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set X-over freq or leave it alone?

BassManiacBassManiac Posts: 4
edited May 2007 in PA General Discussion
Hi all!

here is our PA setup:

Mackie onyx 1640 mixer
Driverack PA
2 - JBL SF25 main cabinets (2x 15s and a horn w/built in x-over)
1 - JBL MP418SP powered sub (2 internal Crown 660w power amps w/x-over @ 120Hz)
1 - JBL MP418S
1 - QSC PLX-3402 power amp (for the SF25's)

I used the wizzard to setup the system, I'm going to run the PLX 3402 in stereo to the SF25 cabinets.

my question is, should I set the crossover freq in the driverack for the MP418 sub or just leave it alone?



  • Options
    GadgetGadget Posts: 4,915
    Ok.. I have to tell you that after searching out the two subs ... since you DIDN'T include any amp info for the 418 unpowered.. that I have to ASSUME.. and you know what that means right.. I HATE being an ASS... BUT you left me no choice here... you are running in the sub + sub mode and that means you are TERRIBLY underpowered in the sub category...

    I would select a 2 x3 with 100 hz LPF for the subs at LR 24, with an HPF of 50 hz and bw 18 slope...Likewise a 100 hz LR 24 HPF for the SF25's use about 8.5 ms of delay for the tops...there is no LPF so 'out' would be the correct term here...

    So yes, I would cross the subs and the tops at the same point.. in the future it would be appreciated if you would include ALL the info you have and all of what you want to know...

  • Options
    BassManiacBassManiac Posts: 4
    sorry bro,

    here is the only info I could find on the SF25:

    Features & Specs

    3/4\" MDF advanced cab construction
    2 - 15\" woofers with 2-1/2\" voice coils
    Ferrofluid-cooled titanium driver
    500W program handling
    2,000W peak handling
    Advanced crossover topology
    4-ohm nominal impedance
    18.25\"W x 43\"H x 17\"D
    94 lbs.

    and here is what I found on the MPro MP418SP:

    Speaker System Type: Powered 18\" subwoofer, bass-reflex enclosure
    Frequency Range (-10 dB): 36 Hz - 150 Hz
    Frequency Response (±3 dB): 40 Hz - 120 Hz
    Sensitivity (1w/1m)1: 101 dB SPL
    Nominal Impedance: 4 ohms
    Rated Maximum SPL2: 132 dB SPL peak
    Dimensions (H x W x D)3: 617.9 mm x 538.1 mm x 776.6 mm
    (24.33 in x 21.19 in x 30.57 in)
    Net Weight: 54 kg (119 lbs.)
    Drivers: 1 x JBL 2241G
    Optional Accessories: SS3BK pole
    Amplifier Power4: 660 watts @ 4 ohms (per channel)
    400 watts @ 8 ohms (per channel)
    Crossover Frequeency: 120 Hz
    Required AC Mains: 50/60 Hz (North American units are 60 Hz only);
    120 and 230-240 VAC (±10%) units are available
    AC Line Current: 120 volts: 9.5 A; 230 Volts ±10%: 5.0 A
    Power Consumption at Idle: No more than 90 watts
    Total Harmonic Distortion: 1 kHz rated power, 0.5% or less true THD from
    20 Hz to 20 kHz

    and the QSC PLX3402:

    STEREO MODE, Both Channels Driven
    8 ohms (20 Hz-20 kHz 0.03% THD) 700 W
    4 ohms (20 Hz-20 kHz 0.05% THD) 1100 W
    2 ohms (1 kHz 1% THD) 1700 W
    16 ohms (20 Hz-20 kHz 0.1% THD) 1400 W
    8 ohms (20 Hz-20 kHz 0.1% THD) 2200 W
    4 ohms (1 kHz 1% THD) 3400 W
    Signal to Noise (20 Hz-20 kHz) < -107 dB
    Input Sensitivity @ 8 ohms 1.9 Vrms
    Input Sensitivity @ 4 ohms 1.7 Vrms
    Voltage Gain 40x (32 dB)
    Output Circuitry 2-Step Class H
    Power Requirements
    (1/8 Power Pink Noise @ 4 Ohm) 12A
    Distortion (SMPTE-IM) Less than 0.01%
    Distortion (Typical)
    20 Hz-20 kHz: 10 dB below rated power
    1.0 kHz and below: full rated power
    Less than 0.01% THD
    Less than 0.01% THD
    Frequency Response 20 Hz-20 kHz, +/- 0.2 dB / 8 Hz-50 kHz, +0, -3 dB
    Damping Factor Greater than 500
    Input Impedance 6k ohms unbalanced, 12 k ohms balanced
    Input Clipping 10 Vrms (+22 dB)
    Cooling Variable-speed fan, rear-to-front air flow
    Connectors, each channel Input: 3-pin XLR & 1/4\" TRS balanced
    Output: Neutrik® Speakon® and touch-proof binding posts
    Amplifier Protection Full short circuit, open circuit, thermal, ultrasonic, and RF protection
    Stable into reactive or mismatched loads
    Load Protection On/off muting, DC-fault power supply shutdown
    Dimensions 19\" (48.3 cm) rack mounting, 3.5\" (8.9 cm) tall (2 rack spaces)
    13.25\" (33.7 cm) deep (from front mounting rails)
    Gain 40x (32 dB)
    Weight 21 lbs (9.5 kg) net, 27 lbs (12.3 kg) shipping

    and yes, I am using the MP418SP in sub+sub mode with the MP418S (unpowered), so that's 660w to the unpowered sub.
    what would work better for power on the subs?

    also, the wizard setup the system as 2x4, and since my speakers are listed in the wizard, is the crossover already set for the SF25's and the MP418SP?
    the reason I'm asking is because I did some more reading on this forum and the \"old\" forum and I was lead to believe that if your speakers are listed in the wizard, the crossover is set by the wizard, is that correct?

    Thanks again!
  • Options
    DraDra Posts: 3,777
    From the 260 wizard the tops are crossed at 100hz as Gadget recommends. The subs are listed as full range (120hz internal), but that is not good mojo. Go with Gadget, he's one smart feller.

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