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How can I tame these wild modes? Studio Monitors
Old 3rd September 2011
  #31
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SörenHjalmarsson's Avatar
 



/Sören
Old 3rd September 2011
  #32
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Very educational thread.

Thank-you Gentlemen !
Old 4th September 2011
  #33
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Jens Eklund's Avatar
Quote:
Originally Posted by boggy View Post
No, I don't agree, because we have more near walls in small rooms that are close to our speaker (side walls, ceiling, floor, back wall), and this situation isn't described.
In Genelec text we have a situation with only one boundary in a theoretical half space, even floor SBIR isn't modelled.

With all our boundaries, we have more SBIR issues that can be only solved with basic loudspeaker placement methods, using measurements (easier) or with listening sessions (much more time consuming). And this is a only one way to find a compromise between all real SBIR issues in a small room, not only one that is idealised and isolated.
Did you read the text at all?

I am not getting enough bass?
Old 4th September 2011
  #34
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boggy's Avatar
Quote:
Originally Posted by Jens Eklund View Post
Did you read the text at all?

I am not getting enough bass?
Yes, especially proposed solutions.

Sorry, I never accept anything a priori, that I can read, if I have different experience and/or different knowledge. If I'm unsure, I will check practically...
Old 4th September 2011
  #35
Gear Maniac
 

Some interesting thoughts there

My thoughts on how thick the absorption on the front wall needs to be was much simpler:

Basically, the absorption serves 2 purposes: a) attenuate the room modes, b) counteract the SBIR effect between the speakers and the front wall

40cm (16") of rockwool (GFR 6000) has an absorption coefficient of 0.64 at 62 Hz, where the first mode is. This will certainly help a lot.

If I install 40cm of absorption and place the speakers right in front of it, the drivers will be 70cm away from the wall. This should result in a SBIR effect at about 123 Hz. At this frequency, the absorption coefficient is almost 0.8, which means that there shouldn't be an audible SBIR effect.

BTW, the front wall is a thin brick wall (10cm / 4"), the other walls are very thick stone walls.

Before I even started with any treatment, I experimented with speaker placement and found that the position close to the front wall was best. Also, it leaves more space for recording.

Anyway, I'm gonna do some more experiments with speaker placement today, but they will more or less remain where they are.
Old 4th September 2011
  #36
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boggy's Avatar
Quote:
Originally Posted by bermudaben View Post
...
My thoughts on how thick the absorption on the front wall needs to be was much simpler:

Basically, the absorption serves 2 purposes: a) attenuate the room modes, b) counteract the SBIR effect between the speakers and the front wall
Yes.
Quote:
Originally Posted by bermudaben View Post
BTW, the front wall is a thin brick wall (10cm / 4"), the other walls are very thick stone walls.
Yes, this is a different problem if wall isn't enough thick...
Quote:
Originally Posted by bermudaben View Post
Before I even started with any treatment, I experimented with speaker placement and found that the position close to the front wall was best. Also, it leaves more space for recording.
Ok.
Quote:
Originally Posted by bermudaben View Post
Anyway, I'm gonna do some more experiments with speaker placement today, but they will more or less remain where they are.
Try to change your listening position, forward/backward following room axis, too. For each different listening position, try to find a best loudspeaker position... etc, after all this, you can choose the best compromise.
Old 4th September 2011
  #37
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trafficarte's Avatar
 

I'm still doing measurement in my home studio, waiting for material to use as bass trap in a corner where I found a bass boost of almost 25dB at 110Hz, the same frequency that gives me a huge notch cut in measurements. Using spare panels of acoustic cellulose I noticed an improvement, but I need more panels. I also found that a SPL is a cheap "must-have" for acoustic DIY treatment.
I also found a big improvement placing my Genelec 1030A really close to the front wall, almost touching it.
Old 4th September 2011
  #38
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boggy's Avatar
Quote:
Originally Posted by trafficarte View Post
.........
I also found a big improvement placing my Genelec 1030A really close to the front wall, almost touching it.
My experience:
I recently did loudspeaker placement for two pairs of Genelec monitors, one pair of 8040A and one pair of 1030A.

"Best position" distance from back wall to tweeter of 8040A that was found is 1.068m, room is 5.577m long
For 1030A distance from tweeter to back wall was 0.650m, room is 3.612m long.

It's possibly curious that in first CR, distance from back wall was ~19% of room dimension, and for second CR this distance was ~18% of room dimension

I found this positions only with measurements, and I was free to move listening position anywhere in the room(s).

I never calculate percentage ratio of distance from back wall, and room dimension, until now, I mean... I never follow any percentage "rules" for loudspeaker positioning, so, I calculate this only because my curiosity.
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