What are the Requirements for Loudspeaker Configuration in Public Adress Speaker Systems?

Usually, the background noise of office corridor is about 48-52 dB, and that of supermarket is about 58-63 dB, and that of busy section is about 70-75 dB. Considering that the scene may be very confused in the event of an accident, the background noise should not be estimated too low for the need of emergency broadcasting, even if the broadcasting service area is an office building. Therefore, as a general consideration, in addition to busy and lively places, background noise may be roughly regarded as 65-70dB (except in special cases). According to this calculation, the sound pressure level in the broadcast coverage area should be above 80-85 dB.

Since public adress speakers are usually distributed, the sound pressure level in the adress coverage area can be approximately considered as the contribution of a single public adress speakers. According to the relevant electroacoustics theory, the sound pressure level SPL in the speaker coverage area has the following relations with the sensitivity level LM of the speaker, the power P fed to the speaker, the listening point and the distance r of the speaker, etc.

SPL=LM+10lgP-20lgrdB(1)

The sensitivity level of smallpox loudspeaker ranges from 88 to 93 dB, and the rated power is 3 to 10 W. Calculated by 90dB/8W, the sound pressure level at 8m away from the loudspeaker is about 81dB. The contribution of early reflected sound group is not considered in the above calculation. Indoor, the contribution of early reflected sound group and adjacent loudspeakers can increase the sound pressure level by about 2-3 dB.

According to the above approximate calculation, the ceiling loudspeakers can be arranged evenly at a distance of 5-8 m in a venue whose ceiling is not higher than 3 m. If only background music is considered and emergency broadcasting is not considered, the distance can be increased to 8-12 M. In addition, the design and installation code for fire accident broadcasting in mainland China (hereinafter referred to as "code").

There are basically no early reflective sound groups in outdoor areas, and the effective coverage of a single public address speaker can only be taken as the lower limit calculated above. Since the lower limit corresponds to a very short distance, in principle, a sound column composed of multiple speakers should be used. The sound pressure level can be increased by 3dB for every doubling of the signal power to the speaker group (such as the sound column) provided that the group is acceptable. From 1 to 2 is double; from 2 to 4 is double. In addition, the sound pressure level will decrease by 6 dB for every doubling of distance. According to the above rules, it is not difficult to calculate the configuration distance of outdoor sound column.

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