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Intensity tells you how sound energy propagates through space, but the only way you can measure intensity is by measuring the pressure. Now there is a big theoretical question, why do we have two definitions for the same quantity, is this really the same thing, or just made the same, or just coincidence? It is interesting to note that this is not neccessarily true for underwater acoustic, where they use different reference sound pressure and possibly different reference sound intensity too. Taking for air $\rho = 1.2$ kg/m $^3$ and $c = 340$ m/s, you readily obtain Where $\rho$ is density of medium and $c$ is speed of sound. This can be proven by taking the well-known relation for sound intensity In principle they could be different, depending on the defition of reference values, which are completely arbitrary! But for study of air sound, they are the same because $I_0 = 10^$ Pa. Where $I$ is sound intensity, $I_0$ reference sound intensity, $p$ is sound pressure (RMS) and $p_0$ reference sound pressure. Looking at the link you specified I think that you really want to compare sound intensity level $L_I$ and sound pressure level $L_p$. Sound intensity $I$ is not measured in dB but in W/m $^2$. If he doubles his sound INTENSITY, you need to nail down whether that is in units of pressure or power.įirst of all, there is a mistake in the question. If he doubles his sound PRESSURE, that is a 6dB increase. If he doubles his POWER level, that is a 3 dB increase. So, you need to watch your units, and make sure the other guy is watching his. Note that I did not explicitly state what increased by 20dB in that last sentence. These two actions are synonomous, and result in a 20dB increase. Thus, if you increase sound PRESSURE by a factor of 10, you have increased POWER by a factor of 10^2 = 100. Sound power is proportional to sound pressure squared. Sound intensity (if expressed as a pressure) and Sound Pressure Level (SPL) are the same. The answer to your question is: It can be. A sound with POWER 100 times the reference would be 20 dB. So a sound with 10 times the POWER of that reference would be 10 dB. I think the reference used is the sound pressure which is the threshold of human hearing. In most sound references, "dB" means "dB in reference to (as a ratio over) 'X'." Where 'X' is a reference level. And dB always refers to a ratio of power. It does not matter whether it is sound or electricity or whatever. A decibel slices each Bel into ten parts. A Bel is the base-10 logarithm of a power ratio.
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More specifically, a logarithm of a ratio of power/power (which is why dB has no units). The first thing to understand is that dB is a logarithm of a ratio.