Diesis Audio Roma uses a BMS coaxial driver

morricab

Well-Known Member
Apr 25, 2014
9,391
4,988
978
Switzerland
I was reading about the Diesis Roma and they highlight that they are using a coaxial compression driver from 600-20Khz. They claimed, somewhat incorrectly, IMO, that other 2 inch drivers cannot get to 20Khz (ok it is mostly true but a Beyma CP750Ti can get really close) but their's being coaxial can. The thing was that I know BMS is the only game in town for a coaxial compression driver but the driver in the Diesis didn't look like the ones I had seen. That's because, as I found looking at the BMS site, while most of the BMS coax compression drivers are with Nd magnets , they do have one that has a ferrite magnet (4590). Comparing photos, it is clear that the Diesis driver is the ferrite BMS coax. Nearly everyone else wants to use the Nd versions because they have a bit higher output (as if 110db is not enough) and are much lighter weight. However, looking at the data, it seems the ferrite version is smoother ( I still don't like the amount of distortion I see on the higher frequencies of BMS drivers though) and maybe that is why Diesis chose it rather than an Nd driver because they didn't need that sensitivity nor did they care about the weight it seems. Given what I heard from the Roma Triode in Munich, I have to say that this seems to be a damn good driver when implemented as they have done.

Just thought some here might be curious about this discovery...
 
  • Like
Reactions: christoph

kodomo

Well-Known Member
Apr 26, 2017
1,002
1,612
330
It is bms but there are differences that help with the treble response like their use of phase plug.
 
  • Like
Reactions: christoph

morricab

Well-Known Member
Apr 25, 2014
9,391
4,988
978
Switzerland
It is bms but there are differences that help with the treble response like their use of phase plug.

I see what you mean, the Roma Triode has a brass bullet in throat of the horn it looks like. Also, it seems that the Roma Triode, which is the one I heard in Munich actually, is NOT a coaxial driver but a 2 inch throated midrange driver. That one may or may not be BMS.

The "basic" Roma has a Coax with no apparent phase plug and then a small supertweeter. The Roma Triode goes from a 2inch mid to 16mm bullet tweeter made from brass.

Would be curious to know if the Roma Triode model is also BMS or something else. IMO, the highs I have heard so far from BMS were not my favorite so that was partially why I was so surprised at first...now looking closely at what I actually heard in Munich the upper highs were being done by that bullet on the Roma Triode, which is probably a metal diaphragm compression tweeter.
 
  • Like
Reactions: christoph

morricab

Well-Known Member
Apr 25, 2014
9,391
4,988
978
Switzerland
It is bms but there are differences that help with the treble response like their use of phase plug.
From what I saw on the BMS website, the Coax doesn't need a bullet phase plug to help it get to 20khz.
 
  • Like
Reactions: christoph

kodomo

Well-Known Member
Apr 26, 2017
1,002
1,612
330
I do not know the new Roma triode. The one I am talking about with bms also had phase plug but not brass, I think the model was called caput mundi and had bms4590.

Other models did not extend to 20khz with just one horn, they had an extra tweeter to do that
 
  • Like
Reactions: christoph

morricab

Well-Known Member
Apr 25, 2014
9,391
4,988
978
Switzerland
Interestingly, I am getting to 20Khz with this Beyma CP755Ti. I need to give it a bit of boost because of the constant directivity horn but it appears to stay smooth. They are using a similar concept to Radian, metal diaphragm with plastic surround, although the Beyma I have uses Ti instead of the Radian Alu. You compared the Alu+plastic to Be, right? What was your finding (not that I can upgrade mine anyway as there is no aftermarket Be available for this driver)? I may adopt a supertweeter like you someday but for now the highs are quite ok in fact.
 

Mark Seaton

WBF Technical Expert (Speaker & Acoustics)
May 21, 2010
381
141
390
47
Chicago, IL
www.seatonsound.net
There are multiple compression drivers readily available which can push breakup past 20kHz. There were fewer options 10 years ago. As the diaphragm/VC size gets bigger, the options narrow further, as the compression chamber and pathways have to be designed with this extension in mind.

One significant benefit of the BMS coaxials come from the potential for low extension on the right horn. The different ferrite vs neo magnet and throat versions have different strengths and limitations for different applications and horn coverage angles. Most forget that the dispersion or limitations of the very highest frequencies are often partially defined within the exit of the horn driver itself. When you change the thickness of the magnet and the size of the horn throat, you change the angle inside the driver, and thereby how it interacts with the horn. In the case of the ferrite 2" BMS, it works surprisingly well, and in some ways better than the neo versions if you don't go too wide with the horn.

With respect to the phase plug you may see or not, BMS has a "HiFi" version of the driver available with a copper cap and extended phase plug that protrudes well past the mounting surface and is supposed to help with off axis dispersion at the higher frequencies. Most often this is seen on the 1.4" exit neo driver, but there is a phase plug on all of the drivers, where most have the shorter plug which allows the screen to seal out debris from the exit.

B&C also recently introduced a competing coaxial compression driver of their own that looks quite good, but it does take a dive around 19-20kHz.
 

Audiophile Bill

Well-Known Member
Mar 23, 2015
4,293
4,093
675
Well I have the BMS coax in my Swings albeit the neo version and modded by BD designs. I am not sure what Bert does to the standard version btw. There is also a phase plug in the upper horn.
 
  • Like
Reactions: christoph

Folsom

VIP/Donor
Oct 25, 2015
6,024
1,490
520
Eastern WA
Some distortion in 12khz+ range will almost assuredly be welcomed by many audiophiles.

Look for numbers on the driver, I believe I found it once (but didn't save it). The numbers were not exactly the model number IIRC.
 

DaveC

Industry Expert
Nov 16, 2014
3,899
2,141
495
You can build an excellent speaker, in the realm of cost-no-object designs, simply by buying the BMS coax, using their xo design and a horn from DIYSG and throwing it on top of a Big-A$$ woofer powered by a class D amp w/ built-in DSP and using a good SET amp for the BMS.

It's very similar to my speaker and the same horn would even work well with an adapter, eventually I'll make an adapter and xo and have a speaker I can switch between the BMS CD and my own wideband driver. It's just the BMS is a CD and CDs are imo harder to make a seamless match w/ a conventional woofer vs the paper cone wideband midrange I use.

edit: You could also buy a pro/ht speaker like JTR that uses the BMS, I'd probably make my own xo and biamp, but the price is very reasonable, in fact IDK how he can sell speakers so cheap.

http://jtrspeakers.com/noesis-215rt.html
 
Last edited:
  • Like
Reactions: christoph

morricab

Well-Known Member
Apr 25, 2014
9,391
4,988
978
Switzerland
You can build an excellent speaker, in the realm of cost-no-object designs, simply by buying the BMS coax, using their xo design and a horn from DIYSG and throwing it on top of a Big-A$$ woofer powered by a class D amp w/ built-in DSP and using a good SET amp for the BMS.

It's very similar to my speaker and the same horn would even work well with an adapter, eventually I'll make an adapter and xo and have a speaker I can switch between the BMS CD and my own wideband driver. It's just the BMS is a CD and CDs are imo harder to make a seamless match w/ a conventional woofer vs the paper cone wideband midrange I use.

edit: You could also buy a pro/ht speaker like JTR that uses the BMS, I'd probably make my own xo and biamp, but the price is very reasonable, in fact IDK how he can sell speakers so cheap.

http://jtrspeakers.com/noesis-215rt.html
Yeah, those prices are insanely cheap...is there any margin in that at all? Pricing out approximately what is in there you get not so far below the factory direct prices (not counting cabinets and labor). A hobby business where he doesn't need the money?? Lot of work for that...

Thing I have been discovering is that there are some 1.4" CDs that can cover from about 500-600 to just about 20khz, which makes the coax CD somewhat unnecessary along with the complication of having another crossover. This Beyma I am using (but I know some Radians will also extend up nicely) with only minor EQ (and probably given the sensitivities I need flattening the lower end as suggested to me will work even better) can get right out to 20Khz without major breakup. Now, the BD Swing seems to get down to 300Hz with the Coax driver but this is at the limits for that driver.

I plan to blend my CD with a wide bander and then use woofers only to reinforce the last couple octaves. My thinking is that an 8 inch widebander does a better job of mid to upper bass than a 12 or 15 inch woofer.
 

Robh3606

Well-Known Member
Aug 24, 2010
1,471
463
1,155
Destiny
"My thinking is 8" widebander does a better job "

Yeah I agree my active mains use 10" mids between a 15 mid woofer and my 1.5 " compression driver. Lots of snap and clean vocals out of the 10"

Rob:)
 

morricab

Well-Known Member
Apr 25, 2014
9,391
4,988
978
Switzerland
"My thinking is 8" widebander does a better job "

Yeah I agree my active mains use 10" mids between a 15 mid woofer and my 1.5 " compression driver. Lots of snap and clean vocals out of the 10"

Rob:)
What are those speakers?
 

DaveC

Industry Expert
Nov 16, 2014
3,899
2,141
495
Yeah, those prices are insanely cheap...is there any margin in that at all? Pricing out approximately what is in there you get not so far below the factory direct prices (not counting cabinets and labor). A hobby business where he doesn't need the money?? Lot of work for that...

Thing I have been discovering is that there are some 1.4" CDs that can cover from about 500-600 to just about 20khz, which makes the coax CD somewhat unnecessary along with the complication of having another crossover. This Beyma I am using (but I know some Radians will also extend up nicely) with only minor EQ (and probably given the sensitivities I need flattening the lower end as suggested to me will work even better) can get right out to 20Khz without major breakup. Now, the BD Swing seems to get down to 300Hz with the Coax driver but this is at the limits for that driver.

I plan to blend my CD with a wide bander and then use woofers only to reinforce the last couple octaves. My thinking is that an 8 inch widebander does a better job of mid to upper bass than a 12 or 15 inch woofer.

IMO you should take dispersion into account wrt sizing the drivers so you can get a smooth off-axis response.

This is also where it's handy to have a mid horn that can play down to 3-400 Hz, there are plenty of 15" woofers that can play up that high where if you cross much higher it becomes more of an issue as far as which woofer... there are many that can extend higher, but a more limited selection and generally the woofers have a lighter cone and smaller voice coil diameter. In this case I'd agree that you may be better off with a smaller mid.

I'd also look to cross a smaller midrange higher if you choose to do that, if you cross too low the midrange will have too much excursion, which will limit clarity on more complex music or higher SPLs. I also think surface area is important for midbass impact, so I'd prefer to have the woofers extend up to ~200 Hz ideally.

IMO, the AE TD8M or 10M combined with the TD15H+ would be pretty close to ideal when used with a CD for highs. The 15H+ uses the 18H+ motor, and a heavier cone... it's not on the site but can be ordered. It's better vs the regular H by a good bit but won't play as high of course. I use the 15H+ and have tried the H, the M and a few other woofers.

http://aespeakers.com/shop/td/td8m/

http://aespeakers.com/shop/td/td18h/
 
  • Like
Reactions: Mark Seaton

Folsom

VIP/Donor
Oct 25, 2015
6,024
1,490
520
Eastern WA
I find the TD8M QTS slightly on the low side. It makes it complicated. I'm not sure you can bring it up with enough R in front of it...
 

About us

  • What’s Best Forum is THE forum for high end audio, product reviews, advice and sharing experiences on the best of everything else. This is THE place where audiophiles and audio companies discuss vintage, contemporary and new audio products, music servers, music streamers, computer audio, digital-to-analog converters, turntables, phono stages, cartridges, reel-to-reel tape machines, speakers, headphones and tube and solid-state amplification. Founded in 2010 What’s Best Forum invites intelligent and courteous people of all interests and backgrounds to describe and discuss the best of everything. From beginners to life-long hobbyists to industry professionals, we enjoy learning about new things and meeting new people, and participating in spirited debates.

Quick Navigation

User Menu

Steve Williams
Site Founder | Site Owner | Administrator
Ron Resnick
Site Co-Owner | Administrator
Julian (The Fixer)
Website Build | Marketing Managersing