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LAMGeezer 6th February 2013 04:49 PM

Large scale open baffle
I'm working on the use of a large-scale dipole to use as a "music speaker system" in an installation where there is a center-mounted "speech-optimized" loudspeaker.
The point to this question is: Has anyone in the DIY community ever tried anything like this on the scale of an auditorium seating about 600 people?
The application is in combination with the existing center speaker as part of a left/center/right idea, where the left/right are either side of the dipole...
Some of you may have figured out what I'm up to - it's a case where I'm doing the job at cost to help out the congregation. We have tested a prototype, on a smaller scale, on the platform, and the ability to cover what was a difficult coverage seating plane is SPOOKY!
It should be noted that left/right imaging is not being sought, here - just a sense of "difference" in the listeners interaural sensate observation.
I'm hoping other "pro" consultants with "enthusiast" leanings might be willing to share thoughts, in the "Synergetic Tradition".

turk 182 17th February 2013 09:48 PM

couple of things id like to know is can your test location be the final position of the new speaker or is that out of the question,and was this test conducted with all operating conditions as in all sources and any and all mic & source combinations?

LAMGeezer 18th February 2013 05:08 AM

We are receiving the drivers, as I write. The whole lot is apparently to be in two shipments. We have a few procedural points to observe: 1. Each driver will be run through the LMS "rub and buzz" to assure they're viable. 2. Each piece will get its own documented impedance curve in free air, and on a baffle designed to avoid exact multiples of dimension in any direction. 3. Each device will be documented for frequency response. Then, 4. We will start grouping the drivers on various baffles to observe how that "figure-of-eight" pattern "lands in the seating...
We are testing with the baffle(s) on the platform, to simulate the boundary behavior of the ceiling. As the testing continues, microphones and other sources will be introduced and the effects of the polar behavior on things like intelligibility and feedback noted - also note: The existing center-mounted speaker is speech optimized and the dipole is intended for music playback and some other hoped-for effects.

More to come...

turk 182 18th February 2013 11:25 AM

i'll eagerly await your next installment.

LAMGeezer 18th February 2013 04:48 PM

A side note: This whole experiment is a result of the idea that appearance trumps acoustic merit.
An very wide seating plane resulted from the length/width ratio created by a "value engineering" effort on the part of the major investor in the construction project, combined with ignoring what a cube produces in modal behavior. One would have required an "exploded array" to cover the seats. The other lead to some really excessive corner-terminated low-mid frequency modes with almost no glass to help leak it out - even though part of the standing waves were moved around a bit. The modes will have to be tolerated. The seating was dealt with by the design of a custom 130X52-degree horn driven by a Renkus CDT-1, with a pair of 10" Emminence woofers in a D'Appolito-style box. The result was a horizontal directivity match across both crossover points. Vertical pattern behavior was maintained down to about 300 Hz. The whole thing is tri-amped and processed by a Behringer DCX-2496. I've seen commentary on the last item in this forum. I, personally am not impressed by the user interface - while it does appear to work quietly...
Add to all that, the dipole, and it becomes another example of what happens when someone says: "We can deal with THAT problem..."
We shall see...

Stay tuned...

LAMGeezer 6th March 2013 05:32 AM

For those that might still be watching this thread, the curve off the back of a Galaxy S5N8 starts to dive at about 4k.
Also, as many have noted, shooting polars on an open baffle is almost useless - after about 20 degrees rotation that back-side energy starts to sum with the front - with the inevitable phase issues added to the "mix". Listening to a single driver along the "edge-axis" of the panel still sounds intriguing.
I'd like to know more about how the voice coils are being wound. It almost looks like a turn-counter is used. Whatever comes up for a DCR and the resulting Free Air Resonance seems to wander a bit, from driver to driver... The sound is nice, and averaging will help.
Stay tuned...

sangram 6th March 2013 05:42 AM

Though this is well beyond my technical ability, I do have a small line array mounted on an OB. My observation is that best results are only achieved when the back and front have similar frequency response, which is very problematic at high frequencies primarily because of dynamic drivers' physical design. I did manage to counter some of the issues with a rear-firing tweeter but that only fixed it for one seating position (mine).

There are many advantages I see from this arrangement such as very high usable sensitivity and lowering of distortion - and averaging of drivers - specially cheap ones, but the polar response (specially vertical in my case) is still less than desirable.

I will be watching your thread keenly. Eager to learn more about what you finally end up with.

turk 182 6th March 2013 11:39 AM

i don't know if the project budget would allow and no dis to behringer but have you looked at other system processors like dbx drive rack or ashly protea.

LAMGeezer 7th March 2013 12:10 AM

Turk, I own a Driverack PA. The client insisted on the DCX. My brother has done a fair bit of contracting using various versions of the Driverack to good effect. Even the client has admitted the next processor will be a different item!

Sangram, it is likely that the way we are doing this project, we may go the other direction.
I'll try to get some diagrams up so you can see what we are doing.
We are lining up two rows of drivers, one in front of the other, one set facing one way, the other in the opposite direction.
What it appears to be getting us is additional energy below 4k based on the rear-firing driver's output, added to the front firing drivers on-axis energy. So far the judgements on the listening quality are empirically based - when it gets ugly, we sit down and figure out why, supplementing our decision making with measurement data.
We are not under deadline, so have the luxury of taking our time. In addition, we are waiting for delivery of the rest of the drivers!
Part of the idea going forward might be to try and shift the effect of the so-called Baffle Step by selctively damping the backside output to make the rear firing energy sum with the front of the other row to mitigate the low (relatively low) frequency rolloff. Polars will follow to see what the ramifications are. Remember, the angle of observation will always on both sides of the figure-of-eight radiating pattern!
The function of this panel is to serve as a difference source, using surrounding walls to reflect acoustic energy out to the congregation. The effect on the platform for the performers is a factor we'll start to study - how it will interact with the monitors - or even replace their function, is up for research...
It's getting to be a lot of FUN!

Stay tuned...

ClackS02 12th March 2013 02:45 PM


Originally Posted by turk 182 (
i don't know if the project budget would allow and no dis to behringer but have you looked at other system processors like dbx drive rack or ashly protea.

Im looking at getting behringer power amp... have you had problems with them before ?? im interested to know before i make a purchase ! lol

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