Like I said a P****contest. !.

**Sound Pressure • terms • definitions • units • measurements ...**
Sound Pressure is the difference between the

pressure caused by a

sound wave and the

ambient pressure of the

medium the sound wave is passing through.

Sound Pressure is a

sound field quantity, not a

sound energy or

sound power quantity.

Sound Pressure Definition

IEC 801-21-20, root mean square of the

instantaneous sound pressures over a given time interval, unless specified otherwise

Sound pressure is measured in

pascals, symbol Pa. However the immense range of human hearing, 0.00002 pascals up to 200 pascals, means the

pascal is not practical for everyday use. Fortunately the sound pressure level in

decibels, detailed below, neatly solves this problem.

Sound Pressure Level (SPL) = 20 log (p/po) dB, where p is the sound pressure in

pascals and po is the

reference sound pressure of 0.00002 pascals = 0 dB in air ≡ to the

threshold of hearing at

1KHz
Some typical Sound Pressure and Sound Pressure Levels

Sources at 1 m Sound Pressure SPL re 20 μPa

Rifle 200 Pa 140 dB

Threshold of pain 20 Pa 120 dB

Pneumatic hammer 2 Pa 100 dB

6 dB = twice or half the pressure 1 Pa 94 dB

Street traffic 0.2 Pa 80 dB

Talking 0.02 Pa 60 dB

Library 0.002 Pa 40 dB

TV Studio 0.0002 Pa 20 dB

Reference Sound Pressure 0.00002 Pa 0 dB

Sound Pressure Level is a

sound field quantity and uses the 20

log factor so, as a rule of thumb:

6 dB = a factor of 2 in sound pressure (double or half the sound pressure)

10 dB = a factor of 3 in sound pressure

20 dB = a factor of 10 in sound pressure

Sound Pressure Level Definition

IEC 801-22-07, logarithm of the ratio of a given

sound pressure to the

reference sound pressure in

decibels is 20 times the logarithm to the base ten of the ratio.

● Note 1 : unless otherwise specified, the reference sound pressure is 20 μP for airborne sound and 1 μPa for sound in

mediaother than air.

● Note 2 : unless otherwise specified, the sound pressures are understood to be expressed in

root-mean-square values.

See also our

sound pressure level calculations article

Related Terms - listed alphabetically

Average Sound Pressure see

effective sound pressure
Band Sound Pressure Level Definition

IEC 801-22-12, level of the sound pressure produced within a specified

frequency band.

● Note: the band may be specified by its lower and upper

cut-off frequencies, or by its geometric

centre frequency and

bandwidth. The width of the band may be indicated by a modifier such as one

octave band (sound pressure) level, one-half octave band level, one-third octave band level.

Effective Sound Pressure is the

root-mean-square of the

instantaneous sound pressure.

Effective Sound Pressure is also known as the average sound pressure.

See also • the

Effective Value Definition IEC 103-02-03
Equivalent Continuous Sound Pressure Level Definition

IEC 801-22-11, logarithm of the ratio of a given

root-mean-squaresound pressure, during a stated time interval, to the

reference sound pressure. Average sound pressure level in

decibels is 20 times the

logarithm to the base ten of that ratio.

● Note: unless otherwise specified, the reference sound pressure for airborne sound is 20 μPa. Also known as the

time-average sound pressure level.

Equivalent continuous sound pressure level should not be confused with

Equivalent continuous sound level. To compare these definitions directly

click here
To make it more interesting... The Pascal is a unit of pressure, and watts is a unit of power the relationship between them is.

Derived Unit Measures,Formal Definition,

newton (N) force kg·m·s-2

**pascal** (

**Pa **) pressure kg·m-1·s-2

joule (J ) energy or work kg·m2·s-2

**watt** (

**W **) power kg·m2·s-3

To save you the work of doing the conversion...

The actual average threshold of hearing at 1000 Hz is more like 2.5 x

**10-12** watts/m2 or

**about 4 decibels**, but zero decibels is a convenient reference. The threshold of hearing varies with frequency, as illustrated by the measured hearing curves.. in other words a power level of 1 picowatt / m2 is defined generally as the lowest intensity sound that humans can hear, at the most sensitive frequencies in the lower Kilohz range. When one realises that the ear lug is only about a 2 cm in diameter,the actual power which gets into the ear is really really tiny.

Finally if one had a device generating an SPL of 1watt/ m sq of acoustic power level at a distance of 1 m, it would be at the threshold of pain ,and assuming it was non directional (isotropic) the area of the sphere is 4 pi metre sq so the total acoustic power outputted is 4pi Watts