poor neglected fella was purchased in July of 2015 and lay around
waiting for attention. The reason for that procrastination was due
to its being face down on the floor next to a pair of restored
W15s. I guess I thought it was also restored but that changed on
June 20, 2017 when I happened to flip it over for some unknown reason
and was surprised at what I saw. So, without further
hesitation, it went onto the bench.
T/S parameters for this speaker: Re=10.6 ohms; Fs=20.615 hz; Sd=95 sq.in.; Vas=21.962 cu.ft.; Mms=48.263 gm; BL=15.711 T/M; Qms=56.678; Qes=0.276; Qts=0.265; Xmax=4mm; No=2.079%(half space ref.eff.); Sensitivity=95.196 dB 1w/1m
This is the coil of the above speaker. The spider disintegrated like a piece of papyrus from an Egyptian tomb.
|A new cone and coil assembly, the last one of four I had imported from Wharfedale of England back in the early seventies. I decided against using this cone as I wanted to keep the speaker as original as possible, not to mention the fact that the label on the back plate of the magnet assembly states CS, not FS and also that the original felt annulus was still in very good condition.|
The coil of the above assembly; it's the same length as the original.
There is one in my collection of cone assemblies that has a shorter winding. See the next photo.
The coil on the right is from a very old W15. It is the only one of it's shorter length I've seen
The left one is that on the replacement cone. All the coils on all but one of the cones are this length.
The left is 17mm in length and the right one is 15mm. The left one has a dcr of 10.46 ohms and the right one is 11.13 ohms.
The left one is wound with 124 turns of 33 AWG (0.007") wire which is equivalent to 40 BSW, also (0.007")
|It appears that the longer coil was adopted to accommodate a longer excursion without introducing non-linear distortion. Also, since the field extends a little above the gap, the result would be more wire in the field. Since the force, F, exerted on the coil and diaphragm is a product of the magnetic flux in B the field, the length of the wire in that field and the current through the wire, a larger force could be applied with minimum loss due to extra wire mass thus making the speaker more efficient. F=BLI. Also, F=ma. Therefore, we can conclude that BLI=ma. Now, since the field B is constant, and if we hold the current L constant and since the mass m of the moving system is also constant, increasing L will increase a, the acceleration. The result, better transient response, meaning that the forward and backward motion of the moving system more closely follows the variations of the electrical signal applied.|
|My collection of W15 cone and coil
assemblies salvaged from a speaker recone shop in during the late
seventies and during the eighties. The one on top is the new one
shown earlier and the bottom one one I removed from a W15 I sent to be
reconed in the late seventies. When is was returned, it didn't
have an original cone and coil which I expected. It had a Waldom
VC-2000 coil and a Waldom WHF-5421 cone which was modified to fit.
The W15 is actually a 14" speaker if measured across the diameter
of the basket. The 15" is derived from measuring across the
four mounting tabs. It was this disappointment that prompted me to
The Waldom coil, VC-2000 is the same size as the original, no problem there. It's form length is 1.375"; winding length is 0.59375" (19/32", 15mm); inside diameter is 2.015"; dcr is 10.8 ohms and the impedance is specified as 15 ohms. However, the coils on these cones measure 15mm to 17mm in length.
The cardboard frame and wood dowel are those used in the original shipping carton, which I still have.
The original cloth/felt annulus. It was decided to use this instead of foam as the label does state "CS".
The replacement assembly with one coat of Titebond® around the circumference
|Same as above with two coats of Titebond®. This stuff takes about 30 minutes to set to the point of no return so it gives one ample time to fiddle with things. Two coats were used to allow the first to impregnate the paper cone circumference.|
The annulus applied. By now, the glue was slightly tacky but liquid enough to impregnate the felt.
|One thing that surprised me was the paper spider, something I have not seen. It was detached from the coil form and cone apex. After removing the cone, I proceeded to remove the spider which crumbled in my fingers. Below is a close-up of part of the spider and a photo taken through a microscope showing the paper fibers.|
Three views of the completed speaker.
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