Selection and configuration principles of broadcast speakers
September 08, 2022
In principle, broadcast speakers of different specifications should be selected according to the environment. For example, in a room with a suspended ceiling, it is advisable to use a built-in ceiling speaker without a rear cover. This type of loudspeaker is simple in structure, relatively cheap in price, and easy to construct. The main disadvantage is that there is no rear cover, and it is easy to be bitten by insects and rodents. In the room with only frame ceiling and no ceiling (such as open-frame shopping malls), ceiling-mounted barrel speakers or ceiling speakers with rear cover should be used. Since the ceiling is equivalent to an infinite baffle, using a speaker without a back cover under the condition of a ceiling will not cause an acoustic short circuit. The situation is very different without the ceiling. If you still use the ceiling speaker without the back cover, the effect will be very poor. In this case, ceiling-mounted speakers should be used in principle. However, if the investment is too large, ceiling speakers with a rear cover can also be used. The rear cover of the ceiling speaker with the rear cover not only has the general mechanical protection function, but also plays the role of preventing sound short circuit to a certain extent.
In rooms without ceilings (such as underground parking lots), wall-mounted speakers or indoor sound columns should be used.
Outdoors, it is advisable to use an outdoor sound column or horn. This kind of sound column and horn not only has the function of rainproof, but also has a large volume. Since the outdoor environment is empty and there is no reverberation effect, it is necessary to choose a variety with a higher volume.
In gardens and grasslands, lawn speakers should be used. This type of speaker is rainproof, beautiful in shape, and more particular about volume and sound quality. In the halls with exquisite decoration and high ceilings, it is advisable to choose ceiling-mounted speakers with elegant shapes and harmonious colors. In occasions with high requirements for fire protection, fire-resistant speakers should be selected. This type of loudspeaker is fully sealed, and its outlet can be mated with a flame retardant sleeve.
Configuration of broadcast speakers
In principle, the broadcasting speakers are arranged in the broadcasting service area with the principle of uniformity and dispersion. The degree of dispersion should ensure that the signal-to-noise ratio in the service area is not less than 15dB.
Usually, the background noise of high-end office corridors is about 48-52dB, the background noise of supermarkets is about 58-63dB, and the background noise of bustling roads is about 70-75dB. Considering that the scene may be very chaotic when an accident occurs, for the needs of emergency broadcasting, even if the broadcasting service area is an office building, the noise floor should not be estimated too low. In this regard, as a general consideration, in addition to prosperous and lively places, the background noise may be roughly regarded as 65 ~ 70dB (except for special circumstances). According to this calculation, the sound pressure level of the broadcast coverage area should be above 80-85dB.
Since broadcast loudspeakers are usually distributed, the sound pressure level of the broadcast footprint can be approximated as the contribution of a single broadcast loudspeaker. According to the relevant electro-acoustic 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+10lgP-20lgrdB (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 from the speaker is about 81dB. The above calculation does not consider the contribution of the early reflection sound group. In the room, the contribution of the early reflection group and adjacent speakers can increase the sound pressure level by about 2 to 3 dB.
According to the above approximate calculation, in a venue with a ceiling not higher than 3m, the ceiling speakers can generally be evenly arranged at a distance of 5-8m from each other. If only the background music is considered and the emergency broadcast is not considered, the distance can be increased to 8-12m. In addition, the Fire Accident Broadcasting Design and Installation Code (hereinafter referred to as the "Code") applicable to mainland China has the following rigid regulations: "The number of speakers in public places such as aisles, halls, and restaurants should be able to ensure that the The walking distance to the nearest speaker is no more than 15m.
