[Conference Microphone] How to choose a conference microphone in detail to explain the selection and use of conference room microphones
The sound in the conference room usually needs to be bright, clear, and moderately loud. When setting up the venue, the speaker cannot go to the venue to audition. Therefore, in order to achieve a bright and clear sound effect during live sound reinforcement (the loudness is just right but not howling), there is a certain knowledge in the selection and placement of microphones.
1. Selection of microphones
Since different microphones have different effects on different sound sources, it is necessary to go deep before selecting microphones. Learn about the technical characteristics of microphones, how well they function, and where they are suitable. When selecting a microphone, in addition to considering the sensitivity of the microphone, the matching of the output impedance and the input impedance of the mixer and other electro-acoustic indicators, it is also necessary to consider the directivity characteristics, frequency response characteristics and the shape of the microphone in the conference room.
In terms of directivity, supercardioids are suitable for farther distances, cardioids are suitable for most situations, and non-directional microphones are not suitable for speech microphones, because the simplicity will cause echoes. In addition, in the conference room, it is necessary to select a microphone with suitable directional characteristics according to the planning of the speaker. For a sound reinforcement system with a centralized or semi-centralized design, the directivity of the microphone should be cardioid or supercardioid; for a sound reinforcement system with a decentralized design, a cardioid microphone should usually be selected. The reverberation time of the hall is not too long, and non-directional microphones can also be selected; when the sound source is very close to the microphone, the near-talk cardioid microphone can be used to eliminate the near-talk effect.
As far as the frequency response characteristics of the microphone are concerned, the microphone with a slightly lower static technical target and better transient characteristics is usually better than a microphone with a slightly higher static technical target and poor transient characteristics. The microphone is better. Two, a microphone with a uniform and smooth frequency response from low frequency to high frequency is generally better than a certain frequency band, because some good ones can also cause howling.
In addition, dull accents are often exacerbated by too close a microphone. Of course, it can be compensated by electronic proofreading (in the sound transmission circuit), which has no effect on the voice that the audio frequency is too low, but there are constraints on the front and rear movement, and the distance between the speaker and the microphone must be kept stable, otherwise there will be low frequency components. changes, and the ratio between direct sound and reverberation sound (in a sound field where the acoustic condition is “lively”) changes.
Mikes that peak heavily between 6000-9000Hz can make sibilant accents more sibilant. Of course, proofreading can also be done electronically, but at the cost of bringing dead spots at the peak. Therefore, it is usually not necessary to use a high-quality microphone in the conference room, and a microphone with a smooth response is sufficient. As far as the internal structure of the microphone is concerned, dynamic microphones are usually used in conference room sound reinforcement. Over the years, with the enlargement and widening of the conference table, most of the condenser gooseneck microphones are now selected. In this way, when the conference table is relatively wide, the speaker will not be pushed to the edge of the table and the sound will not be picked up. In addition, the microphone head of the condenser microphone is relatively small, so as not to cover the speaker’s face is also one of the reasons for the choice.
In summary, except for special needs, conference rooms usually recommend the use of condenser gooseneck cardioid microphones with wide frequency response, uniform frequency response transmission characteristics, smoothness and low distortion.
2. Microphone placement
The microphone placement in the conference room is usually divided into two types: desktop placement and microphone stand placement. When placing the microphone on the table, pay attention to the angle and interval between the speaker’s mouth and the microphone. It is best to align the middle axis of the microphone with the speaker’s mouth. At this time, the frequency response characteristics of the microphone output are the best; The farther the part goes from the center axis, the worse the frequency response, the more severe the loss of treble, and the reduction of the output voltage of the microphone. Usually a cardioid microphone, the angle between the mouth and the center axis is within 450 scale.
When speaking in the conference room, in order to enhance the clarity of speech, it is advisable to place the microphone 20-30cm away from the mouth. Picking up too much reflection and reverberation can easily lead to howling. At this moment, if the mixer is pushed too low, the loudness of the sound will not meet the demand, and the audience cannot hear the content of the speech. Therefore, it is very important to accurately estimate the speaker’s speaking interval when placing the microphone.
When there are multiple people speaking and multiple microphones need to be placed, the interval between the microphones should be greater than 3 times the interval between the sound source and the microphone (that is, 3:1 is satisfied). criterion) to reduce the phase interference phenomenon that occurs when the signals are added.
When a person speaks and needs to be picked up with two or more microphones (such as making a presentation), keep the two or more microphones as close as possible, and stick to each microphone to the sound source ( The interval between the speaker’s mouth) should be as flat as possible to avoid phase interference when the signals are added. At this moment, special attention should be paid to the same phase of the microphones. Take two microphones as an example. If the volume of the two microphones is not loud enough, it means that the two microphones are out of phase. At this moment, the phase of one microphone needs to be adjusted. Generally speaking, the problem lies in the microphone cable. On, just adjust the wiring of one microphone. When placing the microphone stand, since many microphone stands are triangular brackets, after the microphone is installed, the center of gravity of the microphone should be projected on a certain foot. In addition, the movable rod of the installed microphone should not be drawn too long to avoid the center of gravity of the microphone being exceeded. The stand falls outside the scale.
3. Audition of the microphone
Due to the particularity of the conference room, in most cases, the speaker cannot be auditioned in person (for example, the leader speaks) ), so you only need to adjust the volume according to the normal person, try to make the speaker’s first sentence reach a moderate volume (the sound is moderate and not whistling), but it must have a sufficient conditioning capacity. But if there are many microphones, the tuner needs to repeat the debugging between the mixer and the microphone, which is very laborious and low power.
Here’s a little trick, after setting up the mics, put all the mixer faders on Adjust the power amplifier to the proper position for normal use, push the main output of the mixer to 0dB, then push the corresponding fader of a certain microphone to the highest level of the channel (usually the mixer is 10 ~ 12dB), and then slowly Adjust the gain knob of the microphone on the mixing console and monitor the sound carefully. When you hear a slight whistling sound, move the knob back 3dB, and then pull the fader back to 0dB. In this way, the microphone can ensure that the speaker has a satisfactory volume and loudness, without causing howling. When the speaker’s voice is small, there is a sufficient margin (13dB) for adjustment. Do the same with other microphones. After this adjustment, turning on multiple microphones at the same time will not cause howling.
