Specifically, I’m wondering about the approximate dB level of a yappy little dog as it compares with, say, a conversational human voice, or a car alarm.
Also, is there a formula for approximating the diminishment of sound over distance?
And how much does a plate glass window muffle noise?
Just wondering.
First, let’s get the formula for decibels expressed. Divide intensity, expressed in watts per square meter for example, by the threshold of hearing expressed in the same units. Ten times the logarithm of this value (log[sub]10[/sub]) is then the decibel level. Expressed:
Intensity (in dB) = 10 log[sub]10[/sub] ( I / I[sub]0[/sub]), where I[sub]0[/sub] is the threshold of human hearing.
This means the threshold of human hearing is 0 dB. By contrast, the threshold of pain is around 130dB, or 10[sup]13[/sup]I[sub]0[/sub].
This page gives a table (at the bottom of the page) that lists some various levels for comparison.
No, that’s 20 log[sub]10[/sub] ( I / I[sub]0[/sub]).
55 dB is the conversational level for people at a distance of 10 feet.
I should have been clearer. 55- 60 dB is pretty standard as noise regulation level at night. So if you can’t carry on an average conversation while the dog is barking it probably is exceeding your local regulations,
Er, no. Check here. The factor of two comes from comparing things that are proportional to the the square root of power; in logarithms, exponents may come out as factors. This would account for the extra “2”.
Almost certainly not. The regulations will only ever cover average levels over a period of time. A dog barking, or a car backfiring, or a thunderclap will all have a peak well into three figures dB, but over a fraction of a second. While unpleasant, this will do no damage to the ear.
Q.E.D. that is the logarithmic equation for the power of sound. Although your values should be voltage A over voltage B.
Actually, ZebraShaSha, the 20log is for pressure. Power is at 10log, same as intensity. Voltage doesn’t enter into it, since we’re talking about sound.
Exactly which one you’re working with is often the source of much confusion, since dB is commonly used for both. Even though without a reference it’s meaningless, we often see figures with just ‘dB’ in reference to sound. (dB used in other fields usually get a proper suffix, like dbU, dbm, etc.)
By far the most common when referring to sound is the SPL (Sound Pressure Level) since this is the easiest to measure. Probably any table with ‘sound levels’ in decibels is using SPL. If a distance is indcated, it’s almost certainly the SPL (intensity also varies with distance but is rarely used). db-SPL is the recommended format to avoid confusion. The formula is 20 log (p/p[sub]0[/sub]), with p[sub]0[/sub] the threshold of hearing, ~2 x 10[sup]-5[/sup] Pa rms.
To help answer one of the OP’s questions, a doubling of distance from the source yields a drop of 6 dB-SPL, assuming an idealized open area with no reflections or dampening due to material.
Along with intensity, the sound power level uses the 10 log formula ( 0 dB = 1 pW ). The power is independent of distance to the source, it’s simply the total amound of power being emitted. Figures of ‘sound levels in dB’ for gerneric sources without reference to distance ought to be referred to power level, as it seems the most useful in that case. Most of the time this isn’t what’s used, however.
The first link erislover posted covers this a little bit, but perceived loudness is a function of frequency as well. The Fletcher-Munson Curves are based on experimental data, although this is a subjective measurement. The y-axis is intensity, meaning that a higher plotted value on a curve indicates a higher SPL was required for that tone to sound as loud as one lower down (on the y-axis) on the same curve.
Thus a higher-pitched yipping of a dog will probably sound louder than a low growl, even if they have the same intensity. (For reference, a 1kHz pure tone is commonly used as a test signal, possibly heard in the past on signed-off television stations).
Panamajack covered it pretty well. I’m used to working with dB[sub]SPL[/sub], which is the equation I posted. I like the idea of one concept, one equation. sigh
Oh, sure, make things simple whydontcha. 