Isobarik OB line array ?

[johninCR]

I'v been playing around with OB line arrays using readily available cheap drivers down here in Costa Rica where shipping and import duties double driver cost, so "good" drivers are cost prohibitive. The big, open, natural sound I'm getting is better than anything I've heard before.

In the past I've used iso loading to make poor drivers sound worlds better in woofer or subwoofer boxes. Now I'm toying with the idea of iso loading (front-to-back or back-to-back) a dipole array. Could I expect similar individual driver sound improvement gains in the higher frequencies that I have experienced by clam shelling cheap woofers for the lower frequencies?

I am trying to improve upon the 12 driver array that I already built. It sounds great on everything at moderate volumes and most stuff at high volumes, but on complex passages I can hear that the cheap little $1.50 4" drivers are struggling.

Any ideas or input are greatly appreciated. Which would be better back-to-back or front-to-back? I'm thinking front-to-back since that way the highest frequencies are naturally attentuated.

[Bill Fitzpatrick]

It would be destructive to the sound quality to mount additional drivers in the iso configuration.

[johninCR]

Bill,
Please explain....At least a little.
Thanks,
John

[Bill Fitzpatrick]

Well, let's say you mount them front to front.

You have two choices. Wire them in phase or out of phase.

If you wire them in phase the effective result will be a little tiny cabinet for the drivers; Q and Rf will skyrocket. And, they won't be dipoles anymore. So that's out.

If you wire them out of phase Rf and Q will stay the same. SPL won't increase but you will be doubling the input power to the array. The poor little things will still be struggling. So, up to this point you haven't gained anything and it costs power.

What exactly will happen within the cavity formed by the two drivers when the frequency goes higher than the point where the drivers are behaving as pistons I couldn't say. My guess is that it will be a mess.

Mount a face to face pair on a piece of ply and wire them in phase. Mount a single driver on the same size ply and compare the two. Then, report your findings. I am curious.

[454Casull]

As Bill mentioned, you don't get anything out of it.

[johninCR]

Face to face or "clamshell" configuration is definitely not a viable option because a lot of the Hf response of a driver is not radiated out of the back. This fact may make the push-pull alignment with the drivers back to back the better option and I have heard of higher end speakers set up that way. Push-pull is better at correcting individual driver non-linearities anyway. It would just mean a little more Hf attenuation needed on the back.

[johninCR]

Originally posted by 454Casull
As Bill mentioned, you don't get anything out of it.

You definitely get something out of it using woofers and it's not just the ability to use a smaller box, I'm talking about drastic increase in sound quality. That makes me think it would be beneficial for at least part of the remaining audible spectrum.

I'd lose 3db of output, but power handling doubles and I don't use a set anyway. Plus these arrays are already over 100db in sensitivity and distance has only half of the effect due to the line array effect.

Maybe I should break down and do an exhaustive search of Cost Rica for Dammar varnish and Puzzlecoat to treat the paper cones before I start a new construction project. I tested yellow wood glue on 1 but it attentuated the highs too much, but it sure did make the cone a lot stronger.

[454Casull]

I meant when used in OB. How are you going to mount the drivers facing away from each other?

[DrSplodge]

Maybe you should post a photo of what you have so far?

[johninCR]

I need to get the film developed and get them scanned, but they're coming.