【 Weak current College 】 microphone and sound mixer level---Power By 【 China power house network 】

The receiver's specification is chosen and an important basis for using the microphone. 　　Only understand the exact meaning, it can reasonably be disposing of the microphone and the sound source distance, control their sound pressure and voltage conversion, and the microphone is on sound field of sound pressure level accurately converted into sound mixer input level, which determines the sound mixer input gain, the highest signal-to-noise ratio, lowest distortion of linear signal. So what are the indicators of the microphone and the sound mixer are closely related to the input? how it was in at the same time determine the working-level sound mixer? a few important indicators means broadcast microphone specifications are close to 10, for the sound source and a mixer, the most important is the following three: maximum input sound pressure level, sensitivity and maximum output level. Maximum input sound pressure level is the microphone can afford 0.5 total harmonic distortion of the maximum sound pressure level of the measure, its relationship with the sound pressure is defined as: 0dB SPL = 2x10-5Pa professional microphone maximum input sound pressure level is generally set at a higher, as long as it is the distance between the sound source properly, will not produce audible distortion. 　　So here we focus on the direct effect mixer work level of the latter two indicators. 1. sensitivity sensitivity is the microphone in the unit of sound pressure excitation output voltage and input sound pressure ratio, it is in mV/Pa. As with circuit-level metrics consistent sensitivity can also be a decibel value. 　　Early DB more units dBm and dBV: 0dBm = 1mW/Pa, that is, under the input sound pressure 1Pa to 600 Ω load of 1mW power output defined as 0dB; 0dBV = 1 V/μ b a r, in 1 μ b a r input sound pressure produced by 1V voltage output defined as 0dB. 　　Now the unit of DB d B μ: 0 d B μ = 0.775V/Pa, coming under the input sound pressure 1Pa Mike 0.775V voltage output defined as 0dB (so that the microphone sound pressure — voltage level measurement after the conversion, the circuit generally 0 d B μ = 0.775V this reference units). 　　Obviously, no matter how sensitivity that we can convert it to d B μ, subject line enter into Pa this unit. 　　For example: NEUMANN U89 microphone sensitivity is 8mV/Pa, can directly by 20lg [(0.008V/Pa)/(0.775V/Pa)] its sensitivity is about-40 d B μ. AKG C414 again where: the microphone's sensitivity to-60dBV by 0dBV = 1 V/μ b a r = 10V/Pa first find the sound pressure-1Pa 60dBV output voltage X: 20lg [(X V/Pa)/(10V/Pa)] =-60 that X = 0.01 (V), that is, its sensitivity to 10mV/Pa. 　　Then-20lg [(0.01V/Pa)/(0.775V/Pa)] can have its sensitivity is about-37 d B μ. 2. the maximum output level microphone in maximum input sound pressure level of the output level is the maximum output level. As maximum input sound pressure level qualified with the microphone and the distance between the sound source, maximum output level directly determines the sound mixer input work level. 　　For a given handset, known for its sensitivity and the high pressure level, you can calculate its maximum output level. Microphone NEUMANN U89 still as an example: its sensitivity to 8mV/Pa, maximum input sound pressure level for 134dB SPL (in 10dB input attenuation stalls). First the input sound pressure level is converted into sound pressure sensitivity, and the maximum output level: 0dB SPL = 2x10-5Pa, maximum input sound pressure X by 134dB SPL = 20lgX/2x10-5Pa arrive at X = 100 (Pa). By sensitivity 8mV/Pa, at maximum output 100Pa as 800mV into output level: 20lg [(0.8V/Pa)/(0.775V/Pa)] is about 0 d B μ. This is U89 microphone theoretical maximum output level. 　　In fact, the normal use is not generally choose 10dB attenuator stalls (to reduce the input noise), so long as the receiver of a substantial distance, before U89 maximum sound pressure level normally does not exceed its normal stall under 124dB SPL, therefore its maximum output level is generally much lower than 0 d B μ. The second working level determines the sound mixer technology, sound mixer work level is based on the maximum signal level does not exceed the manufacturers set maximum dynamic allowance limit to specifications (actual working level also in the basis of programmes need to be determined). 　　Here, the maximum dynamic margin means the total harmonic distortion indicators of the maximum levels and 0 d B μ above a paragraph-level scope, such as a diagram. 　　So, as long as the receiver-side known sound source possible maximum sound pressure level and the sensitivity of the microphone, you can calculate the corresponding maximum output level; this level and mixer difference dynamic allowance limit is a mixer input, which is the microphone amplifier (words) in the input gain; the gain of the signal level is mixing console's work level. To the sound source to spend cavity soprano, adopt U89 microphone and AMEK RemBandt mixer, for example, to illustrate: If the distance between the microphone 70cm Office sound source maximum sound pressure level is 112dB SPL (peak, A-weighted), the receiver can withstand the maximum input sound pressure level is 124dB, sensitivity is 8mV/Pa, by-112dB SPL = 20lgX/2x10-5 shows the 112dB sound pressure level equivalent to 8Pa sound pressure, it may have 8Pax8mV/Pa = 64mV voltage output, that is, a level output: 20lg [(0.064V/Pa)/(0.775V/Pa)] =-22 d B μ thisLevel join to 70dB words gain, words-level dynamic margin in total harmonic distortion is 0.017 12 d B μ in a mixer (the sound mixer line zoom-level dynamic allowance for 28 d B μ), and + 12 d B μ ceiling there 34dB of allowance (+ 12dB-(-22dB) = 34dB), this is a mixer should have input gain. 　　This will determine the level of the mixer's work. Actual operation, to make sure that the mixer in the maximum signal level total harmonic distortion lower than 0.017 should generally gain the above words and then reduce the number of decibels. Reduced rate consists of the following methods to determine the first channel, sniffing and total output for third part of the push-pull Attenuator is over 0dB work location, and then watch this input and output of the meter, with its direction in the normal range is a reference to determine the number of DB drop.