The signal level produced by an electret element under these conditions is calculated to be:Īn orchestra may produce an SPL of more than 105 dB, but loud musical instruments such as horns and drums could easily produce a local SPL of 115 dB when closely miked. It is not unusual for electret microphones to have a rated output of –40 dB relative to 1 volt measured at sound pressure of 1 Pascal (Pa), which is 94 dB SPL. Where C t is the variation in capacity due to sound pressure. The output voltage change of a condenser microphone is expressed as the fixed voltage times the relative change in capacity: Either way, a fixed charge is maintained across the capacitor.įor a charge Q, the expression is: = C 0 × E 0Ĭ 0 is the capsule capacitance, and E 0 is the capsule capacitance. One advantage an electret has is its intrinsic charge, which eliminates the charging resistor, as shown on in Fig. The resistor must have a value of hundreds of megaohms to avoid a cutoff in the bass range. 3.īecause the capacitance is very low (around 50 picofarad, ☓0 pF), the resistor forms an R/C network that rolls off the low frequencies.
2: Inside the Neewer NW-700.Īs discussed previously, all condenser microphones generate a small voltage as their diaphragm changes capacitance in an electric field, when moved by sound pressure waves.Įxternally-polarized mikes charge the diaphragm/backplate condenser through a resistor from a source of 40 to 200 volts, as shown on the left in Fig. Neewer was kind to let us share some of the NW-700 schematic, which we examine below. In this chapter, we’ll examine the anatomy of the circuitry following electrets and how they affect the sound output.įor our study, I picked a Neewer model NW-700 “Professional Studio Broadcasting & Recording Condenser Microphone,” which at the time of writing is listed at only $14.70 by the manufacturer, including a web shock mount and cable, shown in Fig. One hundred years later, modern materials and manufacturing have made electret condenser mikes cheap and plentiful - and with careful design electret audio performance can rival the best of their powered cousins. 19, 2016), we’ve traced the origins of electret condenser microphones to their externally-polarized ancestor, patented in 1916. In two articles thus far (RW Engineering Extra, Aug. If you like this content you should subscribe to Radio World Engineering Extra. 8, 2017, edition of Radio World Engineering Extra and was posted on this website Feb.
This article originally appeared in the Feb. 1: The Neewer NW-700 provides excellent performance and costs less than $15.
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