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Need some help from experienced DATS users

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  • Need some help from experienced DATS users

    Hi All,

    First post but hoping to stick around =)

    A long time ago when I was a teenager I built a set of three 3-way speakers using Vifa P17WJ, P21WO and D27TG drivers. I've had these speakers for years and they sound awful due to my complete lack of knowledge at the time (lol). I finally decided to pull them apart and remake them with with proper port tuning crossovers etc and along the way I decided to grab a DATS v3 to assist not only this build but many others.

    However, I seem to be having trouble getting reasonable results from DATS. The params I get seem so completely off what you'd expect that I've either gotten something horribly wrong or my unit is defective.

    For example, DATs is telling me that for the P21WO-20-08 woofer fs=119hz, qts=0.8388, qes=1.745, qms=1.615 & vas=8.39L. With these params this 8 inch woofer wouldn't play a note under 100hz in a 40 liter box...?? I've tried with two examples of this woofer with close-ish results between them but wildly different from manufacturer specification. Just for comparison the manufacturer specs are fs=28hz, qts=0.33, qes=0.41, qms=1.6 & vas=113L.

    Same sort of creative results from the two P17WJ units. And I also get different numbers every-time I run the test with the same unit.

    Unit has been connected and calibrated as instructed. Woofers are free air sitting so vented pole piece inst obstructed.

    I'm not sure what I'm getting wrong and yet the DATS is promoted as 'very accurate'? The measurements I'm getting are closer to a gimmick.... :(

    Appreciate any help/advise anyone might have.
    Last edited by DeZZar; 12-23-2019, 06:12 PM. Reason: added tag

  • #2
    1) Post some screen shots of the results and settings in DATS
    2) Where are you located? Other DIYers might be close by to double check your measurements.


    • #3
      Screenshot of Dats attached. I'm located in Melbourne Australia!


      • #4
        If your test lead calibration looks like I straight line then I don't have any other ideas. Maybe measure a inductor and cap of known value. Have you talked with tech support?
        John H

        Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower


        • #5
          I just tested a capacitor, inductor and resistor and it gave results that I guess are within tolerance - similar to my multi-meter. I haven't contacted tech support (bit of a time difference). What's the general experience with these things - do they usually measure close to whats expected for the drivers?


          • #6
            Drivers can be off due to damage, age, break in, etc. The impedance graph seems like a functional driver. Might try exercising the cone by hand, by gently moving it in and out then retesting. If these drivers are over 20 years old I would not invest much time in them. I've seen surrounds stiffen up, but then they disintegrate.
            John H

            Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower


            • #7
              Thanks for the tip John. The drivers have had a pretty easy life and are still in perfect condition. They haven't been hooked up in a couple of years so I did as you said and played a little music through them and tested again. fs is now showing at 76hz and vas now 23 - improving but still a long long way off from whats expected. Qts although better @ 0.64 is still so far off from the expected 0.33...

              What the general experience with variance to manufacturer specs? Does anyone check when measuring??


              • #8
                They will probably loosen up and get close, but after many years who knows. The Vifa, Tymphany, Peerless drivers always measured close to the spec sheet, but I can speak for those specific drivers.
                John H

                Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower


                • #9
                  I bought a pair of Vifa P17WJ drivers in about 1992. They sat on my shelf unused for about 20 years. When I measured them with my WT3 they measured so far off Vifa's specs I thought something was wrong with them. I flogged them to death with sine waves trying to loosen them up and lower their Fs. They loosened up a little bit, but in the end I threw them away. I think the spiders and surrounds changed their characteristics over the two decades as well as the magnets maybe losing some strength. Also mine were stores sitting cone up, so there may have been some serious sag going on over the years. Too bad, I bet they were great drivers when they were new.

                  The lowest possible F3 box alignment is not always the best alignment.

                  Designing and building speaker projects are like playing with adult Lego Blocks for me.


                  • #10
                    Well, actually, if you model it, it'll do 50s in a 2cf box tuned to the mid 60s (this is w/your initial run screen data).
                    DATS has NO trouble spitting out Qs, Fs, Re & Le numbers w/ very high accuracy.
                    Vas can vary a LOT based on the operator's "experience".
                    Show us your tweeter run. (Even though you don't use T/S parms to model a box for a tweeter, you'll still see its resonant freq. - helpful for determing a proper Fc.)

                    I see on your Vas run that you DO have a driver diameter entered, but you have to tell DATS how much mass you added on your Vas run. I generally just add US nickels to the cone (one Nickel is close enough to 5.0 grams). Even if you've added 10 Nickels (50g), your Vas results will keep changing if you change what you TELL DATS what you added for added mass (or/and, if you change your entry for driver dia.). Pretty sure your DATS is working fine. Good luck, have fun, and Merry Christmas.


                    • #11
                      Can you supply a screen shot of what you get with the "measure free air parameters" with the driver removed from the box?
                      "Everything is nothing without a high sound quality." (Sure Electronics)


                      • #12
                        With your revised parms (after break-in), it'll do upper 40s in 2cf tuned to the low 50s (4"id x 3" long).


                        • #13
                          Thanks all for the responses.

                          Originally posted by ernperkins View Post
                          Can you supply a screen shot of what you get with the "measure free air parameters" with the driver removed from the box?
                          Yeah this was already all free air - no box.

                          At this point I guess the conclusion is that given the age of the drivers, stiffened surrounds and spiders I should probably trust the DATS results over an expectation that the drivers should measure better.

                          Disappointing as I really hoped to re-use these drivers as they are otherwise in great condition and still seem to work perfectly well when I put them through some sine wave punishment.

                          Guess I will start hunting for some replacements - can anyone recommend a good 8" driver that will get me f3 ~30-35Hz in 40L (~1.2cf) ??


                          • #14
                            Try exercising the driver suspension with your fingers. Just push the cone in with your fingers until the surround is stretched to it's limit or it becomes noticibly harder to push it in any further. Then do the same thing by pushing from the back of the cone. Repeat 10-20 times. This is more effective at loosening up new drivers or drivers that have been sitting, than playing tones or music in my experience.

                            If the speaker terminals are old and oxidised you may also need to press down on the jaws of the alligator clips and wiggle them around to achieve good electrical contact and therefore accurate/repeatable measurements.

                            If you want to double check that there isn't something wrong with the DATS, you can check Fs with just a multimeter, amplifier, a resistor and some test tones. Connect the woofer in series with a power resistor (1-10ohms, a few watts rating), to the amp. Make sure that any EQ, 'loudness' or bass/treble controls on the amplifier and playback source are disabled. Connect a multimeter on AC volts across the woofer terminals. Play test tones at various frequencies around the expected resonant frequency and monitor the voltage measured by the multimeter. At Fs the voltage should be the highest.

                            Also for drivers which have a pole piece vent, make sure you're not blocking the vent. You may need to hold the driver in the air as placing it magnet side down on a table blocks the vent and will alter T/S parameters.

                            Also worth noting that temperature affects the operation of driver suspensions. If it is very cold the suspension becomes stiff and when it is hot it softens. The temperature needs to be 20-25*C to achieve comparable T/S measurements to the datasheet.


                            • #15
                              I wouldn't give up on these drivers just yet.

                              Some suspensions really need to be flexed quite a bit to loosen them up. I suppose this is especially true for older suspension pieces that may have had their physical properties changed a bit... case in point... Chris's responses above and how the F3 has changed just from playing some tunes through them a bit.

                              What I'd do is hook these up to a subwoofer amplifier if you have one or a regular amp with just these hooked up and play some bass test tracks (available online through youtube) and really get these drivers pumping to maybe 80% of their Xmax for 5-10 minutes. Let them cool down temperature-wise for 20 minutes or so... and re-DATS them at that point. Then you'll have a good picture of what they can really do once flexed for awhile.

                              The spider especially can be very stiff and some drivers may benefit from 'breaking in' much more than others. When I DATS a new woofer that might show an FS of 75 Hz, just flexing the cone a dozen times or so quickly may reveal an FS of 68 Hz right afterwards. A few minutes later it may creep up a few Hz, maybe to 71-73 Hz... that shows that the suspension really needs to be 'broken-in' more than just a little bit on some drivers. Modern drivers are usually designed for more excursion than in days past, and that excursion needs to be counteracted with a stiffer suspension. When I've used bass signals to break in drivers for a good 20 minutes, they usually keep most of the gained FS excursion.

                              I think if you'll really work these drivers in with some serious bass tones, you'll find that -- although some of the specs may still be off a bit from published -- overall, they will balance out to yield a similar response in a similar sized cabinet. Chris Roemer has shown this to be the case many times with many drivers over the past several years.

                              Anyway, just thought I'd interject my 2 cents and what I'd do if it were me.

                              *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                              *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                              *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF