[FredT300B]

The midwoofers cross to the tweeters at 1.2khz using a 48dB/octave LR slope. Before settling on the 1.2khz and the 48dB slope I did some A/B comparisons of various crossover frequencies and slopes, including 800hz, 1khz and 1.2khz frequencies, and 12, 24, 48, and 96dB/octave slopes. With the DEQX you can set up different combinations and switch between them on the fly. I expected a lower crossover frequency to sound better, but in every A/B comparison I preferred the 1.2khz 48dB/octave. The DEQX model I'm using is the HDP Express.

All the above was done when the drivers were mounted in a 6 cu ft ported enclosure. I'm still waiting for some hookup wire to get the OB version playing. I have no doubt the OB version will require different equalization, and my crossover preferences may be different as well. Also, for those who are familiar with the functions of the DEQX, I have found its automatic speaker correction doesn't work as well with line arrays as it does with point source speakers, and I do the correction manually using the OMNI Mic system with the mic placed about eight feet out from the baffle. Any closer and you get a significant comb filter effect, and even that far out it's necessary to measure at various mic heights and average the results.

[versus rider]

The midwoofers cross to the tweeters at 1.2khz using a 48dB/octave LR slope. Before settling on the 1.2khz and the 48dB slope I did some A/B comparisons of various crossover frequencies and slopes, including 800hz, 1khz and 1.2khz frequencies, and 12, 24, 48, and 96dB/octave slopes. With the DEQX you can set up different combinations and switch between them on the fly. I expected a lower crossover frequency to sound better, but in every A/B comparison I preferred the 1.2khz 48dB/octave. The DEQX model I'm using is the HDP Express.

All the above was done when the drivers were mounted in a 6 cu ft ported enclosure. I'm still waiting for some hookup wire to get the OB version playing. I have no doubt the OB version will require different equalization, and my crossover preferences may be different as well. Also, for those who are familiar with the functions of the DEQX, I have found its automatic speaker correction doesn't work as well with line arrays as it does with point source speakers, and I do the correction manually using the OMNI Mic system with the mic placed about eight feet out from the baffle. Any closer and you get a significant comb filter effect, and even that far out it's necessary to measure at various mic heights and average the results.

I guess the driver error correction feature would be a problem with an array, you could try measuring just one driver and going with the result for all the drivers. The thing I like about DEQX is the three different crossovers changeable on the fly. I was more interested in your low pass of the midwoofers, 1.2Khz for midwoofer- tweeter sounds reasonable. 

[FredT300B]

They are playing for the first time. All the settings, including crossover frequencies and slopes, woofer vs tweeter levels, equalization and room correction are the same as when they were configured as a bass reflex design, but the sound is very satisfying. The term "Towers of Awesomeness" comes to mind.

[FredT300B]

A view of the backside. It takes almost 100' of wire to connect all the drivers to the speaker terminals.

[PDR]

Congrats on your towers of awesomeness Fred.......they look stunning!

[dBe]

Very cool, Fred.  Open baffles changed my world and open baffle line arrays are something to behold in the immediate, "they are here" context.

Dave

[FredT300B]

I finally got around to trying two H-frame open back Eminence Alpha 15's instead of the ported TC Sounds Epic 12. The results were disappointing. The Epic 12 beats the OB Eminence drivers in every important category, especially bass extension and control. The measured in room response of the Eminence drivers extends to the high 30's, below which it falls off precipitously. The Epic 12 extends into the mid 20's, a feature that's clearly audible with pipe organ bass notes. Even more importantly, the Eminence drivers sound flabby in comparison the Epic 12. Also, the Eminence drivers have the same room induced 40hz peak as the Epic 12, along with the added  bonus of a 60hz peak that's not there with the Epic. So the Epic 12 has gone back into the system.

So that does this mean? It absolutely doesn't mean that ported subwoofers are superior to dipoles! I've heard several dipole subwoofers that had the bass extension, musicality and control of the ported Epic 12. As far as I can remember, all of the ones I've liked were more expensive than the Eminence Alpha 15 drivers and were servo subs. So my conclusion is there's no substitute for quality. A dipole sub is still a good alternative, but only if you're able to invest in a high quality one, especially if it's the servo kind.

[dBe]

So that does this mean? It absolutely doesn't mean that ported subwoofers are superior to dipoles! I've heard several dipole subwoofers that had the bass extension, musicality and control of the ported Epic 12. As far as I can remember, all of the ones I've liked were more expensive than the Eminence Alpha 15 drivers and were servo subs. So my conclusion is there's no substitute for quality. A dipole sub is still a good alternative, but only if you're able to invest in a high quality one, especially if it's the servo kind.

For the DIY guys like us, GR Research open baffle servo controlled drivers kick butt in combination with Brian Ding's amps.  The sensing coil type control is much more musical than accellerometer servos.  The accellerometer based systems sound mushy to me.

Dave

[FredT300B]

For the DIY guys like us, GR Research open baffle servo controlled drivers kick butt in combination with Brian Ding's amps.  The sensing coil type control is much more musical than accellerometer servos.  The accellerometer based systems sound mushy to me.

Dave

I agree. It was the GR Research speakers and the dipole speakers Danny designed for another manufacturer that I heard at the LSAF and liked very much. The bass was extended and controlled like a high end subwoofer should be. It's not that the Eminence Alpha 15 with a non-servo amp sounds bad, just that it's a very inexpensive driver with a very small magnet, and it's not even in the same league as the multiple servo sub implementations I've heard. But it's still a good choice for the DIY builder who's on a very limited budget.

I wish I were going to the RMAF to hear those new Mockingbird Audio line arrays that are pictured on the GR forum. The BG Neo 8's sound much better to me as dipoles that they do in a closed back implementation - it's not just the dipole openness, but the clarity improves too. And there's something irresistible about a large scale line array playing very dynamic music at a concert volume levels. I call it the goosebump factor . With multiple servo subs per side those speakers should sound awesome. http://www.audiocircle.com/index.php?topic=120057.0 

[MarvinTheMartian]

I've always wondered about having OB tweeter and mid bass on the same panel.
Wouldn't the mid bass back wave take the shortest path back to the front ie. through the tweeter?
With just the mid bass playing it would be interesting to measure if there is any voltage output across the undriven tweeter.
Many people on this forum have commented that putting a woofer on the same panel muddies the mid range.
Is this direct vibration from the woofer or is it the bass wave return path modulating the mid range driver?

Shawn

[FredT300B]

I've always wondered about having OB tweeter and mid bass on the same panel.
Wouldn't the mid bass back wave take the shortest path back to the front ie. through the tweeter?
Shawn

I feel like I'm over my head attempting to answer this, but it seems to me the effect of the back wave of an unenclosed midwoofer array upon an adjacent array of unenclosed planar tweeters would be inconsequential. When there's no enclosure there's no internal pressure.

[FredT300B]

The DR912ad Towers of Awesomeness have taken on a more slender appearance. I've replaced those long klunky-looking diagonal painted mdf braces with some smaller (13" by 20") shelf brackets from Home Depot. No audible difference in the sound, but a much more pleasing silhouette. The wife approves.

[JohnR]

Looking nice, Fred 

Do the woofers induce much vibration into the panel?

[FredT300B]

Do the woofers induce much vibration into the panel?

There's almost no panel vibration. There's no way to verify this, but I suspect those red 2-3/4" wide side braces help quite a bit with the panel damping. After working with a few open back speakers and many enclosed speakers I've decided much of the panel vibration of enclosed speakers is caused by the pressurization/depressurization cycle, with peaks at specific frequencies, typically in that very ugly 200 to 300hz range. Vibrations at these frequencies can easily felt by placing your hand on a panel. This is especially true with many large speakers built of a single layer of 3/4" MDF with inadequate bracing. Those large panels can be noisy. You get none of that with the typical open baffle speakers - there is no internal space to pressurize/depressurize.

One downside of these speakers is their height. While it may be cool to look at a 7' 9" tower, it's very hard to handle it during the building process. I found every time I tried to turn it in the workshop, I was bumping a wall or a nearby piece of woodworking equipment. And after finally placing it in its home you need to be especially careful of ceiling fans. That big assed 6' diameter fan with it's large solid wood aerodynamic blades in my family room is a notorious line array eater.