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  • Vas vs Box Volume

    If you have the Vas for a sub, how do you determine the box volume? I'm looking at buying a 299-106 10" sub and the Vas is 3.15 cu ft

  • #2
    Re: Vas vs Box Volume

    One of the box modeling programs is your friend.

    I generally pick a box size that I'd like to have, then model the driver and box size to see what the response looks like. The modeling programs will typically offer a standard size and tuning that you can consider as well.
    I was so much older then, I'm younger than that now.
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    • #3
      Re: Vas vs Box Volume

      Download one of these programs, input your driver's parameters (pay attention to metric/imperial conversions) and it will tell you optimum box size and configuration. You can also play with the Vb and see the alternative results.

      http://audio.claub.net/software/jbabgy/WBCD.html
      http://www.linearteam.dk/default.aspx?pageid=winisdpro

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      • #4
        Re: Vas vs Box Volume

        Thanks for the quick responses..... I tried downloading those programs.... the fisr one didn't seem to respond to the specs I entered.... there was a certain driver already in the graph and when I entered my driver's specs, the box volume info didn't change?? The second program was more confusing for me and I got constant error message as I entered my driver's specs.... If there is a simple (generel rule of thumb so to speak) formula for Vas to Vb formula, that would probably work.... it's just for a sub to go in my garage.... I was looking at this particular sub because PE has it on asle for $14.... thanks...

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        • #5
          Re: Vas vs Box Volume

          The basic calculations are straightforward for a sealed box, but for a ported box, it gets more complicated. In either case, there are several freeware programs (as others have noted) that do the calculations for you, and provide a graphic simulation as well.

          That being said, if you want to run through some basic calculations yourself, what you need to know for a Sealed Box is
          Vas, Fs, and Qts.

          Select the box volume, Vb (use same units for Vb that you use for Vas)

          alpha = Vas/Vb

          then,
          Qtc = Qts * sqrt[(alpha^2) + 1]
          and
          Fc = Fs * sqrt[(alpha^2) + 1]

          A target for Qtc is often between 0.65 and .90. Most often, the "optimally flat" value for Qtc is 0.71.

          If you're interested in other calcualtions, such as ported boxes, check out Brian Steele's site:
          diysubwoofers.org

          Again, there is freeware out there that can do all of this (and more!) for you. If you're like me, I try to understand basic calculations as well.
          - Dave R
          the 200% Norske

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          • #6
            Re: Vas vs Box Volume

            Originally posted by hotrod View Post
            If you have the Vas for a sub, how do you determine the box volume? I'm looking at buying a 299-106 10" sub and the Vas is 3.15 cu ft
            Box volume is determined by 2 specs, Vas AND Qts.

            What is your driver's Qts?

            How deep a woofer will reach is determined by 2 specs, Fs AND Qts (you see, Qts ends up being one of THE most important parameters as it determines box size AND low end extension).

            Tell me your Qts and I'll tell you my "secret formula". BTW, are you looking to go vented or sealed? Is this for in home, or auto?

            Chris

            ps - I looked up that driver, and I'd probably go with a 3 cf sealed box, stuffed with polyfill or fiberglass. It should be able to reach into the mid to low 30s, which is pretty dang good.

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            • #7
              Re: Vas vs Box Volume

              I was leaning towards a sealed box and it is for home use... the specs for the driver are:

              150 watts RMS/300 watts max *VCdia: 1-1/2" *Le: 1.24 mH *Impedance: 4 ohms *Re: 2.65 ohms *Frequency response: 27-1,000 Hz *Fs: 27 Hz *SPL: 86.5 dB 1W/1m *Vas: 3.15 cu. ft. *Qms: 9.83 *Qes: 0.65 *Qts: 0.61 *Xmax: 6.0 mm *Dimensions: Overall diameter 10", Cutout diameter 9", Depth 4-1/2". Note: All specifications are with voice coils connected in parallel.

              Thanks....
              Last edited by hotrod; 11-17-2010, 08:39 PM. Reason: add info

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              • #8
                Re: Vas vs Box Volume

                Based on the specs that you give, this would probably be better sealed than ported.

                Using the specs, here are a few options for Sealed Boxes:

                Vb = 2.65 ft^3 (75 liter)
                Qtc = 0.90
                Fc = 40 Hz
                F3 = 29 Hz
                F10 = 18 Hz

                Vb = 3.40 ft^3 (96 liter)
                Qtc = 0.85
                Fc = 37.5 Hz
                F3 = 28.3 Hz
                F10 = 17.2 Hz

                Vb = 4.41 ft^3 (125 liter)
                Qtc = 0.80
                Fc = 35.3 Hz
                F3 = 27.8 Hz
                F10 = 16.4 Hz

                Vb = 6.00 ft^3 (170 liter)
                Qtc = 0.75
                Fc = 33.3 Hz
                F3 = 27.4 Hz
                F10 = 15.8 Hz

                The F3 and F10 are the -3 dB and -10 dB points below the sensitivity, respectively.
                - Dave R
                the 200% Norske

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                • #9
                  Re: Vas vs Box Volume

                  Originally posted by daver View Post
                  Based on the specs that you give, this would probably be better sealed than ported.

                  Using the specs, here are a few options for Sealed Boxes:

                  Vb = 2.65 ft^3 (75 liter)
                  Qtc = 0.90
                  Fc = 40 Hz
                  F3 = 29 Hz
                  F10 = 18 Hz

                  Vb = 3.40 ft^3 (96 liter)
                  Qtc = 0.85
                  Fc = 37.5 Hz
                  F3 = 28.3 Hz
                  F10 = 17.2 Hz

                  Vb = 4.41 ft^3 (125 liter)
                  Qtc = 0.80
                  Fc = 35.3 Hz
                  F3 = 27.8 Hz
                  F10 = 16.4 Hz

                  Vb = 6.00 ft^3 (170 liter)
                  Qtc = 0.75
                  Fc = 33.3 Hz
                  F3 = 27.4 Hz
                  F10 = 15.8 Hz

                  The F3 and F10 are the -3 dB and -10 dB points below the sensitivity, respectively.

                  WinISD Pro (alpha) shows that it will reach 33 Hz in a 3 cf stuffed/sealed box, but at 33 Hz, it can bottom out with 15 watts at 109 dB.

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                  • #10
                    Re: Vas vs Box Volume

                    Originally posted by Chris Roemer View Post
                    WinISD Pro (alpha) shows that it will reach 33 Hz in a 3 cf stuffed/sealed box, but at 33 Hz, it can bottom out with 15 watts at 109 dB.
                    Mechanical power handling is just as important as anything else. It's a balancing act.

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                    • #11
                      Re: Vas vs Box Volume

                      When I model this sub in a 3cf box I see it hitting xmax at 20 watts. Does this match what you've seen? (I used winISD alpha)

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                      • #12
                        Re: Vas vs Box Volume

                        I was planning on using amp part # 300-784 from PE.... it is rated 70W @ 4 ohms..... I was going to wire the sub's 2 8-ohm coils parallel for 4 ohms....

                        Thanks for the help....
                        Last edited by hotrod; 11-18-2010, 07:30 PM.

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                        • #13
                          Re: Vas vs Box Volume

                          Seems like this 10" needs a rather large box? I'm much more familiar with car audio subs where average 10" sub can work well with a .65-1.25 cu ft sealed box....

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                          • #14
                            Re: Vas vs Box Volume

                            Originally posted by hotrod View Post
                            Seems like this 10" needs a rather large box? I'm much more familiar with car audio subs where average 10" sub can work well with a .65-1.25 cu ft sealed box....

                            In a (small, closed) car, the bottom end gets boosted by +12dB due to "cabin gain". You won't have that "in home". You CAN put this sub in a 1 cf box, but it won't reach flat down low if you due that.

                            Not only THAT, but Vas, Fs, and Qts ultimately determine box size and extension.

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                            • #15
                              Re: Vas vs Box Volume

                              For that small of a box,

                              Vb = 1.25 ft^3 (35.4 liter)
                              Qtc = 1.14
                              Fc = 50.7 Hz
                              F3 = 33.3 Hz
                              F10 = 21.9 Hz

                              Also, this higher Qtc creates a boomy peak of over +2 dB above sensitivity between about 50 and 80 Hz. (+2.5 dB centered at 60 Hz).

                              Might be alright, if that's what you're looking for. Usually most prefer to have smoother bass response for home audio. Always tradeoffs between size, deep bass, and loudness.
                              - Dave R
                              the 200% Norske

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