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Open Baffle Epiphany!

baco99 said:
so it's really more about removing the "box" rather than being a dipole.
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Well, both actually. Removing the box means it becomes a dipole which means the driver is able to send a rear wave of sonic content into the room rather than confining the rear wave to the box. Sending that rear wave into the room is what gives OB's/dipoles a unique sonic character....provided the speakers are positioned properly.
 
baco99 said:
so it's really more about removing the "box" rather than being a dipole.
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I would agree with that also, removing the box is the largest factor. Bass response of an open baffle is surprisingly clean. The dipole effect may or may not help in the tweeters range. Many people like dipole tweeters, but it is hardly mandatory. I agree that the dipole midrange affect is probably more important.
 
If using one closed back tweeter you're better off firing it to the rear. With two you can have them firing in opposite directions.
 
Removing the box, or more appropriately, not containing the backwave allows the dipole to have the figure 8 radiating pattern which can help reduce the effects of the room. I can't remove the effects, obviously, but like a constant directivity horn, it can make room issues more manageable.

I have never experienced the lowest couple of octaves present any clear perceived advantage in quality over an appropriately built monopole.
 
dnewma04 said:
I understand that we are discussing monopole tweeters, but I'm confused by why you'd prefer a back firing monopole to a front firing monopole?
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I've experimented with it too and have seen it work pretty well.

I think it has to do with the fact that you don't have the top end covered by something physically offset from the mids and it may be more forgiving of the crossover. Maybe.

But rear firing seems to blend in with the character better.

With a stack of FR being pretty efficient, I need something with the output of a little horn tweeter. It seems to be hard to blend in when firing direct, but when rear firing...it just added the top end sparkle.

EV3
 
tomlinmgt said:
I don't think you'll be missing out....since all of your mid range content is still being propagated to the rear. Paul has done some designs with and without a rear firing tweeter and IIRC he preferred no rear firing tweeter with some designs. The Hawthorne designs that use the coaxial Iris or waveguide don't propagate any HF information to the rear. I think the meat of the OB experience is hearing all the mid-bass and mid range information propagated to the rear and whether or not having HF information propagated to the rear is beneficial is determined on a case by case basis.
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That's not quite true. I have a pair of 10" Sterling Silver that have an optional cap for the tweeter that is open and allows the back wave out. So it is a dipole design.

Regards
Mister Pig
 
dnewma04 said:
MP, is it just a vented pole piece?
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Yup pretty much. It's the factory back plate that has been opened up with a screen over it to protect the Radian diaphragm. I have both sets, open and closed, and have been able to listen to the speaker in both configurations.

Regards
Mister Pig
 
I now have drivers and wood to do an open baffle build. I have laid out three configurations, but I'm not sure which would be "best", if any. The woofers are 12" 8 ohm drivers from Peavey cabinets. Probably not ideal, but should be useable...and free. The FR driver is a Fostex 103 clone. I've tried it by itself and it sounds fantastic, just nothing useable below about 100Hz.

Centered:


Offset:


Staggered:


Which do you think, and why?

Thanks!
 
Regarding the question about closed back tweeters. I first had these pod tweeters firing forward and didn't care for the results. Danny Rich told me they should be reversed ( firing to the rear ) and explained that they were causing major disruption to the on axis response. I wasn't sure that was the case until I reversed them and learned differently.

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dnewma04 said:
Ah, compression drivers. Got it.
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That's what I thought...that it was a compression driver. CDs can be dipolar? If it's a compression driver doesn't that mean the magnet covers up the back-side of the diaphragm? I thought cd's by design had a magnet as the entire rear structure of the driver assembly.
 
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Poultrygeist said:
Low Qts woofers designed for enclosures don't work so well in OB.
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Well, it's what I have, and I'm going to make the best of it. My baffles are 24" wide, as opposed to the "MJK reference" 20", and I'll be running two 12" drivers, with an active crossover and TPA3116 amps in front of them. Maybe someday I can spring for Alpha 12A's.
 
FWIW, I would center the woofers and "mirror" the tweeters. Staggering the woofers may very well cause unequal diffraction and imaging problems in the end. Go for it, and let us know!.....Spooker
 
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