First DIY sub - initial rendering (1 Viewer)

[Mark Tranchant]

I'm planning a small-ish electronically-assisted sealed sub for my small HT setup. Priorities are:
* High-quality response down to 20Hz
* Compact size (10" or 12" driver max)
* Low cost
* Very high WAF
I am not interested in high SPLs, and will be driving it from a
BK Electronics 100W MOSFET amp I have lying around. I'll build a suitable circuit around the ESP Linkwitz Transform circuit once I've selected a suitable driver for the box. For an example, using a JBL GT3 12" would give me up to 92dB at 30Hz and 80dB at 20Hz, limited by amplifier power.
This is more of a design and construction question than a speaker design question. See the rendering below - the top is 1.5" pine, and the legs are 3" diameter pine with a 90 degree "cutout" to hold the black-finished MDF box. The MDF box has the down-firing speaker 3" off the ground in a 45L enclosure, with a small upper cavity for the electronics. The pine top has a glass inlay, and the blue thing is a 12" ruler for scale. The MDF isn't translucent - that's the reflection of the skirting board in my perfect piano-gloss finish.
Any comments on construction? I plan on getting a local pine shop to do the pine bits, but I'm concerned about the feasibility of the accurate 90deg cutout in the legs.
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[Jeff Rosz]

hello mark,
will they do one leg at their expense first?

it can be done on a table saw using a dado cutter. they would just need a suitable jig to hold the pine rod. looks like from the rendering the legs are ~3"D .... a couple of passes through the saw, no prob. i guess it boils down to the capabilities of the pine shop. i think this may be a question Pete Mazz may answer.

 

[Michael_UK]

Looks great.

If you are going to built this, I would recommend a Subwoofer with a much X-max as you can afford.

 

[Dave Poehlman]

Any comments on construction? I plan on getting a local pine shop to do the pine bits, but I'm concerned about the feasibility of the accurate 90deg cutout in the legs.

I like it. I don't think the cutting of the leg pieces should be too difficult. If it's a respectable woodshop, they should have no problem.

 

[Mark Tranchant]

Thanks for the compliments and advice so far. I think the tricky bit will be the bottom of the groove, where it finishes 3" from the end of the leg - see below. The table saw will not do the nice square end, so there'll probably be some fine chiselling involved!
Michael - my simulations suggest that the 100W amp, rather than the Xmax, will be the limitation. Only one of the woofers I've looked at (a cheap Rockford Fosgate) runs out of excursion before the amp runs out of puff. I'll try to leave some headroom to allow me to upgrade the amp later if necessary - a Shiva would allow me to pop in a 400W amp at a later date!
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[Bryan_G]

I wouldn't think that the legs would be a problem for most woodworking shops. You might even be able to find something like that premade. I would look around if the pine shop can't do it.

 

[Brian Bunge]

You could cut out the wedge on the table saw and then cut across with a bandsaw. That might work.

Brian

 

[Mark gas]

45l may be too big sealed for it but you should look into imagedynamics IDQ subs. very good sq and can be had used for around $100.
http://www.imagedynamicsusa.com/webs...ducts/idq.html

 

[David Ison]

use a 3inch bannister rail cut in half down the middle;take one half cut it into 2 quarters,now you have 1 half round and two qurtr rounds cut the quter rnd into 3 icnch pieces,you need four of these.glue a half section to a full lentgh section to qurtr.inch section and one of the three inch section for each leg. all pieces cut to the proper length for each leg of course . so we have 4 half rounds ,4 qutr. rounds and 4 qutr.rounds three inches long. mim.skills required.

 

[Jack Gilvey]

45l may be too big sealed for it but you should look into imagedynamics IDQ subs. very good sq and can be had used for around $100.

On the contrary, when using a LT circuit to shape response it's beneficial to have as much Vb as possible thereby raising efficiency/lessening power requirements down low. This is especially important with such a small amplifier.

 

[Michael R Price]

How about a Blueprint 1203? It should work well (Q=.577 or less) in a real small box. I'm not sure about its efficiency though.