Compromises with a "boxed" dipole speaker

[mazeroth]

I purchased a boatload of Elemental Designs EHQS8 8" woofers a few months back for $5 each and am actually very impressed with them for what I paid. An honest 6mm xmax and some very impressive distortion measurements above 40 hz (mostly below 0.05%) that I took with Arta. I had an idea to build a pair of very inexpensive dipoles that could be crossed to a subwoofer and here's what I'm thinking. Four EHQS8s in the front and back of an enclosure wired out of phase. The front baffle will extend an additional 10"+ to allow for a dipole MT or MTM. Using a box instead of a typical U or H frame I'm hoping to gain the ability to cross over higher and avoid the peaks the other two formats are prone to. If I can get a healthy cross around 300-400 hz I could use smaller mids and alleviate some crossover component costs. Another nice thing I'm hoping this will give me is deeper bass, as I can build the enclosure quite large, increasing my effective path between sets of woofers. I'm thinking somewhere along the lines of 11-12" wide and up to 20" deep.

With that, can you see any flaws with doing this? Will I need to include some type of sound absorption for the internal waves?

Thanks.

It will look something like this, only larger:

[BHTX]

Hi. I do believe your dipole idea would end up being a waste of power/money/time/space/etc. I was hesitant to post my opinion since I don't really have any supporting facts at the moment, but I do remember reading other threads regarding this in the past. Unfortunately, I can't seem to find them at the moment. Mainly, it seems to me as though the distance between the front and rear woofers would have to be much greater to obtain any of the possible benefits you're probably hoping for. I just don't think it'd work very well. The extra woofers could definitely be put to better use, and there are other ways of dealing with problems in the low frequencies besides limiting yourself to dipoles. Hopefully someone else will chime in with more answers..

[bzfcocon]

Not really answers but a few comments:
- people have build "bipoles" before (drivers on both sides of enclosure) - some claim very good results
- however not on bass: 2+2 8" woofers mounted as you say will simply not displace enough air IMHO. You need more driver area here !
- This does not mean that dipoles can't do bass - they do, and very good- but, as I said, you need a lot more area (see MJKs designs and technical studies)

[mazeroth]

Originally posted by BHTX
Mainly, it seems to me as though the distance between the front and rear woofers would have to be much greater to obtain any of the possible benefits you're probably hoping for.

Actually, the distance between my front and rear waves would be larger than most dipole designs.

Originally posted by bzfcocon
[B]Not really answers but a few comments:
- people have build "bipoles" before (drivers on both sides of enclosure) - some claim very good results
- however not on bass: 2+2 8" woofers mounted as you say will simply not displace enough air IMHO. You need more driver area here !
/B]

This speaker would actually have 4+4 woofers. 240 cm2 Sd x 6mm xmax x 4 drivers = a single 12" with 12mm xmax. I've heard a dipole speaker (Monte Kay's) with dual 10s with 7mm xmax (less than this design) and it had usable output below 40 hz. at very high volumes.

[pedroskova]

One thing a configuration like this can offer you is the ability to create a cardioid output by using a number of drivers that differ between front and rear, i.e., 4 front firing drivers and two rear firing drivers.

[Andy G]

I hope you have a very big room !!

If not, just use monopole vented or sealed bass with the MTM open.

Also go to HTGuide and look for Jed's "Tombstone" speaker

[sreten]

Hi,

You could wire the bass units in phase as bipoles. Out of phase will
simply not work very well. As bass bipoles it should be possible to
smooth the cancellation from the rear wall somewhat.

/sreten.

[bigwill]

Distortion below 0.05% from a speaker??

[mazeroth]

Originally posted by bigwill
Distortion below 0.05% from a speaker??

My bad. I meant to type 0.5%