Kingdom hall or Church Sound Systems - Avoiding Feedback Recommended Microphones: Main | Handheld | Loop System
Feedback and Volume Issues - Every sound system has an acoustical limit to the amount of microphone volume before feedback (the uncontrolled howl / whistle sound) that can be achieved. Some systems have expensive devices to try and reduce feedback - Sabine, Beheringer or a Frequency Shifter but even if your system has one fitted, it still has an acoustic limit above which no increase in volume is possible. In the case of the Frequency Shifter (fitted to Electronic Services amplifiers), the whistle / ring sound is replaced by a tremulant warbling sound which gets progressively more apparent as the gain is increased making the spoken voice sound quite emotional at times and totally destroying the quality of any music.
Feedback Avoidance - Feedback is entirely the product of a slow, uncaring or untrained sound operator and should NEVER EVER happen - He /She has sole and ultimate responsibility.
Quite simply, if you turn ANY sound system microphone up too high, it WILL feedback in an explosive manner. However, there are ways to avoid completely or reduce the onset of feedback:
- System Design - Use cheap microphones, a nondescript amplifier and poor speakers in a cold room with no soft furnishings and it will do nothing BUT feedback! Improving each element will make the system better such that top quality kit with a flat frequency response, controlled feedback frequencies and an alert, trained operator can produce alarmingly loud sounds ie live rock concert! Note though that the price difference between the two systems may be £30000 or even more.
- How to avoid feedback on your system - If you are experiencing moderate or bad feedback, the single biggest change you can make is to Replace the Operator!. After that step (seriously) you can look at each element of the system in turn. Consider buying an automatic microphone mixer to assist your human one - it will work faster and more reliably though it will not replace him / her entirely.....Automatic Microphone Mixer
- Training - Are the microphone handlers trained? Will they make sure that the microphone is the correct distance from the mouth of the user and at a slight upward angle pointing at the chin (not ear, nose, hairline or ceiling)? Are the users so timid that they whisper making it impossible to pick up what they say? Training microphone handlers and users will make a big difference. Has the system operator been allowed time to get used to the system, listening critically to the sound as the microphone volume is increased very slowly and learing to distinguish between a stable system (sounds normal) and one on the verge of instability where the sound goes "hollow" and rings slightly after each word?
- Have the microphones been dropped or damaged? Even a minor knock can change the frequency response and increase feedback. Usually there is a change in sound quality as well or you will find that one microphone feeds back whilst an identical one works OK. Radio microphones when dropped tend to do this and since repairs are expensive (£60++) try not to drop them.
- Are the microphones the right TYPE? Omnidirectional microphones pick up as much sound from behind (unwanted sound) as they do from the front. Cardioid, Super Cardioid, Rifle or Microline (especially) pickup patterns are much better for stage use though you should be aware of the drawbacks with each type. For example Super Cardioid pickup patterns might reject sound from the back very effectively but they are also very susceptable to handling noise and tend to emphasise "P" and "B" consonents explosively through the sound system especially when used close to the mouth. Seek advice on this BEFORE buying the wrong types! Remember that Microline elements tend to be extremely thin so not only do they pick up well with minimal feedback, but also have a very small visual impact unlike Cardioid dynamic microphones. Without doubt, the best microphones to use on a platform are ....these.
- Microphone Cost - Buy a cheap £15 dynamic microphone from xyz electronics and you will get feedback. Studio microphones cost in excess of £1500 EACH!! No doubt your requirements are somewhere inbetween and a good quality microphone with flat frequency response WILL minimise feedback.
- Speaker Cost - Like microphones, cheap speakers will promote and enhance feedback. If you fit a large number of cheap speakers in a ceiling array (LISCA or distributed array) this will improve the system over a smaller number of speakers. However fitting £5 speakers (as is common practice) in any such array will not produce good sound as each speaker will have a frequency response that looks similar to the Himalayas on a clear day and no amount of equalisation will flatten all the peaks! It is much more difficult to specify good quality speakers than it is microphones because the costs can be very much higher. However, using a quality Point Source speaker in a LISCA type housing and specifying enough speakers would be the best option for a relatively low level suspended ceiling type installation. Improvements could be made to this by using a number of higher quality speakers (ie Tannoy I8) and a delay network dependant on size of hall. Indeed two really high quality speakers (T300) and an associated EQ would probably be the best solution for a smaller hall of square proportions but the cost would likely be at least 6x higher than a distributed ceiling speaker layout.
- Have the speakers been damaged? Feedback is an uncontrolled output from the system and can damage the loudspeakers, even tearing the delicate cone structure. This can modify the frequency response and again cause feedback. Usually there will be some strange noises eminating from the speaker itself - rattles or groans!
- Have the tone or EQ settings on the equipment been changed from how they were originally set up? If so, your system will likely have deteriorated and may need re-adjusting. Note that setting these controls accurately is a specialist job by a highly qualified engineer using proper analysis tools - it cannot be done accurately by ear.
- Try reversing the connection between amplifier and speakers - Can have dramatic effects.
- Phasing - Is all the equipment properly phased? Speakers especially need to be wired up properly and like batteries - have a polarity which MUST be observed otherwise some speakers will push the volume of air whilst some will pull the same volume with unpredictable results. Likewise microphones must be wired to give the same output phase. The only way to guarantee this is right is to use a proprietry tester or call on the expertise of a qualified installer Speaker Wiring.
- What about the acoustics of the building? - Feedback is additive and every little improvement helps to reduce it. For the main platform area make sure that there are no hard reflective surfaces at the back. Feedback occurs when sound from the loudspeakers manages to find a way back into any microphone that is in use. A hard surface reflects sound like a mirror so do everything you can to eliminate hard surfaces especially at the back of the platform or stage area. Thick curtains arranged in deep folds will help, but two layers are better. If you coat the hard walls with sound absorbing tiles and then curtains this will be better still. Don't forget that floors (especially concrete ones) will also reflect sound in unwanted directions so fit a thick underlay and deep pile carpet. Exposed hard walls and especially large glazed areas will also degrade feedback performance.
- Temperature - The colder the room, the worse the feedback. So if your system is on the verge of feedback all the time, simply turn the heating up.
- Operational Tips: - Keep all unused microphones turned OFF or at least down from their normal level. Follow the action by having just ONE microphone at full gain - the one that is being spoken into. As the action moves, follow it. Automatic microphone mixers do this much better than any human can and costs are now reasonable.....Automatic Microphone Mixer
Be aware that pointing the microphone at the speakers WILL cause feedback - train the operatives NOT to do it.
Holding a microphone 12" or more away from the mouth is a recipe for feedback - turn up the gain as high as it will go without feedback or unatural sounds and have the common sense to realise that you just cannot get any additional volume. Go and MOVE the microphone closer if the sound is not loud enough.
Timidity - Some people are nervous about using microphones and either whisper or strangulate their voice so that a high pitched squeak is all that they produce. In this case, the microphone must be even closer to the mouth to pick anything up at all. Coaching and training of the offending person is the only answer - after all, what is the point making the effort to speak if no-one can hear the comment?
- If all else fails! - Install one of these in the microphone mix only. Giving up to 12dB of additional gain, this unit can transform an average sound system into a star performer. In borderline systems, two or three extra dB of headroom can make a HUGE difference to the sound quality, especially if used within an auto mixing environment. This unit is different to most other 'feedback eliminators' which seek to set realtime notch filters and are at best, marginally successful.
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