New cheap OB Line array build begins

As fall and winter approach, time to start my yearly exercise in self indulgence. The introduction last year of the two dual 18 dipole subs to the studio has taught me not much can beat OB in this space so the focus on this project will follow suit. Hopefully these will fall into use as dynamic midfield mix/mastering monitors as we expand.

We added a 16 channel Trident console for a hybrid system this spring so the budget is blown for the year…..all spare change for this one resulted in driver element choices are all value driven. High efficiency means we won’t need a lot of power to drive these to crazy levels when needed…..a repurposed Parasound 5 channel home theater amp we picked up at an estate sale a few years back along with a miniDSP should take care of things.
 
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For mid/highs in a dipole configuration i‘m going with 8 of these per side

https://www.parts-express.com/GRS-PT6816-8-8-Planar-Slim-Tweeter-8-Ohm-272-128?quantity=1

It’s just about the most affordable lines source that I can think of from 1khz and up and its short comings should be offset by the multiple drive units. While not a ‘full’ line source for floor to ceiling, 64” should do it in this room as we’ve got 3 tilted floating clouds up front where we don’t have to worry about ceiling reflections…only floor bounce and that‘s a non issue for this design.

I’ll be experimenting with different treatments for the rear wave output/ loading on these. Narrow tensioned felt strips seem to work for some folks so we’ll give that a go first after fully open.

Yes….there’s not much there above 14khz……and I can’t hear much above 13khz after years in this game and the aging process. For the critical work, the Audeze phones still reign supreme anyways…..always put a smile on the client’s faces with em.
 
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For bass/mid bass we‘re looking for an initial cheap investment as a proof of concept. This will start out as two individual baffles side by side anyways which leaves for a not so destructive re construction is the concept works. I’m using eight of these per side

https://www.parts-express.com/6-1-2-Poly-Cone-Woofer-4-Ohm-299-609?quantity=1

They‘re cheap…..and they’re the right size and Q for OB use. When I first started my journey in audiofoolery, poly cone Infinity drivers always tickled my eardrums…..not too damped like paper with just enough snap…..and there wasn’t a lot of metal cone offerings to compare to back in the 80’s so the nostalgia will have to do.

I’m not asking a lot from these…..100-1000hz and i‘m sure these will be up to the task for the design phase. If they prove to be to wimpy when pushed, I’ll do an upgrade when funds allow.
 
So the two independent side by side baffles serves a secondary design purpose……I have a suspicion that the light diaphragms of the planar drivers will benefit from the lack of mid bass resonances. I’ll likely hang these with cables from the ceiling for total isolation with a pair of tension cables from the bottom to the base for stability.

Individual nearfield drive measurements will be done outside but all system measures will be done in the studio in the midfield…..this is a purpose built installation so it makes the most sense to get the most from the drivers, the design and the room.
 
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I’ve decided to increase the woofer count to 9 units per side arranged in the series wired groups then wired in parallel for more output. The 8” GRS mid tweeter line length allows for the lines to be symmetrical in length.

So far I’m REALLY IMPRESSED with the cheap 6.5” woofers! Haven’t done any measurements yet…..just some critical listening and voicing. I’ve assembled a small test baffle of 4 drivers and listened both full range and with a 2nd order low pass at 1000hz. Even full range there’s nothing terribly objectionable sans what I perceive to be a little energy storage up in in the 3-4khz range. With the low pass, the tactile mid bass of just the four drivers is pretty impressive.

Yes….the baskets are really flimsy stamped steel……but because of the smart stamping design, a lot of strength is added. I am concerned with the reduced exit path for the rear wave due to the small windows though……the back wave measurements will tell the whole story. I’m using a 1” thick baffle with the drivers flush mounted for testing as I think the 1” thick material is going to be needed to support a final baffle of 80”

I‘ve only built the one test baffle so far mind you. Was hoping to do the outside measurements this morning but my neighbor decided to do some lawn maintenance this morning :( The plan here is to hang the test baffle 6 ft or so from the ground in free space and get front and back measurements and then start experimenting with side panel depth.
 
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This is a 3rd party close mic measure of the woofer in a box which I found on the web which is pretty consistent with what I’m hearing on a narrow test baffle. With such a high QTS, I suspect an actual f3 around 60hz in room with 9 per side and some DSP manipulation.

What‘s most impressive is the response from 250 to 1k…..very smooth. Crossing at 800-1k should be super simple. The question is whether or not a line of 8 of the GRS tweeters can go that low and still play clean up to 100db.

I can’t say that the woofer breakup in the 3-5k range has manifested as poorly in listening as it shows in this measurement though…..as I mentioned earlier, it’s more of an energy storage thing to my ears. It should be waaay down with a 2nd order low pass filter though. I hope to be able to use that little 3db dip at 1k to my advantage.
 
Those look like the old RS 6 1/2" drivers I used to use, I loved them, been wanting to get some of those and build two stacks up.
Maybe for my ESL builds.
I had great results using 6x6 1/2" RS drivers on my Bass rig in an open back box just big enough to fit them in a 2x3 array on top of my RS18" sub at the time(1996).
I spent hours with just a sig gen sweeping the lows for fun, they were very clean and low with 6 of them, sadly that box got stolen along with my Marshall 8100. :/
Cheers !!
:cheers:
jer:)
 

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