Plywood thickness for 15 inch subwoofer

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frugal-phile™
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The baffle is the weakest panel on the box because of the holes in it. The metal structure bolted to it is vibrating and feed directly into the baffle. In a woofer (and often elsewhere) i will brace the woofer magnet to at least 3 other panels to distribute the basket movement and reduce the energy getting to any one panel reducing the liklihood of setting any potential resources off. Even better is if you can brace it to another driver mounted push-push to achieve active vibration cancelation.

dave
 
The baffle is the weakest panel on the box because of the holes in it. The metal structure bolted to it is vibrating and feed directly into the baffle...
Yes, sometimes, sort of.

In the present case, we have a steel or cast aluminum girder held by prolly 8 steel bolts. Allowing for an internal piece of wood along each box edge (necessary to make such a box), there's barely room to install the driver (assuming for simplicity a cube box). No part of the driver is more than a few inches from an edge structure and half of the driver circumference is within an inch or two.

BTW, there are long-running arguments about whether the ancient horror of cabinet vibration matters. Even when vibration measurements are taken, there is still no consensus on whether it (as an ordinary harmonic of the music being played) can be detected anyway.... esp given the distortion of woofers.

Frankly, if there's too much wood in your shop, much better to use it to make a bigger box (with good cross-bracing, of course).

B.
 
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Was wondering myself, as I'm currently building a rather large 18inch horn+br hybrid. I used 18mm MDF all around, as ply was around double the price, and it's obviously got a huge amount of unsupported area inside the box, while the speaker can obviously provide a serious shaking (unfiltered, this thing will put out 100+dB/W/m between 40 and 300Hz). Since I don't want to spoil the horn geometry by internal bracing and external appearance is really not too much of a priority (will get integrated into a bench anyways), I'll go for external bracing using either 20x40mm pine, or doubling up the walls.

Point being: I'll soon be in the lucky position of recording a before-and-after of the distortion this thing produces. Any bets on how bad the effect will get? I'm thinking, if it's less than a 0.1% reduction in THD in such a monstrosity, it's probably not worth the effort in a comparatively tiny speaker.
 
Another option is what I use in all of my speaker builds. I use either 1 1/2" or 1 3/4" thick maple butcher block. It is generally sold as a counter top or work surface material. Due to it's thickness and inherent strength it requires no internal bracing. I use dowels and glue without issues but I'm sure screws and glue would work as well. This material makes for a seriously robust (solid, somewhat heavy) enclosure.
 
" I use either 1 1/2" or 1 3/4" thick maple butcher block."
If you have a money tree and forklift at home...... hollowing out a tree or rock are other options..... or just stick with 18mm or 3/4 (and some bracing on big overspans) and you will be more then fine.
The glue makes it airtight, strong and stiff; screws, nails and/or clamps are there for the time the glue dries.
 
Heyho,
I collected some experience with subwoofer builds with/without bracings.
The last woofer enclosure i built needed to be very stiff because a 18 inch woofer
from a carhifi enthusiast needed to be transformed into a downfiring hometheater sub.
At first, we made a simple enclosure without bracing and it was horrible sounding.
The walls seemed to work like membranes (22mm plywood).
Then we made some triangles and put two of them per side without huge success.
After I made a bracing as Dave said with connecting the driver by felt to the bracing
the situation was absolutely good and the whole sound went from rattling/muffling
to nice more or less clean bass.
I would guess(without any measurements!) that in planning any kind of box implementing a bracing brings you to a result that you are expecting.
In the end it's only a little bit more sawdust :)
 
Yup. In my experience, adding braces makes a subwoofer sound significantly better (tested with my POC #2 design).
LOL, that's not what he meant, but you are right.
It's all about the stiffness of the box or minimizing warp in the flat panels of the box.
You can build a canoe with bracing that weighs 20/30lbs or without; then you have model hollowed out tree trunk weighing over 200 lbs; both work.
 
Yup. In my experience, adding braces makes a subwoofer sound significantly better (tested with my POC #2 design).

LOL!
That`s not what I meant.
Of course bracing will help when using "thin" walls.

But in my 6th orders internal bracing would make them sound "ugly" as opposed to the clean sound without bracing.
Enough wall thickness will preserve the clean sound while adding sufficient strength.
 
LOL!
....
But in my 6th orders internal bracing would make them sound "ugly" as opposed to the clean sound without bracing.
Enough wall thickness will preserve the clean sound while adding sufficient strength.
Have you tested this with 2 boxes with the exact same internal volumes, 1 with and 1 without braces?
I think that there is probably something else going on like the braces taking up space/volume, or a brace near a port obstructing airflow.
 
Have you tested this with 2 boxes with the exact same internal volumes, 1 with and 1 without braces?
I think that there is probably something else going on like the braces taking up space/volume, or a brace near a port obstructing airflow.

It was just one box, close to leave prototype state.
I listened to it without bracing, then added bracing in the hope of more db (it was loud already but if you can get more) which went up significantly in higher bass notes.
Listened to it again.
Removed bracing.
All fine again.
Albeit not as rigid.

I think it was a combination of the above^^ since 6th order bps are very unforgiving regarding chamber volumes, etc. both chambers influence each other, ...

It had somewhat more "punch" but sounded somewhat "ugly" with bracing and low end suffered/clarity.
So I removed it.

Being still a MDF prototype which worked surprisingly well it gets occasional use in-car where it is very efficient even with only 100 watts.
Since then I moved on to other BP6 designs which are more rigid due to shape/construction.
Still no internal bracing as of yet.
 
If there is bracing then I would expect to get more reflections of the sound off the rear panels reflected back to the speaker and affect the sound.
Ideally there should be no reflections off the back panels that's why internal padding/sound deadening is often used.

Adding stuffing or lining to a bandpass subwoofer can reduce the out of band noise. However, it can also reduce the efficiency of the subwoofer. There are better ways of reducing the out of band noise. I've discovered for example that careful positioning of the vent's opening in the vented chamber can null out the first (and most annoying/audible) out of band resonance.
 

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