I don't know. In real life it seems to work as any compressor. Without it,
the frequency curve gets jumpier, exactly the same but more up and down. It
is a part of the complete analog machine, made in Germany sometimes around
1980. Only the HP XY printer is separate.
This machine has been very handly, as - when I work with a microphone
capsule - I can set the machine to make a sweep "loop", around and around,
and in the same time see the measured frequency response on a special
cathode-ray tube. It looks exactly as a log. frequency scale, with x=3Dfreq
and a glowing dot following the Y=3Doutput from the microphone. The tube ha=
s a
delay, that is - I can see the entire diagram on it until the next sweep
overwrites it. This way I can follow the frequency diagram in "real-time".
Example: If I put a piece of cloth, or foam, between the loudpeaker and the
mic, I can see the immediate result of it. Or I can put some dampening
between the mic and the PZM plate, and see the result of it immediatelly.
I can also make the frequency output manually, by turning a knob. The
glowing dot will follow the output frequency, as well as the printer. Both
will show the actual db output of the microphone, and the display will show
exactly which frequency it is.
Until now it has been a really good set-up. Now, it seems, the same thing
can be done much easier and more acurate with a PC. I just don't know how
yet. The FFT analyser would work very well with noise, (they tell me) but
how do I get a loudspeaker generate enough powerful noise, enough flat and
smooth? The Scanspeak globe HF loudspeaker can be equalised so that it
performs fairly flat from 500 Hz, but below that? And even so, it has a few
narrow band peaks/gaps.
I mean, in a anechoic chamber you let the loudspeaker be as it is and
compare your measuring object with a reference object, "hearing" the same
sound as the measuring object. But I don't have any similar "reference"
parabol. And if I had, I would never be sure that this "reference" parabol
would "hear" the same thing as my measuring object. I would say it is
impossible (at high frequencies) to make one parabol "see/hear" exactly the
same as another. They are too much apart, and pointed differently.
Therefore I need a sound source which is "flat" from the beginning, and
regarless of official loudspeaker specs and figures - they are all terribly
unlinear.
Klas.
At 12:31 2003-07-05 -0700, you wrote:
>>The mic beside the loudepeaker, about a meter away, is only a "leveler". =
It
>>flattens out some of the irrgularities caused by the loudspeaker.
>
>How does it do that?
>
>-Dan
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Phone & fax int + 295 310 01
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