Help for my bass setup with active tops processed by DR PX?

desiBel

Hi guys,

I haven't posted for a long time, I was wondering if anybody could possibly explain a problem I have with my general setup. However, this is a more general troubleshooting question. I have only used this setup at a gig once.

The problem that I am having is that my tops (JBL PRX 515, active), occasionally cut off left and right sides alternately for a couple of seconds when I am using bass bins. Everything is processed through a DriveRack PX.

Now, my tops are fine when used alone, which I have done so on numerous occasions, but they seem to give this problem intermittenly. Once on a home test, with the bass setup they gave a few pop sounds like and electrical problem?

My unprofessional theory is that because I have placed the active tops directly on top of the bass bins the bass is maybe causing the components in the active tops to move?

My Equipment Setup is as follows:

Mixer Studiomaster Horizon 16ch
DriveRack PX
JBL 515 Tops (x2)
JBL SP128s Bass (x2)
Crown I-Tech 5000 HD Amplifer (Bass)

Ps. Monitor mix is also present via FB and aux's and seperate amps.

I use the bass amplifier parralled. I take a mono line (left) out from the DriveRack PX and Y link the amp on the amp setting on the amps display. The JBL SP128s bass drivers are dual 18" 1600Watts per side, which run 4 Ohm, of which I place the tops straight on top of, as they are tall standing bins, and the stack looks nice.

Thes are the specs for the tops and subs if needed:

TOPS: JBL PRX515
System Type: Self powered 15", two-way, bass-reflex,
Frequency Range (-10 dB): 45 Hz – 20 kHz (EQ in flat position)
Frequency Response (±3 dB): 52 Hz – 20 kHz (EQ in flat position)
Coverage Pattern: 70° x 70° nominal
Directivity Index (DI): 10.3 dB
Directivity Factor (Q): 10.8
Crossover Modes: DSP controlled 48 dB filter slope
Crossover Frequency: 1.6 KHz
System Power Rating: 500 W continuous, 1000 W peak
LF Power amp: Class-D, 400 Watt (continuous) at driver impedance
HF Power amp: Class-D, 100 Watt (continuous) at driver impedance
Distortion: Less than 0.1% at rated power
Maximum SPL1: 133 dB SPL peak
Signal indicators: Overload: Red LED indicates input overload condition
Signal: Green LED indicates signal presents
Input sensitivity: Mic position: –25 dBu to 0 dBu
Line position: +28 dBu to +10 dBu
Input Impedance: 64 K Ohms (balanced), 32 K Ohms (unbalanced)
EQ: Presets for Flat or Boost
LF Driver: 1 x JBL 265F 380 mm (15 in) Differential Drive® woofer
HF Driver: 1 x JBL 2408H 37.5 mm (1.5 in) annular polymer diaphragm,
neodymium compression driver
Enclosure: Trapezoidal, 18 mm, plywood with polypropylene end caps
Suspension / Mounting: 36 mm pole socket
Transport: 2 x die-cast handles with backing cup
Finish: Anthracite DuraFlexâ„¢ finish
Grille: Powder coated, Anthracite black, 18 gauge perforated steel
with acoustically transparent black foam backing.
Input Connectors: Balanced XLR / ¼ inch combo jack with XLR loop through,
Dimensions (H x W x D): 815 mm x 440 mm x 465 mm
(32 in x 17.25 in x 18.25 in)
Net Weight: 26 kg (57 lb


Bass: JBL SP128S
System:
Freq. Range (-10 dB): 32 Hz - 2.3 kHz
Freq. Response (-3 dB): 36 Hz - 1.4 kHz
Recommended High Pass: 25 Hz, 12 dB/Octave
Recommended Low Pass: 150 Hz, 12 dB/Octave
Transducers:
Low Frequency: 2 x 2242H, 460 mm (18 in) dia., 100 mm (4 in)
edgewound ribbon voice coil
Nominal Impedance: 4 Ohms / (2 x 8 Ohms)
Input Power Rating: 1600 W, AES; 6400 W Peak
(2 x 800 W AES, 3200 W Peak)
Sensitivity1: 102 dB, 1 W, @ 1 m (3.3 ft)
Calculated Maximum SPL: 140 dB, @ 1 m (3.3 ft)
Recommended Amplifier3: 2000 W
Physical:
Enclosure: Rectangular, birch plywood
Environmental Specifications: Mil-Std 810, IPX3 per IEC 529
Suspension Attachment: 12 points; accepts M10 threaded hardware
Finish: Black DuraFlex coating
Grille: Black powder coated zinc treated 18 gauge
perforated steel grille with foam backing
Input Connectors: 2 x NL4 Neutrik Speakon connectors
Dimensions: 1213 mm x 572 mm x 572 mm (47.75 in x 22.50 in
x 22.50 in)
Net Weight: 63.5 kg (140 lbs.)

Pleasse forgive me if I have forgotten to mention something! I would very much appreciate your help, I know you guys are great...
Thanks,

Tony

Gadget

Perhaps it's power sag... you have the Itech 5000 and the tops on what? a 14 gauge 50 ft cord? Are you plugged into a standard 15 amp household outlet? Lots of venues have bad power and that is often exacerbated by cable too small to carry the system load. I generally try and get a 50 amp 208-230 line for the audio alone. I can and have run the system on a single 20 amp breaker and achieved 105-108dB without tripping the breaker. I do however have very efficient LABsubs, and tops that have great efficiency which is the key to powerful sound with little draw. I'm not using the high efficiency amps either..Mac 3600, QSC RMX4050..and I have a 4 wedge bi-amp monitor rig to boot.

Otherwise I can't believe the vibration is causing the problem, and from your description it sounds like the speaker was popping...and that usually means over driving the speakers, or lack of power, or intermittent connection. But if it happens to both speakers

Can you post your processor settings?

JBL Sp128s???
G

desiBel

Hi Gadget,

Thanks for the prompt reply. I am in the UK and the household supply is 13amp 230V (three prong plugs).

I currently use good quality (Van Damme), but normal microphone cable for the tops out from the DR PX outs straight to the powered tops, which are about 12 Metres long. Running on their own, that is without the bass, I have never had any such problem...

It may well have been a power issue, as this particular gig was outdoors, but this dosen't explain the sudden pops I got, when the tops and subs were set up for a home test. These pops occurred even at low power, or even no material was running?

The DR PX settings are tops preset on the PX and custom subs, whIch I set mono, but use both channels parrallel on the bass amp to run two seperate cabinets. I cross over at about 112.

Bass:
High pass: 27Hz LR24 or BW18
Low pass: 112Hz LR24

Tops:
High pass: 45Hz LR24 to Out

I hope this is enough info, I have typed off my Blackberry and these are the settings off the top of my head!

Thanks,

Tony

desiBel

Sorry, I forgot to mention that the JBL SP128S are an old model found in the vintage section of the JBL pro website, if that's what you meant at the end of your last reply...

It might be helpful to know that the Crown I-tech 5000HD is a US model I brought, that came with UK power leads and is said to have a global power supply, but the bass seem fine!
Thanks again...

Gadget

Are you overlapping the sound that much all the time when you run tops and subs?

Tops:
High pass: 45Hz LR24 to Out

I can see running the tops fullrange when used without a sub... but overlap of that much (45 - 112hz) would cause massive interactions in the LF (below 112 hz) region due to the proximity of the tops and subs both reinforcing the 45-112hz range...

Are you aware of the fact that two speakers in near proximity that are reproducing the same frequencies can cause massive frequency anomalies as any that are out of phase by even a little will cause some degradation of the signal, and those that are significantly out of phase will cancel partially to completely..

Have you placed the speakers on something OTHER than the subs to see if the problem persists? A speaker that cuts out when set on a speaker is nearly useless... since the vibrations it makes itself could start causing the problems...I still suspect power as an issue...

G

desiBel

Hi G,

Sorry for such a late reply! Yes, I am aware of frequency cancellations, however, this crossover overlap sounded good, which was setup in my kitchen at home, it sounded full and heavy...however, this was just a test as I brought my new amp the Crown I-tech 5000HD for the bass! What crossover setting would you suggest? I thought maybe running the tops down to about 100Hz then?

OK, I will try and place the speakers elsewhere and see if the problem persists, but your right, I think this must be a power problem, will have to try in another venue.

Will post back soon,

Thanks.

Gadget

Hey Tony..
No problem, no foul... been very busy myself. Had a show this weekend outdoors...about 3000 people outdoors. pretty amazing. 4, 2x12" tops (2" exit B&C and 12" neo, 2 LABsubs and 4, 18" turbo manifolds... running 4 way... sound was amazing for such a small system.. people were like "where the "hell o" is all that sound coming from?" Actually got complaints it was too loud! Found out the system draws about 40 amps for the mains alone. 129 dB subs and 127 tops, flown array style @16' trim height using 15deg down angle.

As for your setup, ya,100 hz would be a good starting point, but try90, and 70 as well...see whatr you think.
G