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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
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.
stilljd OP
163 posts
 
Plato,
Thanks for the encouragement. I will work at it and see what I can learn.

Soundgravy,
No, I did not know the Rat Shack SPL meter was seriously inacurate. I will reread the thread (probably many times) and try to understand. Thanks for posting.

BTW- Do you guys miss Sean? (From the RS meter thread, and many others, that Soundgravy cited.) He really relished the technical and did a lot of work to solve problems. I notice he doesn't post as much as when I started following Agon threads.

Jim S.
onhwy61's avatar
onhwy61
5,289 posts
 
the 1.6's probably average -7 or -8 db. from 80 hz. to 290 hz. (the range of this test CD is 10 hz. to 300 hz. in 1 hz. increments)....
FYI- The 1.6's are -15db. @ 35hz., -7db. @ 40hz. -3db. @ 47 .hz or so.

1 - don't measure in 1Hz increments. No speaker/room will measure smoothly at that level. Use either broad band noise or a slow moving sweep type signal to measure.

2 - Are you interpreting your measurements correctly? Rather than a broad dip from 80 to 290Hz, do you really have a boost in the 40 to 80Hz octave? If so, it's a fairly common problem that in relatively easily solved. How does the overall bass level compare to midrange (400 to 2000Hz) levels?
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