For example, 200 µPa corresponds to 20 dB (re 20 µPa), while 2000 µPa corresponds to 40 dB.īecause of large sound pressure amplitude changes, the sound pressure level in decibels (Lp) is used rather than Pascal units.
![equal loudness spl hl decibel scale equal loudness spl hl decibel scale](https://i.pinimg.com/originals/6f/16/52/6f16523945898f38d714c6813d7a308b.gif)
When measuring sound pressure in Pa, adding 20 dB to the dB level is equivalent to multiplying the sound pressure by 10. At an SPL of 120 dB, the sound is considered to be at the threshold of pain, and any sound louder than this can cause permanent hearing loss. This is much louder than the threshold of hearing, but still relatively quiet.Īs the sound pressure increases, so does the SPL. Taking the logarithm (base 10) of this ratio gives you 1, and multiplying by 20 gives you an SPL of 20 dB. On the other hand, if the sound pressure is 200 µPa, then the ratio of the RMS sound pressure to the reference level of sound pressure is 200/20 = 10. This is the lowest possible SPL, which corresponds to the threshold of hearing.
![equal loudness spl hl decibel scale equal loudness spl hl decibel scale](https://www.protoolreviews.com/wp-content/uploads/2019/10/Change-in-Perceived-Loudness-1-800x482.jpg)
Taking the logarithm (base 10) of this ratio gives you 0, and multiplying by 20 gives you an SPL of 0 dB. This gives you the SPL in decibels (dB).įor example, if the sound pressure is 20 µPa, then the ratio of the RMS sound pressure to the reference level of sound pressure is 20/20 = 1. To calculate SPL, you take the ratio of the sound pressure to the reference level of sound pressure and then take the logarithm (base 10) of that ratio, and then multiply by 20.