Equal loudness contour of the human ear

Sound pressure level (abbreviated as "SPL") is a measure of the pressure of sound relative to a reference value. SPL is measured in decibels. SPL measures how "loud" a sound is.

Perception of SPLEdit

The human ear does not have a flat frequency sensitivity. This is shown in the figure to the right. The human ear perceives higher frequencies as much louder than lower frequencies, even at the same sound pressure level.

"Rules of Thumb"Edit

Doubling the total cone area of all the subwoofers in your vehicle should theoretically make the vehicle's audio system 3 decibels louder. The same goes for power; doubling the total power that the subwoofers see will theoretically make the vehicle 3 decibels louder.


Many organizations have SPL competitions with various rules and regulations.

  • DB Drag
  • MECA
  • USACi