Sony / Coral 103a "Holey Basket"

As children, my brother and I were given my father's old Sony TC-630 reel to reel which we enjoyed immensely, spending many hours recording ourselves and digging through old stacks of tape. Eventually the motor died (i'm told it was replaced more than once prior to our using it) and the reel to reel was forgotten. At some point, while moving between houses the device was slated for the garbage bin but (thankfully) not before I pulled off the speaker cabinets. ...12 years later, I discovered that they contain the 16 ohm version of the 4" Coral "Holey Basket  / F103a" full range drivers.

Not the nicest looking flange...

When these photos were taken, the original speaker wire with 1/4" TRS plugs was still attached.

Sony 211-12 16ohm 5W

I mounted the speakers in an open baffle roughly 16" x 24" and let them run with some acoustic guitar music, and they definitely showed off the mid-range smoothness I have read about. I took a quick measurement to get an idea of what I was actually hearing.

Frequency response with smoothing (N=12)

Other than the dip at 1.5K, it looks OK (ignore everything below 300hz, room influence). For those that may be interested, I have some T/S numbers from DATS. Please take with a grain of salt...
SPL = 91.3 dB/W
R(e) = 14.8 ohm
F(s) = 114 Hz
Q(ts) = 0.809
Q(es) = 0.934
Q(ms) = 6.059
L(e) = 0.543 mH
V(as) = 5.47 L

Now the real question is what should I do with them? Two way with a sealed vintage 10" crossed at 400-500hz? Open baffle above an H frame woofer section? ...and do I really want a super tweeter to get some meaningful response above 10k?

BR-26 New Baffle

The somewhat unusual construction of the cabinet allows for a new rectangular baffle to be cut and installed without major modifications to the rest of the enclosure. In order to achieve this, I have fabricated a new 1/4" ply backing plate which is glued into the cabinet, forming a back stop for the new 5/8" mdf baffle.

Clamping backing plate in place

Backing plate with rough cutout to ensure driver clearance

Both drivers are flush mounted in new locations, with the woofer centered horizontally, and the tweeter offset slightly in order to make better use of the available space.

New baffle with cutouts being clamped in place

Aesthetics are not a priority at this time

Res-stuffing with the original material

 Unfortunately the Visaton woofer does not come with a gasket so I had to make my own from a sheet of fibre reinforced rubber that was in the shop.

New woofer gasket

 I hacked apart two PE buyout terminal cups in order to make a 4 conductor plate and allow for bi-wiring the drivers and external crossover adjustment.

Parts from $2 Energy branded terminals

Everything in place with temporary screws

Grill

Visaton W130S

Here are some photos of the new 5" woofer. Considering the $25 price tag, I am happy enough with the build quality, but not in any way impressed. The basket is stamped steel, which is fine, but I would have preferred a sharper edge on the exterior of the flange. I believe it might look there is a bit of a gap (as though the mounting hole is too large) when flush mounted, even when the back side of the flange is perfectly fit...

Measurements to come at a later date.

RFT BR26 Classic

RFT BR26 Classic

I purchased a pair of RFT BR-26 speakers from a garage sale in the spring of 2008 or 2009 with the intention of using them in the workshop I share with my father. I had not heard of RFT before and was not able to listen to the speakers prior to buying them, but made the purchased based mostly on the appearance of the drivers and the mass of the enclosure. I was able to buy the pair for $10, so it was not a great gamble. Unfortunately once at home and set up, the foam on one of the woofers began to deteriorate and after a few minutes of operation the surround was damaged to the point that voice coil rub was noticeable at moderate levels. I sighed and stuffed the cabinets onto a shelf in the corner and forgot about them. My set of Celestion SL-6 bookshelves made their way into the workshop and were paired up with a Yamaha CA-610 integrated amp, and then later with a nice Denon unit. In the summer of 2012 I suddenly had a lot of free time, and took interest in the RFTs.

 

Initially I began a search for replacement foams for the woofers with the intention of fixing and then selling the speakers. Finding a source with the correct roll dimensions proved to be difficult, but eventually I found a few potential candidates.

Damaged Foam - 5" Woofer

 

The reconingspeakers.com “RFK5 Angle” refoaming kit with two foam surrounds, 1.6” dust caps, glue, and shims for $16.00 seemed like best bet – until I noticed the shipping cost of $27.75. I’m not willing to pay $43.75 + tax for a set of new foams. The only other option which matched the dimensions that I could find was on ebay from “Audiofriends” out of the Netherlands. These foams are specifically marketed for the RFT BR-26 but again, the cost was beyond what I consider to be reasonable. For reference, the dimensions I measured from the speakers are as shown below. 

Woofer foam surround dimensions

Having spent some time listening to a friend’s pair of BR-26’s with good condition foams, I was impressed by the high frequency performance but completely underwhelmed by the bass produced by the original woofers. As a result, it seemed like a perfect opportunity to plan a potential upgrade by substituting a modern 5” woofer for the existing faulty one. My original goal was to find a low cost replacement (ideally a $15 MCM), but finding an inexpensive 4 ohm 5” woofer proved difficult, and almost impossible with sensitivity in the realm of 86-87 dB. In the end, the Visaton W130S was identified as the best candidate (though at $25, it is more than I had wanted to spend).

BR26 Crossover - Note Foil Inductors

Schematic from www.rft-hifi.de

Textile dome tweeter with small waveguide

The BR-26 is crossed over at 2k with a 12dB/oct electrical slope on the woofer and 18dB/oct on the tweeter.  There is a zobel on the woofer, and the tweeter has a notch filter and overload protection in the form of a 21W light bulb. The Visaton W130S’s response is smooth up past 3K, with a slight dip around 2100Hz, and in the pursuit of simplicity (and low cost) will be integrated at the existing 2K Hz crossover frequency. Fortunately the W130S should work nicely in the existing 8.5L (net volume) enclosure if converted to a sealed arrangement. This is convenient as the existing port is located on the front baffle which needs to be replaced anyways. Sealed alignment yields a Q of 0.73 and an estimated f₃ =80Hz (f₆=61Hz) with a nice smooth 12dB/oct roll off. 

The new woofer crossover has not yet been designed... I plan to prototype with a miniDSP, prior to buying passive components.

Peeling baffle out/off for replacement

Empty enclosure

Back Side