In-line xover question

Audiokinesis-
Thanks for taking the time to respond to my post. Guess I opened a can of worms. I'll try to answer your questions best I can. This experiment came about when I installed a pair of in-line filters I had on hand which xover at 65hz. After a few minutes ajdusting the low pass on my subs (which only go down to 40hz), I was relatively pleased by the results (which cleaned up the bass quite a bit) and now assume I can do even better. My main speakers are front vented (VSA 4JR) and I run a pair of old Velodyne HGS-10 subs crossed over at 40hz (I do not know how steep the low pass filter is on the subs-are you referring to slope?). The NHT X2 filter Bob-reynolds (thank you) suggested is intriquing as well.

I use the Harrison Labs Fmod 70 hz hi-pass RCA connected filter. It seems to attenuate the overall signal a few db but is actually quite transparent. For $20 they're worth a try.

I have no experience with the Harrisons. For such simple circuits, I would build it myself. A decent purpose-designed crossover would always be more effective.

Kal

Hello Sydneysophia,

Thanks for replying.

Okay, when doing a crossover I try to get a symmetrical slope on both sides of the crossover frequency. In my opinion, this applies to subwoofers as well.

The Velodyne HGS-10 has a second-order (12 dB per octave) variable low-pass filter. So, we'd like for your main speakers to also have a second order rolloff (12 dB per octave).

Your main speakers, being vented, have a 24 dB per octave (fourth order) rolloff below the port tuning frequency - this is inherent in the breed. If I understand correctly, your speakers are the Von Schweikert VR-4 Jr, with claimed bass extension to 23 Hz (-2 dB). Is that correct? If so... well, this gets a bit complicated because your main speakers' inherent bass rolloff is way too low to be part of the crossover to your subs, but on the other hand I think that can be changed.

I suggest stuffing the port tightly with closed-cell foam which will turn the box into a low-Q quasi-sealed enclosure. The bass will then probably (or should I say hopefully) roll off at 6 dB per octave starting somewhere above 40 Hz, transitioning to 12 dB per octave somewhere well below 40 Hz. I do not know the exact frequency that would work best for your in-line filter, but your 65 Hz filter might work just fine. [Make sure that your in-line filter is designed for the specific input impedance of your amplifier, as the frequency where it starts rolling off will be different otherwise.]

The idea is to change your bass enclosure's characteristics to give an inherent 6 dB per octave acoustic rolloff in the crossover region, and to accelerate that by using your in-line filter so that you get a net 12 dB per octave high-pass characteristic. You should be able to match this up well with your subs given their variable-frequency 12 dB per octave low-pass filter.

Just to see if this idea is in the ballpark, try the closed-cell foam with your present filter before investing in a new in-line filter. I'm guessing that you'd use a setting of around 50 to 60 Hz for the sub's low-pass filter. I would also guess that a 50 Hz in-line high-pass filter would probably be closer to ideal (along with a lower low-pass setting on your sub), but try what you have on hand first.

No guarantee that this would work of course, but it's what I'd attempt.

Duke