Because broadcast speakers are usually distributed, the sound pressure level in the broadcast coverage area can be approximately considered as the contribution of a single broadcast speaker. According to the related electroacoustic theory, the sound pressure level SPL in the horn coverage area has the following relations with the sensitivity level LM of the horn, the electric power P fed into the horn, the distance R between the listening point and the horn, etc.
SPL = LM+ 10 lgp-20 lgrdb( 1)
The sensitivity grade of ceiling speakers is between 88 and 93 dB, and the rated power is between 3 and 3 ~10w. Calculated at 90DB/8W, the sound pressure level at a distance of 8M from the loudspeaker is about 8 1DB.
The contribution of early reflected sound group is not considered in the above calculation. Indoor, the contribution of early reflected sound group and adjacent speakers can increase the sound pressure level by about 2~3DB.
Extended data:
The wire is composed of one or more flexible wires, and the outer bread is covered with a light and soft protective layer; A cable consists of one or several insulated wires covered with a tough outer layer made of metal or rubber. Cables and wires are generally composed of three parts: core wire, insulating sheath and protective sheath. ?
The characteristics of common cables are as follows: CEF- EPDM insulated neoprene sheath, marine flame retardant power cable. Marine CVV PVC insulated PVC sheathed flame retardant power cable. ?
BV, BX, RV and RVV series wires are commonly used for oxygen cabin wires, among which: BV-copper-core PVC insulated wire, with long-term allowable temperature of 65℃, minimum temperature of-15℃, working voltage of 500V AC, DC 1000v, which is fixed indoors and outdoors, and can be laid openly or concealed.
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