2.5cu ft bipole, Suggestions?

[johnnyb831]

Hi all.

I could be considered a "noob" by the standards of many of you. I have built 3 systems before, and various test systems.

I'm looking to build a new system, possibly a 3-way. My budget is around 1500 total (maybe more), and I need each speaker to be ~ 2.5 cu ft (ideally 6d x 10w x 60h) - ported. I want to try to build a bipole system, as I have not yet built one (I am also in love with backwaves).

My top priority is a smooth frequency range, but I would also like the system to be able to handle about 100w/ch. Additionally, I would prefer then to be able to handle at least down to 30-35hz.

I've been looking at various drivers, and was hoping someone has some suggestions.

[Jack Caldwell]

Hi, I've worked a lot with bi-poles, and came up with some variants that take it a lot further and into omni-radial response. Virtual point source type of stuff. Conclusion #1: Bi-poles and omni perform way better than conventional front-firing systems when they are placed in normal rooms.

Lately however, I have been researching what happens with properly equalized di-poles or "open baffles" and have concluded that for most rooms, di-poles are the superior option as they greatly reduce the effect of the room modes... theory says 2/3 of the modes, in practice it's about a 50% subjective reduction in room coloration.... but 50% is a whole LOT of reduction!

In the process I found some stellar combinations, one of which uses the Dayton ps220 and the Eminence Beta 15a on an open baffle, while using a modded Behringer DEQ2496 to provide EQ and Timbral correction. These drivers are relatively inexpensive, and when combined with the proper EQ and crossover the results are spectacular, with FR virtually flat within 1 dB from 40 Hz to 20KHz+. And, being completely time and phase coherent, it sounds BETTER than those numbers would imply. The total investment for the kit version (including the DEQ) would be less than $1500 if you can build your own baffles. I don't have this on my web-site yet, so if interested just PM me.

[ttan98]

Originally Posted by Jack Caldwell

Hi, I've worked a lot with bi-poles, and came up with some variants that take it a lot further and into omni-radial response. Virtual point source type of stuff. Conclusion #1: Bi-poles and omni perform way better than conventional front-firing systems when they are placed in normal rooms.

I am interested in building a bi-pole, can you outline for what you would avoid/traps when designing bi-pole. Also if you can describe the "must" include aspects of bi-pole design, e.g., the rear driver normally placed somewhere closer to the floor(say 1/3 from the bottom), whereas the front driver at normal listening height. In other words your design philosophy.

Thanks.

[RockLeeEV]

Originally Posted by Jack Caldwell

I don't have this on my web-site yet, so if interested just PM me.

Considering his last activity was just under 5 years ago...

[Jack Caldwell]

Originally Posted by RockLeeEV

Considering his last activity was just under 5 years ago...

You must be thinking about someone else, my commercial website has only been up for about 18 months.
We introduced one series of products at RMAF 2010, and are seriously thinking of taking our newest designs there this year.

[Jack Caldwell]

Originally Posted by ttan98

I am interested in building a bi-pole, can you outline for what you would avoid/traps when designing bi-pole. Also if you can describe the "must" include aspects of bi-pole design, e.g., the rear driver normally placed somewhere closer to the floor(say 1/3 from the bottom), whereas the front driver at normal listening height. In other words your design philosophy.

Thanks.

I tried lots of variants on the bi-pole theme, many of them worked very well. In nearly all cases it ameliorated, but did not completely solve the baffle lift problem, and still required compensation filters. Despite claims to the contrary, with most bi-poles you'll still get some baffle lift, although much less than with a single front firing driver.
The basic issue is to try and design so that the on and off axis response is exactly the same as the acoustic power response... and uniform.... and extended.... and phase coherent. Hard to do with any back to back type of design, very hard. I ended up moving to the omni-radial approach as it was about the only way to achieve the uniform power response criteria.

Placing the rear drivers nearer to the floor may average out the vertical modes a little, but it creates non-symmetrical vertical response, and IME the symmetry is important. It helps the room reflections be quite a bit more coherent with the direct path signal. This coherence or lack of makes a big difference in our ability to decode the spatial qualities of the music.

If you really must have a bi-pole, one tip I would give is that the optimal front to back distance seems to be between 8" to 16", with 12" being perhaps the best. This is likely caused by the Haas precedence effect, where the delayed signal from the rear arrives during the "optimal" time window and is perceived as part of the original impulse.

Look at the info I've given for the H3 speaker on my website, it will give you the most complete picture on what I ended up doing as the "best" implementation of the omni-radial approach. It might give you some ideas. To check it, click on the link under my signature.

I've been overly busy with the new developments, but hope to be updating the site soon with the OB models.