Vifa C17WH-69-08 + SEAS 27TFFC
Copyright 2006-16 © Troels Gravesen

CROSSOVER     CABINET     MEASUREMENTS     OLD C-17 DRIVERS

2-way d'Appolito
Get 95 dB/2.8 volts sensitivity for your low-wattage amp - in case it runs 4 ohms speakers.

Go to: C17-II
Go to: C17-III
Go to: C17-IV

Workshop set-up with a d'Appolito arrangement in 39 litres vented cabs.
These speakers are sensitive! Watch that volume knob before you turn on the music.

The Vifa C17WH-69-08 is a "special" driver. Special because it's so ordinary - probably made in tenth of thousands - and special because a lot of things went right with this driver. Sometimes a driver turns out to have the right cone material and coating for a given size, thickness and weight; the right voice coil diameter; the right surround providing the right damping to cone motion; the right magnet size to provide useful TS-data, etc. When all the individual parts are made right, the result may be better than what we might expect from the sum of the parts.
A curvilinear cone like this will mostly have a smooth frequency response compared to a straight-sided and deep cone like the Philips 9710 and this Vifa C17WH-69-08 is no exception. It's basically flat up to 2-3 kHz and what happens above, is a series of modest resonances that are easily taken care of in the crossover. A straight sided cone, like the Philips 9710, has great bass performance, but above 2-3 kHz the response rises some 10 dB and sharp filters are needed.

So here we have a stamped metal chassis, thin paper cone and a foam surround. Some 15 years ago we might have rejected this driver as a useless old-timer. Yet it must be one the most often used drivers. Basically it costs nothing and some may reject this driver due to the fact that it carries a foam surround that will rot in 15-20 years time. Applying some thin silicone liquid to the foam may extent its lifetime but don't use silicone spray due to the solvent used. It must be pure silicone with no additives. The type of silicone that comes in a bottle with a small brush is usually good. A foam surround may be one of the tools to make a better than average midrange presentation. Foam surrounds are still around - and for good reasons. G. A. Briggs found the foam surround superior to corrugated paper and cloth some 45 years ago - but unfortunately didn't compare with rubber. Very little can be found in the books of Colloms and Dickason on the impact on sound and overall performance of drivers due to various outer surround materials.

As long as the C17WH is not forced to play excessively loud, it can deliver some of the best midrange performances available . If driven too loud, it starts sounding compressed, but which driver doesn't? Well, the Audio Technology 15H52 is one, but that's another story for the wide baffle section. The C17 is found in numerous versions, most often the "WG", fitted with a smaller magnet and allowing decent bass from a small cabinet. The "WH" has a larger magnet and sensitivity around 90-91 dB/2.8 volts and from two in parallel we may expect minimum 95 dB/2.8V. However, this will result in an impedance of 4 ohms, or rather 3.5 ohms. So possibly not the ideal partner for single ended triodes. But push-pull triodes and small class A amps may like it a lot. We'll see. (I've already had the question if the "WG" can substitute the "WH" in this construction and the answer is no. Different driver = different crossover and box tuning).

The C17WH-69-08 is not an easy driver to find and it is no longer in the Vifa catalogue. I found a local dealer having some boxes of C17 drivers and I bought four. Try a Goggle search for "Vifa C17WH" and you will find a few dealers still having these drivers.
Make sure the foam surround is looking reasonably fresh and do the nail test before buying. Squeeze a nail into the foam close to the perimeter of the surround and if you are left with a mark and the foam doesn't rise again, we have an old surround that may only last a few years.
This driver came to my attention from visiting a guy having a speaker system from a single C17WH-09-04 in a rather special box. For mid the Vifa was supplemented by an excellent 3" Brazilian pp upper midrange (Bravox) with foam surround, and for treble a 25-something SEAS tweeter. The C17 was housed in an 18 litres vented enclosure where a square, wooden "vent" was loaded by a short exponential horn. I haven't got the drawings but I'll try to push him hard to reveal some more details.

The C17 is also very well know from the Living Voice d'Appolito and a low-cost version is some 1500£.
http://www.livingvoice.co.uk/home.htm.
Now, Living Voice may possibly use 10 ohms (DC resistance) drivers to make an overall claimed impedance of 6 ohms. I haven't seen any reviews including measurements on this speaker. The Living Voice is using a C17 version with a larger magnet compared to this C17WH and the crossover appear to be 6/12 dB and an LCR circuit is keeping the impedance flat in the midrange. To have the C17WH contributing in the treble area may be appealing to some, but to me it isn't. Having the treble beaming at you due to a large cone is not nice, neither from the C17, nor from any other driver.

The C17WH is very much in family with the old SEAS CA17RCY, which Wilson Audio used in the first WATT and the first WATT/PUPPY. The SEAS CB17RCY is heavily coated and has a rubber surround with some trouble around 1 kHz due to a non-optimised outer suspension. The new SEAS CA18RNX has a really strange frequency response profile and some 2-3 dB lower sensitivity compared to the old drivers. I really wonder if it is as bad as it looks from the brochure.

Vintage SEAS CA17RCY.

SEAS 27TFFC tweeter having just enough sensitivity to cope with 2 x C17WH-69-08.

Workshop C17WH set-up with an AudioTechnology middriver following the event.

Crossover:

TS data
Measured with the CLIO and added mass method used (10 grams).

Cabinet:

Measurements:

PS: While writing the draft of this article I had the offer of an original pair of C17WH-09-08 drivers. These are from 1982 and are still going strong. I'll add the measurements asap and we'll see how these drivers did some 25 years ago.

Here's the Vifa codes on drivers.

C17WH-69-08

C = steel basket
17 = diameter
W = woofer
H = 90 mm magnet
69 = custom, coated
08 = impedance.

The really old drivers:

   
Left: 30 years old C17WH-09-08. The foam surround has never been changed, but my guess is that these surrounds
will not last another 10 years unless the drivers are kept away from any UV light.
Right: Current C17WH-69-08.