The MciNSTOSH design has dome tweeters that are about center to center distance is 2.75 inches apart. This causes vertical comb filter distortion to start at roughly 5000hz, which for most people should be clearly audible. While I use dome tweeters too, mine are not 1 inchers, they are 3/4 inchers, and the flanges are cut so that the vertical comb filter distortion for me doesn't start until roughly 15,000hz.

I have only one line of mid ranges so I don't have to worry about getting the close enough to avoid horizontal comb filter distortion. I can't tell from the McIntosh photo whether this is an issue since I don't know what the crossover to the tweeter is. But it may be an issue with the McIntosh models.

My midranges are 3.5 inches but my center to center distance is 5 inches. This means that I need to cross my mids to the tweeters at at least 2671hz to avoid audible comb filter distortion. I cross them at 2400 using a 24 db octave electronic crossover, and I use 30 tweeters per side, so that each one carried only 3.3% of the total tweeter load.

It looks like the McInstosh need to cross at less than 1600hz or so from the c-to-c distance vertically. If they had used ribbons or planars like you do, this wouldn't be a problem, but they've used some kind of dome, so this is a problem. I don't know any 1 inch domes that will cross at 1600hz adequately.

MY SYSTEM WAS DESIGNED USING JIM GRIFFIN'S RESEARCH AND WITH HIS HELP, AND IS VERY DIFFERENT THAN THE MCINTOSH MODEL.

BUT WE'VE HAD NUMEROUS DISCUSSIONS ABOUT THIS IN THE PAST AND YOU ALREADY KNOW THIS.

Marlboro

vs

The Calipso
http://pub48.bravenet.com/photocenter/album.php?usernum=4095425731&album=48032

Pictures are clearly different.

Not all of the McIntosh arrays use the same spacing and driver sizes; however, keep in mind that some of the small drivers they use can be crossed lower than what you use because of the way the drivers are designed.

I never had any intention of adding another row of mid ranges. But then again I've not heard a description from you as to how the sound is better by doing so over a single line.

As to using ribbons planars over domes, one has to cross lower with planars than domes. There is nothing in Jim's work that precludes the use of domes. Using ribbons or planars just gives more choices, and higher quality choices. However when you compare using 8 PT2 planars to using 30 domes, the sound issue quality disappears.

Of course if you use enough of them, like more than 60, the %age of covering of the band can be so low that they are hardly stressed at all. But the whole design system is widely different than using ribbons or planars. You have to allow for that if you want the dome tweeter sound.

My own experience is that only 3/4 inch domes will work though. ONE inchers are too big to make the c-to-c work. 1/2 inchers might work but nobody makes one that doesn't have a huge flange. If someone were to make one that allows a tight edge of dome to edge of dome contact like can be done with the one Dayton Neo they would be super.

Domes can be used in Line arrays; small 3.5 inch mid ranges can be used in line arrays. However this combination requires a narrower choice of speakers, and requires a much tighter management of parameters than does the use of a larger mid range and planar/ribbon speakers. You can't cut any corners at all if you want to make it work, and that includes mandatory electronic crossovers, and separate enclosures for each midrange speaker,plus paying very close attention to the c-to-c distance.

And unfortunately for anyone who likes to buy really expensive raw component speakers, one has no options.

If you want to argue this point, I have no problems keeping it up as long as you want. I listen to my speaker system every day. And you have never even tried to build using my approach much less listened to anyone who has. Unfortunately, if history is any reference you will start making derogatory comments about my design. This will then negate our agreement. Don't go there. I have nothing to lose.

The use of planars or ribbons is better for the following reasons:

1) better sensitivity

2) lower interference patterns in the vertical plane

3) can be operated at a lower crossover point than the small neo dome tweeters

The symmetrical arraying of dual mid-range driver lines around a line of tweeters does create several potential advantages as pointed out by Rick. You can think of this design as a stack of MTM elemental speakers. The key to successful utilization of this design (as with any horizontal MTM speaker) is to cross over to the tweeter from the mids at a low enough frequency to mitigate lobing issues which would narrow the horizontal plane coverage for off axis listeners. Crossing low necessitates a very close spacing between the mid range drivers and a small width tweeter to assure a wide horizontal lobe in the horizontal plane.

The McIntosh XRT28 symmetrical line array design is an example of a line array design that uses the two mid range driver lines and a line of small domes concept. While the XRT28 does have dome tweeters, the drivers are rather different from common small dome tweeters. For example, the Aura Sound NSW1-205-8A (I suspect that McIntosh uses this driver in their XRT28 as the photos indicate this) is a small 1" diameter full range driver (Fs of 220 Hz) which can be used as tweeter in such a symmetrical array. That small driver enables the mids to create a wide horizontal lobe which tight spacing between drivers. The mid to tweeter crossover can be very low in frequency which assure a broad lobe in the horizontal plane. The NSW1-205-8A is listed by Madisound at:

http://www.madisound.com/aurasound.html

You can gain additional information on the Aura Sound site as well.

Robert Greene tested the XRT28 for the Absolute Sound magazine and adds additional analysis in his on-line site at:

http://www.regonaudio.com/McIntosh%20Supplement.html

Greene points out the advantage of this arrangement as the horizontal lobe somewhat limits side wall reflections within the listening room. Thus you'll experience both minimal ceiling and floor reflections inherent with a line array plus minimal sidewall reflections. The sound that reaches the listener is more direct (vs. a mixture of direct and reverb sound) so any room signature is limited.

One final point is that you really need to shoot for a center to center spacing of a wavelength (or less) spacing between the midrange drivers for an optimal near field array. That is the vertical spacing of the drivers. What happens is that the amplitude response of the midrange line tends to droop as you go beyond one WL spacing.

In the dual midrange symmetrical array you need to shoot for a center to center spacing between the mids in the two lines of a wavelength as well to create a favorable lobing situation.

Jim