This has always bugged me: why, when I increase the volume of my amp, does the decibel number get lower? And for that matter, why is it measured in minus decibels?
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Minus decibels?
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Because it's graduated in decibels below the nominal maximum output, which is 0dB of attenuation.
radovantz
Well-known member
This never seemed to make much sense to me either. I set the volume on my receiver so it's plain ol' 0 - 100
I see. What's the logic behind this? When sounds are measured like this chart?
Whisper Quiet Library - 30dB
Telephone dial tone - 80dB
City Traffic (inside car) - 85dB
It would strike me as more sensible to simply have decibels measured in positive figures so it's easier for people to roughly measure how loud their music is / should be.
Whisper Quiet Library - 30dB
Telephone dial tone - 80dB
City Traffic (inside car) - 85dB
It would strike me as more sensible to simply have decibels measured in positive figures so it's easier for people to roughly measure how loud their music is / should be.
Virtually impossible unless the amp has a measuring microphone, as the sound pressure level will be affected by the sensitivity of the speakers in use, the distance you are sitting from them and the level of the input signal, as well as the amplifier's volume setting.
Wiki is your friend
The decibel is useful for a wide variety of measurements in science and engineering (e.g., acoustics and electronics) and other disciplines. It confers a number of advantages, such as the ability to conveniently represent very large or small numbers, a logarithmic scaling that roughly corresponds to the human perception of, for example, sound and light, and the ability to carry out multiplication of ratios by simple addition and subtraction.
Acoustics
The decibel is commonly used in acousticsto quantify sound levels relative to some 0 dB reference. The reference level is typically set at the threshold of perception of an average human and there are common comparisons used to illustrate different levels of sound pressure.
A reason for using the decibel is that the ear is capable of detecting a very large range of sound pressures. The ratio of the sound pressure that causes permanent damage from short exposure to the limit that (undamaged) ears can hear is above a million. Because the power in a sound wave is proportional to the square of the pressure, the ratio of the maximum power to the minimum power is above one (short scale) trillion. To deal with such a range, logarithmic units are useful: the log of a trillion is 12, so this ratio represents a difference of 120 dB. Since the human ear is not equally sensitive to all the frequencies of sound within the entire spectrum, noise levels at maximum human sensitivity - for example, the higher harmonics of middle A (between 2 and 4 kHz) - are factored more heavily into sound descriptions using a process called frequency weighting.
Electronics
In electronics, the decibel is often used to express power or amplitude ratios (gains), in preference to arithmetic ratios or percentages. One advantage is that the total decibel gain of a series of components (such as amplifiers and attenuators) can be calculated simply by summing the decibel gains of the individual components. Similarly, in telecommunications, decibels are used to account for the gains and losses of a signal from a transmitter to a receiver through some medium (free space, wave guides, coax, fiber optics, etc.) using a link budget.
The decibel unit can also be combined with a suffix to create an absolute unit of electric power. For example, it can be combined with "m" for "milliwatt" to produce the "dBm". Zero dBm is the power level corresponding to a power of one milliwatt, and 1 dBm is one decibel greater (about 1.259 mW).
The decibel is useful for a wide variety of measurements in science and engineering (e.g., acoustics and electronics) and other disciplines. It confers a number of advantages, such as the ability to conveniently represent very large or small numbers, a logarithmic scaling that roughly corresponds to the human perception of, for example, sound and light, and the ability to carry out multiplication of ratios by simple addition and subtraction.
Acoustics
The decibel is commonly used in acousticsto quantify sound levels relative to some 0 dB reference. The reference level is typically set at the threshold of perception of an average human and there are common comparisons used to illustrate different levels of sound pressure.
A reason for using the decibel is that the ear is capable of detecting a very large range of sound pressures. The ratio of the sound pressure that causes permanent damage from short exposure to the limit that (undamaged) ears can hear is above a million. Because the power in a sound wave is proportional to the square of the pressure, the ratio of the maximum power to the minimum power is above one (short scale) trillion. To deal with such a range, logarithmic units are useful: the log of a trillion is 12, so this ratio represents a difference of 120 dB. Since the human ear is not equally sensitive to all the frequencies of sound within the entire spectrum, noise levels at maximum human sensitivity - for example, the higher harmonics of middle A (between 2 and 4 kHz) - are factored more heavily into sound descriptions using a process called frequency weighting.
Electronics
In electronics, the decibel is often used to express power or amplitude ratios (gains), in preference to arithmetic ratios or percentages. One advantage is that the total decibel gain of a series of components (such as amplifiers and attenuators) can be calculated simply by summing the decibel gains of the individual components. Similarly, in telecommunications, decibels are used to account for the gains and losses of a signal from a transmitter to a receiver through some medium (free space, wave guides, coax, fiber optics, etc.) using a link budget.
The decibel unit can also be combined with a suffix to create an absolute unit of electric power. For example, it can be combined with "m" for "milliwatt" to produce the "dBm". Zero dBm is the power level corresponding to a power of one milliwatt, and 1 dBm is one decibel greater (about 1.259 mW).
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