Helium - a true micromonitor

[Jake]

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

I actually Pm,d  Scott this very question recently. He said he hasn't done it, and referred me to page 7 of this thread as a starting point.

[mga2009]

Hi,

These are 4ohm, correct?

I am looking a set of satellites/surround to use my AVR, but I need 8ohm (6ohm at best) and found these while looking for JB's Quarks.

[Jeff F.]

Hi,

These are 4ohm, correct?

I am looking a set of satellites/surround to use my AVR, but I need 8ohm (6ohm at best) and found these while looking for JB's Quarks.

The original design is 4 ohms. If you want to build the 8 ohm version see post #236. It has a revised crossover.

[scottsehlin]

Since I modeled that crossover, I voiced the Helium soundbar, which uses the 8 ohm version of the ND-91. The crossover will work for the Helium cabinet.

[mga2009]

Jeff, Scott,

Thanks for your replies.

Scott, so I just need to use the crossover design for the "Helium Soundbar" in the Helium standard cabinet. Regarding the XO, I noticed the 3 Ohm 5w resistor is no longer in stock in PE. Can I just use a 1Ohm and 2Ohm in series? Also, is there any chance to change the dimensions on the cabinet, keeping the internal volume (and the components location in the baffle)??
I need them a little bit shallower and taller to get them behind my couch.

[scottsehlin]

The driver spacing for the soundbar is close to the same as the original Helium, so it should work fine. The 8 ohm version of the ND-91 has a slightly larger optimal cabinet than the 4 ohm, but as a result can play a little deeper. The soundbar has isolated chambers for the left and right channel that would be 4" wide by 4.75" deep by 9" tall as stand-alone speakers. You could flip that around and make them 4" deep by 4.75" wide by 9" tall. The port for the soundbar is 3/4" schedule 40 PVC, 4 inches long.

[mga2009]

The driver spacing for the soundbar is close to the same as the original Helium, so it should work fine. The 8 ohm version of the ND-91 has a slightly larger optimal cabinet than the 4 ohm, but as a result can play a little deeper. The soundbar has isolated chambers for the left and right channel that would be 4" wide by 4.75" deep by 9" tall as stand-alone speakers. You could flip that around and make them 4" deep by 4.75" wide by 9" tall. The port for the soundbar is 3/4" schedule 40 PVC, 4 inches long.

Scott,

Thanks for your reply. Very clear explanation.

Regarding the XO and the 3ohm resistor, I remember from school that if I install them in series they sum up the individual resistance, but I don't know if this will affect negatively on the SQ or any other spec of the speaker design.

Thanks!

[scottsehlin]

I've only put resistors in series during prototyping, but it won't hurt anything. A 3 ohm 10 watt resistor will also work, I chose the 5 watt because it was smaller.

[howey]

I'm intending to build these but to also incorporate a small sub and use the Sure electronics combination of JAB2 and JAB3 with DSP in 2.1 config to drive the whole thing. I can use the DSP to cross from sub to heliums. I'm just wondering if I need to do anything to adjust the passive crossover in the heliums to account for the DSP filtering the lowest frequencies away?

[mga2009]

Just got the drivers and now I am buying the parts for the 8ohm crossover @PE.-

Any final recommendation aimed to improve SQ is welcomed!

Picture is the ND91-8 compared to the Dayton DS135-8 for a Matt Grant's Nexus TM. ND16-FA tweeter not shown.

[scottsehlin]

You need 4 of the 2.7uF caps. Everything else looks right.

[mga2009]

thanks scott! will add another two. regarding the port tube, can i make it in a different ID and modify the lenght? i couldnt find 19mm ID sch40 tubes in my country. regards Sent from my ONEPLUS A3000 using Tapatalk

[Chris Roemer]

sure, but you probably can't go any smaller (chuffing), and bigger will make it longer (box fitment issues - also you'll lose a little interior volume).
Be sure to check the tuning w/ith WinISD (or equivalent).

[mga2009]

sure, but you probably can't go any smaller (chuffing), and bigger will make it longer (box fitment issues - also you'll lose a little interior volume). Be sure to check the tuning w/ith WinISD (or equivalent).

chris, thanks for your reply. i can get 20mm tubing, which is only 1mm bigger than the 3/4 so i will make it a little bit longer. i will recheck it with winISD. my cabinet will be a bit bigger (taller) so maybe i can make a longer port and get a few hz lower? can i do that and keep the same XO and components location in the baffle? regards Sent from my ONEPLUS A3000 using Tapatalk

[Chris Roemer]

I would NOT sweat 1mm, at ALL. Proceed!