Can you correct nulls with acoustic treatments.

Speaker and/or listener placement along with capacitive style low frequency traps can help. The first thing is to figure out why you have the nulls. Are they uniform around the room (a suckout), are they caused by a piece of furniture (I've gotten my share of surprises here), or are they a basic function of room dimensions. I won't go into great detail for any of these, but rule out furniture first--remove anything that might be causing the problem and remeasure. Second is to map the room with your problem freuqencies--do they vary relative to the wavelength of that frequency? If so, it's a basic room mode issue. Placement can be a big help here as can the traps.

Now one thing you need to be aware of is there will always be one frequency at the centerline of the room that will be peaked, and another nulled. There is very little you can do about this with parallel walls. Calculate F1 and F2 for the width and that will tell you what those frequencies will be (this assumes you sit at the centerline of the room as most people do--while it has modal issues it typically has the best imaging). Now if there are other freuqencies you can see if you have an 1/4 wavelength cancellations. Are the speakers 1/4 of a wavelength off a boundary of that frequency? If so, they are cancelling that frequency out to some degree and should be moved to a distance that helps balance other peaked modes. Sounds easy--but it's a little more daunting because you'll find you will fix problem A reduce problem B and create a new set of problems.

Here is a link which may be of more help on this issue.
Rives Audio Listening room tutorial. There are also some good software programs such as Cara and RPG room optimizer that can help you as well.

What I didn't expect was 10 to 15 hz. wide nulls (-10,-15,even -20 db.) at several other frequencies.

No need to panic. This is quite normal. Do as Plato suggests first (try speaker positioning).

You will need very serious room treatments for these null problem areas if they are below 60 HZ (and I doubt you can cure them entirely without turning your room into something like a set from Flash Gordon). Fortunately you don't need to cure it entirely. For starters, you can easily reduce the worst bumps with a PEQ. (Bumps are more of a problem due to their masking effect). Although nulls cannot be boosted (can't boost what is not there)....smoothing out the peaks will really help.

Try listening to Rebecca Pidgeon The Raven, "Spanish Harlem" and adjust so that you can hear the bass notes evenly and with roughly equal loudness. Good luck...

When I have these issues, I end up using two tools. The first one is a rough estimator and it's online.
CaraQuick

Just punch in the dimensions of the room, fill in a little bit about your room (number of chairs, etc.) and then pick a loudspeaker in their dropdown that is close enough to Maggies. Main thing here is you can move your listening positon and speakers around and see the nulls come and go.

Then I use a measurement device like the Velodyne SMS-1 ($600) to read my room realtime and deal with the small movements, even if you don't use the subwoofer EQ function. There are cheaper analyzers, but I use it cuz I also EQ my subs.

Start with the Cara and at least find out what you're dealing with.

Thank you all for your responses. I was hoping to see 7 or 8 posts saying that's easy, diffusion. But I posted to leverage your experience before purchasing and it has already paid off.

Did a little more testing and review of the data. Found some hope in speaker placement and an interesting (and depressing) overall trend.

The room is a 60' long X 30' wide irregularly (almost a backward L) shaped finished basement. There is a "stadium" wall 9' wide at a 45 degree angle in one corner. That is where the system is set up, shooting out into the long part of the room. The only wall parallel or perpendicular to the speakers is the angled "stadium" wall. I think this contributes to the lack of boomy nodes.

The really serious nulls (-20 db.) are very location dependant. Move your head (or the meter) a foot or two and they change. Common sense seems to say that you would never be able to eliminate all the 2, 3, 4 hz. wide strong cancellations at a single position.

I moved the 1.6's straight back 5 inches and most of the nulls improved 4 or 5 db. I don't know if I like how it sounds as much (soundstage), but I may have to move my listening position to correspond to speaker movements. Classic chasing your tail.

The disturbing overall trend is.... 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). That seems like a lot. A quick review of old Stereophile freq. response graphs shows the speakers fairly flat from 50 hz. to the crossover @ 600 hz.

Care to venture an opinion of the trend?

FYI- The 1.6's are -15db. @ 35hz., -7db. @ 40hz. -3db. @ 47 .hz or so. Didn't change a lick with speaker movement or starting SPL.

Jim S.

"New speakers may be far cheaper - or may do nothing to correct the problem".

How would changing speakers change the room acoustics?
bob