Have been having a bit of creative fun with these speakers over the last couple of days, but first a bit of background:
For my 61st birthday back in January, my daughter bought me a tube amp book. She thought I'd already got plenty of tube amp books about hi-fi audio stuff, so she got me a very interesting book on guitar amps by Dave Hunter, entitled "The Guitar Amp Handbook - Understanding Tube Amplifiers and Getting Great Sounds"
The book is full of sensible stuff, that can be applied to hi-fi amps as well as guitar amps. If we forget the sections on tone stacks, which are nevertheless very interesting, there is a ton of stuff on how to set about voicing an amplifier, that I knew little or nothing of. BS free sections on coupling capacitors, which take the piss out of the expensive audio signal coupling capacitors and stupidly priced resistors that the DIY tube amp builder can't seem to escape from. A great book I thought.
It was the section on output attenuators that piqued my interest. These enable the guitarist to obtain a cranked up, flat out tone in a studio environment without deafening themselves in the process. These attenuators go in the speaker circuit of a guitar amp and are normally comprised of a network of high powered resistors in series with the speaker line. If you know anything about speaker design, you'll realise straight away that such a network is neither use nor ornament for a domestic hi-fi speaker. BUT one particular attenuator, the Weber "VST MASS" output attenuator made me sit up and pay attention. The MASS uses a magnet/coil speaker motor as the series element rather than a big resistor, meaning that the attenuator provides a proper reactive load that mirrors the way a speaker works with an amplifier output stage in a way that a simple resistor does not.
Now I'm currently in the process of building a single valve output transformerless amplifier using the 13E1 radar power regulator and LW transmitting tube and although the breadboard I built, will drive an 8 Ohm speaker, OTLs work far better into a higher impedance load and 8 Ohms is considered marginal. 4 Ohms is right out, 16 Ohms and we're getting somewhere.
Left over from my omni experiments I have a couple of 8 Ohm Faital Pro 6inch drivers, one of which I put the cone through with a screwdriver. I wanted a way to make my Fane speakers a 16 Ohm load without having to carry out irreversible mods to the fabric of the cabinet and adding a driver. There are no 16 Ohm Fane 12-250-TC drivers nor any plans to make any, so series connecting two 8 Ohm drivers is for now, the only way of getting to 16 Ohms. I decided therefore a couple of days ago to do a jury rig of twin drivers to make a 16 Ohm speaker.
Inside both of my Fane cabinets, there is a horizontal stiffening brace below the main driver cutout. This brace has a number of four inch holes in it that maintain the cab volume whilst providing stiffening to the side and back walls. I figured that an extra internal driver could be fastened over one of the holes in the stiffening brace and wired in series with the main driver, to provide a 16 Ohm load without any visible evidence on the outside of the cabinets, so yesterday I spent a couple of useful hours fitting a scrapped Faital Pro 6" driver inside each cab. The DC resistance of each speaker system is now 13.5 Ohms, so a nominal AC impedance of 15 Ohms is not beyond the bounds of reason. What effectively we now have, because of the other holes in the brace, is a small, up/down firing open baffle speaker operating
inside a sealed box speaker
I mean, how fecking stupid can you get!
Connected up to my A20/P20 amp, with LS5 speaker cable, the result is hilariously good! The volume is of course slightly lower for the same setting, but when that is corrected I'm well pleased with the sound. Interestingly, the on-axis, tipped up response of the main Fane full range driver is no longer evident, which initially seemed curious, but it's explainable; at least I think I can explain it.
There is a bit more ease and liquidity to midrange instrumentation and electric guitars in particular sound spot-on (no surprise there then) loads of harmonics revealed within the distortion envelopes. Vocals come over with natural tones and free of residual shoutiness. Bass instruments can be followed more easily with acoustic bass twang and buzz more obvious; demonstrated to good effect by Ray Brown's playing on Oscar Peterson's "We Get Requests"
The configuration shows great potential and I've one or two ideas on how I can refine the concept.
Allright, yes I know that the obvious answer is identical drivers, series wired in an isobaric arrangement, but that'll mean building new cabs, so for now this'll do me.
For now, it's amazing what a guitar amp handbook and a bit of lateral thinking creativity can get you.