On 28 Jun 2005 13:40:54 GMT, "Pink_isn't_well"
wrote:

I have some speaker systems and I want to test their frequency
response. I'm not a sound engineer or anything and I don't really
know much about audio. But I assumed I could do this in the
following way.

I found a test clip on the net which has several frequencies in the
audible range 20 Hz - 20 kHz, each playing for 2 seconds. I open it
in Nero Wave Editor and it shows that it has the same level from
start to finish.

Then I take my mic and place it close to a speaker, I mute the
other speaker and playback this file, recording with the
microphone. I then save the recording uncompressed and open it in
Nero Wave Editor to see how loud/quiet each frequency is.

My understanding is that the recording should be as close as
possible to the test file that I use as input.

I did this with two different speaker sets and you can see the
results below:

http://img224.echo.cx/my.php?image=t...esponse7xo.png
http://img224.echo.cx/my.php?image=o...esponse8hv.png

Original test file (downloaded recording):

http://img156.echo.cx/my.php?image=testclip7ci.png

Is this lousy frequency response or what? Am I doing something
wrong with my testing method?

What you are trying to do here is really difficult, even for experts
with many years of experience. You are suffering from a few specific
problems. First trying to do it in a normal room instead of an
anechoic chamber; I know you are trying to mitigate the effects by
close miking, but that doesn't help - a speaker is not designed to be
flay close up. Then you are using tones; this is virtually impossible
with speakers. You need to use filtered noise, perhaps a third of an
octave wide. This is to provide some averaging of the residue of the
room's effects. Lastly, you have overdriven the sound card with the
mic signal, causing clipping.

I'm sorry to have to tell you this, but unless you are prepared to get
really serious, give up with this plan.

d

Pearce Consulting
http://www.pearce.uk.com