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help with jbl speakers setup


Hi all I am in search of some help/advice. Here is the equipment that I am working with.
QSC 2450 x 2
QSC 5050 x 1
JBL SRX 725 x 2
JBL SRX 728 x 2

I am thinking about running the QSC 5050 bridged to the SRX 728s so I could get as much juice to them as possible. Also I want to use the other 2 QSC 2450 amp on the SRX 725s.. one to drive the hf and the other the lf ..in biamp mode that is.
What is the best approach to setting this system up using the biamp swtich that is placed at the back of the SRX 725s? Also is there a specific way of wiring the Neutrik® Speakon® NL-4 connectors on the speaker wire in this setup? My main concern is the wiring and the connecting them properly.
Also just for general knowledge what is the purpose of the switch on the back of the JBL SRX 728 ... i know it allows the speaker to use wirings of either +1 -1 or +2 -2 ...but does either wiring determines whether the speaker is driven in 4 or 8 ohms ...
might be dumb question but I am just curious ... thanks so much for the feedback
August 6, 2009 @07:09pm

Wiring up a PA should be pretty straightforward, especially a nice one like you have! Have you tried the instruction manual? Also, try experimentation...just don't plug a speaker output into a line input! Really how you set up a PA depends on how you are going to use it. Feedback and distortion are what you should avoid at all costs...everything else is pretty much secondary, a PA is a PA, they all have their limits. Like I said, avoid feedback at all costs, keep the distortion to a minimum (usually turning the amps up to about 90% and controlling the levels from the FOH is the best bet for maximum dynamic range. Some people reccomend going 100%, but I find that most amps induce distortion and feedback at this level no matter what the input level. Never blast the FOH volume and attenuate with the amps, you will almost certainly get feedback from the board/pres...that is my experience anyways.
August 6, 2009 @08:48pm

This isn't quite so straightforward. Wiring is a little bit tricky on these. Here's what I'd do...
First of all, don't run both subs off of the RMX5050 in bridge mode. That will bring the impedance down to 2 ohms, and the amp isn't happy with anything below 4 ohms when bridged. You can run ONE sub off the 5050 in bridge mode (and it will KICK - the 5050 can pump out 5000 watts at 4 ohms mono), but not two.
You can run each amp off of one channel of the 5050 in stereo mode, but they could take a lot more juice than that. The subs are rated at 1600w continuous, 6400w peak at 4 ohms. The 5050 will be giving them 1600w each. In a perfect world, you'd have two RMX5050s, each powering one sub. With the gear you've currently got, you may have to settle for 1600w and be very careful not to allow the system to clip or risk damage to the speakers.
As for the SRX725s, they are rated at 1200w program / 4800w peak passive, 4 ohms. If you bi-amp them, then the lows are rated at the same 1200w / 4800w 4 ohms and the highs are 75w program / 300w peak at 8 ohms.
I'd run each of the cabinets lows off of one of the RMX2450s in bridge mode. If you want to bi-amp, add a smaller amp (maybe an RMX1450) and run the highs off of it in stereo mode.
Regarding wiring the Speakons...
If you wish to run the system bi-amped (tops and subs, in other words), use 4-conductor speaker cable with 2 dual banana plugs on one end and a Speakon NL4 connector on the other. Plug the banana plug corresponding to pin 1+/- of the Speakon into the amp powering the top cab. Plug 2 +/- into the amp powering the sub. Set your SRX728s to pin 2+/- operation and use a Speakon to Speakon cable (can be two or four conductor) to jump up to the SRX725, and set the switch on the SRX725 to passive mode.
If you want to run the system tri-amped (HF, LF, and subs), you'll need two cables for each side. Use 4-conductor cable for the SRX725. Plug the banana plug for 1+/- to to LF amp (RMX2450), plug the banana plug for 2+/- to the HF amp (something smaller, like an RMX1450), and connect the Speakon plug to the SRX725 and set the switch to bi-amp mode. Use 2-conductor cable for the SRX728s. Connect it to your sub amp (RMX5050) using either banana plugs or a Speakon, and set the switch to the 1+/- operation mode.
I hope this helps.
August 6, 2009 @09:44pm

And BTW - I'm moving this thread to the Noise Gate forum where it will hopefully get a little more attention.
August 6, 2009 @09:46pm

My speaker wires have speakon one end and banana plug on the other ... if I am to bridge my 5050 amps is there a specific way the speakon connector must be wired?
August 6, 2009 @11:43pm

I would run each sub with a 2450 bridged, and then use the 5050 on the mains, one per side. This is UNTIL you are able to get another 5050. I would just run the mains full range, but that’s me.
When you can , buy another 5050.
run each 5050 bridged on a sub, and then run each 2450 bridged on the mains.
I have the dual MRX subs, and i use the QSC PLX 3602's on them, sounds great. I could imagine that the SRX 728's with a bridged 5050 would sound amazing :)
The dual 18" SRX 728's are always 4ohm cabinets, that switched allows you to run each 18 separately, or to run them together. You could use two amps, one for each speaker in the cabinet. Or just run them together off 1 amp (most common)
August 7, 2009 @12:40pm

My speaker wires have speakon one end and banana plug on the other ... if I am to bridge my 5050 amps is there a specific way the speakon connector must be wired?

Right on the back of the 5050, there's a chart specifying the speakon wiring. It says for bridge you wire your cable to +1 and +2. Be sure to label that the amp end, as the speaker end will still be wired to +1 and -1. Use the same wire for the +2 and the -1 (negative).
EDIT: Sorry, missed the part about the banana. Above directions are for Speakon on both ends. In your case the speaker end is clearly marked! All you have to do is open the Speakon and move the wire in -1 to +2.
August 8, 2009 @02:43am