Film-Tech Forum ARCHIVE: 3722jbl biamp xover and delay settings..

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Posted by Kurt Werbrouck (Member # 2667) on 06-19-2015, 03:43 PM:

Hello,
Can someone provide me the correct xover freq and delay for the 3722jbl. I am using qsc dcp300 for an Auro system.. I using the 1300hz, filter butt or LR,4th order?

Also, seems that the hf driver needs a lot of pushing from 6khz, same driver as the 3632 from jbl..

Thanks

Posted by Steve Guttag (Member # 268) on 06-20-2015, 08:31 AM:

Well...looking at the spec sheet for the 3722...the crossover point for BIAMP (as your description says) should be 350Hz.

It doesn't specify the crossover type but if you don't know, it is safest to START with an L-R 24. It has steep slopes and keeps both sides in phase with respect to each other. Butterworth, though smoother at crossover will introduce a phase shift.

Now, if you are TRI-AMPING the system, then, according to the spec sheet, the MF/HF crossover is at 1.2KHz, not 1.3KHz as you state you are using.

Delays are more tricky. This is particularly true where you have DSP processing going on where that processing time adds into the latency so what applies to one DSP may not apply to another. They will be in the ballpark but you may have to experiment to find the right point. This can be a little frustrating on the QSC DCP line since with each change the unit briefly mutes the audio and comes back but if you pay attention to your analyzer at the crossover region, you should be ale to find it.

Also beware of factory presets in products where the manufacturer isn't the same as the speaker...often they are going off of what the speaker company told them it should be. It may be a good starting point but don't believe that it is the best fit to your speakers.

If you look at the Crown spec sheet for their "PIP" used on the 3632, your comment about a lot of boost above 6KHz is consistent:

http://www.crownaudio.com/media/pdf/pips/135801.pdf

The DCP300 comes with a 3632 preset. It is interesting that it comes with a 450Hz crossover rather than 350. I wonder if it is a mistake or perhaps the result of actual use. The delay it comes with is 1000μsec. Again, I'd verify that by actual measurement.

JBL also has their Cinema Sound Manual (a bit dated) that lists the DSC260 tunings for the 3632. On the LF they use a 378Hz 4th order LPF (Butterworth) but on the HF they use a 450Hz LPF (Butterworth). As for internal EQ, they applied a -4dB cut at 6KHz but an 11dB boost at 16KHz...again, consistent with your findings. They went with a .396sec delay but given the Butterworth crossovers and non-overlapping points, that may affect things a bit.

But again, you can only get a feel for the tuning looking at a different DSP...it can be a starting point but not necessarily applicable to a different DSP since how the DSP is constructed can affect the final results. Speaker manufacturers also have a bad habit of using anechoic chambers for setting such things. They don't take into consideration the acoustics of a cinema...but again, you have to start somewhere.