Retrofitting a SVS driver

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  • Patrick Sun
    Super Senior Member
    • Aug 2000
    • 1380

    Retrofitting a SVS driver

    SVS has offered owners of their sub a driver upgrade, and many have upgraded, and offering their old drivers for $40 plus shipping (the credit that SVS is willing to "buy back" the old drivers), but many don't want to pay for shipping, so by selling to other people who'll foot the shipping bill, they recoup the entire $40 for their drivers.

    Well, I bought one of these old SVS drivers to retrofit into an old 2.5-2.75ft^3 ported enclosure that was built for a Shiva.

    Here's 4 photos of the SVS "upgrade" process:

    Photo 1: Here's the raw SVS driver (I took off the rubber surround ring in order for it to fit the cutoff from an old sub enclosure that was made for a Shiva 3 years back by another member here).

    Photo 2: Here's the old box sans old driver. You can get a glimpse of the extensive plumbing job I did on the port.

    Photo 3: Here's a closer shot of the innards of the box. The original port was about 8" long, but I went overboard and used some 45 degree PVC pipe bends to get the port length around 22"-24" long. It was not fun getting all that extra stuff in that box. What it's tuned to? I'm hoping down in the low-20Hz range. I'll play around with the calibration and measurements later and find out.

    Is the porting ideal? No. I'm just trying to make lemonade with the lemons I've got on hand.

    Photo 4: Here's the subwoofer put back together with the SVS driver in place.

    I had to go buy banana plugs for the driver because I couldn't get the 5-way binding posts on the drivers to screw down on bare wire - no big deal. The driver is supposed to be recessed, but the outer recessed driver rim is just too tight, and I basically have the driver screwed in on half of its right side, and wedged in, hammered in, and screwed in on the left side. I the did the tissue test and couldn't find a leak on the driver "installation". I'll have to mess up the front baffle to get the driver out of there if/when I decide I need to fix this problem. I have a cover for the driver, so with the cover on, no one is the wiser.

    I don't know how "ideal" this enclosure is for the driver, but I calculate internal volume to be around 2.5-2.75ft^3, which is pretty close to the old SVS 25-31 CS model.




    PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
    PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15261

    #2
    Looks like pretty good bang for the buck, Pat!

    Let us know how the port works out, and how the tuning checks out- can you plot the impedance curve? TL's have usually used folded paths for the backwave, but ports have higher velocities- I don't know how your "plumbing job" will affect things. You would compare to a more "ideal" situation (just as a check?) by making what I call a "wood stove sub", where the port is all external, just a straight shot like a stove chimney pipe. It would look a little funny, but it might make pretty good sounding lemonade....


    -Jon




    Earth First!
    _______________________________
    We'll screw up the other planets later....
    the AudioWorx
    Natalie P
    M8ta
    Modula Neo DCC
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    Modula Xtreme
    Isiris
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    In Development...
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    Resistance is not futile, it is Volts divided by Amperes...
    Just ask Mr. Ohm....

    Comment

    • Patrick Sun
      Super Senior Member
      • Aug 2000
      • 1380

      #3
      No can do on the impedance graph (no truck to move it to a friend's place for measurement purposes - nor desire) But I'll do the Helen Keller test for minimal cone movement at resonance with my BassZone test CD in a few days or earlier.

      I figure it'll make an ugly HT present for one of my friends later in the year once I get the plate amp I ordered from MCM last week when they had it on sale. (Can't you tell I'm the budget minded DIYer?) Hehe.




      PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
      PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs

      Comment

      • Patrick Sun
        Super Senior Member
        • Aug 2000
        • 1380

        #4
        Well, for some reason, my current Sunosub's placment seems to be the best spot in my room. The SVS sub is on the other side of the TV, and at my main listening spot, it's sounds like it's in a bit of a null. I say this because I get closer to the SVS sub, I feel the null going away and it thumps just dandy. I'm not going to swap out the 2 subs because Sunosub II has a bit of a weak leg at the moment. And as expected Sunosub II has a bit more low end extension.

        I took some quick-n-dirty measurements, and you'll see what happens when you over-port an enclosure (I'm using 1/3 octave sine waves and a Radio Shack SPL meter, and the readings have been adjust per generic correction table):

        Graph 1:

        The light blue line is a near field measurement of the sub, and as you can tell, the low end isn't extended too far, with a F3 around 28Hz (using a Shiva to model the enclosure size and porting, LspCAD predicted a F3 around 27Hz, so this jives). Also, my snake-like porting gives me a Fb around 20Hz (I did the Helen Keller method of determining Fb by playing low frequency test tones and when I got the test tone that moved the driver cone the least, I called that Fb). LspCAD told me that the FB would be 21Hz, so the reality was very close to the simulation. My room tends to boost 45-60Hz, so there's a slight adjustment to smooth out the curve.

        The fuscia curve is a 1m measurement of the sub. As you can tell over-porting the enclosure does cause a nice dip below 36Hz, and that was also expected.

        Given the size of the enclosure (2.75 ft^3), I could shoot for Fb=25Hz and moving the F3 down a little to around 25Hz. This will involve just taking out one of the two 90 degree PVC bends in the porting. This should give me a little pop while lessening the driver protection for low end material at high volumes. Basically it would mimic the 25-31 SVS model if I changed the porting to a tune of 25Hz. Since I'm enclosure-size-limited, this might be the best configuration for this application. But I haven't decided if I want to do it or not.

        Graph 2:

        Just for laughs, I wanted to see how the response was affected when I sealed up the port with a nerf football. The thin light blue line is the sealed frequency response. As expected, there is a more gradual fall-off in output under 40Hz. This may be what I use for music (the bass is a little tighter in the seal configuration), and then unplug it for DVDs. The fuscia line is the ported frequency response (I will admit to moving the sub around to another spot in front of my current Sunosub, but the response is pretty similar to the initial measurement).

        Anyhow, just thought some of you wanted to see "theory" in action (w/r/t predicted simulations and real world measurements).




        PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
        PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs

        Comment

        • JonMarsh
          Mad Max Moderator
          • Aug 2000
          • 15261

          #5
          Hi Pat,

          Where did you place the mic for the nearfield measurement? Measuring ported systems nearfield is tough to do meaningfully, unless you measure both the port and woofer contributions, and sum them. Otherwise, nearfield, the woofer shows the old minimum excursion null, but it doesn't correlate well. A one to two meter ground plane measurement is often the best single "curve" you can get for evaulating the sub performance. But then there's the room interaction, which is where tools like RPG Acoustics Room optimizer, CARA, and SoundEasy come in real handy. Of course, a good ear doesn't hurt, either, and delivers the ultimate bang for the buck!

          -Jon




          Earth First!
          _______________________________
          We'll screw up the other planets later....
          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

          • Patrick Sun
            Super Senior Member
            • Aug 2000
            • 1380

            #6
            Jon, it was just of the driver, I didn't take measurements of the port. If I get some time, I'll try to get a port output reading and do some logarithmic addition.




            PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
            PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs

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