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RE: MMGW as a midbass driver

Posted by Satie (A) on February 25, 2010 at 01:13:54

In Reply to: RE: MMGW as a midbass driver posted by josh358 on February 24, 2010 at 20:13:10:

Bass should couple for the MMGW, it is a misconception to think the cuttoff would remain at 100 hz. You should get more. It is after all a 400 square inch driver, where the bass just has not been tuned to rise as the frequency drops - to counteract cancelation. I finally found some FR plots for the MMGW. Its nearfield FR drops heavily under 500 hz, indicating that a wide baffle, wing or wall are necessary to fill in the midbass to get a 100hz extension (as intended). Looks like it would not work for you if you insist on pulling it into the room - unless you build it with a wing behind it - or a horn in front of it. But (with wings) stacking should extend the bass to 80 hz.

I guess that leaves you with the rather hard to find Magnepan Bass panels or the Tympani bass panels (suitable models are ID, IIIB, IV and IVA). A "destroyed" MG 3.x would do well too. Or stacked MMGs.

Or this whole idea is moot and you are buying the Apogee Duetta Sig. on A'gon. Great speaker.

Re In front placement.
I did this with my low order crossovers on the Neo8 modified Tympani and I lost some of the midbass because of the lack of baffle (the bass panels) on one side. It was not that much of issue on imaging, which was slightly different.
Here is a local example:
http://www.integracoustics.com/MUG/MUG/pix/MikeBarney/Full~system.jpg

If I remember correctly, the Apogee Midrange/tweeter assembly was structured as a high panel in front of a low panel, spaced to match the wavelength of the crossover frequency. It is entirely useful and not a problem at all. It amounts to the line source version of coaxial drivers. Actually, if I had not been so fearful of blowing the tweeter with the Neo8's output I would have placed them that way in a new frame.

A Neo8 line of 8 units would be 62+ inches, just a few less than stacked MMGW or even stacked MMG (Stack the drivers not the entire speaker- it will just fit in your space, and for mid-bass you can safely place the top driver slightly in front of the lower driver in the stack). So there will not be any kind of height difference effect on images.

Re wall proximity for Bass-Mid:
At 300 Hz you have a 3.7 foot wavelength. So it carries still some significant localization information. But if you manage to get close to ChasW98's cuttoff under 200 hz (and you should come close with just 3-4 inches of baffle on the other side), then you have a 5+ foot wavelength so that localization information is not as fine, and you would have far less of an image smear at closer proximity to the walls.

The main difference between the Neo8 and the Maggie ribbon is in dispersion, where the ribbon is far better past 10khz than the Neo8, and is significantly better than the Neo8 in the 5-10 khz region. The Neo8PDR has about the same dispersion in the 5-10 khz range as the Maggie ribbon. The other difference I noticed was somewhat stronger dynamics on the Neo8, but I would assume that is because I was working the DR-9 over the class A bias on the tweeter at least some of the time, and not working it so hard with the Neo8.


Re Hearing tests. Cheapest way is to get something like the Stereophile test CD 3 and play it on a good system to see at which signal you hear only half of the 1/3 octave signal or nearly none of the signal. I hear only half of the 20 khz signal.

Rebuilding Maggie ribbons is not a big deal at about $150 net each. More if you are on the coasts. They charge you $400 then reverse most of the charge when they get your busted tweeter back.

BTW there is also a complete refurbished Tympani IV on A'gon. And there is this: http://minneapolis.craigslist.org/hnp/ele/1607084736.html which is probably right up your alley.

Re tweeters - if you noticed on my tweeter list, the Dayton and HiVi tweeters are actually more extended than the Neo3 - and the Neo3 PDR. HiVi is a Swan (China) product - if you happened to come across a review of one of their IRS like constructs you know they can do well building quality product. I think they also produce the Dayton tweeter.

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