Feedback Destroyers ? Help please

[generalblue]

I am shortly to be involved in a project where 5 radio mics will be used in close quarters. The users will randomly move to different areas of the room addressing an audience of about 80 people, seated on 8 circular tables of 10. The room itself is 18 metres wide x 25 metres long x 4.5 metres tall with a flat ceiling. There is an existing amp, a front control mixer and 8 wall mounted Work 12" cabinet speakers. We are desperately trying to avoid feedback, interference and any other audio nasties. Whilst we can invest in new equipment and if necessary adjust the layout, we are trying to avoid the need for an on site sound technician with his mixer desk, because this 5 mic event will need to be held regularly over the next couple of years. Any help, advice, equipment recommendations will be greatly appreciated. We are trying to keep the equipment as user friendly as possible.

 

Chris

[sleah]

I've always understood that 'feedback destroyers' are only good (if at all ) for static mics.

A decent EQ would be a good starting point.

 

Better experienced noiseboys will be along shortly with some better advice :D

[Stan Hope-Streeter]

Whilst we can invest in new equipment and if necessary adjust the layout, we are trying to avoid the need for an on site sound technician with his mixer desk, because this 5 mic event will need to be held regularly over the next couple of years.

 

I do quite a lot of corporate seminar events.

 

Some of them are exactly of this type, but with just two presenters working the tables. They are some of the most difficult jobs I do. I have over 30 years' experience, and I need all my skill and expertise to get the high quality results they are paying me for. Plus the service and equipment of one of the best corporate production companies in the country.

 

Five presenters is going to be much harder. What makes you think you can do this without a sound technician?

 

____________

 

 

A feedback destroyer is an excellent tool if used correctly with a full understanding of its limitations. That means treating it as if it were a standard parametric EQ (think KT 410), but allowing it to find the frequencies and set the controls instead of doing it by ear. As with a manual EQ, having set 4 or 5 filters it reaches the limit of diminishing returns. After this it must be locked and left alone.

 

Despite what a lot of neopytes seem to think, these units can NOT be left to seek and destroy feedback during an event. Unlike a competent engineer who will take action on hearing the first sign of a ring, probably before the audience have noticed, they need several seconds of very loud feedback to set a filter and by then you will have lost your job.

 

When ringing out a radio mic, you can set the first few filters at the presenter's home location (lectern or whatever), then move the mic around and set a couple more in each of several alternative positions. This is the only case in which I ever use all the available fixed filters in a FBX.

 

And of course as with any EQ, clear it and start again if there are so many cuts that the mic sounds terrible.

[dbuckley]

Although I'm a big fan of feedback destroyers, it sounds like what you need is an auto mic mixer, look up lectrosonics or dugan.

[Bobbsy]

Well, I'm NOT a big fan of feedback destroyers but I agree with dbuckley that, if anything gives you a snowball's chance in Australia of making this work, it'll be an automixer, not the anti feedback box. Having 5 open mics wandering the room at random (which is what you'll get without having a technician there to fade down unused channels) would make this a tall order. At least the automixer will shut off the mics where nobody is speaking.

 

Bob

[ian hatch]

Just a thought, wouldn't a multigate do the same job as the automixer?

Might even be cheaper?

[chris4monitors]

I dont think gates will work without having an engineer there to set up the thresholds etc., as no 2 people will sound or project their voices the same. Even if this event is going to happen frequently with the same presenters, they will not necesaraly sound the same today as they did last week. I realy do think you need to have a engineer in to control these sort of events in every eventuality. I regularly do these sort of events, and my clients would never do them without someone being there to mix.

[Gareth Owen]

Personally, I'd suggest forgetting about buying equipment and spend the money on decent sound engineer. You can't do something like this automatically. You need ears not algorithms.

[generalblue]

I dont think gates will work without having an engineer there to set up the thresholds etc., as no 2 people will sound or project their voices the same. Even if this event is going to happen frequently with the same presenters, they will not necesaraly sound the same today as they did last week. I realy do think you need to have a engineer in to control these sort of events in every eventuality. I regularly do these sort of events, and my clients would never do them without someone being there to mix.

 

Chris, thanks for response and I hear what you say - maybe we will ultimately need to compromise on quality and hands on/in house limitatios. Do you have any faith/experience in auto mic mixers?

 

 

 

 

 

 

 

A concurrent post has been automatically merged from this point on.

 

I've always understood that 'feedback destroyers' are only good (if at all ) for static mics.

A decent EQ would be a good starting point.

 

Better experienced noiseboys will be along shortly with some better advice :D

 

 

Thanks mate. I am no technician, where do I start with EQ and does this involve ongoing knob , control adjustments?

[sleah]

[

 

I've always understood that 'feedback destroyers' are only good (if at all :huh: ) for static mics.

A decent EQ would be a good starting point.

 

Better experienced noiseboys will be along shortly with some better advice :D

 

 

Thanks mate. I am no technician, where do I start with EQ and does this involve ongoing knob , control adjustments?

 

I have just used knowledge I've pick up from here, I'm no expert but do have a good understanding of sound.

Basically, you set the mic level 'till it's just about feeding back, or ringing. Then go through the EQ channels one at a time dropping the level until the feedback stops. It's called notching out - or something like that :D

You may need to notch out more than one frequency.

 

It can also be done with a parametric equaliser, but I'm still sruggling to get my nogin round them! :(

 

If you search the Blue Room for 'feedback' you will find lots of useful hints and tips.

 

This may only help a little with your problem, as normally a sound engineer would be 'tweaking' away

[slim_mcslim]

These are what I have seen...

 

Shure Intellimix

 

As far as I know they are used in tv land, on programs such as question time & university challenge, however they are not used on their own, only in conjunction with a desk and a sound engineer.

 

I think your biggest problem will be your "work" speakers. We regularly do jobs, with 5 lavs and 3 hand helds, with the 5 lavs on presenters simultaneously presenting and talking from all round the room, walkin around, on and off stage, the mics have to be always open so that they can chip in comments, as well as 3 hand helds for audience Q&A. We do this in all sorts of rooms, but most of them are around 18m x 25m x 4m for audiences of 150ish. We do this with only 4 martin audio speakers, 1 KT graphic and a Mix Wizard 16:2, and it sounds fine, but it needs an operator.

 

Because no automatic gate system would be able to compensate for when the speaker wanders in front of the speaker with and open lapel mic, it needs a man (or woman) constantly watching their position relative to the speakers.

[lostinvegas]

I think you really need to hire a sound tech who knows what they are doing. Eq to prevent feedback takes more than turning the mic up till it feedsback and taking the frequencies out on an eq. Its very easy to kill the sound all together. The one thing your going to want it for the voices to come across the room clearly. It is something that requires someone with a certain amount of experience. Remember the room characteristics will also change with people in it, so something you eq in an empty room may very well change when you introduce an audience.

 

It sounds like you need to get a tech in and it will probably be cheaper than buying lots of gear anyway, especially if this is a 1 off event.

 

Chris

[TallMike]

I'll second hiring the sound engineer.

 

Another way to reduce the susceptibility (sp?) to feedback is to eliminate the lav mics - just use handhelds.

 

Mike

[Stan Hope-Streeter]

These are what I have seen...

 

Shure Intellimix

I use these (SCM810) for some events, but normally only for the Q&A sessions where you have all the presenters chipping in at random. I have also used them for feeding the PA in broadcast discussions.

 

A lot of these are installed in churches for unattended operation and they work well enough for the congregation to hear the service, but their expectations of audio quality are pretty low. They are also used in council chambers and similar venues. In these cases the mics are all in fixed locations so the EQ and rough levels can be set on commissioning the system. The sometimes widely varying levels between the mics are accepted, again because of low client expectations.

 

These units work fine for simple applications, but they are just basic mixers with no EQ. For a quality presentation, or any situation with roving personal mics, the automixer has to be used in conjunction with a "real" mixing console. A personal (lavalier) mic needs careful EQ for the presenter to sound natural, and this is different for each one. The presenters need a fair bit of gain riding, especially when they move close to a loudspeaker or to each other. All of this has to be done in real time and requires real channel strips and an operator.

 

A special insert technique is needed to interface the automixer with the console. This requires a console with postfade direct outs on each channel (watch out for this, a lot of otherwise excellent small mixers don't have them). These feed the automixer, set up for line level inputs, and its output is returned to a spare channel or group return with an inserted (or inline) EQ. In effect the automixer just becomes another mix bus.

 

You then have a choice of manual or automatic mixing depending on how you route the channels to the mix buses. With no bus selected on the channel strip (or with its selected group faded down) that channel become part of the automixed group. So you can mix the presentations manually, then crossfade selected mics to the automixer for the Q&A session.

 

If you haven't tried this, you won't believe how well it can work.

 

 

P.S. for Bob H.

Thanks, I've no idea why the message board software scrambles the quotes ....

[generalblue]

I'll second hiring the sound engineer.

Another way to reduce the susceptibility (sp?) to feedback is to eliminate the lav mics - just use handhelds.

Mike

Mike,

Why will handhelds reduce feedback susceptibility when compared to lav or tie clip versions?

 

A concurrent post has been automatically merged from this point on.

 

These are what I have seen...

 

As far as I know they are used in tv land, on programs such as question time & university challenge, however they are not used on their own, only in conjunction with a desk and a sound engineer.

 

I think your biggest problem will be your "work" speakers.

Because no automatic gate system would be able to compensate for when the speaker wanders in front of the speaker with and open lapel mic, it needs a man (or woman) constantly watching their position relative to the speakers.

 

Slim,

I am interested in your comment re the Work speakers possibly not helping the problem, please expand

 

 

Incidentally, cheers to all who have posted herlp and opinions. It is my first use of the site and the response is overwhelming. It warms the soul. Thanks again !!