Helium - a true micromonitor

[bsl100]

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.

[mmu7]

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.

[mmu7]

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?

[Matt Clara]

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!

[Matt Clara]

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

[Unclemo]

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.

[scottsehlin]

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.

[Matt Clara]

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?

[scottsehlin]

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.

[Matt Clara]

Like, a quarter inch shorter?

[tktran]

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?

[scottsehlin]

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.

[scottsehlin]

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.

[Matt Clara]

Made some progress...

https://i.imgur.com/2jQsYRn.jpg

[davidroberts]

I have read through the tread and found several mentions of a MTM version. Does anyone know if these ever came to fruition?