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Open Baffle Epiphany!

tomlinmgt said:
It gets even worse if one is trying to squeeze a dipole into a small room and places the speakers close to the front wall and the listening position close to the rear wall...in which case the fundamental benefits of a dipole design are impossible to realize.
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This would also mean that dipoles can in fact be more difficult to implement properly in a residential room than the conventional box speakers, wouldn't it?
 
With this OB I use a single cap between the modified Eminence Beta 12LTA and Realistic 40-1310A tweeter. Both are powered by the same SET amp

The H-frame Alphas are driven by a plate amp.

I use a 2 way active but I like the option to run the Beta's full range straight off the SET and use the plate amp's X-over to low pass the H-frames.

With some minor surgery, a phase plug and tweeter the inexpensive 12 inch Beta's can compete with the Lowthers and do some things the Lowthers can't do.

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^^^^^

Very nice.

Is the tweeter forward firing only or has the back been opened up to radiate front and back?
 
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davidro said:
This would also mean that dipoles can in fact be more difficult to implement properly in a residential room than the conventional box speakers, wouldn't it?
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Harnessing the rear wave effectively and finding the optimum location to accomplish that is the fundamental difference between a dipole and monopole. Other than that the placement challenges for the two a similar, with dipoles actually being a little less influenced by the room than a monopole since they have less floor, ceiling and side wall interaction than a monopole that doesn't use some form of controlled directivity.
 
tomlinmgt said:
It should be first priority with any dipole design....otherwise you're neglecting the whole reason for having a dipole. Probably not the best speaker design choice for the lethargic audiophile!
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:thmbsp: well put and the very reason I've not gone the OB/dipole route. In fact, I listen in the near-field for that very lethargic reason. :yes:
 
To increase bass output from a boxed speaker you push it back against a room boundary so that the rear reflections add constructively at low frequencies.

To avoid weak bass with a dipole speaker you pull it out into the room so that the rear boundary reflections do not add destructively at low frequencies.

I don't think it is any more difficult or fussy to place either type of speaker system in a room. The problem is that people want to apply lessons learned from a long history of designing, building, and listening to boxed speaker to their dipole speakers. This starts with driver selection, crossover design, and extends to room placement. If you understand the fundamentals I think dipole speakers are much easier to engineer and site. If you cannot get your head away from boxed speaker thinking you are going to struggle.
 
Linkwitz says we shouldn't blame the room but the speaker design.

He favors a lively room with a variety of features and surfaces vs an over stuffed room.

My room has hard surfaces and windows which never worked as well with box speakers as with OB's.
 
Poultrygeist said:
Linkwitz says we shouldn't blame the room but the speaker design.
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I see that statement as an oversimplification that isn't a practical solution for some and really only addresses his designs. Sure, SL has figured out how to design a speaker that has less interaction with the room, but at the same time the design does have specific requirements regarding what type of room that design will work best in and how it should be set up in said room. I give the guy credit for giving the room as much consideration as he does because I feel it's largely disregarded by most on the manufacturer and and consumer side of things, but designing a speaker that can overcome room acoustics issues results in a design that is only a proper fit if certain circumstances are met. So, what about the folks who have a room that isn't a good fit for one of SL's designs? Are they SOL? Of course not...they just have to go with a different speaker design which brings a different set of concerns wrt addressing room acoustics. Just because his designs overcome many of the typical room acoustic issues doesn't mean he's solved the problem of room acoustics for everyone...or that he's reversed the laws of physics that dictate how a room responds to sonic energy. And his designs do nothing to eliminate the rear wall reflection issue I spoke of earlier...not to mention early reflections from side walls if they are within a given vector distance from the speaker/listening position.
 
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Linkwitz is speaking about OB's in general. He doesn't reference his designs.

And in my sonically challenged listening space I've learned that OB's are far less room dependent than any box speaker I've owned.
 
His designs or OB's in general....doesn't matter. Still subject to laws of physics. See the final statement in my last post. Dipoles only cheat a little...not totally.
 
My point is that after years of experimentation with a variety of speakers my room matters less with open baffle speakers than with conventional box speakers.

I barely passed physics but my hearing is still good. :D
 
^^^

Since you've never implemented any acoustic treatments in your listening space (if memory serves me correctly) and have a somewhat spacious area your observations don't surprise me as your situation creates an acoustic scenario that tilts heavily in favor of an OB design. I can say this...all those box speakers you tried in the past would be totally different animals had your room's acoustics been better optimized...but I'm guessing you're aware of this.
 
tomlinmgt said:
^^^

Since you've never implemented any acoustic treatments in your listening space (if memory serves me correctly) and have a somewhat spacious area your observations don't surprise me as your situation creates an acoustic scenario that tilts heavily in favor of an OB design. I can say this...all those box speakers you tried in the past would be totally different animals had your room's acoustics been better optimized...but I'm guessing you're aware of this.
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I have a wife that's finally able to tolerate large OB's but with room treatments hung in front of windows I'd be pushing my luck.

Pulled 6+ feet out into the room and at low listening levels it's hard to comprehend much interaction with the walls.
 
I threw my hat in the ring today. Ordered the Fostex FF85WK and Alpha-15A to build the MJKing Model 3P OB. Just under $250 for drivers. Now to price the crossover parts. Going to borrow a friends router tomorrow (mine broke). I'm a perfectionist when it comes to woodworking etc, so this will take more than an afternoon to finish I'm sure. I'll post more when I make meaningful gains (maybe a new thread). Thanks for getting me to this point.
 
BHamm said:
I threw my hat in the ring today. Ordered the Fostex FF85WK and Alpha-15A to build the MJKing Model 3P OB. Just under $250 for drivers. Now to price the crossover parts. Going to borrow a friends router tomorrow (mine broke). I'm a perfectionist when it comes to woodworking etc, so this will take more than an afternoon to finish I'm sure. I'll post more when I make meaningful gains (maybe a new thread). Thanks for getting me to this point.
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Good job, BHamm...!

I have received the Tang Band W8-1808's. Alphas will be ordered next week or the week after.

I'll start a build thread as soon as I have all the drivers and am actually starting construction.

My new OB's will follow MJKing's guidelines - with much help from Poultrygeist -for the Tang Band and two Alphas:

MJKing said:
I seemed to remember working out an OB design for the W8-1808 full range driver and two Alpha 15A woofers a few years ago. Looking back in my notes this is what I found, this is based on manufacturer's specs for the W8-1808 driver. I have not built this design so consider it a possible starting point.

OB size is 20" wide by 40" tall

Alpha 15A woofers centered horizontally and vertically at 8" and 23", make sure to measure the actual driver diameters and sketch out the build to check for interference.

TB W8-1808 shifted 1" off center horizontally and at a vertical height of 34", close to ear level when seated.

Low pass the woofers at 200 Hz with a LR 2nd order filter.

High pass the TB at 300 Hz with a LR 2nd order filter, wire the TB out of phase.

No boost required, this system produces 93.5 dB/2.83V/m on axis with the -3 dB point at 45 Hz.
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These will be biamped using a Crown X1000 on the Alphas and either the Quicksilver 300B SET or CazTech SE845 SET amps via the Dahlquist DQ-LP1 or Heathkit XO-1 electronic crossovers.

More to follow.
 
I don't see how I can go wrong or be disappointed, especially after reading this thread and using an MJK design.
 
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