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| With "dB" and "ratio" near the input boxes, you decide what is calculated and which box is the input. With quantity of a "field" and quantity of "energy" you decide if it is 20 times (field, e.g. volts) or 10 times (energy, e.g. watts) in the formula. |
The formulas for voltage and power
and the calculation
| Enter a value in the left or right box. The calculator works in both directions of the ↔ sign. |
dBm indicates that the reference power is P0 = 1 milliwatt = 0.001 watt ≡ 0 dBm.
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Level of field quantities |
Level of energy quantities |
Sound pressure, sound intensity, and their levels:
Conversions and calculations of sound quantities and their levels
Sound Field Quantities
 Sound pressure, sound or particle velocity, particle displacement or particle amplitude, (voltage, current, electric resistance). Inverse Distance Law 1/r |
Sound Energy Quantities Sound intensity, sound energy density, sound energy, acoustic power. (electrical power). Inverse Square Law 1/r² |
a1 and b1 is the reference
'a' could be a voltage V and 'b' could be a power P. P ~ V2
| Sound pressure Sound field size |
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Sound pressure level |
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| Sound intensity Sound energy size |
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Sound intensity level |
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| Sound field quantities: sound pressure, particle velocity, particle amplitude. Field quantities, such as the sound pressure are always expressed in RMS. This is mainly proportional to the electric voltage V. Sound energy quantities: sound intensity, sound energy, sound energy density, acoustic power. This is mainly proportional to the electric power P. |
| Decibel scale for linear field quantities, like volts and sound pressures |
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| The logarithmic scale (ratio) |
| Note - Comparing dB and dBA: There is no conversion formula for measured dBA values to sound pressure level dBSPL or vice versa. |
| If the output voltage level is 0 dB, that is 100%, the level of −3 dB is equivalent to 70.7% and the level of −6 dB is equivalent to 50% of the initial output voltage. This applies to all field quantities. If the output power level is 0 dB, that is 100%, the level of −3 dB is equivalent to 50% and −6 dB is equivalent to 25% of the initial output power. This applies to all energy quantities. Try to understand this. |
| Note: The radiated sound power (sound intensity) is the cause - and the sound pressure is the effect. The effect is of particular interest to the sound engineer. The effect of temperature and sound pressure. |
| Acousticians and sound protectors (noise fighters) need the sound intensity (acoustic intensity). As a sound designer you don't need that. Look out more for the sound pressure that makes an effect at your ears and at the microphones. |
Sound pressure and Sound power – Effect and Cause
| Power is like all energy quantities primarily a calculated value. |
| The defining equation for the level in decibels for field quantities (here voltage) is: LV = 20 × log10(V/V0) (dB) (Z1 = Z2) where V is the voltage being measured, and V0 is the reference to which V is being compared. The equation for obtaining voltage ratio V/V0 from the level LV in dB is: V/V0 = 10(LV/20) The defining equation for the level in decibels for energy quantities (here power) is: LP = 10 × log10(P/P0) (dB) where P is the power being measured, and P0 is the reference to which P is being compared. The equation for obtaining power ratio P/P0 from the level LP in dB is: P/P0 = 10(LP/10) |
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