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Signal Levels: What's Hot, What's Not
A 3 Volt light bulb plugged into a 120 Volt circuit would shatter because the bulb is designed for a much lower voltage. In the reverse, a bulb designed for 120 Volt circuit connected to low current batteries will be very dim at best. In a similar way, audio systems are comprised of devices designed to operate within a certain range of voltage and current. To connect sound system equipment together properly, it is important to have a basic understanding of these signal levels. SIDE NOTE: It is easier to talk about voltage amplitudes as a ratio, called dBV, with the reference being 1.0V. For example, if you double a voltage, the ratio would increase by 6 dB. So, a 2V signal would be 6 dBV or a 0.5V signal would be -6 dBV. Microphone Level: This is the smallest audio signal. This category of signal typically falls within the range of -60 dBV to -30 dBV. This represents a voltage range of 0.001 Volts and 0.032 Volts. Microphones, direct boxes and some acoustic guitar pickups will produce this very low signal. Line Level: Line level signals vary from -20 dBV to 24 dBV. Within this range of signals are two subcategories. Semi-Professional Level: The output signals of "consumer" grade cassette decks, CD players, FM tuners, etc. are usually measured to be approximately -20 dBV to -10 dBV. This represents a voltage range of 0.1 Volts to 0.32 Volts. Professional Level: The output of most mixers and signal processors such as compressors, equalizers, and crossovers are usually in the range of 4 dBV to 24 dBV. This represents a voltage range of 1.6 Volts to 15.8 Volts. Loudspeaker Level: This is the signal amplifiers produce. The output feeds the loudspeakers of the system. The power output of most amplifiers range from 50 Watts to 1000 Watts. Watts?! What about Volts?!! Well, if you use an 8 ohm loudspeaker, the voltage range is approximately 20 Volts (26 dBV) to 90 Volts (39 dBV) and more. A Final Note: Matching signal levels is an essential part of both installing and operating a sound system. If you have any questions or sound system problems, please give your local contractor a call. by Travis Ludwig © 1996 Internet Sound Institute (www.soundinstitute.com). This article is for personal use only. Any commercial reproduction is not permitted without permission. To obtain permission, contact ISI at hopi@soundinstitute.com
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