[AlliumPorrum]

I'm not sure if this should be on this circle or the GR Research- one, since it concerns both areas. But my question is; does anyone have any experience on building cardioid basses with GR Research's 12" drivers? Different setups can be seen for example in here: http://kotisivu.dnainternet.net/anukaa/CardSub/CARDSUB.html

[ttan98]

Hi,

Interesting Designs, nice woodwork as well must take you hours to do.

[studiotech]

Sounds like a fun experiment.  You're going to want a big bag of this stuff:

http://www.bondedlogic.com/construction-products/ultratouch-denim-insulation

Greg

Check your PM, I sent you one the other day.

[AlliumPorrum]

No one??

[scorpion]

Hi Allium,

Perhaps you are not familiar with John Kreskovsky's longtime used damped U-frame woofers, which I suppose will be
a better match for Danny's servo woofers than box designs. As you can read in these papers by JK the damped U-frame will
tend to cardioid response for the low frequencies.

http://musicanddesign.com/NaO-II-U-frame.html  and  http://musicanddesign.com/u_frame.html

/Erling

[JohnR]

I keep meaning to try the "dual monopole" approach to simulating a cardioid.

[Danny Richie]

I have experimented with several drivers using various shaped enclosures. The biggest problem I see, especially with U shaped cabinets, is the amount of coloration you can easily get from box panel resonances. The pressure created in some of those boxes can be very hard to control. Most boxes that I have seen are no where near heavy or solid enough for the amount of pressure and panel flexing that can occur.

[sfdoddsy]

The major  resonances from a U frame (or indeed an H-frame) are quarter wave resonances due to the frames acting like short transmission lines rather than panel resonances.

Thus it will make no difference how solidly built the enclosure is, it will always have a resonance which needs to be taken into account. This resonance is higher in frequency for an H-frame, and lower for a U or W.

To answer the OP, you could certainly build John K style damped U-frame cardiods with the GR drivers.

Details here:

http://musicanddesign.com/NaO-II-U-frame.html

[stevenkelby]

Thus it will make no difference how solidly built the enclosure is, it will always have a resonance which needs to be taken into account.

Are you saying that sound quality will be the same for an H frame built from 1/4" or 2" material? It makes no difference?

[sfdoddsy]

Basically yes. I completely understand the overbuilding of box theory when you are constructing normal sealed speakers. The drivers are enclosed, there is nowhere for the sound to go except to bounce around inside the enclosure.

Most really high end speakers like Wilson or Magico spend all their effort (and your money because the enclosure is by far the most expensive  thing to build) strong-arming resonances into submission.

But a dipole is different. There is no front or back, hence no box to excite. There is no bouncing back and forth. Not no resonances, but fewer.

I owned Wilsons whilst building my dipoles and whilst their engineering is remarkable, it all seems kind of pointless when you disrupt the category by simply removing the box.

Of course you still get mechanical vibrations, notably from the bass drivers, but nowhere as much as from box speakers.

So no, I don't think it makes any difference to the quality of bass if you build your H-frame from 17mm or 72mm and line it with antivibratory cream. Constructing them the same way you'd build a sealed sub makes no sense, except to stop rattles.

It just makes it heavier.

But the bass section will vibrate mechanically and titillate the front baffle.  So I think it is wise to make the front baffle as rigid as possible, or decouple the mid and tweeter, or even more logically decouple the entire baffle from the bass altogether.

It strikes me as kind of odd that speakers like the Super Vs, Orions etc have their midrange section plopped on top of big vibrating bass sections so they can waggle back and forwards whereas a single front baffle decoupled from the bass is both stronger and much easier to build.

SL's new LX521bridge is the obvious solution that only surprises me in how long it took.

[Danny Richie]

The major  resonances from a U frame (or indeed an H-frame) are quarter wave resonances due to the frames acting like short transmission lines rather than panel resonances.

Thus it will make no difference how solidly built the enclosure is, it will always have a resonance which needs to be taken into account. This resonance is higher in frequency for an H-frame, and lower for a U or W.

This is correct. The quarter wave resonances are the source but they do excite the panels. Because of the depth of the typical U frame this can be a big problem. And the resonance frequency can be very close to the frequency range covered by the woofer. So it must REALLY be taken into account just as you said. I stress REALLY because it is very important. Some that I have heard were little buzz boxes.

I like the H frame because the frequency range of the resonance is pushed up beyond the range covered by the woofer to where it is not an issue.

It strikes me as kind of odd that speakers like the Super Vs, Orions etc have their midrange section plopped on top of big vibrating bass sections so they can waggle back and forwards whereas a single front baffle decoupled from the bass is both stronger and much easier to build.

SL's new LX521bridge is the obvious solution that only surprises me in how long it took.

The Super-V is a heavy speaker that is very solidly built. And the heavy side panels that support the upper section really help keep vibrations to very minimal levels. Even when the speaker is really pounding some high SPL levels there is very little cabinet vibration to be felt anywhere on the structure.

I like the idea behind the LX521, but to me it looks very lightly constructed. And the side panels of the sub structure look very lightly constructed as well. While they may not be attached to the upper drivers there could still be a considerable amount of panel resonance that could color the sound.

I don't point that out to knock it but to say to you guys that are considering a DIY effort that is similar to that design to be sure to not underestimate the importance of a solid lower section.

[JohnR]

It seems to me that the simple way to do it is move the subs away from the main panels.

[Davey]

Yes, but I think it depends upon how low the crossover frequency is and what the crossover slopes are.  The higher the frequency the more it becomes necessary to integrate (geographically, maybe not physically) them with each other.
Steve, to his credit, implemented something like this many years ago.

It's interesting to note, the even if resonances excite panels and cause buzz in open-baffle constructions, those buzzes are also radiating in a dipole nature.  Some folks might consider that an advantage....or another feature. 
There's a fellow in the Magnepan world who's established a nice business embracing/harnessing transducer vibrations and radiating them with the baffle. 

Cheers,

Dave.

[JohnR]

Yes, but I think it depends upon how low the crossover frequency is and what the crossover slopes are.

Yes of course.

Steve, to his credit, implemented something like this many years ago.

Yep

It's interesting to note, the even if resonances excite panels and cause buzz in open-baffle constructions, those buzzes are also radiating in a dipole nature.

Hm... I'd never considered that. Say, you don't happen to know of a relatively inexpensive contact microphone for measuring panel/baffle noise? (If there is such a thing, I would assume so...?)

[Davey]

Sure there is.  And not expensively either.  The Measurement Specialties ACH-01 is only twenty bucks at Digikey.

http://www.digikey.com/product-detail/en/1-1001497-0/MSP1002-ND/279642

Bill Waslo has nice page on his website outlining how to use accelerometers with your favorite response measuring program.  Your existing microphone preamp may even provide the proper excitation (phantom) voltage.

http://www.libinst.com/accel.htm

Dave.

[AJinFLA]

I'm not sure if this should be on this circle or the GR Research- one, since it concerns both areas. But my question is; does anyone have any experience on building cardioid basses with GR Research's 12" drivers? Different setups can be seen for example in here: http://kotisivu.dnainternet.net/anukaa/CardSub/CARDSUB.html

Don't see any reason why they wouldn't work well. The keys, as always, would be implementation (especially the damping) and ability to measure.

cheers,

AJ