The History of Loudspeakers

and where they came from. And today we're gonna cover speakers. I was gonna cover both in one episode. That turns out there's just too much to talk about if I really want to explain where these things came from and how they evolved over time. They are very closely related, but I feel like I'm gonna have to save headphones for a future episode. Uh So, this ties in really closely with some of the other recent episodes I've done about tech and music, like Middy and turntables. In fact,

the turntables and record player stuff. The speaker development goes hand in hand with that because it was all part of the development of the recording industry as a whole. Well, a quick reminder we're talking about sound, and I promise i'll make this brief. Sound travels through a medium. It can be any sort of medium. Really can be solid,

it can be liquid, it could be gas. Sound is vibration, So molecules or atoms within this medium are going to bounce against each other and propagate sound throughout that medium, So you have to have molecules there. This, by the way, is why sound does not travel in outer space, because while outer space is not totally empty, there are particles in outer space, they're so far apart from each other that you can't have them bump against each other and

propagate sound. So that's why there's no sound in space anyway. Uh, we experience sound when vibrating air molecules change the air pressure in our air canals. At least this is the primary way we experienced sound. And when that happens, the air pressure means that it either presses against our ear drums also known as the tympanic membrane, or the pressure is reduced so that our tympanic membrane presses out because there's there's not as much pressure as there normally would be.

As these vibrations that then gets sent through a series of tiny bones that then send vibrations to a structure called the cochlea in our inner ears that wiggles around some fluid which then wiggles around some special nerve cells which send electrical impulses to our brain that we then interpret as sound. And I know I've said that a couple of times in recent episodes, but it always bears repeating, because we have to remember, ultimately, sound is this physical phenomenon.

It's not just some magic stuff that floats through the air. It's actual physical vibrations, and it's in warn't to know that because as we got a greater understanding of the nature of sound, we were also building on our understanding of physics, of electrical engineering, of lots of stuff that

all together made it possible for us to make speakers. Now, before electric loud speakers, we mainly relied on just acoustics, the physics of sound, and for a while we didn't necessarily have very detailed mathematics to describe the acoustics of sound, which by the way, are incredibly complicated. I could do a series of episodes about the acoustics of sound, and it would take a really long time to do so.

I'm only going to touch upon acoustics in this, but acoustics involve everything from the design of say a room, like have you ever been in a room that was designed acoustically for the performance of music? You've probably experienced some really nice performances that way. But there's also acoustic design in things like instruments, including horns, and horns would largely represent the way we would try to amplify sound before the electric loudspeaker like the megaphone is a classic example.

So how can a simple shape make a sound louder? Well? Again, to dive into all the details would be an episode by itself. Plus I would kind of need visual aids to really explain it properly because doing this all just an audio format is very challenging. But in general, when you have a horn or a tapered tube where it tapers down to a narrow end and then you've got a wide end on the other side, you can send sound waves down the length of this tube as plane waves p L A n E. Those are waves that

travel in parallel with one another. So you have one wave behind that, you have another wave in parallel behind that, you have another wave in parallel and so on. It's kind of like a stack of waves. Now, the tube needs to be narrow at one end to fit the source of the sound, such as your mouth or with acoustic speakers. Back in the old days when you had the gramophones, you know those big trumpet looking things that

stuck out of what looked like a record player. Well that had to be right around whatever the membrane was or the speaker driver in order to help amplify sound. The tube then has to flare out because if it remains narrow, sound waves would start to reflect off the sides and that would that would start to affect the loudness as it went down the path. And that's largely because of wave size. Lower frequency sound waves have longer wave forms, so you need to flare out the horn

to allow for those longer frequencies. And this is why instruments like the tube but have such a large flared horn at the end because they're playing those lower frequency sounds, whereas something like a trumpet can have a smaller flare because they are not playing notes that are at that

low of a frequency. The design of a horn transforms sound waves by taking the high pressure, low velocity waves emitted into the narrow end also known as the throat of a horn, and then converts those into low pressure, high velocity vibrations at the wide end, so high pressure low velocity to low pressure high velocity, and the high velocity vibrations can move through the air more efficiently. In addition, a horn restricts the spreading out of sound waves. It's directional.

Sound will emanate out in all directions from a source normally, but with a horn you can restrict that a bit. You direct the sound a little bit toward an intended target and thus deliver a more concentrated collection of sound waves at that target. But while horn acoustics are pretty amazing and fascinating, they are not the ideal solution for amplifying sound in all situations, which brings us to the

invention of the electric loudspeaker. Also, I should mention that electric loudspeakers frequently make use of the principles of horn acoustics in their design. So just to get that out of the way, it's not like horn acoustics no longer or apply. It's just we're not relying solely on horn acoustics for amplification. At this point. The first electric loudspeaker

was part of an invention called the telephone. Now we all know Alexander Graham Bell gets the credit for inventing the telephone, but it was actually another person, a German teacher, Johan Philip Rice, who was actually the original inventor of a device called the telephone. He called his device a telephone. It was different from the telephone that Alexander Graham Bell would invent, but it was a device. It was called the telephone, and it came out about two decades before

Alexander Graham Bell got into it. Uh so it's not nearly as transformative as Alexander Graham Bell's invention in eighteen sixty So okay, more like fifteen years before Graham Bell's breakthrough, Rice was hard at work creating an electrically powered device meant to mimic the human ear. In fact, his early early versions of this look like a human ear carved out of oak, and even had these little metal parts that were supposed to replicate the way the bones in

our ear drums work or behind our ear drums work. Well, he thought he could transmit sound through electric wires, harnessing something called magnet restriction Now, this is a phenomenon in which a feral magnetic material like iron will change in dimensions due to a change in the magnitude and direction

of its magnetization. So essentially what this means is if you get something that's feral magnetic, like an iron bar, and you put it inside a magnetic field, and it's a weak magnetic field the h and you put it in such a way so that the direction of the rod, as in the length of the rod, match the magnetic fields direction. The rod would actually get a little bit

longer through this weak magnetic field. Now, if it were a strong magnetic field, the rod would actually contry tracked a little bit, would be a little shorter than normal. And if you had a very precise way of measuring the rod, you could actually see that the length of the rod changed as the magnetic field changed. So if you change the field strength, you could actually dynamically change the length of the rod by a very small amount. And moreover, doing this would cause the iron rod to

create a tick sound. Passing a variable current through a coil of wire could cause the rod to tick repeatedly, generating a sort of tone, and that became the receiver of Rice's invention, it became his speaker. This ticking iron bar was essentially a speaker. Rice created a device that acted as a transmitter. The ear had a parchment membrane inside of it that mimic the tympanic membrane in our ears.

Against that membrane was a little metal strip, So he had essentially glued like a platinum strip to this membrane, and resting a against that platinum strip was a second strip of platinum which was just barely touching the membrane due to gravity. So they were just making gentle contact

with each other. In fact, we would have called this a loose contact if it had been done on purpose for an electrical circuit, and when the circuit was powered, when electricity was flying going through it, uh, it would actually everything's working fine. The two contacts are in in connection with one another. Uh, you would be able to

have pass electricity through without any issues. But Rice believed that if you made sounds into this simulacrum of an ear, you could make the membrane vibrate, and he believed this would cause the metal contacts to bounce against each other and cause the current passing through the circuit to become intermittent, and this would be what he would call and what

others would call a make or break transmission. So if you think about something like a telegraph, where when you press down on the key, it completes a circuit, and when you let off of the key, it breaks the circuit. He was thinking along those same lines, except he was thinking this would be a way for you to transmit actual sounds, not just uh, the the signal that there

is an electric circuit made and broken. That's what he thought was behind this whole idea, and so he started to experiment with this, and he thought eventually he could do he could create a system this way where you

could transmit sound through electricity. You would put the sound into the transmitter, it would do this make or break series of connections, and then on the other side you would have this iron bar that would start ticking, and the ticking would be done in such a way that you would be able to make out what was the original sound put into the transmitter. Side now in a courtroom, because eventually his design would be brought into court proceedings.

When Alexander Graham Bell came forward with his invention of a telephone, well, we'll find out what happened in the courtroom, but first let's take a quick break to thank our sponsor. Scientists testified that the only way this even worked at all was if the sound was not too loud, and so the two strips of metal would never lose contact

with each other. They would press more gently against each other, but they would still remain in contact, and that this would end up varying the electrical resistance of the circuit, which would change make it a variable current flowing through the circuit, and that is what made the signal that made it possible for you to hear something on the

other side. So not that there was a make or break connection, but rather that the connection that was made had a variable resistance and thus a variable current, and that is what drove the receiver on the other side. The reason this is important as they were saying, yeah, technically Rice's inventions sort of works, although it wasn't producing clear representations of the original sound. You could tell that it was making a sound based upon the original one,

but it wasn't clear. You couldn't get intelligible speech out of it. They said, yes, it is working, but it's not working the way he thought it was the way he described it. It can't work that way, because that's not the way that that's not what we're seeing. What we're seeing is the only way it works is that the sounds are quiet enough to not break the connection, but only change the electrical resistance of the circuit. So while his his invention works, it doesn't work the way

he wanted it to. So his patent is invalid, and the courts upheld this. And some people find this really interesting that you could have something that technically works, but if you describe how it works and you get the description wrong, that is what ends up being important, not whether or not your invention actually does anything. Uh. And that in fact was the case. And Rice got really kind of disgusted by all this and kind of got out of that area of study. After the Brewjaja over

Alexander Graham Bell's invention. Speaking of Alexander Graham Bell, we should chat about his version of the telephone. He patented his first electric loudspeaker as part of his telephone invention in eighteen seventy six. Now, later on he did acknowledge Rice's work as part of the inspiration for his own invention, but Graham Bell avoided the problems Rice encountered. Alexander Graham Bell was in a race to patent his invention before a rival of his named Elisha Gray could get his

own implementation patented. So he had Elisha and you had Alexander Graham Bell, and they were both working on this furiously, and in fact they both filed for patents on the exact same day. There are people to this day who argue that Elisha Gray should get the credit for inventing the telephone rather than Alexander Graham Bell. Now, their inventions

were similar but distinct. They were not exactly the same thing, so it wasn't necessarily that one was copying the other, although there have been allegations that perhaps Alexander Graham Bell had a look at Elisha Gray's um design and then based some changes in his own design on that. Whether those allegations holding the merit, I'll leave to other people. It gets real ugly if you want to read into this.

But the two had been in competition for years. They had been working against each other in the field of telegraphy well before they started getting into the idea of a telephone. And I'm not gonna go any further into that, just to say, if you want to look up some pretty interesting muck raking, look at Alexander Graham Bell and

Elisha gray Well. Alexander Graham Bell mounted a piece of magnetized iron to a membrane, or rather he told his assistant Watson to do this, and an electro magnet would attract or repel this magnetized iron as it received the incoming variable electric current from the transmitter. The membrane was able to reproduce sound, but at a low volume, So in other words, he would speak into a transmitter. The transmitter had a membrane in it that would, through its

vibrations very an electric current. That electric current would travel through a wire to the receiver. And on the receiver side you had another membrane on which was a piece of uh magnetized iron, and you had an electro magnet just below it that would receive this variable electric current and thus attract and repel the iron that was on this membrane, making the brain vibrate. That's what ended up

replicating the sound. In eighteen seventy four, another inventor named Ernst Siemens, the co founder of the Siemens Company, made an important contribution to the development of the modern speaker. He received a patent for his description of an electro mechanical dynamic transducer which used a coil of wire suspended in a frame so that it could move axially and

only axially. So his patent described a magneto electric apparatus for obtaining the mechanical movement of an electrical coil from electrical currents transmitted through it, which would become the basis for electric loudspeakers decades later. Now, basically the idea is this, imagine you have a frame. So you've got a frame. Let's say it's a square frame. It's got sort of a circular opening in the middle of the square frame.

Inside this frame, you suspend a coil of conductive wire, so it's spend it in such a way where it can swing towards the back of the frame or towards the front of the frame, but it cannot move up or down or side to side with respect to the frame. So it's if you're thinking of like the x y and Z axis axes. Rather, uh, the Z axis is what we're concerned with here, not the X Y. So it can move if you're looking dead on in the frame. It can move towards you or away from you, but

not side to side or up or down. When you apply a magnetic field, you can induce electricity to flow through this conductor. The flow of electricity creates some magnetic field, and you can use the attraction and repulsion properties of magnets to move the coil back and forth within this frame. Now, Siemens did not originally intend for this invention to be used for acoustics. He had come up with this idea, but he wasn't thinking about loud speakers. He was just

talking about this basic apparatus. But after Alexander Graham Bell patented the telephone in eighteen seventy six, Siemens was motivated to apply for a new patent for a non magnetic parchment diaphragm as a means of sound radiation on a moving coil transducer. He received his patent in eighteen seventy eight. And we call the coils on speakers that drive the speaker's motions a voice coil. So if you ever hear anyone talk about the voice coil of a speaker, that's

the coil that is part of the speaker system. It's it's attached to the diaphragm of the speaker that makes the diaphragm actually vibrate. At this point, I need to mention there were numerous scientists, tankerers, and engineers amateur inventors

who made numerous contributions to allowed speaker designs. Now I'm going to talk about just a few of them, because to cover them all would take a couple of episodes, and some of those contributions, while important, were of such a specific nature that would become kind of tedious pretty quickly. Just know, a lot of folks worked on this stuff.

In the late eighteen hundreds and early nineteen hundreds, twenty years after Siemens received his patent for a voice coil speaker mechanism, this would be about eight In other words, there was a man named Oliver Lodge who filed for a patent in the United Kingdom for a loud speaker that included non magnetic spacers that were intended to keep the proper air gap between the inner and outer polls of a moving coil transducer, which would help prevent issues

with the transducer getting stuck within the frame. In nineteen o one, John Strow suggested a conical paper diaphragm to act as the sound radiator, and went further to suggest such a design could be used so that the end of the cone stopped at the rim of the speaker in a flat section covered by a corrugated surface. So in other words, it's kind of like what a speaker

cabinet looks like today. If you take a speaker cabinet that being what we commonly referred to as just a speaker, and you look at you can see you have a mesh covering of some sorts, probably made out of fabric, but it could be made of something else, and then through it you'll see the circles that represent the cones of the speaker drivers. Well, it was John Strow who actually said you could design a speaker in this kind of fashion, So that was back in nineteen o one.

In nineteen eleven, Peter L. Jensen and Edwin S. Pridham founded the commercial wireless and development company Jensen and Britain would actually build a practical moving coil loudspeaker in nineteen fifteen. So people have been talking about this for decades, but this was the pair that built the first practical one, not just a prototype in a lab, but one that

could actually be used out in the real world. Together, they created a public address system that would allow huge crowds of people to hear a presentation or music distinctly over loud speakers, and they called their system Magnavox. Later they would use that as the name of their company. They renamed their company Magnavox. And I'll have to do an episode on Magnavo Box at some point because it's a big company. It's been around for a long time.

They've done a lot of important things. Jensen and Pridum attempted to patent their design with the intent of working with record companies and radio manufacturers, but they were denied their patents for those applications, which is why they instead

focused on public address systems. In two engineers for General Electric named Chester W. Rice and Edward W. Kellogg applied for a patent for a dynamic loudspeaker in n They published their work in an article titled Notes on the Development of a New type of hornless Loudspeakers, and it was all on the Journal of ai E Transactions. Their design described what would pretty much be the foundation of

all electric loudspeakers from that point forward. So in a bit i'll describe what it consists of and how it works. But first let's take a quick break to thank our sponsor. All Right, now, I'm gonna focus on the speakers themselves, and after we talk about speakers and how they work, we'll talk a bit about amplifiers, as that was a piece that was missing from the Rice and Kellogg loudspeaker. And yeah, I know that sounds like I'm talking about

Rice Crispy treats, but no, uh. The the guys who got the patent for the Dynamic Electric loudspeaker were Rice and Kellogg, and the two mentioned in their article that there was a need for more work and amplification in order to get the volume levels you want out of a speaker. But we're gonna get to that in a

little bit, so we'll put that aside for now. So if you were to take a speaker apart, and you have essentially was called a speaker cabinet, you would find that inside that speaker cabinet are one or more drivers, typically more than one if you're talking about a big stereo speaker. Now, a driver consists of a cone shaped frame, which is called a basket. The basket contains the other components of the loudspeakers, so they're all housed inside this frame.

Attached to the interior of the frame is either an electro magnet or a permanent magnet. It just depends upon the speaker. In the early days of speakers, manufacturers almost always used electro magnets because permanent magnets were difficult to come by and thus they were very expensive. Also attached to this frame is a cone. The cone might be made out of paper or metal, or these days plastic.

This is the diaphragm of the speaker. This is the part that vibrates and it's what pushes air molecules to propagate sound outward to the listener. It's typically in a cone shape that's sort of like a horn. It's depending upon those acoustics, uh, you know, the same acoustic properties of horn loudspeakers that I mentioned earlier. But there are some that are not in a horn or cone shape. Their dome shaped, or they might have a slightly different shape,

but they work in largely the same way. They vibrate and push air molecules. This cone or diaphragm attaches to the suspension that's also known as the surround. The suspension is a rim of flexible material that's mounted on the end of the basket, So the the end that faces outward towards the listener. That's the side that the cone attaches to, so right there at the very end. So in short, we've got the suspension mounted to the end of the basket. Attached to the suspension is the cone.

On the narrow end of the cone is the voice coil. That's the conductive wire that coils around the base several times. The coil also attaches to the basket through a ring of flexible material called the spider. He is our hero if you know that reference, so you'll let me know.

But no, the flexible material is called the spider. Its job is to hold the coil in a position that is stable within the frame but still allows for that axial movement, to let it swing back and forth freely, or more appropriately, to vibrate backwards and forwards with relation to the frame. So, in other words, it's doing the job that Ernst Siemens described in his patent back in the eighteen seventies. The secret to making a driver work

is all in electro magnetism. Whether the speaker is using permanent magnets or electro magnets on the basket, the principle remains the same. I'll talk more about the principle in our next episode, but for now we're going to conclude part one of How Speakers Work. If you guys have suggestions for future episodes of tech Stuff, I highly recommend

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You can join in on all the fun, jump into the chat room, make fun of me when I say weird things incorrectly, and then I have to make a deep noise so Tari nose to cut it out of the recording, and sometimes we forget to do that and you get to hear me say beep. It's like a giant bonus for everybody. Anyway, I record on Wednesdays and Fridays. Go to twitch dot tv slash tech Stuff. You'll see the schedule there and I'll talk to you again. Really sion for more on this and thousands of other topics.

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