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-   -   110 hz freq resp dip (http://www.diyaudio.com/forums/subwoofers/64355-110-hz-freq-resp-dip.html)

MichaelJHuman 15th September 2005 07:59 PM

110 hz freq resp dip
 
I see a 10+ dB dip in freq. response in my mains when runninng 100-120hz test tones.

I have filters between the pre amp and power amp at 88 dB, but I don't think that's creating the issue.

If I setup my powered sub to try to compensate for this dip, I would be overlapping too much with the mains (at least the way I currently have things setup.)

Any ideas? I am not sure what's most effected in that range, but it seems to be that's the kick drum range.

simon5 15th September 2005 08:37 PM

It's probably a room interference if your speakers are supposed to play much lower than 110 Hz.

What's your room dimensions? Distance between speakers and each wall too?

You could test this by moving your speakers somewhere else to see if the dip is still there.

DSP_Geek 15th September 2005 10:50 PM

Re: 110 hz freq resp dip
 
Quote:

Originally posted by MichaelJHuman
I see a 10+ dB dip in freq. response in my mains when runninng 100-120hz test tones.

Any ideas? I am not sure what's most effected in that range, but it seems to be that's the kick drum range.

Let me guess, your driver is about 2 to 2 1/2 feet from the wall, right?

If that's the case, then you're getting a destructive interference from part of the wave diffracting around the enclosure, propagating to the wall, then returning forward and mixing with the direct wave. The distance for destructive interference is a half-wave, so from the source to the wall in that case is a quarter-wave. Since you told us your problem is around 100 to 120 Hz, let's split the difference and say 110 Hz. Sound travels at 1125 ft/sec, so the full wave is about 10 feet, ergo a 2.5 foot quarter wave.

Simple solution: turn the subwoofer so the driver is closer to the back wall. The interference wavelength will shorten, its frequency increases in proportion, and you don't have to worry since that'll take it out of the subwoofer's range.


Francois.

DSP_Geek 15th September 2005 10:57 PM

Oops. Missed the part about the dip being in your mains.

In that case you could always keep the sub turned, cross over around the dip frequency, and let the sub fill in partially for the hole. It won't be perfect - with a Linkwitz-Riley filter you'll still get a 3 or 4 dB drop - but it's better than nothing.


Cheers,
Francois.

SY 15th September 2005 11:54 PM

Important question- is this dip present regardless of measurement position?

eRiCdWoNg 16th September 2005 09:28 PM

Try lowering the low pass of the sub and then try its phase in 0 and 180 in relation to the main speakers?


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