The Pros & Cons of Dual-concentric/Coaxial drivers

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J

jtgofish

Member
Joined 2018
Diogenes said:
I'm fond of the Tannoy dual concentrics. I've owned the 12" and still own a pair of 15"s (had both at the same time, sold the 12"s and kept the 15"s because they were better in every way but WAF). They've stayed in rotation when I've dabbled with different speakers (typically my on again, off again love affair with planars), but never going far. They're keepers for me especially after reconing (the spiders in the older Tannoys get so soft that the Qms becomes very high even with new surrounds making the Qts unusably high in anything but a large sealed box). There's just something a 15" DC does very well that very few other speakers can approach, certainly non-point sources. Zero minimum listening distance, fantastic imaging and that big 15" cone gives the appropriate weight to the lower midrange and midbass that smaller drivers just cannot do. Get a pair set up right and listen to something that requires dynamic scale and weight like a piano recording and very few speakers can touch it. Coaxials that have a separate treble horn in the middle just don't have the same integration, to me, always sounding a bit off compared to the Tannoys.

Unfortunately, they're not perfect, hence why they're not my mains. Mine have the alcomax magnet, which gives the horn much better geometry than the newer models with the shallower ceramic magnets. Unfortunately, they have the "PepperPot" phase plug from the 1940s that's over half a century out of date. Between that and the older horn contour, they have a pretty nasty honk on axis that can only be addressed by listening about 10-15 degrees off-axis (ie solving it by not toeing them in). However, that knocks down the treble response up high and makes it a bit more ragged as well. So, it's a trade-off. The older crossover design is less than ideal and makes them change over between drivers a bit less than ideal. Most importantly, using the cone as part of the horn, clever as the idea is (something I do really appreciate about them) means that bass excursion does audibly and, yes, measurably muddy up the midrange. The biggest upgrade I ever found with my DCs was to properly integrate a subwoofer with them to relieve the cone of the bass, even the 15" model. Really did a lot to clean up the midrange (I no longer have the measurements due to a dead computer, but it was a not insignificant reduction in measured THD for whatever the mechanism may have been even if it was just keeping the VC in the more linear region of the gap) and helped with the integration to the tweeter. Just made them whole new, much better speakers. Tannoy understood this weakness, which is why their best models, the Kingdom series, did the same thing by adding a separate bass driver to handle everything below 120Hz.
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Yes I am very fond of my Monitor Gold 15s in 270 litre Canterbury style cabinets.I have owned a lot of speakers including 3 way horns but there is just something special about the way that the big Tannoys fill a room with engaging music.You listen to the music in the room and not the speakers in the room.
I have experienced a slight muddling of the midrange but that is mostly overcome by finding the right amplifier.They are far more amplifier fussy than people think.I think you need to find an amp with the ideal damping factor.Most tube amps[especially SETs] are underdamped and most SS amps have too low output impedance so overdamp them.Push pull tube amps of around 50 watts are generally considered best but you can do a lot better.
The biggest godsend for Tannoy owners in my opinion is the availability of affordable Chinese copies of the Dartzeel NHB 108 power amp which seems to suite them perfectly and produces very clean and beautiful midrange as well as deep and textured bass.There are a few versions of them but the Weiliang /Breeze version 3 with the big blue Sprague caps and two pairs of transistors per channel is the one that works superbly on mine .
They need to be used with a go0d active preamp however.Supratek works well on mine.
 
profiguy

profiguy

Member
Joined 2007
Based on my experience working with coaxial drivers, the doppler distortion can be noticeable if the driver has to do more than about 1mm +/- excursion. On a 12" driver, that will practically translate to 100 - 103 dB going lower than 80 - 90Hz @ 1m with a 2nd order rolloff (sealed enclosure without any other low end reinforcement ie. porting or horn loading). Thats a rough figure which has worked well for me, but the problem is you may have other things like BSC to factor in.

In the case of my Eminence KL3012CX8 and Faital Pro HF108 in a sealed enclosure, I used a 120 hz xover to the LF drivers (2x B&C 12MH32). That keeps the excursion on the coax way down and sounds significantly better than running rhe coax fullrange in a ported box. Im still working out the details in DSP to EQ the coax, which has proven tricky based on off axis behavior. I'll post the results in an older coax thread of mine when I get closer to an acceptable result.
 
profiguy

profiguy

Member
Joined 2007
@jtgofish - Thats why many mastering and recording engineers like Tannoys. They sound the most correct of the available large format coax drivers in the appropriate baffle setup. Tannoy has made a few great drivers. The price is however way up there for what you get and their passive crossovers have room for improvement IMO.
 
M

Mister Audio

Member
Joined 2013
YES -
Seeing some of the Tannoy crossovers, I can't quite equate the excellent sound coming from them ???
Some kind of 'magic', I just don't know - Imagine replacing all components with the very best!
I must say though, I have never heard 'old classic' Tannoys driven really hard >
I imagine those little iron-core inductors would saturate & distort.
 
J

jtgofish

Member
Joined 2018
Mister Audio said:
YES -
Seeing some of the Tannoy crossovers, I can't quite equate the excellent sound coming from them ???
Some kind of 'magic', I just don't know - Imagine replacing all components with the very best!
I must say though, I have never heard 'old classic' Tannoys driven really hard >
I imagine those little iron-core inductors would saturate & distort.
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Why would you want to drive them really hard? They only handle about 50 watts anyway but are pretty sensitive.20 watts will produce plenty of loudness in a typical home or recording studio.I have used them with a 28 watt valve amp and that works fine.They are not a speaker that needs to be played loud to sound good.

There is nothing wrong with the sound of Tannoys with the original crossover components as long as they are within value.[and they usually aren't].I have upgraded crossovers with some expensive Mundorf Supreme and Clarity Cap components which probably do sound slightly better but it is only slight.A modern moderately priced replacement crossover using all modern components did not sound as good as the originals.
 
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J

jtgofish

Member
Joined 2018
Gruesome said:
Are any of the speakers mentioned so far still available, or is this thread mostly a big nostalgia trip? I was hoping to learn about other coaxial speakers besides the KEF's that test well and show good horizontal and vertical dispersion patterns. Are there any?
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There are modern Tannoy and Fyne Audio coaxials .No nostalgia there.
Who cares about 'test well"? They might or they might not.Many of the all time best sounding speakers probably don't test well".The naive objectivist mindset and its associated expectation bias will rob you of a lot of the potential enjoyment available in this hobby.
 
J

jtgofish

Member
Joined 2018
Mister Audio said:
YES -
Seeing some of the Tannoy crossovers, I can't quite equate the excellent sound coming from them ???
Some kind of 'magic', I just don't know - Imagine replacing all components with the very best!
I must say though, I have never heard 'old classic' Tannoys driven really hard >
I imagine those little iron-core inductors would saturate & distort.
Click to expand...

Troels Gravesen measured them and concluded
"these distortion measurements display very low levels at significant sound levels."
 
freddi

freddi

Member
Joined 2005
I've enjoyed some of Eminence's cast frame 12cx and 15cx but not seen them for sale in a long time. Many had a horn pretty much like the front horn from the ancient Electro-Voice CDP ("Compound Diffraction Projector", and magnet slug ranging from 54/56oz to 109oz. I liked the 80oz magnet 12cx with 2.5" coil, but the 12cx with 4" coil and 109oz slug magnet is decent.

An LC-LC allpass on the woofer seemed to help things congeal.

I've heard "gargle" from a Beta15cx with sustained bass with flute. DJK (R.I.P.) indicated that coax were more prone to it than having the tweeter element offset - so a K-tube 2-way Karlson coupler might sound a bit cleaner than a CX. (case dependant - 604 are pretty good)

This is a 109oz magnet 12cx with 4" coil and 4.6mm overhang. It sounded pretty good with Fritz Wunderlich singing lieder in a Karlson 12.

I had Beta10cx - dismally bland and opaque with EM's 2K5 network - maybe Mike Chua got it right with his Osprey xover.

BTW - on CX with a secondary spider/dust cover, its helpful to have a felt or foam damping ring over that piece as it emits nasty HF junk which interferes with what we want from a speaker.
 

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AllenB

AllenB

diyAudio Moderator
Joined 2008
Paid Member
"Point source" is a theoretical construct, and not one that any real speaker can categorically be called. A regular two-way can display significant point source behaviour and a coaxial speaker can show non-point source behaviour.
 
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