[sdiy] Harmonic bandwidth

[Nicholas Gregorich]

Ian Fritz wrote:
> At 12:48 PM 1/9/2008, Nicholas Gregorich wrote:
>> Ian Fritz wrote:
>>> Speaker dynamics: If you put a perfect sawtooth into a speaker you 
>>> would be asking for its displacement to change instantaneously.  If 
>>> you rephased the harmonics then you would no longer have this step.  
>>> Of course you never have exactly this situation, but the transient 
>>> mechanical response of the speaker to a step should be kept in mind.
>>> For this reason I think the sawtooth does not make a very good test.
>>
>> This seems like a valid point, but what bothers me is that there isn't 
>> much of a transient effect since there are only 32 harmonics. Adding 
>> sines from 100Hz to 3.2kHz shouldn't be causing a speaker to struggle, 
>> should it?
> 
> I have to admit, I don't really know what this waveform looks like.  How 
> fast is the rise, say 10% to 90% at 100 Hz?  What happens when you drive 
> a speaker with a square wave?  Isn't there a lot of slewing and ringing?
> 
> Ian
> 

The 10-90% rise time on a 100Hz sine wave is approximately 1.5ms.

The 10-90% rise time on the saw wave [100 cps] with 32 uniform phase 
harmonics is approximately 89.5us [~11kHz?].

I don't know what happens when you drive a speaker with a square wave 
with lots of high order harmonics. I imagine it must filter the 
harmonics that are excessively higher than the frequency response of the 
speaker. But in this case since the highest frequency is only 3.2kHz I 
find it hard to imagine that the speaker is slewing already.

I have to admit I don't know much about speaker physics. :)

Nick.