Openminded--A Mark Audio Alpair 10.2 Open Baffle Project

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Jim Griffin

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Joined 2003
Erling,

Thank you for your simulation of my speakers. I deliberately chose to center the Alpair 10.2 driver on the 18" wide baffle in the horizontal plane--thus 9" center to each side). In the vertical plane the driver is located 10.5" up the 19" baffle height. With the H-frame and its feet (totals 19.5" high) locates the A10.2s 30" (to the driver center) above the floor. Thus a seated listener would likely have their ears positioned 3-6" above the center of the driver.

My choice to position the driver as I did is that you will have a horizontal plane glitch regardless of where you locate the driver in the forward hemisphere. If you center the speaker on the baffle, the glitch is on axis as you show in the analysis in Message #22 of this thread. If you use Edge (or other sims) and locate the driver offset in the horizontal plane, you essentially locate the glitch off axis. But, the typical listener usually is positioned (for the sweet spot) some 15-20 degrees off axis--not on axis. Researchers such as Dr. Linkwitz (Orion and Audio Artistry open baffle designs) and John K. (Music and Design) center their drivers for their open baffle designs.

My next speaker likely would have a baffle with sloping sides along the driver so that the glitch is more disperse across frequency.

Jim
 
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Rudolf

Rudolf

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Joined 2003
dipolplus.de
Godzilla said:
I think we can put a lot of drivers onto a baffle the width of our H-frames (using either 15 or 18" drivers) and create a relatively clean looking, great sounding open baffle.
Click to expand...

You may take the effort to download my new treatise on OBs. Use the upper download button for the german version (the english version is outdated now). At pages 21-24 you see my last system with a trapezoid baffle for the midrange driver. The pictures tell it all. At pages 25-26 is my latest system "Swingers Club". If you follow my personal "dipole history" at page 27 - it is all about shrinking the baffle size (relative to frequency involved). Every step in that direction improved the precision of imaging for me.
 
planet10

planet10

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andb said:
First, I found that localization wasn't as precise...
What ruined it for me though was that the soundstage "bunched up" at the speakers. While there was imaging to some extent, to my ears the sound was coming largely from the speakers.

In the end I put the A7's in Dave's Slim classic GR dMar-Ken7 (a slim ported enclosure). Dramatically better imaging
Click to expand...

The preciseness is likely do to the nature of radiation of a dipole (similar happens with bipole).

Localizarion of the sound to the speakers is a result of the speakers being boxy -- a large diffraction signature. An OB won't suffer to anywhere the same degree as an enclosed box wrt time-smeared stuff coming back theu the cone, but the baffle itself, and the often large time delta to the baffle edges, can cause an OB to be boxy.

dave
 
J

Jim Griffin

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Joined 2003
In a way it is much to do about very little. While you would theoretically have a glitch on axis (you do because I can measure it coming from one speaker), if you move slightly off axis the hole fills in. Also the dip is very narrow in frequency. Next, if you add the stereo contribution from the opposite speaker, you'll will not hear that glitch. Finally, within the room you heard an ensemble of sound from both speakers and the reverberant energy within the room. My listening tells me that I can not hear any perturbation in the sound.

Rudolf is on the right track to full mitigate or eliminate any glitch by baffle design or via no baffle. Trending toward a more narrow baffle will improve the imaging and be beneficial to the sound.

Dave is right on about the impact of a baffle on sound localization.

Jim
 
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J

Jim Griffin

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Joined 2003
Dave, we are not on the same exact wavelength. I'm talking about open baffle design with Godzilla's and Rudolf's comments in mind. I'm especially refering to Erling's sim plots vs. how that glitch can be addressed. Your reply jumps back several posts to andb's comments on imaging. But I'm pointing out Rudolf's contribution to narrow/no baffle design as a way to eliminate edge effects. That can offer superior imaging vs. a wide baffle as in my original design.

Jim
 
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R

ra7

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planet10 said:
An OB won't suffer to anywhere the same degree as an enclosed box wrt time-smeared stuff coming back theu the cone, but the baffle itself, and the often large time delta to the baffle edges, can cause an OB to be boxy.
Click to expand...

Boxy sound and sound that sticks to the speakers are too different things. Boxy, in my mind, refers mainly to the bass frequencies. OB excels in this department.

Sound sticking to speakers can also be down to the drivers. Usually full range drivers have plenty of breakups and resonances that make their presence known.

In general though, OB sound is more easier to listen to. If done correctly, it is actually less taxing on the brain. According to SL, it illuminates the room more evenly resulting in better directional cues compared to boxed speakers. I've found this to be true in that OBs are really relaxing and easy to listen to, despite the diffuse soundstage.
 
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andb

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Joined 2008
I've also tested with a set of Fostex 126e's that Dave treated in the same dimension OB, as I remember there was much the same sound bunching up at the baffle, but not as much as the A7. My goal was to XO the FR's as low as possible as it seems to me that they would be more accurate than the big 15"... So it seems a trade off between two evils - narrow baffle and rely on the big woofer more, or bigger baffle and stickier sound.

Would covering the front of the baffle with an acoustic fill sheet, with a cutout in the center for the driver, reduce the diffraction and large baffle size issues? It would be ugly as can be obviously, a sock to cover it all would definitely be more aesthetically pleasing...

When I find some time, I'll try front "stuffing" to see what the actual effect is.

So far the best disappearing act has been with a pair of CHR-70's in Ikea bowl spheres, not even flush mounted, though I still prefer the A7's in the slim GR which disappear nearly as well and are more detailed.
 
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skorpion

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Joined 2004
Rudolf, very interesting OB write up, but do translate also this into English. You address all the up to date Open Baffle thoughts in your paper.

Otherwise I want to comment a bit about Dave's statement about the Silver Iris. In fact I and a Stockholm friend was conducting a comparison with the Silver Iris and my B200. I thought my B200 sounded way better than the Iris. But he really liked the much more laidback sounds from his Irises. I suppose it is what you are used to and like that's setting the standards. There are a lot of Silver Iris users around who love what they hear.

Myself have also been through a bit of this compare process. I substituted the Eminenca Alpha15s for AE IB15s in my Blindsone OB, already given the thread: The BlindStone OB with in my opinion a mayor breakthrough. You should put up this woofer like I have done and play Beach Boys live 'California Hotel' and report back what you hear. :)

/Erling
 
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planet10

planet10

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skorpion said:
Otherwise I want to comment a bit about Dave's statement about the Silver Iris. In fact I and a Stockholm friend was conducting a comparison with the Silver Iris and my B200. I thought my B200 sounded way better than the Iris. But he really liked the much more laidback sounds from his Irises. I suppose it is what you are used to and like that's setting the standards. There are a lot of Silver Iris users around who love what they hear.
Click to expand...

I know there is an appeal to many for the things the Silver Iris does -- at one diyFEST where they appeared there were a number of people head over heels. I was not one of them -- the lack of any midrange definition, and the audible resonance train from the midrange up to the top of the 15s BW which is, i am sure, the major contributor to their "boxiness"

dave
 
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chrisb

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Joined 2002
planet10 said:
I know there is an appeal to many for the things the Silver Iris does -- at one diyFEST where they appeared there were a number of people head over heels. I was not one of them -- the lack of any midrange definition, and the audible resonance train from the midrange up to the top of the 15s BW which is, i am sure, the major contributor to their "boxiness"

dave
Click to expand...



I was certainly not a fan of them either, on at least 3 different occasions. Rather like another DIY project that I'd consider a spiritual sibling of sorts - the Hammer Dynamics Super 12, these can be very impressive in terms of dynamics and scale, but far too much upper mid-bass and mid-range coloration for my taste, and very poor cohesion of imaging.

There are many accounts of inexpensive Eminence woofers used in support of a variety of OB etc projects not to consider the XO's contribution to performance of this system.

While by no means perfect itself, I found the Visaton B200 to perform very well indeed in exactly the areas were the SI and Super12 stumbled.
 
jmillerdoc

jmillerdoc

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Joined 2009
I have a par of MA10's and a pair of Visaton BGS40's as used in the visaton No Box BB design. I have had thoughts of replacing the visaton B200 with tue MA10 and redoing the XO. I was wondering if I might get some suggestions here in doing this....where would you cross these in this combination?
Thanks,
Jeff
 
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