Subsonic filter

Hey guy's,

   I have read that there are several advantages to running a subsonic filter. Any inputs here?

  Also, does anyone know of any manufacturer that makes an out board filter, only a filter not a whole crossover unit?

 Chris

I have read that they have advantages when using them with a sealed enclosure as well. As I understand it, keeping out the low unheard frequecies can make the amp run more efficiently as well as keeping the speakers from being damaged. Subs are rated for certain frequencies and for the sub to try and reproduce frequencies under its rating can cause damage to the speaker. Is this right?

Chris

I guess that this one fell be the side! HA HA

racer, it all will depend on how big the sealed enclosure is.  In almost every case of using a sealed box the response curve will decrease fairly quickly well above the 20 Hz point...so that frequencies that low are going to be attenuated anyway at probably a steeper slope than the filter will do it.  But there certainly is no harm in using it anyway, you may just be creating a steeper dropoff at the low end which, of course, is fine to do. 

TruckSystem, I think it just makes good sense to use it in all situations if it is there and available.

This really isn't correct.  We ask subwoofers to play below their fs all the time.  Simply reproducing frequencies below fs will not damage speakers.  Speakers break because of use for two reasons, either over-heating or over-excursion. 

Most cases of over-heating and over-excursion can be avoided simply by setting the gain correctly and operating the volume knob with a brain.

Do subsonic filters have a place? Sure.  Distortion increases rapidly under the tuning frequency in ported enclosures.  If your tuning frequency is high, you should always set the subsonic filter. 

Other than that situation would I say this is an "always set" situation? No.  Why?

(1)  Some subsonic filters cut too high or use too wide of a Q.  I wouldn't want to kill some of my ~~30hz frequency response unnecessarily, especially if I own a sealed enclosure.

(2)  Unless you push your subwoofer to its limits, over-excursion simply isn't an issue; neither are thermal problems.

(3)  If tuning frequency is low AND you listen to your subwoofer within its capabilities, there's probably little real audible and power benefit to buying a subsonic filter or making amplifier decisions based on the presence of a subsonic filter.  Indeed, there's really very little information below 30hz in most music.

Great, thanks guy's. I am not gonna worry about using one then. I always run sealed enclosures and listen mainly to rock. Thanks again for the information.

Chris