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The D'Appolito, MTM Configuration

One speaker technology which is I think old but hasn't gotten the praise it deserves is the Joseph D'Appolito configuration.  In short, it uses a tweeter vertically sandwiched between two midwoofers.  Using two actual midranges is a variation on the theme. 

What got me thinking of this was the $220,000 speaker pair that appeared on Stereophile's coverage of the Florida Audio Expo, which made me think, fondly, of the original, 1980's era  Focal Utopia where I first heard this arrangement. 

It's a very good arrangement for those who love detail and want a speaker that's relatively easy to live with.

How about you? Have a pair of D'Appolito-like speakers ever won you over?

erik_squires
knotscott
814 posts
 

I always liked this design option. If the.crossover point is low enough and the driver centers are close enough, comb filtering shouldn't be an issue.  Always many variables in play, and pros and cons to each design choice.

kennyc
1,191 posts
 

When auditioning the Kef LS50s, I also demoed the R700 which sounded like the LS50 but more extended.  It sounded very good then but was also demoing many other speakers searching for a speaker that would resonated with me.  

bache's avatar
bache
503 posts
 

We slightly modified D Appolito design in our Sofia loudspeaker line . using very small tweeter between two flat sides of woofers . quasi coaxial design

 

milpai's avatar
milpai
2,322 posts
 

what’s between my two MTM speakers now, and just to the outside of them on either side, the result produces amazing midrange and depth of stage. There is a cohesiveness in how the mids and high frequency blend together in a uniformed manner. Its just more engaging to me.

@decooney, you nailed it, as I experience the same with the ProAcs. It is amazing how deep the sound stage goes behind the wall that is behind the speakers.

audiokinesis
2,722 posts
 

Joseph D'Appolito's original design had a few characteristics which have not made it into everything "MTM". 

He used an odd-order crossover (3rd order), which would have a lobe at 45 degrees above the tweeter axis in a normal tweeter-on-top two-way configuration.  With the MTM topology, we get one lobe above the tweeter axis and another lobe below the tweeter axis, resulting in significantly more uniform vertical coverage in the crossover region than we'd get with an even-order crossover.

Also, the original tweeter was a horn-loaded Dynaudio dome, and the physical set-back of the tweeter's voice coil due to the horn depth contributed to time-alignment in the crossover region.

Finally, the narrower radiation pattern of the horn-loaded tweeter resulted in better pattern-matching through the crossover region than we'd get with a conventional dome tweeter. 

The advantage of the more-commonly-used 4th order crossover for an MTM configuration is that it allows a lower crossover frequency, but along the way some of the desirable attributes of Joseph D'Appolito's exceptionally well-thought-out approach have been traded off.

I've used an MHM format ("H" for horn tweeter) several times over the years, mostly in custom studio monitors.

Duke

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