Loudspeakers How to use a passive split so amps get the same input?

[Brentgi]

In a nutshell, I'm curious to know the best AND/OR most cost effective way to passively split a signal so that two amps get the same input signal.

Now here's the long version:

In our installed space, we are running BSS BLU-100 as well as BSS BLU-BOB1. We recently had a failure of one of our main subs which was a powered sub being ran directly from the console. Before my time, these subs were installed after the rest of our current system was installed and currently sit in speaker pits under the stage. Long story short, installers used flown subs, but it wasn't enough low end in the room. So it was decided that additional subs were needed.

Fast forward to now. We've decided to replace 2 active powered subs with 2 passive subs that will run off of a pair of Crown CDi 4000 amps. We can continue to run these subs straight from the console, but as it stands, we have the subs on aux and have to mix to not only the installed flown subs, but also to the subs under the stage (i.e., two aux's for two sets of subs). I'd like to leverage the BSS London gear to do the processing of one aux and send it separately to each sub 'channel'. However, I have only one open output on the BLU-100 and am wondering if it is ok to just split to output to two different amps. My long term goal is to invest in an additional BLU-BOB to get more outputs. I appreciate your thoughts on the matter.

 

[Aaron Becker]

Short version: Use a passive Y-splitter for the line level signal. You'll experience a 3 dB loss on each side and you'll have to use the amp's gain/trim to compensate for that.

I like the idea of using the DSP's outputs as you can compensate for things such as delay correction, additional EQ, leveling, etc, not to mention compression/limiting for equipment protection. You'd also have the option to use separate inputs AND outputs if you ever decided you wanted a different input for one set of subs (depending on the venue/show requirements).

So yes, you can passively split the output. Many amps even have a "pass thru" specifically for this, too, but it sounds like your amps are probably not co-located.

 

[RonHebbard]

In a nutshell, I'm curious to know the best AND/OR most cost effective way to passively split a signal so that two amps get the same input signal.

Now here's the long version:

In our installed space, we are running BSS BLU-100 as well as BSS BLU-BOB1. We recently had a failure of one of our main subs which was a powered sub being ran directly from the console. Before my time, these subs were installed after the rest of our current system was installed and currently sit in speaker pits under the stage. Long story short, installers used flown subs, but it wasn't enough low end in the room. So it was decided that additional subs were needed.

Fast forward to now. We've decided to replace 2 active powered subs with 2 passive subs that will run off of a pair of Crown CDi 4000 amps. We can continue to run these subs straight from the console, but as it stands, we have the subs on aux and have to mix to not only the installed flown subs, but also to the subs under the stage (i.e., two aux's for two sets of subs). I'd like to leverage the BSS London gear to do the processing of one aux and send it separately to each sub 'channel'. However, I have only one open output on the BLU-100 and am wondering if it is ok to just split to output to two different amps. My long term goal is to invest in an additional BLU-BOB to get more outputs. I appreciate your thoughts on the matter.

@Brentgi First a few quick queries followed by a couple of economical suggestions and by then the marvelous masses ought to have chimed in (If they haven't already while I've been typing):
1; Running mono subs or stereo?
2; Doing any fancy / trendy pseudo-cardioid subs or?
3; Do you have output transformers within the outputs of your BSS gear or are you running active outputs?
4; What impedance are your passive subs and what is the resultant combined load impedance your passive subs will be presenting to the outputs of your amplifiers on a per channel, or bridged, basis?
Suspicion: I suspect one output of your BSS London BLU-100 will drive two comparatively high impedance inputs of your amplifiers assuming we're talking a balanced output to two balanced inputs without connecting either leg of the BSS's output to ground or effectively shorting out one side of the balanced output. BUT I WON'T BE THE PERSON TO PUT THAT IN PRINT!
5; When in doubt, summon @TimMc and / or Danley Sound's Ivan Beaver.
6; RDL, Radio Design Labs, likely has an economical solution that will let you sleep nights.
7; Rane's tech notes will likely have economical passive balanced and / or unbalanced split circuits on-line that you could easily assemble on perf' board or DIN mounted terminals.
That ought to have opened the floodgates for you.
@FMEng Care to wade in?
Toodleoo!
Ron Hebbard

 

[FMEng]

These days, nearly all balanced*, line level outputs are low impedance, <100 ohms. Nearly all balanced* inputs are high impedance >10 kohms, known as bridging inputs. Bridging means the input impedance is 10 times or more higher the the source impedance. It would take a dozen inputs to significantly load the output. A simple Y cord will do the job here and there will be no loss of level or change in frequency response.

Bridging inputs only need voltage, not power, so impedance matching, and the resulting splitting losses don't come into play. Really old equipment with 150 or 600 ohm inputs, or transformer ins and outs are the rare exception. Basically, unless a spec sheet says it is transformer balanced, assume it is electronically balanced. The exceptions to that are vintage tube gear, hum eliminator/isolation boxes, DI boxes, and passive microphone splitters.

*Unbalanced and impedance balanced (pseudo balanced) are another discussion.

 

[TimMc]

Short version: Use a passive Y-splitter for the line level signal. You'll experience a 3 dB loss on each side and you'll have to use the amp's gain/trim to compensate for that.

I like the idea of using the DSP's outputs as you can compensate for things such as delay correction, additional EQ, leveling, etc, not to mention compression/limiting for equipment protection. You'd also have the option to use separate inputs AND outputs if you ever decided you wanted a different input for one set of subs (depending on the venue/show requirements).

So yes, you can passively split the output. Many amps even have a "pass thru" specifically for this, too, but it sounds like your amps are probably not co-located.

No, you will not lose 3dB. The amplifier's input impedance likely is sufficiently high (>10k Ohms) to not load down the source. With most "recent" amplifiers you can usually Y-cord (or daisy chain units with built in "thru" connections) anywhere from 5-10 times, depending on source and input impedances. You'd have to go back into history a fair bit to find low impedance, current-driven amplifier inputs.

 

[Aaron Becker]

No, you will not lose 3dB. The amplifier's input impedance likely is sufficiently high (>10k Ohms) to not load down the source. With most "recent" amplifiers you can usually Y-cord (or daisy chain units with built in "thru" connections) anywhere from 5-10 times, depending on source and input impedances. You'd have to go back into history a fair bit to find low impedance, current-driven amplifier inputs.

Happily stood corrected.

 

[Brentgi]

So yes, you can passively split the output. Many amps even have a "pass thru" specifically for this, too, but it sounds like your amps are probably not co-located.

The amps (Crown CDi 4000's) are racked together, but they do not have a "pass thru" feature, at least not from what I can tell.

@Brentgi First a few quick queries followed by a couple of economical suggestions and by then the marvelous masses ought to have chimed in (If they haven't already while I've been typing):
1; Running mono subs or stereo?
2; Doing any fancy / trendy pseudo-cardioid subs or?
3; Do you have output transformers within the outputs of your BSS gear or are you running active outputs?
4; What impedance are your passive subs and what is the resultant combined load impedance your passive subs will be presenting to the outputs of your amplifiers on a per channel, or bridged, basis?
Suspicion: I suspect one output of your BSS London BLU-100 will drive two comparatively high impedance inputs of your amplifiers assuming we're talking a balanced output to two balanced inputs without connecting either leg of the BSS's output to ground or effectively shorting out one side of the balanced output. BUT I WON'T BE THE PERSON TO PUT THAT IN PRINT!

Toodleoo!
Ron Hebbard

1; Mono
2; QSC E118SW
3; There is nothing between the outputs of the BSS London BLU-100/BLU-BOB and the inputs of the amps other than the wires themselves.
4; Input impedance is 20 kilohms balanced, 10 kilohms unbalanced and we'll be running the outputs at 4Ω.
Skipping to 6; I have some passive rack mountable splitters, but I'd rather not add another piece of equipment and more connections for something seemingly simple, if I don't HAVE to.

With most "recent" amplifiers you can usually Y-cord (or daisy chain units with built in "thru" connections) anywhere from 5-10 times, depending on source and input impedances. You'd have to go back into history a fair bit to find low impedance, current-driven amplifier inputs.

Since the amp has terminal block inputs, can I just simply daisy chain the inputs? @RonHebbard's comment has me thinking that I should do something differently with the ground leg, but I don't completely understand.

Thanks again for everyone's input! I really appreciate it!

 

[MNicolai]

The Crown CDi 4000's have DSP built in. Might as well take the AUX into both of them and skip the BSS unless you already have the AUX wired into the BSS. Using the DSP inside of the amps, you can give each pair of subs its own delay/LPF/gain/EQ rather than sticking a generic layer of processing on all of your subs.

Daisy-chained amp inputs is common. Don't overthink it, but ground your shield wires at the SOURCE end of the cable (i.e. the DSP, or the console) and lift the shield at the RECEIVE end of the cable (i.e. amps). This is to avoid ground loops while still giving EMI a path to drain off of the cable.

 

[TimMc]

While we have $200K in Crown amplifiers in our shop we don't use the CDi models... but... yes, you can just install a jumper between 2 amplifier inputs. Make sure you can fit 2 wires in each screw terminal and make absolutely sure that you don't change the which color of wire goes to which screw. Do it wrong and you'll wonder where your sub woofers went...

If the easy button is to put an XLR "Y" cord on the mixer's subwoofer output, go for it and see/hear if you get the results you desire.

 

[RonHebbard]

The amps (Crown CDi 4000's) are racked together, but they do not have a "pass thru" feature, at least not from what I can tell.



1; Mono
2; QSC E118SW
3; There is nothing between the outputs of the BSS London BLU-100/BLU-BOB and the inputs of the amps other than the wires themselves.
4; Input impedance is 20 kilohms balanced, 10 kilohms unbalanced and we'll be running the outputs at 4Ω.
Skipping to 6; I have some passive rack mountable splitters, but I'd rather not add another piece of equipment and more connections for something seemingly simple, if I don't HAVE to.



Since the amp has terminal block inputs, can I just simply daisy chain the inputs? @RonHebbard's comment has me thinking that I should do something differently with the ground leg, but I don't completely understand.

Thanks again for everyone's input! I really appreciate it!

@Brentgi Sorry if I didn't phrase my questions better. In my point 2; I wasn't asking what make and model your subs were but rather if you were planning to do anything "fancy" in the way of the relative positions of your various subs and playing with delays to potentially create a cardioid array with whichever boxes you had.
In my point 4; I was asking specifically about the impedance of your passive subs, NOT your active subs. My thinking was are you sure you won't be paralleling too many low impedance cones together on any one amplifier output or mono bridged pair of outputs?
Sorry @Brentgi I've got to dash to an appointment.
EDIT: @Brentgi Re: My point 6; Not being familiar whatsoever with your Crown CDI4000 power amplifiers, my concern was you may be interconnecting one of your BSS's balanced outputs into an unbalanced input (or 2) and depending upon your connections you may end up effectively connecting one side of the BSS's balanced output directly to ground on your Crown's input(s) or possibly using one balanced output with one side driving each of two unbalanced inputs possibly leading to inadvertent polarity inversions and near flawless signal cancellation.
[It wouldn't be the first time this mis-connection has occurred.]
If I'm recalling correctly, I believe regular poster @MNicolai already posted regarding which end of your shield you should ground and which you should float (Insulate to ensure it doesn't come into contact with anything including any chassis' and /or racks.)
Toodleoo!
Ron Hebbard.

 

[Brentgi]

Thanks everyone for the comments! I think I have the info that I need. I'll let you all know how everything works out.

 

[Jay Ashworth]

A passive Y-split cable to the amp inputs should be fine; those amps are plenty new enough.

It's *combining* (2 outputs to 1 input) that you can't do with a passive cable; google "Why not Wye" for those details.