Originally Posted by ymalmsteen887
regardless of what youre saying a sinewave is always present in any sound. If you have changes in pressure at 20 cycles a second you will hear 20hz if cycles occasianlly speed up they will sound louder if they often more or less often you would get a higher or lower frequency and if it wasnt consistent you would get a vibrato or tremolo when you say the wave is not perfectly smooth youre saying there are other frequincies present if you saw a frequency represented by voltage you would see it go up and down at different amplitudes and cycles its always going to be smooth.
Here is what the waveform of a violin looks like...
Image from: http://musikality.net/general/audio-...riertransform/
That is not a pure sine wave. There are waves there, but it is not a sine wave. However, that signal is what your speaker will see. And that is how your speaker will have to vibrate to reproduce that sound.
As explained on the site I sourced the image from, the sound of a violin is made up of several frequencies. The fundamental, and all the harmonics of that frequency. Now, let's examine this waveform.
Right near the zero crossing line, there are little ripples in the waveform. Very small, but there nontheless. A cheap speaker may not be able to recreate those ripples accurately. Perhaps it's mass overshoots, and exaggerates the ripple. Perhaps it's not sensitive enough to react to such a minute change.
Sensitivity is an important spec in any speaker. Lets say that speaker A will generate 85db when fed a 1KHz tone at 1 watt. Lets say that speaker B will generate 101db when fed a 1KHz tone at 1 watt. Which speaker is going to be better at reproducing that slight ripple in the violin's waveform? Speaker B, because it's much more sensitive to variations in sound.
An interesting thing to note is that while in the above example speaker B is the better of the two, there are cases where it will sound worse. If you feed speaker B a well recorded signal, you will get great sound out of it. But let's say you play a vinyl record on speaker B. You'll hear the music, and you'll also hear every scratch, pop, and other imperfection in that record wonderfully reproduced on the highly sensitive speaker. Garbage in, garbage out. But the less sensitive speaker A, will still reproduce some of the imperfections, but they won't be as easy to notice.
Okay, let's try another exercise. Total Harmonic Distortion, or THD. THD is how much distortion is introduced to a sound. In another thread I started, I did a hearing test where I asked people to listen to a 10Hz - 19Hz tone to see if they could hear it. Here is a spectogram of the source file:
The sound file starts at the bottom of the picture, and slowly works its way up to the top, from 10hz to 19Hz. Notice how there is one single vertical line per tone. This is the sine wave. The second and third harmonics of 12Hz would be 24Hz and 36Hz. Looking over at the 24Hz and 36Hz portions of the graph, we see only inky blackness. So our source signal has no harmonic distortion. Just a clean 12Hz sine wave, and nothing else.
Now, this was recorded from my headphone output:
Now look at the 12Hz fundamental (3rd orange line from the bottom) Look to the right. There is another line at 24Hz, and a third line at 36Hz! That audio was NOT in the source file. But the speakers in my headphones produced it nontheless! This is distortion. This is the speakers in my headphones not reproducing the 12Hz (or any other frequency on this chart) accurately.
Let's look at a different chart. This is my headphones producing 10Hz.
Recall that the original source file had zero distortion. However, on this graph, note the areas marked 2 and 3. These are the 2nd and 3rd harmonics of 10Hz (20hz and 30Hz) Those little spikes there standing above all the others are distortion. They were NOT in the source signal. But they are there now.
Now, let's look at a slightly more expensive sound system built by notnyt:
My headphones produce about 5.7% THD at that frequency. But notnyt's system produces 3.8% THD at that frequency. (and notice his level is over 30db louder than mine).
There they are. Objective measurements from two sets of speakers being fed the exact same 10Hz tone. Yet one is clearly doing a better job than the other. If a speaker is a speaker is a speaker, and they all sound the same, then both I and notnyt should have the same results. But we don't. Why? Because different speakers do sound different.