Wharfedale, No. Barker, Yes.

[AvSat44]

Sifting through the eBay adverts as I do looking for Wharfedale bargains when I came upon a listing for "Wharfedale 12" Vintage Speakers England". This is on the Australian site. What first got my attention was the price. $1600.00!!! checked it out only to discover that the only thing Wharfedale about these items where the badges.
Laminex clad cabinets with metal trims around the rather unusual grill cloth where definitely not a typical Wharfedale style but I thought they must have been built by someone else.
Then I saw the pic of the drivers. A.C. Barker 12" Duode! I did a little research and discovered that there is hardly anything on the web relating to these drivers other than a few old adverts. from around 1951 and that they were manufactured in London, England.
Does anyone know anything about these drivers?

 

[stickman]

Here's an explanation of the design from the Hartley-Luth speaker website that explains how they improved upon and perfected the Barker Duode design in their 220 MSG and 207 MSG models that have a tweeter element in the middle of the woofer cone area where you would normally have a dustcap.

"
The dual voice coil in the HARTLEY speakers (220 MSG & 207 MSG) is based on a principle first developed by the

British physicist, A.C. Barker, in 1938. Barker's "duode" coil consisted of two coaxial windings, isolated by a plastic film.

By transformer action, high frequency signals imparted to the copper windings were induced on the aluminum shorted turn.

The aluminum tube could move independently of the copper windings to vibrate the speaker cone to which it was connected.

Barker's voice coil, although sound in principle, was never fully successful because he was never able to fully isolate the two

sets of windings with the materials available at that time. However, developments in synthetic chemistry have enabled us to

produce a highly compliant silicone compound, only 4 mils thin, which isolates the windings effectively and permits the

inner aluminum tube to move independently at high frequencies. The HARTLEY aluminum tube is a complete circuit not

slotted. It should be noted that in the HARTLEY speaker, the aluminum and copper windings are each connected to

respective sections of a dual cone. In the Barker voice coil, the aluminum tube was the only part of the assembly fastened

to the cone.

Electrically, the dual voice coil may be considered an air-cored transformer, modified somewhat by the presence of a small

amount of iron on the pole piece of the speaker magnet structure. The copper windings and aluminum tube comprise a

voltage step-down transformer, in which the copper turns are the primary and the aluminum tube the secondary. Signals

fed to the copper windings of the voice coil are induced by transformer action on the aluminum shorted turn. Because it is a

step-down transformer, the induced voltages are lower and the current higher than the primary voltages and currents.

Air-cored transformers are quite inefficient at low frequencies. Consequently, the current induced in the aluminum tube

begins to drop sharply at 2000cps and virtually disappears at 1000cps. An elegant way of eliminating a crossover with its

losses and distortions."

Interesting design concept to be sure.

 

[AvSat44]

Thanks for the info. The Hartley (and Barker) speakers are quite removed from the conventional designs so it seems. Rarely see Hartley in Australia so didn't really know anything about them or the Barker speakers for that matter.
According to the listing, these Barker Duode speakers are "in excellent working condition" but considering that they were manufactured in 1951, you would have to wonder about that. Also, unlike conventional voice coils, who would be able to repair them if required? I'd say that nobody in Australia would.
Then there's that elephant in the room: $1600.00. Whew!

 

[VanArn]

The Barker Duode speakers that I recall used a linen cone and the patented voice coil was an aluminium wire coil that inductively coupled to the inner aluminium tube via a latex rubber sleeve. The latex sleeve deteriorates with time and the linen cone tends to lose its shape. There were two versions of this speaker which differed only in the strength of the magnet. It is not a speaker that could be restored to its original condition. The vintage Wharfedales and Goodmans 12'' full range speakers are the ones to look out for; the condition of the cones is the important aspect to consider , as originals are unavailable.

 

[AvSat44]

Thanks VanArn. I collect Wharfies. Some might say I have to many but what the heck. The feedback that I've been getting has convinced me to let these slide. Seems like they are fraught with danger and the price had just about frightened me off anyway. Being that you are located in Melbourne you would probably know of the Magnavox brand which, along with Rola, were very popular among hobbyists in the 1960's. I purchased a pair of Wharfedale designed "Column 8" enclosures but without drivers. They sat in my workshop for about 6 months and finding it impossible to get the special "8/145" drivers, I decided to fit a pair of very good condition Magnavox 8WR speakers that I had obtained in a lot of 12 various speakers. I really wasn't expecting much but to my surprise they sound really good. I am sure it is a case of really great cabinet design getting certain drivers to punch above their weight. I was in the process of building up a system for my eldest daughter (age 24) and was in the process of refinishing a pair of small Wharfedale's for her but she now wants these. I suspect partly because they look really cool. Total cost to me for this system is around $80.00 plus a couple of hours rewiring and cleaning. We have tried them with a Marantz 1030 amplifier and it is a good combo.
Thanks again for the info. on the Barkers.