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May 1, 2007 - 5:54pm
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Bipole speakers reviewed
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We have reviewed a number of "bipole" speakers -- see the Mirage reviews here and here. The main problem is that the inevitable spacing between the front and rear drive-units gives rise to comb-filtering that may or may not be audible, depending on the room acoustics. Personally, I believe it misguided design, though some of my writers have been impressed by the idea.
There is no such thing as a bipole at low frequencies, because even the largest dimension of the speaker is way smaller than the wavelength of sound at these low frequencies. The Vandersteen's subwoofers are all omnidirectional regardless of where they are mounted.
John Atkinson
Editor, Stereophile
Mr. Atkinson!
I may not state the following correctly but this is why I am asking here at Stereophile. What I had heard was that firing the sub toward the rear wall, and placing the driver closer to the rear wall rather than out into the center of the room made the bass couple with the wall and enhance lower frequencies. I do not know if the low frequencies heard are going to be accurate however.
I am looking for some guidance on this as I am studying speaker design for DIY and was considering firing two Focal Power Flower drivers, a 10" to 11" and a 13" to 15" toward the rear wall for reinforcement. None would be forward firing. The target is sound equal to something along the Wilson Maxx. I'm looking for accurate, powerful low frequencies.
Thank you!
http://www.stereophile.com/floorloudspeakers/689mirage/index1.html
/quote/
With dipoles, there is also a penalty. At low frequencies, the in-phase rear-firing wave comes back to meet the front wave 180
This is correct.
They will be increased in level, so you need to use a woofer alignment that allows for that effect.
It doesn't really matter what direction the drive-units face as their radiation in their passband is omnidirectional. Many designers will site the subwoofer on the base of the speaker, firing into the floor (which requires raising the speaker a few inches of the ground, of course). You need to position the drivers closer to the boundary than one half-wavelength at the highest frequency you want covered.
I recommend you buy a copy of Vance Dickason's Loudspeaker Design Cookbook, available from Amazon.com. This is an essential guide to anyone wanting to design their own speakers.
John Atkinson
Editor, Stereophile
You might also find this site interesting. The book is available from them, as well. Link
I might try to aim for the floor then. But the speakers that I designed are eh...I cannot say or I'll let the cat out of the bag!
I am designing everything from the ground up and I have never seen a pair of speakers like the ones I am designing. :-)
This is going to take me about another year....as I am researching everything and I mean everything. I say why not reinvent the speaker. Many of the designs seem fairly staid, are too safe in their approach and designers are overlooking or not addressing the problems associated with the most simple things. Well lets just say that if you compile design artifacts from the top twenty speaker designers you still have wiggle room to come up with something interesting.
Thank you both.
What is your opinion of dipole speakers?
Dipole speakers
It is not quite this easy but you get the idea, the overall effect is the same. Take a cabinet with four 8" drivers and remove the cabinet, then replace each 8" driver with a 15" driver. Now you have a dipole with four 15" drivers, and people who think that the number of drivers and the overall size of drivers is all that matters will flock to your doors.
Dipoles do work however, but they are no better than any other design its all in the execution.
http://www.legacyaudio.com/engineer/comparisons-technology.pdf
http://www.legacyaudio.com/engineer/imaging-index.pdf
http://www.legacyaudio.com/Engineers.html
The worst thing I can say about Legacy speakers is that if you buy them, you will forever be associated with DUP.
No, if you go Legacy you will not be DUP'D. That's the difference. There are some mortal really good audio products out there, too bad so much is nonsense, it blurs reality. How many audio grade outlets do you use? Did you update your Mapingo discs, to ayre magic wood? Maybe even audio grade non resonsant AC wall outlet COVERS!!!! From the wizzards of nonsense and BS....Surely you can hear a wall outlet cover can't you? Lotsa good stuff, also lotsa grossly overpriced hyped nonsense. How many "audio grade" fuses are in your system, and certainly you can hear that fuse.
Not I not be flocking to YOUR door. Since arbitrarily changing drivers just to say gee, these are bigger must be better. I ain't that dopey. Might as well find a Fisher rack system from teh 90's. they had some nice tall cabinets with a nice big woofer in it. Size matters, but only when done right.