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Cloth surrounds and sealed cabinets

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  • Cloth surrounds and sealed cabinets

    Hi, I'm just trying to understand what would happen with a lossy surround like cloth when that driver goes in a sealed cabinet.
    I see a lot of recommendations from Eminence and others for their drivers to be placed in sealed enclosures that seem undersized vs the driver's TS parameters. If I assume no loss at all through the driver's surrounds, then the resulting curve in the seemingly undersized box usually gives a massive bump in the bottom end that would seem like it would be very inaccurate.

    Does the lossy surround mean that said driver can go into a smaller enclosure without a massive bump in the response? Is it kind of like an aperiodic enclosure then - the surround being a resistive loss?

  • #2
    Cloth surrounds are typically treated with a doping material to seal them.
    Paul O

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    • #3
      Originally posted by Paul O View Post
      Cloth surrounds are typically treated with a doping material to seal them.
      ​Oh I had no idea. I just assumed because light was passing through quite easily, that its not sealed. Well this is very good to know Many thanks for that info!

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      • #4
        Another thing to remember... Just because it isn't a sealed box, doesn't mean that it doesn't have pressure inside. A bass-reflex design will actually have higher internal box pressure than a sealed enclosure.

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        • #5
          Originally posted by contoursvt View Post
          Hi, I'm just trying to understand what would happen with a lossy surround like cloth when that driver goes in a sealed cabinet.
          I see a lot of recommendations from Eminence and others for their drivers to be placed in sealed enclosures that seem undersized vs the driver's TS parameters. If I assume no loss at all through the driver's surrounds, then the resulting curve in the seemingly undersized box usually gives a massive bump in the bottom end that would seem like it would be very inaccurate.

          Does the lossy surround mean that said driver can go into a smaller enclosure without a massive bump in the response? Is it kind of like an aperiodic enclosure then - the surround being a resistive loss?
          ​Vance Dickason talks about this in the LDC. Quote: "Air leakage caused by a speaker's lossy surround or porous dust cap should probably be ignored since attempts at correction can create as many problems as they solve. Lossy pleated edge surrounds are generally not appropriate for closed boxes and should not be used at all."
          Brian Steele
          www.diysubwoofers.org

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          • #6
            Originally posted by Brian Steele View Post
            Vance Dickason talks about this in the LDC. Quote: "Air leakage caused by a speaker's lossy surround or porous dust cap should probably be ignored since attempts at correction can create as many problems as they solve. Lossy pleated edge surrounds are generally not appropriate for closed boxes and should not be used at all."
            One method of testing dual (or more) woofer sealed cabs for leakage loss is to press in one cone, watch the other cone extend, then hold the first cone in place to see how long the second cone will stay extended. If it's really lossy it will fall back quickly. If it's unacceptably lossy the second cone won't extend at all. I've not seen cloth surrounds to be any better or worse than foam or rubber in this respect.

            www.billfitzmaurice.com
            www.billfitzmaurice.info/forum

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            • #7
              Thanks everyone for all the help. I'm going to try building a pair of sealed two way speakers using a pair of Eminence Beta 15A 15" drivers, a pair of SEOS 12 waveguides and the Dayton D250P compression drivers. The goal is to have a nice sounding speakers for music playback in a system I've got set up in the living room. I've tried the Beta 15A in an open baffle setup and while its a bit lean in the bass, I found it to be a nice driver. When I was modeling the woofers in a sealed, I was leaning towards a 6cf enclosure which is far larger than what Eminence recommends (they recommend a 2.6 as the Max which would give a massive 6db bump). With 6cf, bump is around 0.8db and I'm sure if I stuff it a little, I can get that down to like 0.5db.

              ​Maybe my logic is wrong but I'd imagine a massive bump would make it sound like its got that one note thumpy bass. Anyway I had built a pair of budget econowaves (with a slight mod on the xover) using the Dayton woofer and selenium tweeter and was very pleased so I'm leaning towards this as a next step to see how I like it.

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              • #8
                Originally posted by contoursvt View Post
                Maybe my logic is wrong but I'd imagine a massive bump would make it sound like its got that one note thumpy bass.
                It would, with recorded material. But it's usually used as an electric bass driver, with low powered tube amp. That bump gives it adequate sensitivity for professional use with only 35 to 50 watts driving it.

                www.billfitzmaurice.com
                www.billfitzmaurice.info/forum

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                • #9
                  Originally posted by Brian Steele View Post

                  ​Vance Dickason talks about this in the LDC. Quote: "Air leakage caused by a speaker's lossy surround or porous dust cap should probably be ignored since attempts at correction can create as many problems as they solve. Lossy pleated edge surrounds are generally not appropriate for closed boxes and should not be used at all."

                  While Dickason's work has been a valuable addition to the speakerbuilding community, I think he's off the mark there. There's not a good pathway between dustcap and cabinet volume (most porous/vented dustcaps have solid backplates instead of vented) and pleated edge surrounds aren't inherently problematic for sealed box any moreso than other surround types IMO, with the caveat that they're usually found on low QTs pro-style drivers which usually want a vented alignment for good bass extension. The Lower Qms of stiffer surrounds (pleated IS generally stiffer than a foam or rubber half roll) is usually only a minor contributor to the lower Qts piece, the motor strength of pro-style drivers means that Qes is the vastly larger contributor to low Qts.

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                  • #10
                    Thanks Bill and badman on the added information. I guess I didn't think about what or how the driver was originally marketed for and thus, how that affects their recommendation on cabinet size and response.
                    ​In this case, if I want to make a sealed cabinet for this driver as a standard driver in a two way system, looks like I need to go with 6-7cf.

                    ​I was reading on the eminence site about ebp (first I've heard of it - FS/QES) and in this case, this driver gets a value of around 55 which lends it closer to a sealed setup. Looks like a fairly small magnet on a large driver. Well I'll know in a couple weeks what happens with this two way

                    http://www.eminence.com/pdf/Beta_15A.pdf

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