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Old 7th March 2002, 07:02 AM   #1
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Question Tempest Ported Enclosure

I am going to build a sub for my home theater system, and I ordered a tempest driver with a 250W @ 4 ohms plate amp from Adire. My goal is to make a sub that sounds awesome with music and movies alike. What I am a little unclear about is what dimensions to use for the box. I used the WinISD program, and played around with different values for port tuning and box size.

The graphs looked nice and smooth with a 260 L / 9 cu. ft. box. The port is 3" diameter and 6.8" long, tuning the box to 15 Hz. Is this a good way to go? If I make a 2.1 ft cube with 3/4" MDF, will that be sufficient? The graph didn't shift too much with slightly different values, so I gather that lack of extreme precision will not ruin my project results. Also, will I need to reinforce the MDF somehow? Or will gluing and caulking it be enough to keep it together?

One last thing...I was originally going to get a router, but then I figured that getting a rotozip would be better for this project. There is a circle jig accessory for the rotozip, is there any particular reason I should get a router instead?

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Old 7th March 2002, 01:35 PM   #2
Super is offline Super  United States
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Its ok to be off in your measurements a tiny bit here or there, although sealed enclosures tend to be more forgiving. You still have to account for any additional bracing or stuffing you will use, and if vented, the port.

You will definitely need to internally brace your box. In fact, the more bracing you can have without restricting airflow, the better. 3/4 inch MDF held together with screws and caulk really wont suffice. I strongly suggest you use either 1 inch MDF or double up on your 3/4 inch MDF as well, and if not all around, at least on your front baffle, because it will lose considerable strength due to the driver cutout. Be sure to use t-nuts and screws to fasten the driver to the front baffle.

Although I use a RotoZip, you may be better off with a router. You have to go slower with a RotoZip, the bits wear out very quickly, and you'd have to get a separate router attachment if you wanted to flush mount your driver. Its also much easier to radius and edge with a router. Although you can use a RotoZip, a good router and a Jasper jig might be the way to go.

By the way, the AVA-250 is a great plate amp; make sure you take advantage of the crossover and phase controls though, these will take a lot of playing with to make the sub integrate well.
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Old 7th March 2002, 03:43 PM   #3
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How would I go about including stuffing and vent tube in the internal enclosure displacement?

What is the best way to brace the sub enclosure? Would using little steel 90 degree straps be sufficient? I was also wondering if lining the inside of the box with dynamat would make it sound better. Whad do you think? Dynamat is a sound dampening material made for lining cars.

Yeah, the ava250 seemed to be an excellent amp for a HT sub. It might not be 1 kW, but I think it'll suffice for my first DIY sub project. Is there a way to connect that amp so that it drives both voice coils in parallel, or can I only drive one coil?

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Old 7th March 2002, 08:10 PM   #4
Super is offline Super  United States
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For bracing, you will need to couple the walls together. This can be done by attaching wooden dowels to the sides, or window pane or circular type bracing. Take a look at these sites for some ideas:
http://terryctheater.tripod.com/shiv...um/page12.html
http://www.diysubwoofers.org/sbc/sbc1.htm

As for vent and stuffing displacement, the stuffing will vary. In a ported enclosure, you should typically only line the walls. Dynamat will provide good damping, and an acoustic foam should be used to help break up standing waves and provide further damping. Just add the amount of stuffing used, to the overall internal volume of your enclosure. The port should be treated as though it is a solid cylinder, and that should be added to the internal volume as well.

Yes, you can wire the VC's in parallel. I connected each VC to a separate pair of binding posts, and connected the amp to a single pair of terminals. I then ran 2, equal lengths of wire from the one terminal and connected each one to one of the 2 VC terminals. This runs them in parallel, and wont void any warranties on the amp. (By the way, I built a separate enclosure for the sub amp.)
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Old 9th March 2002, 07:50 PM   #5
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I just started working on my box, and immediately I was faced with a problem. I do not have the proper tools for doing this project...to that end, the 22" square end pieces I cut came out terribly. I was using a saber saw at first, then I tried a dewalt rotary cutter. The rotary cutter was barely able to cut the MDF. I think after cutting 22" one way, the bit wore out because it refused to cut anymore. The saber saw did a better job of cutting, but I couldn't keep it straight.

What are the proper tools for this job? I originally wanted to get a router and a table, and use that for everything. It could gut straight, it could cut holes and round the corners...but no store had a router and circle jig.

Which tools should I get, that will work well, without emptying my pocket too much? SHould I order a router, table and jig off some internet shop like amazon.com or something??

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Old 9th March 2002, 11:50 PM   #6
MikeA is offline MikeA  Canada
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Check out this link .. it is a worthwhile article,



For the enclosure cuts, unless you have a decent table saw I would recommend getting the cuts done at your local hardware store/lumberyard/Home Depot/Building Box.. whatever.. the price paid for accurate, clean cuts are well worth it.
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Old 10th March 2002, 12:05 PM   #7
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ss-I've been using a Dewalt cutout tool for MDF and getting good results.Are you using a woodcutting bit?They make different kinds.I've also found I need to go slowly and I get better control going clockwise.For cutting straight lines a circular saw with a clamping straightedge works great. I like the Tru-fit Clamp n Tool guide-about 25 bucks for a 2 ft.,35 or 40 for a 50",which will cut 4x8 sheets crosswise.These prices are catalog or discount tool place.
John
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Old 10th March 2002, 05:33 PM   #8
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I'm giving up on the cutout tool...it doesn't provide the results I'm looking for, and home depot did not have any bits for it. I picked up soe rotozip wood bits, but they don't work any better than the general purpose bit that came with the tool.

IT looks like I'll return the cutout tool and get a circular saw and straight guide, a good blade for it, and blades for my saber saw. I'll use the saber saw to cut out the speaker mounting circle and the circular saw for straight cuts.

Another thing I am wonder...when you cut wood along a line, is it necessary to compensate for the width of the sawblade? FOr instance, I need to make 22" squares...if the circular saw blade is 1/8" wide, will I end up with 21 7/8" squares instead?

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Old 10th March 2002, 06:23 PM   #9
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Yes-you must include the blade thickness.If you use a clamping straightedge you also have to include the width of the saw baseplate-mine is an even 5" but yours is probably different.You also need a carbide-tipped blade or the MDF will ruin it pretty quickly.When you cut along a line do it to one side;that way you can monitor it as you go(sabre saw)
John
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Old 10th March 2002, 07:17 PM   #10
MikeA is offline MikeA  Canada
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If you are going the circular saw route invest in a sturdy carpenter's square as well. They are invaluable to ensuring the straight edge is perpendicular to what you are cutting into. If this is going to be a 1 person job, also look into picking up some 90 degree mitre clamps.. they are pretty handy to have in addition to your regular clamps during the enclosure assembly. Good luck!
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