Say your chilling, listening to some great music.
Ever wondered how you can hear a bass guitar and, say, a bass kick at the same time from only one speaker?
Two sounds, at one time, from one vibrating surface.
As an example. Lets say we have a bass guitar, it hits "A note" (440Hz)
We also have a kick drum which is somewhere around 60Hz. (for arguments sake.
The sound of a kick drum is a complex system spreading from low (30hz) way up high (200hz).
How can a speaker possibly play at 440Hz (440 cycles per second) AND 60Hz, to reproduce the
sound of both bass guitar and kick drum? Isn't that like saying i'm running at 5km/h AND 20km/h
at the very same time....?
In reality, this is an incredibly complex system of music. A bass kick or guitar not is NOT a simple tone,
its a complex series of harmonics and frequencies already! Combining the two sounds, is combining two
very complex systems. Its almost impossible to mentally picture the actual wave-form of dynamic music
on the fly. Try watching a visualisation program in winamp, for instance, without the sound on.
It can all be a little confusing, at first glance.
To understand how it works, we need to simplify things.
Lets follow the old adage, K.I.S.S. Keep it simple, stupid!
So, lets pretend instead of a complex, layered sound like a drum kick, or a guitar chord,
we are simply trying to play two, simple tones.
A simple, 440hz tone. A simple, 60hz tone.
How does a speaker play a simple tone?
A speaker produces vibrations in the air we hear by rapidly oscillating back and forth.
On a sine wave graph, this can be represented as positive and negative voltage.
Due a speaker design, a positive voltage will make the cone move in one direction lets say "outwards".
Zero voltage will keep the cone at rest, at its centre point.
Negative voltage will make the cone move in the opposite direction, lets say inwards.
To produce a tone, the speaker moves outwards from the rest point, back through it, and then inwards.
It constantly oscillates. You can see this on the graph below.
It basically follows the voltage applied to it.
(Try this with a 9volt battery on the speaker terminals of a woofer, you'll see the cone move one way, reverse the battery and the cone moves the other way. Dont leave the battery connected too long).
What it means in practice
Now, picture someone flipping the battery around 440 times a second.
Thats your 440hz tone (Basically. In reality, the voltage smoothly peaks and dips, its not on/off).
Imagine someone flipping the battery around 60 times a second. 60hz.
Now imagine two people doing that, on the same speaker, at the same time.
If they both have the battery on the same way at the same time, the cone moves twice as far in that direction.
If both batteries are on the opposing ways (only one flipped), at the same time, the cone wont move at all but hold its position for
a split moment.
Any audio signal is a mixture of different voltages at different frequencies, so the shape of the voltage on the speaker
determines the cone position at any time.
Now, heres a graph of two different frequencies occuring at the same time.
The big sine wave, is about 1khz. The smaller "fuzzy" wave, is roughly 80khz.
You can see how one frequency, the big sine wave, has a constant centre point like
on the first graph (Horizontal line with the big dashes). The second frequency, however, uses the big sine
wave as its centre point. When the curve of the big sine wave rises/drops, the centre point of the 80khz
frequency follows it.
The speaker is vibrating very fast (80khz) while slowly moving in and out (1khz).
We know the cone follows the voltage. Is it clicking yet?
You've probably picked this up by now, but if not heres a simply way of thinking of it.
You can do this right now.
Get your hand.
Hold it steady in front of you. Now move it up and down slowly around a point.
Say, 30 cm up and down.
Stop. Do it again, but over a 5cm distance.
Combine them.
basically, flap your hand over 5cm while your moving your whole arm up and down.
Thats exactly how a speaker does it.
So, while the speaker cone is slowly moving in/out at 60hz for that phat bass kick, its also rapidly
cycling at 440hz for the bass guitar note.
The 440Hz signal is only a tiny vibration and doesn't actually have to return past the cones initial starting
point, it only has to move a few millimetres in and out whilst the cone is still travelling outwards completing
the first half of the 60Hz signal.
So now you know.
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Major contributors to this FAQ were (in no order)
Shinanigans, Pulse-R and Trism.
I basically re-wrote a lot of their concepts, introduced some of my own, and edited it all.
Original thread at http://www.caraudioaustralia.com/forums/in...opic=68619&st=0