37Hz axial mode between side walls of my contol room

[jacko]

What would be the best way of attenuating the room mode at 37Hz?
It's the first axial mode between the side walls of my control room.

I am going to place rigid fiberglass panels on the walls that are 4" thick and are spaced 4" from the walls (8" total). Should I be looking at some different solution?

What's best in my case?

[PaulP]

To me the huge null at ~43hz is more worrysome. Fix that and there
won't be much of a peak anymore at 37hz.

Paul P

[Jens Eklund]

At these low frequencies pours material is often useless (unless unrealistically thick!) since the particle velocity near the boundaries is close to zero. Perforated panel or normal panel absorber will at least have a chance of doing something useful (if tuned and placed correctly) since they combat the pressure variation (which is high near the walls).

[tonio]

+1 to PaulP,

Let me guess, the LF starts(specs) @ 35hz on your monitors?

T

[Jens Eklund]

My guess is that the room is roughly 4,6 x 4 x 2,7 meters and the listening position is (unfortunately) in the middle of the room facing a 4,6 meter wall.

[tINY]

How many subs do you have? If you run 4, you may be able to not excite those nodes.




-tINY

[jacko]

Originally Posted by PaulP

To me the huge null at ~43hz is more worrysome. Fix that and there
won't be much of a peak anymore at 37hz.
Paul P

take a look at the waterfall before I put 19 broadband absorbers, the dip was larger:

Also, currently only a subwoofer is being used for those measurements. As soon it becomes cleaner (I stop drilling holes and I clean the dust) I will bring my normal speakers (Proacs).

[jacko]

Originally Posted by tINY

How many subs do you have? If you run 4, you may be able to not excite those nodes.
-tINY

I've got only one... but what you say is very interesting! I will consider that solution.

[jacko]

What will be better - Helmholtz absorbers or panel absorbers?

[Magickman]

Originally Posted by jacko

What will be better - Helmholtz absorbers or panel absorbers?

At 37Hz, Helmholtz is about your only option, unless you build some hangers.

Can we see a pic (photo or drawing) of your treatment placements?

[jacko]

here is the picture and waterfall (there's 50Hz electrical hum, so disregard it)

What you see is the ceiling, front wall (with monkey picture) and right hand side wall

[tINY]

Bag End makes some electronic "helmoltz traps" as well.

Untitled Document



-tINY

[DanDan]

Hi Jacko. 37Hz seems low, it seems to suggest a wide but shallow room. What are you room's dimensions? You may have the speakers facing the worst direction. The modal response of the room is very different in different directions. Normally the speakers should fire into the longest dimension of the room. Move them there and try another measurement, the difference should be easily visible in the Waterfall.
DD

[jacko]

Originally Posted by DanDan

Hi Jacko. 37Hz seems low, it seems to suggest a wide but shallow room. What are you room's dimensions? You may have the speakers facing the worst direction. The modal response of the room is very different in different directions. Normally the speakers should fire into the longest dimension of the room. Move them there and try another measurement, the difference should be easily visible in the Waterfall.
DD

4.85*5.4*3m
37Hz mode exists almost everywhere I place the sub.
Tomorrow I will do first tests with normal speakers.
There is also 27Hz mode but I think it is so low that it doesn't really matter.

[DanDan]

Hi Jacko, that was quick! The 37 Hz mode exists between the 4.85m walls. It will peak at each wall, and there will be a strong null at the room centre. Play a 37 Hz tone into the sub and you will find where it hangs out.
It would be best to point your speakers firing into the longer dimension 5.4m.
Try the sub at each wall and measure, there should be a winner. In this case I would chose which direction improves that dip. Measure at 38% from the front wall, in each case.

DD

[jacko]

Originally Posted by DanDan

Hi Jacko, that was quick! The 37 Hz mode exists between the 4.85m walls. It will peak at each wall, and there will be a strong null at the room centre. Play a 37 Hz tone into the sub and you will find where it hangs out.
It would be best to point your speakers firing into the longer dimension 5.4m.
Try the sub at each wall and measure, there should be a winner. In this case I would chose which direction improves that dip. Measure at 38% from the front wall, in each case.
DD

the speakers will be firing the longer dimension because there is no other way from the technical/architectural point of view

I already know that this is axial mode between the side walls (4.85m) - look at the topic
The sine wave test confirms it.

I am just trying to find out how I should try to absorb this mode. Helmholtz? Panel Absorber? How large area it should cover on the walls?

[DanDan]

That is good to hear. Since you are working lengthways, you will be sitting in the null of the 37Hz mode, i.e. the centre of the room. You will not hear it. Because you won't hear it, IMHO it is not the most important issue, the null is.
By adjusting your listening distance and the speaker distance from the front wall you should be able to cut that null around 47Hz a little. I suggest moving some of your Traps. Straddle all four vertical corners floor to ceiling. That should greatly diminish that null, improving your bass a lot.
Here's a nice little tool to find out where these modes live
http://www.hunecke.de/en/calculators...igenmodes.html
DD

[Rocket Ronnie]

wow....19 broad band absorbers and graphs like that!!! Thats depressing.

[jacko]

Originally Posted by Rocket Ronnie

wow....19 broad band absorbers and graphs like that!!! Thats depressing.

I think you don't know how to read it. This graph is quite common and normal for rooms like this. You should have read my posts first, then you should have read the range on those graphs.
Actually the result after placing the absorbers is very good.

[Rocket Ronnie]

Originally Posted by jacko

I think you don't know how to read it. This graph is quite common and normal for rooms like this. You should have read my posts first, then you should have read the range on those graphs.
Actually the result after placing the absorbers is very good.

Generic treatment trumps again hey.

[jacko]

These measurements were taken using subwoofer only. The idea was to focus on the most difficult range of the room were further placement will be installed (for example Helmholtz resonators) later.

Broadband absorption was installed to smooth out the room response above 60Hz and to minimize the effect of 1st reflections.

Because the subwoofer doesn't work very well above 100Hz I will show you the range 20Hz - 120Hz. The improvement of broadband absorption is very obvious from 50Hz above. Please notice especially how the change affected 50Hz. There is 20dB improvement at 50Hz!



The next step will be to minimize the 42Hz dip and damp 37Hz decay time if possible.

[Rocket Ronnie]

looks like you still got 25dB variation. The more threads like this I view the more I am beginning to question the Gearlslutz approach of throwing panels at the room.

[jacko]

Originally Posted by Rocket Ronnie

looks like you still got 25dB variation. The more threads like this I view the more I am beginning to question the Gearlslutz approach of throwing panels at the room.

I see 5dB variation in the range 50-100Hz...
Perhaps you should show us your room.
I think you should realize that broadband absorbers have little to no effect below 50Hz. I think you should also be aware that it is very difficult if not impossible to treat low end in a small room like mine. Very even room response above 50Hz is a great success in my case. There might be a slight improvement in the range below 50Hz if I come up with a good plan for treating that. Obviously you don't seem to be very helpful in this case.

[tINY]

The right placement of multiple subs will even out the lower frequencies.

But 1 or 3 more subs is a lot more expensive than DIY absorption....



-tINY

[DanDan]

jacko, +1 to tiny's comment. Room treatment trumps electronics, including financially if you go DIY. I can't see how two subs would fix your dip either.
I put 3 of the 34 inch wide SuperChunks in a room. A 35 Hz mode, went from 1.3 S down to 0.6 seconds. If you do your corners, floor to ceiling with these you will see a strong change. I reckon you will greatly improve that dip also. Corner straddling panels are a cheaper option. Can you modify your broadbands by sticking a sheet of thick paper or light card onto the batt?
This significantly increases LF absorbtion. It not publicly tested but I am quite sure such a sheet on the front of a Superchunk will work wonders also.
DD

[tINY]

And pushing out one of the walls a few feet and angling it at 20 degrees or more will help too. That's the best acoustic treatment - make the room big enough and angle the walls enough to spread out the Q of the axial nodes. Just watch for sound focusing problems.

Of course, that DIY project is bit more ambitious....



-tINY

[Jens Eklund]

Originally Posted by tINY

And pushing out one of the walls a few feet and angling it at 20 degrees or more will help too. That's the best acoustic treatment - make the room big enough and angle the walls enough to spread out the Q of the axial nodes. Just watch for sound focusing problems.

Of course, that DIY project is bit more ambitious....



-tINY

http://www.gearslutz.com/board/5440603-post14.html

[tINY]

Data?

If there is a resonance between the two largest walls in the room, then angling them enough will certainly reduce the ringing at that frequency. Of course, you probably made your room smaller to do it, which can cause other problems.

Usually the largest two walls in a room are the ceiling and floor - and vaulted ceilings are popular for a reason....



-tINY

[Jens Eklund]

Originally Posted by tINY

Data?

-tINY

Nimura, Tadamoto and Kimio Shibayama, Effect of Splayed Walls of a Room on Steady State Sound Transmission Characteristics.

Gilford, Christopher, Acoustics for Radio and Television Studios.

[tINY]

Link?

I've read some information on this. In large rooms, it typically doesn't make enough improvement to worry about. In smaller rooms, it can help, but you typically make your room smaller with the probelms common to an even smaller room.

If you are designing dividing walls between rooms in a modest sized complex, angling the walls can help with axial ringing. If you lower the Q, the ringing will not persist as long.



-tINY