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post #1 of 11 Old 03-19-2008, 08:16 AM - Thread Starter
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I'm building a box that will be 19" deep and have a 4" Aeroport that is 18" long. How much of a gap should there be between the end of the port and the wall of the enclosure? 2"? 4"?

Also, I'm building a 1.5" thick front plate for the box using two pieces of .75" thick MDF. I see people recessing the subwoofer in designs like this by making the first sheet opening larger and then mounting the sub to the second sheet. Doesn't this effectively eliminate the strength of having two sheets together if you are mounting to one only? Or is the added mass of the rest of the boards enough to make a difference?

Thanks!
Dave
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post #2 of 11 Old 03-19-2008, 11:20 AM
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The general rule of thumb is at least one port diameter away... in this case 4" would be sufficient. 19" box inside with 18" long port... not so good.

Even single 3/4" mdf is sufficient for large heavy drivers. ( 35-40 pound range ) There is nothing wrong with adding a double baffle and if the panel dimentions are large, I would double up on the baffle, to prevent sagging. This also adds weight which can be either beneficial ( less chance of moving ) to detrimental... ( hernias / injury from moving it )

There exists a fine line between good enough and overkill.

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post #3 of 11 Old 03-19-2008, 01:07 PM - Thread Starter
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Quote:
Originally Posted by michael hurd View Post

The general rule of thumb is at least one port diameter away... in this case 4" would be sufficient. 19" box inside with 18" long port... not so good.

Even single 3/4" mdf is sufficient for large heavy drivers. ( 35-40 pound range ) There is nothing wrong with adding a double baffle and if the panel dimentions are large, I would double up on the baffle, to prevent sagging. This also adds weight which can be either beneficial ( less chance of moving ) to detrimental... ( hernias / injury from moving it )

There exists a fine line between good enough and overkill.

Michael,

Thanks for the info! I had figured that one port diameter was sufficient. I have actually changed the design of my box so that I didn't have add a turn in my port. The box is now 21" deep and the port is 17" long leaving 4" of clearance which should be perfect.

My front baffle will be 21x21" so I had planned on double-thickness to add rigidity as I plan on having one brace in the middle.

The box I'm planning on building is actually a 21" cube (~4.1cf with a 17" long, 4" diameter port netting a ~21-22hz tune).

Thanks!
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post #4 of 11 Old 03-19-2008, 03:02 PM
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No real need for doubled 3/4 on a 21 inch square baffle... but no problem if you do it. If you were throwing something like an LMS in that box... I would double it. Having 65 pounds hanging on a 7 inch lever off the front face can cause the MDF to sag.

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post #5 of 11 Old 03-21-2008, 08:58 AM - Thread Starter
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One more question on bracing: should I worry about bracing this thing if the largest internal dimensions are 18.75 x 19.5 x 19.5"? I had thought about a brace in the middle each way, but that might be overkill. The front baffle is 1.5" thick and the driver will be flush mounted 0.5" deep.

Thanks!
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post #6 of 11 Old 03-21-2008, 09:01 AM
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Quote:
Originally Posted by dykz34 View Post

One more question on bracing: should I worry about bracing this thing if the largest internal dimensions are 18.75 x 19.5 x 19.5"? I had thought about a brace in the middle each way, but that might be overkill. The front baffle is 1.5" thick and the driver will be flush mounted 0.5" deep.

Thanks!

It is a good idea to have bracing every 10-12 inches. In that enclosure I might have one brace in the middle...
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post #7 of 11 Old 03-21-2008, 12:23 PM
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In those panel sizes, I would simply glue a 3/4 strip of MDF or ply diagonally on each wall. IE from one corner to another. This takes less engineering than making a shelf brace and is just as effective. The strip need only be 3/4-1 inch wide.

I would recommend one layer of compressed rockwool on the bottom of the box though, as it will reduce any higher frequencies emitted from the port. Even though the resonances might be out of the passband of the sub, they can still be triggered by the active driver. Also any suspension / motor induced noises will be also reduced.

You could also use foam in place of the rockwool or compressed fibreglass insulation.

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post #8 of 11 Old 03-25-2008, 07:21 AM - Thread Starter
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Alright, I've got the box completely built except for one last question: what adhesive should I use to attach the port to the MDF? The MDF has been recessed so the port will be flush-mounted if that matters. I am using a 4" AeroPort, as well.

I have four things at home that I could use:

1) Elmer's Wood Glue (probably won't bond to the plastic)
2) Plastic Epoxy (probably won't bond to the MDF)
3) RTV/Silicone (probably isn't the strongest)
4) JB Weld (this might be the best option)

Any input is appreciated!!!

Thanks,
Dave
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post #9 of 11 Old 03-25-2008, 08:21 AM
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They don't say what the ports are made of, but it's probaly polyethylene or polypropylene, in which case neither JB Weld ot Elmers will stick to it.

The manufacturer recommends an epoxy adhesive; that should stick just fine to both the plastic and the MDF.
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post #10 of 11 Old 03-25-2008, 08:48 AM - Thread Starter
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Quote:
Originally Posted by Kevin_Wadsworth View Post

They don't say what the ports are made of, but it's probaly polyethylene or polypropylene, in which case neither JB Weld ot Elmers will stick to it.

The manufacturer recommends an epoxy adhesive; that should stick just fine to both the plastic and the MDF.

Thanks Kevin! I will probably use the JB Weld, then.
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post #11 of 11 Old 03-25-2008, 01:01 PM
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The port kits are ABS.... you can use pretty much anything ( hot melt glue, silicone, epoxy, etc... ) I would not use contact cement or regular wood glue.

Keep in mind silicone will affect finishes.... so unless it is done, I would not use it. Another alternative would be a urethane adhesive / sealant.

With the products you have I would use epoxy. ( JB weld is also an epoxy )

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