Feedback prevention trick:Myth or Fact (live sound question)

[LazarusLong]

yay! can we finally put this BS to bed?

OP is satisfied, unless any technical explanations or test results are posted...

-c

I, for one, would like to note how much I enjoy your avatar. No idea who or what it is, but it is wrought from pure awesome.

[kevin206]

I'm so confused now. I used to set preamp gain by clipping then backing off a bit. Now I set it to 12 oclock and go for it. I sometimes have to make slight adjustments, but this allows me to get very quick and predictable mixes. I think I'll experiment tonight at practice. I also normally crank the power amps all the way and control overall levels with my master on the board.

On the topic of feedback, it's usually in my monitors. I never thought about the presence boost, but it does usually start at 4k. I roll all the lows out of my monitors and then ring out the system. I found that by doing this I can really crank the monitors to ear bleed levels and get a mix that cuts through stage volume. I love it when some guy tells me to crank his monitor then promptly tells me it's TOO LOUD. It's the only enjoyment I get from all the freebie things I do!
Anyone need a sound guy?

One more thing. I can be having zero problems, then a singer will put on a ball cap and the feedback will be uncontrollable. It's like a parabolic dish sitting on his head!

[chconnor]

I'm so confused now. I used to set preamp gain by clipping then backing off a bit.

(I assume you're referring to my post.) I don't mean to condemn that as a practice, since on a board without the ability to view PFL on a meter, that's what you have to do... I was just referring to my compulsive tendencies to set just the right input gain, which i'm told is often a lot lower than "as hot as possible", especially on prosumer gear which is apparently designed for average peaks at something like -18 (?) dBFS (dBFS for digital gear, but i understand that similar headroom is good for the sonics of prosumer analog stuff, too. Lots of posts about this issue on the net...). I was theorizing that reckless gain setting might be a contributing factor to the generation of the "myth".

Though now that everyone is mentioning the monitor side of things; i'm wondering if that in fact is the main source of the idea: since monitors are usually harder to hear from the FOH mixing board or require effort to check up on, turning the gain down and the fader up decreases the monitor levels (and even if you compensate with the send knob, you're probably cautious and may well end up not compensating all the way.)

I think I'll experiment tonight at practice.

I'd guess, especially for live sound, this issue may fall into the "not a big deal where the gain is as long as it's in a reasonable range" category...

I enjoy your avatar.

I'm flattered. :-) That's me, at a particularly scruffy stage of life, at a restaurant in New Orleans. Cleaned up in Photoshop, but the glint is 100% authentic!

[dsw]

I get feedback off my glasses sometimes, turn my head just right and a short whistle spits out...annoying at best.

[Scodiddly]

Here's what I did in between coats of lacquer this morning:



What you're seeing is three different measurement traces all overlaid, one trace each for gain knob at 25%, 50%, and 75%. Difference made up for with the aux send knob. Can't see a difference? Correct!

I used a Shure SM58, Mackie 1402VLZ, and with a Meyer UPJunior as the speaker for testing purposes. Cheap mixer, dynamic mic, so any "cheap mic pre" differences should have been obvious.

[chconnor]

But wait! There's a slight anomaly at 4.2k!

Nice one, thanks for posting. That's a pretty convincing graph.

-c

[Spindrift300]

I think where this "myth" may have started is that when you turn down the preamp gain, the gain to the monitor sends are also reduced, therefore giving the impression that preamp gain adjustment tackles feedback better than the fader. A true assumption but for the wrong reason.

Remember, the channel fader controls only what's going to the house mix, not the entire channel gain (which affects ALL sends and the house mix).

[Gentleman Jim]

I join the chorus who wish this thread would die, but I have to point out an inaccuracy. Not doing so would cause my internal organs to melt.

Spindrift300 wrote:

Remember, the channel fader controls only what's going to the house mix, not the entire channel gain (which affects ALL sends and the house mix).

Don't forget pre-fade/post-fade.

'Nuff said.

[Spindrift300]

Yeah, I see the subtlety of your clarification. PreFade/PostFade on the Aux Sends...most monitor sends should be set to "prefader".

My general assertion still stands: If you pull down the mic-pre gain, you're decreasing the send's gain regardless of whether it's pre/post fade....hence the possible origin of the "myth".

Now, shall we bring cheap transformerless mic splitters into the mix? OK OK, enough!