Why do receivers display -Db ? - Axiom Message Boards

I guess the title says it all but can anyone please explain why a receiver will display from -80 Db to maybe +17 Db? A display of maybe -30 Db generates an SPL of about 60 Db in my room. Are these indicatations that arbitrary, what ever happened to 0 -10 ?

When you turn up the volume on your receiver, you're not adjusting the power of your amplifier -- which is constant. You're actually "un-damping" the source signal.

0 dB corresponds to an unrestricted line level signal. So when a receiver displays -80dB, this means it has reduced the line level signal by 80dB. When it displays +17dB, it means it has boosted the line level signal by 17dB.

My receiver, an Onkyo TX-DS575 gives me the option of choosing between displaying absolute volume values (0 - 79) or relative values (-infinity dB through +17 dB).

Some pre-amps still have the old 0 - 10 scale, but you won't find that on any modern receiver.

In reply to:
Some pre-amps still have the old 0 - 10 scale, but you won't find that on any modern receiver

And some Spinal Tap models go up to 11.

But seriously... the reading on your receiver is a relative power level, and the dB you're probably more used to (and confusing it with) is dB SPL, sound pressure level...

dB is a bit confusing, since it can refer to many things, usually a letter will be added to the end to give you an idea of what it refers to... ie :
dBm - referenced versus 1mW
dBFS - referenced vs digital full scale (say a square wave alternating between the values 0 and 65535 for a 16bit sample)
dBv - referenced vs 1V RMS (root mean square)
dBu - referenced vs .75(?)V on an unloaded circuit
dB SPL - dB sound pressure levels (logarithmic - where a 3dB increase is a doubling)
there's also a dBa, which has something to do with the psychoacoustic properties of the human ear as it relates to different frequencies... not often used.

As you can see, dB can refer to voltage, power, or sound pressure.

Bren R.

Hi Audiobob,

Thanks to BrenR for the very complete explanation of dB.

To answer your question, it's rather arbitrary on the part of A/V receiver manufacturers to do this, and quite counter-intuitive for many consumers. The speaker's sensitivity will always vary from one brand and model to the next, and this sort of "calibration" assumes a totally standarized line-level analog output from DVD players, CD players, VCRs, etc, which is not the case with lots of consumer gear.

It's become somewhat fashionable for receiver designers to do this--they believe it makes the unit more "professional," but it's much easier for most users to understand that a "1" is a low volume setting and a "10" is higher (louder). I like the idea that the Onkyo is switchable from the dB to the absolute numerical values.

Regards,

So how is it that you can determine when you have reached max power output.The reciever we have goes from -85 to 0.Most of the time for a reasonable level I have it at -20.At that point it does not even get warm.Quite confusing to me.

Richard, you should understand that you might never reach max power output; merely turning the volume all the way up doesn't do it. At typical comfortably loud listening levels(such as your -20)the speakers are using about 1 or 2 watts. Extreme peaks in the music might draw 50 or 100 watts(at the same -20 setting)for a few thousandths of a second.

In reply to:
At typical comfortably loud listening levels(such as your -20)the speakers are using about 1 or 2 watts. Extreme peaks in the music might draw 50 or 100 watts(at the same -20 setting)for a few thousandths of a second.

Which is where we start getting into RMS (Root Mean Square) versus PMPO (Potential Maximum Power Output) or subtitled Why these 200 watt (PMPO), $10 computer speakers sound crappy compared to a pair of 8 watt (RMS) Klipsch speakers".

Ooh, I got a compliment from Alan, whose articles I've read since this goatee was a lot thinner and darker than it is now.

Bren R.

I think the reason why one couldn't match receiver knobs with even power output is that there's a lot of variation in the incoming music (or signal in general); you could calibrate the receiver to show '100 watts' at a certain point on the dial, assuming a 1khz tone, but music is far from a 1khz tone!

Thanks everybody!

In reply to:
dBu - referenced vs .75(?)V on an unloaded circuit

Looked this up tonight... it's actually vs. .775V, not .75.

Bren R.

Whew! That was keeping me up at night, not knowing.

OK, no one's answered, so I guess the question is open: Is Peter right?