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3K views 8 replies 5 participants last post by  F1 fan 
#1 ·
I have built the box for my Rythmik Audio DS15. I should be receiving the kit on Tuesday, and I will be spending Thanksgiving weekend finishing the build. All that is left to do is cut out the amp & speaker holes and attach the top.

The inside dimensions of the cabinet are, 29"W x 14"D x 14.25"H the cabinet is 3/4" MDF glued inside of a 7/16" particle board cabinet with a Naugahyde covering. The total wall thickness is about 1-3/16".

My question is;

Should I add bracing, reducing my interior volume, or is the thickness and combination of two different wood types enough to reduce/eliminate resonances? If so what type of bracing would be recommended?

The DS15 has a 15" driver that seems to have a 17mm xmax and I will be sealing the box as tight as possible. I have already glued and caulked all the interior joints and intend on painting the entire inside of the box with latex house paint (If I'm feeling particularly energetic, I may mix some sand in the paint). So the box should be very well sealed.

The trade off is reduced interior volume vs rigidity.

Paul
 
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#2 ·
I'll be curious to see what others say about your question.

If I were to guess, I don't think it would matter much either way. However, if I had to choose, I'd probably add more rigidity. I've got nothing to back that up save my "gut" feeling. The actual t/s parameters are (very) often different than the 'posted' parameters, so I think you've got a little wiggle room there anyway.

That being said, you do have a pretty thick enclosure already, so extra bracing may be overkill.

So, in the end, I'm sure I was a BIG help.. :whistling:

Hopefully the smart folks around here can chime in and give you some better advice.

JCD
 
#4 ·
Exactly! :nerd:

In all seriousness though, I'd probably NOT brace it, install the parts and see how it sounds and then make a determination then as to whether you need extra bracing or not. If you HAD to do it now or never, I'd be inclined to go ahead and add some bracing that would minimize the internal volume being displaced. I would think that you could come up with something that wouldn't take up too much room on the inside.

JCD
 
#5 ·
Hi Paul,

The general rule of thumb for DIYing a sub box is to brace every 16 inches or so when using MDF. Since your length is nearly double that, adding a shelf brace in the middle will ensure that cabinet resonances are pushed well beyond the passband and at a level below the hearing threshold.

The shelf brace can cover the back and sides, and if you shape it to the driver depth, can be used to "butt up" against the magnet to strengthen the front. You can place the brace slighly off center if the sub has a pole vent. A single piece of 3/4" MDF should do it. You can use a piece of felt where the magnet meets the wood for tolerances.

Cabinet losses with a single brace like this are minimal, but you can always add a bit of fibreglass to dampen things a bit. R8 or R12 would do just fine here. Line the back and sides - you'll be good to go! :T

BTW, I wouldn't bother with the paint...

Best regards,
Mark
 
#6 ·
Mark:

I haven't decided yet where I am placing the driver or the amplifier. The driver will be going somewhere on the bottom, and the amp somewhere on the back. This will leave only two unbroken walls of the cabinet longer than 16", both will be 29" in length.

There is no clearance between the walls of the cabinet and the sides of the driver based on the published specs so putting a shelf brace over the speaker would mean I would only be able to attach it to the top, and part way down the sides.

If I can center the driver & amp I could put a shelf brace on either side of the driver. If I put the driver on the left (or right) and the amp on the other side I could put the shelf brace in the middle. Which brings up another question;

If you have a cabinet that is about 31"W x 15"D with a downfiring driver, what effect would having a 15" driver off center have on the sound?

Back to bracing, I could put one or more triangle braces (quarter or half shelf) without too much problem, if you think that would be ok. They would connect the front wall and the top which are the walls that have nothing else on them and would be most susceptible to resonances, I think.

Paul
 
#8 ·
Mark:

There is no clearance between the walls of the cabinet and the sides of the driver based on the published specs so putting a shelf brace over the speaker would mean I would only be able to attach it to the top, and part way down the sides.

Paul
That's ok. If you can get it a number of inches down the sides, you're strengthening the whole box by doing so and minimizing resonances of the longer sides.

If you have a cabinet that is about 31"W x 15"D with a downfiring driver, what effect would having a 15" driver off center have on the sound?

Paul
None. We're dealing with a sub here. Bass frequencies are not directional. I'd be more concerned about the height of the driver from the floor. In fact, you would be doing more good by going this route. Having the sub closer to a side will help to minimize the amount of vibration on the baffle.

If you can mount your driver closer to one end, and say, the amp closer to the other end, you should be able to extend the middle brace a significant amount. As mentioned, a simple shelf brace will suffice. If long enough, you can punch a couple of 3" or 4" holes in it to ensure air flow past the brace without losing its strength.

And, to add to the confusion, closed box designs are a little more forgiving than other designs. You can get away with adding an extra inch or two without any ill effects if you need to. ;)

Best,
Mark
 
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