Helium - a true micromonitor

[kejolly]

Re: Helium - a true micromonitor

Thanks Andy!

Question for anyone that can answer it. What are the odds that I can use the same crossover network with the ND91-4 and the new Dayton PT Mini planar tweeter (275-083)? I know that the tweeter was mentioned earlier in this thread. Looking at turning the box on the side and placing the planner tweeter vertical like it should be. I would only use a single box and make it into a tabletop radio. I would also move the port to the backside.

If I am reading the crossover correctly, the tweeter has a pad on it to lower sensitivity and the full-range has a zobel to limit power. The other parts are just a 2nd order cross-over components.



Thanks
Kevin

[Chris Roemer]

Re: Helium - a true micromonitor

A Zobel doesn't "limit power", it's used to flatten out a moving coil driver's inherent impedance rise (with inc. freq.). 2nd order on tweeter, 1st on woofer.

[Herman Trivilino]

Re: Helium - a true micromonitor

If I am reading the crossover correctly, the tweeter has a pad on it to lower sensitivity and the full-range has a zobel to limit power.

The tweeter does have a series resistor to lower its output, but it also has a parallel 40 ohm resistor that's not shown in the schematic. That 40-ohm shunt resistor actually brightens the tweeter. Together the two resistors have an effect on the overall impedance of the high pass filter and tweeter combination, so presumably both are needed to achieve the proper balance with the woofer's volume.

I think that you'd need to create a new model to be able to answer your question, and I'd be very surprised if the new model gave you the same crossover.

[kejolly]

Re: Helium - a true micromonitor

Wishful thinking I guess. Thank you anyway.

Kevin

[scottsehlin]

Re: Helium - a true micromonitor

It's unlikely that you could substitute the tweeter and change the layout without requiring a redesigned crossover to get satisfying results. It sounds like an interesting project, though.

[randyohoh]

Re: Helium - a true micromonitor

I have what may be a very dumb question. Could an mtm version be made with two of the 8 ohm ND90's in parallel?

[randyohoh]

Re: Helium - a true micromonitor

I meant ND91.

[Herman Trivilino]

Re: Helium - a true micromonitor

Randy, look at Posts #93 through #99. There's a bit of discussion there on the MTM. Scott says the woofers would be in series. Has anyone done a sim?

I just completed my second pair of Heliums and they will eventually replace my two surround speakers. Meanwhile though I want to do some finish work on my old center so I'm going to use one of the Heliums as a center for a while and see how it sounds.

[scottsehlin]

Re: Helium - a true micromonitor

I did a quick sim of two of the 4 ohm ND-91's in series before I wrote post #99. That sim indicated that doubling the values for the inductors and resistors - and cutting the capacitor values in half in the woofer circuit would give a nearly identical frequency response with respect to the original Helium.

The caveat is that sims are not always perfect. I tried the same thing when I made the LithMTM from the Lithium, and wound up tweaking a little to get the sound and response I wanted. I would say, based on the sim, that the Helium MTM (HeliMTM?) based on sim will at least be pretty good with no major problems.

[Herman Trivilino]

Re: Helium - a true micromonitor

I like the name Helium-3 (³He).

[johnnyrichards]

Re: Helium - a true micromonitor

15,000+ views! That many views would not fit in this little guys

I wish I had more time with these, I am usually so busy running around on the stage that it can be difficult to get an impression of them. Having heard a lot of Scott's work in the past though, for anyone hesitant on building these - his voicing is spot on, so go right ahead.

[Herman Trivilino]

Re: Helium - a true micromonitor

Those are some powerful endorsements, Johnny. Thanks for sharing. I'm inclined to build Scott's sim of the MTM and send it to him so he can voice it.

If you've followed this thread you may remember that I built a pair of these Heliums and mounted them up in the front corners of my living room, replacing floor-standing monkey coffins. They're part of a 5.1. It's a change I'm getting used to, but I have no regrets.

I've built another pair and the plan is to use them to replace the surrounds. Meanwhile though I've taken one of them and am trying it out as the center. It's a temporarily replacement for my old UA721 (http://www.parts-express.com/dayton-...binet--302-854) that I've built a new cabinet for and am trying to get a finish on it to match the new table it sits on.

I just hooked up the Helium center and ran Audyssey. I'm very impressed and right away I think it sounds better than the UA721! Now I'm thinking a part of that sound improvement may be placement. The AU721 was sitting on the table at about knee height. The Helium hangs on the wall above the table at ear height.

Waiting to gauge the WAF. If she prefers the look this could become a permanent arrangement. I'll keep you posted.

[Herman Trivilino]

Re: Helium - a true micromonitor

She likes the look and the sound ...



So it looks like I'll be building a 5th Helium!

Or maybe the Helium MTM?

[djkest]

Re: Helium - a true micromonitor

I was researching woofers to use with the new Dayton Mini-AMT and I remembered this design. It seems to me in theory that you could drop the Mini-8 AMT in place of the tweeter. A 5Khz crossover point looks to be nearly ideal for the AMT. Anyway, just a thought. I know this design is good to go as is.

[arrayed]

Re: Helium - a true micromonitor

so, how do these compare to the Overnight Sensations? I ask because they are somewhat similar in cost and these are smaller, but both are fairly 'small' speakers. Thanks!