Just finished my second DIY sub this weekend. The first was a 12" DVC in 1 cu ft sealed for a car. This one is a 12" DVC in a 3.5 cu ft box tuned to just under 20Hz. Walls covered with polyfill. Port is 4.5" wide x 4" tall x 32.75" long (I hope I got that right). Sorry, no pics. But the box is unfinished so its really not much to look at. I've got a cheap Pioneer stereo receiver that is used for amplification. 70 watts x 2 channels at 8 ohms and that's how I connected it - one voice coil per channel. I unplugged and moved the SVS so the new DIY sub could take its place. After the wife left to shop I calibrated to the level the SVS was at ... or at least close. I've not tried both subs at the same time yet. So how does it sound? Well, let me start by saying that I had very high expectations. I've had the 25-31PC for about a year and it produces amazing SPL levels considering my large, open living room. The goal of this project was to get more SPL and a little more low end to compliment the SVS. As it turns out, they sound very similar. I probably couldn't tell which was playing in a blind test. Looking back, this makes sense - my hearing drops off in the mid to upper 20's (Hz) so it's not like I'm going to hear the extra extension anyway. It does seem like this front-firing, front-ported box sub may be more sensitive to room placement than the SVS but I'm not sure yet. What surprised me was that the excursion was significantly greater than the SVS at the same volume level. This sounds like a good thing, but what it really means is that it reaches its limits long before the SVS does. I normally listen to Toy Story 2 and Titan AE at 60 on the volume dial (10dB under reference, sub about 3dB hot) and have never bottomed it. With the new sub I didn't dare go over 57 during TS2 and I think it bottomed at 55 during Titan. I don't think I was clipping the amp. My only explanation is the extreme low-frequency material in these tracks. With only 140 watts on tap nothing over about 16.5Hz should reach Xmax. The 25-31 is obviously saved by its sub-harmonic filter. Otherwise I would expect it to be even more suseptible to over-excursion. The new sub may have some lower frequency vibrations going on (hard to sense) but the reduced volume level is what I notice the most. So apparently I made the right choice with the 25-31PC. All the low-end I can hear plus lots of rumblings without the fear of bottoming. I'm thinking that a DIY active filter or maybe a PE plate amp with modded filter should bring this up to that performance level. If this is true then I think the value of a sub-harmonic filter may be underestimated quite a bit. The ability to play Titan AE 5dB louder is no small feat. That's almost like getting a 2nd subwoofer! So here's a lesson learned the not-so-easy way: If you're not going to tune it LOW, LOW, LOW then plan on a hi-pass filter. So far I've spent less than $150 so its great performance for the price of a Sony SA-WM40. But I know it can get better. Tom/Ron if you're reading this I must say kudos to you. My SVS with the original driver continues to amaze me. You have an uncanny ability to extract 110% out of each component. If you don't mind, I'm curious about the sub-harmonic filter on the original PC series. What type (Butterworth?), order and 3dB frequency was used? Was this the same for all 3 models or adjusted for each tuning point?