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Old 08-30-07, 06:27 PM   #1
root11
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how do loudspeakers produce > 1 sound at a time?

Just how does a single speaker produce the sound of more than one instrument/voice at a time? And I guess the natural followup question is how does the eardrum "hear" it all? It seems that if the cone is vibrating along at 100hz for a bass note, that would have to stop before a drum beat at 3000 hz (or whatever it would be) could happen. Or do our brains fill in the blanks?
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Old 08-30-07, 06:40 PM   #2
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Just how does a single speaker produce the sound of more than one instrument/voice at a time? And I guess the natural followup question is how does the eardrum "hear" it all? It seems that if the cone is vibrating along at 100hz for a bass note, that would have to stop before a drum beat at 3000 hz (or whatever it would be) could happen. Or do our brains fill in the blanks?
This use to bewilder me all the time, then without studying it at all i think i kind of figured it out on my own one day, so please correct me if i'm wrong.

What you hear is not a bunch of sounds, but rather one sound. This goes for anything that passes through our ears. So you hear a 100hz bass note and a 3000hz drum beat. These two would mesh together in a sense.

Sound waves are tend to be thought of as traverse waves by people, because in their origin they kind of are...that is until the speaker does its job. Really what speaker is doing is changing its signal into longitudinal waves which is how we hear sound. Sound is nothing more then air moving in longitudinal waves.

So picture your bass wave if you will with these vertical lines

| | | | | | | | | |

Now picture your drum beat

llllllllllllllllllllllllllllllllllllllllllllllllllllll
Now the two at the same time

|llll|llll|llll|llll|llll|
The waves aren't separate, they are instead just meshed together. The thing is, it isn't the actually sound waves that are different, the difference between a drumb beat and a bass note, the thing that enables us to pick those noises out, to distinguish them...is our brain
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Old 08-30-07, 06:48 PM   #3
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It's not more than one sound. When the music is recorded (and mixed assuming more than one mic) it is converted into a signal that is just that, signal. A singular thing. So although there may be many elements to one recording, there is only one final recording to be sent (as signal) to the speaker, which plays that out.

This also helps to understand why more complex setups with subwoofers, tweeters and the like are needed for high quality sound. It's very difficult for a machine that relies on vibration to rapidly accelerate and decelerate its mechanism.
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Old 08-30-07, 06:53 PM   #4
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Its all in the wave form.
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Old 08-30-07, 06:59 PM   #5
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Speaker cones utilize multidimensional hyperspace muxing. It's really quite simple. A child with an advanced degree in hyperspace engineering could figure it out. Sheesh.
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Old 08-30-07, 07:16 PM   #6
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also most speakers have 2 speakers built into them, a tweater and a base, giving you 2 different ranges and 2 different sounds
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Old 08-30-07, 07:27 PM   #7
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its a mystery.
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Old 08-30-07, 07:31 PM   #8
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also most speakers have 2 speakers built into them, a tweater and a base
Better speakers have a tweeter (small cone), a woofer (large cone), and a midrange (take a wild guess what size these are. ). Each is better at producing certain ranges of sound, and combined are much better at producing a wide range of sound than would a speaker with one cone.

Some larger speakers have more than one of each type, as well.
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Old 08-30-07, 09:19 PM   #9
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Saw the word produce. Noticed it wasn't about produce. Not my area of expertise. See ya.
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Old 08-30-07, 09:20 PM   #10
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I thought there were tiny musicans at the bottom of each speaker.
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Old 08-30-07, 09:31 PM   #11
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here's my question... the spoke on your bike goes spinning around the hub. The outside tip of the spoke (connected to the rim) makes x revolutions per second. The inside tip of the spoke (connected to the hub) also makes x revolutions per second. The outside tip of the spoke travels much further around than the inside tip of the spoke in the same amount of time; therefore, it must be going much faster. How the eff does part of the spoke go faster than the other part? Is there more force being exerted on the outside part of the spoke than on the inside? I know there's probably a very logical physics-related answer to this. So let's hear it. But at the "Mr. Wizard" level, please, so I can understand it.
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Old 08-30-07, 10:19 PM   #12
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The nipple end of the spoke is going faster. But it's covering a proportionally longer path, so it finishes its circle in the same amount of time as the hub end.
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Old 08-30-07, 10:31 PM   #13
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here's my question... the spoke on your bike goes spinning around the hub. The outside tip of the spoke (connected to the rim) makes x revolutions per second. The inside tip of the spoke (connected to the hub) also makes x revolutions per second. The outside tip of the spoke travels much further around than the inside tip of the spoke in the same amount of time; therefore, it must be going much faster. How the eff does part of the spoke go faster than the other part? Is there more force being exerted on the outside part of the spoke than on the inside? I know there's probably a very logical physics-related answer to this. So let's hear it. But at the "Mr. Wizard" level, please, so I can understand it.

It is a very logical physics question and its really one of the first things most physics teachers are going to teach you, one of those things that starts getting you in the right frame of mind.

You should actually just be happy that you figured it out on your own

It's really not as complicated, the outside has to go faster so it can keep up with the inside.

Every child experiences this before they even touch multiplication, on a merry-go-round. Stand up in the middle...easy, stand up on the edge? Good luck.
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Old 08-30-07, 10:34 PM   #14
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http://phun.physics.virginia.edu/top...ntrifugal.html
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Old 08-31-07, 05:18 AM   #15
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I hope this answers your question.
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Old 08-31-07, 06:43 AM   #16
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Originally Posted by timmyquest View Post
This use to bewilder me all the time, then without studying it at all i think i kind of figured it out on my own one day, so please correct me if i'm wrong.

What you hear is not a bunch of sounds, but rather one sound. This goes for anything that passes through our ears. So you hear a 100hz bass note and a 3000hz drum beat. These two would mesh together in a sense.

Sound waves are tend to be thought of as traverse waves by people, because in their origin they kind of are...that is until the speaker does its job. Really what speaker is doing is changing its signal into longitudinal waves which is how we hear sound. Sound is nothing more then air moving in longitudinal waves.

So picture your bass wave if you will with these vertical lines

| | | | | | | | | |

Now picture your drum beat

llllllllllllllllllllllllllllllllllllllllllllllllllllll
Now the two at the same time

|llll|llll|llll|llll|llll|
The waves aren't separate, they are instead just meshed together. The thing is, it isn't the actually sound waves that are different, the difference between a drumb beat and a bass note, the thing that enables us to pick those noises out, to distinguish them...is our brain


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Old 08-31-07, 07:44 AM   #17
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It's simple. Magic.

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Old 08-31-07, 08:25 AM   #18
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Its easier to think in the power spectrum I think.. The fourier transform of a waveform decomposes any signal into sinusoids across the spectrum, each at different power levels. A pure tone will produce one spike at its frequency till its hits the noise floor, but any impurities will produce whats known as a harmonics (2nd, 3rd being the most prominent in power).

In reality when you look at a sound waveform, its different frequencies signals multiplied with each other, ie different fundamentals and their harmonics. One of the properties of the fourier transform is that time domain multiplication, yields to frequency domain addition, hence in the frequency domain you can just add the power levels and come up with a composite power spectrum that represents your signal. When you apply this electrical impulse to a speaker, the frequency response of your speaker will guarantee that the output is comprised of similar power levels at all the applied frequencies.

Now how you hear would be similar too but I have very little insight into how the signals are interpreted by the brain how the sensing (or sampling?) is done.

EDITED for clarity.

Last edited by skinnyone; 08-31-07 at 09:09 AM.
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Old 08-31-07, 08:47 AM   #19
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Old 08-31-07, 08:59 AM   #20
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I hope this answers your question.
This was the image I was thinking of, but it needs some explanation. I think (correct me if I'm wrong) the blue sine waves represent "separate sounds," and they add together to produce the yellowish-white wave, which is a combination of the sounds that has the same effect on your eardrum.
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Old 08-31-07, 10:26 AM   #21
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another of life's mysteries resolved. Thanks for the answers!
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Old 08-31-07, 11:18 AM   #22
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This was the image I was thinking of, but it needs some explanation. I think (correct me if I'm wrong) the blue sine waves represent "separate sounds," and they add together to produce the yellowish-white wave, which is a combination of the sounds that has the same effect on your eardrum.
Looks like it, and also the two different beat-frequencies timmyquest posted are summed together. This can represent the spacial location of the speaker cone at any moment in time.
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Old 08-31-07, 11:25 AM   #23
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What I can't figure out is how you can have 2 tones, exactly the same frequency, but yet sounding so different. You can have a cello produce a concert A, which I think is 442 hz?, and a guitar that produces the exact same concert A, but the sounds are so distinct. Same note, same volume, but yet worlds apart.
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Old 08-31-07, 11:50 AM   #24
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What I can't figure out is how you can have 2 tones, exactly the same frequency, but yet sounding so different. You can have a cello produce a concert A, which I think is 442 hz?, and a guitar that produces the exact same concert A, but the sounds are so distinct. Same note, same volume, but yet worlds apart.
Hmm.. I would guess that they look different in the time domain as in their spectrum would look different depending on the shape of the waveform.

A triangle wave spectrum looks markedly different from a sine wave and they will sound different when you put them through a speaker.
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Old 08-31-07, 01:59 PM   #25
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"What I can't figure out is how you can have 2 tones, exactly the same frequency, but yet sounding so different. You can have a cello produce a concert A, which I think is 442 hz?, and a guitar that produces the exact same concert A, but the sounds are so distinct. Same note, same volume, but yet worlds apart"
Thier pitch and frequency is the same, but thier timbre is different. The concert "A" that each instrument produces is the fundamental frequency, but there would also be a heap of overtones along with it (unique to each instrument) that help form a sound specific to that instrument. There's also the different attack and envelope of each that shape how it is perceived by our ears. I think.

Here's a Wikipedia article on timbre that probably 'splains it far better...

Timbre
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