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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: coupling cap -3db point posted by Tweaker456 on May 16, 2016 at 15:24:04:
You are speaking as if there is only one pole, one roll-off point, and that would be a wonderful thing to deal with.
But seldom is there only one capacitor roll-off in the audio signal path.
What happens when there are five capacitors all in the signal path?
Let's use a simple example:
Capacitors chosen to roll off at 20 Hz, five of them.
One cap: -3 dB at 20 Hz, approx. -1 dB at 40 Hz.
Two caps: -6 dB at 20 Hz, approx. -2 dB at 40 Hz.
Three caps: -9 dB at 20 Hz, approx. -3 dB at 40 Hz.
Four caps: -12 dB at 20 Hz, approx. -4 dB at 40 Hz.
Five caps: -15 dB at 20 Hz, approx. -5 dB at 40 Hz.
Now, aside from the massive amount of phase shift this causes (225 degrees at 20 Hz), the amplitude response is now down 5 dB at 40 Hz.
Unless you know what the OTHER roll-offs are in the rest of the system, and what the implications are, it is not wise to start a roll-off too high, even with one single stage involved.
Jon Risch
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Follow Ups
- Can't look at it in isolation - Jon Risch 20:20:16 05/18/16 (0)
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