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12-16-2004, 05:18 AM
I recently purchased an SPL meter for my HT. When I used it last night I first tested the speakers at 1 meter at 80db. Once I reached 80db with the front left I tested the front right and got a reading of 78db at the same volume. Is this normal? Then I found my center speaker was about 72db. (I'm guessing on that, I can't remember off the top of my head but it was much lower). Also, the pink noise wasn't isolated only to the channel I was testing. I noticed it coming from the other channels too, although only a very slight bit. Is this problem a function of the receiver or DVD player or just a crappy test disk? Or is it a problem at all? I was using Steroephile's test CD 3.

My set up is:
Polk R50 - Fronts
Polk CSi30 - Center
Polk R15 - Rears
Pioneer VSX-D711 - Receiver
Pioneer DV363 - DVD

Any suggestions or comments about any of the above would be greatly appreciated!

12-16-2004, 05:55 AM
I wouldn't worry too much about your results. Your Polk speakers' drivers are most likely not matched and tested to the stricted tolerances, hence you can expect some variability in their sensitivity and performance. If they were matched and tested to more strict tolerances, the price would go up considerably, while the performance would only be a bit better, not value added at all.
Also, even at 1 meter, it is possible that the environments immediately around your speakers could cause reflections, echoes, etc, and cause a slight variation. That's why receivers have level settings.

As for your center channel...I assume all your speakers' level settings were at zero when you did this? It's possible your center channel has different senstitivity than your main speakers, though I'd usually expect it to be higher...still, no major concern...

Your receiver should be able to emit a white noise test tone through each individual channel. If it's not, disconnect all except the speaker you are testing to obtain more accurate results. at 1 meter, it's doubtful there's much interaction from other speakers, but depending on your room's acoustics, not out of the realm of possibility.

One last thing...you are better off to set the levels of your speakers from the listening position than from 1 meter distance...this will compensate better for any possible room interactions, etc.

12-16-2004, 06:48 AM
Thanks Kex.
I did use the meter at my listening position after I did the above. When I had the fronts at 80db it again seemed like I had to jack the volume fway up for the center to get the 80db. Should I try 70db instead? I did test with all the speaker levels at zero. Also, one last thing which may be a huge factor, my listening position isn't dead center unfortunatley. This could explain my center speaker discrepancy, which is why I then tested at 1 meter.

12-16-2004, 06:51 AM
Yeah, if you aren't close to the center you'll have some discrepancy...and 80 dB is pretty loud at the listening position, try leveling to the volumes you'd listen to music/movies at.

12-16-2004, 07:55 AM
What level you measure it (70dB vs 80dB) isn't nearly as important as simply making sure everything is registering at equivalent levels. Just pick a level and make sure they are level.

12-16-2004, 11:32 AM
The others are right. The sensitivity of the speakers and the room environment can influence your SPL readings. In order to balance out the levels up front, my center channel output is adjusted about 4 db higher than the mains, and my left channel is bumped up about 1 db higher than the right channel.

Another issue that you should look out for is how you position yourself when taking the SPL reading. Wave reflectings off of your body can actually affect the readings (I've gotten variances of around 2 db by just changing body position). Radio Shack's instructions indicate that you should be perpendicular to the direction that the microphone points in order to minimize the sound reflections that result when you're right behind the meter.

The way that I take the SPL readings is I mount the meter on a camera tripod and angle it at 45 degrees. That ensures that the height and angle of the SPL meter is consistent for all channel readings. The tripod readings varied up to 1.5 db compared to what I obtained from just holding the meter by hand.

12-16-2004, 12:31 PM
Thanks everybody for all your input.