a Waldom Speaker Repair Manual, dated July 1, 1988, the following
replacement coils are listed
Super 3 VC-1175 I.D.= 1.022" (25.959mm) FORM= 0.5" (12.7mm) WINDING= 0.25" (6.35mm) 2 Layers; dcr=12.3 ohms; Z=16 ohms
Super 8 FS/AL VC-9919 I.D.= 1.020" (25.91mm) FORM= 0.8125"(20.64mm) WINDING=0.25"(6.35mm) 2 Layers; dcr=8.7 ohms; Z=10.0 ohms
|The coil on the left came from a Super 8, probably a later model of the ceramic magnet era, NOT a Super 8 FS/AL of very early vintage, the gold one with an Al-Ni-Co magnet. The left coil is copper wire and the right is aluminum. The one on the right came from a Super 8 FS/AL. Neither coil winding measures 1/4 inch. The left measures 11/32" (0.34375" / 8.73125mm) and that on the right measures 9/32" (0.281125" / 7.14375mm). It seems to make sense that the Super 8 FS/AL coil be longer as that speaker's intended use was for a full range or a midrange in a two way system to compliment a W12FS or W15FS. While the extra length of the coil wouldn't be necessary in a two way system as a high frequency reproducer due to the Wharfedale 2 way crossover's crossover frequency being 1000 hz, the extra length would certainly be necessary if used as a full range as low frequency diaphragm excursions would certainly need it to maintain a more linear force in the magnetic field.|
|This cone & coil assembly obviously comes from a Super 3 but the cone is not original; it's a Waldom WT-18. The coil clearly measures 0.25" as does the Waldom replacement, albeit its being copper. This coil is open at one of the coil wire ends to the braid; I remember futile attempts to fix that but hadn't had aluminum solder nor flux. Another project now that I have the aforementioned solder & flux. It might be interesting to see a spectrum analysis on each since the originals don't have the ribbing.|
the 3 units below, the one with the aluminum dust cap is Nutone 4.
The left rear is J2 and the right rear is J1. These designations
are references in the later SPL and impedance curves. The apparent
tear at 10 o'clock in the left rear unit is fixed but I goofed on the
overlap during repair; that's why its so prominent.
test setup used to derive the curves in the following second and third photos.
The 1w was derived at the driver impedance of 5khz, which is 3.05v into
9.3 ohms and 4.123v into 17 ohms, respectively for the J1 & J2 units
and the Nutone 4 unit, the latter being re-coned way back in the 80's
and in all probability has a Waldom voice coil.
The mic is 1 meter from the plane of the cone at the annulus and the response was gated to simulate anechoic response; it eliminates room reflections to about 325 hz. The response was stopped at 2 khz and the curves shown are not smoothed.
The following derivation may be pure coincidence or not but here it is.
The 9.3 ohms units will draw 0.328A while the 17 ohms unit will draw 0.243A from the amplifier at the voltages specified above, The amplifier, an Adcom GFA-535L is direct coupled, i.e., no output impedance matching transformer.
If we take 20*log(0.328^2 / 0.243^2) we get 5.21 dB, which is the difference between the red&black pair of traces and the blue trace in the SPL vs frequency graph below.
|A side note on the speaker cabinet shown. A pair had be made in 1991 and not used until a few weeks ago. It houses a 10 inch Bostwick 1028, also purchased around the late 80's. The mid-range is a Fountek FW-146 and the tweeter is a Vifa BG25TG15-04, both recently purchased||The internal volume is 2.9 ft^3 and the
response, according to BassBoxPro v6 is down 3dB at 34hz.
The gated response is flat within +/- 0.75dB from 350hz to 17khz and is about 4 dB down at 20 khz.
A full response will be performed outdoors in the very near future, followed with a paper on the project.
The pencil lines on the front and side indicate where it will be truncated to eliminate most of the diffraction.
3 voice coil temperature
A comment was made in an audio forum concerning the Super 3 voice coil temperature. The statement was made somewhat arbitrarily, without reference to any test. Well, my curiosity got the best of me and since I have the necessary tools to make such a determination, here it is, for all it's worth.
|The coil used is most likely from a Super 8 FS/AL due to it's winding height. The columns on the left show the coil impedance/reactance at various frequencies. The voltage and current figures in the rough drawing were noted for quick reference as they change as the coil temperature rises. Ambient temperature was 80F. The coil was driven with 5v @ 5khz from the amplifier. After 1 minute, the coil temperature was noted as 125 degrees and after 2 minutes, 140 degrees. The dc resistance was quickly measured to avoid cooling of the coil and that was noted as 9.1 ohms, 0.77 ohms above the 8.33 ohms at ambient temperature. the lower drawing of the series coil and resistor was used to measure the phase shift of the coil at 5khz, which was noted as 18 degrees, using a dual trace squiggle toob (scope). The same result was noted using the Nutone 4 Super 3. I took the chance of driving it with 2.5v @ 5khz sine wave.|
should be noted that contrary to some popular beliefs, power does not
equal voltage squared divided by the impedance, Z. P=E^2/R for a
dc circiut but for an ac circuit, P=E^2*cos(a) / Z, where a is the phase
shift angle. Since, in this case, a=18 degrees, the cosine is
0.951 so a 5% error is introduced if this is ignored.
Practically speaking, it seems that E^2/Z is good enough for a loudspeaker.
As for the temperature rise of 45 degrees after one minute of continuous sine wave, such a condition isn't going to exist in any music. Based on that, it's seems safe to conclude that voice coil temperature rise in a tweeter is moot, at least for home systems.
A Fluke temperature probe, Model 89T-150U was used to measure the temperature. It can be seen plugged into the top Fluke DMM.
Close-up of the probe tip against the coil
And a closer close-up
A pair of after market Super 3 cones I didn't know I had until a week ago.
Why anyone would use a roll surround on a tweeter is beyond me.
A Super 8 FS/AL coil, the one used in the above temperature test.
An unwound coil from a damaged W10FSB. For years, I thought the coil wire was bronze as that's what the B stands for. The FS is foam surround.
The wire is actually aluminum. According to the book, "A Pair of Wharfedales, the basket was bronze, yet if the paint is scraped off,
it looks like aluminum. I was later to find out that there actually is a white bronze, although rarely used.
These W10FSB's can be seen HERE.
The Super 8 FS/AL aluminum coil as seen under a microscope
The copper and aluminum coils under a microscope
And this is ............
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