[FredT300B]

http://fredt300b.smugmug.com/gallery/2040368/3/104742208

[Daygloworange]

I believe that's the OB 5 from GR Research that he's building.
http://www.audiocircle.com/index.php?topic=32448.0 RAW has a finished set that look awesome.

Cheers

[jeffreybehr]

http://fredt300b.smugmug.com/gallery/2040368/3/104742208

This open-baffle, dipole (bass and MR) system was the best-sounding at the RMAF, in my and many others' opinion.  It was VERY detailed...transparent...open, spacious, dynamic, etc.  My personal preferences would have several dB less treble and more bass, but more good news is all that's quickly programmable (by Emerald); the DBX (?) digital eq. stores many contours.

Only $6750 per pair.

[AJinFLA]

The subwoofer isn't a dipole, its a quadrupole. I confirmed this with the designer.

cheers,

AJ

[James Romeyn]

http://fredt300b.smugmug.com/gallery/2040368/3/104742208

This open-baffle, dipole (bass and MR) system was the best-sounding at the RMAF, in my and many others' opinion.  It was VERY detailed...transparent...open, spacious, dynamic, etc.  My personal preferences would have several dB less treble and more bass, but more good news is all that's quickly programmable (by Emerald); the DBX (?) digital eq. stores many contours.

Only $6750 per pair.

I hope this speaker is present 10/07 when I plan to attend.  Programmable may not mean achievable.  Is not the biggest Achilles heel of OB decreasing maxium output as frequency decreases? 

[Rudolf]

The subwoofer isn't a dipole, its a quadrupole. I confirmed this with the designer.

Lateral quadrupoles are terribly inefficient. The examples I know of (almost all theoretical models, not actual working ones) are designed as horizontal arrays. I can´t see what the advantage of a vertical quadrupole should be. Did the designer explain his reasons to do so to you?

Rudolf
www.dipolplus.de

[Rudolf]

Is not the biggest Achilles heel of OB decreasing maxium output as frequency decreases? 

Yes, it is. But you have to see this in perspective: Much of the bass energy conventional "box" speakers radiate into a room is "wasted" in detrimental energy storage effects like room modes and reflections. So the additional effort you have to put into good dipole bass is honored by better effortless reproduction.

Rudolf
www.dipolplus.de

[James Romeyn]

The question is: Which design's problems are easier to work around?  A speaker w/ 4-15s that tilts upward in tonal balance & also lacks bass (the speaker pictured in the link of the 1st post, as described by one listener in the RMAF show report) is an astounding problem by box speaker standards. 

When treating the bass problems arising from OB vs. box speakers, the OB's excursion & power handling seem more difficult obstacles than the box speakers' room modes.  Amplifier power is affordable for OB systems, but exursion & power handling are still difficult.  Modern programmable digital eq has eased the treatment of room modes in bass frequencies, caused by closed box designs. 

My 2c.   

[hum4god]

here are some glass open baffles that look stunning:

http://www.gwabsynect.com/laglass/index.htm

i am doing some research trying to find out if i could built my own OB but i realize that there are a lot variables . which driver , tweeter , sub . what design etc....

that might be a long term project.

thanks
malcolm

   

[Bob in St. Louis]

i am doing some research trying to find out if i could built my own OB but i realize that there are a lot variables . which driver , tweeter , sub . what design etc....

When treating the bass problems arising from OB vs. box speakers, the OB's excursion & power handling seem more difficult obstacles than the box speakers' room modes.. but exursion & power handling are still difficult.

But they're so CLEAR. No EQ, No arrays, No elaborate box design.... Just driver, and source (maybe an amp if needed)

Bob

[James Romeyn]

With all due respect, & absolutely not being a wise guy in any way...in any comparison of two speakers one might say the speaker w/ less bass is more clear. 

I'm considering OB only in the 2-octave band 70-280 Hz (the lower range will be sealed, the range above is a panel array).  If anyone can describe a proven custom system for 70-280 Hz I'm all ears...er rather, eyes...then ears.  My goal is to minimize the rear wave bouncing against the cone's back side, muddying the sound.   

[hurdy_gurdyman]

With all due respect, & absolutely not being a wise guy in any way...in any comparison of two speakers one might say the speaker w/ less bass is more clear. 

Any music with less bass will sound more clear. However, clarity alone isn't what high quality reproduction should be about. It should be about accurately reproducing the origional musical event as close as possible. I'm sure classic rock bands like the Rolling Stones, the Beatles, CCR, the Who, etc, all would have sounded clearer if the bass player would have stopped playing or turned it down, but then a lot of the special experience would have been lost. Same with the great jazz bands, classic orchestras, etc. The bass is there for a good reason. It makes no sense to listen to it in playback at a reduced level, at least not to me. I'll take accurate playback of ALL the frequencies in the origional performance over enhanced perceived clarity by reducing the bass anytime.

Dave

[Rudolf]

I'm considering OB only in the 2-octave band 70-280 Hz (the lower range will be sealed, the range above is a panel array).

In this thread you are mostly critizising what others do, but only now revealing (sparsely) what YOU intend to do. And the result: With your range decision you are effectively ruling out the most convenient dipole configurations aka H- and W-frame. 
Let me explain: To reach 70 Hz would necessitate a really large flat baffle or something like two octaves of 6 db/oct EQ for a 50 cm wide OB. So many people would recommend a W- or H-frame here (which could happily support 40 Hz too). At the opposite end of your range, 280 Hz would be VERY near to the typical first manifold resonance of those W- and H-frames. You would need a 24 dB/oct. LP at least to subdue that resonance effectively.
Without necessity you are pushing yourself into the situation you don´t want: the need of much EQ at the lower or upper end of the passband. If you could move that band to 40-160 Hz (two octaves too) you could happily get away with some proven W- or H-frame solution, demanding much less EQ.

My goal is to minimize the rear wave bouncing against the cone's back side, muddying the sound.

Funny, that you intend to stop with the OB just were the bouncing really starts (280 Hz).

Rudolf
www.dipolplus.de

[Bob in St. Louis]

Jim, I cannot speak as eloquently as Dave or Rudolf. I can't give numbers and facts. I am not an electrical engineer, scientist, or even a 'spec geek', like some here. My arguments are not strong, I can't back them up. All I have as proof of my beliefs is my passion. That is very hard to convey over the internet.
But what I can say is this, "A 100% NO baffle configuration is the best sound I've ever heard. Period".
I've heard some high dollar systems and the best sound I've heard was with my drivers fresh out of their boxes, sitting on their boxes.
Here's a picture of what I like to call, "The Evolution".
To me, it represents not just the evolution of the drivers/speakers I've had in the past couple years, but also the evolution of what an Open Baffle configuration has done to MY way of thinking regarding audio reproduction.

http://home-and-garden.webshots.com/photo/2094682740085868784zrnaEW

Jim, I have no idea of your financial situation (nor is it my business), but if you have $300, I have a prescription for you.

Bob

[AJinFLA]

Lateral quadrupoles are terribly inefficient. The examples I know of (almost all theoretical models, not actual working ones) are designed as horizontal arrays. I can´t see what the advantage of a vertical quadrupole should be. Did the designer explain his reasons to do so to you?

Rudolf, it's a longitudinal quadrupole (+--+, 2 vertically stacked if you wish). Force cancellation and far field dipole like behavior. And even more inefficient than a dipole, as you mentioned. Worth the trade-offs?
I don't think so, but Clayton Shaw promises a full technical dissertation of the design on the upcoming website. We'll see .

cheers,

AJ

http://www.kettering.edu/~drussell/Publications/MDQSources.pdf

[Rudolf]

Rudolf, it's a longitudinal quadrupole (+--+, 2 vertically stacked if you wish).

Thanks AJ
for correcting this. Now that is what I would call real luxury: Throwing in four 15" (or 18"?) to get the ultimate bit of bass directivity while abandoning a whole bunch of bass volume at the same time. I really look forward to that dissertation.

Rudolf

[James Romeyn]

I'm considering OB only in the 2-octave band 70-280 Hz (the lower range will be sealed, the range above is a panel array).

In this thread you are mostly critizising what others do, but only now revealing (sparsely) what YOU intend to do.

I appreciate your input.  With all due respect, I would like to clarify that one thing I've learned over years of forum posting is not to be critical of others & not to criticize what other's do (it's hard to seperate the two).  I have done it in the past, so I'd appreciate no one dredging up old posts.  But I haven't for some time.  If I have presently criticized what someone else has done, I apologize.  I think I have only posted what I perceive as problems in OB designs.  If that is perceived as criticism it was not meant that way.  My sole goal is to explore if the alleged problems can be solved for the narrow range I mentioned.     

My goal is to minimize the rear wave bouncing against the cone's back side, muddying the sound.

Funny, that you intend to stop with the OB just were the bouncing really starts (280 Hz).

Rudolf
www.dipolplus.de
[/quote]

The system above 280 Hz will be an unboxed panel array, completely devoid of any rear wave reflections except for those within the room itself.  Thanks very much for your input & thoughtful remarks.

[James Romeyn]

With your range decision

I'm looking for the two octave range 70-280 Hz.

you are effectively ruling out the most convenient dipole configurations aka H- and W-frame...To reach 70 Hz would necessitate a really large flat baffle or something like two octaves of 6 db/oct EQ for a 50 cm wide OB.

OK, this is what I like, hard numbers.  20" wide baffle & 12 dB of EQ over my two octaves.  So...let's say you have a closed box w/ 89 dB senstivity & 400WRMS power handling @ 4-Ohms (reasonable, easy to accomplish).  For an OB design w/ a similar 89 dB sensitivity to equal the output of the above system would require a SIX-THOUSAND FOUR HUNDRED WRMS POWER AMP & THE SAME POWER HANDLING IN THE DRIVERS!!!!!!!!!!!!  That is an astounding fact.  If accurate this certainly demonstrates well the shortcomings of OB design & fully explains their general neglect in the marketplace.  This is not meant as an attack or claim that the design is inferior overall or anything else.  It is not an attack on anyone who loves these designs.  It's just an interesting point.   

So many people would recommend a W- or H-frame here (which could happily support 40 Hz too).

I sure don't see how any OB design could support 40 Hz based on your numbers above, at least not for the SPL I'm interested in.

At the opposite end of your range, 280 Hz would be VERY near to the typical first manifold resonance of those W- and H-frames. You would need a 24 dB/oct. LP at least to subdue that resonance effectively.

"At least" scares me.

Without necessity you are pushing yourself into the situation you don´t want: the need of much EQ at the lower or upper end of the passband. If you could move that band to 40-160 Hz (two octaves too) you could happily get away with some proven W- or H-frame solution, demanding much less EQ.

My goal is to minimize the rear wave bouncing against the cone's back side, muddying the sound.

Funny, that you intend to stop with the OB just were the bouncing really starts (280 Hz).

I'm actually not "pushing" myself into anything.  I'm interested in the theoretical question whether or not an OB design could practically replace a box system for the range of 70-280 Hz.  This is the range, period.  Not higher, not lower.  The range above 280 Hz is not in question.  I'm not open to changing it or to even thinking about changing anything else in this system.  To suggest otherwise would be like me stating here that an OB design is far inferior to what I've employed. 

If OB proponents wish readers to get the impression that OB designs are difficult to isolate to reproduce this two octave range, that is the exact impression I'm getting.   

[scorpion]

Jim,

Why do you want some advice from us? I have given you what I think a very fair proposal for a test if OB is something for you and you stand to neglect it altogehter in your posts. I do not want to stress you but its your turn proving to us that our advice are neglectabale. I have given you the link to Siegfried Linkwitz web. There is a spreadsheet there comparing monopole and dipole loads. It's just to use it. Your figures in your last post are meaningless. You have to tell us what your aims are also in terms of SPL. What it boils down to is speaker size and ability to move air, nothing more and nothing less. Baffle response will however also depend on speaker parameters and equalization, but that is a thing to decide when you have told us what you want to achieve. If you are as you state going OB down to 280 I don't se no strong reason not doing so further down. It certainly won't hurt the sound you are hearing.

I must say when reading all posts throug that I do like Rudolf's and Bob Jackson's posts. Rudolf is emphasizing the same things as I ventured in my posts. Bob Jackson is plain right, or very close !

/Erling

[JohninCR]

With your range decision

I'm looking for the two octave range 70-280 Hz.

you are effectively ruling out the most convenient dipole configurations aka H- and W-frame...To reach 70 Hz would necessitate a really large flat baffle or something like two octaves of 6 db/oct EQ for a 50 cm wide OB.

OK, this is what I like, hard numbers.  20" wide baffle & 12 dB of EQ over my two octaves.  So...let's say you have a closed box w/ 89 dB senstivity & 400WRMS power handling @ 4-Ohms (reasonable, easy to accomplish).  For an OB design w/ a similar 89 dB sensitivity to equal the output of the above system would require a SIX-THOUSAND FOUR HUNDRED WRMS POWER AMP & THE SAME POWER HANDLING IN THE DRIVERS!!!!!!!!!!!!  That is an astounding fact.  If accurate this certainly demonstrates well the shortcomings of OB design & fully explains their general neglect in the marketplace.  This is not meant as an attack or claim that the design is inferior overall or anything else.  It is not an attack on anyone who loves these designs.  It's just an interesting point. 

Jim,

It might be interesting if it were true.  70hz is a piece of cake.  If you want to set spl/frequency goals for OB
you need to use Linkwitz's free DipoleSPLmax spreadsheet.  To match your sealed box example, the minimum
cab would be the same driver as your sealed box in a 16" deep U-Baffle, and that could easily be smaller than
your sealed box.  From 70hz, response would rise by 6db to a peak at about 210hz followed by a deep null at
about 410hz, which you could use judiciously as part of your low pass filter.

To answer your driver question, for running up into the hundreds of hz, use a mid Q pro type woofer.  A perfect
candidate was in one of these threads recently for $40/pr in a scratch and dent sale.  For a heavy duty 15"
that can play way down low and have no problems up to several hundred hz with a low order XO, then the
Hawthorne Augie is what you need.

I need exact performance goals and size and $ budget to be of more assistance.