Revisiting the past- a bandpass subwoofer update with Hypex DS 8.0

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  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15261

    Revisiting the past- a bandpass subwoofer update with Hypex DS 8.0

    Life can be a bit strange at times- certain dates roll around, and certain items in the closet, and one may be reminded of past projects and activities. And ponder "What ifs"?

    What are the linking factors today?
    • An NIB (new in box) Hypex DS 8.0 subwoofer plate amp- like the mate, which was used for building a subwoofer with Dayton UM15 for Beverly's HT system some years ago. Came across it earlier this week organizing some things...
    • A NIB B&C 15SW115 pro woofer, from storage in the garage- organizing things there, too... and a POC test cabinet with its baby brother, a B&C 15NW100. (yeah, some of you may be thinking I have a bad habit about pro drivers... topic for a different post)
    • Tomorrow is the anniversary of when Beverly entered into Hospice in 2018 after a long battle with Pancreatic cancer from mid 2016. Another reminder of the sub I built for her which was passed down to her son....
    • A number of discussions lately about sub builds and alternative plans for them... (can't say a guys thoughts turn to subwoofers in the spring, as spring certainly isn't here yet!)

    So, this almost belongs in a category of retro technology, but still intriguing to me. And there are a lot of options to consider and ponder in one's spare time... I could use a bit extra of that myself!


    So let's recall this very traditional but unfortunately unobatainium style of plate amp...



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    Straight forward connectivity and filter controls.


    And the 15SW115 under consideration for a new POC bandpass test build...


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    Key parameters- Qts in particular, and Xmax. The ultra low Qts is critical to getting the driver to do what the enclosure wants- forget conventional sub drivers.


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    VituixCAD makes the calculations a LOT easier than back in the 80s, but there are still things to work out that could be called "secret sauce" as regards the front chamber and porting.

    Next up I'll post examples of possibly the more extreme variations for chamber volume, to give an idea of the tradeoffs. The last test build was on the smaller end, for the 15NW100. I'm thinking about keeping Steve Mannings admonition in mind for the next one, "Go Large or Go Home!"




    the AudioWorx
    Natalie P
    M8ta
    Modula Neo DCC
    Modula MT XE
    Modula Xtreme
    Isiris
    Wavecor Ardent

    SMJ
    Minerva Monitor
    Calliope
    Ardent D

    In Development...
    Isiris Mk II updates- in final test stage!
    Obi-Wan
    Saint-Saëns Symphonique/AKA SMJ-40
    Modula PWB
    Calliope CC Supreme
    Natalie P Ultra
    Natalie P Supreme
    Janus BP1 Sub


    Resistance is not futile, it is Volts divided by Amperes...
    Just ask Mr. Ohm....
  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15261

    #2
    I have not finalized what POC build I want to do next for testing- this post will just be to highlight a couple of options in the range of possibilities, all bound by Hoffman's Iron law, of course!

    First, a relatively compact build, with 50L main cabinet volume, and a tuning that trades off some degree of flatness for extension in the low end for this enclosure size:


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    Box Fb tuning and enclsoure volume interact to determine the overall bandwidth and sensitivity. This is for 2.83VRMS applied. Keep in mind the 15SW115 has a nominal sensitivity of 96 dB for 2.83VRMS. This is a nominal 8 ohm impedance driver.



    Now, let's stretch our legs to a different extreme, with 125L rear enclosure volume and a bandpass tuning of 50Hz. In this case, the intent is greater LF extension, with a flatter anechoic response. Keep in mind that with boundary effects, the in room response will be altered by the proximity to the major nearby boundaries, usually three dominating, floor, side wall, and rear wall. Flat extension to 20Hz may not sound flat at all, but boosted; for music, there can be a valid argument to shoot for 30 Hz in stead of 20. But, boys will be boys, and they do love their boom... and for the purists, there is active EQ.



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    I expect the next build to be a two piece experimental component, probably just 75L, with a removable section for the porting arrangements as I continue experimentation with that aspect. I'm going to focus further on something like a planar loaded slot port, a bit like the REVA concept.

    For those interested in knowing more about bandpass enclsoure characteristics, this link at JL Audio may be of interest.



    https://jlaudio.zendesk.com/hc/en-us...haracteristics









    the AudioWorx
    Natalie P
    M8ta
    Modula Neo DCC
    Modula MT XE
    Modula Xtreme
    Isiris
    Wavecor Ardent

    SMJ
    Minerva Monitor
    Calliope
    Ardent D

    In Development...
    Isiris Mk II updates- in final test stage!
    Obi-Wan
    Saint-Saëns Symphonique/AKA SMJ-40
    Modula PWB
    Calliope CC Supreme
    Natalie P Ultra
    Natalie P Supreme
    Janus BP1 Sub


    Resistance is not futile, it is Volts divided by Amperes...
    Just ask Mr. Ohm....

    Comment

    • technodanvan
      Senior Member
      • Nov 2009
      • 998

      #3
      Looks like a fun little project Jon. Are you planning on actually using this?
      - Danny

      Comment

      • theSven
        Master of None
        • Jan 2014
        • 855

        #4
        For those interested in knowing more about bandpass enclsoure characteristics, this link at JL Audio may be of interest.
        In high school those were my dream subs to use in a car stereo!!! However as I got older and realized I would rather spend time in my house than a car the new dream was for HT/2.0.

        This build is very enticing, I'm always looking to up my sub game to have more boom! I have been thinking about a custom sub enclosure to hold the new center channel that should be starting sometime soon... JonMarsh is correct, that boys will be boys and love their boom! I certainly do 😂
        Painter in training

        Comment

        • JonMarsh
          Mad Max Moderator
          • Aug 2000
          • 15261

          #5
          Originally posted by technodanvan
          Looks like a fun little project Jon. Are you planning on actually using this?
          I'm actually planning on building and refining POC example for this- the usage case will probably be the living room setup, though that might change.

          I've done a few with this concept, mostly in the 80's, but know have better development tools for modeling and a better shop for building!

          I built a test version already with the B&C 15NW100, which does not have as high an Xmax or power handling as the 115SW115. Though in a smaller cabinet than I preferred to build (due to materials on hand and limited time frame) it agreed well with the VituixCAD sims.

          Philosophically, I've always considered this a "music" sub approach, and usually tuned for a anechoic response flat to about 32 and used boundary reinforcement to get things in room down to 20, as the roll off rate is slow and well controlled, as is the transient response (in a properly designed configuration.). That is the crux of the matter, you can do all kinds of crazy stuff with a BP design IF YOU CHOOSE TO, and that's why it's popular with the car guys and the volume competition stuff. It's like a DOHC flat six or flat 8... or V6 or V8, what you wind up with depends on the design of the cam timing. For the BP, sort of similar situation. But for a music sub you have a rather different starting proposition- a large Sd pro driver with moderate Xmax and the lowest possible Qts. These drivers are typically in the 95-97 dB sensitivity range, and really come into their own only when horn loaded for live sound... or in a BP cabinet. Then, you're burning up 10-15 dB of sensitivity with the enclosure "forcing" a desired response profile.

          I have a lower cost Faital woofer I'm also looking at for this sort of application, the 15FX600. But haven't bought any to test- so far, just the two B&C models.
          the AudioWorx
          Natalie P
          M8ta
          Modula Neo DCC
          Modula MT XE
          Modula Xtreme
          Isiris
          Wavecor Ardent

          SMJ
          Minerva Monitor
          Calliope
          Ardent D

          In Development...
          Isiris Mk II updates- in final test stage!
          Obi-Wan
          Saint-Saëns Symphonique/AKA SMJ-40
          Modula PWB
          Calliope CC Supreme
          Natalie P Ultra
          Natalie P Supreme
          Janus BP1 Sub


          Resistance is not futile, it is Volts divided by Amperes...
          Just ask Mr. Ohm....

          Comment

          • JonMarsh
            Mad Max Moderator
            • Aug 2000
            • 15261

            #6
            Originally posted by svenarajala

            In high school those were my dream subs to use in a car stereo!!! However as I got older and realized I would rather spend time in my house than a car the new dream was for HT/2.0.

            This build is very enticing, I'm always looking to up my sub game to have more boom! I have been thinking about a custom sub enclosure to hold the new center channel that should be starting sometime soon... JonMarsh is correct, that boys will be boys and love their boom! I certainly do 😂
            Now, this is an interesting thing to think about, as regards my own feeling about the BP enclosures I've designed in the past and am working on now- I got interested in bandpass enclosures because of the Janis subwoofers we used to sell at the Boulder Sound Gallery in the mid 70's. And the thing is, designed properly and setup properly, you don't hear the sub, you don't hear the boom, you just hear the music!

            In fact, this was the lead in on their own promotional materials...

            How do you reproduce bass? Not just artificial low frequencies which appear as if the "bass" is always on, but a bass such as is perceived in real life. You just know that it must be on modern recordings, but somehow it never comes off.



            That was their credo, and that's how we marketed them, as part of a Levnison HQD system, replacing the Hartley 24" woofer. HQD stood for Hartley-Quad-Decca, as it used Quad ESLs in a special stand for the midrange and Decca ribbons for the top end, with Mark Levinson active crossovers.

            Click image for larger version  Name:	HQD single.jpg Views:	0 Size:	158.5 KB ID:	927974


            Now, this picture here is hopefully NOT how these speakers were setup for listening; if so, you wouldn't get close to your money's worth.

            Now, this is what a Janis W1 subwoofer looks like- it used an Altec-Lansing pro driver.


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            And if you pondered whether I might actually have one of these around, well, you need not wonder! It's not in as nice a shape as this one though.


            The developer of this product didn't have the calculation tools and theory we have available now, back in the early 70's, and it is reported he built quite a few prototypes before getting one that worked the way he wanted.


            Now, lest you think all I play around with is old quirky stuff, I could point out that I have some "new" quirky stuff, a pair of the Peerless STW350F 15" subwoofers, picked up a couple of years ago while they were briefly available (Peerless has discontinued them, but I know of a distributor that has about 180 pcs in stock) and it is ALSO a VERY QUIRKY design, IMO.

            Very odd motor concept, both long coil and long gap, as if they couldn't decide whether they wanted an overhung or underhung motor design, and decided to go for some of both. By conventional gap metrics, the Xmax is only 10.5 mm to keep the VC within the 36mm gap, but the 58mm VC can travel quite some ways maintaining BL force, about 40mm one way.


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            Now, if you're thinking this looks like a bit of a beast, take a look from the back side...



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            The frame incorporates threaded holes to facilitate mounting the rear part of the frame near the magnet to an internal brace in the cabinet to help support it and stiffen the cabinet.

            This part with its high Qts is meant for sealed enclosures, and normally fairly large ones or IB, but one can go relatively small (75L) with the right EQ profile to get a credible overall response profile.


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            But then, one should be able to get an anechoic profile that looks like this, with sufficient power (note the 10 dB boost):


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            And with enough watts, two of these would certainly play loud- probably be a lot of fun for HT.


            So, this is a "Boom Box" recommendation...

            ​​​​​​​Complicating the issue for the STW350F is the variation in quoted specs between different versions of the spec sheets. Fs ranging from 20Hz to 31Hz, Qts ranging from 0.5 to 0.7. I'd say some care is required...


            Last edited by JonMarsh; 18 January 2023, 13:33 Wednesday.
            the AudioWorx
            Natalie P
            M8ta
            Modula Neo DCC
            Modula MT XE
            Modula Xtreme
            Isiris
            Wavecor Ardent

            SMJ
            Minerva Monitor
            Calliope
            Ardent D

            In Development...
            Isiris Mk II updates- in final test stage!
            Obi-Wan
            Saint-Saëns Symphonique/AKA SMJ-40
            Modula PWB
            Calliope CC Supreme
            Natalie P Ultra
            Natalie P Supreme
            Janus BP1 Sub


            Resistance is not futile, it is Volts divided by Amperes...
            Just ask Mr. Ohm....

            Comment

            • technodanvan
              Senior Member
              • Nov 2009
              • 998

              #7
              Originally posted by JonMarsh
              The frame incorporates threaded holes to facilitate mounting the rear part of the frame near the magnet to an internal brace in the cabinet to help support it and stiffen the cabinet.
              I like this idea a lot, and wish other manufacturers would do something similar on their heavy subs. Very heavy, in some cases...

              https://stereointegrity.com/product/hs-24/

              - Danny

              Comment

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