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SRX725/718 Tuning and Gain Settings


Mark Wanless:
I am having a mental block I just can’t seem to get over in regards to driver delay and gain settings.

I am running PER SIDE (Left/Right Mono):

SRX725 Bi-amped;
           PLX 2402 Bridged for Lows
           One side of a PLX 1202 for Highs,
Two SRX 718s hooked up in parallel
           PLX 3402 bridged.   

These are fed from a DBX DR260 utilizing Aux Fed Subs.

When I look at the tunings from the JBL website (downloaded ZIP file) a couple of things I am having a hard time wrapping my head around.

1)  In accordance with the tunings, when running a 725 Bi-Amp over a 718, there are no delay settings for any of the drivers. (Other speaker settings list delays) Seems to me, there would be a delay setting on the Lows and maybe the sub, to match the horn. 

On a side note, the 715 set up shows a delay, but they show the highs being delayed.   I’m not too familiar with the construction of the horns and woofers and how they placed in the cabinet but is seems there would be a delay on the woofer, not the horn.   The 738s tunings have the lows delayed. 

Anyway, thoughts on a delay on the 725 bi-amp, 718 set up?

2)  IAW the tunings PDF, the gain settings for sub, lows and highs are +6, 0, -9 respectively.  I am assuming this is set on the crossovers on the DR260.  My Non-understanding is:  are those settings dialed in as PART Of  setting the INITIAL SYSTEM gain structure or AFTER setting the initial gain structure?

Again, maybe I do not understand things correctly.  What I have done is:

1) Run a pink noise signal through one of my channel strips adjusting channel fader and master fader to "0" and then setting input gain to show just below peak on my board meter.
2) Adjust input on DR260 to read same as board
3) Set each amp (Sub, Lows, and Highs) to just below clip, back it off another click, then set limiting as required.

My question is would I set the gains from the tunings listed and make a step 4) or would I insert it in between 2) and 3)?  Also, would the size of amp affect those gain settings listen in the tunings, IE, using PLX 3402 on the lows, vise a PLX 2402? 

Lastly, since I am running two 718’s per side, would I still use the +6 gain setting as described by the tunings using their tuning (and I assume one 718) or maybe use the 728 gain setting of +1.7? 


Bob Leonard:
Being that I also run an SRX system I want to start by saying you may be putting too much thought into the process. Download the settings from the JBL site and import them into the DR260. Set up the 260 using the wizard. From that point you may need to work the eq a bit but other than that I have found this method to work quite well 99.9% of the time. As for the subs, if you have a pair of 718s per side use the settings for the 728 and you'll be fine. You may find that adjusting the gain for the subs to be beneficial. I find that I generally have to set my subs at -3db down from my 725s. The difference will be the amplifier you input when using the wizard. For my subs I use QSC 4050HDs.

Chuck Simon:

--- Quote ---Other speaker settings list delays
--- End quote ---

No, the settings for 722 tops, for example, don't use any delay.  The 715 and 738's use a different Hi Freq driver and horn than your 725, so their settings are not relevent.  Use the JBL settings and adjust gain by ear.

Tim McCulloch:

--- Quote from: Mark Wanless on February 20, 2011, 10:24:10 PM ---I am having a mental block... 


--- End quote ---

If JBL doesn't show an inter-band delay for your EXACT product, don't use one, at least until you find an actual problem.

Using bridged amps along with unbridged amps will give you a gain discrepancy of 6dB in favor of the bridged amps.  Reduce the outputs of the DR that drive bridged amps by 6dB.  Also understand that this will affect your protective limiter settings.  It might be simpler to reduce the AMPLIFIER INPUT CONTROLS by -6dB, and put gaffers tape over the knobs.

And blow up some stuff!  Seriously.  You can't call yourself a sounddood until you've learned to replace a HF diaphragm and paid for a few re-cones.  I say this partly for fun and mostly because you need to hear and recognize what your rig sounds like under stress, and that comes from experiencing a little destructive testing.  Consider the money spent on repairs as tuition at Ye Olde Skool of Hard Audio Knocks™.

Mark Wanless:
Thanks for the advice!!!  It has been taken on board.
Tim…LOL, although I am not an Alumnus of Ye Olde Skool Of Hard Audio Knocks, I have taken a few classes to included one of the core requirements:  “Changing Out Speaker Components 101”.  I think I have also taken an upper lever course somewhere along the way.  The system I have now is an upgrade (to say the least) from my prior system, and I find myself not so much worried about blowing something up but more so with the never ending desire for improved sound.   I would truly enjoy the opportunity to “open this thing up” and see what it is capable of and I’m sure that day will come.  And when it does, I will have taken the sage advice from this forum and put it to good use while HOPEFULLY not sacrificing any components to the SoundGods…. I don’t know if I will ever truly qualify as a Soundood, but it is fun and a great learning experience (on many levels).


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