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Old 28th February 2010, 10:51 PM   #1
Loren42 is offline Loren42  United States
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Default Cabinet Wall Construction Questions

Greetings!

I have a question about wall construction of cabinets. First, the ultimate goal is to beef up my existing cabinets without loosing too much internal volume, but before I do that, I was wondering if anyone had experience with lining the interior of a cabinet with 3/8" thick drywall?

My current cabinet is minimally braced. While I would love the idea of adding more internal bracing panels, getting them inside the cabinet would be very difficult since the only orifice is the 15" speaker cutout.

This is the current internal bracing of my cabinet. Not shown is the 3/4" by 1-1/2" braces that run on all corners of the cabinet. They join the main panels together. All panels are 3/4" MDF. Internal braces are hardwood. Those shown are either 3/4" by 2-1/2" (actual dimensions) or 3/4" by 1-1/2".

Click the image to open in full size.

The thought I had was use construction cement to attach a layer of sheetrock to each MDF subdivided panel. To keep loss of internal volume of the cabinet to a minimum I was thinking of using 3/8" household drywall or sheetrock.

Additionally, I was thinking of adding a layer or two of the 050" thick self-stick rubber roofing sheet available at the lumber store (Poor Man's Damplifier Pro). This stuff has foil paper on one side and pull-off paper on the other. It comes in rolls 6" wide.

The end sandwich would be three layers of different density material, but I have no idea if this is a valid mechanism to reduce cabinet resonance or to what degree.

I have an accelerometer, so in theory it is possible to test this approach, but I don't want to waste time if there is prior art to show that it is a poor or even bad approach.

I am interested in your thoughts on the subject and perhaps alternatives that might yield better results.

Thanks!
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Old 28th February 2010, 11:48 PM   #2
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The fact is that by using different materials which have different resonances,you'll end in choosing one which will have its own resonance shifted outside the audible range . For each one you'll have to consider also : rigidity ,weight and damping , applied also to the lengths and dimensions of the project / box . Looking at the picture , the braces seems well done ,as they break in the middle of the panels . I tried lead ,but with little boxes ,so it may not work in a bigger box . Maybe Loren ...you should focus in cutting stationary waves , and I would avoid putting the big reflex ports in the front.
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Old 1st March 2010, 01:08 AM   #3
Loren42 is offline Loren42  United States
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Originally Posted by picowallspeaker View Post
The fact is that by using different materials which have different resonances,you'll end in choosing one which will have its own resonance shifted outside the audible range . For each one you'll have to consider also : rigidity ,weight and damping , applied also to the lengths and dimensions of the project / box . Looking at the picture , the braces seems well done ,as they break in the middle of the panels . I tried lead ,but with little boxes ,so it may not work in a bigger box . Maybe Loren ...you should focus in cutting stationary waves , and I would avoid putting the big reflex ports in the front.
Here is a little more information: Each panel is asymmetrically divided by braces, which should help further brake up compound resonances. The ports are already located in the front and changing that would not be trivial. It can be done, but is not a simple matter. However, I do not understand why it would work to have them located anywhere else but the front baffle.

Here is my reasoning, which I hope you might help find the flaw. I think that the ports reinforce and cancel the wave front from the woofer based on the desired frequency of resonance. If the ports are located at a different panel, then the distance from the port to the woofer changes and impacts the phase relationship of the port/woofer and some degradation would result. Is this not the case and why? Additionally, firing the ports to say the rear would then fire into the corners where the cabinets face and create a corner horn. That would seem to complicate the predicted behavior. At least that would be my concern. Is that based on solid ground?

When you spoke of considering "rigidity, weight, and damping" when selecting the material, what does that really mean with the material that I have proposed? What I am trying to grasp is if the combination I proposed is a good one or a bad choice and why. Can you elaborate on that some more?

Thanks for your input and I really appreciate your thoughts and opinions.
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Old 1st March 2010, 01:28 AM   #4
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Plaster sheeting ( drywall for the Americans ) works but if I'm doing this I prefer to mix PVA with shredded newspaper and then mix in the dry Plaster of Paris.

I then trowel it on making coves in the corners and a little goes a reasonably long way
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Old 1st March 2010, 01:32 AM   #5
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dual wall filled with sand.......................
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Old 1st March 2010, 01:35 AM   #6
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You might consider an exoskeleton... in cases like this, as chris says to me all too often, it is probably easier to just start over again.

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Old 1st March 2010, 01:40 AM   #7
Loren42 is offline Loren42  United States
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...as chris says to me all too often, it is probably easier to just start over again.

dave
I know. That thought keeps looming in my mind. I would do that if it wasn't for all the complex cuts involved with the design.

In your mind, what would that exoskeleton consist of?
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Old 1st March 2010, 01:40 AM   #8
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I hate starting over, cabinet construction drawing looks OK, and OP wants to work on it with=out losing internal volume so adding to exterior makes sense.

Anything that creates a discontinuity makes walls less resonant, to what degree I haven't ever managed to quantify ( maybe one day i'll buy some test equipment ) but I have had subwoofer boxes on which I could mount my Turntable
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Old 1st March 2010, 01:45 AM   #9
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Originally Posted by Loren42 View Post
I know. That thought keeps looming in my mind. I would do that if it wasn't for all the complex cuts involved with the design.

In your mind, what would that exoskeleton consist of?
How about sheetrock- green glue and minimum plywood of 4mm
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Old 1st March 2010, 01:50 AM   #10
Loren42 is offline Loren42  United States
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Originally Posted by Moondog55 View Post
How about sheetrock- green glue and minimum plywood of 4mm
Thanks! Seems like sheetrock has a place.

I am considering working on the inside of the cabinet because I designed for an internal volume of 6 cubic feet, but when I did an analysis I found the actual volume was 6.7 cubic feet, so I have some wiggle room.

Nevertheless, it is far easier working on the outside of the cabinet and plywood would be a better material to attach veneer to. My veneer is not paper backed.
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