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Xmax....LOTS of Xmax

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  • Xmax....LOTS of Xmax

    I'm working on a lab set-up that is not really audio related. I need to vibrate a surface up to about 1kHz while also being able to move it at low frequency (10 to 30Hz) up to about 1cm. I will be looking at the surface with a LASER vibrometer that has a very small field of view (less than 5mm in diameter), so really just the dust cap or some other point on the cone. Given all that, I don't really care about break-up modes on the cone. Sound quality is not an issue, really. There will be no baffle at all as I'd really rather not have the lab super noisy. T/S parameters won't really matter as there is no box involved and I can EQ as needed (Linkwitz transform, for example).

    So my question is what driver shall I look at that has huge Xmax and perhaps a light cone (for higher frequency performance)? Cost and size are not really an issue (within reason).

    Thanks in advance for your suggestions!

  • #2
    What size driver? The Anarchy woofers have huge Xmax for 5 and 7 inch drivers, but you can get a 18" subwoofer with more.

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    • #3
      You only need to move 1cm?
      Francis

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      • #4
        Originally posted by fpitas View Post
        You only need to move 1cm?
        +1, 10mm xmax isn't all that much or hard to find.
        www.billfitzmaurice.com
        www.billfitzmaurice.info/forum

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        • #5
          Driver diameter is unimportant for this. Smaller would probably be better (lighter cone).

          Moving ±1CM is my minimum need. More would be nice. What I am trying to avoid is to have to build a hybrid system - where a loudspeaker is used for the lower amplitude, higher frequency (>30Hz) components and this speaker is mounted to a linear motor which moves the loudspeaker to provide the <20Hz, large amplitude components.

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          • #6
            The RSS210 (11mm) and Ulitimax 8 (16mm) come to mind. Both of those will gladly run a 1k tone over subsonic cone motion. The actual frequency response at 1k is unimportant in your case I imagine, just that they can do it. It's just a matter of increasing the amplitude of your 1k signal until you see it on your vibrometer.
            Electronics engineer, woofer enthusiast, and musician.
            Wogg Music
            Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat

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            • #7
              Is distortion a concern?
              Don't listen to me - I have not sold any $150,000 speakers.

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              • #8
                I think he is trying to build one of these> https://www.youtube.com/watch?v=o7aLvfIaLO4 LMAO

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                • #9
                  How about using a combination of a 12" subwoofer with inverted dust cap plus a small piezo transducer that you glue in the middle of the dust cap?
                  Charlie's Audio Pages: http://audio.claub.net

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                  • #10
                    Vibroseis

                    https://en.wikipedia.org/wiki/Seismi...ismic_vibrator

                    might be overkill
                    It is estimated that one percent of the general population are psychopaths - New Criminologist: Understanding Psychopaths

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                    • #11
                      Mattk and Unbiasedsound - Funny, but not what I'm looking for.

                      Johnnyrichards - Distortion is probably not an issue. I would like the higher frequency components (say 30 to 200Hz) to be fairly clean, but the sub 30Hz stuff can tolerate a fair amount of distortion. I expect this will not be a problem as the expected amplitude for the higher frequency stuff will be under 0.1mm. The very low frequency stuff will be >1cm displacement.

                      Wogg - Thanks for the Ultimax-8 suggestion. Might be just what I'm looking for. OTOH maybe I'll just spring for the monster Peerless (https://www.parts-express.com/peerle...ofer--264-1652) that claims 90mm total excursion.

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                      • #12
                        If distortion isn't an issue, then over driving any of the Dayton DVC subs will work fine.
                        Don't listen to me - I have not sold any $150,000 speakers.

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                        • #13
                          Any driver (cheap or expensive, small or large) will do what you want as long as it has sufficient xmax/xlimit. For 1cm, I'd look for 5 mm xmax drivers to be safe. Note that virtually no driver will move the same distance given the same power input at different frequencies. If this driver is powered in free air (e.g., not a designed enclosure), it will have a resonant frequency where very little power will drive it beyond it's limits. You need to be concerned with that. That is, you just can't sweep frequency at one power level lest you hit the resonant frequency which will overdrive the speaker. Given your freq test range, you'll hit the resonant frequency on just about all woofers. Even in a closed (e.g., airtight) box, there will be a resonant frequency but may be manageable by the boxes design.

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                          • #14
                            Mike - I plan to measure the cone excursion with a LASER vibrometer and sweep across the frequency band of interest. At which point I will have a displacement versus frequency plot which I can use to "pre-distort" the input so as to linearize it all. (it all sounds so overly complicated, but it is for a lab set-up...)

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                            • #15
                              I'm here.
                              Guess xmax's age.

                              My guess: 15. His grammar is passable. His trolling is good.

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