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Ideal Crossover Frequency for JBL Combo

RRJRRJ Posts: 17
edited December 2009 in DriveRack PX
Hi Guys,

So here is my setup:

2 - JBL PRX-515
1 - JBL VRX-918SP

From reading I know for HP I will use is BW 18 and for LP LR 24. Question is, what frequency for both? Should I use the JBL+-3dB, -10dB, or just "out" for the HP on the sub?

On the LP specs say 80/120 Hz for the sub. 80 Hz sounds right to me. Since I have only one sub I'm assuming the best best is to offload some of the bass frequencies to the tops to try to even out/balace the tops to sub. From reading I understand this might take away from the clarity of the mids, so wondering if I should go to maybe above 80 Hz somewhere, and back down the gains on the tops.

Any comments or recommendations would be greatly appreciated.

Thanks in advance.

Comments

  • GadgetGadget Posts: 4,915
    You appear to have been reading...thank you for that... normally, when were addressing xover points we ask for amp power ratings... but then again were generally speaking of passive speakers and power amps... here you have powered speakers all the way so we can dispense with that pretty much all together...

    Myself, I do NOT like putting the crossover point on top of one of the most important and one note instruments in our arsenal... that is the kick drum. The fundamental frequency for a kick is in the 300-400 hz frequency range, but the first lower harmonic (the thump) is usually 75-85hz (80hz) and so if I'm going to choose a xover frequency it's usually <75 or >85hz... NOT ...80hz...

    That said, we can easily try different slopes and xover points to find the best one for these speakers...I'm a bit worried that with one sub and 2 tops capable of 133dbspl that the sub will be " overwhelmed" and I think that is what you will find as well...you will need to balance the subs output with the tops...especially if you attempt to get full low output of these subs...I guess if you limited the subs frequency range to say 40-45 hz BW18 you could capture a bit more output from them...

    The LPF for the subs really doesn't give you output benefits but allows for better low mids for the tops...the higher the xover point (to a max of around 120hz where the subs start to sound honky) you will get better midrange if the tops aren't trying to reproduce the lower frequencies...

    So if that doesn't answer the question... by all means ask away
    Gadget
  • RRJRRJ Posts: 17
    Gadget,

    Here are the relative specs for the speakers:

    PRX515:
    Frequency Range : 45 Hz – 20 kHz
    Frequency Response : 52 Hz – 20 kHz
    Rated Maximum SPL : 133 dB SPL peak

    VRX918SP
    Frequency Range : 31 Hz – 220 Hz
    Frequency Response : 34 Hz – 220 Hz
    Maximum Peak Output : 126 dB SPL at 1m

    So I WILL stay away from 80 Hz as you mentioned. I know I have a sub deficit so I will try the 40Hz setting on the sub to see how that sounds.

    Funny thing on paper you would think the tops would overpower the subs right? Well with my first test with the HP @ "out" and the LP @ 80Hz , including the tops and subs setup to peak with my mixer (using a loop of music), the 1 sub seemed to be on par with the 2 tops! I read and have been told the JBL's SPL ratings can be a bit fishy. Also note, that for the VRX it spells out specifically more details on how the SPL is achieved. I wonder how they come up with the one for the PRX line since it is not stated in the spec sheet or the manual. Hmm...

    So based on the above specs, would the old 100Hz "standard" recommendation be the best bet for the LP if I want to the best tops/mid clarity? I've been messing with it, by my ears are acting up. I think room acoustics in my house are all over the place. Will have to test outside tomorrow.

    Also, I have read in other post people always say match the "subs to the tops" as you mentioned. In my case, with 1 sub only, should I be matching the tops to the sub instead?
  • GadgetGadget Posts: 4,915
    So based on the above specs, would the old 100Hz "standard" recommendation be the best bet for the LP if I want to the best tops/mid clarity? I've been messing with it, by my ears are acting up. I think room acoustics in my house are all over the place. Will have to test outside tomorrow.

    That's probably a decent place to start, each speaker exhibits it's own characteristics and it's pretty simple to experiment..if your ears are working that is...yes I have found I get better clarity ...especially in tops with 15" low drivers...and with 12" I usually push that up toward 120hz
    Also, I have read in other post people always say match the "subs to the tops" as you mentioned. In my case, with 1 sub only, should I be matching the tops to the sub instead?

    That's a very confusing question...if your asking should you overlap the xover points the answer is usually no, and if your going to the Butterworth 18 and 24 db/octace slopes are best... JBL does sometimes overlap their xovers but usually with a bi-amped/tri-amped setup on up in the SR range... not their fullrange cabs/powered cabs Just decide on a crossover point and set the both the same or perhaps a slight (few hz) spread if your perceiving crossover point interaction/interference.

    Gadget
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