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  • Dustcaps and Woofers

    In theory, if you are using a woofer below 500 Hz, is there any advantages/disadvantages to a larger/smaller dustcap?

  • #2
    Re: Dustcaps and Woofers

    Does a larger dust cap provide more support for the cone?

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    • #3
      Re: Dustcaps and Woofers

      Originally posted by vanapplebomb View Post
      In theory, if you are using a woofer below 500 Hz, is there any advantages/disadvantages to a larger/smaller dustcap?
      One may alter the size and mass of the cap to fine tune the Mms and Fs and all else that's affected by it, and you can do that with all drivers.
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

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      • #4
        Re: Dustcaps and Woofers

        Or, do away with it entirely as Acoustic Elegance does, and some of the Eminence drivers do. (In 12"s and 15"s), and Seas and others do in smaller sizes.

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        • #5
          Re: Dustcaps and Woofers

          If you have a somewhat flexible cone, such as a polypropylene cone, can a dust cap about 2/3 the cone diameter substantialy increase the stiffness of the cone?... say an 8" woofer with a 6" diaphragm, with a 4" dust cap?

          I notice B&W has a similar theory with there "mushroom" dust caps.
          Last edited by vanapplebomb; 01-12-2010, 08:10 PM.

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          • #6
            Re: Dustcaps and Woofers

            Originally posted by vanapplebomb View Post
            If you have a somewhat flexible cone, such as a polypropylene cone, can a dust cap about 2/3 the cone diameter substantial increase the stiffness of the cone?... say an 8" woofer with a 6" diaphragm, with a 4" dust cap?
            It can.
            www.billfitzmaurice.com
            www.billfitzmaurice.info/forum

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            • #7
              Re: Dustcaps and Woofers

              How much of a gain would you get?...enough to hear an audibly tighter bass in the lower regions?

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              • #8
                Re: Dustcaps and Woofers

                Originally posted by vanapplebomb View Post
                How much of a gain would you get?...enough to hear an audibly tighter bass in the lower regions?
                If this is a DIY attempt at making a driver 'better' you may do more harm than good. And there's no such thing as 'tighter bass in the lower regions'. You may be just trying to get more from the driver you have than it's capable of giving, especially if it's only an eight.
                www.billfitzmaurice.com
                www.billfitzmaurice.info/forum

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                • #9
                  Re: Dustcaps and Woofers

                  Originally posted by vanapplebomb View Post
                  How much of a gain would you get?...enough to hear an audibly tighter bass in the lower regions?
                  You're not going to get tighter bass by changing the size of a dustcap!
                  Hey, but if you think you will, go for it and learn by doing.

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                  • #10
                    Re: Dustcaps and Woofers

                    Sorry, i Think i had something else in mind related to the effects of cone break up modes.

                    B&W's acclaimed mushroom bass driver is full of baloney? another marketing schema? I would think that a company of that kinda caliber would have a solid reason for every little detail of there products.

                    on the other hand, i should think that a solid cone should be beneficial to sound quality!

                    I believe Vance Dickason refers to this type of cone brake up as "Concentric Cone Modes" if that helps anyone see what i'm talking about. It would seam logical that one who specializes in driver design would take the dust cap into serious consideration. If you can eliminate some of the concentric cone break up modes, then it would be only logical that your subjective sound quality would rise due to lower distortion due to cone resonance break ups.



                    I'm not trying to come across harshly or anything,

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                    • #11
                      Re: Dustcaps and Woofers

                      Musical instrument speakers are a prime example of this type of break up...break ups in general. Guitar speakers are specially designed for these breakups which give them there tone. Ever play with a guitar speakers cone? Extremely thin and flexible.

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                      • #12
                        Re: Dustcaps and Woofers

                        The size and rigidity of the dust cap can affect the high frequency response of the cone it is attached to. A solid-composition dust cap provides annular stiffening at the point of attachment, and that is probably the effect that most driver designers are going for when they use large dust caps, but a large dust cap also causes diminished high frequency response, due to a phenomenon called doubling and its interaction with the space underneath the dust cap. As the cone is driven at frequencies above its pistonic range, it still radiates pistonically over smaller and smaller areas with increasing frequency, and once this pistonic radiation area fits completely inside the dustcap's diameter, the energy is radiated into the cavity under the dust cap and the amount of energy radiated into the room diminishes because of the non-pistonic motion of the exposed radiating area. The space under the dust cap essentially acts like an acoustic bandpass filter, vented through the pole piece vent. This seems like it could be used to cause a steeper upper-midrange rolloff, but it's also why many full-range drivers eschew the dust cap entirely and use phase plugs. The driver essentially becomes a ring radiator at high frequencies.
                        Best Regards,

                        Rory Buszka

                        Taterworks Audio

                        "The work of the individual still remains the spark which moves mankind ahead, even more than teamwork." - Igor I. Sikorsky

                        If it works, but you don't know why it works, then you haven't done any engineering.

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                        • #13
                          Re: Dustcaps and Woofers

                          Originally posted by vanapplebomb View Post
                          If you can eliminate some of the concentric cone break up modes, then it would be only logical that your subjective sound quality would rise due to lower distortion due to cone resonance break ups.
                          ,
                          Break up occurs in the upper end of the driver's range, not the lower end, so eliminating it won't affect the low end response. The easiest way to eliminate break up is to just cross over from the driver below where break up occurs, and that's exactly what designers do.
                          www.billfitzmaurice.com
                          www.billfitzmaurice.info/forum

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                          • #14
                            Re: Dustcaps and Woofers

                            Hmmm....

                            so, lets suppose an individual has a XO phobia....

                            If they wished, they could then design drivers with the proper inductance and dust cap size to have a specific natural high end role off. Then they could just put a blocking cap in series with the next driver to provide it with a high pass...

                            just ideas that are going through my head...

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                            • #15
                              Re: Dustcaps and Woofers

                              Originally posted by vanapplebomb View Post
                              Hmmm....

                              so, lets suppose an individual has a XO phobia....

                              If they wished, they could then design drivers with the proper inductance and dust cap size to have a specific natural high end role off. Then they could just put a blocking cap in series with the next driver to provide it with a high pass...

                              just ideas that are going through my head...
                              It's generally accepted that a minimum of 3rd order filtering is required to minimize destructive interactions between drivers in the crossover region. Driver and cabinet design can be employed to get that combining 2nd order electrical and 1st order acoustical slopes, and if you're very good you can get 2rd order and higher acoustical slopes, allowing 1st order electrical filtering. But it's not easy.
                              There are those who insist that the benefits of 1st order electrical filtering outweigh the problems raised by not having at least 3rd order total slope. I'm not one of them, but to each their own.
                              www.billfitzmaurice.com
                              www.billfitzmaurice.info/forum

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