How strong does the box need to be? - diyAudio
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Old 3rd January 2008, 04:11 PM   #1
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Default How strong does the box need to be?

long time reader, first time poster.

I'm getting a box design for my HT subwoofer, and I need a hand.
I'm a car audio person, and usually only deal with frequencies down to about 33 or 34 hertz. However this enclosure will be tuned to 17.7 hertz.

Some information about it..
amplfier will be a Dayton HPSA1000 (1000 watts RMS at 4 ohms)
subwoofer will be a RE Audio SX18 (dual 2 ohm rated for 1000 watts RMS)
enclosure: 60" tall, 24" wide, 24" deep.
17.14 cubic feet total
8.74 cubic feet after displacements
tuned to 17.7 hertz

Now, I have already figured out the bracing. They will be "squares" that have 2.5" rails (not sure what to call them) and go around the box, exept for the one that is next to the woofer (see pictures). I'm debating whether or not to double up all 6 sides of the enclosure to make it more rigid.

suggestions?

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Old 3rd January 2008, 04:53 PM   #2
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Have you modeled that box in MJK? With the size of the port this is going to behave more like a daline (ie transmission line with a pre-chamber) than a bass reflex so any modeling you have done in a standard issue modeller is going to be off.

Also, the bracing would likely be more effective if run the other way (but i guess that fits in with the folded port/TLine. I'd run the line vertically with a lot less folds.

Are you going to build it out of void free plywood?

dave
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Old 3rd January 2008, 05:43 PM   #3
95Honda is offline 95Honda  Germany
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Box would more than likely be plenty strong with your bracing.

I have had strange responses (not ending up like the model said) when I put a bunch of folds in a vent like that, I have done it several times. I have switched to running the vent on the bottom, up the back and along the top if need be, so only 2 folds max, most of the time only one. That has always seemed to work more reliably for me...

If you have the time and patience, roundover all the internal brace edges with a router, and any parts of the port(s) you can on the inside...

I have built many H/T subwoofers using SE and SX 15s and 18s.... I love them for that application... They are bulletproof...

Last one used an SX15 and that same amp... Go figure... LOL!
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Old 3rd January 2008, 07:40 PM   #4
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I use bassbox pro to do the basic design... it works nice when it comes down to accounting for brace/driver displacement. Then I just draw it with Google SketchUp. I'll probably give this enclosure a try to see if it works. I have the same idea designed except with 2 folds going down, then up. The only problem is that it would be hard to brace.
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Old 4th January 2008, 03:23 AM   #5
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The first thing I notice is the port and as others said, it's not going to function like a traditional port according to the model. You should always try to avoid any angles of 90 degrees or more if possible. A pair of 45 degree angles or even 45degree piece in the corner greatly improves things. In this case you have four 180degree changes in direction. You are expecting air to go one way, stop, then go the other way 4 times. All the changes in direction will cause a serious decrease in vent velocity, which means you lose output. Air also compresses easily, especially when asked to change direction 180 degrees. This will cause you to lose even more output. While you have a lot of vent area you'll end up with an effective area moving maybe 1/4 of air that you are expecting. That means you've lost a lot of output.

I'm assuming the vent is something like 6" x 22.5" cross section? That is probably more than you need for this kind of tuning. Although if you did that, you could open at the front on the bottom, come to the back then go straight up, and again go forward to the front. You can get about 100" that way. Put a 45 degree piece in the top and bottom corners, round the inside corners of the port there too. That essentially leaves you with 2 rounded 90 degree corners instead of 4 180degree changes in direction. You'll be capable of much more output.

John
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Old 4th January 2008, 03:51 AM   #6
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alright, so if I do that, the could I get away with the same type of bracing to the port, probably about 5 of them, and instead of bracing the rear, top, and bottom of the cabinet, just double the pieces up?
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Old 4th January 2008, 04:32 AM   #7
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Default Re: How strong does the box need to be?

Quote:
Originally posted by wasted911
enclosure: 60" tall, 24" wide, 24" deep.
17.14 cubic feet total
8.74 cubic feet after displacements
tuned to 17.7 hertz

Hi,
If you can live with a box that big, you might as well make it a TL. TLs are much more tolerant of design errors than bass reflex.

Here's how I did it before.
There is a full brace down the middle (that which has all the holes). This will give you amazing bass.
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Old 4th January 2008, 06:34 AM   #8
simon5 is offline simon5  Canada
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You could also consider using passive radiators.

BTW, nice project, I hope everything goes well. You'll have incredible low bass with that.
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Old 4th January 2008, 07:17 AM   #9
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Well I've been looking at doing a TL, but I havnt the slightest clue on how to do one. I think I'll stick with the bass reflex.

Then again, I am looking for an enclosure to give me the most out of my woofer. I'd like to explore all boundries as I compete in DB drag (car audio).
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Old 4th January 2008, 07:30 AM   #10
MaVo is offline MaVo  Germany
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Quote:
Originally posted by wasted911
Then again, I am looking for an enclosure to give me the most out of my woofer.
that would be a tapped horn
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