Just read an interesting article based on the Precision Rifle Blog piece on Muzzle Brake noise.
It is an informative and interesting article BUT part of it is based on a gross error.
How do I know this? I am an Electronic Engineer and took the masters program in Audiology.
Error to wit;
The article uses a proper Sound Pressure level meter and careful measurement techniques. and the data listed looks very accurate.
The glaring error is the fact they brought in both sound pressure AND sound energy (intensity).
In the measurement of sound level is always measured in sound pressure level (SPL). Sound energy is pretty much only used only in determining potential damage to the ear by excess sound and by Physicists.
The reason the two scales are different is that the equations for SPL is expressed as
20log SPL1/SPL2 and Sound Intensity is expressed as 10 log energy1/energy2.
The resultant change in dB changes from 10db per X10 increase in energy to 20dB per X10 increase in SPL. And 6dB equals 2X, not the 10dB the article claims for SPL.
This means the article expresses their data in SPL but uses the energy equations to convert the dB SPL into ratio of change. They also used as a reference the SPL of a conversation when the actual reference for SPL is approximately the threshold of hearing for the average human (actually 0.002dynes/cmsquared or 20 uPascals). Sound power (intensity) is expressed in Watts /meter squared).
As an example, comparing a rifle sound level at 160 dB SPL to a speech conversation the difference is 100,000X and not the 10,000,000,000Xin the article!
The article shows an illustrations of different sound level sources but talks about both sound level (20log x) and damage/intensity (10log x). If the data is in SPL, you cannot convert the dB SPL to energy ratios! You must measure the actual energy of the sound you want to convert to a ratio.
It is an informative and interesting article BUT part of it is based on a gross error.
How do I know this? I am an Electronic Engineer and took the masters program in Audiology.
Error to wit;
The article uses a proper Sound Pressure level meter and careful measurement techniques. and the data listed looks very accurate.
The glaring error is the fact they brought in both sound pressure AND sound energy (intensity).
In the measurement of sound level is always measured in sound pressure level (SPL). Sound energy is pretty much only used only in determining potential damage to the ear by excess sound and by Physicists.
The reason the two scales are different is that the equations for SPL is expressed as
20log SPL1/SPL2 and Sound Intensity is expressed as 10 log energy1/energy2.
The resultant change in dB changes from 10db per X10 increase in energy to 20dB per X10 increase in SPL. And 6dB equals 2X, not the 10dB the article claims for SPL.
This means the article expresses their data in SPL but uses the energy equations to convert the dB SPL into ratio of change. They also used as a reference the SPL of a conversation when the actual reference for SPL is approximately the threshold of hearing for the average human (actually 0.002dynes/cmsquared or 20 uPascals). Sound power (intensity) is expressed in Watts /meter squared).
As an example, comparing a rifle sound level at 160 dB SPL to a speech conversation the difference is 100,000X and not the 10,000,000,000Xin the article!
The article shows an illustrations of different sound level sources but talks about both sound level (20log x) and damage/intensity (10log x). If the data is in SPL, you cannot convert the dB SPL to energy ratios! You must measure the actual energy of the sound you want to convert to a ratio.
