DIY 12" DVC sub vs. SVS 25-31PC - interesting conclusion

Discussion in 'Archived Threads 2001-2004' started by Ryan Schnacke, Apr 22, 2002.

  1. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    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?
     
  2. Rudy H

    Rudy H Stunt Coordinator

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    With 140watts you shouldn't be able to bottom it until 15hz in that box. You probably were hearing clipping, same thing happened to me with my 12inch Dayton Titanic MK2 running from the PE 300-794 plate amp. I had a friend run LEAP simulations based off teh drivers MLS measurements, and it showed an excursion peak of 16.5mm @ 35hz in the 1.75cf sealed box. The MK2 has an 18.9mm Xmax BTW. Watching the driver while it was playing confirmed the excursion plot.

    However while playing music (sub only and very loudly) I could hear a "whomping" sound, but even when I looked at the cone, it wasn't moving much. I have no doubt that the amp was clipping, not only because bass does require a LOT of power to reproduce, but because the LEAP graph said it shoudln't bottom out at all. And yes, the box is VERY well sealed.

    Finally, doesn't the SVS only have a ~12mm Xmax? The 12inch DVC was Dumaxed at ~16.3mm, with it's suspension limit just past 20mm.

    I would bet that the DVC also has a softer suspension.
     
  3. Dustin B

    Dustin B Producer

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    I always understood it that the original SVS driver was in the 1.1-1.3L Vd range and the new ISD was in the 1.4-1.6L range. A Dayton DVC12" is 1.55L according to it's reported specs.
     
  4. Patrick Sun

    Patrick Sun Moderator
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    I think enclosure/porting optimization is part of the disconnect in terms of performance. The SVS is a highly optimized sub. Is the current enclosure for the DVC the best one for that driver? (I have no idea, never modelled the DVC).
     
  5. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Rudy,

    Maybe it was the amp clipping. I was ready with the remote and listening for anything unusual so I reacted quickly when it happened. I can't really remeber exactly what it sounded like. But that woofer was MOVING! Definately traveling farther than the SVS driver does under similar circumstances. I have no trouble during music playback.

    Dustin,

    I agree, according to displacement ability the DVC should outperform the SVS. But it just doesn't work out that way.

    Maybe I've got some losses. The box seems solid and I did the Kleenex test on some of the joints that I thought would be most susceptible to leaks. Didn't find anything.

    But then again, if this is just "par for the course" then I'd think that 25-31CS owners without the benefit of a hi-pass would bottom their subs often. My living room is completely open to the kitchen - 6000 cu ft. Then there are openings to a formal living room, dining room and hallway. I guess it could just be the price you pay for an open floorplan.

    I'm approaching this project as an experiment. And I'm learning a thing or two, so I'm happy. I've still got some experimenting to do. Any ideas where to pick up some halfway decent audio op-amps and a dual rail power supply?
     
  6. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Patrick,

    I still consider myself a novice at this, so I wouldn't claim this enclosure is optimal. But I simulated in Unibox with a goal of flat response down to the low 20's. I used an average of the Dumax and the Manufacturer values.
     
  7. Patrick Sun

    Patrick Sun Moderator
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    Ryan, no shame in your attempts at comparing the 2 subs, you're getting some good hands-on experience with what is beneficial to extracting performance out of drivers and enclosure. It's much more fun than just reading and speculating.
     
  8. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    "It's much more fun than just reading and speculating."

    You got that right! And if nothing else, its big (wife rolls eyes).
     
  9. Robert_Gaither

    Robert_Gaither Screenwriter

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    I'd blame the Pioneer amp because I wouldn't be surprised that it was clipping (don't forget Pioneer claims 70 but most likely at 1 khz).

    I think a more fair (and a lot more time consuming) test would be is to hook up the new "kid" (my subs and dog are my kids) to the plate amp and give a second go of it.

    I know on my Adcom 535 (60 wpc @ 8 ohms, 90 wpc @ 4 ohms) the distortion alerts would pop on when I ran it into an 8 ohm a channel pushing my Tempest or Shiva (or in the past my Optimus SW-14P) running one to each voice coil but when I forced the amp to run in a 4 ohm load the amp clipped at a higher volume level and sounded much cleaner while doing this.

    All this is not to state that your current sub should out do the SVS (it might, but then it might not..) as I think it's one of the best subs in it's price bracket (large volume cabinet, decent size port, and quality amp; this would be the sub I'd own if I didn't DIY myself...) but you might want to match these subs later when you add a decent amp for it to feed off of. Let us know the results and good luck.
     

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