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[Dan Booth]

Hi Folks,

Been a lurker here for a while, now find myself in a bit of a pickle and in need of some help.

I've been running a pair of PRX718XLFs with a pair of PRX725s for a while, and of course the Hi-Pass was managed by the subs. Nice and easy!

I recently sold the PRX718XLFs and bought a pair of SRX818SPs.

Being a bit daft I didn't realise that the SRX818SPs pass a full range signal out rather than a hi-pass (I think!?)

I have a dbx Driverack PX knocking about so I can use this to manage the crossover so that the PRX725s only get a Hi-Pass signal, however I've not used it in a long while and I'm totally rusty on what crossover settings to use. LR 6/12/24 vs. BW etc... and the actual frequency of the crossover itself. I'm guessing something around 100Hz but would really appreciate a bit of help here.

Thanks in advance!

Dan.

[Bob Leonard]

You'll find the correct settings for the speakers at the JBL Pro web site. And the high pass for the sub won't be at or near 100hz. More like 90hz.

[Dan Booth]

You'll find the correct settings for the speakers at the JBL Pro web site. And the high pass for the sub won't be at or near 100hz. More like 90hz.

Thanks for your reply Bob.

The PRX725s have a Frequency Response of 49Hz to 17kHz at +/-3dB

The SRX818SPs have a Frequency Response of 35Hz to 120Hz at -3dB

I’ll set the crossover frequency to 90Hz as you suggested. I’m still uncertain what kind of slope to select in the Driverack options though... any ideas welcome!

Cheers,
Dan.

[Gordon Brinton]

Thanks for your reply Bob.

The PRX725s have a Frequency Response of 49Hz to 17kHz at +/-3dB

The SRX818SPs have a Frequency Response of 35Hz to 120Hz at -3dB

I’ll set the crossover frequency to 90Hz as you suggested. I’m still uncertain what kind of slope to select in the Driverack options though... any ideas welcome!

Cheers,
Dan.

I prefer to "sweep" back and forth, while listening carefully, to find the best crossover point. Some subs sound different/better at different x points. Like Ivan always says, it depends.

As far as type, (LR, Butterworth or Bessel,) these refer to the shape of a filter's curvature (or knee,) at the cut-off frequency. They actually start sloping downward at some frequency higher (or lower if low-pass) than the crossover point. Some have a sharper knee at the x-over point or simply start further away from it. This affects the way two adjacent pass bands interact at the crossover point. It can leave the crossover frequency with a hump or a dip of up to 6dB.

The steeper the slope, the more abruptly the pass band will drop off. There is no best slope for every application. Too much slope can begin to sound wonky or phasey, so experiment to see which one sounds most pleasing and natural in your system. While experimenting, you may even have to switch polarity as a try-it-and-see test.

24dB/oct Linkwitz-Riley filters seem to be the most popular and the easiest to use, but not always. Again, it depends on your system.

EDIT:
The trick is to keep frequency response flat across/through the x-over region without it sounding odd. It may be difficult to hear the difference with just music. Instead you may want to use test tones while measuring the level of each one. Good luck.

[David Allred]

Very common to use LR24 between sub & tops, BW18 for the sub's HPF.  Are you only using the PX for the filter to the tops from the sub's output?

[Dan Booth]

Helpful stuff!!!

Thanks very much Gordon, very helpful!

[Dan Booth]

Very common to use LR24 between sub & tops, BW18 for the sub's HPF.  Are you only using the PX for the filter to the tops from the sub's output?

Hi David, thanks for that.

I'm feeding the mixer into the PX inputs, then out from the PX to the subs and the tops. I hadn't actually thought of setting up the signal path the way you describe, would that be better do you think? It's a DJ setup, no live instruments or mics.

I've set the crossover in the PX at 90Hz LR24 for both subs and tops outputs but I haven't set a low cut on the PX's subs output as I'm assuming the onboard DSP on the subs themselves is better designed to handle that.

Did a little bit of EQing with the PX's GEQ.

I had it set up earlier and it sounded great to me! Always open to tweaking suggestions though.

Thanks again,
Dan.

[Paul G. OBrien]

JBLs spec sheet for the 818sp says it's internal lowpass is set at 80hz, no indication what slope or filter type however.

[David Allred]

Hi David, thanks for that.

I'm feeding the mixer into the PX inputs, then out from the PX to the subs and the tops. I hadn't actually thought of setting up the signal path the way you describe, would that be better do you think? It's a DJ setup, no live instruments or mics.

I've set the crossover in the PX at 90Hz LR24 for both subs and tops outputs but I haven't set a low cut on the PX's subs output as I'm assuming the onboard DSP on the subs themselves is better designed to handle that.

Did a little bit of EQing with the PX's GEQ.

I had it set up earlier and it sounded great to me! Always open to tweaking suggestions though.

Thanks again,
Dan.

You are correct in that you should allow the DSP in the subs to take care of that.  Make sure that you run the LPF on the sub out of the PX really high (at least 500hz) so the filters don't stack at all, and the HPF of the sub to 20hz or so.

[Mac Kerr]

You are correct in that you should allow the DSP in the subs to take care of that.  Make sure that you run the LPF on the sub out of the PX really high (at least 500hz) so the filters don't stack at all, and the HPF of the sub to 20hz or so.

Huh???

Why would you run the LPF on the subs above 90 or 100Hz? Running higher increases the overlap and any phase interaction between the subs and mains, as well as possibly putting information in the subs you really do not want there.

Mac

[David Allred]

Huh???

Why would you run the LPF on the subs above 90 or 100Hz? Running higher increases the overlap and any phase interaction between the subs and mains, as well as possibly putting information in the subs you really do not want there.

Mac

Because the sub's DSP is cutting it off at 90hz (or whatever).  The PX's filter has to get out of the way.  If the PX's cuts at 70hz (or whatever) there is a hole between there and the 90hz that was recommended by others for the tops.  If the PX is at 90hz for the sub, now there are stacked filters.

[Tom Burgess]

Seems like it would be simpler to do this:

[Mark Wilkinson]

Because the sub's DSP is cutting it off at 90hz (or whatever).  The PX's filter has to get out of the way.

Can't you just turn the PX's filter OFF?             (The PX's LowPassFilter on the sub channel, that is..)

[Dan Booth]

Seems like it would be simpler to do this:

Thanks very much for taking the time to make this diagram! Much appreciated!

Is there a benefit to running mono subs as detailed in your diagram rather than stereo subs?

[Chris Hindle]

Is there a benefit to running mono subs as detailed in your diagram rather than stereo subs?

Generally in music, the ELF content is sent to both sides anyway.
Save the extra send for some other use. (fills, delays, Green Room, etc.)
(Effects can be played with of course. That would require 2 lines.)
Chris.

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