Car acoustics loudspeaker regards the efficiency that we care about it naturally as electric acoustics transducer, will express more convenient with sound pressure level, characteristic sensitivity to loudspeaker, here introduce the following a few concepts.
(1) The characteristic sensitivity in the specified frequency band. In the specified frequency band under free field conditions, the input power to the horn is equivalent to 1W pink noise signal, and the sound pressure is 1m away from the reference point on the reference axis. The free field is the space where there is no sound reflection. In space, the relationship between the sound pressure P radiated by the point sound source and the test distance R should be such that P is inversely proportional to R, which is usually measured in an anechoic chamber.
(2) The characteristic sensitivity level in the specified frequency band. That is, the logarithmic characteristic sensitivity. The logarithm of the ratio of characteristic sensitivity to reference sound pressure is multiplied by 20, denoted by dB. The reference sound pressure is 2×10-5Pa.
(3) The pink noise of car audio speakers mentioned here is a kind of noise signal, which refers to the continuous and uniform noise with the frequency band width proportional to the frequency. That is to say, it is noise with the same energy in equal proportion to the bandwidth over a wide band.
Reference axis is mentioned here, is parallel to the horn of a definition of the plane called the reference surface, through the horn axis and the line perpendicular to the reference surface is called the reference axis, the reference axis and the reference surface intersection point is called the reference point.
(4) It is often encountered that when the horn input power is not 1W, but other power values, then the output sound pressure level can be calculated as SPLMAX =Lp+10lgW0, where Lp -- characteristic sensitivity level; W0 -- Input power at this point.