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Manually correcting off-center imaging with DSP speakers

hachre, modified 10 Years ago.

Manually correcting off-center imaging with DSP speakers

Padawan Posts: 27 Join Date: 9/23/11 Recent Posts
I am sitting in a pretty much untreated room that is frankly quite horrible to be in.

However I can't change that and after a lot of experimentation with the 8240A and the GLM set I've found a spot where the frequency response after calibration is surprisingly good.

The only problem that I have in this spot is that the imaging is pulled to the right. I'm testing by listening to a mono source and it appears to come from about 30 degrees (calling the right speaker 60 degrees) to the right while it should be in the center.

I have used the acoustic menu to drop the right speakers volume by an amount large enough to compensate for this. It ends up being -1.5dB (difference to the left speaker).

My question is: Do I have to change the distance setting as well? Is it better to calculate a new distance additionally to the change in volume or should I change just the volume?

My guess is to leave the distance calibration alone.

I think the imaging problem is coming from the fact that the left wall is close to 2.5 meters away while the right wall is just about 2 meters far. However moving more into the center of that wall seems to negatively impact the frequency response (especially below 100 Hz) and I'm more or less very lucky that I have found this spot anyway.

What do you suggest?
ilkka-rissanen, modified 10 Years ago.

Re: Manually correcting off-center imaging with DSP speakers

Yoda Posts: 2564 Join Date: 3/23/09 Recent Posts
Hello,

Distance and level settings are individual settings so you don't need to calculate new distance setting if you change the level. If the speakers are located at equidistance from your ears, I wouldn't change the distance settings. Of course with GLM it's easy to experiment so don't hesitate to try it out.

2,5 vs. 2 meters doesn't sound too bad, and usually it shouldn't pull the stereo image to off-center. Is any kind of acoustical treatment a no no? Treating just the first reflections on the side walls would probably do a lot already.
hachre, modified 10 Years ago.

Re: Manually correcting off-center imaging with DSP speakers

Padawan Posts: 27 Join Date: 9/23/11 Recent Posts
Hey Ilkka,

thanks for the reply!

It's not strictly a no but I have huge bass issues in this room because it has kind of square proportions and I know that fixing those would be kinda expensive so I am hesitant about investing much into this room since it's an apartment I won't be in forever anyway. On the other hand I'm doing mixes and I would like to get into it again (I have had a break from that for over 3 years now) and the bass issues are the most prominent issue here.

I actually have 3 pieces of acoustic absorbers and I've tried experimenting with them on the right side wall but I haven't been able to correct for this imaging problem.

This is a schematic of my room. The basic proportions are 5x5 meters. The wall on the right side that is offset into the room has a length of about 2 meters (roughly) and a width of 0.8m. The way you can see where I have put the speakers up they are slightly to the left of the center if you use the 5 meter wall and slightly to the right if you use the smaller about 4 meter wall behind them as a relative point.

Since my sketch is not really drawn with care it is hard to see but basically I have the mentioned 2.5 meters to my left side and about 2 meters to my right to this offset wall.

I have also attached the AutoCal setup result. The frequency response is the best I have found after a lot of experimentation in this room and trying out different placements. I do not know what accounts for the problem in the 1000-2000 area. I am using a table but the speakers are on stands behind it. But maybe it's still reflections off the table surface? Or it's the ceiling wall? I really have no clue :) The bass response looks somewhat flat (except for the stuff that GLM couldn't correct anymore because the filters ran out) however in reality it isn't really great. Certain frequencies trigger standing waves here that seem to take a time to build up thus were not included in the meassurement and blow my ears out. I guess this is because of the 5x5 dimensions of the room.

Thanks for any comments!
hachre, modified 10 Years ago.

Re: Manually correcting off-center imaging with DSP speakers

Padawan Posts: 27 Join Date: 9/23/11 Recent Posts
P.S.: I forgot to mention the green colors are windows, the blue colors are doors.
hachre, modified 10 Years ago.

Re: Manually correcting off-center imaging with DSP speakers

Padawan Posts: 27 Join Date: 9/23/11 Recent Posts
Ilkka, any suggestions? :)
ilkka-rissanen, modified 10 Years ago.

Re: Manually correcting off-center imaging with DSP speakers

Yoda Posts: 2564 Join Date: 3/23/09 Recent Posts
Hey,

Sorry about missing your reply!

1) Have you checked that the distance compensation done by AutoCal looks realistic? If they are not identical or within a few centimetres, set them manually. After this you should also play with the level compensation.

2) The 1000 - 2000 Hz reflection is most likely off the table in front of the speakers. Or are there any other large enough objects around the speakers (mostly in the front region) that could cause such reflections?

3) Have you looked at GIK Acoustics? http://www.gikacoustics.com/ They have some very nice bass and first reflection absorbers. Especially look at the room kits they offer. Unfortunately there's no way around it, if you want to make your room sound nicer, you need to add acoustical treatment.
hachre, modified 10 Years ago.

Re: Manually correcting off-center imaging with DSP speakers

Padawan Posts: 27 Join Date: 9/23/11 Recent Posts
Hey Ilkka :)

1) The distance compensation is perfect. It's a difference of 2 cm, I have set the right speaker to -1.0dB and it's centered then.

2) Yeah, it's a table, that's gonna be it most likely. But they are standing on stands behind the table - well their fronts are still above the table surface - how far away would I have to put them from the back side of the table so that this reflection gets minimized? Can I do something there?

3) I know, I know.. I'll check it out :) I think especially the bass traps would be required here, because the bass still has standing wave problems now, even after the compensation, because some of them seem to take a few seconds to build up and AutoCal thus didn't catch them...

Thanks! :)