The sound in the conference room is generally required to be bright and clear, and the loudness should be moderate. When setting up the venue, it is impossible for the speaker to audition on site. Therefore, in order to achieve a bright and clear sound effect during live sound reinforcement (the loudness is just right but not the requirement of howling), there is a certain degree of knowledge in the selection and placement of the microphone.
1 Microphone selection
Since different microphones have different effects on different sound sources, it is necessary to understand the technical characteristics, performance advantages and disadvantages of the microphone and the 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, super cardioid microphones are suitable for long-distance sound pickup, cardioids are suitable for most situations, and non-directional is not suitable for speech pickup because it is easy to cause feedback. In addition, according to the layout of the speakers in the conference room, choose a microphone with appropriate directional characteristics.
1) For centralized or semi-centralized sound reinforcement systems, the directional characteristics of the microphone should be cardioid or super cardioid.
2) For decentralized sound reinforcement systems, cardioid microphones should generally be selected. If the microphone is far away from the PA speaker and the hall reverberation time is not too long, a non-directional microphone can also be selected.
3) When the sound source is very close to the microphone, a close-talking cardioid microphone with technical indicators that eliminates the close-talking effect can be used.
In terms of the frequency response characteristics of microphones, microphones with slightly lower static technical indicators and good transient characteristics are often better than microphones with slightly higher static technical indicators but poor transient characteristics. In addition, a microphone with uniform and smooth frequency response from low frequency to high frequency is better than a certain frequency band, because the prominent part is also the part that is easy to cause howling.
In addition, dull voices are often exaggerated due to the close proximity of the microphone. Of course, it can be compensated by electronic correction (in the microphone circuit). This has no effect on the voice with too low audio, but there are restrictions on the movement back and forth. The distance between the speaker and the microphone must be kept constant, otherwise there will be low frequency components Changes, and the ratio between the direct sound and the reverberant sound (in a sound field where the acoustic state is "active") also changes.
Microphones with a large number of peaks between 6 000 and 9 000 Hz will make the sibilant accent become more toothy. Of course, it can also be corrected electronically, but at the cost of causing dead spots at the top of the peak. Therefore, there is generally 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, the general conference room sound reinforcement used to use a dynamic microphone. 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 its choice.
In summary, in addition to special requirements, it is generally recommended to use a condenser gooseneck cardioid microphone with wide frequency response, uniform frequency response transmission characteristics, smoothness, and low distortion in conference rooms.
2 microphone placement
Microphone placement in the conference room is generally divided into two types: desktop placement and microphone stand placement.
When placing the microphone on the desktop, pay attention to the angle and distance between the speaker’s mouth and the center of the microphone. It is best to align the center axis of the microphone with the speaker’s mouth. At this time, the microphone output has the best frequency response characteristics; The farther away from the center axis, the worse the frequency response characteristics, the more serious the treble loss, and the output voltage of the microphone will also decrease. For general cardioid microphones, the angle between the mouth and the central axis is within 450.
When speaking in the conference room, in order to improve the speech intelligibility, the microphone should be 20-30cm away from the mouth. If it is too close, low-frequency spray accents are easy to appear, which affects the clarity of the sound. Reverberation sound can easily cause howling. At this time, if the mixer is pushed too low, the loudness of the sound will not meet the requirements, the audience will not be able to hear the content of the speech, and the push is too large and it is easy to scream. Therefore, it is very important to accurately estimate the speaking distance of the speaker when placing the microphone.