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First time subwoofer design questions

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  • #46
    Originally posted by unclejunebug View Post
    17mm! Don't blow anything on my account haha. I'm using the SA70 but I haven't come across anything in the documentation that states there's any low frequency protection.
    No worries, that was all a while ago shortly after I bought the first one.

    Don't lean on my rough estimate too much though...probably safer to assume somewhere between 12-16mm Xmech and either leave the amp about 3db down from full if you'll be blasting movie sound-effects or think about adding a small 0.5uF-0.75uF capacitor/s to the line level inputs (they're listed as 10.4Kohm in the manual, so I think a cap value around 0.5-0.75uF should give a nice bit of protection for bass under 30hz-20hz). Because a Y splitter/combiner RCA (or stereo sub line-level output from your reciever) is recommended for the SA70, I'm not sure if you'd use a pair of 0.5-0.75uF caps or if you'd need to use half value if capping both inputs....or you could just cap the single output from the reciever if you're only using a single mono output I suppose.

    Probably not really a problem worth worrying about in the first place, but it's an option if you're really nervous about damage and plan to crank it with really deep movie-sound-effect lows.
    I think bass from music this low and this loud is so rare that it's not even a concern at 70watts or less.
    My first 2way build


    • #47
      I realized that I had applied a high and low pass filter to my WinISD project. After turning them both off the excursion graph looks far worse under 27Hz or so. Though I'm not really sure there's any way around this without a high pass filter of some kind which the SA70 doesn't have. Is this just a typical result for a subwoofer design?

      Click image for larger version

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      • #48
        Yeah, that's typical. In real life the amount of content down there is minimal at best and there's nothing to worry about.
        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, SuperNova Minimus


        • #49
          Originally posted by wogg View Post
          Yeah, that's typical. In real life the amount of content down there is minimal at best and there's nothing to worry about.
          Excellent, thanks for the confirmation!

          Without any design experience of my own I have no reference point for how the graphs/models translate to real world performance so I appreciate everyone's help and patience. As you may have noticed I have a tendency to over analyze things

          I think its high time I stop attempting to change up the design and just get started though. I'm making some saw-dust tomorrow!