Why aren't D'Appolito arrays more common?

[radio3]

It seems like all bookshelf speakers are overwhelmingly 2-driver and tower speakers overwhelmingly have a single tweeter up top and then various other woofers below. But point-source speakers are the ideal and ceiling and floor reflections have a huge effect on sound. Furthermore, the more drivers you have, the lower the distortion, and tweeters usually can do more SPL than bookshelf speaker woofers.

Why isn't the standard MTM configurations? Its seems it would be so much better just to have the same basic size speaker but with two slightly smaller woofers and the tweeter in waveguide for uniform dispertion up front, better phase alignment, and less comb filter from boundaries.

I'm sure there must be good reasons why D'Appolito arrays aren't the norm, I'm just interested in what they are. It seems to me that the advantages of coaxial speakers (e.g., Genelec Ones and KEF R3) are very compelling. D'Appolito arrays are a next best thing as far as phase coherency. Anyway, any thoughts on this topic would be greatly appreciated. I'm looking for some bookshelf speakers that can do some good SPL in a large room with subwoofers. Wondering why I can hardly find anything other than the old one mid and one tweeter configuration and can't afford the Genelecs.

 

[Blumlein 88]

That's a very good question. I've wondered the same. Revel uses two woofers over almost their entire lineup. Usually 3 ways. Add a midrange and such an arrangement seems it might be good for directivity. WMTMW. It does make for a taller cabinet if tweeter height is the same.

 

[radio3]

I guess the Genelec Ones are WMTMW, it's just the MTM are colocated. Too bad I can't afford them. There's no intrinsic necessity for WMTMW or MTM to be expensive, though.

 

[SIY]

Pedantic point: d’Appolito is a very specific subset of MTM. It specifically uses an odd order crossover, which in combination with that driver arrangement, serves to control polar pattern.

With modern DSP and active circuitry, there’s other ways of accomplishing that goal.

 

[radio3]

Yes maybe I should have been more general, I just thought maybe using that term it might be more clear that part of the motivation was to make benefit of opportunity to get more advantageous dispersion pattern.

I remember the first time I heard speakers that totally blew me away. They were just a modest pair of JBL SVA 1600s. I had a couple friends come listen to them to and we were mesmerised by how "holographic" and effortless they sounded. I've always wondered if it was because they were the first pair of MTM speakers we'd ever heard.

 

[digitalfrost]

Real D'Appolito is hard to do in real life. Ideally the distance of the two centers of the MTs should not be more than 2/3 crossover frequency. You can calculate that yourself, but in practice it means you can hardly use anything larger than 4" MTs, and even then the crossover frequency would need to be lower than most tweeters can manage.
Because of this, most MTM designs actually have interferences that should not be there.

Also D'Appolito specifies uneven order crossover networks, so most the time this will require 3rd order networks, which I guess are too expensive for most companies.

 

[Cahudson42]

I'm looking for some bookshelf speakers that can do some good SPL in a large room with subwoofers.

Apologize these are towers, but they are 'bookshelf priced" at $299 - the R263:
https://www.harmanaudio.com/infinity/REFERENCE+263.html

Seemingly capable of good SPL w/o bottoming out, given amir's R162 test of what appears to include the same woofer.. Seem to be hard to beat for the price..

I do have the R162 for my BR system..Don Ross playing now..Never an SPL problem..

 

[murraycamp]

But point-source speakers are the ideal

Are they though?

 

[FrantzM]

Apologize these are towers, but they are 'bookshelf priced" at $299 - the R263:
https://www.harmanaudio.com/infinity/REFERENCE+263.html

View attachment 80211

Seemingly capable of good SPL w/o bottoming out, given amir's R162 test of what appears to include the same woofer.. Seem to be hard to beat for the price..

I do have the R162 for my BR system..Don Ross playing now..Never an SPL problem..

Wrong thread?

 

[radio3]

Real D'Appolito is hard to do in real life. Ideally the distance of the two centers of the MTs should not be more than 2/3 crossover frequency. You can calculate that yourself, but in practice it means you can hardly use anything larger than 4" MTs, and even then the crossover frequency would need to be lower than most tweeters can manage.
Because of this, most MTM designs actually have interferences that should not be there.

Also D'Appolito specifies uneven order crossover networks, so most the time this will require 3rd order networks, which I guess are too expensive for most companies.

That sounds like a pretty good explanation. I would think todays driver materials and digital crossovers might finally make it practical, though, don't you think?

 

[Cahudson42]

Wrong thread?

Question was asked. Mentioned multiple woofers. 3 way..Needing SPL. Thought reply relevant. Moderators feel free to delete..

 

[Kvalsvoll]

Because it does not give better sound, in itself.

Here, as usual, what matters is the execution - how it is done - that matters, not the principle.

 

[HooStat]

Most center channel speakers are MTM.

 

[digitalfrost]

Most center channel speakers are MTM.

Which is the absolute worst if they're a D'Appolito design (woofers in parallel) as opposed to a 2 1/2 way. You move the wanted cancellations from the vertical pane to the horizontal pane, meaning everbody who is not sitting dead in the middle will have bad sound.

 

[radio3]

Because it does not give better sound, in itself.

Here, as usual, what matters is the execution - how it is done - that matters, not the principle.

Yes but quality of execution being equal wouldn't they be better than simple MT speakers?

 

[Dennis Murphy]

Real D'Appolito is hard to do in real life. Ideally the distance of the two centers of the MTs should not be more than 2/3 crossover frequency. You can calculate that yourself, but in practice it means you can hardly use anything larger than 4" MTs, and even then the crossover frequency would need to be lower than most tweeters can manage.
Because of this, most MTM designs actually have interferences that should not be there.

Also D'Appolito specifies uneven order crossover networks, so most the time this will require 3rd order networks, which I guess are too expensive for most companies.

Joe actually backtracked on the even-order requirement, and actually used 4th order acoustic for his Thor transmission line MTM. In any event, most companies, or at least a plurality, already use 4th order acoustic slopes for their speakers, whether MTM or otherwise, so 3rd order wouldn't be more expensive. The physical spacing issue is trickier, and I'm currently experimenting on that to see just how serious the interference effects are when you violate the rule of thumb a little.

 

[radio3]

Does anyone know if the Genelec One speakers are in compliance with true D’Appolito? Not that I care about the formal definition particularly much, just curious.

Do I gather correctly that people are saying if you don’t do true D’Appolito then MTM is likely to sound worse than just having one woofer, and that comb filtering or something becomes an issue that isn’t offset by the dispersion advantages over a single larger woofer?

 

[Kvalsvoll]

Yes but quality of execution being equal wouldn't they be better than simple MT speakers?

Not necessarily. At crossover, the radiation typically changes from wide (one small tweeter) to narrow (2 larger drivers at considerable distance apart), and there will be lobing. You have the advantage of symmetrical radiation vertically, but that does not help, if the pattern is wrong.

Ideas that looks nice on-paper, sometimes fall short when you test it. I have done speakers with symmetrical vertical pattern - mids above and below tweeter - and they do not seem to have any advantage in sound quality. If you look at tests and what is being offered in the market, there is no indication of any correlation between symmetrical vertical radiation and sound quality.

 

[thewas]

Does anyone know if the Genelec One speakers are in compliance with true D’Appolito? Not that I care about the formal definition particularly much, just curious.

The Ones do that with woofers to coax (WCW) which is no problem as the wavelengths of the woofer to mid crossover frequencies are much larger.

 

[Senior NEET Engineer]

Bookshelf speaker needs to look agreeable in a living room.