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Discussion Starter #81
Re: Preventing cavities from resonating...

Off the cuff I am thinking I probably should add another layer of 3/4" MDF over the entire riser. :huh:
 

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Re: Preventing cavities from resonating...

I havn't looked at the frequencies the "pipes" are tuned for in the riser & they possibly won't be a problem. However there are several of them and if they are in the audible range may need to be addressed.
Have you thought about putting bracing across the long runs or even breaking them up like a QRD.

Just a thought... it may be too much mucking around?
 

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Re: Preventing cavities from resonating...

I'd fill everything, sub box or not, with insulation fully. Adding another top layer would be a good idea IMO. It will stiffen the box for the sub as well as dropping the resonant frequency and 'efficiency' of any resonances for the platform.

Bryan
 

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Discussion Starter #84
Re: Preventing cavities from resonating...

Adding braces at this point is going to be difficult. I only have access through the two small holes where the sub boxes will sit. However, if I am going to add a layer of MDF, I could cut a few small squares out and add a brace to each section, maybe two braces on the long sections with the ports. That would also make it easier to add insulation.

On adding that insulation, you do not mean packing it tight, but rather just laying it in there? Or would you use polyfil? Insulation is probably cheaper though.
 

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Re: Preventing cavities from resonating...

Just standard wall insulation is fine. No need to pack tight - just fill the cavities.

Bryan
 

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Discussion Starter #86
Re: Preventing cavities from resonating...

It seems like I remember that adding insulation will cause the box volume to calculate more than it is physically. Is that something I need to worry about?
 

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Re: Preventing cavities from resonating...

For the sub cavities, it probably will. That said, they should still have some insulation in them (maybe not full). The cavity size should be adjusted accordingly.

Also, remember that when you're mounting them to a large flat surface like that (especially in the rear by the back wall), you're going to get a lot of boundary gain.

Bryan
 

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Re: Preventing cavities from resonating...

IIRC in order for port to work correctly the air mass of the box needs to be a single contagious space. This means there will be problems with the riser design unless there are many more slots cut between the joist bays.

The first joist to the inside of ones containing the ports should be removed. If not you've created a situation where there's a separate tuned chamber exiting into the ports. This is akin to having a double bandpass design instead of a simple ported box.

It's standard procedure to line the walls of a ported box with damping material. In this instance it should be no thicker than 3 1/2" thick, otherwise you'll negatively impact the operation of the ports.

HTH

Aloha,
WB
 

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Re: Preventing cavities from resonating...

It seems like I remember that adding insulation will cause the box volume to calculate more than it is physically. Is that something I need to worry about?
Filling the tunnels with insulation, loosely or otherwise will effectively reduce the total volume and raise the resonant frequency of the drivers..
I would suggest just lining the sides with some 1" thick Polyfill, which will help to keep box resonance down to a minimum and still give a good air flow through the cavities..
 

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Re: Preventing cavities from resonating...

Ummm. IIRC, adding insulation actually makes the driver react as if the box was larger.

Bryan
 

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Re: Preventing cavities from resonating...

Ummm. IIRC, adding insulation actually makes the driver react as if the box was larger.

Bryan
I agree that is the case when it comes to box enclosures..but my understanding is that the reverse applies in the case of transmission line systems..
But then I'm no expert..
 

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Re: Preventing cavities from resonating...

I didn't see anywhere that this was a TL design. Sorry.

Bryan
 

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Re: Preventing cavities from resonating...

I probably haven't used the correct term when I said "transmission line"..
Nevertheless, a path does exist for the sound waves to pass through..and on that basis, that flow would have to be restricted..to some degree..with the introduction of the chambers being filled with insulation material..Would it not?

With a tuned TL system..If too much or too denser insulation is added in the path of the back sound wave..the lower frequency db. levels are lessened from what the design intended, when the specific amount and or density of the infill has been changed..
Would this still not apply to some degree in Sonnie's system.?
 

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Re: Preventing cavities from resonating...

If it's a sealed system, adding insulation will make the box acoustically larger from the driver's point of view.

In any case, you're correct that you don't want to use a really, heavy, dense insulation.

If it is truly a tuned pipe, quarter wave TL, etc. - you want minimal insulation in the cavity.

I'm certainly not a professional speaker/sub designer. I've built a few and done a bit of research but it's hardly my expertise.

Bryan
 

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Discussion Starter #95
Re: Preventing cavities from resonating...

What I can do is cutout a large section (green area) and also cut the dividers to the floor, allowing those areas to be opened up to the adjacent areas. Then I can add bracing and insulation, cover up the section that was cutout and add another layer of MDF.



Now... the question is how to add the insulation? Obviously I am not going to be able to "line the walls"... that is just not feasible since this is after the fact. My arms are not long enough. I could line probably line a good bit of it though, if that is what I need to do.

My main concern is making sure the enclosure does not create a large resonating cavity. I believe the bracing and add layer of MDF should take care of that. I am not sure what the insulation or polyfil will really do for me and whether it needs to be lined or stuffed. :huh:
 

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Re: Preventing cavities from resonating...

That's a start. A better solution would be to move the first green stripe forward, so the line of cutouts starts directly behind the areas colored in pink. Then add a second line of cutouts 1/2 the distance toward the back.

Typically ported boxes are lined with damping material, they're not stuffed with loose fill.

One option would be to use sheets of OC-703/705 or Roxul. Those can be cut to size and the pieces will slide into place through openings cut in the top.

That said there are those who use no damping in their ported boxes.

Damping is used to make the box look larger, that's not a consideration here. It also absorbs the higher frequencies not filtered out by the crossover. Finally when damping is used in conjunction with port length adjustments, the user is able to fine tune the "Q" and Fb of the system. Since this system seems to be all but done, the tuning procedure typically employed when building a sub isn't really an option.

HTH.

Aloha,
WB
 

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Discussion Starter #97
Re: Preventing cavities from resonating...

Thanks!

Sounds like I could just skip adding any insulation or polyfil and add braces and that other layer of MDF... along with making more cutouts in the current bracing for better airflow.

This is what we will end up with...



EDIT: I ended up going back, cutting out that section as noted above, added more bracing... and added another layer of 3/4" MDF for a 1-1/2" floor. The columns that hold the drivers have a 3/4" MDF back and sides with 3 layers of 3/4" MDF on the front. Bracing is every 9" with four routed square cutouts, except at the driver locations where there is three occasions of strip bracing on the sides.
 

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Discussion Starter #98
I cannot believe I either misplaced the images or just forgot to take them of the actual framing of the riser enclosures. I thought surely I took some pics with the drivers in there, but I cannot find them. :huh:

Maybe I can find them later, but it is not much to see that you really cannot tell about in the following finished pictures.









The end result is supposed to be approximately 80ft^3 tuned to 12Hz, looking at the port, maybe we tuned it a tad lower. I may need to remeasure.

The actual driver vs. port measurement are very strange it seems. This is only one nearfield driver measurement along with the port for comparison.




But what really counts is the overall response...



And let me tell you... these things are un-be-liev-a-ble!!! Awesome! Scott definitely has a winner here... :T
 
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