Front wall treatment vs monitor port design

[tonio]

I've read differing opinions of whether or not to apply treatments for the front wall, assuming we are dealing with front ported monitors in a non soffit config.
It may be a circumstance with SBIR issues and obvious individual set up/use differences at hand in consideration.

Is there a definable difference of consideration based on the monitor port design vs volume of the room, or just a consideration of the modal issues at hand?

T

[DanDan]

tonio, I doubt that the opinions differ as much as it might appear.

Some of us suggest placing Front Wall treatment way down the priority list.
When all of the higher listings are done, time comes to consider FWT.
At which point we often find that little is needed, e.g. to control a flutter with the back wall.

Why down the list?

Bang per Buck.
We have repeatedly seen the sure-things deliver.
Corner Traps, RFZ, Cloud. There is no doubt about their benefits.

Flutter Control.
Well the presence of speakers and screens, large ones these days, renders a lot of the front wall invisible, thus invisible to flutter. If it exists it takes little to kill it. A drape, a painting, a thin trap.

SBIR.
Bass Traps are sometimes recommended behind the speakers in order to diminish the damaging effects of SBIR. Basic theory suggests that they would need to be very thick in order to have significant effect at LF. Empirical tests done here with decent commercial Bass Traps show no effect whatsoever.
I cannot imagine that the port orientation would have any real impact. Bass wavelengths are multiples of the dimensions of the speaker.

BUT, SBIR is real and it's serious. How do we address it? Are we just ignoring it?
Often the back wall has little space for deep traps, so perhaps it is better to half trap front and back?

DD

[Glenn Kuras]

Originally Posted by DanDan

SBIR.
Bass Traps are sometimes recommended behind the speakers in order to diminish the damaging effects of SBIR. Basic theory suggests that they would need to be very thick in order to have significant effect at LF. Empirical tests done here with decent commercial Bass Traps show no effect whatsoever.
I cannot imagine that the port orientation would have any real impact. Bass wavelengths are multiples of the dimensions of the speaker.

BUT, SBIR is real and it's serious. How do we address it? Are we just ignoring it?
Often the back wall has little space for deep traps, so perhaps it is better to half trap front and back?

DD

SBIR is something that should be treated if it is a problem. Read more about it here.
Learn what is SBIR (Speaker Boundary Interface Response).

[DanDan]

Hi Glenn, indeed SBIR is on my list. With a hard concrete front wall the first SBIR cancellation dip can be 20dB. Genelec have an informative note on this.
However they conclude, as I do, that the thickness need to affect the first dip, the big one, would be impractically large in the majority of cases.
I am about to try an experiment.
Bass Trap on a stand behind and very close to the speaker.
I am hoping this will work better than close to or on the front wall for several reasons.
The panel is close to the source of the rear radiating bass. High energy and minimum dispersion.
The panel has a very decent gap from the front wall and should be at a high particle velocity point.

DD

[Glenn Kuras]

Originally Posted by DanDan

Hi Glenn, indeed SBIR is on my list. With a hard concrete front wall the first SBIR cancellation dip can be 20dB. Genelec have an informative note on this.
However they conclude, as I do, that the thickness need to affect the first dip, the big one, would be impractically large in the majority of cases.
I am about to try an experiment.
Bass Trap on a stand behind and very close to the speaker.
I am hoping this will work better than close to or on the front wall for several reasons.
The panel is close to the source of the rear radiating bass. High energy and minimum dispersion.
The panel has a very decent gap from the front wall and should be at a high particle velocity point.

DD

Actually my answer was just a add to yours.thumbsup
I do look forward to your experiment.

[tonio]

Thanks DD and Glenn.

I am using Dynaudio BM6A's which are rear ported. Due to the size of the room & 38% point the speakers are rather close to the front wall. The rear of the speaker is about 6" from the front wall.
Please note the room is coupled with 2 openings. I am getting a rather deep null (measured) @ 118-125 hz , and the fundamental is nulled around 65-80. At the mix position, the bass gtr is really prominent, and kick drum low end is somewhat anemic with mostly the beater click. Listening at the back wall- the kick is like Jose lowrider driving through.

Basically I made a portable trap at one opening and almost finalized the treatments-just a few more on the rear wall to go. I will take some more measurements tonight and see that goes. I had thought perhaps the Auralex space couplers may be a remedy, but resulted to traditional BB type treatment for now before throwing money at the situation - them space couplers ain't cheap!!

T

[tonio]

hmm, having issues with Fuzzmeasure unexpecteldy quiting on me...

On the horn w/ Chris...

IOW bump

T

[subunit23]

I would like to treat the front wall as well. My monitors are about 4 inches from the wall and my computer screen in betwwen the monitors. Do you think that a panel like this one ("Auralex" Auralex Wedge 100mm X1 Charcoal at Studiospares) would help with SBIR issues ?

Thanks

[DanDan]

Sub, I think that would have little or no effect.
Glen, Tonio, I tried a trap close to the speaker, about 0.5m from the front (concrete) wall. No change. I moved the panel to the wall. 1-2dB change.
Didn't think it worth pursuing further.
DD

[Glenn Kuras]

Originally Posted by DanDan

Sub, I think that would have little or no effect.
Glen, Tonio, I tried a trap close to the speaker, about 0.5m from the front (concrete) wall. No change. I moved the panel to the wall. 1-2dB change.
Didn't think it worth pursuing further.
DD

Good deal. I have seen SBIR a non problem and a huge problem. No two rooms and set ups are the same. Actually you can get SBIR from the side walls also.

[DanDan]

Indeed, the side wall actually seems to have a stronger effect. Both are concrete bricks. However trap didn't affect that either!
DD