HERTZ & DECIBELS
In preparation for the next piece, here is some terminology and important technical pointers that will help you grasp the concepts to come.
A dB or decibel is a unit of sound volume – a whispering voice is about 30dB and a jet engine is 160dB (bass frequencies have somewhat different physics, however). As a rough guide a readily discernible increase in sound volume is 3dB; while a doubling in perceivable sound volume is 10dB. How much more power do I need to increase my system by 10dB? 10 times the power – yup that’s right, 10 times the power.
An octave is a doubling of an original frequency; so one octave up from 40Hz is 80Hz and an octave up from 200Hz is 400 Hz and so on.
When using a single capacitor for a high pass or a coil for a low pass crossover the crossover slope is 6dB per octave. So, for example, if you are using a capacitor to highpass a tweeter at 3000Hz then the tweeter will still play frequencies at 1500Hz but a significantly reduced level (approx -6dB).