09 Dec 09

Square Wave: busting your mind, not your speakers

I’ve before puzzled over what it would take to create an extended wave that looks like DC offset or low frequency square wave (not an actual impossible square wave with infinite harmonics, but just one that mostly looks squarish.)  This is a case where the input signal and the speaker cone(s) movement and the resulting air pressure wave can look quite different from each other.

Another common time that square waves comes up is when clipping happens in the amp/interface.  This is a known speaker killer, but maybe not in all cases as I originally thought.

Today I actually googled the topics and found the following decent discussions of them.



The diyaudio thread is huge, with some interesting parts.  Here are the main points I liked:

  • If a speaker receives a DC, it will begin to move at a more or less constant speed proportional to the amount of voltage.  It will take a certain amount of time for the speaker cone to reach the maximum point it was designed for – which suggests that there are many square waves that will not result in blowing up your speakers.  These friendly square waves would then appear to be of relatively lower amplitude and/or higher frequency.  This is probably not so surprising, but now at least you might feel a little better about playing pan sonic at reasonable volumes.
  • There is a derivative (as in calculus) effect between the input signal to the speaker, the speaker cone, and the waveform produced in the air.   You put a square wave into s speaker.  The cone moves in a triangular fashion.  This creates a square wave in the air.  Of course it doesn’t really matter so much except for phase when dealing with sinusoids with their uncreative deriviation and integration laws.

Of course, there are many square waves that will blow your speakers up.

Next, I want to find out what the hell wind is.