High Pass filter subwoofer integration

Currently using a subwoofer with my two speakers that go down to 25hz. The variable low pass on my subwoofer is 40 Hz-120 Hz. I am thinking of going with a high pass filter to relieve the speakers of the very low end and to get a better integration. HSU makes a high pass filter but I am concerned that It might degrade the sound. Any thoughts would be helpful. My room is not large, about 12x15 with 8 ft ceilings.
It would degrade the sound to a greater or lesser degree. I usually use 2 REL Stadium subs that I start to roll off at 25Hz and run my main speakers full range. They do not have as extended a bottom end as yours does so yours should do even better. If you are using line level signal sent to speakers and subs separately then a really good passive filter in the signal line would be the way to go. I also have older Hsu subs and have both passive and active boxes for them. When I use them with my main speakers I do not run the main signal through them. They are fine for HT use but can be heard in music reproduction. IF your sub has good controls, assuming it is powered, then you should be able to get good results without attenuation of the main speakers.
I use an NHT x-2 between an ARC LS 25 and VT 130SE for this purpose and hear no deterioration. That said, you (or other listeners) might hear something that I don't.

I should probably have added that -prior to the NHT - I used the low cut in my Velodyne SMS sub controller for this purpose. That device operates in the digital domain and subjects the signal to A/D/A conversion which was audible to me. Therefore, I switched to the NHT for low cut in the main signal path while retaining the high cut function of the SMS to roll off the top end response of my subwoofers.

The trade-off is between the distortion of the high pass filter versus the distortion produced by the woofers in your main speakers. Your room is not large, so unless you listen to bass heavy material loudly you may not be stressing the woofers in your main speakers. Thus, a HPF may not be of much benefit in your system. However, it does not take much for the distortion of a woofer to exceed that of electronics. For reference, scan the speaker measurements over at SoundStageAV.

Besides distortion there is the issue of attaining smooth bass response from multiple bass sources.

For stand mount speakers and many floor standing speakers, I think using a clean HPF is a plus.
I have been pondering this same question for some time. I posted a similar thread and got many helpful answers, but the usual range of opinions on either side. It's also worth noting that you can spend $400 on the NHT HPF or $2000 on the Bryston unit.

I tried a passive XLR high pass filter from ACI (no longer offered by them for sale) and it actually messed things up pretty badly in my system -- I have decent measurement software, and the rolloff of the passive filter created integration issues with subwoofer.

Anway, I was able to get a good looking response (which doesn't address possible distorion issues) by running the floor standing speakers full range, and using the SMS correction on my Velodyne DD12 subwoofer.

I am generally happy with how the bass sounds, but there is a little bit of boominess that has me wondering -- should I try an active unit, and if so, is it worth it to spend 5X the money on the Bryston unit or should I try the NHT or maybe I should go all the way and get a TACT.... another little slice of audio hell.

FWIW, I will probably try the NHT unit -- in the grand scheme of things it is relatively inexpensive experiment. At least it's cheaper than the other alternatives, except for the passive filters, which didn't work.

Can you see anything on your measurements that might correlate with the "boominess"? The beauty of the NHT (apart from the fact that I can't tell it's there) is that it will allow you to roll off your mains when the room becomes a problem. IME, boominess usually occurs somewhere between 80hz and 150hz. You can use your SMS to roll in the sub at a frequency above the problem and EQ it away. At the same time, use the x-2 to roll off your mains for most effective integration.

If the "boom" problem proves to be higher in frequency than you like to cross, bassbusters will usually provide another effective solution that allows bringing in the subs at a lower frequency.

Good Luck


PS More expensive x-overs, like more expensive pre-amps may offer more features, higher cost parts, etc. Will you hear a benefit? That depends on you, your system, your room, etc. etc.