How to rid the place of bad equipment

[museav]

I think you mean resonance. In a sense, yes it is, but it's a bit more complicated than that. It's a combination of frequencies near the mic's resonant frequency put out by the loudspeakers. The mic picks up that signal, in a way amplifies it (resonance, but it's not really amplification), sends it down the signal chain to the amps, amplified once again, goes to the speakers, wash, rinse, repeat. At least that's the watered down version I was given a long time ago. I'm sure someone more knowledgeable will be along to correct me.
Therefore more open mics on stage means a greater liklihood of something feeding back.

This is somewhat two different issues. Feedback occurs whenever the system acoustic loop gain exceeds 1 (0dB). The loop gain depends on the physical relationships, environment, patterns of the devices, response of the devices, etc. Since some of these factors differ with frequency, the loop gain can also differ over frequency, this is why the system may be more sensitive at certain frequencies. The Yamaha Sound Reinforcement Handbook has a pretty good presentation on this.

The second issue is NOM or number of open mics. Every time you have an additional mic picking up the same signal, they combine for an increased level. So multiple mics potentially picking up the same sound raises the resulting summed level by a factor of 10log(NOM), or 3dB for two mics, 6dB for four mics, 10dB for 10 mics and so on. Since this is gain, it raises the loop gain. A system that is stable with one open mic may become unstable with additional open mics.

So muting unused channels both makes that particular path loop gain 0 (muted) and minimizes the potential additive effects of the NOM count on the overall loop gain.

FWIW, NOM can also affect the mix. If you have 8 mics run to one group and all the mics are at 0dB from the same source the resulting level for the group is +9dB, something you may have to account for in setting the board levels and gain structure. Remember that just because the input is not clipping and the output is not clipping does not mean the signal is not clipping somewhere between the two, it may be occurring before a fader at a point that is not monitored (commonly on a group, aux or matrix bus). This can even be an issue with a console's outputs, if the faders are at -20 and the levels show 0 (many consoles are calibrated such that 0 on the meters is actually a +4dB output) then that may mean that the level on the bus itself is +24dB and might be clipping.

 

[Eboy87]

Thanks for the long explanation. I left my Yamaha book back in Chicago over break, so I couldn't reference it whilst making my post. That all does make perfect sense, though it took me a few times reading it.

 

[jkowtko]

I don't even look at the lights most of the time, I just feel the mute switch position.
But then again, not everyone is that hardcore.

I guess I should also better qualify the practice I use -- to date I have only run vocals and pit mic, etc ... no band instruments. For instruments -- I imagine after sound check when you have your various band mics at their appropriate levels, unless you have a board with motorized faders you will probably mute those channels rather than touch the faders. I guess this is where mute groups come in handy as well

 

[dunnohowto]

Well bad thing no mute buttons on the yamaha mg24/14fx mixer Wish we had then we wouldn't have to cut the mains if we got feedback. Which would be conveinient if you had a person in charge who said don't touch the mixer even when there was resonance or even feedback.. though yes the chain of command thing but i mean would you take you over over a chaos situation where you were standing behind the board..... So I did... And... I felt happy.....

 

[avkid]

Well bad thing no mute buttons on the Yamaha mg24/14fx mixer

Yet again, you need to get professional help from a real A/V tech.
What do these things do again?

 

[Eboy87]

In a sense, he has a point; those aren't "mute" buttons, they're "on" buttons.


Captain literal has struck again .

 

[dunnohowto]

Yes I know that you can do the mute thing with them but you need the really quick mute button... cant have a super long cut to allow feedback to come through.... btw how do you insert an image in a post?

 

[avkid]

In a sense, he has a point; those aren't "mute" buttons, they're "on" buttons.
Captain literal has struck again .

Somebody needs to slap Yamaha for that design decision.

 

[avkid]

"What's a sound op's biggest turn-on?
Channels 1 through 16."

I have 38 of those buttons I can press.

 

[jkowtko]

You know, I hate to say this, but I think Yamaha got it correct and it's the 40 years of analog boards that had it backwards.

Mute buttons show a light only when the channel is off. Yamaha's 'on' buttons show the light when the channel is on. When you have 16 or 32 faders in a row and are using only a handful in a given scene, isn't it easier at a glance to see which lights are on rather than off? This is a typical UI issue that I deal with in software -- discoverability -- and Yamaha has applied it here.

Fyi, the Cadac J boards also have a light that indicates the fader is not completely down -- again a visual indicator that you may have signal going through the channel.

In general people think lit lights mean something is on, and non-lit lights meaning something is off. So under that train of thought, mute lights are the opposite of what you would normally think.

Obviously the majority of the FOH operators who are used to mute lights for the last 40 years may not have an easy time with the 'on' lights, but that's just a retraining issue.

 

[museav]

In many live sound application you have more channels active than you have muted, running sound for a band you'll often only have a couple of channels that are muted. Even more important, the assumption in operating a console should almost always be that something is live unless you know for certain otherwise. If a mute indicator burns out or malfunctions then I'd rather that I think something is live when it is actually muted than believing that it is muted when it is actually live!

A somewhat related issue could apply to mute groups, do you have "on" groups instead? Do you have a mute group lit when it is active or inactive? Seems much simpler to keep everything the same, muting is muting and any mute is active when lit.

 

[jkowtko]

Yeah, I hear you. Running musicals is pretty different than bands then -- I'll have a lot of mic input channels assigned but only a few actors at a time on stage. So if I'm muting channels I'll likely have most of the channels muted at any given time. Therefore in this situation an "on" indicator is easier to see.

Maybe Yamaha was catering to the theater industry when they made this design decision? Interestingly, their mute grouping is still called "mute" grouping, although there are no mute switches anywhere on the board (at least the 01v96) ... there are just ON switches.

Another way to skin this is to have a two-color indicator light ... always showing either green or red. Then you could call it what you want, and either way you'll have the indicators you need.

 

[dunnohowto]

Well I also do this stuff at school. On our mixer at school its got a mute for all 1-16 channels but not on the new mixer at church. Funny seems old is somewhat better than new in a way.....

 

[Chris15]

Not when you want things to get really interesting, look at something like a PM1D... It has on switches on the inputs, but mute switches on the outputs...