DIFFUSICONE - EIGHT and UL-HC
PHOTO 1
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PHOTO 2
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C15HC DUAL IMPEDANCE HIGH COMPLIANCE WOOFER
Two views of the C-15HC
PHOTO 3
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PHOTO 4
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FIGURE 1
Impedance curves. |
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FIGURE 2
Near field response curves. #7 green: the longest one is the 15 incher. It can be seen to be quite good to 500 hz. #36 black: the 8" diffusicone. The sweep was stopped at 500 hz as the gating becomes erratic at close to 400 hz due to the wavelength approaching the distance of the nearest reflection. It can be seen to be pretty decent to about 4 khz although it could be pushed to 10 khz, depending on one's listening preferences. The horn tweeter (blue) tested here isn't intended or implied to be used in this particular combination. It's output is rather disappointing but may be due to dust or dirt in the voice coil gap. Taking the unit apart was abandoned due to it's not wanting to co-operate. The red curve is the blue curve increased by 14 dB using the LMS software. It's response is very similar to the 8" with the exceptions of a much better response above 10khz and to 15 khz. and its being much smoother, not to mention not having a dip between 2khz and 3khz, centered at 2.5khz. |
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FIGURE 3
The two upper traces are for the Diffusicone 8, black-on axis and green-30 degrees off axis. The three shorter traces are those of the tweeter, mounted with the longer axis vertical. Blue-on axis; red-30 degrees off axis horizontally and dark blue-30 degrees off axis vertically. From the latter two, the tweeter should be mounted with its longer dimension vertical, as it is a diffraction horn. |
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RED
CURVE
Optimum tuning, 9.4 ft^3 Driver Properties |
FIGURE
4
Vented Enclosure, bass reflex
These curves show the level normalized to 0 dB. The high end rolloff is due to voice coil inductive reactance and the low end rolloff is due primarily to the excursion and thermal limitations as well as cabinet loading and tuning. The vent tuning for these alignments are to allow maximum excursion to Xmax, sometimes referred to as maximum power vent. These are the curves for the particular unit I have. The annulus has been softened with acetone and lacquer thinner. It was treated several years ago but that data was lost due to a drive failure. The next set of curves are those of the pre-treated annulus. If you have a way to measure the fundamental (free air) resonance of your C-15HC, the alignments here can be used by selecting the one with the closest Fs to your unit.
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YELLOW CURVE Practical tuning, 5 ft^3 Driver Properties |
RED CURVE
Optimum tuning, 16.4 ft^3 Driver Properties |
FIGURE
5
Vented Enclosure, bass reflex
The untreated annulus. The fundamental resonance, Fs was reduced from 39.77 hz to 30.84 hz. The minimum cabinet volume was chosen at 9 ft^3; at 5 ft^3, the peak at 60 hz was about 5 dB higher which would be very objectionable. Even this 5 dB peak can be objectionable with male voice and cello, depending on one's preference.
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YELLOW CURVE Practical tuning, 9 ft^3 Driver Properties |
TREATED
Driver Properties
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FIGURE
6
Sealed Enclosure A comparison between the untreated and treated units in a sealed enclosure. There isn't much difference between them but the response is 6 dB down at 50 hz. Admittedly, the sealed box will give a better transient response and a bass boost will bring up the bottom end although that can be risky with such an old speaker. The adhesive holding the voice coil winding and layers together have also aged by some 55 years. I had a 60 year old Wharfedale aluminum voice coil come apart with less than 40 watts.
Yellow = closed 4.8 ft^3 grey = vented 1.6 ft^3 both are optimized volumes These two curves are those of an untreated C15W with an Fs of 70 hz. The annulus was very hard and stiff, due to age+. It's difficult to tell it apart from the C-15HC without looking at the label on the magnet cover. The speaker, when new, had to have had an Fs of 28 hz or lower, as would have been the case with the C-15HC. Both units have dual voice coils that can be wired for 4 to 8 ohms or 10 to 20 ohms. |
NOT-TREATED
Driver Properties |
University Diffusicone Twelve
PHOTO 5
These were found on ebay in Dec, 2018. The one on the left a couple of weeks before the other, which, in all probability, has never been used. When I saw the first, it was in such nice condition, I couldn't resist. Since I have a pair of Diffusicone eights, the second was even harder to resist. Thesy are intended for use as full range units, not woofers in a multi-way system. However, a tweeter may be added for extended high frequency response above 7khz.
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PHOTO 6
FIGURE 7
Closed box alignments for each speaker. the slight difference is due to the new speaker probably not having ever been used, thus a stiffer suspension. Design 1 uis 2.3 ft^3 Design 2 is 2.0 ft^3 |
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FIGURE 8a
The theoretical response with a continuous power input of 35 watts. |
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FIGURE 8b
While the maximum electrical input power may seem low in the band below a25hz, keep in mind that the resonant points of the speakers is around 100hz. For a constant voltage applied to the speaker, the power transfer will drop as the impedance rises. It, the power transfer, will be at its lowest at resonance. |
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FIGURE 8c
Cone displacement vs frequency with a constant 35 watts applied. |
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FIGURE 8d
This is the calculated impedance of the speaker in the optimum closed (sealed) box. |
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FIGURE 8e
Ideally, a straight line is desired but a gradual rise is quite acceptable. This is better than many modern drivers. There are two curves here, one for each speaker. |
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FIGURE 8f
Again, very close to the ideal straight line. Remarkable for such an old speaker. these units go as far back as the late fifties to early sixties, making them some 60 years old. |
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FIGURE 9
The light green curve is that of one of the Diffusicone Eights The twelve (pink curve) is quite impressive, not having any seriously high peaks and dips. The darker pink and green curves between 20hz and 300hz are the near field responses of the 12 and 8 inch units, resp. The pink curve correlates well with that of the Custom Amplitude Response of Bass Box Pro. (Fig. 8a, above) A near field response wasn't performed for the eight. Of course, while these curves may look good, they surely don't give a total idea of how they will sound, much less whether one would like them or not. |
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FIGURE 10
This set of curves is for easy comparison of the various alignments. The red and orange are for optimum vented enclosures. They'll give the better bass response, lower in frequency compared to the optimum closed box, white curve. The compromise is that the vented boxes are around 6.5 cubic feet. The green curve is that of a vented box of 3 cubic feet, the design on the left. The vent can be any rectangle of 108 sq. in. cut into the front baffle. It is normalized for a vent length of 3/4 inch, the assumed baffle thickness. This will give that juke box sound remembered by those of the fifties who gathered at the local soda pop fountain shop after school. https://www.fiftiesstore.com/jukeboxes.html
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University Diffusicone Eight
This shows the Normalized Amplitude
Response for the 8" unit in 3 different size boxes. Two closed
and one vented.
This unit, I believe, is intended for use as a full range, not a mid-range. CLOSED BOXES Red: 1.2 ft^3 optimum Orange: 0.2 ft^3 my test box VENTED BOX Yellow:1.5 ft^3 The vent area is 10.5 sq.in. and normalized for a tunnel length of 3/4". ALL cabinets have heavy fill. A wire mesh on the inside of the baffle over the vent is recommended. NOTE A 1.5 ft^3 box can be fitted with a removable panel over the vent to change the alignment to one's preference. |
FIGURE 11
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DIFFAXIAL EIGHT UC-82
PHOTO
7
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PHOTO
8
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FIGURE 12
Inside whizzer is at cone apex BLACK Near Field inside whizzer ORANGE Near Field outside whizzer RED 1/4w-1m gated |
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FIGURE 12a
Added some 7 years later using CLIO. This shows the THD The response, although not gated, is similar to the red trace of fig 12 THD is about 1% between 1khz and 6khz and about 0.32% between 200hz and 1khz which is remarkable considering the age of this speaker, dating to the early sixties, over 60 years old. |
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FIGURE 13
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