harman kardon

RuSsMaN

Tour,

Where is 3db defined as 'double the spl, volume, double anything?'

The only 'double' with 3db associated to it, is it takes DOUBLE the power to increase by 3db.

10 db is a perceived doubling of spl, period.

Burdette? Anyone? Am I THAT high?

Cheers,
Rooster

George Grand

Freakin' kids.

We, as humans, PERCEIVE a 3db increase in SPL as "twice as loud". That is (or was) the big deal about efficiency ratings. If realistic rock was your bag, an 84 required a lot more amp than an 87.

Now, the 10x part comes in here. Because us, and SPL are EXPONENTIAL, it takes 10 times the amplifier to actually MAKE something twice as loud.

Don't bother me about this anymore.

George Grand (of the Jersey Grand's)

Tour2ma

Geez George, it's getting so a day with you is like a day without sunshine... :rolleyes:
I have not a clue as to what you mean by the “us” half of your “us, and SPL are EXPONENTIAL” statement.
The only reason that the SPL, or any other log scale, is created is to yield figures that are easier to manage, e.g., 0.0 to 120.0 dB audible range rather than 0.0 to 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000.0 dynes/ cm2 (or watts/ m2). Count the zeroes if you like, there are 120 of them… Even 1.0 x 10**102 is cumbersome compared to the log scale.

Originally posted by RuSsMaN
Tour,
Where is 3db defined as 'double the spl, volume, double anything?'
... Am I THAT high?

The Magic 8-Ball says, “Decidedly Yes.”

I had the equation wrong that I posted earlier. Corrected the earlier post and now repeat it here in another quote from the link I listed earlier. The subscripts are messed up in copying them over to the post, but should give the idea.

A unit of a logarithmic scale of power or intensity called the power level or intensity level. The decibel is defined as one tenth of a bel where one bel represents a difference in level between two intensities I1, I0 where one is ten times greater than the other. Thus, the intensity level is the comparison of one intensity to another and may be expressed:
Intensity level = 10 log (I1 /I0) (dB)

So to get the dB result of a doubling of sound intensity, i.e., volume, all we have to do is state that I1 is twice the intensity of I0, or I1 = 2 x I0. Then we can substitute 2 I0 for I1 in the equation yielding:
Intensity Level = 10 log (2 I0/ I0) = 10 log (2) = 10 x 0.301030 =~ 10 x 0.3 = 3.0 dB
And there’s the numerical answer you seek…

BTW, if you strip away part of the earlier link’s URL, you get to the index page, here:
http://www.sfu.ca/sonic-studio/handbook/
Awesome looking little reference there, complete with audio to demo certain points.
For example, here’s a link to a 6 db declining scale event followed by same with 3dB steps: http://www.sfu.ca/sonic-studio/handbook/Sound/Decibel_Ramp.aiff

After listening to the 3 dB, would I say that each succeeding beep is half as loud as the prior one? No. Would a say for the 6 dB tones each is 1/4th as loud as the one before it? No. But in neither case, is it because I can’t hear the decline, it’s that ears aren’t calibrated that way. At least mine aren’t…

Dr. Spec

Hi tour:

Tons of good work here.

1) A 3 dB increase is exactly double the sound pressure. The dB scale is log base 10, and it is fairly straight forward math to prove that, as you just did below.

2) The crux of the matter at this point is how does the human ear perceive increases in sound pressure. And while that may at first sound subjective, it can indeed become objective if enough statistical population data sampling is conducted.

This is exactly what Fletcher and Munson did in their landmark 1933 (and STILL 100% valid) study. This study eventually led to the development of standardized ISO Equal Loudness Countours which are still used today.

You will note after studying this chart, that a 10 dB increase in sound pressure level is perceived as being twice as loud, with loudness being measured in units of "sones".

This general rule holds true at most frequencies above 250 Hz at normal volumes. As shown in the chart, the human ear is less sensitive to volume increases in bass frequencies, especially at low volumes. Hence the development and popular use of the "loudness" switch on hi-fi gear in the 70's and 80's.

Hope this helps. Read all about it here:

http://ceae.colorado.edu/~muehleis/classes/aren4020/handouts/lecture7/loudness.pdf

Doc

Tour2ma

Thanks Doc, another nice link for the reference library. Now I even know what A and C weighting mean.

Let me see if I can summarize the preceding technical discussions:
- I got the sound energy part right, it doubles every 3 dB.
- Russ got the "what we perceive as double" part right, 10 dB.
- When George said our hearing is “calibrated” logarithmically, he was correct given the 10 dB doubling.

Should about cover it.

I'd like a read of the Fletcher and Munson work. Anyone have a link?