Twice the sound level is +6dBA right?

[sreten]

Originally Posted by Salas

What do you mean? dbu etc?

Hi,

dB line level gains are 20log(V2/V1), i.e. x10 voltage gain is +20dB not +10dB.
Thats because line levels are expressed in power, not voltage terms.
Squaring V for power dB simply doubles the voltage dB value.

That just the way it is, from telecomms ages ago, a 600R load is assumed.

If a speaker SPL is +/-3dB over a range, actual pressure is +/-1.5dB.
(A specification cheat thankfully no-one seems to have resorted to.)

The -3dB downpoints in FR of a circuit represent the points voltage is 0.7
down, not half, that would be -6dB. Just to confuse matters for say the
low bass roll-off via a coupling capacitor of a circuit, when Zc = inputR
of the circuit voltages are not split 50:50, each has 70% of the voltage
due to the 45 degree phase shift at that point. All makes sense eventually.

-3dB is the half power point, not the half voltage point, it is sensible.
The above simple LF coupling FR case is where it all comes from.

rgds, sreten.

[Salas]

On consoles 0 VU is +4dBu which is 1.228V. So its voltage scale.

[Pano]

It's a mess, that's what it is.

[sreten]

Originally Posted by Salas

On consoles 0 VU is +4dBu which is 1.228V. So its voltage scale.

Hi, clueless, not listening and simply wrong, rgds, sreten.

Different line level standard reference voltages are simply irrelevant.
Relative levels within any standard are the same and as I described.

This is pretty bog standard stuff if you want to understand electronics.

If you want voltage indication simply divide any dB meter reading by 2.
A totally pointless exercise, either scale makes no real difference.
But all dB meters indicate power, double the dB range of dB voltage.

[Salas]

Dear Sreten, you stated that ''SPL is not pressure just as levels in studio equipment are not voltage''. Although the levels on studio equipment meters are referenced to dBu which simply comes from dB ''unloaded''. 0dBu=0.775VRMS. That is they display a voltage referenced scale in dB or not?

[sreten]

Hi,

dB meters display relative power levels. If you want voltage levels halve the indicated reading.
0dB for the meter will be related to to a standard voltage level, related to to that voltage
squared into a fairly meaningless standard load, for a meaningless reference 0dB power level.
But that is the way it is .

Nevertheless the dB indicators on your deck, desk or whatever, show power, voltage squared.

-3dB on a graphic EQ or tone control is power, not voltage, voltage values are half that in dB.


rgds, sreten.

[a.wayne]

Originally Posted by Salas

For the human to roughly describe as twice as loud indeed.

Yes ...

[Salas]

Originally Posted by sreten

Hi,

dB meters display relative power levels. If you want voltage halve the indicated reading.

rgds, sreten.

The audio equipment meters are calibrated on voltage reference. 0=+4dBu on pro equipment.

[sreten]

Originally Posted by Salas

The audio equipment meters are calibrated on voltage reference. 0=+4dBu on pro equipment.

Hi, so ? that and the attachments you posted totally agree with what I'm saying, rgds, sreten.

[Salas]

Originally Posted by sreten

Nevertheless the dB indicators on your deck, desk or whatever, show power, voltage squared.

rgds, sreten.

You probably mix something you remember from telecom practice. From Wikipedia:

"In professional audio, a popular unit is the dBu (see below for all the units). The "u" stands for "unloaded", and was probably chosen to be similar to lowercase "v", as dBv was the older name for the same thing. It was changed to avoid confusion with dBV. This unit (dBu) is an RMS measurement of voltage which uses as its reference 0.775 VRMS. Chosen for historical reasons, it is the voltage level which delivers 1 mW of power in a 600 ohm resistor, which used to be the standard reference impedance in telephone audio circuits."

Just because dBu it can be converted to an easy to memorize 1mW reference if put across 600R, does not mean that it shows power. Whenever you see 0VU on any pro dB meter its 1.228VRMS which is the +4dBu pro standard level 0 and that is all there is to it.