MemberA lot of discussion about decibels is present in this forum, and naturally members discuss what are safe decibels and what is sufficient amount of protection. Also bone conduction, especially when it comes to bass is discussed. However, I've only few times seen people discussing about the fact that decibel levels we see in recommendations, allowed limits and various measurements are A-weighted, or dB(A) which is, and has been for the last 80 years, de facto unit for measuring sound pressure.
The A-weighted dB-scale is based on sensitivity of our hearing system. A-weighting derates the decibel measurement basically by subtracting the equal loudness contour, in a way that 0 dB is subtracted from the 1 kHz. For example 50 Hz, which are usually the low bass notes in music gets a reduction approx. 30 dB. So to hear everything equalized, lower the tone, more sound pressure it needs. So the bass doesn't just vibrate through the earplugs better, it is actually louder, when expressed in terms of true sound pressure. When your meter says 90 dB(A), the low bass notes can still boom at 120 dB. Also the high end is derated in A-weighting.
Other weighting schemes do exist, and usually the next one people encounter is C-weighting. C-weighting derates the low frequencies less than 10 dB in audible reqion (>20 Hz), so it's much more suitable for measuring sound pressure in environments where there is lot of low frequency noise (engine and machine noises, bass heavy music etc.) For example refrigerator can create 50 dB(C) or 60 dB(C) noise, but the difference in dB(A) can only be few decibels. It's also more convenient for measuring high sound pressures, because in very loud environments there's usually lots of sound pressure coming from low frequencies. This usually applies also to heavy impulse noises. The C-weighted dB-reading, or dB(C) is always higher than dB(A). Sometimes a conversion factor dB(C)-dB(A) = 7 dB is used, and this explains the -7 in the often quoted earplug derating formula.
It's usually stated that low frequencies don't hurt our ears. However, I personally believe that if any audible frequency is pushed with high sound pressure for long enough, it will have effect on ones hearing. Please feel free to comment and correct any mistakes I've made above.
The A-weighted dB-scale is based on sensitivity of our hearing system. A-weighting derates the decibel measurement basically by subtracting the equal loudness contour, in a way that 0 dB is subtracted from the 1 kHz. For example 50 Hz, which are usually the low bass notes in music gets a reduction approx. 30 dB. So to hear everything equalized, lower the tone, more sound pressure it needs. So the bass doesn't just vibrate through the earplugs better, it is actually louder, when expressed in terms of true sound pressure. When your meter says 90 dB(A), the low bass notes can still boom at 120 dB. Also the high end is derated in A-weighting.
Other weighting schemes do exist, and usually the next one people encounter is C-weighting. C-weighting derates the low frequencies less than 10 dB in audible reqion (>20 Hz), so it's much more suitable for measuring sound pressure in environments where there is lot of low frequency noise (engine and machine noises, bass heavy music etc.) For example refrigerator can create 50 dB(C) or 60 dB(C) noise, but the difference in dB(A) can only be few decibels. It's also more convenient for measuring high sound pressures, because in very loud environments there's usually lots of sound pressure coming from low frequencies. This usually applies also to heavy impulse noises. The C-weighted dB-reading, or dB(C) is always higher than dB(A). Sometimes a conversion factor dB(C)-dB(A) = 7 dB is used, and this explains the -7 in the often quoted earplug derating formula.
It's usually stated that low frequencies don't hurt our ears. However, I personally believe that if any audible frequency is pushed with high sound pressure for long enough, it will have effect on ones hearing. Please feel free to comment and correct any mistakes I've made above.
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