[zobsky]

I was working through the math to build am open baffle  line array type center channel to match my left and right arrays, .. and wrote up a simple spreadsheet to do this. Could someone check my math on the SPL and power gain calculations?

I uploaded a copy of the sheet at http://www.mediafire.com/?fmycm9wobxe (I'm not sure how to host files on AC)

One thing to note is that when designing a scaled down array,  merely scaling down the number of drivers doesn't necessarily guarantee you the same impedances, power gain, and consequentially mid-tweeter tonality.

As an aside, I plan to split this array into 2 smaller modules. Any ideas on which arrangement would work better:
1. one module on either side of a 8 ft projection screen
2. modules close together but slightly cross-firing to increase horizontal dispersion.



Thanks

[Rick Craig]

I was working through the math to build am open baffle  line array type center channel to match my left and right arrays, .. and wrote up a simple spreadsheet to do this. Could someone check my math on the SPL and power gain calculations?

http://www.mediafire.com/?fmycm9wobxe

One thing to note is that when designing a scaled down array,  merely scaling down the number of drivers doesn't necessarily guarantee you the same impedances, power gain, and consequentially mid-tweeter tonality.

As an aside, I plan to split this array into 2 smaller modules. Any ideas on which arrangement would work better:
1. one module on either side of a 8 ft projection screen
2. modules close together but slightly cross-firing to increase horizontal dispersion.



Thanks

What do you use for measurements? Active or passive crossover?

[zobsky]

Passive Crossover , 3rd order butterworth on both the midwoofer and tweeter on my mains (completed a few months ago). I haven't yet decided what cross over point I'm going to use for this center channel.

I use ARTA for measurements

Thanks

[Rick Craig]

Passive Crossover , 3rd order butterworth on both the midwoofer and tweeter on my mains (completed a few months ago). I haven't yet decided what cross over point I'm going to use for this center channel.

I use ARTA for measurements

Thanks

I think you'll be better off to build a conventional center channel.  The horizontally placed arrays are a recipe for disaster because of the interference effects off-axis horizontally plus the wavefront is not going to match your main arrays. With the dual arrays your screen prohibits a well-defined center image plus you'll have greater interference effects with your L/R speakers.

I've done several L/R array systems with a WMTW center channel and that format works very well. The main drawback is matching the sensitivity of the arrays but a 4-ohm 90+ db CC is certainly possible. That way you can center it below the screen and tilt it upward for on-axis listening.

[zobsky]

Passive Crossover , 3rd order butterworth on both the midwoofer and tweeter on my mains (completed a few months ago). I haven't yet decided what cross over point I'm going to use for this center channel.

I use ARTA for measurements

Thanks

I think you'll be better off to build a conventional center channel.  The horizontally placed arrays are a recipe for disaster because of the interference effects off-axis horizontally plus the wavefront is not going to match your main arrays. With the dual arrays your screen prohibits a well-defined center image plus you'll have greater interference effects with your L/R speakers.

I've done several L/R array systems with a WMTW center channel and that format works very well. The main drawback is matching the sensitivity of the arrays but a 4-ohm 90+ db CC is certainly possible. That way you can center it below the screen and tilt it upward for on-axis listening.

Thanks.
In that case, what about rotating the horizontal arrays by 90 degrees, .. resulting in two short  vertical arrays located around the center of the screen, possibly tilted upwards a bit  to fire at the audience?

[zobsky]

I think you'll be better off to build a conventional center channel.  The horizontally placed arrays are a recipe for disaster because of the interference effects off-axis horizontally plus the wavefront is not going to match your main arrays. With the dual arrays your screen prohibits a well-defined center image plus you'll have greater interference effects with your L/R speakers.

I've done several L/R array systems with a WMTW center channel and that format works very well. The main drawback is matching the sensitivity of the arrays but a 4-ohm 90+ db CC is certainly possible. That way you can center it below the screen and tilt it upward for on-axis listening.

Thanks.
In that case, what about rotating the horizontal arrays by 90 degrees, .. resulting in two short  vertical arrays located around the center of the screen, possibly tilted upwards a bit  to fire at the audience?
[/quote]

[Rick Craig]

I think you'll be better off to build a conventional center channel.  The horizontally placed arrays are a recipe for disaster because of the interference effects off-axis horizontally plus the wavefront is not going to match your main arrays. With the dual arrays your screen prohibits a well-defined center image plus you'll have greater interference effects with your L/R speakers.

I've done several L/R array systems with a WMTW center channel and that format works very well. The main drawback is matching the sensitivity of the arrays but a 4-ohm 90+ db CC is certainly possible. That way you can center it below the screen and tilt it upward for on-axis listening.

Thanks.
In that case, what about rotating the horizontal arrays by 90 degrees, .. resulting in two short  vertical arrays located around the center of the screen, possibly tilted upwards a bit  to fire at the audience?

[/quote]

The problem is that when you reduce the length you lose the main benefits of the array design (nearfield effect, dynamics, output capability, sensitivity) plus you introduce more problems (interference effects, very narrow vertical coverage,etc).

[RAW]

Passive Crossover , 3rd order butterworth on both the midwoofer and tweeter on my mains (completed a few months ago). I haven't yet decided what cross over point I'm going to use for this center channel.

I use ARTA for measurements

Thanks

I think you'll be better off to build a conventional center channel.  The horizontally placed arrays are a recipe for disaster because of the interference effects off-axis horizontally plus the wavefront is not going to match your main arrays. With the dual arrays your screen prohibits a well-defined center image plus you'll have greater interference effects with your L/R speakers.

I've done several L/R array systems with a WMTW center channel and that format works very well. The main drawback is matching the sensitivity of the arrays but a 4-ohm 90+ db CC is certainly possible. That way you can center it below the screen and tilt it upward for on-axis listening.

I agree with Rick , build a WMTW or a WWTMMWW with the tweeter over the twin mids.
Having done a few center arrays with a single tweeter myself the dispersion on the can be very hard to deal with.The largest HT I have done had a large array center as shown below and the person took my advice after I was in person to listen to the set up in Salt Lake City when he went to DEQX.After my recommendation he got out WWTMMWW with the tweeter over the mids and has not listened to a center that comes close to what he has now.Will he miss the array center NEVER.

Shown below the old system as far as center channel with the mains and rear speakers.
Also hidden the 9 Extremis mid woofers in black cabinets as well as a few 15" subs

[zobsky]

Well, I did it anyway. ... haven't built a crossover yet, so I'm merely running the wideband woofers in full-range mode.

The horizontal arrangement worked better than placing the 2 mini-arrays vertically (the vertical placement resulted in a noticeable SPL drop in the vertical plane) .

In practice, the slight concave alignment widens the sweetspot while still locking in dialogue.

Let's see what happens when I get the tweeter lines working. I'm fairly happy with the results so far.