quick crossover questions

stix518

Have read the FAQ's and READ ME FIRST. Have had the drpa for a while and have played/worked with it quite a bit with my Carvin cabs but I now am the proud owner of a set of JBL Stacks so I need to make some adjustments and am looking to the expertise of this board for help.

Mains: JBL 4735
http://www.jblproservice.com/pdf/SR-Series/SR4735.pdf
Subs: JBL 4718
http://www.jblproservice.com/pdf/SR-Series/SR4718.pdf

Amps:
QSC PLX3002 for the subs in stereo
QSC PLX2402 for the mains in stereo

drpa set-up in 2X4 config. I've already done the whole balancing of the system at unity and have set the limiters per instructions found here and the system sounds great but I'm not sure I have the most appropriate xover settings. Here's what I've got... L35.5 BW18, L118 LR24, H 100 LR24. The local JBL rep suggested having the subs higher at the crossover (150) and the mains lower (80) for what he defined as "free bass" but that struck me as strange. Not that I'm all that experienced but 150 seemed awful high. Unfortunately, the drpa wizard uses the X version of these cabs and they are totally different (just like the wizard uses the PLX2 amps).
What do you all suggest?
Thanks in advance

Stix

Gadget

Stix, your really under powered...you only have 425 watts of power for the tops, and 700 for the subs..

Free bass huh :roll: more like funky comb filter/sonic chaos generating LF funk... but it's easy enough to try and see what you get...For some reason JBL does overlap a lot of their crossovers on their older stuff..I'd suggest BW 24 filters if you are going to try it, they sound better on overlaps.

Also, that 30 hz figure is a panacea...there is NO WAY those can output a useful frequency any where in the 30 hz range, AND you are so limited in power that I'd raise that xover point to 45+ hz BW18 filter type.

If you have read all that then you know full well that presets are only a blank starting point. Unless they are for bi-amp applications (JBL does provide some crossover points for some of their new tops/subs combo's but nothing that old) you are just as well off using custom setup in the wizard.

Not that I'm all that experienced but 150 seemed awful high.

Actually, if your not dealing with horn loaded subs it's common practice, when using front loaded subs with smaller tops, to use a higher crossover frequencies. For example, Peavey QW series has a top with 2 10" and they cross them @over 200hz to the subs. Also, think of your typical computer 3 piece system with tiny little mid hi's and a larger sub...they cross even higher.

Gadget

Dennis

The JBL SR4735 is a 3 way cabinet with a 15", 8", and 1" horn. I believe the 15" is a substantial 2226H so a high xo point shouldn't be necessary. The JBL tunings for the SR4735X with sub are all over the map with a HUGE overlap between 4735 and 4718, unlike xo filters, polarity inverted 15", yada, yada.

Since previous research has determined there are no similarities between SR4735 and SR4735X (2 generations apart), the SR4735X tunings are not good for much more than a vague starting point. I feel that reducing the overlap at the sub xo point will not damage anything...probably eliminating overlap and crossing at 100Hz won't hurt either. I feel a small amount of overlap has it's place but should not be applied arbitrarily...the phase response of the speaker cabinet should be monitored on a dual FFT program while it is being applied

Gadget

I feel a small amount of overlap has it's place but should not be applied arbitrarily...

Gadget likes this...and NO I'm not a facebooker :roll:

Dennis, you've never (to my knowledge) weighed in on the crossover point versus amp power issue..."when selecting a crossover point and LPF for subs, what is your feeling about adjusting the crosser point upwards as a way of getting more volume out of the speakers.

It doesn't take rocket science to figure out that the 4718 "Ain't gonna hit 30hz anyway" (JBL spec: 30hz-3.3khz no "dB down provided.. 10dB "minimum" :roll: assumed) so, why set the crossover that low, especially when there is very little useful info down that low unless there is synth or 5/6string bass. That, and with limited amp power to draw from the lower the crossover is set, the less gain will be available for additional volume.

G

Dennis

Gadget wrote:

Dennis, you've never (to my knowledge) weighed in on the crossover point versus amp power issue..."when selecting a crossover point and LPF for subs, what is your feeling about adjusting the crosser point upwards as a way of getting more volume out of the speakers.

Good point...I have never weighed in on the topic and it didn't cross my mind that was the reason you picked a higher xo point. Often, when working for 3rd parties, I will find myself with not enough PA for the venue but I will always have enough amplifier for the individual speaker boxes. between myself, my day job, and the 3rd parties, we have a lot of different amps to choose from. My point here is, I don't disagree with you...it just doesn't cross my mind. My usual reason for raising a sub xo point is because the Mid/Hi cabinet falls a bit short of making it all the way down to 80 or 100Hz and I mistakenly thought that was what you were doing. My bad.

Dennis