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dB meter itself does not exist. We allways measure voltage, current or power, preassure etc. Measuring results expressed in dB are allways relative to some reference. It can be 1V, 1uV(microvolt) 1mW or some other reference depending on what we measure. So we have results expressed in dBV, dBuV, dBm etc.
Because dB=10*log(P2/P1) or dB=20*log(U2/U1) instrument has logarithmic scale if it does not implement logarithmic operation on measuring signal where cale is linear.
The reason why they use dB unit rather than voltage or power is that the sensitivity of human ears is logarithmically, rather than linearly, proportional to the sound power.
Hope it's not off topic
The simplest dB meters are voltmeters with dB scale marking - not high precision.
Do you know a schematic for an wideband log detector (discrete or IC) - in the past I've seen a home made spectrum analyzer that had a log detector based on a limiting amplifier from an FM demodulator IC.
The authors tested several ICs to find the best suited - MC3362, etc
Hi alau, here is a GIF schematic of the inexpensive Radio Shack 33-2050 Sound Level Meter, scanned from my owner's manual dated 1993.
You can also download the full owner's manual for the newer version 33-4050 of this meter, however it doesn't include a schematic. The old and new meters have slightly different plastic enclosures, but their electrical specs look identical. The manual download link is in the lower-left corner: https://www.radioshack.com/product/index.jsp?parentPage=search&productId=2103668
smartshashi,
As flaulent mentioned, in audio work db meters are usually referred to as VU (Volume Unit) meters. Keep in mind, however, that in order to qualify as a true VU meter, the meter must posses certain ballistic characteristics, that is to say, it must respond in a specified manner to step changes in amplitude. For more info, see the following:
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. **broken link removed**
Regards,
Kral
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