Green Mountain clone

[fatmarley]

Hi Guys,

Ok, I don't really want to make a clone, but i'd like to make something that has at least some of the strengths of the Green mountains.

I've got some of those Aura NS6 midbass drivers that are used in the Green Mountain Rio and Eos. I did a google image search and the tweeter in the Rio looks like a Seas 29TFF/W.





I don't know if the tweeter's modified though...

Being a sad git, I printed off a picture of the Green Mountain Eos and it looks like the midbass driver is tilted back 8 degrees and the tweeter 5 degrees (the tweeter on the Eos can be adjusted back and forth, but stays back 5 degrees)

Am I right in thinking that it's important to time-allign the drivers for a first order crossover to work properly ?

Has anyone got any tips for designing a good first order crossover ?

I have a calibrated mic and a copy of LspCAD, so measuring isn't a problem.

[tom_s]

Re: Green Mountain clone

fatmarley,

I thought I read that the tweeter was a Morel.

--Found it in the 6moons review, "The tweeter, sourced from Morel, is a 28mm polymer-coated linen dome with a large rear chamber."

That same review claims there is just a single cap on the tweeter and a coil on the woofer. I find that very hard to wrap my brain around, since the 8 ohm NS6 has a 10db spike at 4.5K. Maybe they have been modified to mitigate that spike? I hope so....

[fatmarley]

Re: Green Mountain clone

fatmarley,

I thought I read that the tweeter was a Morel.

--Found it in the 6moons review, "The tweeter, sourced from Morel, is a 28mm polymer-coated linen dome with a large rear chamber."

That same review claims there is just a single cap on the tweeter and a coil on the woofer. I find that very hard to wrap my brain around, since the 8 ohm NS6 has a 10db spike at 4.5K. Maybe they have been modified to mitigate that spike? I hope so....

Can you leave a link to that review ? I googled, but couldn't find a review of the Rio on the 6moons website.

It looks to me like the pico uses the Seas SEAS T25CF002, the Eos uses the SEAS T29CF001 and that oval faceplate on the Rio has got to be the Seas 29TFF/W.
The World-Audio-Design WD25A gives you a choice of the exact same tweeters, which makes me think they are relatively interchangeable.

I've noticed the 4ohm version of the Aura NS6 doesn't have a spike. I wonder if they use the 4ohm version ?

Some of the guys here have made designs with the Aura driver. I wonder if that spike at 4.5k is really that bad ?

Just a thought, but maybe the reason for the 8 degree tilt on the woofer of the Eos is remove the spike ? I think I need to get the measuring gear out...

[billschu]

Re: Green Mountain clone

Usually Roy Johnson has his own take on the "zobel" to help make the first order time alignment work. He applies one to the woofer and another to the tweeter. I would be surprised if this model does not have the same thing. He never divulged what he was doing there but he said the tools, calculators, etc, don't get near what he ends up with. I couldn't squeeze out of him whether the tweeter zobel was more of an LCR or whether it was to fix the tweeter impedance to keep the impedance flat. Sorry.

The cast marble, time alignment, and felt treatment also help these speakers create that oh so listenable sound. They image like crazy and have a relaxing tonal balance yet don't seem to miss any detail. They guy is pretty obsessive about how he wants things to sound.

He shared a trick with me. He said when he voices a speaker he just does one. When he's satisfied with how the one sounds he'll then make another and go from there.

Bill

fatmarley,

I thought I read that the tweeter was a Morel.

--Found it in the 6moons review, "The tweeter, sourced from Morel, is a 28mm polymer-coated linen dome with a large rear chamber."

That same review claims there is just a single cap on the tweeter and a coil on the woofer. I find that very hard to wrap my brain around, since the 8 ohm NS6 has a 10db spike at 4.5K. Maybe they have been modified to mitigate that spike? I hope so....

[tom_s]

Re: Green Mountain clone

Here's the Callisto review - http://www.6moons.com/audioreviews/gma2/callisto.html

Just a thought, but maybe the reason for the 8 degree tilt on the woofer of the Eos is remove the spike ? I think I need to get the measuring gear out...

I have not done any off axis measurements of the the NS6, but I'll bet you are correct that the spike lessens as you move slightly off axis. I have simmed and listened to the 8 ohm version and got fairly decent results using LR4 acoustic slopes. I think that's what most others here have been using.

The cast marble, time alignment, and felt treatment also help these speakers create that oh so listenable sound. They image like crazy and have a relaxing tonal balance yet don't seem to miss any detail. They guy is pretty obsessive about how he wants things to sound.

I was never completely satisfied with my results. That was prior to finding a methodology where my sims are finally looking quite similar to the system measurements. Some day I'll get back to these Auras, but I may never achieve the sonic results that approach that of the Green Mountain...and I guess I'm OK with that since this is just a hobby. I would love to hear the Green Mountains some day. It seems some speaker designers are like many musicians I know...they just have a gift for making musical sounds regardless of the price of the instrument they have in their hands. I'm intrigued with many of the ideas presented on Roy's site, but would be completely stunned if the Callisto is actually using only a cap and coil.

[2leftthumbs]

Re: Green Mountain clone

I would be surprised if this model does not have the same thing. He never divulged what he was doing there but he said the tools, calculators, etc, don't get near what he ends up with.

I did see in the interview that he used a "zobel" on both drivers.

[billschu]

Re: Green Mountain clone

That's what he told me too. The wrinkle is that he doesn't follow the normal way a zobel is done so we're not really sure what's happening there. He also uses Sonicaps throughout which sound pretty benign and get out of the way without the expense of a "boutique" cap.

I did see in the interview that he used a "zobel" on both drivers.

[2leftthumbs]

Re: Green Mountain clone

I think the rio does use that seas 29 while the Callisto uses the morel. the green mt site specs show a 29 mm tweeter for the rio.

[fatmarley]

Re: Green Mountain clone

Usually Roy Johnson has his own take on the "zobel" to help make the first order time alignment work. He applies one to the woofer and another to the tweeter. I would be surprised if this model does not have the same thing. He never divulged what he was doing there but he said the tools, calculators, etc, don't get near what he ends up with. I couldn't squeeze out of him whether the tweeter zobel was more of an LCR or whether it was to fix the tweeter impedance to keep the impedance flat. Sorry.

The cast marble, time alignment, and felt treatment also help these speakers create that oh so listenable sound. They image like crazy and have a relaxing tonal balance yet don't seem to miss any detail. They guy is pretty obsessive about how he wants things to sound.

He shared a trick with me. He said when he voices a speaker he just does one. When he's satisfied with how the one sounds he'll then make another and go from there.

Bill

Cheers for that Bill. I'll have a play around with zobels when I get the measurements done.

That's interesting about the "tools, calculators etc" not getting anywhere near what he ends up with. I think I need to experiment more and trust my ears more. Rather than totally relying on what LspCAD tells me.

When I made my first pair of speaker, I built the boxes, painted them, fitted the drivers and then measured and built the crossovers. I think It would have been more sensible to build a rough test box or two and play around with different box volumes, diffraction stuff like offset drivers, felt, beveled edges etc and time alignment.
I just wish I had more time to experiment...

[fatmarley]

Re: Green Mountain clone

Here's the Callisto review - http://www.6moons.com/audioreviews/gma2/callisto.html

Oh yea, You can see that's a Morel tweeter by the wires visable on the front of the tweeter. There aren't many tweeters that are suitable for a first order crossover, but I've heard Morel make some that work ok.

I have not done any off axis measurements of the the NS6, but I'll bet you are correct that the spike lessens as you move slightly off axis. I have simmed and listened to the 8 ohm version and got fairly decent results using LR4 acoustic slopes. I think that's what most others here have been using.

If I can't get a first order to work properly then I'll try and go for the lowest order crossover I can get to work (probably an LR4
)

I was never completely satisfied with my results. That was prior to finding a methodology where my sims are finally looking quite similar to the system measurements. Some day I'll get back to these Auras, but I may never achieve the sonic results that approach that of the Green Mountain...and I guess I'm OK with that since this is just a hobby. I would love to hear the Green Mountains some day. It seems some speaker designers are like many musicians I know...they just have a gift for making musical sounds regardless of the price of the instrument they have in their hands. I'm intrigued with many of the ideas presented on Roy's site, but would be completely stunned if the Callisto is actually using only a cap and coil.

It's a shame you didn't get them to work properly. I's imagine Roy is a very clever guy, passionate about designing speakers and has enough time to experiment. I'm passionate about designing speakers, but that's about the only quality I share with Roy :(

[tom_s]

Re: Green Mountain clone

These Auras might be a good guinea pig to try a LR2 approach. I know there are a few folks that think there is a certain quality in a LR2 design that's very desirable...what ever that quality may be. I did get a very pleasing sound out of the Acoustic Reality series crossover, but the tweeter (a Seas 27TDC) cried foul when the volume was raised. Plus, a series crossover is hard for me to wrap my brain around....

[2leftthumbs]

Re: Green Mountain clone

No measurements but the acoustic reality crossover I did (after toms inspiring me) with the sb acoustic 25mm tweeter that is nla sounds good to me. I don't think I really ever cranked it up too much though.

[fatmarley]

Re: Green Mountain clone

These Auras might be a good guinea pig to try a LR2 approach. I know there are a few folks that think there is a certain quality in a LR2 design that's very desirable...what ever that quality may be. I did get a very pleasing sound out of the Acoustic Reality series crossover, but the tweeter (a Seas 27TDC) cried foul when the volume was raised. Plus, a series crossover is hard for me to wrap my brain around....

I'd never heard of the AR series XO until you mentioned it. I just tried to simulate it in LspCAD with my old speakers, but I couldn't get the phase tracking to line up or any kind of null at the crossover point. Is that something I should worry about ?

[fatmarley]

Re: Green Mountain clone

No measurements but the acoustic reality crossover I did (after toms inspiring me) with the sb acoustic 25mm tweeter that is nla sounds good to me. I don't think I really ever cranked it up too much though.

Did you compare the AR XO to anything else ?

[fatmarley]

Re: Green Mountain clone

Just got the phase lined up ok and a good null with a first order AR XO, I'm not sure if the tweeters going to like it though...