QuestionHi, I have a question about avoiding feedback squeal when using wireless mics. We recently added two wireless mics to our system and they produce a lot of squeal and I would like to know how to prevent it. We have an outdoor area about the size of a basketball court with speakers set up at one end of the 'court' and the audience usually sits all over the court except the end with the speakers. Sometimes the audience sites in a circle on the court with activities taking place in the center of the circle. We use this area for our youth club activities; often with a music background we perform songs, skits, dramatic readings, etc. We also need to be able to walk among the audience with microphones.
The equipment we are using is:
1) Audio2000 AKJ7050 - Professional Karaoke Mixing Amplifier with Digital Key Controls & Echo (http://snurl.com/mixeramp)
2) Audio2000 AWM6112 - Plug-In-N-RechargeTM VHF Dual Channel Wireless Microphone System (http://snurl.com/a2kmics)
3) Audio2000 ASP5210 - Two 300W Full Range 10" 2-Way Loudspeakers (http://snurl.com/a2kspkrs)
Everything works fine with this equipment but recently a friend bought some Radio Shack wireless lapel mics (http://snurl.com/rsmics) and when we use the mics they produce a lot of squeal. We are unable to walk around where the audience is seated without the squeal. I know we are in front of the speakers and that would normally be a problem but with the Audio2000 hand held wireless mics there is no squeal.
Do you have any suggestions? We would like to avoid spending a lot of money for lapel mics (in the event you suggest replacing the ones we have).
AnswerThings you should know about wireless microphones and feedback:
Good wireless microphones are not cheap and they are generally UHF which means that they operate at a higher frequency bandwith than a VHF unit and will exhibit fewer problems with interference while giving you greater range of distance from the receiver.
All speakers are subject to feedback if not used correctly or positioned correctly with respect to the microphone/s.
Feedback is a direct result of the electro-mechanical movement of air from an extremely sensitive electro mechanical device (the microphone) to an extremely powerful electro mechanical device the speaker. It will exist with any microphone and any speaker.
A good speaking microphone will be a unidirectional or bi-directional cardioid type microphone which translates into the polar pattern whereby it will pick up your voice at one end and reject some background noise at the other. There are many variations of this. Names associated are hyper cardioid, super cardioid, etc.
A speaker will also have a polar pattern specified by the manufacturer (as will be the microphone) whereby it's direct sound will propagate from the speaker on a horizontal and vertical plain.
The positioning of the microphone should conform with the polar pattern/s of the speaker/s of both the microphone and speaker patterns. The more speakers, the more microphones and the acoustical properties of a space will all affect the 'gain before feedback ratio' which refers to how loud the sound will go before a howl.
Then there is the frequency of the howl. This will be determined you whether the feedback loop is from the tweeter, midrange, woofer or subwoofer. Devices used to control this are manual equalizers (usually graphic) and/or automatic feedback suppressors which in effect are automatic equalizers adjusted to specific frequencies.
To complicate things a bit more, people who have little experience with the use of microphones tend to create feedback by doing the following: holding their hand in front of the microphone, placing it too close to their body or hold it near to or facing a speaker.
Don't think that my dissertations above is anything unusual concerning feedback. As a professional engineer with 40 plus ears of experience on and off the road, I can tell you that I can always learn a new tidbit of information on this subject.
If you follow some of the guidelines above you can logically reduce feedback problems.
Lastly, lavaliere microphones are made for professionals and the ones that really work cost more than your entire sound system. My advice is to stay away from the cheap ones because they'll be the first thing that gives you feedback.
