dB/octave slope question

I have an Alpine cda-9835 with an active crossover in the deck.  You are allowed to change the slope from flat all the way to 24 dB/octave.  I was wondering if this is an audible adjustment or if there is a specific slope for certain speakers.  I purchased infinity kappa 4's and on the features it says 2-way crossover 18dB/octave, 3500 hz high pass and low pass. what should i do. thanks

This is kind of a complex question.  Basically the higher number is a steeper slope.  So let's say the crossover frequency is 100 Hz.  with a 6 dB per octave slope, the level played by the speaker an octave away from 100 Hz will be 6 dB down (assuming the speaker has flat acoustic frequency response otherwise).  For a 24 dB per octave slope, the level will be 24 dB down an octave away. 

The slope you want will depend on how the two speakers converge.  If you go too shallow, then the speakers might produce a peak in the frequency response at the crossover frequency since both are playing that frequency at a high level.  If you go too steep in the slope, then you might have a dip in the frequency response because neither will play that freuquency loud enough.  What you want is to have the proper slope so the frequency response stays flat.

Now this topic can really get complex when you get into phase changes, lobing issues, and the acoustic response of the drivers.  But the above is the more basic principal of crossovers and will be true for active, passive, and digital crossovers.

Steven Kephart

Adire Audio