Advice Needed On Dipole/Bipole Wal Mounted Surround Loudspeaker

[philiprst]

I am considering building a pair of dipole/bipole surrounds for my home theater setup. It is very difficult to find any diy plans for this sort of speaker so I have not have much luck looking online and I am therefore thinking of designing my own.

My first thought has been to utilize a pair of FR125s or WR125 (of similar TB) full range drivers mounted at 90 degrees to each other in a wedge shaped enclosure that is divided into two separate boxes, one for each driver. This would allow for dipole or bipole operation, switching the phase by a DPDT switch.

If the boxes were sealed, can anyone give me some guidance on the optimum box volume. The CSS recommended enclosure volume is 7L ported or sealed but I have read that in a sealed box a larger (10-14L) box is preferred. Because these are surrounds they will be crossed over at about 80Hz by the processor/amp. Unibox suggests that a sealed box volume of 7-8L and Q=0.707 will give an F3 to be in the 80-85Hz range with either driver.

[MJL21193]

Originally posted by philiprst
I am considering building a pair of dipole/bipole surrounds for my home theater setup. It is very difficult to find any diy plans for this sort of speaker so I have not have much luck looking online and I am therefore thinking of designing my own.
If the boxes were sealed,...

Define dipole:
"A dipole speaker enclosure in its simplest form is constructed by mounting a loudspeaker driver on a flat panel. The panel may be folded to conserve space.

The term dipole derives from the fact that the polar response consists of two lobes, with equal radiation forwards and backwards"

I hate to break it to you, but a seal box speaker is not dipole.

[philiprst]

I think this issue has been discussed at length on this forum, but as I understand it the term "dipole" is commonly used in the HT/surround context to indicate a speaker system where two identical and opposite oriented drivers are driven out of phase. This produces a far-field response close to that of dipole radiation field. There are numerous commercial examples of variations of this setup made by M&K, Polk, B&W etc....

In its simplest form, referred to in you definition, a single diaphram in an open baffle also produces a dipole field: it is essentially the limiting case where two out of phase drivers are brought much closer together than the wavelength. The two cases differ in the nearfield response since a single driver on an open baffle is "closer" to being a pure dipole radiator than a pair of drivers seperated in space but driven out of phase. In a bipole the two drivers are driven in phase.

[jm_kzo]

Hi Philip,
did you gete anywhere with this ?

I would be interested as well.

[bzfcocon]

I've also heard the term "dipole" being somewhat misused as you say in HT jargon.
As far as I understand, the purpose there is very different: the idea is to obtain more diffuse sound rather than direct (which is why the "dipole" points with the null axis towards the listener), while in the normal dipole operation the null axis is orthogonal to the listening axis.

In a bipole the two drivers are driven in phase. [/B]

If you drive them in phase, there is no "bipole" but a monopole. Bipole usually denominates a dipole that is build as two out-of phase drivers placed on the 2 opposite sides of the box.

If you need a HT "dipole", I do not think there is much science to that, putting them on a 90 degree wedge should do fine IMHO.

[jm_kzo]

bzfcocon,
when you say "putting them on a 90 degree wedge should do fine IMHO" you do not mean like the attached picture do you ?

I thought the attached would be the best way to produce the most difuse field (with one driver facing screen, the other facing rear wall)... As well it is used in quite a lot of commercial HT surround (Jamo, Klipsh, etc.).

Thanks for the info.

[bzfcocon]

I am no expert in HT design, but what you are describing looks more like classic dipole concept (listener is on the front speaker axis). Of course, you can use dipole speakers for HT just as you do for stereo.

I was referring to the idea of the original poster, which I understand like placing the drivers on the two sides of a wedge which form a 90 degrees angle. The wedge would placed on the wall.

[jm_kzo]

Ok, so a "wedge" would be more something like this then...

[318Shawn]

Make any progress on this?

[jm_kzo]

Not yet, no, I am focusing on the front speakers for now...

It is a bit slow as I do have too many things going on at the same time... Plus the summer did not help (though it was crap).

Will post updates when there will be some... one day.