mtm with the hivi M6a

[k.h]

im new here and i have seen a lot of cool designs with the hivi units :T
and i was thinking would it be good if i make a design with 2 hivi M6a in a mtm konstruktion maybe with an ribbon?? fountek jp2.0 or something like that

[JonMarsh]

Put the soldering iron down and step away from the bench for a moment...

Hello, and welcome to HTGuide.


I see two kinds of processes often in beginning a DIY project. (done both myself). In one case, it goes along the lines of "Gee, this is a cool looking driver, wonder what kind of system I could build with it?"

In the other case, it's "Hmmm, I want a new speaker that does "A", plays XXdB loud with no more than X.X distortion, (roughly), and is no bigger than X x Y x Z dimensions. The latter is more of an engineering approach, but the former can be a lot of fun, IF you understand you may be painting yourself into a corner.

I've designed a number of systems with the HiVi M8a. It's a moderately sensitive driver, nice Q for reflex systems tuned low, is fairly pistonic up to about 2 kHz, and the cone breakup at 2.6 kHz isn't too horendously high in Q. It also has adequate, if not stellar Xmax, about 5 mm.

I've looked at the M6a a few times, becuase it's "cute", but on paper it doesn't work very well for me. It's almost as expensive as an M8a, it doesn't go up much higher (before cone breakup at 3200 Hz)- still wouldn't use it above a 1400 Hz crossover), and being smaller, Sd is about 1/2, and the Xmax is reduced to 3.5 mm in order to keep the sensitivity up. Additionally, the relatively large magent assembly creates some problems with rear shadowning of the driver and getting adequate rear venting with thick front panels (which I always use- usually not less than 1.5").

Add all these things up, and it doesn't make a lot of sense, ESPECIALLY not compared with the Dayton RS180, which has more Xmax, and a more extended top end before things get into trouble. Still, I usually cross over the RS180 at 1400 Hz with a steep filter, and never higher than 1800 Hz.

OK, ribbons. Gotta problem with using ribbons in two ways- they just don't go low enough, and if you push them close to their rated bottom end, they have energy storage/resonance issues. Even the big Fountek ribbons are happier crossed over around 4 kHz, but you can't hardly find a cone driver clean that high. Then, there's the matter of driver center to center spacing as a function of crossover frequency- and MTM's just make that more difficult. A 6" woofer MTM with the woofers touching and using a neodymium small footprint tweeter can be crossoed over as high as 1800-2000 Hz, but that won't work with a ribbon in between. And that low a crossover generally won't work with most ribbons.

Let's not even get into the distortion issues with most "inexpensive" ribbons.

If you really want a ribbon based two way, I'd suggest a minimum configuration to consider might be a Seas W18, 3 kHz crossover, and say, a NeoCD2 from Fountek, or an Arum Cantus G3 (the "i" series Arum Cantus are a bit high in distortion IMO).

Just my 0.02.

If you really like the M6a, a better solution to try it out would be an MTM with Seas H1212 tweeter or Dayton RS28a. That would be fun to do, and as long as you don't push them too hard in the deep bass, or with regards to SPL, it should be possible to get that working well. But the motor isn't quite as clean as the Dayton RS motor- so if I was choosing on specs, I'd go with the RS180. See some of the RS180 MT designs posted on HT Guide for ideas.... and look at the Natalie P design for ideas on how to handle the breakup mode stuff without an overly complex crossover.

~Jon

[Paul H]

If you really want a ribbon based two way, I'd suggest a minimum configuration to consider might be a Seas W18, 3 kHz crossover, and say, a NeoCD2 from Fountek, or an Arum Cantus G3 (the "i" series Arum Cantus are a bit high in distortion IMO).

~Jon

I'm afraid I have to disagree with you Jon (gasp..) on the above Seas W18 suggestion.

I think it's a wonderful driver and am using it in the speakers I'm doing right now, but a crossover at 3 kHz is too close to the 4-5 kHz breakup zone. The cone breakup on the W18 is not subtle or slight - it's fingernails on chalkboard obvious. I'm crossing at 4th order at 1600 Hz and have a notch filter around the resonance frequency and that works nicely.

Paul

[JonMarsh]

You are so right, I was getting the response curves of the W15 and W18 crossed in my mind. 3 kHz with the W15 should be OK. Probably not over 2 kHz with the W18, and that with a steep filter.

~Jon

[k.h]

thanks for the inputs... i would look some more at the Dayton RS180. its look like a nice unit