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The exceptional 15-inchers would be two fitted in two categories: the bass 15-inchers and wide-range 15-inchers. It is imposable to think about the exceptional and wide -range 15-inchers and do not mention the 1946 -1973 production of the Tannoy Dual Concentric drivers. The idea was wonderful, the implementation was very good and the drivers (Gold, Red, Silver) are incredibly interesting. The 15-inchers Tannoy Dual Concentric require custom very sensible enclosure (the default Tannoy enclosures were compromised) that required a lot to taste and understanding. However, if everything is made properly then the Tannoy Dual Concentric does incredibly well. Of course the contemporary production of the Tannoy Dual Concentric is garbage….

Tannoy Dual Concentric

There is one interesting contestant thought…. I have unconfirmed evidence that the infamous Harry Olson had his own 15-inchers Dual Concentric driver. I heard a speaker that reportedly was Olson’s speaker and it was very interesting, free from some problems I observed in the Tannoys. Unfortunately during that the only listening session the Olson’s speaker was in context of an installation where was very difficult to say anything more critical…

That lead us to another category: the bass 15-inchers. The bass 15-inchers are the mostly misused drivers. It is know that the lowest octaves (sub 40Hz) and upper bass (above 40Hz) must not be handled by the same driver. So, if the lowest octaves are the target then why to stay with 15”? The Exceptional 18-inchers would be the direction to go. For the mid bass – the primary duty of the 15-inchers there are: Vitavox AK-151, Vitavox K15/40 and Altec 515G. They all pretty much the same drivers with very slightly different come materials but they all sound very wonderful. Vitavoxes is more advanced tonally then 515G but it is not an issues. The biggest problem is that the 15-inchers mid bass driver practically always misused.  The AK-151 and 515G have free air resonance around 40Hz and they are perfect for a 50-60Hz horn (I mean  a property done horn only). In the 50-60Hz horns they do phenomenally and really define their class. However, the Morons™ are not satisfied with 50-60Hz horns and they do not complement the 50-60Hz horns with the desisted LF sections. Instead they try to push out of their 50-60Hz horns lowers frequencies and by doing this they screw up everything.

Altec 515B

They mostly do it by loading their horns with 15-inchers of lower resonant frequency. There are quite few of them available (even Altec did the 515B and E with Fs of ~25Hz) but as soon this type of the driver loading a 50-60Hz horn then the problems begin as if a horn cares the acoustic pressure lover then it horn rate then it severally compress the 1-3 octaves above the horn rate. As the result we have a family of wonderful paper suspended 15-inchers drivers, with great tone but completely usable: you can’t put them in horn and you can’t put then in a sealed box because they have no excursion. The only suitable mid-bass application for the 15-inchers with Fs of 25Hz that I see would be a large line array of 6-12 drivers per channels where the combined sensitivity would not alloy then to hit their max excursion. Still, it should be only for smaller rooms and good lack to fit in them a pair of enclosures with a dozen 15” drivers….

Vitavox AK line

In the end the 15-inchers is very strange animals. Even for midbass they decay too fast in HF in most of the cases. People use them to get more pressure for the larger rooms. It has usually it’s own set of problems that it very deferent subject…I think that 15-incher should die out at ~250Hz-300Hz where the “fundamentals channel” should take over”. Before the “fundamentals channel” kick in, if you select the “15-inchers solution” then you would hardly find anything more interesting then AK151….

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