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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
shadorne's avatar
shadorne
7,477 posts
 
Depending on the order of the mode and type (Axial, Tangential or oblique) you will get peaks and troughs at different places across the room. The worst effects are when these combine at th elistening position.

Some things go across the entire room. The quarter wave cancellation reflection of the bass frequencies from the wall behind the speakers generally affects the entire room.
darkmoebius
900 posts
 
Hi Dgaylin,

Give us the dimensions of your room so I can post some graphs and data from the room mode calculator. Then, maybe we all can walk you through the most obvious possible culprits.

Also, a picture or two of your listening room would help.
dgaylin OP
255 posts
 
Okay, thanks again guys, and I think based on the additional websites you have sent me that Shadorne is probably correct and this is the quarter wave cancellation -- main listening seating (couch) is right against the rear wall, and so my ears are about 18 inches from the wall.

Darkmoebius, thank you for the willingness to help. I am in a hotel room and can't send pictures, but here are the basic room dimensions:

L: 19' 9"
W: 12' 6"
H: 8'

But it is a bit more complicated than that with the built in bookshelves and cabinets and a couple of small alcoves I can e-mail you a diagram of the room that I have worked up -- it doesn't transfer well as an forum post. Please let me know.

THANKS!!!

--dan
hornguys
180 posts
 
In the boundary dependent region - below 300 Hz - moving the listening location - even slightly - nearly always produces a much more noticeable difference than moving speakers or room treatments.

Best,

Jim
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