What Is a Decibel (dB) in Music?
A decibel, designated by the letters dB, is a logarithmic scale of loudness. Our ears detect changes in volume in a non-linear fashion. Sound loudness—which is not necessarily the same thing as volume—is determined by a variety of factors. These include the amount of air that reaches the ear and the distance between our ears and a sound source.
The Decibel Scale
The decibel scale was created to quantify how loud sounds are. A difference of 1 dB is perceived as a minimum change in volume. A difference of 3 dB is a moderate change, and a difference of 10 dB is perceived by the listener as a doubling of volume. The threshold of hearing is 0 dB. Here are some examples of common sounds and where they typically fall on the decibel scale:
Whisper: 15 to 25 dBBackground noise: 35 dBNormal home or office background: 40 to 60 dBNormal speaking voice: 65 to 70 dBOrchestral climax: 105 dBLive rock music: 120 dB+Pain threshold: 130 dBJet aircraft: 140 to 180 dB
How the Decibel Scale Is Applied
For amplifiers, decibels are a measurement of how much power it takes to produce a specific sound output level. For one amplifier or receiver to be twice as loud as another, you need 10 times more wattage output, so a receiver with 100 WPC is capable of twice the volume level of a 10 WPC amp. A receiver with 100 WPC needs to be 1,000 WPC to be twice as loud. Decibels are also used in relation to the sound output of loudspeakers and subwoofers at specific frequencies and volume levels. A speaker may have the ability to output a frequency range of 20 Hz to 20 kHz, but at frequencies lower than 80 Hz, the sound output level (volume) may be -3 dB less. This is because more power output is required at lower frequencies to produce the same volume level. The dB scale is applied to the sound level output capability of a specific speaker when fed a tone carried by one watt of power. A speaker that can produce 90 dB or higher sound output when fed a one-watt audio signal is considered to have good speaker sensitivity.
How to Measure Decibels
One way that decibels can be measured is with a portable sound meter. There are also sound meter apps that work with the microphone in a typical smartphone. Most home theater receivers have built-in test tone generators that you can use to determine the generated decibel level for each speaker. When all your speakers register the same decibel level at a given volume level, your sound listening experience will be balanced.
Measuring Decibels Without a Sound Meter
Many home theater receivers have an automatic speaker/room correction system that doesn’t require the use of a separate sound meter. A microphone is provided that plugs into the front of the receiver. The receiver sends out test tones to each speaker, which are picked up by the microphone and sent back to the receiver. The receiver then determines how many speakers there are, the distance of each speaker from the listening position, and the size of each speaker. Using that information, it calculates the optimum speaker level relationship between the speakers (and subwoofer) along with the best crossover point between the speakers and the subwoofer.
