> From [email protected] Fri Feb 3 12:55:53 2012
> Date: Fri, 3 Feb 2012 12:55:51 -0500 (EST)
> From: Igor Roshchin <[email protected]>
> To: [email protected]
> Subject: OT question for electronics geeks
>
>
>
> Rick Womer wrote:
>
> >I have this nifty new receiver, which sounds great--a huge improvement
> >over my 38-year-old Pioneer.
> >
> >What puzzles me is the volume control: Minimum volume is -90dB (mute),
> >and maximum is +15dB.
> >
> >Huh?
> >
> >What is zero dB? Is it an arbitrary point? Is it linked to some
> >undisclosed property of the unit?
> >
> >I can tell you that 0dB is too loud to be in the room with using the
> >tuner, barely tolerable with a CD, and just a bit loud with an LP.
> >
> >Otherwise, the scale makes no sense to me.
>
>
> Typically, 0 dB represents 1 mW (milliWatt).
> The formula for power is L_dB= 10 log_10 * (P1 / P0), where P0=1 mW
> So, -90 dB - +15 dB would mean the range from 1 pW (picoWatt)
> [non-audible] to ~32 Watt. That is probably smaller than the max output
> of your tuner.
>
> What bothers me is that in this definition, 600 Ohm load is assumed.
> So, for the typical speaker load of 8 0hm , the same voltage will
> produce 75 times higher power.. But that would be way too much
> (32 Watt * 75)!
>
> But at the same time some sources suggest that 0 dB in case of
> audio tuners/amplifiers corresponds to the maximum output level with
> no noticable distortions.
> Then, I am not sure how the maximum output power relates to this. I can
> see two possibilities:
> 1) 15 dB corresponds to the max rated output power (say, 100 W).
> Then it would mean that you don't have distortions up to about 3 W,
> which is too small.
>
> 2) 0 dB corresponds to the max rated output power (say, 100 W).
> Then it would mean that the amplifier can drive up to 3200 W, which is
> way to much.
>
> So, I am confused by that specification.
>
> Igor
>
While doing some search, I found this definition on one of the forums:
"0dB is supposed to be used as the "Reference Level", meaning that in
room, at the listening position all speakers will produce average levels
of 85dB SPL. This is relative to the speaker efficiency, the amplifiers
sensitivity and the room acoustics."
See this reference related to this definition:
http://www.thx.com/consumer/thx-technology/thx-reference-level/
Igor
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