As we all know, when attending a conference or giving a speech, many people have been disturbed by the accidental whistling of microphones and vague sound reinforcement. Then how to choose microphones when constructing a conference room sound reinforcement project and use them reasonably What? The following is an analysis for you one by one:
The sound in the conference room usually needs to be bright, clear, and moderate in loudness. When setting up the venue, speakers cannot go to the site to audition. Therefore, in order to achieve a bright and clear sound effect during live sound reinforcement (the loudness is just right but not the demand for howling), there is a certain degree of knowledge in the selection and placement of microphones.
1. The choice of microphone
Since different microphones have different effects on different sound sources, it is necessary to have a thorough understanding of the microphone's technical characteristics, function quality, and applicable occasions before choosing a microphone. In addition to the electroacoustic indicators such as the sensitivity of the microphone, the matching of the output impedance and the input impedance of the mixer, the microphone's directional characteristics, frequency response characteristics, and the shape of the microphone should also be considered in the conference room.
As far as directivity is concerned, the super cardioid shape is suitable for distant sound pickup, the cardioid shape is suitable for most situations, and the non-directional microphone is not suitable for speech pickup, because simple will cause echo. In addition, in the conference room, you must select a microphone with appropriate directional characteristics according to the speaker plan. For the sound reinforcement system of centralized or semi-centralized planning, the directional characteristics of the microphone should be cardioid or super cardioid; for the sound reinforcement system of decentralized planning, cardioid microphones should usually be selected. The reverberation time of the hall is not too long. You can also choose non-directional microphones; when the sound source is very close to the microphone, you can use technical indicators to eliminate the close-talking effect of the close-talking cardioid microphone.
As far as the frequency response characteristics of microphones are concerned, microphones with a slightly lower static target and good transient characteristics are often better than microphones with a slightly higher static target and poor transient characteristics. Two people, a microphone with uniform and smooth frequency response from low to high frequency is better than a certain frequency band, because some of the outstanding ones can also cause howling.
In addition, dull voices are often exacerbated by the closeness of the microphone. Of course, it can be compensated by electronic proofreading (in the sound transmission circuit). This has no effect on the voice with too low audio, but it has restrictions on the front and back movement. The distance between the speaker and the microphone must be stable, otherwise there will be low frequency components. Change, and the ratio between the direct sound and the reverberant sound (in a "lively" sound field with an acoustic condition) will also change.
Microphones with a large number of peaks between 6000 and 9000 Hz will make the sibilant accent become more toothy. Of course, you can also use electronic methods to proofread, but you have to pay for the value of the dead point at the top. Therefore, there is usually no need to use high-quality microphones in the meeting room, just a microphone with a smooth response. As far as the internal structure of the microphone is concerned, moving coil microphones are usually used in meeting room sound reinforcement in the past. In recent years, with the enlargement and widening of conference tables, most of them now choose condenser gooseneck microphones. In this way, when the conference table is relatively wide, the speaker will not be pushed to the side of the table and no sound will be picked up. In addition, the microphone head of the condenser microphone is relatively small, so that it does not cover the face of the speaker is also one of the reasons for being selected.
To sum up, in addition to special needs, conference rooms usually recommend the use of a wide frequency response, uniform frequency response transmission characteristics, smooth, low distortion condenser gooseneck cardioid microphone.
2. The placement of the microphone
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 desktop, 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 away from the central axis, the worse the frequency response characteristics, the more severe the treble loss, and the reduction of the microphone output voltage. Usually cardioid microphone, the angle between the mouth and the middle axis is within 450 scale.
When speaking in the conference room, in order to enhance the clarity of speech, the microphone should be 20-30cm away from the mouth. If it is too close, it will easily show low-frequency spray accents, which will affect the clarity of the sound. If it is too far, the microphone will pick up too many reflections and Reverberation sound can easily lead to howling. At this moment, if the mixer is pushed too low, the loudness will not meet the demand, the audience can't hear what is being said, and the push is too big and it is easy to scream. Therefore, it is very important to accurately estimate the speaker's speaking interval when placing the microphone.
When there are multiple people talking and multiple microphones need to be placed, the distance between the microphones should be greater than 3 times the distance between the sound source and the microphone (that is, the 3:1 criterion is satisfied) to reduce the phase interference when the signals are added. phenomenon.
When a person speaks and needs to use two or more microphones to pick up the sound (such as making a statement), the two or more microphones should be as close as possible, and the distance between each microphone and the sound source (speaker's mouth) should be maintained Try to be as flat as possible to avoid phase interference when the signals are added. At this moment, pay special attention to the common microphone phase. Take two microphones as an example. If the sound of the two microphones is not as loud as one of the microphones, it is stated that the two microphones are in phase. At this moment, the phase of one microphone needs to be adjusted. Generally speaking, the problem lies in the microphone line. Just adjust the wiring of a microphone. When the microphone stand is placed, since many microphone stands are tripods, the center of gravity of the microphone should be projected on a certain foot after the microphone is installed. In addition, the movable rod of the installed microphone should not be drawn too long to avoid the center of gravity of the microphone from exceeding The bracket falls outside the scale.
3. The sound test of the microphone
Due to the particularity of the conference room, in most cases, it is not possible to let the speaker come to the venue to audition (for example, the leader speaks), so you only need to adjust the volume according to the normal person's volume, and try to make the first sentence of the speaker arrive. The volume is moderate (the sound size is moderate without howling), but there must be enough conditioning capacity. But if there are many microphones, the tuner needs to perform repeated adjustments between the mixer and the microphone, which is very troublesome and low in power.
Here is a small trick, that is to put the microphone in the future, put the mixer fader of all microphones at the lowest, and adjust the gain knob to the smallest place, and then adjust the power amplifier to the proper position for usual use, and set the mixer as the master. Push the output to 0dB, and then push the corresponding fader of a microphone to the highest level of the channel (usually 10-12dB for the mixer), and then slowly adjust the gain knob of the microphone on the mixer, and Monitor the sound carefully, until you hear a slight howling, move the knob back 3dB, and then pull the fader back to 0dB. In this way, the microphone can not only ensure that the speaker has a satisfactory volume and loudness, but also does not cause howling. When the speaker's voice is small, there is a sufficient margin (13dB) for adjustment. Dispose of other microphones in the same way. After this adjustment, turning on multiple microphones together will not cause howling.