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First time subwoofer design questions

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  • #31
    Question about vented versus sealed. The 10” SD270A-88 has an optimal sealed volume of 1.19 cubic ft. How would this perform compared to the ported enclosure above with the 8” SD215A-88?

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    • #32
      Instead of reaching into the mid 30s, it would roll off just under 50Hz. Also the feet should be 1" taller (due to more area).

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      • #33
        I was thinking it would be nice to move up to larger subwoofer but it sounds like the trade-off is that the sealed 10" won't be as loud under 50Hz as the ported 8" would be. I do like the idea of a larger sub but the SD270A needs a rather large ported box to reach lower frequencies, which isn't going to work here.

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        • #34
          I think it's natural for a louder/more-efficient subwoofer to need a larger box if you want it to reach equally low/deep. You could possibly get a larger sub to reach similarly deep within a similarly small box-size, BUT the physics to allow it to reach that low inside such a small box would also mean it's almost surely a VERY inefficient driver which will be about as loud or less than the smaller driver was...not louder.
          So you might gain some extra headroom which could be useful if you're using a very powerful, high-wattage amplifier....otherwise you won't gain much. At least I'm pretty sure that's how it works.
          My first 2way build

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          • #35
            I can see the larger sub needing a larger box, but that SD270A requires a ported box that's almost 4x that of the SD215A. I'm planning to use the SA70 which I wouldn't consider a high-wattage amp.
            Last edited by unclejunebug; 11-24-2020, 02:24 PM. Reason: Fixed typo

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            • #36
              Originally posted by unclejunebug View Post
              I can see the larger sub needing a larger box, but that SD270A requires a ported box that's almost 4x that of the SD215A. I'm planning to use the SA70 which I wouldn't consider a high-wattage amp.
              In the VituixCAD SIM I'm looking at, the SD270 seems to need roughly 2X the internal box space to reach as deep as the SD215. The SD270 should be about 2db more efficient, which I'd call subtly noticeable but not a nightVSday difference in volume.

              I feel like the SD215 strikes a pretty good balance between efficiency watt-per-watt and box-size requirements for its price. I don't think you'll find anything significantly louder with a 70watt amp that'll reach as deep in a box that small.
              My first 2way build

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              • #37
                Seems like the SD215A will be sufficient unless I'm willing to move up to a higher wattage amp (which I'm not). I will stick with what I have a try not to change it! :D

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                • #38
                  so many good options here.

                  I did something similar with very cheap components -- all in $112

                  now being used every day in my buddy's living room system

                  http://techtalk.parts-express.com/fo...ubwoofer-build

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                  • ceiol
                    ceiol commented
                    Editing a comment
                    and the $112 includes the enclosure, driver, and even the amplifier!!!

                  • LOUT
                    LOUT commented
                    Editing a comment
                    I love the color you made them, it manages black/grey in a warm/"alive" way without looking like grey-fading barnwood. With the nice woodgrain stripes it's like a grey tabby cat..in speaker form.
                    Okay, that sounds weirder reading it back than it did in my head.

                • #39
                  Originally posted by ceiol View Post
                  so many good options here.

                  I did something similar with very cheap components -- all in $112

                  now being used every day in my buddy's living room system

                  http://techtalk.parts-express.com/fo...ubwoofer-build
                  I came across your thread while searching around for small enclosure designs, looks really nice!

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                  • #40
                    I originally did some modeling for this project with the DCS205 but now that I have the SD215A-88 I decided to throw the specs into WinISD and take a look at the performance. The main thing that jumped out to me was the cone excursion graph. The white line in the graph below is the DCS205, the purple is the SD215A, and the red is the SD215's Xmax spec (6mm). With the system input power set to 70watts the excursion of the SD215 is greater than the sub's Xmax spec from about 40-60Hz. Xmax for the DCS205 is 8.8mm so it's under the spec for all of the sub's usable range.

                    If I reduce the input power the excursion obviously is reduced and at 50watts it's right on the Xmax line. Are these graphs showing excursion at full volume? I can't imagine that this sub would be cranked up all the way all the time (or ever for that matter).

                    Click image for larger version  Name:	cone_excursion_comparison.png Views:	0 Size:	211.3 KB ID:	1458184

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                    • #41
                      The excursion is for 70w (if that's what you plug into the "Signal" tab).
                      My SD215 specs might not be the MOST current, but I see it just bumping the Xmax line at 60wRMS.
                      I've used that driver in a vented box using just PE's SA25 amp, and it keeps up OK w/a pair of 6" 2-ways (on the treadmill).
                      The SA70 is a better choice. Don't use all the gain and you should be okay.

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                      • #42
                        Yup, you'll be able to go over Xmax a bit when cranked, but you'll be short of Xmech. That means distortion will increase a bit when cranked, but the woofer will be just fine.
                        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

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                        • #43
                          Thanks for the responses, so distortion will go up a little at high volume but no damage to the woofer will result.

                          Is Xmech a calculated value? I don't see it listed on the spec sheet for the SD215A.

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                          • #44
                            Originally posted by unclejunebug View Post
                            Thanks for the responses, so distortion will go up a little at high volume but no damage to the woofer will result.

                            Is Xmech a calculated value? I don't see it listed on the spec sheet for the SD215A.
                            Xmech seems to rarely be listed by many brands.
                            I've often heard Xmech tends to be roughly 2X the XMAX value, but I'm guessing that's not a hard+fast rule or anything.

                            I tried to do a little testing with an SD215a-88 using low frequency sine waves, a mixer for more visible level setting, and a modest ProAudio amplifier with low-frequency protection disabled. I think I got roughly around 17mm of excursion without any super terrible noises or obvious breaking, but I was too nervous to keep pushing my luck farther.
                            I should probably find a more accurate way of testing and then just go for it. They're cheap enough to replace if I screw up, but I've grown too attached, lol.

                            If the amp has low-frequency protection for frequencies below 25hz I think you'll be totally safe. If there's no protection, then I think super loud bass below 20-25hz might be able to hurt the sub at over 40-50watts.
                            My first 2way build

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                            • #45
                              Originally posted by LOUT View Post
                              I tried to do a little testing with an SD215a-88 using low frequency sine waves, a mixer for more visible level setting, and a modest ProAudio amplifier with low-frequency protection disabled. I think I got roughly around 17mm of excursion without any super terrible noises or obvious breaking, but I was too nervous to keep pushing my luck farther.
                              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.

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