This was one of my earlier acquisitions.  There still is an A and a B and there was a D but it found its way to Japan.  The fella there contacted me asking if I'd part with one for $400.  After several email conversations, we sort of became email pals.  Since the speaker was salvaged from a repair shop many years ago, it essentially cost me nothing, so I didn't feel right accepting his offer.  After some reverse haggling, I settled on $100 as he didn't feel right accepting it for nothing other than shipping any more than I felt about his initial offer.  The shipping cost $265, partly due to the wood crate I built for it.  Monetary transactions were done through PayPal.

Included with the speaker was a corner enclosure design of 6 ft^3, which he had built by a professional cabinet maker.  He sent a piccy of it and it's incredible, finished with a French polish.

Regarding the speaker below, the annulus was cut from a foam sheet obtained at a fabric store.  It's 3/16ths inch thick, 0.1875" and has a fine mesh on one side which is easily removed, although not necessary.  For this unit, the I.D. of the cardboard template is 240mm and the O.D. is 296mm.

This one is all original, the felt (cloth) annulus is long lasting as long as the moths or crickets don't get at it..

The yellow upper marking on the cone dates it to 4/'55.  Below that appears to be the fundamental resonance, 31 hz.

A W15FS (prpple) with a new cone & coil assembly which was one of four purchased directly from Wharfedale in 1972.

The foam is a better type than the original as it lasted without deterioration since '72.

This unit, below, along with its twin, are currently in use in a pair of corner enclosures.

The initial annulus repair was done with purple felt (prpple) but during the test procedure to derive the Thiele-Small parameters with the LMS (Loudspeaker Measurement System by LinearX), I used the delta compliance method out of habit, which requires placing the speaker on a sealed box of known volume.  An impedance curve is then run and LMS compares that with the impedance curve run with the speaker in free air, from which it derives the parameters.  It's a lot easier than doing it manually and still easier than the program I wrote in BASIC some 35 years ago in the early eighties.  It also required manually deriving Fs and two frequencies on either side at which the impedance was at a low for F1, max (resonance) for F2 and another minumin at F3, where F1<Fs<F2.  An analogue meter was used as the maximum and minimum points are easier to find than with a digital meter due to reaction and settling times.  I used both, as the analogue made it easier to find those points but a Tektronix AC voltmeter was far more accurate.  The meters also had to be calibrated with 1% or better 10 ohm resistor, after which, the readings were taken as being ohms.  A mass of accurately known weight was placed on the cone for each of the two above measurements.

The derivation of the Thiele-Small parameters was repeated using the delta/mass method in LMS, but not until after replacing the cone assembly.  When the initial results derived with the sealed box made no sense, I thought I screwed up on the repair job, so I replaced the cone and coil with a new one.  The one that had the purple annulus is stored away with the annulus removed, quietly waiting for a frame.  the results of this new one came out much then same and it was then that I discovered the reason why; the sealed box was leaking through the felt and foam.  It's a good thing that speaker didn't have to fly.

This data, along with the physical dimensions of the cone and it's DCR, were entered into the program and a few seconds later, the results were saved to a file and printed.  The program also would calculate the normalised frequency response for any given box volume as well as vent diameter and length, which could also be manually entered.  When I started building cabinets for musicians, some wanted two or four vents and some even wanted three, the latter being strictly for appearance.  So, I wrote another program to accommodate multiple vents of any quantity, round or rectangular.  Thereb was also a subroutine to normalise short vents to 3/4 inch length, the thickness of the front baffle.  In that case, a hole of appropriate diameter would suffice.

The program itself, if printed, took 9 sheets of paper.   A myriad of other programs were written for horns, eponential and tractrix, straight and folded, which spat out all the dimensions along the horn path, be it single path or twin path, like the Klipschorn and the "W" horns.  They also had subroutines to allow for multiple flares; the Klipschorn uses two.  the pair of Klipsch type corner horns I built in the 80's unload at 34 hz, as compared to the Klipsch, which unloads at 42 hz,  The triple flare allowed the horn to fit through a doorway by shortening its length.

After the programs were written and debugged, they still had to be checked for accuracy and errors caused by certain parameters undetectable by BASIC.  That was time consuming.

There was even a program written to calculate the components' values for a 33 band 1/3rd octave spectrum analyser, using 4 pole filters, 24 dB slopes per band.  It required 33 quad op-amps.  The unit was never built.

I was a lot younger then and had much more energy, stamina and determination that I do now.