The Controversial Fostex/Realistic FE-103

Radio Shack Realistic 40-1197

There has been much controversy surrounding a 4-inch ďfull rangeĒ speaker labeled the FE-103. A cult following believe these tiny speakers to have excellent reproduction capabilities. Their presence and clarity are unmatched even by expensive three-way systems. So, why is this?

I think it has to do with a physical characteristic called the sound envelope. One of the factors of sound reproduction speakers with multiple drivers is the accurate mixing of frequencies of sound. Most speakers rely upon two or more drivers to extend the high and lows (frequency range) and the loud and softs (dynamic range). Accurate reproduction then becomes an issue because each speaker producing the particular frequency range must be mixed with the other speaker ranges. This becomes a problem because of the limitations of the placement of the speakers. The sound sources emanating from two or more different points can cause a mismatch or cancellation of sounds. Though this is really not noticeable most of the time, the seasoned connoisseur listener can become irritated by this. The FE-103 speaker produces all of the sound from one point thereby accurately reproducing the music. However, these tiny speakers lack considerable dynamic range including heart thumping bass that a lot of people seem to crave.

Introduced in 1968, the Bose 901 speakers attempted to address the dynamic range issue by employing nine 4-inch full range speakers. These were mounted into wedged shaped cabinets with 8 drivers facing to the rear reflecting sound off the roomís walls. To clarify the mid and high end, there was an additional 4 inch speaker facing forward. Though a nice dispersion factor was present, much of the musicís direct ambiance accuracy was lost in all of the reflections.

Why the FE-103s sounded so good at a low level listening was because the sound was directed towards the listener from one point and was accurately reproduced by the very low moving mass driver. But again, these speakers lacked a lot of dynamic range, especially on the low end. Today with all the new materials, this has become less of an issue with single driver speakers than it was in the 1960s when the paper cone FE-103 was introduced. Never the less, the FE-103 still does sound really good at low level near-field listening, especially in tiny limited-space dwellings.

Fostex P1000-E

The FE-103 has garnered quite a following since they were released by Radio Shack in the 1960s. There have probably been millions of them that have been sold worldwide under a variety of manufacturing labels. Over time, Iíve had about four or five different types of these speakers. My most recent experience is with an eBay find of a pair of Fostex FE103-SOL mounted in Fostex P1000-E ported cabinets. These I use in the bedroom.

Fostex FE103-Sol 50th Anniversary

10 cm cone shape full range speaker
Impedance: 8 ohms
Freq. response: 85 Hz - 40 kHz
SPL: 90 dB/W (1 m)
Input (MUS.): 15 W (NOM. 5 W)
mm: 2.5g
Q: 0.44
Effective vibration radius: 4.0 cm
Magnet weight: 226 g
Gross weight: 0.65 kg

My first experience was when I was 17 in 1967 when I purchased a pair of used Solo-103s from Radio Shack. These I remember as sounding rather good. Considering their size, they had remarkable bass. I never opened them up so I didnít know what drivers were used in them.

Foster 10T3 in later Solo 103s

Hoping to capture a bit of my youth, I did recently purchase a set of Realistic Solo-103s on eBay, but they sounded rather bad. When I opened them up, I discovered why. Someone had goobed some stuff on the surround which dried up. I used the proper stuff to try to loosen them up, but to no avail. However, they are not Fostex type drivers. The magnets are even smaller. Also, judging by the cabinets, I think these were cheaper versions.

I ended up putting 2 of the following in the above 1979 Solo-103 cabinets replacing the Foster 10T3s. They still donít sound all that great. Though they have better low and mids, they have less high-end than the 10T3s. They definitely donít sound as good as the Fostex FE103-SOLs.

Radio Shack 40-1197

Radio Shack 40-1197 Specifications for the 3A5 Made in Japan version:

Nominal Impedance: 8 Ohm +/- 15% at 1.6 V & 400 Hz
Resonance Frequency: 80 Hz Ė 15,000 Hz at 1.6 V
Sound Pressure Level: 90 dB/W (1m) +/- 2 dB
Power Handling Capacity: 3 W
Music Power: 15 W
Weight: 590 g (20.85 oz)

Dimensions: 80 x 40 x 10 mm
Weight: 188.5 g (6.65 oz)

Nominal Diameter: 20.32 mm (0.8 inch)
Bobbin Material: Paper
Wire Size: 0.12 mm
DC Resistance: 7.6 Ohm
Turns/Layers: 76 Turns/2 Layers
Winding Length: 5.6 mm

The Original 1960s FE-103 Japanese Version

1960s Radio Shack Realistic 40-1197

In 1974, in my third year of college, I moved into an apartment which had been occupied by some hippy who just up and left, leaving his stuff behind. One of the things he left was a set of these little homemade speakers. I opened them up to find a pair of 5A6 version FE-103s. But what was different between the Solo-103 enclosures and these was that these were build according to the Electronic Illustrated plans. They sounded better than my Solo-103s. The bass was deeper and more pronounced. Unfortunately, they were stolen in the early 80s. Notice the two letter Ss marked in the cone? I did this when I took the cabinets apart to reglue them. Ironically, it was recently when these two drivers showed up on eBay and were sold for over $150.

Electronic Illustrated Plans published in the 1960s for an acoustic suspension 4-inch speaker using the 40-1197.

A note about old FE-103s. What I have discovered to my chagrin is the older drivers have aged. The paper has fatigued due to use. Also, the glue, surround sealant, and paper-bonding have all dried up. One would be much better off purchasing a new pair of FE103s from a Fostex distributer. These are, to date, definitely the best.

SteveS, March 2017