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RE: MGIIIa tweeter question

Posted by Davy (A) on August 7, 2014 at 15:17:02

In Reply to: RE: MGIIIa tweeter question posted by Satie on August 6, 2014 at 21:28:46:

Hey Satie and Neo,

Nice to hear from you guys, been a while. Didn't play my Maggies for a few years due to various reasons (had them stored away) but I'm getting back into it again so hopefully I can share some of my experiences on this forum. No worries about the PM Satie. Would be great to hear back from you when you have some spare time to catch up

I am definitely after more sparkle from my MGIIIas so I will certainly try the wide 2 ohm tweeter without the resistor. My amp might not be quite up to it though. It’s a NAD 208, which can drive 4 ohm speakers no problem, but probably is not too happy with lower impedance load like 2 ohms and certainly not 1 ohm. I guess I am risking the amp overheating having a 2 ohm tweeter in the speakers. The amp does have a protection circuit so maybe it will just cut off if there is a problem, but it’s still risky. I suppose I should be ideally be looking for a high current amp with lower impedance drive capability, - Krell, Aragon or Classe etc maybe. I really want something with at least 8 output transistors a channel as (in my experience) that’s the minimum amount you need to get Maggies singing well in passive single amp operation. I am not that clued up on modern amps are there any other ones I should be considering that would do the job OK?

Satie, I guess the potential problems you are explaining with crossover phase etc when not using a resistor is because the 2nd type of wide tweeter is 2 ohms, not the original design’s 3 ohms? Like you say though it’s certainly still worth trying and see how its sounds if my amp can handle it. I suppose I could compromise and put a smaller resistor in there (maybe 0.47, 0.56 or 0.68 ohms) which would attenuate the treble less than a 1 ohm resistor and make life easier for the amp than using no resistors, though sound quality wise no resistor is better of course.

I remember Karen at Magnepan once explaining to me about the tweeter cage being very slightly shorter in the MGIII, MGIIIa and TIVa than the later models. Lengthening it to accept the newer narrow (and superior sounding) 3 ohm tweeter is another possibility. I don't have a router but I guess you could carefully chisel or shave away with something to lengthen the tweeter trough by 0.6 inches. Although I can't buy a new set of narrow tweeters in the cages from Magnepan (as I'm overseas and they won't ship) I do have a pair of 3.3Rs with the narrow tweeter in them which I could donate into the MGIIIa. The MGIIIa has a more solid and punchier bass than the 3.3Rs and sounds more dynamic for some reason (not sure why - perhaps different mylar construction/tension and/or different MDF frame material), so I would probably prefer to "do up" the MGIIIas if possible rather than stick to the 3.3Rs, which (whilst quite good) I’ve never been totally satisfied with.

Neo, I missed your rebuild will look on the forum for it.

I scrapped the stock 18 12 18 12 crossover in my 3.3Rs a few years back (the stock XO has the low tweeter mid crossover point at 1.7 KHz). I scraped it largely as that design had a big suckout in the midrange, - the “audiophile dip” , which I didn’t like and the sound was also a bit phasey and foggy IMO. On Satie’s advice I replaced it with a 18 6 6 6 type crossover very similar to the MGIII crossover (virtually the same values, but no tweeter inductor and a 10uF cap on the tweeter) . The linear phase in mid and treble sounded much better me compared to before. This setup has a higher crossover point at about 3.5 KHz. I thought the original 1.7Khz crossover gave poorer quality treble from the ribbon, but its hard to tell is it exactly why as the new crossover I put in had no audiophile dip and a flatter response, so perhaps that’s why I thought the sound was better, - not completely sure on that one. Certainly the 6dB high pass on the tweeter taxes it quite lot, but perhaps having less components in the tweeter XO cleared up the treble a bit.

I had to sell my Tympani IVas a couple of years ago as I didn't have the right sort of room for them, sadly. The 3 series Maggies are much less room picky. If I had kept the IVas would have definitely put in the better sounding new narrower 3 ohm tweeter after lengthening the tweeter trough, and likely would have also tried the 18 6 6 6 crossover in them which I like a lot. (stock TIVa is 18 12 12 12 if I remember right).

Thanks a lot for your help guys, speak soon.

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