What is Sound Pressure Level?

[JBL 4645]

Altec consultant Robert Heiblim explains about sound pressure level that we like to listen to.

[Akira]

This is supposed to be educational ...waste of time.

3db is not twice as loud

[hjames]

We've been over this before Ashly -

To double the apparent volume requires 10db ... not 3 db
Believe me or don't, Ash, I don't really care - it just IS.
get some technical books if you need to verify this.

or read this ...
http://en.wikipedia.org/wiki/Decibel

The decibel (dB) is a logarithmic unit that indicates the ratio of a physical quantity (usually power or intensity) relative to a specified or implied reference level.

A change in power ratio by a factor of 10 is a 10 dB change.
A change in power ratio by a factor of two is approximately a 3 dB change.
More precisely, the factor is 103/10, or 1.9953, about 0.24% different from exactly 2. Similarly, an increase of 3 dB implies an increase in voltage by a factor of approximately , or about 1.41, an increase of 6 dB corresponds to approximately four times the power and twice the voltage, and so on. In exact terms the power ratio is 106/10, or about 3.9811, a relative error of about 0.5%.

[JBL 4645]

Nice bit of computer modelling.


This one has that one, extra push over the cliff these go to "11"

[timc]

To make it VERY simple.

SPL (sound pressure level) is JUST what it says. The pressure generated by the sound. This is related to the lowest noise we are able to detect. This level is standardized to 0dB SPL
= 20uPa. The relation between the numbers are that the SPL rises with the square of the pressure.

A 3dB equals a doubling/halfing in sound POWER, not level. The percieved doubling to humans is right under 10dB. Think its 9,98 or something like that. This is because our ear also work logarithmically.

So. What can we see from this. Well, it is very important not to mix pressure, and sound pressure level. The sound pressure level is always positive (given that is it pressure^2). The pressure on the other hand, oscillates between positive and negative. Its like a high/low pressure weather system, continually, and gradually changing places. The result of this is that the air isnt actually moving towards you when you listen. The waves just ripple towards you, and the air molecules are just vibrating betwwen the pressure max and min, at the time the soundwave passes through their position.

[ratitifb]

The sound pressure level is always positive

not always, depending on the reference you have chosen. For exemple, if you choose 1Pa as reference level for dB scale, a lot of sound pressure levels will have a negative SPL (dont' forget 20µPa is equivalent to -94dB re 1Pa)


LOUDNESS in sones is the best way to express the perceived hearing level when doubling loudness is twice as loud (equivalent from 6 to 12dB more ... depending on the spectra characteristic of the sound source)

[JBL 4645]

Hey guys I’m not looking for answers? That's why I posted the two videos. I found the two videos a bit unsatisfying they weren’t thorough enough in detail with using test equipment, that's how you get the message across.

It was just a load of talk "use AAA batterers" what? I thought the video was a joke. I think, Carl Sagan could have explained in a more thorough and entertaining way.

[timc]

not always, depending on the reference you have chosen. For exemple, if you choose 1Pa as reference level for dB scale, a lot of sound pressure levels will have a negative SPL (dont' forget 20µPa is equivalent to -94dB re 1Pa)

You misunderstand me. The SPL can be negative on a relative scale, but never on an absolute scale. I was thinking physical here. On the other hand, the Pressure is negative in an absolute manner.

[timc]

Hey guys I’m not looking for answers? That's why I posted the two videos. I found the two videos a bit unsatisfying they weren’t thorough enough in detail with using test equipment, that's how you get the message across.

It was just a load of talk "use AAA batterers" what? I thought the video was a joke. I think, Carl Sagan could have explained in a more thorough and entertaining way.

Erh.....Then what was the point of the post? Just saying that "here is another guy who doesn't really know?

If your intention was to make fun of the guy, you should have stated so in your first post.

[Rolf]

How hard can it be? To increase the level 3db you must double the power they can do. To double by 10db you need about 3,5 more power from your amp. Simple. Here is an example:

You use 10W to produce 100db. 103db you must have 20W. 106db you need 40w, and so on. That is why you need a large power amp. An "ineffective" speaker witch can only give 90db using 1W, you can figure it out yourself.

This has been discussed many times before.

[timc]

To double by 10db you need about 3,5 more power from your amp.

I guess you mean 10 times more?

[Rolf]

Sorry for error. Yes. But the rest should be correct.

I guess you mean 10 times more?

[Ruediger]

A power ratio is power1 divided by power2, P1/P2.
A voltage ratio is voltage1 divided by voltage 2, U1/U2.

x dB = 10 log10(power ratio) = 20 log10(voltage ratio)
The Bel designates a logarithm, it is not a real unit, it can be omitted, does not need to be cancelled.

Example: 10 dB = 10 log10(P1/P2),
ergo 1 dB = log10(P1/P2)
10**1 = 10**log10(P1/P2)
10 = P1/P2

Another one: 10 dB = 20 log10(U1/U2),
ergo 0.5 dB = log10(U1/U2)
10**0.5 = 10**log10(U1/U2)
3.16= U1/U2

So 10 dB is a power ratio of 10 and a voltage ratio of 3.16

ruediger

[Rolf]

This was to complicated for me. Please explain for the ones deadly.

A power ratio is power1 divided by power2, P1/P2.
A voltage ratio is voltage1 divided by voltage 2, U1/U2.

x dB = 10 log10(power ratio) = 20 log10(voltage ratio)
The Bel designates a logarithm, it is not a real unit, it can be omitted, does not need to be cancelled.

Example: 10 dB = 10 log10(P1/P2),
ergo 1 dB = log10(P1/P2)
10**1 = 10**log10(P1/P2)
10 = P1/P2

Another one: 10 dB = 20 log10(U1/U2),
ergo 0.5 dB = log10(U1/U2)
10**0.5 = 10**log10(U1/U2)
3.16= U1/U2

So 10 dB is a power ratio of 10 and a voltage ratio of 3.16

ruediger

[Ruediger]

A power ratio is power1 divided by power2, P1/P2.
A voltage ratio is voltage1 divided by voltage 2, U1/U2.

x dB = 10 log10(power ratio) = 20 log10(voltage ratio) <<< THIS IS THE DEFINITION OF THE dB
The Bel designates a logarithm, it is not a real unit, it can be omitted, does not need to be cancelled.

Example: 10 dB = 10 log10(P1/P2), <<< DIVIDE EQUATION BY 10
ergo 1 dB = log10(P1/P2) <<< RESULT OF DIVIDE
10**1 = 10**log10(P1/P2) <<< RAISE 10 TO THE POWER OF THE LEFT RESP. RIGHT SIDE
10 = P1/P2 <<< RESULT OF RAISE

Another one: 10 dB = 20 log10(U1/U2), <<< DIVIDE EQUATION BY 20
ergo 0.5 dB = log10(U1/U2) <<< RESULT OF DIVIDE
10**0.5 = 10**log10(U1/U2) <<< RAISE 10 TO THE POWER OF THE LEFT RESP. RIGHT SIDE
3.16= U1/U2 <<< RESULT OF RAISE

So 10 dB is a power ratio of 10 and a voltage ratio of 3.16

ruediger