How exactly do speakers work?

Richard Sinkler · From: aka: Rusty Strings -- Missoula, Montana

This is a question has has bugged me for years. How does a single speaker produce several different frequecies at one time to produce, say, a symphony where 30 to 50 instruments are playing at once?

I understand that when a speaker receives a frequency from an amp, the voice coil causes the cone to move in and out at the frequency of the note. Concert A (440hz) would cause the cone to vibrate at 440 cycles per second. Fine and dandy, but how does it handle all the different notes being played simultaneously and all the harmonic overtones associated with thos notes.

I've search the net, but have not found any complete explainations.
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Jonathan Cullifer · From: Gallatin, TN

When you mix different waves together, a new wave at a new frequency and amplitude results.

Think about a couple of basic scenarios. A sine wave is the most basic type of wave you can have. Add it with all the odd harmonics and you get a triangle wave. Add it with all the even harmonics and you get a square wave. Even though you have many different frequency waves involved, all you hear is the fundamental, because all of the other waves mixed together produce one final resuling wave. The same is true with music, albeit the waves that are mixed together are themselves more complex. If you look at the waveform of any sound recording, you will see that each channel is one distinct wave. All the speaker has to do is follow that one distinct wave.

I'm not an expert on this, but I hope this post makes sense.

David Doggett · Posted 12 Feb 2008 9:31 pm

I think Jonathan's explanation is a good start, but the triangle and square wave analogies leave things seeming a little too simple. In music the different notes from the different instruments, and all their harmonics, overlay each other to give a very complicated wave. All the individual frequencies are still there in the new wave. There are low frequencies, and between them are mid and high and ultrahigh frequencies. No single speaker can accurately reproduce all of them at once. That's why better speaker systems separate the frequencies with cross-over networks, and redirect them to tweeters, mids, and woofers. I'm no expert, but that's how I understand it. Confused

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Sound (any sound, be it a violin or and explosion) is merely compression and rarification of air, waves set in motion, which our ears hear as a sound. All the speaker is doing is moving air, the same way a single instrument, a voice, or a symphony does. The speaker doesn't know anything about instruments or voices, how big or how small, how many or how few...it's only reproducing waves of air.

That's all sound is.

Curt Langston · Posted 13 Feb 2008 7:38 am

How exactly do speakers work?

This link is pretty good:

Speakers in action

Scott Swartz · From: St. Louis, MO

Go here and play with the wave generator about halfway down the page, you can see how the waveform changes as harmonics are added

http://www.blackstoneappliances.com/dist101.html
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Richard Sinkler · From: aka: Rusty Strings -- Missoula, Montana

Doony

That is where the confusion is. If a C note is played through the speaker, it should vibrate a certain number of times. An A note, a different frequency. Both together, it should vibrate at both frequencies, because it needs to cause the air to move at those frequencies, which I don't understand. I do basically understand the concept of complex waveforms (as it pertains to synth programming). Do different areas of the cone vibrate at different frequencies?

Well, I'm off to check out those links.

Thanks guys.
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Richard Sinkler · From: aka: Rusty Strings -- Missoula, Montana

Both interesting sites. They didn't answer my question though. I already know how a speaker physically operates and somewhat understand complex waveforms and distortion. How does the speaker actually cause multiple frequencies to be vibrated at any given point in time? To hear all these distinctly different notes and timbres, the air has to move at those frequencies with the right harmonic structure to create the timbre. I don't see how a single cone can do that. I probably never will understand. I am just happy they do what they do.
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Steve Norman · From: Seattle Washington, USA

I dont think the cone can vibrate at different frequencies, I think you are hearing one freq, and your brain makes the separation. Different freqs will move at different speeds, and different freqs will either add or cancel.

I think also since the speaker is being "jammed" forward and pulled backward by the magnet as the coil alternates its charge, you will get 2 kinds of waves coming out.

One is a compression wave, the other the sine type wave. The compression wave hits first since it is directed straight out from the source. I dont think the compression wave is sensed as sound, but its what you feel hit you in the chest at shows.

My understanding of the process is like this...

1. the Strings of an instrument vibrates through a magnetic field created by the pickup, creating a very small electric charge.

2. The pickup sends the electric charge created by the disturbance of the magnetic field, and in proportion to that disturbance through the instrument cable into the amplifier.

3. this charge is amplified and sent to the poles of the speaker, still in the frequency of the initial string vibration.

4. this charge either repels or attracts the magnet of the speaker, causing movement of the cone.

5. the speaker cone moves the air turning mechanical energy into sound.

So the charge moving the speaker is what causes the movement of air, and in any given moment the charge is singular. If the charge at any given moment is singular, then the note being sent through the air is also singular. It happens so fast though, that many singular notes are being transmitted in a short amount of time. The brain takes the average of these many notes and process it as a chord or a single note.

So you are getting many different waves, sent out ONE at a time, of varying frequencies from the speaker. Your ear receives them One at a time, and your brain puts it all together as sound
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Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

When you play one or more notes on a musical instrument, the pickup creates a single waveform which goes through your cables, pedals, effects, and amplifier before being converted into a current signal which is passed through the speaker's voice coil, and so on. The speaker sees a single current waveform. There are not necessarily any actual separate sinusoidal signals, per se.

The speaker reproduces the signal to a degree of approximation - there are limits to the ability of any speaker to faithfully reproduce an input signal exactly, based on physical considerations. There are two big effects. One is limits to cone excursion when the sign of the signal stays the same for a long time, especially noticeable with low frequency signals. Another is limits to response speed due to inertia, especially noticeable at high frequencies. A speaker reacts to the instantaneous value of such a signal as an electromechanical system, pure and simple.

The analytical breakdown of a complex waveform as weighted sum of orthonormal basis functions - audio analysis typically uses sinusoidal basis functions - is called Fourier analysis. This type of spectral analysis is a purely mathematical technique. The result is a representation of the waveform as a weighted sum of orthonormal basis functions.

The choice of sinusoidal basis functions is largely out of mathematical convenience - sinusoids naturally fit problems like the oscillations produced by vibrating strings, and also the analysis of signals amplified by linear amplifiers. In addition, sinusoidal decomposition gives an intuitive interpretation of the actual signal that makes sense to people in this context.

For example, suppose one were to take a single sinusoidal waveform and run it through a highly distorted amp which clipped it so rapidly that it presented something very close to a square wave to the speaker. One can do a Fourier decomposition of that square wave into a sum of harmonically-related sinusoids whose amplitudes diminish as frequency increases. That's all well and good. But the speaker just sees a signal that is constant for a period of time, then rapidly changes sign, then is constant for a while again, then rapidly changes sign, and so on.

Note that sinusoids are not the only possible or reasonable choice of orthonormal basis functions. For different applications, one might use a different set of orthonormal basis functions like Legendre polynomials, Chebyshev polynomials, Laguerre functions, Hermite polynomials, or Walsh functions.

The point is - the signal is just the signal, regardless of the way one analyzes it. This is not to say that complex signals can't make it difficult for a speaker to reproduce them. But not necessarily. Take a whole bunch of sinusoidal signals at different frequencies, and then match them with equal signals 180 degrees out of phase. The result is very easy to reproduce - the overall signal amplitude now is zero. It's the sum that matters.

Larry Robinson · From: Peachtree City, Georgia, USA

A speaker consists of a permanent magnet and an electro magnet. The permanent magnet is what you see on the back of the speaker. This permanent magnet has a groove inside it a few millimeters wide. The speaker voice coil sits inside of this groove. The wires of the voice coil are connected to the speaker terminals on the back of the speaker. When an AC signal is applied to the speaker terminals, the changing of polarity of the signal causes the speaker cone to move “in and out” of the permanent magnet’s groove. The stronger the signal, the farther the speaker cone will travel, and the louder the sound. Based on the theory of opposite polarity signals attract and same polarity signals repel, the speaker moves in and out of the grooves of the permanent magnet because of the changing polarity of the signal. Remember that the permanent magnet polarity does NOT change. This is my basic explanation of how a speaker works.

Jonathan Cullifer · From: Gallatin, TN

I tried this and it's kinda fun...if you graph a high frequency sine wave mixed with a low frequency sine wave, you will see that only one distinct wave is created, but the high frequency sine wave, instead of crossing zero, crosses the zero that is the low frequency wave. It's pretty easy to see if you can see it.

If you look up information on beat frequencies (created by two close notes) and see waveforms for beat frequencies, it's easier to understand.

Don Brown, Sr. · From: New Jersey

Richard, try this site.

Click Here

Hope that helps. Because in reality, human hearing isn't really all that good, as compared with a few other species. The main reason why we all hear something quite different from one person to the other, depending on each person's ability to hear.

Some people could say to another, hear that? And yet the other person may not really be able to detect what the other person is hearing at all.

A speaker works on much the same principles as does the human ear.. Not much below (again depending) 15 Hz, to around 18,000 HZ A good speaker reproduces it's input signal precisely what it receives, only much louder, depending on the driving signal.

"Another example of having a well designed amp as opposed to having one that may not be so well designed."

That's one reason, when folks tell me that the amp has little to do with the sound, they simply don't know what they are saying..

It's the amplifier design, that has all to do with the sound, that the speaker reproduces. The amplifier is the item, responsible for shaping it's output signal before it goes to the speaker, as well as faithfully reproducing the very small electrical input signal, and then after having AMPLIFIED it into a much larger signal, in order to be able to drive the speaker.

You'll never get anything better coming out of a speaker, than what you have going into it. Again, the amplifier's job is to do just that.

After the amplifier, yes! The speaker has to be capable of reproducing a faithful output of it's input.

As well, a well designed pickup, one without the 60 Hz hum, that otherwise mixes with the signal, helps in producing a faithful signal. But again, that too can be taken out at the input stage of a well designed amplifier. And yes! A single coil pickup can be designed to not pick up 60 cycle hum.

Simply my opinions and certainly not meant to be anyone else's at all.

Don

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Brad Sarno · From: St. Louis, MO USA

Richard said:

"Fine and dandy, but how does it handle all the different notes being played simultaneously and all the harmonic overtones associated with those notes."

I'd say that a speaker cone handles all the complexity exactly the same way your eardrum does. Sound waves, however complex, are still ultimately just sound pressure changes over time.

If you looked at (on a scope) a waveform of a 100Hz sinewave it could look big and rounded. If you looked at a 10,000Hz sinewave, it would look like lots of tiny little waves very close together. If you mixed the 100Hz and the 10kHz together you'd have a waveform that still looks like the big rounded wave, but the smooth line would now have all the tiny little 10kHz waves riding on it. That's a very simple metaphor for what sound does in the air. Everything mixes together, but ultimately reaches an eardrum, which is just a speaker in reverse, sort of like a microphone diaphragm. A paper speaker cone is not tuned to any one frequency. It'll vibrate however it's told to from the amplifier. Then those waves propogate thru the air.

Asking how a speaker can do all those frequencies at once is just like asking how the ear can hear all those frequencies at once. Take a look at an audio waveform of music. It's very jagged and bumpy and chaotic looking. If you zoom way in to look at it very closely, it's still just a single waveform, but it's just not smooth and simple. That complex, jagged, spikey and wild looking waveform can be sent out a speaker into the air just like it can be received by the eardrum (a diaphragm).

When viewing a waveform, there is always a flat line across the middle. The wave moves above and below that line. You can equate that above and below to a speaker moving out and in. When that soundwave moves thru the air and hits the eardrum, the eardrum also moves in and out in reaction to the changes in air pressure caused by that waveform.

Is that useful at all???

Brad

Richard Sinkler · From: aka: Rusty Strings -- Missoula, Montana

Don,

That is one of my favorite websites and have seen this info. But none of the websites I have seen (including the ones here) really explain how the speaker can produce multiple frequencies at the same time. I think I have gotten more information from all you guys on the forum than all the websites combined.

I seem to be understanding how it happens a little better.

Thanks to all.
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Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

David Doggett · Posted 14 Feb 2008 12:26 am

Don Brown, Sr. · From: New Jersey

Dave, that sounds logical enough to me. They are quite stiff until they have some playing time on them. I remember a note coming with my JBL, stating to only play at low volume for the first few hours. Was stated something as to why failures occurred that otherwise wouldn't have. They must have been right, because mine sure has been a good one. Don

Richard Sinkler · From: aka: Rusty Strings -- Missoula, Montana

I pretty much understand everything being said except how the speaker physically performs the action.

I understand complex wave forms. But take into account a violin, a guitar and a saxophone. Each playing an A note at 440 hz. The reason they all sound different is the harmonic structue that goes along with each note played. Each instrument is different in which harmonics are present and their amplitude. This is what gives them their distinct sound (timbre). Now that speaker is going to have to play those three A notes and the different harmonics that make up each timber. That's a lot of different frequencies being played at one time.

I know that electricity travels fast and I guess it's possible for the cone to vibrate fast enough to play all the different frequencies so our ear hears it all at once. But to move the air at all those frequencies, the speaker cone actually has to move at those frequencies. Am I wrong in assuming that? In other words, how does air move at a certain frequency if nothing physically pushes the air at the frequency?
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David Doggett · Posted 14 Feb 2008 11:01 am

You're right. The air has to move at not only the three A fundamentals, but also at all the higher frequency harmonics or partials that make up the overtone pattern or timbre that distinguishes each instrument. Believe it or not, that's exactly what the speaker does. Over the decades they developed speaker materials and designs that can do that. You can actually see the speaker move in and out on bass fundamentals, but you cannot see the extremely rapid speaker movements that give those higher frequencies. But rest assured that if you are hearing that timbre, the speaker is making those short rapid excursions while it is moving back and forth on the longer slower excursions. If you could film the speaker with magnification, and run it in slow motion, you could see some of the smaller movements. But I'm sure the highest frequencies would be too fast to capture on film. Nevertheless, the speaker reproduces those frequencies and moves air at that rate, or you wouldn't hear what you do.

Don Brown, Sr. · From: New Jersey

Richard, that IS the key, what you just said.

That speaker, doesn't care, (doesn't even know) what anything sounds like. All it does, is reproduce the very sound waves, that You, I and anyone else can hear. Exactly as what our ears hear. Matter of fact, the speaker was originally invented on the same principles of the human ear.(I believe I'm right in saying this) and how our hearing works.

What we originally hear is what we hear from the speaker as well. None of the multiple tones, regardless of what they are, (that's above our ability to hear) which BTW, is not really all that great, when it comes to higher freqs. And much of nothing above 16 to 18,000 Hz. But that too can vary between people. But not by all that much.

I believe you may be better off looking up Human hearing, to possibly get the answers you're looking for. Because when you do, that will be the key to what you're looking for.

Example, if you simply clap your hands together, there are all kinds of frequencies, involved, but we can only hear the low frequencies. Dogs, that have much better hearing can hear much more out of a simple hand clap than what we can. They can also hear well up and into the range that's far, out of range of human hearing as well.

The speaker is not separating anything, (if it could hear) it's hearing the small signal the same as what we're hearing it, and simply vibrating to whatever frequencys that would be, and reproducing the same, while moving a much more pronounced amount of air, which causes it to be louder. The louder it goes, the more air it moves. Again, the same as if you talked, you would move less air, than if you yelled, you'd move much more air. And, the frequencies would change higher in pitch as well, because usually when a person yells, the pitch is raised along with it, from their speaking tone of voice.

The speaker doesn't care or have to care at all about complex soundwaves, that part gets separated by our ears.. Therefore, it's not the speaker that allows us to hear, it's our ears. The speaker only provides the output amplification, so we can hear things louder.

It's complex, because the human body is complex, imagine how our brains work, if the hearing seems complex. Very Happy

PS: David's answer is correct. Sorry David, I'd not have posted had your post been there a tad sooner.

Hope it was of some help.

Don

Brad Sarno · From: St. Louis, MO USA

Richard said:

"how does air move at a certain frequency if nothing physically pushes the air at the frequency?"

But it DOES push the air at that frequency. The waves that move thru the air are the result of the speaker doing exactly that. The speaker cone moves at pretty much whatever speed the amplifier tells it to. (within the physical limitations of the speaker). A speaker is designed to freely move at ALL the frequencies within it's range. Not any one particular frequency, but any and all of them.

And just as your eardrum can only be in one place at any given instant, a speaker can only be at one place at any given instant. But over time, even super short periods of time, it recreates the complex vibrations. A wave is a function of both amplitude AND time. Time and frequency are pretty much different aspects of the same thing. Take time out of the frequency equation, and you have nothing; remember a single tone is measured in cycles per "second". Hertz. Sound doesn't have to be just a single tone, obviously. What happens during that "second" or time period can be very complex.

Check out these three shots. I created a waveform made up of a 50Hz tone, a 500Hz tone, and a 10kHz tone. See how they all superimpose or mix together to create one waveform. This waveform can be reproduced by a speaker creating a soundwave exactly like it. The first shot is zoomed out looking at the thing from a distance. You can easily see the slow, 50Hz with the 500Hz ripples in it. As we get closer in, you begin to also see the 10kHz tone that rides on this complex wave. Remember that the horizontal axis is time. The waveform (or speaker position) is only at one place at any given instant.

Brad

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

Richard Sinkler · From: aka: Rusty Strings -- Missoula, Montana

Well, I have to say thanks to all of you for the info. I think I have a greater understanding of what is going on.

Don, you're right, it doesn't care, but it still has to produce all those frequencies. I have spent some time studying how the ear works. The workings of the ear was the basis on which microphone diaphrams (and speakers) were founded. The whole concept of sound just amazes me.
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