Helium - a true micromonitor

[corradizo]

Just want to report back in that the Heliums continue to make me smile.

[teookie]

Here's mine!

https://goo.gl/photos/5eQczRmwt1mycQRt6

[scottsehlin]

Here's mine!

https://goo.gl/photos/5eQczRmwt1mycQRt6

Welcome to Tech Talk! The hardwood baffles look good.

[KEtheredge87]

Hi Everyone,

I see Gary built the Helium 2's with Scott's help, but I was wondering if anyone ever followed through and made an MTM version of the heliums for a center channel? I'd be willing to build one, but I have no idea how to work any necessary XO magic to make it match with the current TM design. If no one has built one, I could probably get used to a vertical center channel speaker in the home theater... it just goes against the normal "Home Theater" idea of what a center channel looks like.

Thanks in advance!

[garychelette]

Hi Everyone,

I see Gary built the Helium 2's with Scott's help, but I was wondering if anyone ever followed through and made an MTM version of the heliums for a center channel? I'd be willing to build one, but I have no idea how to work any necessary XO magic to make it match with the current TM design. If no one has built one, I could probably get used to a vertical center channel speaker in the home theater... it just goes against the normal "Home Theater" idea of what a center channel looks like.

Thanks in advance!

I built 3 OS's for my sister n law and that's what I did. 3 on top in a row. Not that bad! Look good and sounds great! Theses are so small, I don't think it would bad at all!

[KEtheredge87]

Alright... anyone who's built Helium's before (Either Scott's 4 Ohm originals, or Gary's 8 Ohm version)... Did you end up using any stuffing in the cabinet?

I know the general rule is to line a vented cabinet and to stuff a sealed one, but since these cabinets are so small, there's hardly any room to line the walls. I'm experimenting right now with a light handful of stuffing inside the cabinet (trying to avoid the port opening). Honest results at the moment are I *think* I can hear a slight difference with the stuffing (bass sounds a tad deeper and it feels like the port velocity is lower). However, stuffed or not, they both sound GREAT!

Just interested to hear what others have decided on their builds. Thanks!

[garychelette]

Alright... anyone who's built Helium's before (Either Scott's 4 Ohm originals, or Gary's 8 Ohm version)... Did you end up using any stuffing in the cabinet?

I know the general rule is to line a vented cabinet and to stuff a sealed one, but since these cabinets are so small, there's hardly any room to line the walls. I'm experimenting right now with a light handful of stuffing inside the cabinet (trying to avoid the port opening). Honest results at the moment are I *think* I can hear a slight difference with the stuffing (bass sounds a tad deeper and it feels like the port velocity is lower). However, stuffed or not, they both sound GREAT!

Just interested to hear what others have decided on their builds. Thanks!

I did the same. I added a small amount of stuffing just to slow down the port noise. It turned out great. That little port does put out a good amount.
These guys would be great as surrounds in a mini surrounds in a mini 5.1! An 8" sub would be perfect match on these. As long as the power is kept low, a 5.1 set would do very well.

[jwjarch]

Hello Helium Builders! I'm happy to be building a pair of these right now as well. The original 4 ohm version. In the interest of WAF, I'm hoping to revive a couple of earlier posts regarding the tweeter being mounted on center with the ND91 and the port being moved to the back of the cabinet. I have a few questions.

1. What, if any ,changes would need to be made to the XO to accommodate the tweeter and port moves? I know Scott talked about potentially modeling this in another post. Any thoughts Scott?
2. I figured I can get a 6.5" port to work in the configuration shown. Does anyone see any issues with the port being glued to the sides of the cabinet or the amount of space/angled port opening near the woofer?

My layout is attached. Hope my CAD work is clear enough.

Thanks for entertaining my noobness.

[KEtheredge87]

Does anyone see any issues with the port being glued to the sides of the cabinet or the amount of space/angled port opening near the woofer?

First off... Hi and welcome to the forum! I'm sure you'll get a few good responses, as there are a lot of smart folks online who like to help.

I don't think I'm the most experienced guy around, but I think putting the port directly against the wall runs a risk of introducing port noise. When I made my 8 ohm versions at Christmas time I was using a front firing port version, but I rotated the port inside the cabinet to try and get more equal air space around my port opening. The angled port opening is a neat idea too. I've never seen that before, so I can't comment, but I hope others can educate us both.

Best of luck on your build!

[Chris Roemer]

I'd put the inside port end up behind the tweeter for various reasons inc. less midrange backwave "leakage" and less turbulence (of the woofer blowing across the back of a tuned pipe). Running the port along the cab side doesn't bother me too much in THIS instance.

The XO MIGHT have been tuned to account for diffraction anomalies, which are altered (typically worsened) by centering the tweeter.
Most often offsetting a tweeter (or a mid) even 1/2" off the baffle centerline can help smooth things out a bit.
Google "Tolvan's EDGE" software to play w/the effect.

[jwjarch]

Thanks KE and Chris! I've been lurking on the forum for a few weeks now and I want to build EVERYTHING! I guess the Heliums are my "gateway drug".

Turning the port up to the tweeter makes a lot of sense. I also thought about introducing a second 90 and turning the port back toward the middle of the box. I'm really making things easy on myself, huh?

And maybe I can convince my better half that the offset tweeter isn't the end of the world. I'd like to keep from having to change the XO, especially since I already bought all of the components. I have the boxes glued up and will work on some walnut baffles this weekend hopefully. Can't wait to get these things pushing some air!

[scottsehlin]

I would expect moving the tweeter to the center axis to have some diffraction related effects. The effects should be relatively minor as they change pretty quickly as you change your listening angle relative to the baffle surface. So, although the results with a centered tweeter might not be optimal, I don't think it will be a deal breaker.

With respect to the port running along the side of the cabinet, the primary effect will be that it will lower the port tuning some amount due to restriction of air movement at the port entrance. The angled port entrance will help somewhat. I would try to make the longest part of the angled cut about equal to the recommended port length as a rough compensation for the close-to-the-wall positioning.

I would like to see someone try the centered tweeter, so if you decide to try it and it doesn't work out, I will provide further support.

[jwjarch]

Thanks for the input Scott. I'm happy to be the guinea pig for the center tweeter. This project has been a lot of fun so far. I'll probably mock up the tweeter using the MDF baffle in case I need to make any adjustments. I wouldn't want to invest too much time in the walnut baffle and have to re-do it.

So here's where am at then (see attached CAD). I redesigned based on the feedback from you guys. I have the port exit at the bottom rear of the cabinet now. Hopefully this helps with port leakage, not that it seemed to be an issue before. I increased the angle of the cut on the interior port end to 45 degrees to allow a clearer path for air movement. This design gives me a port length of 6-3/8" measured on the port centerline, and 6-3/4" on the edge of the longest leg. Scott, does that equate to the dimensions you were referencing in your last post? I see what you're saying about the sidewall lowering the tuning a bit. It's effectively acting a little more similar to a slot port design, right?

Also made some headway on assembling/testing my components last night. I sketched up the XO schematic so I could understand it a bit better before soldering. I soldered one XO together and hooked it up to my TK2050 amp (simultaneous project that will be used to drive the Heliums) Please excise the quick and dirty soldering. I'm planning to clean things up a bit once I get closer to assembly in the box. I also went with Solen caps, PE's new perfect layer air core inductors, and larger than necessary resistors. Overkill I know. What can I say, I got excited while I was sourcing components for my first real speaker build. Anyway, let me know if you see any big issues with my XO's (other than fitting in the box. I have a plan, I promise! ) I'm pretty happy with my first attempt at building one.

So first impressions... I had to put my ear right up to the ND16, then the ND91 to make sure they were both working! What a great XO design, Scott! They sound so integrated, clear, and clean right now. But I really can't wait to get them in the box to fill out the "low" frequency sound.

[Chris Roemer]

For your "beveled" end on the internal end of the port only, port - the effective length (not accounting for any effects of being next to the internal walls) is the ave. of the long side and the short side of the bevel cut (so . . . same as the "average" port length).

[scottsehlin]

Your port dimensions sound right as a best guess for a equivalent tuning. The way I think about the close wall effect is similar to how Chris describes the beveled end. The effective port length gets longer because one of the sides of it extends along the close wall.