Hook up question - DBX 120X Subharmonic Synthesizer

[gsb001]

Hook up question - DBX 120X Subharmonic Synthesizer
I have two JBL SR4735A’s and would like to add at least one and maybe two matching JBL MR918 sub woofers.
My room is 30’ x 40’.
I’m driving the SR4735A’s with JBL 6290 amp.
I have a Yamaha M2 amp I can use for the sub(s).
I would like to use my DBX 120X Subharmonic Synthesizer for both the full range SR4735A’s and the MR918 sub.
On the DBX 120X Subharmonic Synthesizer there is a switch for full range or high frequency only. Instructions say to turn full range off – so high frequency is going to mains (SR4735A) and low frequency is going to subs.
Output frequency split is as follows:
High frequency 120 HZ to 20 kHZ.
Low frequency 20 HZ to 120 HZ.
This is all fine and I think I understand the connections and results.
My question is, if I do turn off the full frequency and split the outputs between the SR4735A and MR918, won’t I be losing much of the lower end sound going to the SR4735A’s and turn them into mid and high only speakers?
For some reason this bothers me. I hate to give up the full range from the SR4735A’s. My goal was to keep what I currently have from the SR4735A’s, while adding the benefits of subs to them.
And finally, I like the idea of being able to control the level of output to the sub’s thru the DBX 120X Subharmonic Synthesizer front output control.
So my question is, how do I hook the SR4735A and MR918’s so I keep full range on the SR4635A’s while adding the sub’s and being able to control thru DBX 120X Subharmonic Synthesizer?
Do I need to add a separate cross over to my system in addition to the DBX 120X Subharmonic Synthesizer?
Thanks
Steve

[jcrobso]

http://www.dbxpro.com/product_downloads/Owner_Manuals/120X%20Owners%20Manual.pdf

This is basically an electronic crossover, but with some interesting bass options.
You could set it up ether way, just use the MR918 to supplement the bass of the SR4735 or go full bi-amp.
I would favor the full bi-amp mode, by reliving the SR4735 of that really low bass the mids that are coming from it will be cleaner by reducing the inter-modulation distortion and this will lessen the power demands on the JBL amp.
Keep in mind the that for every octave down you go the cone excursion doubles. If the cone has to move 1/8" at 200hz it will have to move 1/4" at 100hz, etc.
MR918 is designed for that low bass, run the system full bi-amp and let the MR918 do it's job.
Also read the manual and follow the direction on using the bass synthesizer part, proceed slowly with caution, on older recordings where the bass was limited you can restore most of it, but be careful!;)

[toddalin]

So my question is, how do I hook the SR4735A and MR918’s so I keep full range on the SR4635A’s while adding the sub’s and being able to control thru DBX 120X Subharmonic Synthesizer?
Do I need to add a separate cross over to my system in addition to the DBX 120X Subharmonic Synthesizer?
Thanks
Steve


Use a pair of "Y" cords to split the signal before the dBX. Run one side of the Y output directly to the amp powering 4635s. Run the other side of the Y to the dBX input and run its 20-120Hz output though an amp to your 918s.

[tarior]

Actually, there is a switch on the back of the 120X-DS that allows you to select whether the mains run in full range or high pass. The knob on the back allows you to adjust the low pass frequency.

[gsb001]

Thanks guys.
I like Y- adpt idea. Forgot all about the use of Y- adpts, tks.
More thoughts / questions.
If I by-pass the sub synthesizer using Y – adpt to run the full range speakers, will I miss the features and adjustment capabilities of subharmonic level and low freq. boost changes?
Or – are the subharmonic level and low freq. controls only really meant for the sub?
Must be – I’m sure DBX position would be that when using sub, the best utilization of adjustments to the subharmonic level and low freq. boost controls should be thru the sub. That would explain the “full range only / sub only” logic.
Takes me full circle back to skipping the Y – adpt and hook up according the manual.
Steve

[tarior]

The boost/subharmonics are for the sub.
YOU DON'T NEED A Y CORD, it has a built in bypass.

[gsb001]

tks again. I feel better about the hook up now.
SB