Quoting PA System in plain language

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12 Myths of PA System

Using a microphone
The are two major types of microphone - dynamic and condenser. While it’s true to say the speaker or singer should keep his mouth as close to a dynamic microphone as possible, condenser microphones are much more sensitive and close proximity to the source of sound may course over vibration, resulting in popping sound. Consult the on-site operator or technician on how should it be used.
Microphones do not magically make the speaker’s voice louder, when the operator increases the amplification to pick up a soft voice, the microphone picks up more of the background noise as well, which raises the risks of acoustic feedback (i.e. microphone picking up sound from the loudspeakers). Speakers projecting their voices on stage do not only make the life of sound operators easier but also better entertain the audience with a more energetic atmosphere.
Grasping the head of the microphone will muffle the sound, which is undesirable in most circumstances except beat boxing. Muffling the sound may force the operator to tune up the volume to compensate for the loss of sound level, which in turn increases the risk of acoustic feedback when the head of the microphone was unmuffled. The tail of most wireless microphones are usually fitted with transmitter antenna inside, covering it up may make the wireless signal weaker, inducing unwanted interface signal.
Speakers are generally assumed to remain on stage, and sound testing are done with such assumption. The acoustic response of the whole PA system could be totally different when one of the microphones are taken off-stage, risking unwanted acoustic feedback, particularly when the microphones pass right in front of the loudspeakers. Always inform the technician or operator in advance if the microphones are meant to be used off stage.
Tapping on a microphone are generally not harmful to the microphone (particularly dynamic microphone), however, it is simply annoying to the audience. The habit of tapping originates from “carbon microphones” that were the norm before 1920s. The carbon microphone contains granules of carbon inside, which required some tapping to even them out after it was left unused for a long period of time. Such microphones are rarely seen nowadays. The speaker should simply say “test” to test the microphone.
While it’s true to say the sound level of some instruments maybe loud enough to match the sound level of PA system, tuning a balance among the instruments and miss will definitely be a major challenge to the operator. Moreover, although the live sound may not require a certain sound source to be miked, a microphone may still be required for other purposes like broadcasting to other venues or recording.
Real drums look better when performing live, better engages the audience, generally sound better and are more sensitive to how hard the drummer is playing. However, they are very loud almost in any circumstances and poses a challenge to the operator in tuning an overall balance for the band. The other band members must have equally good equipment to mach the sound level of the real drums. Electronic drums will help achieiving a better balance in small venues.
Dual microphones are usually placed in front of the same source the purpose of backup or redundancy. Two simultaneous signals from the two microphones combine along the sound signal path can cancel out certain frequencies due to “microphone interference” or “acoustic phase cancellation”. A professional sound operator turns one of them on only.
Although wiring up the PA system appears to be straight forward as it’s the profession of any technicians and operators, it takes time for them to do the testing after all the wirings which is rather essential as the same equipment could behave quite differently in different environments. It also takes time for the operators to communicate well with the users and speakers on their needs and expectations. As general rule of thumb, reserve more time for better sound.
While it appears that last-minute addition of another equipment for playback or another microphone might requires one or two more cables only, additional elements disrupt the original settings which alter the frequency response of the system, thus increasing the risks of acoustic feedback. Advance well planning is the key to success of any events whether from a general or technical perspective.
While many have experiences in a university lecture theatre or a hotel meeting that the built-in PA system works perfectly without any technicians or operators controlling the equipment, such are only possible in a stable and controlled environment with the same usage over time, at the expense of general sound quality. In a one-day PA system setup of a dynamic nature, the sound operator will be pivotal in ensuring the overall sound quality in midst of the variables.
While it’s true to say digital mixers offer a lot more functions and options than their analog counterparts of similar sizes, with greater flexibility that brings convenience to the operator, such are largely irrelevant to the end user except the technicians moving and setting less equipment. Some digital microphones use the 2.4GHz band which is the same as Wifi and Bluetooth, which makes them susceptible to interference from more devices.