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Discussion Starter · #1 ·
I'm quite intrigued with what can be accomplished with an open baffle/dipole mains setup for dynamic Hifi and HT use but i can't get my head around the inefficiency of OB bass-no low end extension, lots of drivers, terrible efficiency and so on. For the purposes of efficiency and very high SQ, i pose the question of two drivers sealed and compound loaded back to back and wired out of phase, magnets mechanically coupled. I realize this is really a Bipole but with the correct baffle size the resulting system should achieve the same goal, a hyper cardoid radiation pattern with minimal cancellation, low distortion and high SQ in a smaller box with better low end extension and efficiency. Comments Please ?????????
 

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The reduced bass extention comes from the rear wave cancelling out the front wave. The point at which this happens is based on the size of the baffle (larger baffle = larger path length). This will happen with a conventional dipole or one with two drivers out of phase in a sealed box. It think putting two drivers in a sealed box out of phase would further reduce the efficiency as you are not using the back wave off each driver.
 

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Enclosing your rear woofer that's out of phase would create an isobarik enclosure. What that means is you box size required is dropped in half, but your output also drops by 3db.

With a large enough baffle, you can get have your woofers do midbass. All you need then is for your subs (sealed, ported, IB, ect..) to take over below that. If you don't like that idea, have you though of transmission line?
 

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Discussion Starter · #4 ·
Thats exactly what i'm looking for Looney 80-200hz and a single sub in the middle 60hz and down. As far as connecting the two drivers magnets mechanically, each has a 3/4" pole vent in the magnet. I'm thinking to connect them with PVC pipe with holes drilled for venting. Any problems with that?
 

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Connecting these isobarikly (is that a word?) will reduce the box size by half if there was an enclosure behind the rear one. Since there isn't this is basically an in-phase dipole and the volume of the box will have less effect then the size of the baffle. I still don't see the advantage as a conventional dipole has an infinitely large "box" for all intents and purposes. This design will still have baffle losses like ordinary dipoles based on the size of the baffle.
 

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Oops, I thought he mentioned enclosing the rear woofer.

RE: using PVC to connect the pole vents.
Good god no! One of it's functions is cooling. Imagine if your radiator was placed inline with your exhaust and "cooled" with hot exhaust. That's the same thing with coupling those pole vents together. Each motor would breathe in the others hot exhaust, negating any cooling effects.
 

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Discussion Starter · #7 ·
Both woofers enclosed in the same box, magnets facing eachother. I'll have to find another way to couple the drivers i guess. If i go with no box like ob, excursion will run wild, hence the box.....I think ?
 

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Both woofers enclosed in the same box, magnets facing eachother. I'll have to find another way to couple the drivers i guess. If i go with no box like ob, excursion will run wild, hence the box.....I think ?
Depends what drivers you use and how hard you drive them. A good way to estimate excursion in OBs is to model a sealed box with 9999L of volume and heavy stuffing.
 

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Anthony, Mr. Boom - Been a long time, good to talk again.

A few years ago I built a moddified "Decware Housewrecker". It was a ported isobarically loaded sixth order bandpass with two Dayton 15 SVC drivers. The first version I had the magnets "back to back" in the enclosure. They were mechanically held in place mainly due to the enclosure itself, but in order to make things a little more solid I wedged 'sticks' of MDF. I thought this sounded like what you guys were talking about. Stick this assembly in a large diameter 'sewer pipe', and you might have something pretty cool. I was not a fan of the overall sound quality of the large beast so it's gathering dust as we speak. OB is (IMO) much cleaner sounding. But what you're talking about sounds like it will have better overall sound quality than the bandpass.
There's a couple more photos of the inside of the "Housewrecker" here:
http://home-and-garden.webshots.com/album/549522535hKJQbw?start=12
{Old gallery, not updated recently}

 

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Both woofers enclosed in the same box, magnets facing eachother. I'll have to find another way to couple the drivers i guess. If i go with no box like ob, excursion will run wild, hence the box.....I think ?
It'll make excursion worse. Why? Because that rear woofer will be pressurizing the box while the front is supposed to be creating a vacuum, cancelling each other out. You're now moving the amount of air of one speaker cone (the front speaker) but have two motors working together to move that cone. So, you have twice the HP, but the same amount of tire. Keeping traction will be even harder now. You're better off just using one woofer OB and use a U frame or whichever you like...or seal it.
 

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Discussion Starter · #12 ·
Banged out of work tommorow anyway so i'm gonna build a test box-lots of mdf and ply scraps around. The goal here is for below an OB dipole mid/high for high SQ from 200hz down to 60hz where a single 15" sub will take over. I can get 110 db in that passband with 500w so worth a try.
 

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Discussion Starter · #14 ·
At .7 qtc, would make an excellent active mid bass-cleanest i've ever heard but not very loud of course. So i started a bigger box at 54L ported and tuned to 24 hz. Half way there-will let you know how that goes.
 
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