Which filter alignment for sub...

[JojoD818]

Hi everyone,

How does one choose a filter alignment for a specific application such as a sub amp? Does a Linkwitz-Reiley low pass filter better for this application than a Butterworth? Or is there a more precise alignment for every application?

I know what an order means but for sub applications, must I use a 24dB than an 18dB one? If it is better to use higher order filters then why are those lower order filters like a 6dB exist?

Thanks for the enlightment...
JojoD

[Tony]

a 6db implies pasive single component like a choke or capacitor,

[ashok]

I would think that if you were building a real sub , meaning that it works only below 100Hz or so, you should use a higher order crossover. An active Linkwitz Riley 24db per octave crossover would be preferable . This will ensure that higher frequencies are really well attenuated. If this is not so , it could lead to localisation of the sub. Even a trace of low end voice ( about 200Hz ?) is not good IMO. The sub should actually not be 'heard' when used in a system. By this I mean that it should not be possible to trace the sound to the sub. If you use a low slope crossover you can pick out the sub because higher frequencies ( directional sounds) will also be ( audibly) reproduced from it.
The crossover frequency should be determined by the low end of your main speakers. It is not an arbitrary choice. You need measured data to do this effectively.
On a reflex system you can close the duct and get a 12db slope and add another (active) 12 db to get 24 db for the main speakers. The Q of the crossover will depend on the Q of the main speaker. Using it in reflex mode ( if it is already that way ) already gives it a 24db slope but it may not be as close to ideal as a sealed box which also helps in power handling capability .
A reflex is good when well set up. It can be awful otherwise.
Cheers.