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WT3 First Impressions, Modding the Sub-100

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  • WT3 First Impressions, Modding the Sub-100

    Last week, I posted my first thread asking for T/S parameters of the driver used in the Dayton Audio Sub-100 because I unhappy with its sound and wanted to modify it. I didn't get T/S parameters, but I was successful in modifying the Sub-100, see this thread:
    http://techtalk.parts-express.com/sh...d.php?t=214612

    But, I wanted the T/S parameters! I had always wanted the Dayton Audio Woofer Tester since it came out, and this was the excuse I needed. One week later, FedEx delivered the WT3. Here are my first impressions of the WT3:

    Installation was incredibly simple and the instructions for calibration the hardware and measuring your first driver were very easy to follow. Within 45 minutes I had measured three drivers and compared T/S Parameters against the manufactures (if available) and modeled the Sub-100 in WinISD.

    If I have one complaint about the instructions it was during the Vas measurement step. The most convenient technique to measure Vas is the 'added mass' method using the included mini scale to weigh your ‘added mass’. Measuring Vas apparently requires the 'piston diameter'. This isn't something you can measure accurately with a tape measure. So my strategy was to convert the manufactures value for Sd (effective piston area) to effective diameter to supply as the 'piston diameter'. Some more details on how to use the added mass method with the supplied scale in the Quick Start instructions would be helpful.

    To add mass, I lined nickels around the dust cap. I read about this method in reviews of the WT3 on PE’s website. Nickels aren’t ideal since the coins can shift around while the woofer is excited during the frequency sweep when the impedance response is recorded. Silly Putty would probably be the ideal choice as it has just the right amount of adherence and won’t leave any residual adhesive.


    Silly Puddy

    The amplitude of cone motion is very low so I’d imagine the error resulting from shifting coins is minimal. I would recommend you be organized about how you place the coins on the dust-cap. Balance the load over the voice coil and try to couple the coins together so the shift is minimized and so they act as a singular mass.

    The first Woofer I measured was a Vifa P17WG-09. This is a 6.5" woofer that came with a 2-way car audio 'component' set sold by Madisound. The woofer was used (abused) in my old car for 7 years until it could no longer pass smog and had to be crushed. I was a little disappointed when the T/S parameters were way off from the manufactures. I remeasured and recalibrated several times to make certain all procedures were followed properly. For example, the manufactures Fs is 64 Hz, I had measured 105 Hz. However, I wasn't surprised by the large differences. I had repaired the surround with silicone after sticking it with a screw driver. This could have stiffened the suspension and increased Fs. Results from repeated measurements were consistent, very encouraging. Most of the other parameters were off a similar amount, I’d imagine because of the abuse suffered by the driver.

    The next driver tested was an Adire Audio Shiva MkII. This was also used in my car. Here the results were more typical when compared to the manufactures, see table below.



    The significant differences are Qms and Le. The low Qms is possibly explained by suspension being ‘loosened up’ over time caused by the harsh environmental conditions in my old cars hatchback. I'm not sure what explains the low inductance. Did I miss a coil somehow? I’ll have to look into this later. Overall, I’m very impressed with the ease of use and apparent accuracy of the WT3. It’s difficult to say exactly how accurate it is without a comparison against the ‘industry standard woofer tester’. Comparison with manufactures parameters only tells you are in the ball park as there will be some deviation from driver to driver. With that said, being within a few percent of the manufactures nominal parameters is a good enough result for me, and probably 99% of the DIY audio hobbyist out there. Now, on to testing the Sub-100 driver.

    Recall that it was the unsatisfactory sound of Sub-100 that resulted in me taking it on as a project to attempt to improve it.

    Here are the SPL measurements of the Sub-100 from last weekend:


    For more details on the measurements, see this thread: http://techtalk.parts-express.com/sh...d.php?t=214612

    Measuring the Sub-100 driver was accomplished very quickly following the same procedure described previously for the Vifa and Shiva woofers. Once I had the measured T/S parameters they were input into WinISD. The modeled transfer function of the factory (red) and modified (blue) Sub-100 alignments are shown below:



    My modified alignment is very complicated. What I did was, stuff two towels in the ports to block them. We’ll call this quasi-sealed because the towels are lossy. Think of the ports as Aperiodic vents. I also added 2 lbs of polyfil to the enclosure.

    The transfer function shows the factory Sub-100 alignment has a strong ripple, with 3 dB of gain at 70 Hz. This explains the 1-note bass syndrome I was experiencing. I can appreciate why one would design a sub this way. It’s going to be very efficient and get very loud, but at the expense of sounding terrible—unlistenable for me anyway. Also, this wouldn’t be an effective sub for home theater, as LFE effects are well below the frequencies with the increased efficiency resulting from this gain.

    In comparison, the quasi-sealed version lacks the hump at 70 Hz. The Qtc is modeled as 0.83 after increasing the volume 10% that is effectively caused by the polfyfil. This sealed alignment will not get nearly as loud. But it sounds much better! It's still a little 'boomy', but I’m quite satisfied. I haven't listened to a sealed sub in a long time. I forgot how rich they can sound. Kick drums can sound very life like thanks to the sharp transient response and low group delay.

    To conclude, the WT3 will be a great tool to have around for my next speaker project. Tomorrow I’d like to measure the driver in the enclosure to get a measurement of Fsc.

    Update:

    Here are enclosure measurements of the Sub-100 for the factory and modified alignments:


    Dayton Audio WT3 Impedane Sweeps


    Modeled (WinISD) responses based on impedeance sweeps.


    Summary of Sub-100 Alignments.
    Last edited by frankR; 12-13-2009, 02:24 AM.

  • #2
    Re: WT3 First Impressions, Modding the Sub-100

    THANKS... appreciate you sharing this!!

    Comment


    • #3
      Re: WT3 First Impressions, Modding the Sub-100

      Nice write-up. When making comparisons keep in mind that a lot of manunfacturer's specs can be way off from the actual driver specs, so don't compare your results to those. The agreement you are getting on the Shiva is remarkably close. As for the accuracy of the WT3. It is typically, very accurate. I worked on a project recently with John Janowitz of Acoustic Elegance. He built a couple custom drivers, measured them with Praxis, and sent them to me. I measured them with WT3 and the values were so close you would have thought that I simply copied them from the Praxis data. When we were beta-testing the WT3 I would compare it to my LCR meter with various resistors and inductors, and again extremely close agreement. What is the "industry standard woofer tester" that you were referring to?
      Click here for Jeff Bagby's Loudspeaker Design Software

      Comment


      • #4
        Re: WT3 First Impressions, Modding the Sub-100

        Frank, a couple of things I learned about using WT3 (although not until after I had tested many, many drivers, and therefore having wasted a good bit of time):

        I started with nickels as well, which lead me to make several tests that produced inaccurate results... To use the nickels, naturally, I had to lay the woofers on their "backs" so that they would lay on the face of the cone. I did account for the vent in the back by laying it on a V-shaped clamp to allow air to flow freely. However, after discussing on TechTalk about the unexpected results I was getting, someone (I think it was Jeff B.) mentioned that the driver needed to be mounted "upright" during testing. Sure enough, once I setup a vice to clamp the magnet and hold the woofer upright...and used the Walmart generic silly putty (the tacky dough for hanging posters also works very well...got it at Hobby Lobby), I started getting accurate test results. So, I had to go back and redo all the tests. I found that the small woofers were not as critical about their orientation during the tests.

        Another thing I found was that under certain conditions (I can't recall them well enough to put into words) the application allowed me to use too little Added Mass. I found this by "accident". One particular test on a 8 or 10 inch woofer gave me results that were just way off from the manufacturer's specs. I realize this isn't all that unusual, but these were really off. So, I added more mass and retested; the results were closer...added more mass and got even closer. This is the only issue that caused me a little concern wit the use of WT3. I wish they could provide a guidline for ensuring you are using the optimum amount of added mass.

        Comment


        • #5
          Re: WT3 First Impressions, Modding the Sub-100

          Originally posted by rogoll View Post
          Frank, a couple of things I learned about using WT3 (although not until after I had tested many, many drivers, and therefore having wasted a good bit of time):

          I started with nickels as well, which lead me to make several tests that produced inaccurate results... To use the nickels, naturally, I had to lay the woofers on their "backs" so that they would lay on the face of the cone. I did account for the vent in the back by laying it on a V-shaped clamp to allow air to flow freely. However, after discussing on TechTalk about the unexpected results I was getting, someone (I think it was Jeff B.) mentioned that the driver needed to be mounted "upright" during testing. Sure enough, once I setup a vice to clamp the magnet and hold the woofer upright...and used the Walmart generic silly putty (the tacky dough for hanging posters also works very well...got it at Hobby Lobby), I started getting accurate test results. So, I had to go back and redo all the tests. I found that the small woofers were not as critical about their orientation during the tests.

          Another thing I found was that under certain conditions (I can't recall them well enough to put into words) the application allowed me to use too little Added Mass. I found this by "accident". One particular test on a 8 or 10 inch woofer gave me results that were just way off from the manufacturer's specs. I realize this isn't all that unusual, but these were really off. So, I added more mass and retested; the results were closer...added more mass and got even closer. This is the only issue that caused me a little concern wit the use of WT3. I wish they could provide a guidline for ensuring you are using the optimum amount of added mass.
          The program looks to see if Fs was lowered by at least 25% with the added mass. This should be enough for a good Vas calculation.
          Click here for Jeff Bagby's Loudspeaker Design Software

          Comment


          • #6
            Re: WT3 First Impressions, Modding the Sub-100

            Thanks for reading gc1 and Jeff.

            Originally posted by Jeff B. View Post
            What is the "industry standard woofer tester" that you were referring to?
            I don't know. It was intentionally a generic statement.

            Comment


            • #7
              Re: WT3 First Impressions, Modding the Sub-100

              Just a FYI you can measure your impedance in the enclosure too, this will show you a vented enclosures Fb(between the 2 peaks) and can confirm the alignment or show the difference with stuffing ect.

              Comment


              • #8
                Re: WT3 First Impressions, Modding the Sub-100

                Originally posted by ocool_15 View Post
                Just a FYI you can measure your impedance in the enclosure too, this will show you a vented enclosures Fb(between the 2 peaks) and can confirm the alignment or show the difference with stuffing ect.
                That's pretty cool!
                I just picked one up this week and measured the impedance on my Mini Surrounds, that I just built, in the enclosure.
                I also noticed the full impedance curved match the one in PCD almost exactly. That made me smile.:D
                Dave
                http://www.pellegreneacoustics.com/

                Trench Seam Method for MDF
                https://picasaweb.google.com/101632266659473725850

                Comment


                • #9
                  Re: WT3 First Impressions, Modding the Sub-100

                  Originally posted by ocool_15 View Post
                  Just a FYI you can measure your impedance in the enclosure too, this will show you a vented enclosures Fb(between the 2 peaks) and can confirm the alignment or show the difference with stuffing ect.
                  Results posted.

                  Comment


                  • #10
                    Re: WT3 First Impressions, Modding the Sub-100

                    Another added mass item to use is play-doh. after I first got my WT3 i got sick of adding so many damn coins (I had a lot of LARGE drivers to measure). So i shanghaied my wife's play-doh collection (don't ask why she has it). and it works just fine. I have read in a few places that added mass isn't a good way to go, that is gives false readings due to cone sag and that the t/s specs can be off due to it. Well not all of us can just throw a few "test" boxes together for this reason, Due to budget or space or lack of tools.
                    But thanks to the WT3 I have half a dozen "new" projects to do just with old drivers I have had on hand.
                    the old Pioneer 15"s will sooner or later become some neat di-pole 3-ways. and the cTs 12" far-field drivers I have are going to become some very very loud 3-ways... as soon as I finish fixing the surrounds and stuff on them.

                    you can see the pioneers and the work i have done so far on the cTs drivers in my photo gallery

                    Rene
                    If it doesn't fit, Force it. If it breaks, It needed replacing any ways

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