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D'Appolito Style Coaxial vs Single Woofer (R2C vs R3)

jonfitch

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Seeing as how the Genelec The Ones and Paradigm's Founder series also use this D'appolito style coaxial design, I wonder how would a pair of KEF R2Cs work as vertical mains instead of R3s? Also would there be any deleterious side effects (lobing?) if used this way? Would this be "more of a point source" design (because of woofers above and below the coaxial) necessary than just a single woofer?

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Martin

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The term D’Appolito has been appropriated to refer to any MTM speaker configuration. It is actually a very specific time aligned MTM configuration using a 4th order crossover.

I think OP is simply asking if there would be any issue using an R2C vertically rather than horizontally. I’ve seen plenty of MTM LCR speakers so I can’t think of any but I’m no expert.

A quick search brings up this post: https://www.audiosciencereview.com/...f-r3-speaker-review.12021/page-41#post-437235. While it’s not a spinorama it shows there is no difference when measured on axis.

Martin
 
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Martin

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Total 3rd acoustic order, depending on the slopes of the drivers the electric crossover order can be even lower.

From Wikipedia: “D'Appolito initially configured his design using a 3rd order (18 dB/oct or 60 dB/dec) crossover, D'Appolito has since amended this original recommendation in favor of 4th order topology.” The statement is not referenced so it may be wrong.
 

thewas

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From Wikipedia: “D'Appolito initially configured his design using a 3rd order (18 dB/oct or 60 dB/dec) crossover, D'Appolito has since amended this original recommendation in favor of 4th order topology.” The statement is not referenced so it may be wrong.
Yes, also saw that wiki article after posting my reply and edited it accordingly, although I only knew of the 3rd order version but never tracked its evolution closely.
 

Vladimir Filevski

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... how would a pair of KEF R2Cs work as vertical mains instead of R3s? Also would there be any deleterious side effects (lobing?) if used this way?
No problems here, because crossover frequency is low enough at 400 Hz. But you do need a subwoofer with them as mains - their F3 is 74 Hz.
 
OP
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jonfitch

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Laughing at the term "D'Appolito style", there's nothing D'Appolito about a concentrical speaker design. He would never make such a mistake. Goes completely counter to the entire point of a D'Appolito array.

I realize its not strictly speaking a D'Appolito design, but this is what KEF UK representatives called it when I asked them about MTM coaxials designs, so that's why I went with the naming since that's their preferred description of the orientation with Kef R5/R7.

You can similarly laugh about how the industry uses the term waveguide now just to avoid saying horn.
 
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test1223

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Seeing as how the Genelec The Ones and Paradigm's Founder series also use this D'appolito style coaxial design, I wonder how would a pair of KEF R2Cs work as vertical mains instead of R3s? Also would there be any deleterious side effects (lobing?) if used this way? Would this be "more of a point source" design (because of woofers above and below the coaxial) necessary than just a single woofer?

View attachment 121630 VS View attachment 121633
Yes with two woofers you get more like a point source. The ability to localize the bass in the median plane is not the best, but should be good enough to observe the difference. You also get a more narrow vertical beam in the bass frequencies. Side loops should not be a problem with max 400Hz and about 25cm distance of the woofers.

The two woofer version should be the better option, if there are no other differences with the built.
 

devopsprodude

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The term D’Appolito has been appropriated to refer to any MTM speaker configuration. It is actually a very specific time aligned MTM configuration using a 4th order crossover.

I think OP is simply asking if there would be any issue using an R2C vertically rather than horizontally. I’ve seen plenty of MTM LCR speakers so I can’t think of any but I’m no expert.

A quick search brings up this post: https://www.audiosciencereview.com/...f-r3-speaker-review.12021/page-41#post-437235. While it’s not a spinorama it shows there is no difference when measured on axis.

Martin
Yes, I'm aware of what the design entails. It was used a lot in home THX speaker designs in the 90s because of the controlled vertical directivity inherent in the design. Although companies like Outlaw still sell speakers designed in part by Joe D'Appolito https://outlawaudio.com/shop/speakers-subwoofers/32-lcrv2-loudspeaker.html

My fronts are Kenwood LS-X1F THX speakers I bought in 1995, and while they are probably not truly a D'Appolito array, they are much closer to any concentric designs would be. No concentric speaker could ever get a THX rating from what I understand, because of the problems inherent with the design.

Anyhow, I just found that phrase to be hilarious.
 

aarons915

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Leave it to ASR to argue over what a D'Appolito configuration is instead of the actual point lol. I think an MTM setup might have a slight advantage over the R3 in sounding like a point source but listening to the R series towers I still have the same feeling that the vocals are coming from the entire speaker and not a point like they do in the Q150/Q350/LS50. I think the best we can currently do if we want that point source sound is use a 2 way Coaxial speaker and cross them high enough to play cleanly at our desired SPL levels. As long as that crossover under 200Hz I think the point source should be preserved.
 
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jonfitch

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Leave it to ASR to argue over what a D'Appolito configuration is instead of the actual point lol. I think an MTM setup might have a slight advantage over the R3 in sounding like a point source but listening to the R series towers I still have the same feeling that the vocals are coming from the entire speaker and not a point like they do in the Q150/Q350/LS50. I think the best we can currently do if we want that point source sound is use a 2 way Coaxial speaker and cross them high enough to play cleanly at our desired SPL levels. As long as that crossover under 200Hz I think the point source should be preserved.

It's too bad to the Elac Adante flamed out so badly (only got a 4.1 Pref Score), the concept was promising (200hz crossover).
 

Zvu

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Closest to a point source you can get with coax mid/hi is Blade concept. Adding at least 4 woofers around the midrange does the job so you can shape the frontal lobe to an extent. More the merrier, of course.
 

aarons915

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It's too bad to the Elac Adante flamed out so badly (only got a 4.1 Pref Score), the concept was promising (200hz crossover).

Yes a 3 way with a low crossover like that should sound like a point source as well, I've only heard the reference one and wasn't focusing on that issue but from what I remember it sounded like a point source as well and it has a 270Hz crossover. The Elac Uni Fi also uses a 270Hz crossover I believe and should be good speakers but they also have directivity problems that aren't able to be EQ'd.

Closest to a point source you can get with coax mid/hi is Blade concept. Adding at least 4 woofers around the midrange does the job so you can shape the frontal lobe to an extent. More the merrier, of course.

I'm not sure how that would beat the actual point source of a 2 way coaxial that doesn't have to fake it, of course the 2 way is more limited in SPL and has higher distortion but that's a separate issue.
 

MrPeabody

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There shouldn't be any problem at all with using the R2C as main stereo speakers. The crossover point to the woofer is 400 Hz (true also for the R3), which corresponds to wavelength 2.8' or .85 meter. This should be slightly more than twice the distance separating the two woofers, which means that the two woofers will be mostly coherent until the vertically off-axis listening point is nearly 90 degrees above and below the horizontal. The main lobe will be much, much thicker in the vertical plane than it is with the great majority of other speakers. This of course is consistent with the intent of the coaxial driver. The crossover points are the same for both the R3 and the R2C, which means that it is virtually certain that the crossovers are identical. The only difference that you might notice is a small difference in bass, where the R3 has a slight advantage. You might not notice this difference, however you might encounter a less smooth handoff to a subwoofer with the R2C vs. the R3. Since Kef gives the low-frequency response limit of the R2C as 74 Hz (vs. 58 Hz for the R3), I would plan on needing to cross to a subwoofer no lower than 100 Hz, probably 120 Hz or even a bit higher. (The reason the R3 goes lower is that uses a ported enclosure; the R2C is sealed.) The majority of subwoofers are designed with somewhat high Q, to make the enclosures smaller and to improve efficiency within the band, but the tradeoff is that the response has a broad hump and begins to roll off, at the upper end, somewhere under 100 Hz. You want to pay attention to this when selecting a subwoofer, i.e., you want to study the frequency response plots and choose one that remains flat up to 150 Hz or thereabouts to give you the assurance that you won't encounter a problem in the integration. As long as you pay attention to this, I can't think of any concern with using the R2C as main stereo speakers.
 

Tonygeno

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From Wikipedia: “D'Appolito initially configured his design using a 3rd order (18 dB/oct or 60 dB/dec) crossover, D'Appolito has since amended this original recommendation in favor of 4th order topology.” The statement is not referenced so it may be wrong.
I own Joe's original pair of monitors that he built using Kef 110s and a D28 (if memory serves). It was featured in Speaker Builder magazine in the early 80s and I bought the prototypes from him in the 90s. It definitely used a 3rd order crossover.
 

Zvu

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I'm not sure how that would beat the actual point source of a 2 way coaxial that doesn't have to fake it, of course the 2 way is more limited in SPL and has higher distortion but that's a separate issue.

You can ask the same question then how would 2way coax beat the actual point source one Full Range driver in a box that doesn't have to fake it, of course FR is more limited in spl and has higher distortion.

FR doesn't controll anything, 2way coax doesn't controll the directivity in midrange, and 3way doesn't controll the directivity in bass.
 

Matias

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Why not R5 or R7?
CJH
Larger and more expensive.

The problem of using R2c is that their frequency response plummets below 100 Hz, unlike the larger towers.

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