Helium - a true micromonitor

[dkalsi]

There are a couple of key things that using the Dayton data doesn't take into account.

1. Effects of the baffle. My understanding is that the Dayton FRD files use an infinite baffle measurement. In that case, the driver is mounted on a large (typically 4' by 8') baffle to eliminate baffle effects. The actual baffle causes a reduction in output at low frequencies and some further variation due to diffraction effects at higher frequencies. My driver measurements were taken in the actual enclosure.

2. Time of flight. The sound coming from the woofer is coming from farther behind the baffle than the tweeter. This effects the way the responses of the drivers sum together (frequency response includes a magnitude and a phase). When I measure, I use a fixed microphone position, then measure both drivers from that position so I capture time of flight differences in the phase information.

I know there have been a few articles published about how to use manufacturer's data to do a reasonably accurate sim. Paul Carmody did a good writeup at some point that is still on his website the last time I checked. 15 years ago, when I was getting started with designing crossovers, there weren't very many DIY'ers with accurate measurement capabilities, so we used to do a lot of simulations from manufacturer's data. Now, it is quite a bit easier to pull together an affordable and easy to use measurement setup.

Scott,

Thanks for posting these comments. I'm in the midst of building your Lithium speakers. I'll build the crossover and, as you did when you were designing, take measurements before gluing everything up since one only gets one chance at the crossover before its permanently locked up inside the cabinet.

I recently built Jeff Bagby's Quarks. Unfortunately, my measurements didn't quite match up with Jeff's :-(.

With the Lithium, I plan on following the procedures you indicated above.

Thanks,
D

[Scarface1]

Hi Scott, I also want to build the heliums the question, what is the impedance, can I hook it up to a 8 ohm amp.

[scottsehlin]

There is an impedance plot on page 1. The minimum impedance is around 5 ohms, so most manufacturers would consider it a 6 or even 8 ohm speaker. I wouldn't anticipate any issues with an 8 ohm amp.

[Jeff F.]

Hi Scott, I also want to build the heliums the question, what is the impedance, can I hook it up to a 8 ohm amp.

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

[Scarface1]

Scott and Jeff thanks, I will look at post #236😀

[mrmky]

Shocked at how small they are and how big they sound. First of 5 in a bedroom theater. First attempt at veneer as well

[Deadlytoaster]

You guys think there's enough room in the enclosure for a TPA3116 amp board and 3-4 18650 batteries for it to not impact the sound from the host enclosure?

[garychelette]

You guys think there's enough room in the enclosure for a TPA3116 amp board and 3-4 18650 batteries for it to not impact the sound from the host enclosure?

I don't think so. When I built the 8 ohm version, I barely had enough room to put the Xover! The box is very small!
G

[mga2009]

Hi,

these are my Helium 8ohm for surround duty... still a WIP. Within the next days will veneer them and install the drivers.

As you see they are taller and shallower... and bigger total volume.

[Jake]

Hi,

these are my Helium 8ohm for surround duty... still a WIP. Within the next days will veneer them and install the drivers.

As you see they are taller and shallower... and bigger total volume.

Have you tested the nd91-8 in that larger volume? You may not be happy.

[Chris Roemer]

How big ARE those (internal). Tuning? These are ND91-8s?

[mga2009]

How big ARE those (internal). Tuning? These are ND91-8s?

Yes, I have ND91-8. The design is based on the Helium Soundbar (same crossover and same internal volume).

In post #351 Scott Sehlin said the 8 ohm version required an slightly larger optimal cabinet, and as a result can play deeper.

Also said 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, and that I could flip that around and make them 4" deep by 4.75" wide by 9" tall. Material is 12mm MDF, no bracing. net internal volume is around 1.5 liters I think.

Regarding the tuning it's the same as the soundbar: "3/4" schedule 40 PVC, 4 inches long" with the slight difference the tube I have is 20mm (vs 19,50mm)

Have you tested the nd91-8 in that larger volume? You may not be happy.

Why is that? Any suggestions?

[scottsehlin]

I've used the sound bar as a portable music system at a couple of small gatherings, and it has held up well. The internal volume isn't that much larger than the original Helium, but enough to get another 5-10 Hz on the low end.

[Dunk_c]

Hi
Just did some crude tesing, thought people might find it interesting. I am no audio engineer.

I built a set of Heliums a while ago and they sounded good to me.
I recently bought a pair of BIC DV32 and these have less base and sound harsh and bright to me, probably because they have low output below 100hz
Play the Heliums with the BICs and I feel that the sound is better. I can now hear more of the high frequencies and still get the bass. For my ears the Heliums are lacking some trebble.
I have some hearing damage and cannot hear much above 8khz.

I used an EMM-6 calibrated mic to do some crude frequency response measurements with REW (please don’t give me grief about axis scaling) the speakers were outside on a stand and the mic was about 2ft in front, pointed at the drivers.

First thing I noticed for the Heliums, good output at low frequencies, even response across the range, but with a dip around 5khz. Did I build the crossovers correctly?

I don’t know if the 5khz dip is contributing to my listening experience, but the BIC DV32 are flat in this region. Perhaps that is why I am more satisfied with the listening experience when I play them together.

Any thoughts?

[garychelette]

Amazing! First post of these little guys was, Helium - a true micromonitor

10-29-2014, 09:26 PM

We are still talking about them! I have built both 4 and 8 ohm versions and have been very happy with them!
I am currently building a set for a neighbor. He couldn't believe the sound and had to have a pair!
Maybe PE will make a kit to sell one day!!!

Gary