"Quasi-optimal" crossover for high-efficiency loudspeaker system

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#61
marco_gea said:
In the end, I think those who still think that systems like these (large woofer + horn) inevitably force you to renounce coherence and imaging for the sake of sheer dynamics, should do themselves a favour and give one of these "quasi-optimal" crossovers a go!

Marco
Click to expand...

Agreed. I'm using the Le Cléac'h crossover (3rd order on woofer and tweeter) very successfully with a woofer/horn system. I was pleasantly surprised at the improvement from the previous standard LR4 setup; better sounding transients and generally more natural sounding.
 
#67
Thank you very much for this thread. It's helping me to answer a lot of questions on my JBL horn build. I've had similar problems setting up the crossover for my 2226J in BR box and 2445J in a StereoLab horn.

I started with the basic LR4/LR4 crossover but quickly found that wasn't going to work because of the physical offsets of the drivers. I'm currently using a LR2/LR2 but I planning to try some of the quasi-optimal crossovers here.

I have a question about the 'Offset' figures you represent here. This corresponds to the corresponding delay that crossover creates, and how far back the CD should be from the woofer's acoustic center?

So if I am aiming for a 1kHz x-over point and I use:

4th ordrer Butt Low Pass, -3dB @ Fx* 0,93 (+)
4th order L-R High Pass, -6dB @ Fx* 0,93 (-)
Offset = 0,31*c/Fc

For example, the offset is: .106 (meters?) so the horn driver should be 10.6 cm behind the woofer's acoustic center?

And in this case are my x-over points 930 Hz and 1070 Hz?

Right now my physical offset is measurement at about 0.3ms, or 9.144 CM, which would seem to be pretty close.

I am also having a hard time making credible phase measurements in-room. Is the best tool to do this HolmImpulse with a gated measurement? Should I be measuring in the center of my room at about 1m from both drivers and gating before the first reflection?

Thanks again for the help.
 
#68
I believe the offset is from the point the acoustic centers are aligned. In other words, with the acoustic centers aligned, the woofer then moves forward (less delay) by the specified offset. At least, that approach worked for me.
 
#69
Thank you, and also I may not be reading the nomenclature properly.
Is this correct:

4th ordrer Butt Low Pass, -3dB @ Fx* 0,93 (+) -- 4th order butterworth @ 930 Hz (Fx=1000), normal polarity (+)
4th order L-R High Pass, -6dB @ Fx* 0,93 (-) -- 4th order LR @ 930 Hz, wired in negative polarity (-)
Offset = 0,31*c/Fc == offset is .31 * 341m/s / Fc (how to calculate the corner frequency, is it 930 Hz here? ==.114m?

Am I correct?
 
#75
Francis -- I don't think I can do 3rd order Bessel filters in MiniDSP with advanced bi-quads. I can just cascade 2nd order filters. I can do Butterworth 3rd orders as they are included in the stock x-over options in the MiniDSP.

So I will try the classic Le Cleach.

The other question I had is about the acoustic centers. Where/how do I measure that from. My 2226J is surface mounted to the enclosure. The depth is 5.5" according to the spec sheet. Should I use that figure and then have the rear of my 2445J 3" behind that, or 8.5" from the front of the baffle?
 
#76
I got my acoustic centers aligned by using LR 4th order (acoustic) on woofer and horn, inverting the horn signal, then setting the woofer delay for the best null at my crossover frequency. That amount of delay has been a good place to start.
 
#78

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#79
Here are better measurements the speakers with the crossover. I ended up adding a .2s delay to the woofer to make up the rest of the offset in the miniDSP. The summing is pretty nice and flat now, I think.
 

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