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First time subwoofer design questions

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  • #16
    Originally posted by wogg View Post
    Only concern on back of driver clearance: The pole piece is vented, leave about an inch behind the magnet. Otherwise your plan is solid.

    No experience on the Lepai amp, though I would be concerned that it produce the power it says it does.
    Most excellent! From what I've been calculating for enclosure dimensions I would have at least 2" of clearance behind the magnet so sounds like I'm good there. I'm skeptical of the Lepai amp as well and from what I've read the power output is dependent upon the power brick being used. As much as I'd like to hide the amp in the side of the enclosure I don't think it's worth it as I'd trust the SA70 much more.

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    • #17
      That 205 is a nice driver. I used it in my "Boom Unit" subwoofer design. It's also a very linear driver.

      I haven't used the 215, but it looks more like a woofer than a subwoofer.
      Brian Steele
      www.diysubwoofers.org

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      • #18
        Originally posted by Brian Steele View Post
        That 205 is a nice driver. I used it in my "Boom Unit" subwoofer design. It's also a very linear driver.
        I haven't used the 215, but it looks more like a woofer than a subwoofer.
        I think the SD215 acts a lot like the DS/DA/DSA215 woofers with extended XMAX and some added weight (probably from the extended XMAX coil depth and the DVC added weight rather than cone weight)...so it has a pretty similar frequency response (particularly compared to the DS, according to PE's measurements) but a few db lower sensitivity and better bass-extension from the added weight and more headroom from the extra XMAX.
        I'm guessing this close cousin-ness between the SD and DS series probably lends the SD its oddly nice mid-handling ability compared to many of the more typical lower-efficiency/higher-headroom subs.

        My first 2way build

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        • #19
          Thanks for the help everyone! I ordered the following...

          SA70
          SD215A-88
          2" Flared Precision Port
          Sound dampening foam

          Looking forward to getting started.

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          • #20
            The sd215a is a solid choice. I think you'll like it.
            http://techtalk.parts-express.com/fo...khanspires-but
            http://techtalk.parts-express.com/fo...pico-neo-build
            http://techtalk.parts-express.com/fo...ensation-build

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            • #21
              Originally posted by wogg View Post
              Box is about 0.9cu ft, using a 10" long 2" precision port....
              Just for a bit of clarification you mentioned previously in this thread that a 10" long port was used but the write-up at the link you provided mentions a 9" long port. Can you tell me which is the correct length? I want to make sure I get the length correct. I'm currently mocking up a Fusion 360 design and looking at a low profile enclosure with internal dimensions of about 21"x12.5"x6".

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              • #22
                I used the Precision Port calculator on their site: http://www.psp-inc.com/tools2.html to get the frequency right. With the large radius flares on those things the length isn't super straight forward or easy to measure. With a box that size you should target about 31Hz for the tuning frequency.
                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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                • #23
                  Originally posted by wogg View Post
                  I used the Precision Port calculator on their site: http://www.psp-inc.com/tools2.html to get the frequency right. With the large radius flares on those things the length isn't super straight forward or easy to measure. With a box that size you should target about 31Hz for the tuning frequency.
                  Thanks! Using that calculator with a single 2" flared port, 0.91 cubic ft internal volume, and a tuning frequency of 31Hz looks I need a port length of 9.218307246343667" haha. I guess I'll get it as close possible :D

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                  • #24
                    I THINK a 2" PPort comes w/a 10" straight tube. Each (1" radius) "flare" adds another inch, making the O.A. length close to 12". It ACTs like an 11" long port (when modeled in a box sim). It's VERY typical to count about one/half a radiused end's length when calc'ing Fb.

                    Going by PE specs: Qts=0.39, Vas=1.35cf, Fs=31; I'd prob. tune a 0.9cf box to more like the mid 30s than low 30s, but Wogg has 1st hand experience.

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                    • #25
                      Is there anything "wrong" with placing the port on a side of the enclosure that is NOT the baffle? Are there any design considerations to make in that scenario?

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                      • #26
                        Originally posted by unclejunebug View Post
                        Is there anything "wrong" with placing the port on a side of the enclosure that is NOT the baffle? Are there any design considerations to make in that scenario?
                        I've heard it shouldn't make a difference for port tuning or bass response or anything like that.
                        I think it should work like many store-bought subwoofers that commonly have the speaker on the bottom/downfiring and a port on the front or back (so the port is on a wall that's facing 90degrees compared to the speaker)..except your box will be rotated and flipped so the speaker is facing forward and the port toward the side.
                        My first 2way build

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                        • #27
                          I initially started this project as a surprise gift for a buddy of mine. I decided that instead of building something that may or may not end up working with what he does with his current home renovations I decided to tell him my plans so we could come up with something that would work without issue. Because of that I've ditched the low profile enclosure and have gone back to a more standard design. I'm no Fusion 360 expert and I don't know how to export images with dimensions and what not, but here's what I've come up with so far...

                          Click image for larger version  Name:	down_firing_sub_enclosure.png Views:	0 Size:	236.1 KB ID:	1457032
                          Internal dimensions are 10.5"x10.5"x14.25" and external dimensions are 12"x12"x16.75" including the 1/2" feet on the bottom. The 2" Precision Port is oriented above the SA70 amp which is turned sideways to make room for the flared port (which is quite a bit bigger than I expected). Material is 3/4" MDF except for the very bottom piece which is 1/2" MDF so the baffle isn't quite a "double" baffle. Most edges are rabbeted and the sub will be flush mounted with the bottom.
                          Click image for larger version  Name:	down_firing_sub_enclosure_bottom.png Views:	0 Size:	316.7 KB ID:	1457034
                          Last edited by unclejunebug; 11-19-2020, 11:24 PM. Reason: Fixed a typo

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                          • #28
                            That looks good. You'll need bigger feet though, 1/2" isn't enough to let the driver flow freely underneath. You'll want the area around the driver's circumference to be about the same as the area of the driver. For an 8" woofer that would be 2" tall feet.
                            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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                            • #29
                              ... on the product page, it shows an opening cutout dia. of 7.1" (approx.).
                              Since area is pi*R*R, and circumference is pi*2R, you can just take the radius squared (about 12.6sq.in.) and divide by the dia., giving you about 1.8". That would be the minimum foot height - on a hard surface. Carpeting would require more.

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                              • #30
                                Excellent, thanks Wogg and Chris! I will change the height of the feet to be 2" then.

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