Feedback using SQ where none on old setup

[DaPo]

I’m getting feedback on a mic where previously I didn’t, and hope you can help me identify cause/solution.

I’m trying to capture a pipe organ for output solely to our USB for livestream (a Zoom session, actually).
This ‘acoustic’ feed wants no in-house reinforcement, so it doesn’t go through our house speakers.
The output to USB receives a mix of the “L-R” house sound and this acoustic pickup.
In our old ZED-428, we achieved this using its matrix.
The channel carrying the organ mic was assigned to its own group, and this group was mixed with L-R to go to the USB out.
I described it in this old post: https://community.allen-heath.com/forums/topic/simplest-matrix-control-to-usb-for-zed-428

The organ mic is a condenser mic, facing the rear of the church where the organ is, back far enough away to capture the organ in balance but as close as practical to it under that restriction. It’s a condenser mic, but not a really special one. I’m not looking for audiophile quality at present, just a good level of signal. The distance means the input gain has to be fairly high. Higher than I’d like, but previously it used to work. with the old setup, I could dial up the gain and not get the howling that happens now.

The mic isn’t pointed at the house speakers. The speakers also face the back, but they are partway down the building, further towards the front. As I’ve said, this mic isn’t feeding L-R anyway.

I’ve tried to emulate the same configuration using the SQ-5.
The people set things up with the same channel numbers.
One difference is that the new mixer is fed by a new stage box at the front of the church, where most of the mics are for vocals and piano. It’s an Allen & Heath DX-168 AudioRack.
This is connected to the SQ-5 by SLink.
I understand that the pre-amps being used are in the AudioRack, remotely controlled by the SQ-5.
In the old setup, the organ mic used to be fed directly to an input socket in the back of the old analogue mixer. That mixer’s other inputs were analogue signals brought up by a fat multicore cable from the front with multiple XLR plugs.
Now the organ mic is cabled to the front so that it can be fed into the AudioRack and sent back digitally like the other inputs.

With this setup, I can’t bring gain up much at all without creating howl in the building. The level I can safely use is virtually useless for listening. This is true even if I mute all other microphones. I have turned off USB input (although we like to have the option to use this occasion).

A quick survey of this forum on the word “feedback” reveals some possible areas I’m unfamiliar with – like identifying troublesome frequency ranges and cancelling them out. Is the EQ route worth pursuing? How would one start?

Happy for any suggestions and to supply more detail as required.

Not an audio engineer, quite new to the SQ-5.

** I may need to recheck my facts. I think I failed to get recording success by taking the USB input from matrix 1 and in the end was going with a simple L-R output to Zoom after all. However, in experiment, I’ve experienced this howling feedback with things configured as described above.

[DaPo]

Coming back to report success after another visit to examine this problem.

Initially tonight I again had the problem described above, then I realised that the power amp was turned up to maximum.
We have two groups of people who use this site, and the other group has only one pathway – to “L-R” – that they need concern themselves with. They habitualy turn the power amp to maximum, then reverse-adjust the mixer so that its pre-amps have little work to do. Not much signal, then, going directly from the desk to the USB output.

My error must have had to do with my initial lack of success with getting an audible mix through the matrix onto the USB-based recordings I was making. That, in turn, was due to my inability at the time to adjust the components of that mix (see my other post). I think I then reverted to making do with the USB receiving simply from L-R. That placed constraints on the ambient pickup microphone.

An abiding difficulty was doing this alone, with long walks between tests of inputs, and the slow approach of making recordings on the PC receiving the USB output in order to assess quality. I realise that at one point I was being misled about poor level quality just because I was playing back output from there through the house speakers, L-R, and not realising that the gain had been set low on that SQ input.

I think the key lesson for me here is to use the monitoring tools that the unit comes with. The headphones to hand needed an adaptor to work with the socket on the SQ-5. But I would have done well to have good, well-insulated headphones and a strong understanding of how to test the sound at various points. “PAFL” – it should be “baffle”! The settings screen currently on page 78 of the manual (12.7 PAFL) certainly requires a visit to that page. And what a pity we resorted to Latin at all for our listening standpoints! ‘Pre-‘ and ‘Post-‘ both begin with “P”, so why not go the whole way and call them “BAFL”! Before and After Fade … anyway, I digress. I acknowledge this terminology gotcha is bigger than A&H’s purview.

[SQuser]

If I understand your extensive explanations correctly, it’s about a single microphone, which should not be mixed into the mix of the sound system (PA), but only into a separate mix for a “stream” – correct?
If I misunderstood, then the following may not be helpful.

However, if this microphone produce a feedback into the PA, then it is definitely incorrectly included in this mix and simply needs to be removed from it.
To do this, select the PA mix LR on the right, hold down the Assign button on the left and now press the lighting Sel button of this microphone.
When it is off, the organ microphone is no longer included in the PA mix LR and will no longer produce any feedback.

Alternatively, you can keep the fader closed in the PA mix and set all channels to Pre Fader in the separate mix of the stream (it’s better not to use a matrix) and then create the best mix for the stream regardless of the PA mix.

By the way: If this microphone is closer to your SQ than the stage box on stage, you don’t necessarily have to wire it there, but can – like before – connect it directly to your SQ.
Of course it then has to be patched accordingly in the SQ.

And one more thing: Decades-old technical terms such PFL and AFL (= PAFL) should not be changed.

[SteffenR]

At least he takes just one key lesson!

I’ve tried to emulate the same configuration using the SQ-5.

But this isn’t possible, since these are very different systems.

[Author]

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