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Helium - a true micromonitor

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  • scottsehlin
    replied
    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.

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  • scottsehlin
    replied
    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.

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  • tktran
    replied
    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?

    Leave a comment:


  • Matt Clara
    replied
    Like, a quarter inch shorter?

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  • scottsehlin
    replied
    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.

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  • Matt Clara
    replied
    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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  • scottsehlin
    replied
    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.

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  • Unclemo
    replied
    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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  • Matt Clara
    replied
    Anything like consensus on polyfill or padding in these cabinets? Suggestions?

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  • Matt Clara
    replied
    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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  • mmu7
    replied
    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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  • mmu7
    replied
    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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  • bsl100
    replied
    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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  • bsl100
    replied
    Thanks Chris, Scott.... Am getting the picture that as long as each driver in a 2-way is rated at a nominal / minimum 4 ohm and the amp can handle 4 ohm loads, then it should be fine even if the drivers are connected in parallel.

    Scott... I'm going to try your design using the ND91-4 along with an AMT-8 tweeter. The 8 ohm tweeters are about 89db 1W/M and have a frequency response from 3500-40000Hz. They will be powered by a TPA3116D2 amp.

    Since I had a couple of 0.9mH inductors with me, was wondering if I could use these for the woofer section. Will it affect the other components for the woofer and change the sound signature? Also, would I need to redesign the entire tweeter crossover for the AMT-8?

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  • scottsehlin
    replied
    My sim gets an f3 of around 70 Hz using the parameters posted on the PE website. Chris is correct about the impedance. The second post on page 1 includes a plot of impedance as a function of frequency.

    For Dunk_c: The DTA-120 should be okay. I had it's predecessor, and it could do about 30 wpc into 8 ohms and closer to 50 into 4 - but there were thermal issues running into a 4 ohm load. Mine eventually died (a friend had it powering a pair of Lithiums). If I recall correctly, the DTA-120 was supposed to address that issue. I used the SMSL Q5 Pro for the Helium soundbar and it has several nice features that the DTA120 doesn't, like remote control, USB DAC, and subwoofer out, but it costs a little more.

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