[mcgsxr]

I know that lots of folks around here use the Visaton b200, as do I, but I think a thread around what makes a driver useful for an open baffle application might be valuable to some of the folks interested in OB, but not yet experimenting.

I will try my hand at kicking this off...

QTS - 7.0 is apparently the magic number, I will leave it to folks who know why, to communicate that part...
XMAX - the more the better, especially for bass
Cast Basket - preferred, in my books
Surround - well, you will read lots about this part - some use foam, some use paper, some use rubber.  Rubber for bass please.

I am sure there is a ton more to communicate on this, I will add more as we play along!

[JohninCR]

I believe that any driver that is open in the back can be used in OB.  Once you get below about 200hz, then Qts becomes important since low Q drivers need help to make bass.  I've seen great reports of Lowthers used in OB, and I've personally used low Q Fostex drivers in OB.  With bass augmentation they sound great, and IMHO all but large OB drivers, such as the Hawthorne 15", require bass augmentation to reproduce bass at realistic levels for all but a narrow selection of music.  Sure, gradually rolled off bass can sound really good, like with a B200 alone on OB, especially with some music, but rolled off bass is why subwoofers are so common.

[JohnR]

The reason for Q=0.7 (not 7!) is that, ignoring the cancellation from the rear wave, this will give a flat response down to fs and 6dB/octave rolloff below that. When the cancellation is taken into account, the bass rolls off even more of course. I've seen it recommended that drivers have higher Q than 0.7, in order to compensate for the dipole rolloff. I think there was a famous (?) dipole speaker that had woofers with a Q of something like 3 a long time ago.

[mcgsxr]

Thanks for the typo catch JohnR!

Another one to consider, specific to bass OB drivers, is that if you find a dual voice coil sub, and run only a single voice coil, it doubles the effective QTS, often bringing it right into line with the rest of the desirable specs.

I am aware, and others ought to understand this too, that connecting the sub this way drops efficiency, power handling, etc.

I am also told that you can add resistance to the "open" voice coil, and tune the sound accordingly.

One such woofer, available remarkably cheaply in Canada, is this one.

http://www.mach5audio.com/product_info.php?products_id=41&osCsid=86290b555986cedce02e0ee8df710038

This is the sub I am currently running one of, in each of my main baffles.  I intend to add another set, for fun!

[chadh]

I was wondering...how do the Moth Audio Cicada drivers look for OB potential?

http://www.eddiecurrent.com/cicadaspeakers.htm

If nothing else, they're really pretty.

Chad

[hurdy_gurdyman]

Almost any driver can be made to work on an OB. It's the area of bass that gets problamatic. The Cicada appears to have a suitable Qts and fs to work ok, just might be a bit lean on the bottom. If this is the case, you can always add a bass augmenter. I couldn't tell you how it might actually sound, as each type of driver from different companies have their own character, and I haven't heard these. They appear to be well made.

Dave

[ashok]

Hi everyone,

I have been following the Darkstar thread since it started and would really like to try an OB system. The driver I am considering is the Electro-voice MT12, a 12 inch full range driver and called a triaxial. Does anyone have any experience with this driver, in OB or otherwise?

The set I am considering was apparently used as ceiling speakers, and that makes me think that it is worth trying in an open baffle. Any thoughts are appreciated.

Thanks,

Ashok

[hurdy_gurdyman]

Hi everyone,

I have been following the Darkstar thread since it started and would really like to try an OB system. The driver I am considering is the Electro-voice MT12, a 12 inch full range driver and called a triaxial. Does anyone have any experience with this driver, in OB or otherwise?

The set I am considering was apparently used as ceiling speakers, and that makes me think that it is worth trying in an open baffle. Any thoughts are appreciated.

Thanks,

Ashok

Hi Ashok,

I've used an EV LS-12 in OB's for a few years. It's about the same speaker without the center mounted horn. They work well on OB's. The high Q rating is perfect. They should have good clean bass down to the 50-80 Hz range, depending on baffle size. Very efficient and can handle a surprising amount of power. The tweeter horn is a less expensive version of EV's T-35 tweeter, which is a very good horn tweeter. I believe the biggest difference between it and the T-35 is power handling.
  I've found that the whizzer coned EV's like these can have a bit of a peak in the 5-7 kHz range. If this becomes a bother to you, a simple notch filter should fix it right up with little drawback.
  Old EV's have a very "natural" sound.

Dave 

[markC]

The Eddiecurrent drivers look cool and being 12 ohm you could easily run two per baffle in parallel. The binding post on the driver is a Very good idea for open baffle use IMO.

[ashok]

Hi Dave,

Thanks for your informative reply. I have gone ahead and placed a bid on the MT12 speakers. Should be interesting to try out if I do win them.

Ashok

[morayjames]

The larger Beyma coax drivers could be interesting as they could get you low enough to cross to a sub and are very high efficiency. Worth a look, have not heard them though.
   Radian also have some very nice coax units they cost but they do sound very good. Regards Moray James.

[morayjames]

curious to know more about your Mach 5 - 12 inch subwoofer. The price and the look are right. What is it like with respect to noise generation (vent, spider basket turbulence etc. ? How much excurssion do you get before it makes noise? Thanks and regards Moray James.

[morayjames]

http://www.lorentz-audio.com/page/LA/CTGY/tweeter/SESSION_ID/d1f22d07f1d161bd22df6d214c02db50

   Lorentz has some interesting drivers at very attractive prices. Their Neo series drivers are nice but a tad on the heavy side ans a little inefficient. They do not post the driver Le which may be (probably, my guess) on the hi side of things. The 7 inch mid bass unit looks very good but not as attractively priced bur a very nice looking driver never the less. Regards Moray James.

[hurdy_gurdyman]

I notice that it hasn't been mentioned in this thread, so thought I'd mention it. The Hawthorne Audio Siver Iris OB 15" Coaxial is an excellent choice for open baffle use. It was designed especially for OB use. On a very moddest sized baffle it'll get you down to 50 Hz or lower with no wings or fancy constrution. The rest of the range is smooth and natural and can be driven by almost anything. SET's work fine with it. The new crossover is a must.

http://www.hawthorneaudio.com/drivers.htm

Dave

[opnly bafld]

The new crossover is a must.
Dave

Dave, I bet you would say that even if it was not your "baby".

Lin

[Brad]

Dave,

What frequency is the xover in the SI Coaxes?

[hurdy_gurdyman]

The new crossover is a must.
Dave

Dave, I bet you would say that even if it was not your "baby".

Lin

Just being honest, even if it is my "baby".  The new crossover is a huge improvement over the origional. Besides, I don't make much money on making these. There's lots of things I could be doing with my time that would make lots more. this is more a labor of love. I love the SI's and am doing what I can to make them better. I suspect that someday the production of the XO's will have to be turned over to a regular electronics company, as I won't be able to keep up when sales increase beyond a certain point. Until then, I'll continue making these the best I can at the present low price.
I honestly can say I haven't heard a speaker system I've liked better than these.

Dave

[hurdy_gurdyman]

Dave,

What frequency is the xover in the SI Coaxes?

Brad,

That's actually a tough question. I tried to design these XO's from various standard, and predictable, formulas. None of them turned out right. After a few weeks of frustration, I decided to go by gut instinct and just try different ideas I had. The end result both sounded and measured good over-all. However, the measurements I have show the woofer starting to roll off at about 2.8 kHz and the tweeter roll-off starting at about 2.2 kHz. In theory, this is wrong. In practice, it works great, at least with these drivers. That would put the actual crossover point about 2.5 kHz.
Just goes to show that a good sounding design can't always be modeled by just putting the numbers into a design calulator. Sometimes old fashioned trial and error, with a little outside the box thinking, can do just fine. aa Also, remember that this is not a standard crossover, as it has no low pass filter. It is a notch filter on the woofer with a 2nd order high pass on the tweeter. The woofer rolls off naturally with just the resonant peak tamed by the notch filter.

Dave

[Brad]

Thanks for the details Dave!

makes sense to even this non-xover designer...