test results

[goldenjjg]

My test results, room size is 13'6"x 15'4" one 6' opening to another room about the same. Sub in corner opposite opening. Onkyo 701 receiver, Phillips DVD, Polk 6200 series main,center and surround. I made a sine wave test cd from 18hz to 99hz. All tones at 0db. Modified radioshack analog sound level meter to give direct readings down to about 10hz. 18hz-64db,20hz-71db,24hz-77db,27/31/35hz-81db,39hz-79db, from 44hz to 70hz-73to75db,74hz-68db,78&83hz-73db. The only area that really needs help is at 74 hz. The peak at the low end will probably help for movies. Maybe this sub was designed for a little extra in the 25-40hz range. Overall, in my H.T. room, excellent responce. Tests were made with receiver in dolby pro logic 2 mode and x-over set at 80hz. Test tones were stereo. Hope this helps anyone thinking about buying one of these. Jim

[Lwang]

Looks like the first room mode are 37hz and 41hz, resulting in a significant rise in response below those frequencies due to the whole room being pressurized.

So you pretty much get an 20hz -3dB extension in relation to the >40hz signal, and roughly 25hz -3dB extension when using the <40hz signal as reference.

Maybe you should feed it some narrow band pink noise or warble tone to minimize standing waves when measuring.

[goldenjjg]

When you say warble tone, do you mean sawtooth wave?

[Lwang]

Warble tone meaning a sine wave that moves up and down a narrow range of freq very fast. Prevents the buildup of standing wave, which usually occurs with continuous playback of a sine wave that coincides with a room mode.

Anyway, the lump below 40hz is probably due to the 1/2 wave of sound <40hz being longer than the lenght of your room.

[goldenjjg]

After a little more reading, I see how that can affect meter readings. Thanks for your input. Jim

[Lwang]

And you should put the SPL meter in slow response, so that those momentary peaks would be smoothed out.

BTW, did you modify the SPL meter yourself? After a while, I get tired of doing the correction factor, especially when there are tons of numbers (like when moving the sub to every 1 ft along the wall, etc).

[goldenjjg]

Yes, I did modify it. It is fairly simple to do. Just have to be careful with the mic, too much bending could cause leads to break off. Here is the web address: http://www.gti.net/wallin/audio/rsmeter/33-2050/33-2050.html

[Lwang]

I saw that before, but with all the SMD (I presume that's what's in there), I am afraid things will overheat and burn out almost instantly.

[goldenjjg]

no SMD in the analog meter, probably in digital meter. As the article shows, you can solder the caps directly on the back of the board. I just replaced all of them. One wouldn't fit on top [cover wouldn't close] so I soldered on back. Only did low freq. mod. Took me about 20 min. to do.
If you don't want to tackle this, I can mod meter for you.