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Suck out at 165 hz...can't find the cause

I have been focusing on improving my room and dealing with its effects on sound quality. I have been able to deal with some peaks in the 40-100 Hz region, and my room/speakers now measure generally quite well.

But I have a fairly narrow band suck out centered at 165 Hz, that is fairly deep (around 10 db). I have tried moving the speakers, putting up soft stuff (blankets, pillows, human beings) along the axes of the room, etc. Nothing seems to affect it at all.

Could this be something related to the speakers themselves (e.g. internal speaker cross-overs)?

This is an analog two-channel system with a Jeff Rowland Capri pre-amp, Kharma MP150 ampifiers and Wilson Benesch Curve speakers. Unfortunately, the reviews of these speakers do not have any measurements with them, so I don't have an external reference.

The amps are wonderful but are not super powerful, so I'm thinking that an RCS system won't help because trying to get rid of a dip of that degree will force the amps to work too hard and they probably won't be able to do it anyway.

Your thoughts as to what might be causing this and any advice on dealing with it are most appreciated.

Thanks!

--dan
dgaylin
darkmoebius
900 posts
 
What's the dimensions of your room?

Have you used a graphical room mode calculator to see what modes your room dimensions create?

If not, you can just enter your room measurements into this webpage (for Axial, Tangential, & Oblique room modes), this one or this webpage(if using Internet Explorer & MS Silverlight plugin)

Or, just download and run ModeCalc if you are using Windows
dgaylin OP
255 posts
 
Darkmoebius --

thanks for the response. I have tried a few of these sites before. They are useful, but I've never fully understood what I'm looking at, and I definitely don't understand how you interpret the results to see which frequencies will be emphasized versus those that will be de-emphasized. Any tutoring here would be most appreciated!

Thanks.

--dan
palasr
533 posts
 
I suspect it's something in your room, or as others have noted, something in the speaker positioning. Also, while you confess some degree of confusion regarding room-mode calculations, I'm curious how you arrived at the exact frequency you cite? Do you have access to a spectrum analyzer?

I had a similar problem around 132Hz, with a -12dB dip. As it turned out, it was my built in record shelves which have very deep cavities and a small 2" opening along the top of each shelf of records. Once I placed an airtight backing behind the records sealing this cavity, my problem was solved as I had inadvertently created a perfect Helmholtz resonator at this exact frequency.

I recommend the Master Handbook of Acoustics by F. Alton Everest as a must read for anyone interested in maximizing their listening environment.

-Richard
shadorne's avatar
shadorne
7,491 posts
 
If it is fairly consistent across the room then it could be woofer to floor and ceiling height effect (quarter wave cancellation) - a down firing subwoofer crossed over at 90 Hz might help.

FWIW a null/suckout at 165 Hz is not too bad provided it is narrow.
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