Campus radio speaker settings

Fifth, the configuration of broadcast speakers

Broadcast speakers are arranged in the broadcast service area on the principle of uniformity and decentralization. The degree of dispersion should ensure that the signal-to-noise ratio in the service area is not less than 15dB.

Generally, the background noise of corridors of high-grade office buildings is about 48-52dB, the background noise of super malls is about 58-63dB, and the background noise of busy roads is about 70-75dB. Considering that the scene may be very confusing when an accident occurs, so for the purpose of emergency broadcasting, even if the broadcasting service area is an office building, the noise floor should not be estimated too low. Accordingly, as a general consideration, in addition to the prosperous and lively places, it may be roughly regarded as the background noise of 65 ~ 70dB (except in special cases). According to this calculation, the sound pressure level in the broadcast coverage area should be above 80 ~ 85dB.

In view of the fact that broadcast speakers are usually distributed, the sound pressure level of the broadcast coverage area can be considered approximately as the contribution of a single broadcast speaker. According to the relevant electroacoustic theory, the sound pressure level SPL of the speaker coverage area has the following relationship with the sensitivity level LM of the speaker, the electric power P fed to the speaker, the distance r between the listening point and the speaker, etc .:

SPL = LM + 10 1g P -20 1g r dB (1)

The sensitivity level of the ceiling speaker is between 88 ~ 93dB; the rated power is 3 ~ 10W. Calculated at 90dB / 8W, the sound pressure level at 8m away from the speaker is about 81dB. The above calculation does not consider the contribution of the early reflected sound group. In the room, the contribution of early reflected sound groups and adjacent speakers can increase the sound pressure level by about 2 ~ 3dB.

There is basically no early reflection sound group in outdoor places, and the effective coverage of a single broadcast speaker can only take the lower limit calculated above. Since the distance corresponding to the lower limit is very short, in principle, a column composed of multiple speakers should be used. The signal electric power fed to the speaker group (such as the sound column) is doubled (provided that the group can accept it), the sound pressure level can be increased by 3dB. Please pay attention to the meaning of "double". Doubled from 1 to 2; doubled from 2 to 4. In addition, every time the distance is doubled, the sound pressure level will drop by 6dB. According to the above rules, it is not difficult to calculate:

The arrangement distance of the outdoor sound column. For example, taking the K-503Z outdoor sound column as an example, its rated power is 35W, which is more than 3 times that of a single ceiling speaker. Therefore, its effective coverage distance is greater than twice that of a single ceiling speaker. In fact, this distance can be larger. Because the sensitivity of the sound column is higher than that of a single ceiling speaker (about 3 ~ 6dB higher), and every additional 6dB, the distance can be doubled. In other words, the coverage distance of the K-503Z column can reach more than 20m. However, the radiation angle of the sound column is relatively narrow, and it is only effective within about 60 to 90 degrees (horizontal angle) in front of it. The specific calculation can still use formula (1).