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How Is That Possible?

Y

yustr

AK Subscriber
Subscriber

While walking the dog this morning my thoughts turned to speaker physics (yes, I know I'm not normal that way.) So my question is: How can a speaker reproduce a cord?

My thoughts went something like this: a cord on a piano is made by striking multiple keys simultaneously which in turn strike the corresponding strings causing them to vibrate at their assigned frequency. That combination of sound waves reaches our ears and our brain interprets that as a cord. But isn't a speaker more like, say, a trumpet and can produce only one frequency at any given instant? How then can it reproduce that piano cord?

The only thing I can think of is that our ear-brain is evolved to somehow combine those separate frequencies into that cord even though they arrive at (very) slightly different times.

Thanks for any clarification.

yustr
 
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This might be an over simplification but,
If you took the Electrical representation of the said chord on a scope it would be a mixture of the combined notes instantaneously. The speaker is getting this signal which is actually a mixture of the notes that together mixes and because of differences in frequency, amplitude, duration is an instantaneously composite which doesn't in fact look like the component pieces of the chord so the speaker only (?) Has to produce the whole rather than the pieces in that instant.
Your eardrum is sort of a reverse speaker. It can't do the 3 notes individually simultaneously either. It's an instantaneous composite.
Clear as mud, right.
If I have this wrong, please feel free to correct me.
 
This is quite a difficult concept to explain, but let's have a go.
Firstly, a loudspeaker cone is not like a trumpet horn. It does not resonate at a single particular tuned frequency, it responds to a varying electrical signal.

If you look at a single constant tone displayed on an oscilloscope you will see a wave as a varying amplitude over time. If you now superimpose another fixed frequency on the same screen (dual channel scope) you will see both waveforms), but they are not synchronised because they are oscillating at different speeds . You can now draw vertical lines through these 2 waveforms and add them together at these points. You will get a voltage value at each point. This is precisely how analogue to digital conversion works. In the case of a CD this time slicing is carried out 44,100 times per second. When the digital data stream is played back it will be converted into the same combined waveform.

So, back to our scope trace - If you now add these 2 waveforms together you will get a single funny shaped waveform which is a combination of the 2 individual waves. This combination signal is what is sent to a loudspeaker and when we hear this our brains interpret it as the original 2 individual frequencies that created the combination signal played together. The same process applies however many original notes are played at any given moment.

I hope this makes sense.
 
A chord is a combination of mechanical vibrations.
A speaker output is a combination of electrical impulses.

Easy to see why a speaker isn't going to produce the separate tones without something in the process breaking down the electrical signal.
 
How about, a speaker is a transducer, similar in many respects to a microphone, but acting in reverse. A transducer to begin the chain of reproduction, and another to recreate, as well as possible, given the gazillions of variables, what went into the microphone(s). It's not exactly rocket surgery, but it's not exactly easy to understand, either.
 
I hate to say this but the over all wave form of music is what the speakers is producing, part of the wave form by the woofer part of the wave form by the midrange and part of the wave form by the tweeter. The rather odd looking wave form contains the over all energy of the sound we hear. As far as the amp, pre-amp, and wire are concerned there is only one shape of wave form at any instant. So if the wave form is to be accurate the electronics have to respond to much higher frequencies than we can hear because the device generating the wave form be it a cartridge , tape has many ups and downs around the zero axis for every minute period of time. We hear the results because thats the way are brains interpret the sound. So in away analog is like digital except the clock frequency is determined by the wave form and not the other way around. So if one note and another make a new wave form where the results add to gether thats easy to understand, but if two or more notes add in some ways and subtract in others thats fine too because our brains can take that new very complex wave form and interpret the results to be the sum and difference of the separate notes from separate instruments. Remember we have only one very small ear drum so if the ear drum can convert this complex wave form to influence many small hairs that vibrate at different frequencies combining in the brain to reproduce the different notes that make up a cord. In other words if an ear drum can do the job why can't a speaker cone. Cones are to heavy and not infinitely stiff so the work has to be divided up to multiple drivers . Where the ear drum when young can hear a wide spectrum of cords and transmit them to those resonating hairs of very light mass which generate electrical information sent to the brain. If an ear drum can do it then a speaker can do it. We just haven't developed the perfect single speaker driver as of yet that can.

I assumer you have heard of a square wave and the lesser know tri-angular wave. The square wave is the sum of even harmonics with the principal sine wave at a certain diminishing rate per octave and the triangular wave is the sum of odd harmonics including the fundametal. If one wave form can contain that many infinite frequencies and an amp can amplify that wave form to drive a speaker system and the speaker can reproduce that fundamental and the harmonics at the correct level while keeping everything in time then we will hear the individual notes that wave form contains to make that shape. So an amp isn't always reproducing sine waves. Its amplifying complex wildly shaped waveforms that transmit the fundamentals, sums, and differences at any infinitely small instant. The smaller and more accurate the instant in time is the more accurate the resulting sound we hear via our ear drums. Plus we have to teach are selves to hear just as we have to teach our selves to see. Because what the eye send the brain is up side down and also back wards. So we have to train ourselves to see as well as hear. We have to learn that way with all our senses. Sound is hard to uner stand. We can't see it, touch it, smell it, or taste it, but if loud enough we can Some times pleasantly feel it. But more often than not we painfully feel it in our brains and our ears components. But we have to learn and teach ourselves what this stimulus we call sound is and how it effects us.
 
justjed2 said:
How about, a speaker is a transducer, similar in many respects to a microphone, but acting in reverse. A transducer to begin the chain of reproduction, and another to recreate, as well as possible, given the gazillions of variables, what went into the microphone(s). It's not exactly rocket surgery, but it's not exactly easy to understand, either.
Click to expand...
I would add one thing, the speaker doesn't just make a single sine wave, it moves any which way the input signal tells it to. Well, that is the ideal, of course no speaker is perfect. While it is often very useful to think about the frequency components of a signal, sometimes it is easier to just think about the signal itself. If The microphone picks up a square wave, it converts it to an electrical square wave, and the speaker converts it back into a sound square wave.
 
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