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How do I know what frequency my sub is outputing w/ reciever test tones

702 Views 10 Replies 5 Participants Last post by  DMF
I just bought an spl meter from radio shack. I was using it yesterday to set up my speakers and subwoofer. I know that the meter is not accurate for low frequencies w/ the sub, but how do I know what frequency my sub is putting out. I just used test tone from my receiver and set everything equal at 70db. How do I know how much to compensate the sub though?

Also, since I balanced all of them at 70db's does that mean they will stay balanced at say 80 or 90 db's?
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The receiver puts out pink noise, so it's not one frequency. Best number we've come up with is 3 dB to compensate. That means if you are setting everything to 70 dB, set the sub to 67 dB on the meter. (Adding 3 dB gets you the correct 70 dB).

The balance will be good at any volume (until you start to get power compression at high volumes).

Unfortunately, getting a rough balance with the SPL meter on the sub is not enough. Where you are in the room can have a tremendous effect on what you (and the meter) hear from the sub. As a test, move a couple feet in either direction and take another reading. It will be different, and the difference is frequency-dependent. Some frequencies will be higher and some lower. (You'll get the same effect from moving the sub.) Easiset way to deal with this is to place the sub where the frequencies are as equal as possible at your listening position.

Also unfortunately, the SPL meter by itself isn't very good for this. You'll have to use your ears. Easiest method is the "crawl around test". Place the sub up in your listening position, play some bass, then crawl around the room at sub level listening for the best bass. Place the sub there and re-balance.
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Thanks for the info DMF. So are you saying that where my sub is placed now, if I do the crawl test and find the area where I can hear the best bass, that is where I should place my sub?

Also, does it matter what db level I balance my speakers at, i.e. is it more accurate at say 80db then at the 70db's I'm using now?
No. Put your sub where you normally sit, then crawl around.
Some people like to set their sub 3dB or more higher than the other speakers, but that depends on personal taste. As far as speaker placement goes, I had my sub right next to my main speaker, and the bass was very weak. The bass also reduced greatly as I increased the volume.

The speakers were in phase and changing the phase did not help.

I moved my sub about one foot over --closer to the corner of the room, and the deep strong bass magically reappeared, although the bass was now a little too boomy. I moved the sub out from the wall a few more inches and lowered the sub volume, and the boominess disappeared. Now the bass is deeper and tighter than ever, proving that sub placement makes a huge difference!

For a room with bass peaks (which includes just about every room), wouldn't setting the sub level according to pink noise result in the sub being set too low? For example, assume that my frequency response for a given setting is relatively flat at 80dB, but at 70Hz, I have a peak of 100 dB. Now, if I'm sending out pink noise and measuring with an SPL meter, it would show 100 dB, right? (Ignoring meter calibration issues) So if I set my system based on that reading, wouldn't 95% of my sub's frequencies be set too quiet (because they only give 80 dB at that volume setting)?
My experience, and that of a number of other members who have posted on the subject, have observed that automatic parametric equalization programs often set the sub at too high a level. This happened to me when I used the YPAO program built in to my Yamaha RX V2400 receiver. I learned the hard way that I had to use an SPL meter to get my subs' level to match the level of the other speakers. I have never heard a satisfactory explanation of why this happens.
Originally posted by BigDog84
For a room with bass peaks (which includes just about every room), wouldn't setting the sub level according to pink noise result in the sub being set too low?
No, and yes. Pink noise is all frequencies at once. The meter reads the *average*, meaning it is affected by the peaks, but not so as to set the whole band at -20 dB because there is a single -20 dB peak. A peak, of course, will affect the average, but most room peaks are fairly narrow.

I'm fairly new to the use of meters for speaker setup, but it doesn't make sense to me that the meter would read an average SPL. As an example, lets say that I'm playing a test tone of 100 Hz at 80dB. At the same time, a mouse squeaks in the corner at 15kHz at 5dB. Under the assumption that the meter takes an average, that means that the meter would drop to just 42.5dB because it would be averaging the 5dB sound and the 80dB sound. That just doesn't make sense to me. It makes more sense that the addition of the 5dB sound would increase the overall SPL in the room (although by a negligible amount), which is what the meter would show. Could you please help me understand how my logic is flawed?
I'ts not an average as you're understanding it. More like a histogram, which samples each slice in a range and averages the result.

Check out this site for a discussion of sound measurement: http://www.termpro.com/articles/weight.html
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