From the point of view of directivity, the supercardioid shape is suitable for long-distance sound pickup, and the cardioid shape has a wider range of application. Non-directionality is likely to cause feedback, but it is not suitable for sound pickup. In addition, the microphone must match the layout of the speaker system.
(1) In centralized and semi-centralized sound reinforcement systems, the directional characteristics of the microphone should be cardioid or super-cardioid.
(2) In a decentralized sound reinforcement system, cardioid microphones are usually selected. If the distance between the microphone and the sound reinforcement box is far, and the hall reverberation time is short, a non-directional microphone can also be selected.
(3) When the sound source is very close to the microphone, the cardioid microphone can eliminate the proximity effect through technical indicators.
From the perspective of frequency response characteristics, microphones with generally lower static technical indicators and better transient characteristics are better. In addition, because the protruding part is easy to cause howling, you should choose a microphone with uniform and smooth frequency response from low to high frequency.
In addition, the heavy accent is always overemphasized because the microphone is too close. Although it can be compensated by electronic correction (in the microphone circuit), there is no limit to the low-audio voice, but it will be affected by the position movement, requiring the distance between the speaker and the microphone to be fixed, otherwise the low-frequency part will change , And the ratio between the direct sound and the reverberant sound (in a sound field where the acoustic state is "active") will also change.
Microphones with many peaks between 6000 and 9000 Hz will cause the sibilant accent to be heavier. If it is calibrated electronically, it is easy to bring a dead point at the top of the peak. Therefore, high-quality microphones in the conference room are not necessarily suitable, just choose a microphone with a smooth response.
From the perspective of the internal structure of the microphone, usually a dynamic microphone is used for sound reinforcement in a conference room. Over the years, with the increase of the conference table area, more choices are made of condenser gooseneck microphones, which can avoid being pushed by the speaker to the table and fail to pick up the sound. Moreover, the head of the condenser microphone is relatively small and will not be used in video recording. Cover the face of the speaker.
In general, except for special circumstances, it is generally recommended to choose a condenser gooseneck cardioid microphone with uniform frequency response transmission characteristics, wide frequency response, low distortion, and smoothness in conference rooms.
There are generally two ways to place microphones in conference rooms: desktop placement and microphone stand placement.
For microphones placed on the desktop, pay attention to the angle and distance between the mouth and the center of the microphone. Keep the mouth aligned with the center axis of the microphone. This will make the microphone output the best frequency response characteristics; the farther the mouth is from the center axis , The worse the frequency response characteristic will be, the more severe the treble loss will be, and the output voltage of the microphone will also decrease accordingly. For cardioid microphones, keep the angle between the mouth and the central axis within 45º.
In order to improve speech intelligibility, the distance between the speaker's mouth and the microphone should be 20-30cm. If it is too close, low-frequency spouts are likely to appear, which will adversely affect the clarity of the sound; if it is too far, the microphone will pick up too many reflections and reverberations and cause howling. Therefore, it is very important to accurately estimate the speaking distance of the speaker when placing the microphone.
If there are many people talking, you need to place multiple microphones. At this time, 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 principle is satisfied), which can avoid the phase interference when the signals are added. phenomenon.
When the speaker needs to use multiple microphones to pick up the sound, the multiple microphones should be as close as possible, and the distance between each microphone and the sound source should be kept as the same as possible to avoid phase interference. Pay special attention to keeping the phase of the microphone consistent. Take two microphones as an example. If the pickup volume of the two microphones is less than that of one microphone, it means that the two microphones are in reverse phase. At this time, the phase of one microphone needs to be adjusted. The problem often lies in the microphone line. Just adjust the connection of the microphone.
When choosing a microphone stand, because many microphone stands are tripods, after installing the microphone, the center of gravity of the microphone should be projected on a certain foot. The movable rod for installing the microphone should not be drawn too long to avoid the microphone's center of gravity from falling outside the range of the stand.
Taking into account the particularity of the conference room, it is not allowed to let the leader come to the venue to test the sound, so we must adjust the volume according to the normal person's volume, and try to make the first sentence of speech to be able to achieve a moderate volume without whistling, but there must be enough The adjustment margin. If there are many microphones, the tuner needs to perform repeated tuning tests on the mixer and the microphone, which is both troublesome and inefficient. In fact, there is a little trick, that is, after placing the microphones, put the mixer faders of all microphones at the lowest and the gain knobs to the lowest, and then adjust the power amplifier to the commonly used suitable position, and push the main output of the mixer. To 0dB, then push the corresponding fader of a microphone to the highest level of the channel (generally 10-12dB for the mixer), and then slowly adjust the gain knob of the microphone on the mixer, and monitor carefully at the same time When you hear a slight whistling sound, move the knob back 3dB, and then push the fader back to 0dB. At this time, the microphone can ensure that the speaker has sufficient volume and loudness performance without causing howling. When the speaker's voice is low, there must be enough margin (13dB) for adjustment. After other microphones are processed in the same way, turning on multiple microphones at the same time will not cause howling.