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Old 4th December 2003, 09:20 PM   #1
BAM is offline BAM
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Default Crazy Super-Cheap Dipole Speaker

I have an idea for an incredibly cheap speaker project. It is a two-way with a dipole mid-tweeter.

The idea is this: Parts Express has some little 2" paper full-range drivers that reach up to 20,000 Hz and down to 200 Hz, as part of the Pioneer buyout. In addition, as part of the Onkyo buyout, they have some 6" car woofers, that extend to 80 Hz and have bumped backplates and all that good stuff. My idea is, there's probably a way you could build an entire dipole/box hybrid speaker out of these, for under $40 for everything. It would be far from hi-fi, but probably passable as a blasting garage system with 15 watts. First-order XOs.

I am thinking of trying a different bass loading style on the woofer. The woofer is designed for an infinite baffle application (as a front door woofer for a car or SUV), though I do not know what the T/S parameters are. I think it would have to have a Qts near 0.7 for that kind of work, and so I need to find a way to bass-load a woofer like that. The idea I had is to try and put it in a "Line Tunnel" aperiodic enclosure like the ones used by Fried, way back when. The Line Tunnel is an enclosure that replaces the line with an air space and a slot port filled with an open-cell foam block. To the casual eye, it looks like somebody plugged the port of a ported box with a block of foam. Apparently this simulates the type of bass loading characteristics of a transmission line, in a smaller space.

Will I be able to do something like this or is there a better way for me to approximate this infinite baffle thing without the sacrifices in bass of a dipole woofer? If it comes to it, it might not be such a bad thing, because the woofers are cheap enough that buying 8 instead of 2 would not be a problem. Then I could do something like the Linkwitz dipole woofer.
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Old 4th December 2003, 09:40 PM   #2
sreten is offline sreten  United Kingdom
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I can't find the 2" pioneer drivers you refer to.

The one's I can find go down to 2000hz and have a sealed back.

/sreten.
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Old 4th December 2003, 10:54 PM   #3
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I already have a pair, though I imagine this same project could be done with the Tang Band 2" driver as well. The part number is 269-566 on the Pioneers.

There are two real options as far as the Tangband drivers go. One that I think is real interesting is the use of the 2"x3" #264-830 driver. It does not extend completely to 20kHz but I would be inclined to think that two drivers, aligned vertically along their tallest dimension, would behave like a small line source. The only thing that concerns me with that plan is that the driver has a high-frequency limit of 15,000Hz according to the Parts Express website. The second option is the use of the #264-806 which is a stylish-looking 2" unit. This one could be good. The one that would really hit the would be the 3" unit that All Wooley had made for Nuera and the one that CSS sells, with the silver paper cone and awesome phase plug. Of course, if you spend that much money on a mid-tweet, you might want to up the woofer a bit to something like the #295-300 Dayton 5.25" unit in a transmisison line. I think that by that time, though, you have gon a significant bit outside the "super-cheap" aspect of this project. The woofer I originally specified is the #269-707. It looks like something you'd see in a Bose but it is only $2. There is also a full-range version of it, but this one has an extended pole piece, which I would assume translates into better excursion. With a first-order crossover at about 250 or 300 Hz, these drivers ought to really .
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Old 4th December 2003, 11:17 PM   #4
PRR is offline PRR  United States
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> this simulates the type of bass loading characteristics of a transmission line, in a smaller space.

And a TL can simulate a lossy sealed box in larger space.

For garage work, put the 6" woofers in 500 to 1,000 cubic inch boxes. A couple Sixes won't do a "blasting garage system", so if they are cheap then get a full-crate and figure a sealed box with 500-1000 ci per driver. Nine Sixes in 82"x10"x8" towers would rattle your wrenches.

Yeah, you can compute TL and compute curves. But a Six is too small for high level low bass, and a pile of Sixes still isn't going to rumble 20Hz happy. A simple sealed box will give a pleasing boom-da-boom bump at 80Hz and control cone motion for all lower tones, preventing slap and ripping.

I assume you have the math for a dipole. With cheap drivers and LOTS of space, it is a perfectly good option. But it becomes non-dipole if a wall is within a half-width of the panel, so they tend to sit well out in the room and be in the way.

If you hate your neighbors and your garage door: drill a dozen 6" holes in the garage door and use the whole world as your back-box. Seriously: you could cut a 96"x8" board, mount a row of drivers, raise the garage door 8" then lower it on the board. Infinite back-box and perfect corner coupling. Boom-da-BOOM.

All the Tang Band drivers seem to be marginally low sensitivity for low-power use. If there were an old Pioneer in the catalog, I'd favor that for low-price blasting. They were never flat, but often a lot of fun. (I'd rather enjoy the music than strain to hear the difference between 15KC and 20KC.)
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Old 5th December 2003, 12:23 AM   #5
sreten is offline sreten  United Kingdom
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Default re parts express part 269-566

No wonder I couldn't find it, its not listed under Pioneer.

The accompanying frequency response graph is awful.

So an non-starter IMO.

The TANG BAND W2-880S 2" looks like it would be quite tidy
slightly off axis so possibly a place to start, but its not really
in the same price league is it ?

Crossover would need to be around 500Hz IMO.

/sreten.
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