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Helium - a true micromonitor

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  • Scott.... I just re-read your post #110. You mention that you'll need to redesign the entire tweeter section for the planar tweeter.

    Would like inputs on how to go about it though. I recently built a 2.1 boombox with a BT 4.2 TPA3116D2 2.1 subwoofer plate amp with variable crossover 30-200Hz and independent vol controls. For drivers I used a pair AMT-8 tweeters with the RS100-8 pair crossed 1st order at 9000Hz and for subwoofer duties I used the W6-1139SIF. The AMT-8's really open up the sound. Hence, the plan to use these tweeters in the Helium build.

    I'll also await a response on the woofer section regarding the 0.9mH inductor instead of the 1mH coil.

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    • Pics of progress:

      https://1drv.ms/u/s!AvuMkGVjog3NoII647pJ5-qNWCW-zA


      It's tight fit but I think it will all work out.

      Instead of a flatpack I did my own CNC flatpack. The port is going to be rear mounted and the woofer drivers installed from behind.

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      • I might actually redo the enclosure, I kinda sanded the edges too much and it has a slight curvature.....

        Out of curiosity and fun, what if I swapped the tweeter with Dayton Audio ND20FA-6 it has similar specs to the tweeter in the original design. Would I have change anything?



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        • Originally posted by scottsehlin View Post
          Re: Helium - a true micromonitor

          Yes, 3/4" ID on the PVC. I have not heard any port noise and it wasn't for lack of trying :D The bass is rolling off pretty steeply below 60 Hz, which I think is helping.
          Where do you guys get the true 3/4" ID pvc? Everything around here is .8 something. Thanks!

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          • Anything like consensus on polyfill or padding in these cabinets? Suggestions?

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            • These are a pretty tight fit once the crossover and port are in. I didnt put any fill in mine. I think you would be hard pressed to try and line the inside with padding.

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              • That's pretty much how I wound up. Once all the crossover parts and the ports were in the enclosure, adding anything else didn't seem like a good option.
                Keep an open mind, but don't let your brain fall out.

                Sehlin Sound Solutions

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                • Originally posted by Matt Clara View Post

                  Where do you guys get the true 3/4" ID pvc? Everything around here is .8 something. Thanks!
                  I'm looking at the formufit furniture pvc. True .75 internal dimensions. Or should I just use the regular stuff?

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                  • I just used 3/4" schedule 40 pvc, which has an average ID of 0.824". If you find something with true 0.75" ID, you can shorten your port a little.
                    Keep an open mind, but don't let your brain fall out.

                    Sehlin Sound Solutions

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                    • Like, a quarter inch shorter?

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                      • To give more room for the crossover, could one of the new ND series passive radiators be used? Which model do you recommend, and how many (1 or 2) per cabinet?

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                        • Originally posted by Matt Clara View Post
                          Like, a quarter inch shorter?
                          A true 0.75" inner diameter port would be 5.75" long to give the same tuning as 7" of 3/4" schedule 40 pvc.
                          Keep an open mind, but don't let your brain fall out.

                          Sehlin Sound Solutions

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                          • Originally posted by tktran View Post
                            To give more room for the crossover, could one of the new ND series passive radiators be used? Which model do you recommend, and how many (1 or 2) per cabinet?
                            I would go with MattP's approach in his recently published "Passive Aggressives". It uses the ND91-4 and the same cabinet with dual ND90PR's. Matt indicates he added all of the included tuning weights to get to his low 60's tuning.
                            Keep an open mind, but don't let your brain fall out.

                            Sehlin Sound Solutions

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                            • Made some progress...
                              https://i.imgur.com/2jQsYRn.jpg

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