# How to rid the place of bad equipment



## dunnohowto (Jan 8, 2008)

I have a problem at one of the places i started sound work at and i might ask here.
ok, i have a system that always feedsback at you. multidirectional mics......


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## museav (Jan 8, 2008)

Okay, admitting you have a problem is the first step...

Can you tell us anything more about the situation? What is the application? What are you doing? What equipment is involved? What do you mean by 'multidirectional' mic? Are there any factors that seem to affect the feedback? The more information you can provide on the specifics of the situation, the greater and more relevant the help that can be provided.

Feedback is usually not just an equipment issue, it is an acoustic and overall system phenomena. Often the system setup, the relationships of mics and speakers, the physical environment and the operation of the system are more likely to be the cause of feedback than it being simply an equipment issue.


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## dunnohowto (Jan 9, 2008)

Ok the sound system is being used in a hall setting. It is being used for mass. There are 4 500W RMS 1000W max speakers powered by 4 power amplifiers from a yamaha mixer. We have 3 multidirectional speakers, one uni directional mic and two wireless mics. The current setup has two front speakers pointed at the back of the hall which probaly echos off the rear wall. The setup also has the rear speakers pointing at the stage at an angle. I dont know if it will cause problems. It also doesnt take too much gain and volume to cause feedback. Btw would adding an equaliser be better? 

Thanks


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## Eboy87 (Jan 9, 2008)

Where are your mics positioned in relation to the speakers? Are they in front of or behind? Are the rear speakers being used as monitors for people on-stage so to speak, or are they getting the same feed as the L-R mains? Also, when you say unidirectional mic, there's more than one kind of uni mic, i.e. cardioid, hypercardioid, supercardioid, etc. You wouldn't happen to know which kind of those it is, or make/model number.

An EQ will help to a point, but only if the person using it actually knows how to use it. True, they are able to notch out the frequency feeding back, but they can cause a lot more harm than good when someone "helps" by hacking up the curve. 

Definitely place the speakers ahead of the mics, if possible. Putting them behind will just cause the mic to pick up the sound from the mains and reamplify it, thus creating feedback. I have a theory on what might be causing feedback, but need more information on the placement of speakers and mics to confirm/debunk it. You wouldn't happen to have a drawing of the space, would you?

Also, try positioning the L-R mains on an angle down towards the seating.  THe church I worked in had a marble back wall, and the reflections could and would make the system get away from you if you weren't watching. But the main thing is keeping the mics behind the speakers.

Sorry if that didn't help at all


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## dunnohowto (Jan 9, 2008)

As you can see the picture is not to scale. Currently the placement of the system is a bit odd  but our budget doesnt allow for moving to the back  but need some help. btw i wouldnt have the brands of the mics on hand

Thanks


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## museav (Jan 10, 2008)

By 'multi-directional' mic, I assume you mean omnidirectional (although that could also define bipolar/figure 8 or hypercardioid) while the uni-directional is probably cardioid.

What is the purpose of the rear speakers? Since you indicated that they are getting the same signal as the front speakers, my first thought is that they are probably causing more problems than they are providing any benefit. And getting the front speakers to be aimed at the audience while minimizing the sound hitting the walls would probably help.

EQ may help, but there are certain things that may be related to your room and system that equalization cannot really address. For example, you might reduce the energy driving a particular room mode using an EQ but you can't actually fix the problem that way. And as Eboy noted, too often you end up with a conflict between the equalization necessary to correct problems and that equalization negatively impacting the sound quality. This is especially true with wide band, such as octave, equalizers since each band affects a fairly wide range of frequencies and problem frequencies often fall between two bands.

Is this a traditional mass with all vocals and speech with no stage monitoring or is it a contemporary mass with live music, instruments on stage, stage monitors and higher sound levels? How are the mics being used both functionally (lead vocal, choir, instrument mic, etc.) and physically (handheld, stand, overhead and so on)?

How big is the room and the audience? What are the room finishes? Do you get an echo off the rear wall even with the sound system off?


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## jkowtko (Jan 10, 2008)

Some thoughts/comments:

* rear speakers -- turn them off and see if the feedback goes away. If it does, then the rear speakers are probably playing too loud. Either leave them off, or you have to find a way to attenuate (lower the volume of) them. You can also EQ them to drop the feedback frequencies, but that requires an EQ -- do you have a 31-band EQ?

* omni mics -- the term "omnidirectional" is generally used over "multi-direcftional". Are these just handheld mics? If so, they should not be omni's -- they should be cardiod. How much budget do you have to buy new cardoid mics? orangecountyspeaker.com has great Shure SM58 (the "staple" mic) knockoffs for very little money .. you can get three of them, including shipping, for under $100 total. I have one and it sounds the same as an SM58 to me, and also appears to be pretty durable, so in my opinion a great deal.

* I also second the suggestion of the previous post to tile the main speakers down a bit. It can make all the difference in the world in killing reflections and reducing feedback.

Please let us know what budget $$ you have for this -- it will help with the suggestions


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## Eboy87 (Jan 10, 2008)

I think we're all in agreement that the best starting solution is to lose the rear speakers, and to angle the front ones down. 

It would really help if you could get us make/model numbers for the mics. If it's for a church service, I'd be willing to bet they're 58's of the wired and wireless variety, or even a crown PCC. 

Also, to reiterate what Museav said, a few more details about the room itself would help out. I think it's an acoustic issue, so I don't think an EQ is really absolutely necessary at this point. Electronic solutions to acoustic problems usually don't end up well, especially in churches.


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## dunnohowto (Jan 10, 2008)

Thanks for the rear speaker cut suggestion. We have a congregation of about 200-300. The walls are made of wood with holes drilled in to it. The microphones sit on the lecturns and one on the altar. The room size i'll probaly say, i'll go check check, will be about 45m*20m and in the US thats about (don't mind the conversions) 147ft*65ft. btw since this is now an acoustics problem i'd like to show that the ceiling is low 3m 9ft and is angled then is about 8m 26ft as shown by this attachment. Theres a choir but theres no band, the organ does it all. It's more the traditional mass. We do have monitor/foldback speakers but their not used a lot. I currently don't have an 31 band EQ but the amp has a knob on it so i can turn it down or off, so i'll try down and then off the following week. I'll also try and get a budget for it. I also find that with the sound off theres a echo of people talking, but thats cause they talk so loud.


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## avkid (Jan 10, 2008)

dunnohowto said:


> The room size i'll probaly say, i'll go check check, will be about 45m*20m and in the US thats about (don't mind the conversions) 147ft*65ft.


Hmm..you might actually need delays in a room that size.
I think you should consult a professional.


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## Eboy87 (Jan 10, 2008)

You don't need delays. That adds a whole new set of problems. For 300, the L-R mains will do fine.


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## avkid (Jan 10, 2008)

Eboy87 said:


> You don't need delays. That adds a whole new set of problems. For 300, the L-R mains will do fine.


I meant zoned, not delayed.
Speakers recessed into the ceiling with a system processor that has been set up by a professional.


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## dunnohowto (Jan 10, 2008)

Ok can you try to explain that to me a little better

Thanks


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## avkid (Jan 10, 2008)

dunnohowto said:


> Ok can you try to explain that to me a little better


What you need is a professional A/V installer.


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## dunnohowto (Jan 10, 2008)

Ok. Well we have a budget  Would changing all of the mics to SM 58 be better (less feedback)?


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## avkid (Jan 10, 2008)

dunnohowto said:


> Ok. Well we have a budget  Would changing all of the mics to SM 58 be better (less feedback)?


Alright, that question sealed the deal.
You are in way over your head.
I will contact you.


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## cutlunch (Jan 11, 2008)

Dunnohowto
Could you please explain something for me about the rear speakers. Are they actually right at the back of the room behind the last row of seats? Or are they part way down the rows moving towards the front? Roughly how old is this installation?

How long has this feedback been a problem? If the feedback wasn't always there try and findout what has changed. A basic guide for microphones is to try and keep them behind the speakers.

Let us know how you get on with disconnecting the rear speakers.


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## dunnohowto (Jan 11, 2008)

Hello,
Ok the speakers are installed at about the second last row of seats. The installation was about 3 months ago. We usd to have another sound system but they retired it. Meanwhile we'll have to wait till the 13/1/08 when we have a mass to test it.


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## cutlunch (Jan 11, 2008)

dunnohowto said:


> Hello,
> Ok the speakers are installed at about the second last row of seats. The installation was about 3 months ago. We usd to have another sound system but they retired it. Meanwhile we'll have to wait till the 13/1/08 when we have a mass to test it.



Who did the install? If it was professional company you should be going back to them to sort it out.


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## dunnohowto (Jan 11, 2008)

It was a DIY install


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## museav (Jan 11, 2008)

So it's a 147' deep by 65' wide room with a 9'-10' ceiling and the system is used primarily for speech. I can see why the existing system is problematic and this sounds like a great application for a distributed system.

With the relatively large room you probably have to have the front speakers quite loud to get sound to the back. However, the low ceiling prevents you from getting them up higher to where you can get good coverage of the room and almost certainly results in a lot of sound hitting the ceiling and rear wall. This system was probably way down in level and had poor intelligibility further back in the room. Based on what I've seen elsewhere, the rear speakers were quite likely an attempt to address this, but just as in almost all of those other cases, ended up causing as many or more problems than they solved.

It also seems that you have primarily mono sources but a stereo (and with the rear speakers almost a quadraphonic) configuration, meaning that you have the same signal coming from multiple speakers. This results in all sorts of interactions in the listening space as at any one point the listener is getting the same signal from four different sources but with the four signals arriving at different times and with different levels. These timing and level relationships differ at every point, meaning you get different interactions everywhere, some of which may be rather undesired. For speech, in some ways you may actually be better to have it come from just one speaker.

A distributed system uses many small speakers distributed throughout the space with each speaker covering a small are. This places the listeners closer to the speakers and allows the sound from the speakers to directed at the listeners rather than at where they aren't. This can not only reduce the levels and echoes on the stage, and thus help address your feedback issues, but could also improve intelligibility so that people better understand what is said.

Unfortunately, many people seem to look down on distributed systems, perhaps seeing them as old technology or relating them to inexpensive installations they've seen. However, none of the physics involved has changed and with some of the current processing and high quality ceiling or small speakers available, they can be very effective. If you want to get real fancy, and have the budget, you could even look at a distributed system with electronic acoustical enhancement systems (LARES, LCS VRAS/Meyer Constellation. ERES, etc.) that can help emulate different acoustical environments, letting the space sound like a lecture hall or a cathedral at the push of a button.

Another alternative would be to use one of the steerable arrays that are now available. such as the Duran Audio Intellivox or Renkus-Heinz Iconyx. These use advanced digital processing to control and steer the speaker's vertical coverage, in some cases into a very tightly defined pattern that can help keep the sound aimed at the audience.

If you don't have a large budget then I would guess that a properly designed and installed distributed system might be the best approach for this application.


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## dunnohowto (Jan 12, 2008)

So the problems coming from the fact that 1. the speakers are not positioned correctly meaning that there are so many other problems. Would using Yamaha's SFXs for one of the halls be better? But won't that cause futher feedback? I was thinking we should re-aim the speakers at the rear and turn down the rear speakers after they have been re focused. But meanwhile I am going to shut off those rear un focused speakers which shoot on to the stage And..... I'll turn up the front speakers


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## museav (Jan 12, 2008)

It would take physically being in the room to really make any really accurate assessment of the situation. The preferred approach for this type of functional application is traditionally a flown center cluster. However, the low ceiling height here makes this quite impractical.

You are simply going to have difficulty getting good coverage of the congregation, good intelligibility for them and good gain before feedback on stage in that space using traditional full range speaker cabinets. Attempts to address any one of these areas may negatively impact the others, for example adding rear speakers to address the coverage and drop off in level at the back of the room is most likely hurting the intelligibility and feedback.

About all you can do without a dramatically different system approach is to keep playing with various combinations of speaker and microphone locations and aiming to try to optimize what you have. It may even end up that a single speaker off to one side and aimed at the person furthest away in the opposite corner of the room with the system run at as low a level as practical gives the best result.


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## avkid (Jan 12, 2008)

museav said:


> The preferred approach for this type of functional application is traditionally a flown center cluster. However, the low ceiling height here makes this quite impractical.


Nah, just prohibitively expensive.


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## dunnohowto (Jan 12, 2008)

Ok I'll try it today. Thanks

I'll ask if there are any other problem


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## David Ashton (Jan 12, 2008)

I might suggest selling the rear speakers and amplifier and buying some heavy curtains for at least the back wall.
The sound can then travel in waves down the hall and be absorbed into the back wall, not reflected back. 
I find that thinking in terms of water waves in a pool can give a visual idea of what is occurring.
I also find that a few curtains can have a dramatically positive effect on the acoustic in a way that no amount of electronics can.
Acoustics is as much art as science and it is often easier to play around with different options in the venue to see which works best, trying some curtains for example is a low cost option to look at.


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## Hughesie (Jan 12, 2008)

dunnohowto said:


> It was a DIY install



your name says it all, get a pro, or leave the country now phil is chasing you


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## dunnohowto (Jan 13, 2008)

Yes Yes Very funny 

If Phil's chasing me then BAIL!!!!


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## avkid (Jan 13, 2008)

dunnohowto said:


> If Phil's chasing me then BAIL!!!!


I'll stop when you get a proper contractor in there.


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## dunnohowto (Jan 13, 2008)

I believe that we have found the problem 1. There was nobody controling when i started2. the levels were too high 3. There were multiple mics oncausing echo 4. A mic in front of the speaker  for singing \ 5. Not a good place to control


Solutions
1. Took over
2. Adjusted them as they went although now that the guy in charge is back says leave it until theres feedback (who would want to do that?!?)
3. turned on nesscary ones when needed
4. Notified the head of the choir to move the mic
5. Trying to move it but it won't happen, wish they built a control room when they built the hall


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## avkid (Jan 13, 2008)

dunnohowto said:


> 3. There were multiple mics on causing echo


How exactly does that work again?


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## dunnohowto (Jan 14, 2008)

well it pics up the output to a non feedback level and puts it out


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## jkowtko (Jan 14, 2008)

dunnohowto said:


> Solutions
> 2. Adjusted them as they went although now that the guy in charge is back says leave it until theres feedback (who would want to do that?!?)
> 3. turned on nesscary ones when needed


As the FOH mixing board operator you should in general turn mics off when they're being used. The only exception might be cardiod mics which are not directly in front of a noisy area. But omni mics, definitely, never just leave them on. Part of live mixing is continually adjusting input volumes and EQ, so if you have to sit their intently with your fingers on the faders, that's normal.


dunnohowto said:


> 4. Notified the head of the choir to move the mic


If this was an omni mic, it cannot be anywhere near the front of a speaker unless you have a good EQ ready to squash feedback frequencies. 


dunnohowto said:


> 5. Trying to move it but it won't happen, wish they built a control room when they built the hall


If you can't get the sound board into the acoustic center of the room, you should at least understand how the center of the room hears the sound compared to where you are on the side. I would suggest playing a familiar CD and walk around the room to understand how it sounds in different place. Try it softly, then try it really loud. See if it's too soft or too loud in some places, etc. Then you can mix for the audience even though you're in a different location.


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## dunnohowto (Jan 14, 2008)

The one for the choir is a wireless microphone (a rather sensitive one) 
I'll guess I'll have to test the speakers with the music. But who knows how to deal with someone who has to take over the show and have feedback squeeling in your ear for testing


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## avkid (Jan 14, 2008)

dunnohowto said:


> well it pics up the output to a non feedback level and puts it out


That's not really echo.


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## dunnohowto (Jan 14, 2008)

Ok its reminance??


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## Eboy87 (Jan 14, 2008)

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.

As a general practice, whenever I'm mixing, if a mic isn't being used, I mute it. It gets fun when you have to keep track of a script, ride faders and EQ, and worry about unmuting things when your board doesn't have lights that tell you when a channel is muted


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## dunnohowto (Jan 14, 2008)

Thanks for that. I will turn off any un used mics and fix all those litlle bugs well problems.


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## jkowtko (Jan 15, 2008)

Eboy87 said:


> As a general practice, whenever I'm mixing, if a mic isn't being used, I mute it. It gets fun when you have to keep track of a script, ride faders and EQ, and worry about unmuting things when your board doesn't have lights that tell you when a channel is muted



Our CFX-20 does not have mute lights, and subsequently I will never mute an input channel during a show ... too many times I have been caught wondering why I can't get sound out of a channel, only to remember 30 seconds later to check the mute. Even two seconds later and you've already dropped one or two of your actor's lines! Having "discoverable" visual indicators are key to convenient and error-free operation. 

If you don't want to drop the fader all the way because it will get lost in the rest of the turned-off faders, then keep it up half an inch so you know which one it is. At -40 or -50db no one will hear anything out of that channel. I will tend to do this for scene changes, i.e. bump up all faders a bit so I know who's coming on in this scene.

Also, get into the practise of color-coding your faders to match the color-coding on your Excel spreadsheet mic map (which you should make), or script notations. Use spike tape or colored console tape if you have it (findtape.com), second choice is colored highlighters on console, gaff or masking tape. This "best practice" works wonders for my sanity ...!


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## avkid (Jan 15, 2008)

jkowtko said:


> Our CFX-20 does not have mute lights, and subsequently I will never mute an input channel during a show ... too many times I have been caught wondering why I can't get sound out of a channel, only to remember 30 seconds later to check the mute.


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.


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## museav (Jan 15, 2008)

Eboy87 said:


> 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.


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## Eboy87 (Jan 15, 2008)

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.


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## jkowtko (Jan 15, 2008)

avkid said:


> 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


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## dunnohowto (Jan 15, 2008)

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.....


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## avkid (Jan 16, 2008)

dunnohowto said:


> 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?


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## Eboy87 (Jan 16, 2008)

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


Captain literal has struck again .


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## dunnohowto (Jan 16, 2008)

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?


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## avkid (Jan 16, 2008)

Eboy87 said:


> 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.


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## avkid (Jan 16, 2008)

charcoaldabs said:


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


I have 38 of those buttons I can press.


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## jkowtko (Jan 16, 2008)

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.


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## museav (Jan 16, 2008)

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.


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## jkowtko (Jan 16, 2008)

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.


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## dunnohowto (Jan 16, 2008)

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.....


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## Chris15 (Jan 17, 2008)

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...


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