Why Does my Amp Start at (-) 30dB
 

I have a new Sony Home Theater Amp/Receiver (HDMI, etc.). There is an LED display that indicates the volume level. When you power up the amp it indicates -30db. 0 db is quite loud. What is it that I do not understand about dbs?

Furthermore, have you noticed that the manuals that come with these things do a very poor job of explaining what the various features actually do? They show conventional hookups, and how to access various features, but not why. In fact, if not for a blurb on the box label I would not have understood one of the really cool features of the system. Maybe it's just me...

The number on the dial is the degree of attenuation. A volume knob is a really a throttle, if you didn't have it in the circuit the amp would run wide open.

Wouldn't it be a lot less confusing to just have 0-10 (or 11) or 0-100?

+1 what John Cramer said. If you want to get a handle on the basic idea, Odb is how loud your receiver would be if it had no volume knob at all to get in the way of things(in theory). Some people call it "unity gain" and there's a mathy way to describe it, but that's how I wrap my pea brain around it. Maybe someone will describe it better or more correctly. Actually I'm sure someone will try.

"This one goes to eleven."

The way I understand it, and I'm not an authority, is that 0db is reference for your receiver's test tones. That should put the test tones at either 75 or 85db depending on the requirement for your particular receiver. As you said, 0db will most likely put normal sound over 100db so be careful. Actual sound level is based on amp power, speaker resistance, speaker efficiency, and room acoustics.

So if you were to manually calibrate your sound room with a sound pressure meter, you would run the receivers internal test tones at 0db.

David

Your receiver (preamp) is set up so that 0db is actually unity gain. This is the point where the signal is not affected by the device. For example: +10 db is boost and-10 db is a cut by 10 dbs. Unity gain is considered ideal gain staging where as little noise, distortion, etc is introduced into the signal by the electronics.

Or something like that.

-e.

I am very sorry - But I just don't understand the above. I'm sure it's me, but what's wron with a scale of 10. Is the display giving me any useful information?

daepp:

Put on some music and if you want it louder, turn the knob clockwise, or push the (+) button. For quieter, counter-clockwise or the (-) button.

DONE!
:D

Uh, no Terry. The actual SPL of your system will vary quite a bit with speakers of different efficiency. The "O dB" etc. stuff inside the receiver has very little to do with dB in SPL (sound pressure level) terms.

hmmm.. I thought that was exactly what I just said. :confused:

zero is used for reference calibration

edit: Each speaker is calibrated to 75 or 85db(dependent on your manual) with SPL meter with the volume set to 0db running test tones. This is how I understood it was done.

Obviously with a real signal through the system you could be over 100db with the dial at 0db.

Well said - forget I brought it up. I'll just crank it to 11!!!!!

- that would work for a pre-amp - BUT not for a Receiver or an Amp (i.e. anything that drives the speakers).

JC's and Wayne's answers are the on the mark. Except instead of "real' measurement in Wayne's answer re dB, substitute "absolute" measurement...

Yes - in fact, it is giving you more useful info, since it is telling you when you have moved 1 dB. A 1 to 10 scale wouldn't do that.

Just twist 'till it sounds good...

I guess what I'm saying is, What Manual? The receiver manual? or the speaker manual? And how could either manufacturer have any clue what other components you're going to be using, and what kind of SPL you'll get?

It's Bush's fault. And the gun lobby.:D

Turn knob left. Sound is quiet.

Turn knob right. Sound is loud.

When you can walk the rice paper, and leave no path......

As above, 0dB (in theory) is the maximum output of the receiver at it's rated power & distortion specs. But speaker efficiency will change the actual real-world 'loudness'.

Depending upon the receiver & the source & the loudspeakers & the air volume of the room, straying above 0dB could damage the speaker. Or not . . .

Ian

Logarithmic scale (dB) is very practical since our hearing is ~ logarithmic.

Below one of the funniest clips on Youtube.

http://www.youtube.com/watch?v=AhVWJgIzftE

For the most part the speakers are a fixed entity. We adjust the current sent to them, so my reference is to the amp/receiver. The amp doesn't know what the efficiency or ohm rating is for any given speaker, using test tones allow for compensation. As each speaker sounds its tone, adjustments are made when taking readings (SPL meter) from the "sweet spot" of the room. This is usually the triangular spot drawn among the two main speakers and the point they intersect at the seating area.

Not every room allows for perfect balance or reflection/reverberation, so calibrating loudness and the distance is a way of compensating to get the best sound possible.

My understanding is that a receiver is a composite device comprised of a tuner and preamp and amp (sometimes, and apparently in this case). The gain control on the front of the receiver would be for the preamp. In most cases the amplifier is operating at full gain. At least it should be.

-e.