HERTZ & DECI­BELS

InCar Entertainment  - - FEATURE -

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).

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