Dipole Surround Speaker Design

[standingwave26]

I wanted to design my first pair of dipole surround sound loudspeakers. I have order 4 Vifa 4.5" midbass drivers and 4 TB 1" tweeters. I would like to place a midbass and tweeter on one side and another pair on the other.

Questions:
1. Should the two midbass drivers be in separate chambers?
2. What is the angle the two baffles should be mounted 30, 45, etc.?
3. Should The opposite pair of drivers be wired in the opposite polarity?

Any help and weblinks to more information would be appreciated

 

[Ap]

If I were going to make rear firing speakers I would consider upward firing bass drivers & direct firing tweeters - with drivers firing up & bouncing off the ceiling you get this huge diffuse sound field without the phase addition/cancellation issues with dipole/bipoles.

Having said that it few answers...
1. No they can share the same volume - just remember double the size needed for one driver.
2. I would go with both at 45deg - so 90deg between them.
3. Try & see. Out of phase is considered dipole, in-phase is considered bipole (go figure).

 

[Ap]

Oh I forgot to add - dolby recommend side placement (or slightly rear of listening position) for rear speakers (just like at the cinema) - in just about every setup Ive come across no-one does this!

http://www.dolby.com/Consumer/HomeEntertainment/Setup/

I would aslo add that 80% of signal comes from the centre - make it the biggest & best you can it is the most important!!

 

[rnoble]

Speakers that are Dipole are in opposite polarity while Bipole are the same polarity. But this is subjective to ones tastes so what you would ideally do, because it's DIY, is add a switch that allows you to change them over.

 

[454Casull]

Speakers that are Dipole are in opposite polarity while Bipole are the same polarity. But this is subjective to ones tastes so what you would ideally do, because it's DIY, is add a switch that allows you to change them over.

Bipole drivers are wired with the opposite polarity.

 

[sreten]

Bipole drivers are wired with the opposite polarity.

Nope, thats dipole, bipole are the same.

sreten.

 

[Timn8ter]

Re: Re: Dipole Surround Speaker Design

Nope, thats dipole, bipole are the same.

sreten.

Yep, it's easier to keep straight if you remember that an open baffle speaker is a dipole with the front and rear waves in opposite phase.

 

[454Casull]

Sorry, I had too much Linkwitz on the brain... I was thinking that the two drivers would be facing the same direction.

 

[johninCR]

First, regarding construction: Bass isn't important for surrounds, so I'd go OB with the mids and put a front a rear firing tweeters and use the woofers for something else or mabe make 2 pairs of surrounds on OB (but your system would need to handle the different distances to listening position or use the extra pair for a rear channel surround). If you want to go with boxes, then you need separate chambers. Otherwise you'll have an isobaric alignment with a big relative distance between cones and your upper mids will get messed up because the back waves will interfere with the opposite cone.

Regarding placement: Keep in mind that in a cinema, the surrounds consist of a number of speakers on the sides and back of the theater to result in sound from many directions aligned in time for the proper effect. From what I've read, dipole surrounds recreate this better than monopole because you have 2 wave fronts instead of one and that they should be placed even with the listening position firing directly forward. That puts you in the null of the speaker, so what you hear is just the reflections "surrounding" you with their reflected waves but still maintaining the left and right separation.
http://webcenter.soundandvision.netscape.com/electronics/ns/article/0,aid,79,00.asp

 

[standingwave26]

Thanks for the tips. I plan on using a switch for the tweeters to make them bi- or dipolar. I agree that using a separate chamber is crucial, if the speakers share the same volume and are out of phase bad things will probably occur (I'm hoping for fire and big sparks for that engaging cinematic experience).