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Helium - a true micromonitor

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  • Originally posted by scottsehlin View Post
    In this larger box, the 8 ohm ND-91 would work better. It can be tuned to 60 Hz using a 1" diameter by 6.5" long port, which gives an f3 of about 56 Hz. For the 8 ohm ND-91, the best option is to use the crossover for the Helium Soundbar, which you can get from the Sehlin Sound Solutions link at the bottom of this post.
    Scott, What the optimum volume/tuning for the nd-91 8ohm? 12mm thick material its enough right? i am assembling 2 heliums 8ohm using de XO for the helium soundbar. will build them within the next weeks and upload pictures. Sent from my ONEPLUS A3000 using Tapatalk

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    • Did a little reading of this thread and also did my own Sims of the ND91-4 and -8 using the box modeler in PCD. I was seeing little difference in the response graphs for the two drivers in my larger box, so I must be missing something. Since these would be driven by a mini Panasonic DVD receiver with only 15 watts/channel, I'm thinking going with the 4 ohm version would be a better match because of the low efficiency of the speaker. Like most digital amps, the Pioneer puts out more power into 4 ohms than 8. Even at that, I doubt it could drive the speaker hard enough to cause problems with over excursion. Does this all make sense?

      I also opened up the old speakers I planned to use. They were Standard Radio Corps that come with a matching receiver. Bought them in Japan back about 1970. I was impressed with the build quality. Box is nicely veneered with a brace, the 4 inch woofer has a cast frame and large magnet and the crossover is second order on the woofer, with a cap and two resistors (L-pad) on the tweeter. I was never thrilled with their sound. Probably because it's sealed (not much base) and a cone tweeter. Caps are all NPEs so probably bad or out of spec.

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      • Thought I'd share some pics of my paint job. I'll be applying another round of paint and a clear coat. Let me know if you want to know more! More details to follow in the next weeks.

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