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Old 07-14-2002, 07:58 PM   #1
Lee

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What is meant by "frequency response?"

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1.2 What is meant by "frequency response?" [JSC]
The frequency response of a device is the range of frequencies over which that device can perform in some fashion. The action is specific to the device in question. For example, the frequency response of the human ear is around 20Hz-20kHz, which is the range of frequencies which can be resolved by the eardrum. The frequency response of an amplifier may be 50Hz-40kHz, and that of a certain speaker may be 120Hz-17kHz. In the car audio world, frequency responses should usually be given with a power ratio range as well, such as (in the case of the speaker) 120Hz-17kHz +/-3dB. What this means is that given an input signal anywhere from 120Hz to 17kHz, the output signal is guaranteed to be within an "envelope" that is 6dB tall. Typically the extreme ends of the frequency range are the hardest to reproduce, so in this example, the 120Hz and 17kHz points may be referred to as the "-3dB points" of the amplifier. When no dB range is given with a frequency response specification, it can sometimes be assumed to be +/-3dB.
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Old 02-15-2004, 06:15 AM   #2
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Old 02-15-2004, 06:34 AM   #3
Mark Zarella

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Suggested Corrections

"The frequency response of a device is the range of frequencies over which that device can perform in some fashion. The action is specific to the device in question. For example, the frequency response of the human ear is around 20Hz-20kHz, which is the range of frequencies which can be resolved by the eardrum."

**Not quite. The ear drum is responsive over a much broader frequency range. The frequently-quoted 20-20kHz is a figure limited primarily by the mechanical transduction process of the inner ear. Also, a more realistical number would be somewhere between 30Hz and 18kHz.

**Moreover, the phrase "frequency response of the human ear" is a bit faulty because it's not really a frequency response (the transfer function is a lot more complex, and it's modulated by other factors). It's a sensitivity function. Anyway, I'd take that line out.

**This, by the way, also brings up a glaring ommission. There's nothing written anywhere about the most important part of the audio chain: the human observer!

"The frequency response of an amplifier may be 50Hz-40kHz, and that of a certain speaker may be 120Hz-17kHz. In the car audio world, frequency responses should usually be given with a power ratio range as well, such as (in the case of the speaker) 120Hz-17kHz +/-3dB. What this means is that given an input signal anywhere from 120Hz to 17kHz, the output signal is guaranteed to be within an "envelope" that is 6dB tall. Typically the extreme ends of the frequency range are the hardest to reproduce, so in this example, the 120Hz and 17kHz points may be referred to as the "-3dB points" of the amplifier. When no dB range is given with a frequency response specification, it can sometimes be assumed to be +/-3dB."

**An important point, but it seems buried in the numbers. I think it should be stressed that the frequency response must be accompanied by the "attenuation" numbers, and a sample freq response graph can even be provided to illustrate how freq response can change if you use different values as your threshold (a picture says a thousand words). It should also be pointed out that improving freq response beyond human detection capability is fruitless.
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