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[Matt Sherer]

I posted this in another thread and couldn't delete it so sorry about the cross posting.

We have a large table in the Alumni Center with 12 EV wireless mics, 12 EV speakers and 2 wireless EV lavs. The are all going to a Lectrosonics DM1624 DAP. Each speaker is on it's own zone. The theory is when a mic is active that the speaker over that area drops in level to avoid feedback. We are also using the ADFE function of the Lectrosonics DAP. This system has been a hit and miss as far as functionality goes. Sometimes it works well and other times there is terrible feedback. We normally use Shure wireless mics but EV had a solution that fit this unique need. The association did not want wires running across the table (the table is cherry and walnut and is 20'x35'). This room is used for Alumni Association meetings and they rent the space out for other various large meetings.

Anyone have any ideas on what we could do to fix this problem? I've pretty much ran out of ideas. Let me know if you need more information. Thanks a bunch!

Matt

[Rob Timmerman]

Does the system work as designed?  Have the wireless table mics gotten rearranged by accident, so that the speaker above them isn't the one ducked by the mic?

[Matt Sherer]

The wireless table mics are marked.  The table was built in sections so it made it easy to make sure the mics were placed in the correct locations but that's not to say they are setting it up wrong.  They call after a problem, I go over set it up and haven't found anything wrong.  The system is working as it was designed.  Several times we had 36 people in the room to simulate a full meeting and nothing happened.  Yet they are still having major problems.      

[Rob Timmerman]

Can you be at one or more of the meetings and see if something odd is happening in the way of use?

If you can't duplicate the problem, this likely means that one of a few things is happening:

The system is being used in a way that you didn't anticipate or duplicate in testing (passing mics around, perhaps?)

The problem isn't feedback, but an external interference that sounds like feedback (RFI between mics, or perhaps from GSM phones?)

You have a problem with your mixer.


I'll also venture to guess that the problem is with the lavalier mics, and not the table mics, as the table mics are ducked.  Another possibility is that the automixer is attempting to increase the gain on one or more channels by too much, sending the system into feedback.  I'm not that familiar with the algorithm that Lectro uses, so that last one is a stab in the dark.

[Karl Winkler]

Rob Timmerman wrote on Tue, 27 March 2007 14:15

Another possibility is that the automixer is attempting to increase the gain on one or more channels by too much, sending the system into feedback.  I'm not that familiar with the algorithm that Lectro uses, so that last one is a stab in the dark.

We'd be happy to help with this if you can contact us and we can have the opportunity to learn more about how the system is configured. Gordon Moore is an expert on these types of systems, and is a certified installer (CTS) via InfoCOMM. He can be reached at 800-821-1121 ext. 117.

Our automixers never add gain, only distribute the total power based on the NOM (number of open mics). If only one mic is active, then it gets full gain. If another mic receives a signal, then the two mics share the power, based on which mic has more signal, thus the gain is reduced on the two mics, from full level. The mics are not gated, but instead the algorithm smoothly changes gain.

It is of course possible to set the system up so that it does not work as it is supposed to, so that's why we would need to know more about it before we can figure out what's wrong.

-Karl

[Matt Sherer]

That sounds like a good idea to me.  Thanks!

[Brad Weber]

I don't know the size of the room or relative arrangement of the speakers and mics, but have you thought of setting up a mix minus array?  Instead of muting or ducking a speaker when a mic in that area is active, would it be feasible to simply not route the affected mics to that output (or to include them at a lower level) and to rely on natural voice to provide the reinforcement for the nearby listeners?

Essentially you setup a separate mix for each speaker, one that excludes and/or includes at a lower level any mics that speaker affects.  A typical setup might have a mic right under a speaker not in that output mix at all, the next closest ones are down 6-10dB, the next 3-6dB and so on.  I have found this much more effective than outputting ducking/muting in boardroom type applications and a great benefit of matrix DSP devices.