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In Reply to: the Analog meter posted by Joe Murphy Jr on January 05, 2002 at 22:35:29:
I'm quite interested in your rational for describing the "A" weighted scale for SPL sound calibration. Can you give a bit more detail?Typically the "A" scale is used to quantify the amount of "damaging to the ear" SPL levels in the workplace or anywhere else for that matter. Because of this the scale is limited in frequency response (no bass) to the range -> 500Hz to 10kHz.
The "C" scale, on the other hand, measures over a more musical range from 32Hz to 10kHz. Measuring with the "C" range may also capture room mode peaks when using pure tones as the test signal source, but this can be corrected by using "warble" tones such as those found on the "Stereophile test CD disk 2 & 3".
I recommend using the "C" scale, or you will never be able to calibrate your sub correctly in relation to the rest of your speakers.
Now the meter does have some deviations from flat response, but those can be corrected for by applying well known adjustment figures available here as the "RS SPL meter correction values".
bstan
Follow Ups:
at the same time, since the pink noise is pretty much random. So for sub adjustment, you would never know the real SPL of the system. Unless you figure out the bandwidth and distribution of the pink noise, do a weighted response drop of the meter for that freq range, and compensate for that. Plus one might have to compensate for the premature rolloff of the sub, since if the sub is not producing any sound below 30hz, the level will be boosted by the person to bring the whole level up to 75dB.
That is why I recommend doing the level matching @ crossover freq, plus plot the whole sub range and maybe mains to 200hz see the integration.
I have another reference (still looking for it) that indicates the low frequency response for the RS SPL meter with pink noise is only 2-3db less than at 1kHz.bstan
If you are only measuring 20-80hz, and the meter starts going low @ 60hz, then the avg as a whole would be off. So if you measure 75dB on the ratshack meter for LFE, it might be actually producing 78-80dB, depending on the sub rolloff & meter inaccuracy.
But you can't accurately measure the pink noise SPL below 500Hz with the "A" weighting on the SPL meter, because the "A" weighting response sensitivity drops off substantially below 500Hz.How do you correct for that?
bstan
This gentleman has done some work with RS spl meter's.
Perhaps it is of help.http://www.gti.net/wallin/
Bill
Thanks,Yes, I have built the calibrated mic-wand and a battery operated mic-preamp displayed on that site and they work quite well.
The mods to the RS SPL meter are designed to correct the response curve for the "C" weighted curve which does measure below 500Hz, but the "A" weighted curve still doesn't measure below 500Hz.
bstan
I'm looking at getting a Behringer DSP 8024 analyzer. might be a ok measuring device with the ability to make some system changes.Bill
Yes, it gets pretty good comments here, but if you are using it to eliminate room peaks in the subwoofer range, just be aware it is limited to only a few parametric EQ filters, unlike the BFD-1124 which provides for 12 filters per channel.bstan
ok, I give. I cant find info for a BFD-1124 anywhere.regards,
Bill
although bfd.com has a pretty cool web page (very off topic)
It is currently being sold as the replacement for the BFD 1100, Behringer just hasn't upgraded their webpage yet for the 1124.Maybe this is a first! Instead of vaporware we have webvapor.
bstan
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