A Few Suggestions To Help Understand The Signal-To-Noise Ratio Of Recent Audio Amps
To help you select an audio amp, I will explain the expression "signal-to-noise ratio" that is commonly used to describe the performance of audio amps.
As soon as you have selected a range of amps, it is time to investigate several of the specifications in more detail to help you narrow down your search to one product. An important criterion of power amps is the signal-to-noise ratio. To put it simply, the signal-to-noise ratio describes how much hum or hiss the amp is going to add to the audio signal. This ratio is typically described in decibel or "db" for short.
Comparing the noise level of different amps can be done rather simply. Simply get together a couple of models that you wish to compare and short circuit the inputs. Afterward put the amplifier gain to maximum and verify the amount of noise by listening to the loudspeaker. You are going to hear some amount of hissing and/or hum coming from the speaker. This noise is created by the amp itself. Make sure that the volume of the amps is set to the same level. Otherwise you will not be able to objectively compare the amount of static between several amplifiers. The general rule is: the smaller the level of hiss that you hear the better the noise performance.
A lot of of recent amps are based on a digital switching topology. They are known as "class-D" or "class-T" amps. Switching amps include a power stage which is continuously switched at a frequency of around 400 kHz. Because of this, the output signal of switching amplifiers contain a rather big amount of switching noise. This noise component, though, is typically impossible to hear since it is well above 20 kHz. However, it may still contribute to speaker distortion. Signal-to-noise ratio is typically only shown within the range of 20 Hz to 20 kHz. Therefore, a lowpass filter is used while measuring switching amplifiers to remove the switching noise.
The signal-to-noise ratio is measured by feeding a 1 kHz test signal 60 dB underneath the full scale and measuring the noise floor of the amp. The amplification of the amplifier is set such that the full output power of the amp can be achieved. Subsequently, only the noise in the range of 20 Hz and 20 kHz is considered. The noise at different frequencies is eliminated by a filter. Subsequently the amount of the noise energy in relation to the full-scale output power is calculated and expressed in db.
Often the signal-to-noise ratio is expressed in a more subjective manner as "dbA" or "A weighted". In other words, this method tries to express how the noise is perceived by a person. Human hearing is most sensitive to signals around 1 kHz while signals under 50 Hz and above 14 kHz are barely noticed. The A-weighted signal-to-noise ratio is generally higher than the unweighted ratio and is published in the majority of amp spec sheets.
As soon as you have selected a range of amps, it is time to investigate several of the specifications in more detail to help you narrow down your search to one product. An important criterion of power amps is the signal-to-noise ratio. To put it simply, the signal-to-noise ratio describes how much hum or hiss the amp is going to add to the audio signal. This ratio is typically described in decibel or "db" for short.
Comparing the noise level of different amps can be done rather simply. Simply get together a couple of models that you wish to compare and short circuit the inputs. Afterward put the amplifier gain to maximum and verify the amount of noise by listening to the loudspeaker. You are going to hear some amount of hissing and/or hum coming from the speaker. This noise is created by the amp itself. Make sure that the volume of the amps is set to the same level. Otherwise you will not be able to objectively compare the amount of static between several amplifiers. The general rule is: the smaller the level of hiss that you hear the better the noise performance.
A lot of of recent amps are based on a digital switching topology. They are known as "class-D" or "class-T" amps. Switching amps include a power stage which is continuously switched at a frequency of around 400 kHz. Because of this, the output signal of switching amplifiers contain a rather big amount of switching noise. This noise component, though, is typically impossible to hear since it is well above 20 kHz. However, it may still contribute to speaker distortion. Signal-to-noise ratio is typically only shown within the range of 20 Hz to 20 kHz. Therefore, a lowpass filter is used while measuring switching amplifiers to remove the switching noise.
The signal-to-noise ratio is measured by feeding a 1 kHz test signal 60 dB underneath the full scale and measuring the noise floor of the amp. The amplification of the amplifier is set such that the full output power of the amp can be achieved. Subsequently, only the noise in the range of 20 Hz and 20 kHz is considered. The noise at different frequencies is eliminated by a filter. Subsequently the amount of the noise energy in relation to the full-scale output power is calculated and expressed in db.
Often the signal-to-noise ratio is expressed in a more subjective manner as "dbA" or "A weighted". In other words, this method tries to express how the noise is perceived by a person. Human hearing is most sensitive to signals around 1 kHz while signals under 50 Hz and above 14 kHz are barely noticed. The A-weighted signal-to-noise ratio is generally higher than the unweighted ratio and is published in the majority of amp spec sheets.
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