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How much internal bracing is too much?

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stevef22

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Oct 28, 2022
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I already purchased some Siless Max 120 mil (3mm) 30 sqft Car Sound Deadening mat - Butyl sheets.

My plan is to put these in each box evenly.

Then take some polyfill (I have old pillows) stuffing and install inside box.

However I have some odds and ends of wood left over. For example the cutouts for speakers etc.

Is it wise to put this in random spots around the inside cabinet?



Thank you,


Driver: RSS390HF-4 15" Reference HF Subwoofer 4 Ohm

Internal Dimensions: 18.5" X 14 1/4" X X 25"


IMG_1030.jpgIMG_1040.jpgIMG_1043.jpgIMG_1044.jpgSCR-20250718-oogq.pngSCR-20250718-ooao-2.png
 
You probably can't have too much bracing as long as it doesn't eat-up a lot of internal volume.

If you knock on the cabinet and it "rings" (or otherwise resonates) it's not stiff enough. It should sound solid and "dead".

Is it wise to put this in random spots around the inside cabinet?
Click to expand...
Probably not the best strategy or the most effective use of bracing...
 
In a subwoofer, what you're normally trying to do with bracing is prevent entire panels (sides, back, top) from resonating as a whole like a drum head, and also to raise their natural resonant frequency out of the bass bandwidth. That's why you often see bracing attached to the middle of one side, going all the way across to the middle of the other side; that helps keep both sides from flexing, and also sort of "cuts in half" the panels which raises the resonant frequency.

I'm not sure adding additional bits and pieces will really help anything.
 
Not a DIY sub person, but making sure your box is well sealed on all 6 panels would be my first worry. How do you actually achieve that given the pressure that will build inside the box?

I have some decent subs and know their limits, but that would be mostly port and SPL related. They otherwise stay coherent no matter what hits them.
 
Thans very much for the tips everyone. This is extremely well glued and screwed. So its very tight for sure.

I will make sure no pannels are without a brace as well.

Static V3. Im still going to try the rubber as well. I will let you know if it just falls off etc. It has very sticky 3M style adhesive. ( I used it in my car before )



Thanks again
 
Connecting opposite sides together with something very stiff in tension and compression (solid wood is much better than MDF for this) is generally the most effective way to stiffen the box at the frequencies of interest. Except for quite large boxes, the panel resonances of a subwoofer are usually well above the passband even without bracing (i.e. >>100Hz), so only the first mode is of much concern.

The butyl damping mat won't really do much if the panel resonances are well out of band. There's nothing to damp if the resonances aren't excited in the first place.
 
Ok thank you. WOW thats allot of bracing. Im concerned with loosing cu feet.
Internal Dimensions: 18.5" X 14 1/4" X X 25"
sealed box has a volume of 108 liters (or about 3.81 cubic feet).

Am I still ok?

Driver: RSS390HF-4 15"


Thank you
 
bmc0 said:
Connecting opposite sides together with something very stiff in tension and compression (solid wood is much better than MDF for this) is generally the most effective way to stiffen the box at the frequencies of interest. Except for quite large boxes, the panel resonances of a subwoofer are usually well above the passband even without bracing (i.e. >>100Hz), so only the first mode is of much concern.

The butyl damping mat won't really do much if the panel resonances are well out of band. There's nothing to damp if the resonances aren't excited in the first place.
Click to expand...
Thank you
 
stevef22 said:
Ok thank you. WOW thats allot of bracing. Im concerned with loosing cu feet.
Internal Dimensions: 18.5" X 14 1/4" X X 25"
sealed box has a volume of 108 liters (or about 3.81 cubic feet).

Am I still ok?

Driver: RSS390HF-4 15"


Thank you
Click to expand...
The pictures I sent are for a very large sub (24" x 24" x 46") so you don't need that much bracing but I do like to tie all the panels together to, as mentioned, "create smaller effective panels" with resonance higher than the operating frequency of the sub.
 
stevef22 said:
sealed box has a volume of 108 liters [...] RSS390HF-4 15"
Click to expand...
I have two of these in ~87L sealed boxes (no stuffing), but I also use a Linkwitz transform (Fs=37Hz Qts=0.87, transformed to Fs=20Hz Qts=0.7). You have a lot of leeway with sealed box volume if you intend to use EQ anyway.
 
That Siles butyl rubber will stick to just about anything.

You can brace with 2 to 2-1/2" wide strips of hardwood or plywood. People use MDF and particle board often, but it really is not nearly as stiff as real wood. Don't just brace side-to-side, but top-to-bottom and front-to-back if you can. The driver on the front baffle is creating the vibrations, so if you can brace front-to-back that is key, but of course having a big 15" driver in the middle of the baffle limits what you can brace.
 
a4eaudio said:
That Siles butyl rubber will stick to just about anything.

You can brace with 2 to 2-1/2" wide strips of hardwood or plywood. People use MDF and particle board often, but it really is not nearly as stiff as real wood. Don't just brace side-to-side, but top-to-bottom and front-to-back if you can. The driver on the front baffle is creating the vibrations, so if you can brace front-to-back that is key, but of course having a big 15" driver in the middle of the baffle limits what you can brace.
Click to expand...
I chopped up the speaker cutouts and made half moons to hold these pine braces

(I know the braces need to be cut flat and rest against the MDF as flat as possible. This is just a mock up.

I rounded the edges of the pine as well.

Video



Am I on the right track?


Thank you

IMG_1048.jpgIMG_1047.jpg
 
Last edited:
stevef22 said:
I already purchased some Siless Max 120 mil (3mm) 30 sqft Car Sound Deadening mat - Butyl sheets.

My plan is to put these in each box evenly.

Then take some polyfill (I have old pillows) stuffing and install inside box.

However I have some odds and ends of wood left over. For example the cutouts for speakers etc.

Is it wise to put this in random spots around the inside cabinet?



Thank you,


Driver: RSS390HF-4 15" Reference HF Subwoofer 4 Ohm

Internal Dimensions: 18.5" X 14 1/4" X X 25"


View attachment 464099View attachment 464100View attachment 464101View attachment 464102View attachment 464097View attachment 464098
Click to expand...
Maybe use Line-X?
 
Gotta be careful with using solid wood for braces if the cabinet is a manufactured wood like ply/mdf. I've done that before and the braces just broke off inside from seasonal changes.
 
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