Helium - a true micromonitor

[Herman Trivilino]

Re: Helium - a true micromonitor

The port is 3/4" pvc. There are two straight sections and an elbow (which barely fits in the box). I'll check the length of the straight sections tonight, but the tuning frequency should be between 65 and 70 Hz. Total length is about 6.5"-7".

The project can be built as posted, but lately, I've been listening with an added 40 ohm resistor across the terminals of the tweeter, which knocks down the highs by about a dB and like that a little better. Dayton has a 39 ohm 5 watt Xicon resistor that would be a good choice for that addition.

I'm planning to reconfigure the living room, which will involve getting rid of the monkey coffins and mounting something very small on the walls. Yes, pure WAF. These seem like they'll do it for me!

It looks like most everything is documented well in the first post, which I appreciate very much because using other people's designs is the limit of my skills. :D

The port is 3/4-inch PVC, 6.5" to 7" long with an elbow.

Adding a 40-ohm resistor across the tweeter might be a good idea.

Did you add any sound dampening material?

[scottsehlin]

Re: Helium - a true micromonitor

I'm planning to reconfigure the living room, which will involve getting rid of the monkey coffins and mounting something very small on the walls. Yes, pure WAF. These seem like they'll do it for me!

It looks like most everything is documented well in the first post, which I appreciate very much because using other people's designs is the limit of my skills. :D

The port is 3/4-inch PVC, 6.5" to 7" long with an elbow.

Adding a 40-ohm resistor across the tweeter might be a good idea.

Did you add any sound dampening material?

When I did the demo in Grinnell, there wasn't anything as I was concerned about blocking the port and there wasn't much room anyway. I may still do some experimentation, so if you do, feel free to report back.

I think the 40 ohm (or 39 if you go with the PE Xicon 5W resistor) is an improvement, but some of that will depend on room and source gear. They are small and cheap, so there is almost nothing to lose by getting them. If you think the high end with the resistor is too laid back, you can just cut one of the leads to remove it from the circuit.

[flyfishingnitin]

Re: Helium - a true micromonitor

The parts express package with the flat-packs is finally here and time to get cracking.

Question about the front baffle: Is the mid flush mounted? i.e., a simple circular hole or a more complicated router job?

Thanks,
NS

[bkeane1259]

Re: Helium - a true micromonitor

The parts express package with the flat-packs is finally here and time to get cracking.

Question about the front baffle: Is the mid flush mounted? i.e., a simple circular hole or a more complicated router job?

Thanks,
NS

It is surface-mounted. Flush-mounted would require a funky odd-shaped recess. The driver flange is really thin, so it's just plopped in a circular cutout. Does that make sense?

[flyfishingnitin]

Re: Helium - a true micromonitor

Thanks and yes, makes sense. Three circular cutouts it is

[Herman Trivilino]

Re: Helium - a true micromonitor

Hey Scott, I'm getting ready to start assembly here, but I want to make sure I'm building the crossover circuit correctly. Something you said makes me think I'm doing something wrong.

For the 0.2 mH inductor, I used a surplus inductor from some old Klipsch crossovers I bought from Ken McCullough. The closest match I have been able to find is a 23 ga Visaton air core sold by MCM Electronics. The 20 ga Jantzen air core from Parts Express will also work fine. Since there is a 2 ohm resistor in series with that inductor, the small change in DCR of the inductor will have no significant impact.

According to the way I read your circuit diagram there's a 2 ohm resistor in series with the 4 microfarad cap. Can you please verify that the circuit diagram is correct? I don't see any resistor in series with the 0.2 mH inductor.

[scottsehlin]

Re: Helium - a true micromonitor

My apologies - I was not remembering correctly when I made that comment. There is a resistor in the parallel leg in the woofer circuit, but not in the tweeter circuit. The circuit diagram is correct.

As mentioned in previous comments, a 40 ohm (or something close) resistor can be added across the tweeter terminals to bring down the tweeter level slightly if it needs that (it will be somewhat room/application dependent).

[Jackson54]

Re: Helium - a true micromonitor

I am interested in building the Helium speakers for use at work. Would these items I have saved work for the crossover? The 1.1 mH inductor value and 15 ohm resistor are the changes that would be necessary to order everything from PE.

Also, If I have the room would it effect the crossover much if I made the cabinet a little deeper?

[Naught1]

Re: Helium - a true micromonitor

I am interested in building the Helium speakers for use at work. Would these items I have saved work for the crossover? The 1.1 mH inductor value and 15 ohm resistor are the changes that would be necessary to order everything from PE.

[ATTACH=CONFIG]52458[/ATTACH]

I was able to get everything from PE. For the 1 mH inductor, I ordered a 1.0 mH Jantzen air core, PN 000-1056. For the 14 ohm resistor you could series up a 12.5 and 1.5. Or just call it good with the 15 ohm, and save a bit of space and wiring hassle.

However, this is very tight design, and the crossover is a tight fit, using air core coils and metalized polypropylene caps. My crossover is external, but even then, it takes up more room than I planned on. I don't know how I would cram it into the enclosure, but I'm sure it could be with some creative planning!

[johnnyrichards]

Re: Helium - a true micromonitor

I really wish I had had some more time with these. Scott's voicing and design work is always spot on, and he has a habit of milking every drop of performance out of drivers. Makes me a mite nervous to see how he does with those tweeters I just sent his way lol!

[Jackson54]

Re: Helium - a true micromonitor

I was able to get everything from PE. For the 1 mH inductor, I ordered a 1.0 mH Jantzen air core, PN 000-1056. For the 14 ohm resistor you could series up a 12.5 and 1.5. Or just call it good with the 15 ohm, and save a bit of space and wiring hassle.

However, this is very tight design, and the crossover is a tight fit, using air core coils and metalized polypropylene caps. My crossover is external, but even then, it takes up more room than I planned on. I don't know how I would cram it into the enclosure, but I'm sure it could be with some creative planning!

Thanks for the part number. I too plan on having the crossover outside of the speaker. Maybe like Wolf did with his xenums.

[scottsehlin]

Re: Helium - a true micromonitor

1.1 mH and a 15 ohm resistor are close enough. With that combination, you probably won't want the extra resistor across the tweeter.

If you make the cabinet deeper it won't have any effect on the crossover, but may have a slight effect on port tuning.

I don't think there would have been much hope of getting the crossover inside the box without using that tiny 1 mH inductor from Dynavox. I should take some pictures of the inside to show how tight the fit is.

[scottsehlin]

Re: Helium - a true micromonitor

I really wish I had had some more time with these. Scott's voicing and design work is always spot on, and he has a habit of milking every drop of performance out of drivers. Makes me a mite nervous to see how he does with those tweeters I just sent his way lol!

If I can get them to sound like yours did, I will be quite happy.

Erich and I have discussed a small 3-way that these would work well in, but if that doesn't go forward, they clearly are robust enough to work with a lot of midwoofers on their own.

[Herman Trivilino]

Re: Helium - a true micromonitor

Thanks, Scott, for the verification of the circuit diagram.

I got the parts from PE the other day and was shocked to see that the tweeters are so small. I had made a cardboard mock up of the cabinet just to show Donna how small the cabinets will be. Looking at that along with the woofers I see why it's all going to be a tight fit! All this talk about room for fitting the crossover components in the cabinet got me thinking that they may make up a significant fraction of the cabinet's volume and have to be accounted for in the same way as the drivers and port tube volume are accounted for. Some calculations indicated that maybe that's not true. Scott said the cabinet volume should be in the 0.03 to 0.04 cubic foot range, and the cabinet has a volume of 77 cubic inches, or 0.045 cubic feet, so maybe it's all good. Still, that crossover has to fit in that tiny cabinet and I won't be able to figure out placement until I actually mount the drivers in the cabinets, so I'm thinking crossover construction will be the last step.

I ordered that tiny 1.0 mH inductor, along with the caps, from Dynavox. They shipped last Tuesday and should have arrived here in Texas by now. I'm getting worried.

The 5% tolerance resistors from PE are smaller than their 2% audio grade resistors, so that's one way to save space. Since a 14 Ω resistor is unavailable, using 15 Ω will save space as it eliminates the need for a combination that adds up to 14 Ω and it may also eliminate the need for the 40 Ω resistor across the tweeter as Scott mentioned. I ordered the 2 μF caps from Dynavox. But if ordering from PE, I think the NPE caps are smaller, and since they don't offer a 2 μF NPE cap, it might be better to get two of the 1 μF NPE caps and put them in parallel.

[flyfishingnitin]

Re: Helium - a true micromonitor

What was the secret to drilling a hole for the port? I am having a hard time finding a 1 1/6" holesaw bit or even a spade drill bit.