because my ears 0:11:21.559 --> 0:11:26.400 are not great at picking up those lower, super low frequencies. Also, 0:11:26.440 --> 0:11:29.280 I should mention that while sound waves come in different frequencies, 0:11:29.520 --> 0:11:33.240 sound itself travels at a speed that is dependent upon 0:11:33.280 --> 0:11:36.079 the medium through which it travels. So, in other words, 0:11:36.320 --> 0:11:39.760 low frequency sounds and high frequency sounds travel at the 0:11:39.800 --> 0:11:43.160 same speed through the same medium. Otherwise you would have 0:11:43.240 --> 0:11:45.800 all the high pitched sounds hitting your ears before the 0:11:45.840 --> 0:11:49.680 low pitched ones and conducting an orchestra would drive you crazy. 0:11:50.240 --> 0:11:53.200 The speed of sound is defined as the distance traveled 0:11:53.480 --> 0:11:55.920 by a sound wave in a certain unit of time. 0:11:56.320 --> 0:11:58.400 But hey, Jonathan, some of you might be saying you 0:11:58.440 --> 0:12:00.880 were just talking about frequencies. If a high frequency sound 0:12:00.880 --> 0:12:04.080 has twenty sound waves pass a certain point in the second, 0:12:04.160 --> 0:12:06.480 and a low frequency sound has twenty waves passing that 0:12:06.559 --> 0:12:10.560 same point in the second, are they traveling at different speeds? No, 0:12:10.760 --> 0:12:13.320 they're not. This is easier to imagine if we take 0:12:13.320 --> 0:12:15.960 an analogy. So let's say you're standing on the side 0:12:16.160 --> 0:12:20.080 of the road. Every single vehicle going past you on 0:12:20.120 --> 0:12:23.480 this one way road is traveling at a smooth twenty 0:12:23.480 --> 0:12:26.280 miles per hour or about thirty two kilometers per hour 0:12:26.320 --> 0:12:29.000 if you prefer. But they're all going that speed. Doesn't 0:12:29.000 --> 0:12:30.920 matter what kind of car it is, they're all going 0:12:31.000 --> 0:12:35.480 exactly twenty miles or thirty two kilometers per hour. Some 0:12:35.600 --> 0:12:38.800 of these vehicles are very tiny, little smart cars. Some 0:12:38.920 --> 0:12:41.920 of them are super long extended buses, but they're all 0:12:41.960 --> 0:12:45.040 traveling at that same speed. So even though they're going 0:12:45.080 --> 0:12:48.000 at the same speed, the buses take more time to 0:12:48.080 --> 0:12:51.240 pass you than the smart cars do because the buses 0:12:51.280 --> 0:12:54.280 are longer in the time it takes one super long 0:12:54.360 --> 0:12:56.920 bus to go buy you, like the front passes you 0:12:57.200 --> 0:13:01.000 and you time it out. Maybe four smart cars could 0:13:01.000 --> 0:13:02.920 go buy you and that same amount of time, even 0:13:02.960 --> 0:13:05.360 though they're all going at twenty miles per hour. The 0:13:05.440 --> 0:13:07.560 same is true with sound waves, so we're not just 0:13:07.640 --> 0:13:12.040 talking about speed but wavelength. So low frequency sounds and 0:13:12.120 --> 0:13:15.080 high frequency sounds are traveling at the same speed. It's 0:13:15.120 --> 0:13:19.280 just you can fit more of the waves in at 0:13:19.320 --> 0:13:23.360 that time than others because of the length. All right 0:13:23.840 --> 0:13:26.240 back to the speed of sound. Now, I cannot give 0:13:26.280 --> 0:13:30.040 you a standard speed of sound for all occasions because 0:13:30.080 --> 0:13:32.439 the speed of sound depends on a lot of little things, 0:13:32.800 --> 0:13:35.560 For example, how much moisture is in the air or 0:13:35.559 --> 0:13:39.800 how cold is the air. Sound passes through the air, 0:13:39.880 --> 0:13:42.079 and air is made up of gases, and gases are 0:13:42.080 --> 0:13:44.960 made up of molecules. So as you heat up a gas, 0:13:45.000 --> 0:13:47.640 the molecules move apart from each other and they bounce 0:13:47.679 --> 0:13:51.920 around more. They're more able to move. As gas is cool, 0:13:52.280 --> 0:13:56.920 the molecules pack around together and they move around less, 0:13:56.920 --> 0:14:00.120 so they get more tightly packed. So a cold gas 0:14:00.120 --> 0:14:03.880 will transmit sound at a slightly slower speed than a 0:14:03.920 --> 0:14:06.839 warm gas will if the temperature outside is sixty eight 0:14:06.840 --> 0:14:10.120 degrees fahrenheit or about twenties celsius and the air is dry, 0:14:10.440 --> 0:14:14.240 sound will travel at one thousand one per second or 0:14:14.320 --> 0:14:17.760 three forty three meters per second. And it doesn't matter 0:14:17.800 --> 0:14:21.400 what frequency sound waves you're working with, that's the speed 0:14:21.400 --> 0:14:24.280 they're going to travel at. And again, at different temperatures 0:14:24.280 --> 0:14:26.440 and there are different media, sound will travel at a 0:14:26.440 --> 0:14:28.440 different speed. All right. Now, let's go back to the 0:14:28.440 --> 0:14:32.520 different types of drivers. After you handled the sub whoffers 0:14:32.560 --> 0:14:36.840 and the whoofers, well, the whoffers will still handle lower frequencies, 0:14:37.080 --> 0:14:40.400 but sub whoffers are are specialized whoffers, largely because they 0:14:40.400 --> 0:14:44.640 will frequently be paired with special circuits and cabinets dedicated 0:14:44.640 --> 0:14:48.240 to creating those very very low frequencies in an effort 0:14:48.240 --> 0:14:50.760 to produce a specific quality of sound, such as let's 0:14:50.760 --> 0:14:53.320 say you're watching an action film and something done blowed 0:14:53.400 --> 0:14:56.320 up real good. You want to have that rumbly low 0:14:56.440 --> 0:14:58.680 base for those moments, you know, the kind where you 0:14:58.720 --> 0:15:02.280 can actually feel it because it's vibrating the chair and 0:15:02.320 --> 0:15:04.640 the air around you, and so it's it's that kind 0:15:04.640 --> 0:15:06.720 of rumble you can feel in your chest well. That 0:15:06.800 --> 0:15:09.640 frequently means you need a dedicated subwhiffer unit that has 0:15:09.640 --> 0:15:13.520 its own power supply to generate the vibrations with enough 0:15:13.600 --> 0:15:16.600 force necessary to create that effect. So it's not just 0:15:16.680 --> 0:15:21.120 the speed but how hard it's pushing. After subwhiffers and whoffers, 0:15:21.400 --> 0:15:24.800 you've got mid range drivers or mid range speakers, and 0:15:24.840 --> 0:15:28.160 as the name suggests, these drivers are responsible for producing 0:15:28.160 --> 0:15:31.120 sounds in the middle range frequencies of human hearing. A 0:15:31.160 --> 0:15:34.880 typical range might include two fifty hurts to two thousand hurts. 0:15:34.920 --> 0:15:38.359 You may have also heard the term squawker when referencing 0:15:38.360 --> 0:15:41.640 mid range speakers. They're made of lighter materials and they 0:15:41.680 --> 0:15:45.360 can vibrate at higher frequencies than whoffers and subwhiffers, which 0:15:45.400 --> 0:15:48.520 is necessary to create those mid range tones. And then 0:15:48.640 --> 0:15:51.960 you have tweeter speakers. These are made of the lightest 0:15:51.960 --> 0:15:54.680 weight material and they vibrate the fastest in an effort 0:15:54.720 --> 0:15:57.840 to reproduce frequencies on the upper levels of human hearing, 0:15:58.200 --> 0:16:00.640 which tends to be between two thousand and twenty thou 0:16:00.920 --> 0:16:04.040 hurts at least for consumer speakers. There are tweeters that 0:16:04.040 --> 0:16:06.800 can be made for special purposes that can generate sound 0:16:06.880 --> 0:16:09.800 frequencies well above the range of human hearing, some of 0:16:09.840 --> 0:16:12.040 them as high up as a hundred killer hurts or 0:16:12.040 --> 0:16:15.520 one hundred thousand hurts. That's five times higher than the 0:16:15.560 --> 0:16:19.040 highest frequency the average human is capable of perceiving. So 0:16:19.080 --> 0:16:22.040 why would you want a tweeter that could go beyond 0:16:22.360 --> 0:16:24.800 the range of human hearing. Well, you might use it 0:16:24.840 --> 0:16:28.880 for scientific research purposes, like finding out what high high 0:16:29.000 --> 0:16:33.920 high pitches the ultrasonic pitches might due to affect animal behavior. 0:16:34.200 --> 0:16:36.200 So you might be able to do that to learn 0:16:36.400 --> 0:16:39.480 how high a pitch a dog might be able to hear, 0:16:39.520 --> 0:16:42.080 for example, because dogs can hear at a different range 0:16:42.080 --> 0:16:44.920 than humans can. Or you might want to do experiments 0:16:45.240 --> 0:16:49.640 to see if those imperceptible frequencies have an effect on 0:16:49.680 --> 0:16:53.600 the sounds we can here. So there are audio files 0:16:53.680 --> 0:16:57.640 who insist that frequencies beyond the human range of hearing 0:16:57.960 --> 0:17:01.240 can change the quality of the sounds that we do here, 0:17:01.600 --> 0:17:04.480 and thus it's imperative to get a sound system and 0:17:04.560 --> 0:17:07.840 a type of media capable of reproducing sound frequencies at 0:17:07.880 --> 0:17:10.560 every level if you want a true reproduction of an 0:17:10.560 --> 0:17:14.000 original sounds quality. Uh this falls into the realm of 0:17:14.080 --> 0:17:19.560 psychoacoustics the study of sound perception. Because hearing involves processes 0:17:19.600 --> 0:17:23.080 in the brain, there is a subjective component to it 0:17:23.119 --> 0:17:26.280 that cannot be easily described through physics. We can talk 0:17:26.359 --> 0:17:29.320 all about the physics of sound waves and sound propagation, 0:17:29.560 --> 0:17:32.879 but ultimately, when it comes to the way we experience sound, 0:17:33.119 --> 0:17:36.080 we have to take gray matter into account, and that 0:17:36.119 --> 0:17:39.399 gets tricky since our experience of perceiving sound can depend 0:17:39.480 --> 0:17:42.399 upon other things unrelated to the actual physics of the 0:17:42.400 --> 0:17:45.440 sound itself. For example, if I were to tell you 0:17:45.840 --> 0:17:48.119 that I have a sound system, and I've set it 0:17:48.240 --> 0:17:51.280 up and it consists of the most expensive and most 0:17:51.320 --> 0:17:55.280 technologically advanced components, and the media that was going to 0:17:55.320 --> 0:17:58.959 play represented the most true reproduction of an actual sound, 0:17:59.400 --> 0:18:02.040 that might be an enough to influence your perception of 0:18:02.080 --> 0:18:04.639 the sound. Even if what I was really using was 0:18:04.720 --> 0:18:08.240 just good equipment, not the best, but just good stuff. 0:18:08.480 --> 0:18:11.040 Even if all all that stuff I told you wasn't true, 0:18:11.080 --> 0:18:13.640 your perception of sound might make it seem like you're 0:18:13.640 --> 0:18:16.520 listening to the most perfect reproduction of the original performance 0:18:16.600 --> 0:18:19.840 as could be attained. Or if I did play a 0:18:19.880 --> 0:18:23.240 sound back on what really was an amazing sound system, 0:18:23.440 --> 0:18:25.440 but before I did it, I made a whole bunch 0:18:25.480 --> 0:18:28.160 of apologies for how the system I was using could 0:18:28.200 --> 0:18:31.800 not faithfully represent high tones, or had a very weak 0:18:31.840 --> 0:18:34.600 base output, or something like that. You might perceive the 0:18:34.600 --> 0:18:39.000 playback as following these trends that I had mentioned, even 0:18:39.040 --> 0:18:41.840 if scientific recording instruments were to show that the playback 0:18:41.880 --> 0:18:45.080 didn't suffer from those problems at all. All that being said, 0:18:45.280 --> 0:18:48.800 the psychological aspect of how we perceive sound does have limitations. 0:18:48.840 --> 0:18:52.080 No amount of snake oil salesmanship is going to convince 0:18:52.119 --> 0:18:55.240 you that a truly subpar stereo system is capable of 0:18:55.280 --> 0:18:59.240 reproducing the glory of the Philharmonic Orchestra, for example. But 0:18:59.320 --> 0:19:02.720 because there is the subjective element and how we perceive sound, 0:19:03.080 --> 0:19:06.080 there's the opportunity to exploit that element and make a 0:19:06.080 --> 0:19:08.359 lot of money in the process. I've talked before about 0:19:08.359 --> 0:19:11.000 how certain manufacturers have used this to market high end 0:19:11.040 --> 0:19:14.080 audio equipment, and some of that has little to no 0:19:14.200 --> 0:19:16.760 scientific evidence to back up the claims that they make 0:19:16.800 --> 0:19:20.600 about those gadgets, and yet they're able to set exorbitant 0:19:20.600 --> 0:19:23.600 prices for components that audio files will cover it because 0:19:23.600 --> 0:19:26.680 they're always in a quest to get that perfect representation 0:19:26.760 --> 0:19:30.840 of a sound. Uh so this stuff does happen. I 0:19:30.840 --> 0:19:33.800 also covered this when I talked about MP three compression, 0:19:33.840 --> 0:19:37.119 because if you remember an m P three's part of 0:19:37.160 --> 0:19:40.520 the compression strategy is to take all the different parts 0:19:40.560 --> 0:19:44.159 of a sound that we humans typically don't notice, and 0:19:44.200 --> 0:19:46.359 you just cut them. You get rid of them, because 0:19:46.400 --> 0:19:48.560 that way you cut down on the size of the 0:19:48.600 --> 0:19:52.960 sound file. The strategy is, if you can't perceive it, 0:19:53.400 --> 0:19:56.040 then we don't need it in the information. We can 0:19:56.040 --> 0:19:58.480 just cut it that. Audio files say no, if you 0:19:58.560 --> 0:20:01.240 do that, it affects the off that we can here, 0:20:01.680 --> 0:20:05.760 and thus you are changing the nature of the audio recording. 0:20:06.480 --> 0:20:09.080 Just because you couldn't hear the thing doesn't mean the 0:20:09.119 --> 0:20:13.879 thing wasn't doing something else. I think the jury is 0:20:13.920 --> 0:20:15.920 still out on that in a large part. I mean, 0:20:16.440 --> 0:20:19.679 there are some legitimate arguments to make about harmonics and 0:20:19.760 --> 0:20:22.920 things that do come into play, but I'm not sure 0:20:22.960 --> 0:20:24.919 it gets to the level of subtlety that a lot 0:20:24.960 --> 0:20:27.760 of audio files argue. At least I don't see the 0:20:27.800 --> 0:20:30.639 scientific evidence supporting it. That doesn't mean it's wrong, It 0:20:30.720 --> 0:20:33.920 just means I haven't seen the evidence supporting it. Anyway. 0:20:34.680 --> 0:20:37.000 As soon as we come back. I'm gonna go into 0:20:37.160 --> 0:20:40.520 talking about amplification and why that's important, but first let's 0:20:40.520 --> 0:20:50.560 take another quick break to thank our sponsor. All right. Now, 0:20:50.560 --> 0:20:53.000 Back when I was talking about the development of the loudspeaker, 0:20:53.040 --> 0:20:55.800 I mentioned that Rice and Kellogg observed there needed to 0:20:55.840 --> 0:20:59.200 be advancements and amplification, and by that they meant there 0:20:59.200 --> 0:21:02.080 needed to be a way to boost the electrical signal 0:21:02.400 --> 0:21:06.399 from the risk the transmitter the microphone in order to 0:21:06.480 --> 0:21:09.760 give a speaker enough oomph to vibrate at a force 0:21:09.880 --> 0:21:12.760 strong enough to play back the sounds at a suitable volume. 0:21:13.240 --> 0:21:17.159 Without amplifiers, the signal strength might only allow a speaker 0:21:17.160 --> 0:21:19.720 to play back a sound at a low volume, or 0:21:19.800 --> 0:21:22.720 if the signal is very weak, it might not even 0:21:22.760 --> 0:21:26.120 move the speaker significantly enough at all to create any 0:21:26.200 --> 0:21:29.359 real sound. The reason the signal tends to be weak 0:21:29.720 --> 0:21:32.360 goes back to the limitations we face when we record 0:21:32.440 --> 0:21:35.800 sound in the first place. So using the microphone effect, 0:21:36.160 --> 0:21:40.280 we transform sound into electrical signals by making the microphones 0:21:40.320 --> 0:21:44.080 diaphragm vibrate, mimicking the way our ear drums work. Right, 0:21:44.160 --> 0:21:47.000 So it's like we're speaking into someone's ear when we 0:21:47.040 --> 0:21:51.520 talk into a microphone. Then we transform sound into electrical 0:21:51.560 --> 0:21:56.359 signals by making that microphone diaphone vibrate, and those small 0:21:56.440 --> 0:22:01.240 vibrations introduced fluctuations into an electrical signal in some way. 0:22:01.240 --> 0:22:04.040 But for sound to affect the diaphragm at all, the 0:22:04.119 --> 0:22:08.080 diaphragm has to be very lightweight, very sensitive, and it 0:22:08.119 --> 0:22:10.919 has to make very small movements. Otherwise we'd have to 0:22:10.920 --> 0:22:13.639 make sound an enormous amplitudes or volume in order to 0:22:13.680 --> 0:22:17.000 generate the force necessary to vibrate the diaphragm. So it 0:22:17.040 --> 0:22:20.640 has to be very lightweight, very very sensitive, and it's 0:22:20.680 --> 0:22:23.720 moving in a very small distance, so it can only 0:22:23.800 --> 0:22:27.880 make tiny changes in electrical current or generate a very 0:22:27.920 --> 0:22:30.800 tiny electrical current. Now that's good enough for the purposes 0:22:30.840 --> 0:22:33.359 of recording the sound. You can do that. You can 0:22:33.440 --> 0:22:36.040 use that to record sound. It's fine because it can 0:22:36.240 --> 0:22:39.119 record at those tiny details. But if you want to 0:22:39.160 --> 0:22:41.639 play the sound back on a speaker, you have to 0:22:41.760 --> 0:22:44.960 boost that signal in order to drive the speakers to 0:22:45.080 --> 0:22:48.160 physically move them. You want to make the signal more powerful, 0:22:48.320 --> 0:22:51.119