Should It be worth the trouble?

[FargateOne]

Please take a look at the photo. The MLP is on the leather couch, left side of the couch . MLP is 8 feet from the front speakersThe back wall seperate the room and the shop in my basement. You see 3 DIY panels on the back wall. Between them, there are 2 square frames (31inch H x 24 inches large) where it was 2 windows. On the shop side of those frames I've put 8 inches Rockwool AFB.
I can't get rid of the back wall to get a deeper room. But, I could do on the upper part of the wall one large "window" of approx 7 feet large x 3 feet high behind the MLP to replace the 3 panels and the 2 windows and fill it with mineral whool in the shop side of the wall.
Am I wrong to think that it will change the main room modes (room dimensions, tangential and diagonals ) at the MLP and help to smoothen the response to lower the highs and lows differences between 20Hz and 500ish Hz.
Please see mdat of a mic 9 positions measurements for the fronts and the sub.
Thank for your help.

 

[Todd Anderson]

Paging @Matthew J Poes and @AudiocRaver

I think these two can help you!

 

[Matthew J Poes]

Sorry I missed this. I will respond as soon as I have a chance to look at the data.

Can you share how many subwoofers you have and where they are placed?

 

[Todd Anderson]

I knew it Poes... ready to dig into the data!

 

[Matthew J Poes]

Well as you would expect I need more info. I’m not sure these are all room modes. I think these are also SBIR effects. I need more info on setup. Speaker type, placement, etc.

I suspect you won’t be able to address this with just more treatment. Bigger bass traps could help but if it’s SBIR then you need them on the front walls. Especially corners.

The most effective universal solution to SBIR and room modes is multiple subwoofers. That would be my suggestion.

If you can give me more info I can at least narrow the problems and suggest better solutions. Maybe some passive acoustic ones too.

 

[FargateOne]

Hello Matthews,
I have one sub only and it is behind me where I stood to take the photo. Sub is at the front right corner of the room

 

[Matthew J Poes]

Hello Matthews,
I have one sub only and it is behind me where I stood to take the photo. Sub is at the front right corner of the room

Honestly your measurements are very good. There isn't much to fix. Generally I prefer to look at the individual measurements rather than averages to see what kind of variation you are getting, but based on what I saw, it looks good.

The suggestions I gave you are really the best way to smooth bass over a wide range of seats.

If you want to increase LF absorption, I might consider bass traps, which are really most effective when built using high density insulation or really thick. Anything under 10" thick should be 6lb or 8lb density. Anything over 10" should really be more like 2lb to 4lb density, obviously going to a lower density the thicker it gets. I like Gik's approach of using a membrane and I've found that Carpet protective film make a good membrane. It's too low density to be very reflective, it really only reflects high frequencies. But it's surface tension and density over the mineral wool help boost LF absorption by about an octave or so.

Is the "front" wall where the speakers are treated? The corners? I'm not against treating the back wall, I just am not sure it will make as big a difference given that there is already some treatment there. LF treatment works best when placed on the offending walls causing the specific reflections you are trying to address. They can only do so much, of course. I like to treat the walls closest to the speakers with bass traps to solve things like floor bounce/ceiling bounce cancelation, SBIR effects, etc. Room modes are trickier, I just prefer multiple subs, but certainly nothing wrong with having some LF damping as well.

As for your window idea, I wouldn't bother. It's much better to keep a room as close to a classic cuboid as possible as it makes the response predictable and treatable. Making changes like you describe would have unpredictable results. A hole in a wall is also resonant, so its possible it could cause a new problem.

 

[AudiocRaver]

My own tendency is to not worry too much about the frequencies of the room modes, and as Matt says, SBIR effects are often what we are actually seeing. I prefer the approach of damping everything out for super-quick decay times at LF. Lots of batting, broad-spectrum damping.

 

[FargateOne]

Hi,

Bigger bass traps could help but if it’s SBIR then you need them on the front walls. Especially corners.

The most effective universal solution to SBIR and room modes is multiple subwoofers. That would be my suggestion.

thanks for your comments. See my speakers in my profile. The room is 15 ''long x 11.5'' large x 7.5 h. Th MLP is at the center of the long wall (not ideal but...) .

Honestly your measurements are very good. There isn't much to fix. Generally I prefer to look at the individual measurements rather than averages to see what kind of variation you are getting, but based on what I saw, it looks good.

The suggestions I gave you are really the best way to smooth bass over a wide range of seats.

If you want to increase LF absorption, I might consider bass traps, which are really most effective when built using high density insulation or really thick. Anything under 10" thick should be 6lb or 8lb density. Anything over 10" should really be more like 2lb to 4lb density, obviously going to a lower density the thicker it gets. I like Gik's approach of using a membrane and I've found that Carpet protective film make a good membrane. It's too low density to be very reflective, it really only reflects high frequencies. But it's surface tension and density over the mineral wool help boost LF absorption by about an octave or so.

Is the "front" wall where the speakers are treated? The corners? I'm not against treating the back wall, I just am not sure it will make as big a difference given that there is already some treatment there. LF treatment works best when placed on the offending walls causing the specific reflections you are trying to address. They can only do so much, of course. I like to treat the walls closest to the speakers with bass traps to solve things like floor bounce/ceiling bounce cancelation, SBIR effects, etc. Room modes are trickier, I just prefer multiple subs, but certainly nothing wrong with having some LF damping as well.

As for your window idea, I wouldn't bother. It's much better to keep a room as close to a classic cuboid as possible as it makes the response predictable and treatable. Making changes like you describe would have unpredictable results. A hole in a wall is also resonant, so its possible it could cause a new problem.

The front wall is treated (see photo but note that I get rid of the 2 DIY traps on the floor because it gives poor results for the trouble mean WAF.) More sub is not an option for lack of space. 2 tri-corners are treated. Now about SBIR see photos here. B&W recommandation is to put out at least 50cm from the back wall. You see the result if I move the speakers closer at 20 cm from the wall. To my ears (is my brain tricks me ?) it shrinks the SS&I.
I give mdat for one measurement .

So I will forget the window idea (Yeh!). Now, about membrane, if I go there, the trap must be sealed correct?

 

[Matthew J Poes]

Hi,



thanks for your comments. See my speakers in my profile. The room is 15 ''long x 11.5'' large x 7.5 h. Th MLP is at the center of the long wall (not ideal but...) .



The front wall is treated (see photo but note that I get rid of the 2 DIY traps on the floor because it gives poor results for the trouble mean WAF.) More sub is not an option for lack of space. 2 tri-corners are treated. Now about SBIR see photos here. B&W recommandation is to put out at least 50cm from the back wall. You see the result if I move the speakers closer at 20 cm from the wall. To my ears (is my brain tricks me ?) it shrinks the SS&I.
I give mdat for one measurement .

So I will forget the window idea (Yeh!). Now, about membrane, if I go there, the trap must be sealed correct?

This all looks good. These measurements are much more in line with what I expect to see with non-averaged measurements and because they reveal more of what is going on, more helpful (to me) in treating a space.

To treat SBIR effects caused by the front wall behind the speakers, you actually need traps designed to be effective at those frequencies. A dip at 55hz is so low that normal velocity absorption won't do much. You would need to have like a foot of insulation on the wall and covering most of the wall. Might not be worth trying to treat anymore.

I believe that you should always place main speakers where the SS&I is best, not where the bass response is best. Fix the bass using other means such as subs, acoustic treatment, and EQ. If moving them closer to the wall makes things worse, don't do that. Sometimes moving the speakers farther forward into the room can lower the dip frequency to the point that it appears to disappear, and....make SS&I even better. In big rooms, I much prefer this approach.

Now as for membrane traps, the trap does not need to be sealed. That is a panel trap you are thinking of. The mass of the membrane acts on it's own, it doesn't need "contained" air to increase the spring, it doesn't work that way in this case. In this case, the mass is the membrane and acoustic fiber material combined and the spring is the fiber compliance. In the design I'm talking about, the membrane is adhered to the fiber directly. With a low density membrane like I'm talking about, the operate over a wider bandwidth. They don't have the same peak in LF absorption that a panel trap or limp mass membrane would have, but provide a useful improvement over other designs.

http://realtraps.com/p_mondotrap.htm
the Mondo trap has a low density membrane over its front as I understand it.

and so does Gik's
http://www.gikacoustics.com/product/gik-acoustics-monster-bass-trap-flexrange-technology/
Flexrange technology is the same thing, some kind of membrane over the face of the panel.

Neither of these are sealed in anyway, they create the mass/spring by virtue of the membrane itself and the insulation. Works well and the chance of success is a lot higher than with other tuned trap methods. I've read forum post after forum post of people building tuned traps and showing no improvement in the LF's. I have build about ten different types in my lifetime and bought 3-4 different kinds. What I can say are that the ones I bought always made a measurable difference. The ones I built were hit or miss. Some of my goofier ideas did not work out well. Many ended up missing their desired tuning frequency by enough to be not so useful. Many made a difference, but it was far smaller than expected and needed, given the cost and effort.