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Can you correct nulls with acoustic treatments.

I have Magnepan 1.6's. After hearing a musical clarity I really liked in a listening session at someone else's house, I broke down and bought a Rat Shack SPL meter and dowloaded some test files. I wanted to see if it was the acoustics or the type of speakers and system that made the difference.

A brief testing showed a 65 to 80 hz., 5 or 6 db. bump (the drywall bump?) that I had expected. What I didn't expect was 10 to 15 hz. wide nulls (-10,-15,even -20 db.) at several other frequencies.

I tried moving speaker positioning and the frequency of the nulls moved but the pattern was basically the same.

Acoustic treatment to tame + nodes seems intuitive. Can you treat nulls or is this a different problem?

Would really appreciate your thoughts.

Jim S.

stilljd
ngjockey
1,042 posts
 
The worst room I ever heard had one 8' diagonal wall in the rear corner. It had two 300Hz nodes just in front and to the side of the listening position that were painful, even with music. I helped him get some materials for DIY tube and panel traps and that helped quite a bit, except aesthetically.

You might have to completely rearrange the room with the speakers on the long or short wall. The good news is you have lots of room to deal with and, apparently, bass is not the problem. It's easier to deal with higher frequencies.
stilljd OP
151 posts
 
Ngjockey,

Thanks for the reference information. I was actually hoping the nonparallel walls would be helpful, not detrimental. Such is life!

I have some work to do. I now have an idea what to look for. I will do more detailed measuring with the easy modifications and see if I can't find a pattern as you and others have suggested.

I can eliminate the furniture 1 piece at a time and make sure it is not a suckout issue. There is an open stairwell right around the corner from the listening position that may be providing a broad suckout. Not as easy to deal with, but I can work a temporary solution for testing.

Anyway, thanks for your time and advice!

Jim S.
plato
1,543 posts
 
Possibly putting a diffuser behind each speaker could help since you're dealing with cancellations from the rear output waves colliding with that of the front wave.

I had a room similar to yours and it was kind of tough finding the best speaker position and the best listening position. I had Acoustat dipoles and I recall that the bass was all over the map depending on which wall the speakers backed up to and where the listening seat was. With a lot of trial and error, you can probably find a configuration that will work pretty well. I remember that the Room Tunes worked very well in that room as did some home made Helmholz resonators (like the Argent room Lenses). Good Luck!
soundgravy
23 posts
 
Here it is, I knew I seen it somewhere.. :)

http://forum.audiogon.com/cgi-bin/fr.pl?htech&983682086&openflup&1&4
soundgravy
23 posts
 
Did you take in to consideration the fact that the Radio Shack SPL meter is not acurate? There is a page that shows the corrected calibrations for that specific meter. So your room may not be as bad as you thought. I will try to find that info for you if you dont already have it.
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