On 26 Feb 2006, at 22:49, Kevin Cosgrove wrote:
On 26 February 2006 at 20:50, Dan Mills
<dmills@xxxxxxxxxxxxxxxxxxxxx> wrote:
Surely -INF dB SPL?
Negative dB would imply that the unit absorbs sound. Do you think it
does that? 0dB indicates it neither creates nor absorbs sound.
Err No!
0dB indicates a signal having the same power as the reference (in
this case 0dB indicates a signal having an amplitude of 20uPa). Note
that referencing a scale based on power to a pressure level is a
little unnatural, but as long as the base pressure and viscosity are
constant it can be done.
No power is -infinity in any dB scale by definition, and Negative dB
levels are routinely encountered, for example a transmitter may be
specified as having an output of 20dBm, or -10dbW, these two are
equivalent it is just that one is referenced to 1mW, the other to 1W.
Regards, Dan.
