[mjkempton]

Evening to everyone,

I've been lurking for a while and this is my first post.

I've just put together a 24" by 48" OB for a Lowther EX4 and an Eminence 15".  Got it passively bi amped at the moment but I am investigating active crossover options.

I do want to try an H baffle to reduce the visual impact somewhat.  Also to give me the opportunity to play with time aligning the Lowther to the bass.

Any thoughts on two drivers in an isobarik configuration in an H baffle ?  I've built isobariks many years ago and always liked the results.  I can think of no reason why it work, but can't work out what the advantages might be.  Many people have built double woofer OBs to good effect but always both on the same baffle - the Orion comes to mind as the only real variation I can think of.

many thanks for all input

Jim

[opnly bafld]

You mean like the Legacy Whisper?
It has 2- 15" drivers at the top and 2- 15" drivers at the bottom.

Here is a link with a picture of the back/side view near the middle of the page:
http://legacyaudio.com/index.php?option=com_content&task=view&id=120&Itemid=227

Lin

[mjkempton]

Not sure how they are placed.

I meant two woofers in the H frame, the front one facing forward and the rear one also facing forward but placed on another baffle directly behind it.  The gap between the two being an air tight seal.  The distance between the two is as close as possible, i.e. so the cone of the rear woofer doesn't touch the magnet of the front one.  I hope that makes sense - and I really wish I could draw !

I still can't think of any reason why it won't work ?  It should produce a tighter and deeper bass due to more surface area and each driver doing less work.

Jim

[opnly bafld]

If I understand what you are saying, I would call it a bipole sub (or dipole if wired out of phase), a sealed box with drivers on opposite sides.
The Whisper is open baffle/dipole with the drivers on separate baffles with the distance between the two determined by calculations from a formula, the area between them is open.

Lin

[mcgsxr]

I asked Planet_10 about this a few years ago.

As I recall, his answer dealt with moving air, and since they are both open air, there is not a reduction in box size needed...

I use an isobaric setup in my car, a pair of 10's clamshell, and ported.  Not a common alignment, but a good one when well sorted.

Not likely useful for open air though.

[dyohn]

IMO there is no point to iso loading in an OB alignment.  The only reason to iso two drivers is to cut the Vas in half so you can use a much smaller conventional enclosure and achieve the same system resonance frequency.  In an OB you are not concerned with driver loading or port tuning by an enclosure.  I think in an OB alignment the added dbSPL from two drivers mounted conventionally would far outweigh any possible benefits of iso using the same drivers, plus you lose 6db sensitivity when compared to conventional mounting.  Unless I am missing something in your thinking, I can see no benefit to iso loading in an OB.

[tubamark]

Not sure how they are placed.

I meant two woofers in the H frame, the front one facing forward and the rear one also facing forward but placed on another baffle directly behind it.  The gap between the two being an air tight seal.  The distance between the two is as close as possible, i.e. so the cone of the rear woofer doesn't touch the magnet of the front one.  I hope that makes sense - and I really wish I could draw !

I still can't think of any reason why it won't work ?  It should produce a tighter and deeper bass due to more surface area and each driver doing less work.

Jim

As described, surface area is actually identical to a single woofer, displacement is identical to a single woofer.  Fs might lower a Hz or two becuse the trapped slug of air between the cones.  Power handling (per driver) will probably be reduced slightly.  Max output (excursion-limited) and efficiency is less than a simple H or U-frame using the same pair of drivers.

The only benefit would be if both cones faced outward (magnets face each other) to form a truly "pure" dipole with identical radiation on both sides.  Pretty impractical and inaudible in the bass range.  The best way to achieve the results you cite above would be as linkwitz has already done with the tall H or compact W alignments.

-- Mark

[mjkempton]

Many thanks to all who answered.

There are no advantages.

I see that now 

Jim