The Diminui Dipole Project

[fernandov]

Hi Guys/Gals,

Just documented a fairly comprehensive dipole project with two primary goals in mind.

1) A small room friendly OB using the Peerless 3" 830987 wide range driver
2) Cost effective suggestions for bi-amplification, xo and equalization

I am pleased with the results and welcome your comments and suggestions for possible improvements.

http://home.comcast.net/~cunundrum

Thanks

Ed

[honfatboy]

Re: The Diminui Dipole Project

Thanks so much for posting this! I run a similar set up and was glad to read about yours!

Do you have them on stands or on the floor? How much bass response do you get?

[fernandov]

Re: The Diminui Dipole Project

Do you have them on stands or on the floor? How much bass response do you get?[/QUOTE]

I do not run them on stands, instead opting for the additional low end gains from floor bounce and only a slight decoupling from the floor, using sorbothane pads. The bounce is compensated for in the xo design.

Instead of stands, I believe the next version I build will just extend the height of the slim baffle and raise the wide range driver to about 32" off the floor, leaving the helper woofer exacty where it is in relation to the floor.

The low end response is very good, and quite surprising for a dipole using only a single 10" helper woofer. The drivers high excursion and corresponding highish QTS plays a significant role in the design. The lows remain strong and taut up through about 30 degrees off axis, where the null begins to take over. I am very pleased with the quality and quantity of bass.

I have since started to use a pro audio amp (Crown XLS1000) for only the low channel. I continue to use the DTA-100 for the highs and am very pleased with the sound of the T amp. The tripath simply didnt have the output for marginally efficient woofers.

Ed

[blair]

Re: The Diminui Dipole Project

Hello,

Very interesting project! I'm sure if you had a measurement system you would have displayed it, but do you have any measurements by chance?

Thanks!

Blair

[honfatboy]

Re: The Diminui Dipole Project

Thanks for the response!

Instead of stands, I believe the next version I build will just extend the height of the slim baffle and raise the wide range driver to about 32" off the floor, leaving the helper woofer exacty where it is in relation to the floor.

With the low pass for the woofer so high, do you worry about driver spacing smearing the image?

[fernandov]

Re: The Diminui Dipole Project

Hello,

Very interesting project! I'm sure if you had a measurement system you would have displayed it, but do you have any measurements by chance?

Thanks!

Blair

Correct. Plus with the DEQ2496 (part of the system detailed) I can get close to flat in-room response from around 60Hz to well over 18K with no more than 1dB deviations for the 31 frequencies I checked. I am using the Behringer measurement mic through the DEQ to take readings, allbeit with some expected margin of error.

[fernandov]

Re: The Diminui Dipole Project

Thanks for the response!



With the low pass for the woofer so high, do you worry about driver spacing smearing the image?

Ordinarily I would say yes. However there are a good number of existing OB projects that seem to adopt this philosophy with good results. The M. King whitepaper which uses an Eminence Alpha 15" helper woofer and a small 3" Fostex fullranger has similar spacing. I believe the crossover points are almost identical to what I am using, except my system is active. I have some scrap MDF and will try to test this.

Do you have any experience with batting placed behind the drivers to possibly attenuate some of the back wave? I wonder how much of a role the additional reverberation from OB's plays in image smearing?

[blair]

Re: The Diminui Dipole Project

In my experience, it doesen't. You should leave the back alone. I have enjoyed all of my open baffle projects without padding the backwave. I notice no imaging issues at all.

Blair

[fernandov]

Re: The Diminui Dipole Project

In my experience, it doesen't. You should leave the back alone. I have enjoyed all of my open baffle projects without padding the backwave. I notice no imaging issues at all.

Blair

Thanks Blair, that's very reassuring. Imaging seems spot on for me as well, but one or two others have suggested it. Are your OB designs biamped? How did u xo?

[blair]

Re: The Diminui Dipole Project

Most of my speakers are open midrange speakers. I do not design my crossovers, but they incorporate much of the theory you are referring to as far as crossover points are concerned. I find NOTHING wrong with the imaging in my system though.

Blair

[J.Lee]

Re: The Diminui Dipole Project

Way Cool Fernandov -

I like the reasoning you use for not needing huge baffles for OB as most think are needed. I followed 'Gainphiles' experiments over at DIYA . If done right a huge chunk of wood isn't necessary.

I'm curious why you didn't chose drivers with a higher QTS but I do like your choices.

[fernandov]

Re: The Diminui Dipole Project

Way Cool Fernandov -

I like the reasoning you use for not needing huge baffles for OB as most think are needed. I followed 'Gainphiles' experiments over at DIYA . If done right a huge chunk of wood isn't necessary.

I'm curious why you didn't chose drivers with a higher QTS but I do like your choices.

The QTS on the woofer is actually .61, which isn't that low for a driver with a large motor and 13mm of excursion. The Orion's actually use Peerless 10" drivers with a much lower QTS and about the same xmax. I felt the Alpine driver was a good compromise. Some drivers with a high QTS (greater than 1.0) have a fairly sloppy feel often resulting in that one note bass drone instead of tighter, more articulate bass. The QTS on the full range driver is actually muich less important, since the bulk of the low frequencies are covered by the woofer.

Having worked with both low excursion/high QTS drivers and high excursion/lower QTS drivers, I would usually opt for the latter. I believe it is a quality of sound issue where dipoles are concerned, especially if the music you listen too might call for the added cone movement w/o bottoming out. This factor is often overlooked when the theories are discussed.

[J.Lee]

Re: The Diminui Dipole Project

Excellent reply... well thought out and things I hadn't considered due to all the supposed 'expertise' to date.

This gives me a much better choice in woofers.

[[email protected]]

Re: The Diminui Dipole Project

a truly wonderful writeup. thanks.

[fernandov]

Re: The Diminui Dipole Project

a truly wonderful writeup. thanks.

Glad you found it helpful.