[JohninCR]

Maxro,

A U doesn't manipulate anything any more than an H.  An H just does it to the front as well.  I'd expect an H to offer less top end extension since damping typically isn't used.  That's why I don't understand everyone's fixation with H's.  Double the size with the difference being polar response, for which I question whether or not there's a benefit, especially since dipole response in the bass region isn't possible with typical in-room placement.

"Asymmetrical dipole" is an oxymoron.  "Open Baffle" makes sense to me as the appropriate all encompassing term unless someone comes up with something better.  Both sides of the driver mounting baffle is always open to the room.

[maxro]

I suppose it is an oxymoron, using the Oxford English Dictionary definition of dipole.

A U baffle does manipulate the wave differently at the rear than at the front, unlike an H baffle. May I say that some open baffles are more equal than others (equal in radiation pattern on each side of the baffle, that is)?

Don't get me wrong, I'm not dissing U baffles. My next speaker project will be open top U baffles for a pair of high Q Goodmans 12" fullrangers I've had sitting around. I just wanted to agree with Rudolf and his distinction that a U baffle may be a type of open baffle, but it is not a true dipole.

[Rudolf]

John in CR,
I am perfectly in tune with your definition of "Open Baffle". So I certainly would coin a U-frame without a dampened back as open baffle too. Pity is that this U-frame will change its radiation characteristic with rising frequency from real dipole to almost monopole. (BTW: This is a "problem" every non-symmetrical OB will develop in some way.)

As JohnK. states: "... At 20 Hz the undampened U-frame does exhibit a dipole like response but as the frequency rises the response is neither dipole or cardioid like. This is due to the asymmetry between the front and rear radiation as the resonant frequency is approached."
This may or may not be helpful in any way. Haven´t made up my mind about that. But at the moment I would prefer radiation patterns that stay constant from down low to 500 or even 1000 Hz.
A U-frame can do that when properly dampened. But this "properly" seems to be hard to achieve. And it would make that U-frame no open baffle any longer - even by your very own words.

Regarding my personal "line of development" this would be much like Erlings: Avoiding the dipole efficiency struggles below 30-40 Hz and trying to keep the same radiation pattern from there up to regions, where driver basket geometry is of more influence than baffle geometry.
Hopefully this can be achieved with less "exposure" than Svalander´s OBs.

It seems that maxro is thinking along my lines too: OB is everything that is open to the front and back (within the limitations you already stated in your earlier post), and the range of applications would run from "true dipoles" (symmetrical radiation pattern) to preferred forward radiation (like cardioids).

I believe we all could happily meet there.

[JohninCR]

Re terminology that makes sense.  I just wanted us to start the consensus here because people take OB to mean different things.  I like the broad definition, since we don't have another term for it.  I don't think adding damping to a U makes it "closed", because the low frequencies go right through, seemingly unaffected.  IME undamped U's don't sound good.  If undamped H's do, then there must be significant dipole cancellation of the resonances.  WRT the shift to monopole at HF, all coned drivers do this anyway making that a non-issue to me.  I'm not a dipole purist, although some of my opinions may change once I start measuring.

FWIW, the sub I'm currently using is an 18" driver in a 60cm deep U.  For damping I just have what I had available stuffed in the back between the bracing.  It has plenty of output into the 20's with the ~50hz Fequal.  Sure I have to compensate for the sloped response, but I have no problem running it crossed at 300hz if I want.  I wouldn't think of calling it anything other than an open alignment for 2 reasons.  First, the rear output seems as strong subjectively as the front, and second, the net pressure input into the room in the time domain still seems to be zero, since the bass remains so much better contained in-room than even relatively low bass output boxes.  The cardioidish polar response is a further benefit for me, since the rest of the house is behind that front wall, so I get even less sound transmission through that wall than with a dipole.

Also note I have some U's that approximate circular straight pipes that are an average of 37cm in depth.  I run them full range with a 15" coax without damping.  The staggered cross bracing and shape of the rear terminus work to prevent resonance.

[Rudolf]

Re terminology that makes sense.  I just wanted us to start the consensus here because people take OB to mean different things.  I like the broad definition, since we don't have another term for it.  I don't think adding damping to a U makes it "closed", because the low frequencies go right through, seemingly unaffected.

That renders "our" definition of open baffle useless. I can´t see the difference between your U-frame and a transmission line of the same length.

IME undamped U's don't sound good. If undamped H's do, then there must be significant dipole cancellation of the resonances.

Resonance peaks become less annoying with shorter frame length. One tries to put the cutoff-frequency of a H-frame in such a way that the dipole resonance is sufficiently subdued.

WRT the shift to monopole at HF, all coned drivers do this anyway making that a non-issue to me.

John K. did not talk about a 1 kHz shift, but about 100 Hz.

I wouldn't think of calling it anything other than an open alignment for 2 reasons.  First, the rear output seems as strong subjectively as the front, and second, the net pressure input into the room in the time domain still seems to be zero, since the bass remains so much better contained in-room than even relatively low bass output boxes.  The cardioidish polar response is a further benefit for me, since the rest of the house is behind that front wall, so I get even less sound transmission through that wall than with a dipole.

If "the rear output seems as strong subjectively as the front" you still have a long way to go before getting cardioid response. I have read comments of people who listened to true cardioids and the difference between front and back output was LOUD vs. "nothing".

[JohninCR]

Rudolf,

What is "your" definition of an OB?  It may be useless with other terms existing that better describe it.  What term would you use to encompass all forms of open alignments, which also excludes IB?  If there's a better term, I'll be happy to start using it.

At what length does a TL cease to be one?  I'll submit that it's really only a TL when it's used as one.  eg  A very long and very heavily stuffed TL could easily be called a sealed labyrinth.  Here's another one for you, I consider anything that extends further toward the rear a U shape.  If you take it to the extreme in terms of compact size, it's a driver on the end of a short pipe, but the more compact the shape the more you have to deal with resonance.  Open U's have less need for damping.

If that's really the only reason you use H's, then the front portion serves no purpose except to cause it to be a dipole, and I question that since in room it can't truly operate as a dipole at low frequencies anyway, so where's the benefit?

If JohnK said that, which you appear to be taking out of context, he's talking about improperly constructed U's.

Regarding output I was talking about nearfield and only to make the point that the alignment is open and not trying to change the rear wave into something different, like a BR, TL, or RLH does.  Also, I'm not building speakers for concerts so I really don't care if they are cardioid.  In fact, a true cardiod response may be problematic in room.

I'm not trying to be argumentative.  I just don't understand why people restrict themselves to pure dipole attempts, H's for example.  The front portion seems to be a waste of material and space.  Plus it limits upper end extension.  Shifting the radiation pattern away from dipole, and moving the region of greatest null somewhat rearward, like with a shallow U, even seems beneficial.  If I'm missing something with my point of view, please let me know.