Decibel levels decrease with increase in volume

[tikka]

So I have what may be an embarrassing simple question but one that has bothered me enough that I'm willing to look the fool to find an answer.
Why do some electronics have a display that reads a decreasing noise or dB level as you increase the volume? Anyone else understand what I'm describing?
We've got an older amp that when completely quiet reads "80". When you crank up the volume, the scale works its way down to 79, 78, 77, etc.....into the 20's and then the teens.

Is this a chip that was reversed when the electronics were assembled?
Thanks.

 

[Superduper]

db is a logarithmic unit used to describe a ratio.

You aren't seeing it count down, because if you look closely, what you are seeing is a minus number, counting up to 0db, which is an arbitrary starting point, probably representing maximum power.

So -60db compared to 0db is larger than -70db compared to 0db. Get it?

 

[tshorba]

Zero on the display is what the manufacture classes as "reference level", this is the supposed level they take their power rating from.

The negative level is a numerical value given to the attenuation applied from the pre amp to the power amp. It is common on newer amps and AVR's.

Zero does not indicate maximum volume, most intergrated amps will go to positive 15 on the display. Once you hit positive 1 you are applying gain to the power amp (as opposed to attenuation) and will soon send it into clipping, killing your speakers and possibly the output devices.

 

[Superduper]

Ok. What Tshorba said. Except that's probably only true if we are speaking of a VU meter scale as opposed to the markings on a volume control scale. I just turned around and looked at the first amplifier I could find sitting behind me -- a Pioneer Spec-1 preamp and the volume control reads, at the very end of the scale -- a big fat ZERO and -infinity at the other end of the scale. I presume that when my Spec-1 volume control is turned ALL THE WAY to the right, that I'll be hearing maximum power. There was no scale past Zero. Whether it's clipping or not, or overdriven at that point is irrelevant. The reason you can't affix reference level to a volume control is that there is no way to guarantee that the injected signal meets that particular manufacturer's observed reference level.

I'm talking volume control here, which I presume is what the OP is speaking to also, since I've never seen a VU meter read 80, 79,78, etc. and also where I would expect to see -(x)db 0db +(x)db range (on a VU meter).

I'd admit I have not seen every amplifier out there, and there probably exists some with volume controls scaled that way, from (-) to zero to (+). But not mine.
In any event, the point is that db is a ratio and anything on the left of ZERO is smaller and anything to the right (if any) is greater.

 

[tshorba]

I took it that the unit has a digital display/representation of the "level", there was no mention of "vintage" but a mention of "display" in the op. Older analog pre's and volume controls used a printed scale around the knob (like :superduper: spec pre) this style never showed gain, just zero attenuation.

Maybe the op can tell us what amp it is.

 

[Superduper]

Well, Tshorba is probably right. I don't own any modern amps -- only the classic stuff, and forgot that display could mean, a digital MCU controlled display. I simply presumed classic.

 

[tikka]

Thank you for your interest and postings Tshorba and Superduper.

Upon closer inspection, the screen on the amp does in fact read negative numbers, correspondingly increasing with an increase in volume.
The box is a newer one, from around 2002 I think. While this forum is geared towards classic and vintage electronics, I thought I'd plumb the waters for help anyways. Lucky for me there are knowledgeable folk about.

While I do think I understand the explanations, I do find it odd that manufacturers would use dB on their scales indicating volume output.

Is it fair to say that if I rotate the volume knob and the value displayed climbs from -55 to -65, I have increased the volume by 10 dB?

 

[Superduper]

No. -55 should be louder than -65.

It might be easier to understand if you think about a number line. Put or find ZERO on the line and anything to the left would be less than zero, anything to the right would be above zero. So -65 on the scale would be further left than -55, so it would be a smaller number, lower volume, less power, etc.

softer louder
or
softer louder

 

[tikka]

Ah dang. :annoyed: I meant -65 to -55. Call it a typo.

 

[Superduper]

Ah dang. :annoyed: I meant -65 to -55. Call it a typo.

You mean I typed all that for nothing.

 

[tikka]

No, man. I appreciate your efforts. I'm grateful for your help and patience explaining this to me.

Sorry I got my numbers turned around there.

 

[tshorba]

Is it fair to say that if I rotate the volume knob and the value displayed climbs from -55 to -65, I have increased the volume by 10 dB?

No the dB on your display is not a representation of SPL, there are many types of dB measurements. The manufacture(s) do not put the suffix after the dB on displays. You have not increased the volume by 10dB(SPL) but decreased the attenuation by 10dB(?). Less attenuation (-60 to -50) applied to the power amp = higher the output (loudness or SPL) from the power amp.

Again it is a numerical value of the attenuation applied to the power amp from the pre, it is not a representation of dB-SPL (sound pressure level). There is no way the amp can know it's SPL due to input sensitivity variances, speaker sensitivity and room acoustics, without a mic providing constant feedback to the amp.

If you have a reading of lets say -30 (my everyday listing level) and you stop a DVD (no sound from the source), the dB representation does not change, if it was an SPL reading it would automatically read -80, which is essentially mute.

I hope this has made it a bit clearer for you.

 

[tikka]

Yes, indeed. Thank you again!