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A Subwoofer Experiment w/DSP

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  • A Subwoofer Experiment w/DSP

    I have had a love/hate relationship w/ subwoofers since I first started fooling around with them many decades ago- and there weren't many options then. Of course, a lot has improved- perhaps because of home theatre and car audio, oddly enough. And, I've always been putting them to a difficult challenge- usually trying to get subwoofers to 'blend' with speakers like Quad electrostats, a near impossibility.
    Fast forward to a few years ago. Our small home theatre system in the den was using an old Meridian processor that had been cast-off from the main home theatre system upstairs. Since the Meridian was well past its shelf life, I replaced it a couple years ago with a more modest consumer electronics unit- a Marantz that had a pretty basic Audyssey program in it. After I set that up, I was pretty impressed with how effectively the DSP controlled a very small subwoofer on that modest system (in addition to the fact that Marantz actually sounded better overall than the Meridian at a fraction of the cost- showing, t at least in the realm of mass market electronics, technology and sonic improvement as well as price reduction is possible).
    My Avantgarde horns present a similar challenge to electrostats and I never seriously thought about adding a subwoofer. The horns come with woofers that, if you cross them over too high or run them too loud, mess up the presentation. To get the integrated woofer system to 'blend' well with the horns, you have to back them off a bit- hardly a surprise, since, like electrostats, you'll otherwise hear the discontinuity of the different drivers- planar or horn v dynamic woofer. I worked with acoustic treatments and placement over the years and my system sounds better than pretty good but it is still a bit bass shy except on records where the bass seems to be pronounced. I have no intention of investing more in this system or room at this point, because I'm still planning on relocating. But the idea of DSP woofer correction intrigued me. I didn't want to shell out for a set of big JL subs, or their equivalent with DSP on board, but have a few old subs that were languishing, unused, from the big home theatre system (which I have simply quit using- I have no interest in running a big projection system these days with the "theatrical experience").
    Just as an experiment, I bought one of those inexpensive DSpeaker subwoofer interfaces- little bigger than a pack of cigarettes, with wall wart (ugh), and hooked it up to one of the smaller old subwoofers (a front firing 15" Velodyne). I electrically isolated this package from the rest of the system through a 240 volt line and step-down (another remnant from the old home theatre upstairs). Despite the low cost of the DSPeaker, it seems to do a pretty effective job- and after it self-calibrated, I adjusted the sub crossover so it hinges at around 45 hz- making it 6db down at 90hz and 30db down at 180 hz. It matches up pretty well with the Avantgarde woofers and isn't cranked up very loud- if you listen to the sub alone it is very subdued, both in volume and range. But it does add some gravitas. Total investment was about $350 dollars plus a set of long interconnects (and I used bargain basement ones at that, plus a positively ancient MIT Shotgun CVT that was pulled out of a box in the basement for the short jump from the DSP unit to the sub).
    A thousand years ago, when I was experimenting with multichannel sound in the era before discrete multichannel was available, I had an old Sony digital delay line (that was marketed as an early home theatre enhancement before pre-pros, AC-3 soundtracks on Laserdisc, DVD, etc. existed.). I ran this as a rear channel system with a modest set of bookshelf speakers using my Quads, ARC tube gear and table on the front end. When one of my truly blessed audiophile buddies came over for a visit (Myles- the late, great Chuck Lamonica), he was horror struck that I had this purist system combined with some crappy gear as an add-on. He said, turn it off. Then, turn it on. Ultimately, Chuck said, Leave it on. (It wasn't effective on all recordings but when it worked it added a real third dimension to the presentation, beyond what the Quads - no slouches in the the imaging department- were capable of).
    Long way of saying that I've been having fun with this latest cheap, kludged together experiment. Perhaps that means I can have it all- full range, dynamic, jump factor and clarity with deep bass. (Granted, a modern woofer system will undoubtedly improve things even more, as a pair, but remember, I'm on a desert island right now making things out of coconuts). And that little DSPeaker woofer controller --not the Dual Core device which purports to do far more- is well worth the modest investment. Fun!

  • #2
    Hey Bill, this is a timely post. So happens I'm running two SVS 12" subs with the Quad ESLs and yes it is possible with today's bass drivers that employ underhung voice coils and switch mode amplification (high damping factor) to achieve an articulate and 'fast' bass response that blends very well with 'stats. The DSpeaker anti-mode sounds very interesting, it looks like I'd have to run two for stereo. Right now I have the signal split with the Pass (first watt) active crossover at 75hz, the anti-mode would go between it and the LFE input on my sub? Which model do you have and was the calibration easy?
    Last edited by Rob; 04-16-2016, 10:05 PM.


    • #3
      Rob- the instruction manual is online at the DSPeaker web site. You should probably talk to me before you buy. I'm using the 8033SII, and take a stereo line level signal from my line stage (output 2) to the DSP, so it is not in the circuit path of my main line stage/ amp/ speaker combo. The 8033II will sum the L+R signals and offers a 0 or 180 degree polarity mono output that you plug into the line level input on your sub. The manual suggests that you need a pair of these for two subs; I've seen some chat group mentions of splitting the signal at the 8033 output for multiple subs- but that would seem to defeat the whole purpose of having the thing tune each sub based on its position and interaction with the room. Apparently, the Dual Core product can do stereo subs (I'd need to check) and a lot more, but I had no interest in putting any DSP in the main system signal path; in effect, i'm running the 8033 in a "parallel" system. In terms of how it integrates w/ a Xover, I did the calibration by turning the Xover on the Velodyne wide open (highest db- 100, if memory serves) so it had the least interference with the calibration process. (For you, I'd imagine it means hitting "bypass" on the active crossover, but that's worth checking.Once calibrated, you then adjust the crossover and woofer gain. The calibration was painless. Unlike the Audessey, you don't have to check multiple locations; the supplied mike, which is tiny, was clipped to a mike stand w/ boom at precisely ear level in the sweet spot. You activate the calibration and stand back. It ran for a while- multiple sweeps starting very deep. Once done, the lights stop flashing, and calibration is done. You then adjust your crossover and gain (increase, b/c the sweep tones are pretty intense and you want the woofer gain pretty low in calibration mode). There is a processing delay which the manual suggests you compensate for by moving the woofer closer than the main speakers- I got around that by using the 180 degree output on the DSP, which seemed to synch better with everything else. My horns and the Avantgarde woofers are out of phase in relation to each other because they are not time aligned, so, given the quirks of my system, it all seemed to gel pretty nicely.


      • #4
        So, further adventures here, with noticeable improvements- maybe I'll decide otherwise, but i've done more homework, legwork and added a little. First, a smallish Rythmik 12" enclosed sub with the paper cone, rather than the metal one; I was originally going to run this from the DSP unit in summed mono --Rob, even the 8033II will permit dual subs if you stay in mono and use the 180 polarity output with a woof that (re)inverts phase, but i was getting some hum running both woofers - unmatched of course, through the DSP. So went stereo, played around with placement of the smaller Rythmik, which is crossing over slightly higher than the old 15" Velodyne, which is X'ing at around 45 hz. Levels matched at listening position, the Rhythmik is slightly more forward, physically in the room, but still reinforced by a corner--it's an odd room, and combined, they smooth out the bass nicely. I've been reading some of the stuff Duke from Audiokinesis has posted about "swarm" woofers, which makes sense. So, DSP'ing only the old Velodyne, and the Rythmik is running without any DSP or its adjustable EQ.
        Jim Smith will kill me, but this brings foundation to the Duos without any muddiness to the mids. Given that the woofers of the Avantgarde go up pretty high- they aren't really subwoofers, so I'm really enhancing the existing woofer system and letting that handle the transition to the mid horn, which I have set to cohere, at the expense of bass loudness. None of this stuff is tied into the Lamm/Avantgarde system, but running parallel, so no high pass involved. For an on the cheap experiment, it is bringing me much interim joy- I never listen super loud to begin with, but now, with a little deep bass that is not dependent on cranking the Avantgarde woofers too high and causing a discontinuity with the midrange horn, I have way more dimension at my somewhat modest listening levels.And none of this seems to be at the expense of what the horn/SETs do so well. The Rythmik seems to be a bargain given the quality I'm getting, in this context. Sure, a bigger more powerful woofer would do a lot more, but this is doing the trick right now, and I've run out of dedicated lines in this room.
        Last edited by Bill Hart; 05-02-2016, 09:00 AM.


        • #5
          Originally posted by Bill Hart View Post
          Jim Smith will kill me, but this brings foundation to the Duos without any muddiness to the mids.
          Actually I agree, in general...


          • #6
            Hey, Jim! I was going to change my name and identity after that post, glad to see you!