Nagaoka Tetsuo Designed BS-10 Fostex & Koizumi Wireless Collaboration FK10P Equipped

Width: 186 mm, Height: 260 mm, Depth: 190 mm
Approx. weight: 2.2 kg
Set of 2 units

These are bass-reflex speakers designed by Tetsuo Nagaoka, model BS-10 (L-shaped folded slot), featuring the 10cm full-range FK10P unit, a limited production of 500 pairs co-developed by Fostex and Koizumi Musen. They were featured in the Music Friend Publishing's Audio DIY as a weekly magazine-sized bass-reflex speaker. Published in 1975 (Showa 50). At the time, there was no model number, but this is an early design by Mr. Nagaoka that later gained a solid reputation.
As shown in photos (4, 5), the front, top, and back panels of this unit are 15mm thick. The side panels are 18mm thick, and the bottom panel is 21mm thick, all made of birch plywood. The finish is three coats of Turner water-based milk paint (Snow White) applied with a roller (photo 11).

The white parts of the mounted unit are the sub-cone paper (photos 7, 8), making it a double-cone design.
The opening size on the front baffle is 93mm.
The diagonal mounting size for the unit is 116mm, with M4 T-nuts installed. This size can accommodate many 10cm full-range units as is.

FK10P Specifications (quoted from datasheet)
Lowest resonant frequency: 74Hz
Impedance: 8Ω
Playback frequency range: 74Hz - 35kHz
Output sound pressure level: 86dB
Input: 36W
Moving mass (mo): 3.7g
Effective radius of vibration (re): 4cm
Magnet weight: 271g
Total weight: 645g
Baffle opening: 93mm
*Unused, stored item

Comparative Listening Impressions (personal opinion) (photo 12)
1. My own build using Fostex FE103En, conforming to the manufacturer's standard bass-reflex design. The 103 has high efficiency and a sense of sound diffusion. I had high hopes for this unit's high frequencies up to 35kHz, but it was just okay. Overall, the 103 sounds lively and boisterous, while this unit exudes a calm atmosphere. It's a matter of personal preference which you prefer.
2. Double bass-reflex speaker using the German Visaton 10cm full-range FR10 unit. It has beautiful high frequencies, but perhaps due to insufficient aging, the sound is stiff and the bass is lacking. This unit is superior.

Please understand that this is a homemade item by an amateur. There may be imperfections in the craftsmanship, scratches from the manufacturing process, and unevenness in the paint. Please judge based on the photos. The cones will be protected with bubble wrap and shipped in a used cardboard box.