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Author Topic: Si Expression L&R + Sub  (Read 904 times)

William john Lewis

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Si Expression L&R + Sub
« on: September 14, 2022, 12:01:21 PM »

Hi Guys, I am new here, and could do with some help. We are currently installing a new PA system.  I would like to set up L & R speakers plus sub speakers on the Si expression.

For the subs:

Am I right in saying that I set up a post fade sub group say (mix 14) and choose the mono button rather than L&R.
Do I then allocate a physical output to the Sub say xlr14

I know that I can then adjust the faders within the sub group for the instruments I want in the subs, ie kick, bass and keys.

My question is do these Channels also go to the L&R fader.  Our cross over point is 100hz

Am I on the right track or if not could someone advise please.
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lindsay Dean

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Re: Si Expression L&R + Sub
« Reply #1 on: September 14, 2022, 01:31:29 PM »

My advice set the system correctly ,let the subs do their job on the same Left Right stereo mono fader with the mains. If and when you need more sub or bass or keyboard bottom, Slide the fader up on that channel,
 set your high-pass on inputs etc. channels the way you want them to keep them out of the subs.
        The original idea in my opinion for separate sub control was for drastically changing styles of music in a venue artist to artist. (edm) . If you have enough rig for the gig and it's set up properly.
             You don't need it, it's a waste of time, it's sophomoric.

Don't get offended just my opinion.
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William john Lewis

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Re: Si Expression L&R + Sub
« Reply #2 on: September 14, 2022, 02:32:50 PM »

Thanks Lindsay for the reply. 

With our current system the tops and subs are positioned quite close together.  Both are fed from a crossover.

On our new system we hope to fly the tops (Rcf hdl10As) that will increase the distance from the subs on the ground quite a bit.

I think what you suggest is similar to our current setup.

How would I introduce a delay to the subs if I need it using your method?  My thinking is if I need to delay the subs I can do it using the separate sub send.
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Patrick Tracy

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Re: Si Expression L&R + Sub
« Reply #3 on: September 14, 2022, 03:10:46 PM »

You could keep it simple by using the Mono output to drive the subs and only assign the relevant inputs to that output.

Or, you could replace what I assume is a simple crossover with a digital speaker processor that had delay available on the outputs. One with at least three inputs would let you do a conventional stereo in setup to start, then experiment with mono bus or aux driven subs.

John Schalk

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Re: Si Expression L&R + Sub
« Reply #4 on: September 15, 2022, 10:27:11 AM »

For the subs:

Am I right in saying that I set up a post fade sub group say (mix 14) and choose the mono button rather than L&R.
Do I then allocate a physical output to the Sub say xlr14
I have an Si Performer 2 and this is how I run my system.  I use mix 14 because it's the last mix button, so easiest to "grab" and because it's already post-fader in the default layout for the console.  I did look at using the Mono "mix" on the console, but there isn't a direct mono level control for the channel's mono send like there is on the X/M 32 consoles, so I opted for the sends on fader approach using a standard mix bus.  One thing to note if you decide to use the console to set a delay for your mains or subs is that the delay on my Performer starts out in tiny micro-second increments.  If you're not paying attention, you will think you've dialed up 5 milliseconds of delay when you've only added 5 micro-seconds! 
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Patrick Tracy

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Re: Si Expression L&R + Sub
« Reply #5 on: September 15, 2022, 11:31:14 AM »

I did look at using the Mono "mix" on the console, but there isn't a direct mono level control for the channel's mono send like there is on the X/M 32 consoles, so I opted for the sends on fader approach using a standard mix bus.

The Expression has a mono master fader. It becomes the master fader for whatever aux send you might have selected so the LR fader is available regardless.

[Edit] I probably misintepreted that. You want per-channel control.

That brings up a question. If you're going to make the effort to align the tops and subs to make them phase coherent, doesn't having different gain at the channel level defeat that? If you change the gain in one band relative to another, you effectively change the crossover frequency and thus the phase alignment. It seems inconsistent to me.
« Last Edit: September 15, 2022, 11:48:54 AM by Patrick Tracy »
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lindsay Dean

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Re: Si Expression L&R + Sub
« Reply #6 on: September 15, 2022, 12:50:27 PM »

The system would should be designed / installed by vetted professoinals versed in rigging calculation, system alignment preferably mounting the subs with the mains, that's going to require more subs or higher effiency  but having the subs flown would be more evenly distributed.
         Stereo depending on the size and shape of the room would require more cabinets to create the stereo field in different areas of the space.


All of this is dependent on your budget but in no way is rigging a DIY gig
« Last Edit: September 15, 2022, 12:53:39 PM by lindsay Dean »
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ProSoundWeb Community

Re: Si Expression L&R + Sub
« Reply #6 on: September 15, 2022, 12:50:27 PM »


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