Fostex FE108-SOL Limited Production 4" Full Range

Fostex FE108-SOL 4" Full Range

Special Limited Production
Made in Japan

The FE108-Sol has been developed to be most suitable for use in back-loaded horn. This model is built using the technologies we have cultivated over the years. It consists of a large magnetic circuit, supported by highly rigid frames, with a lightweight and highly responsive vibration system. The speaker provides excellent response, typical of a small-diameter full-range speaker. It offers a well-balanced low frequency, a delicate and powerful midrange, and a naturally extended high-frequency. We hope the music will deeply immerse and move you.

• ES cone diaphragm with double layered paper making technique High density ES cone made of fine and smooth fiber produced by the double layered paper making technique offers light weight but high rigidity and high internal loss. The base layer mainly consists of long-fiber pulp, which provides high rigidity and internal loss due to thickness rigidity. The surface layer is made of short-fiber pulp, which increases the propagation speed on the surface of the cone paper. This has preserved the bright, pasty tone of the mid-range and enables reproduction of highs with good rise and sharpness and bass with thickness. *Double layered paper making is our proprietary technology, which involves crafting cone paper in two distinct stages, resulting in a single cone paper comprising two layers: a base layer and a surface layer.
• Large ferrite outer magnetic circuit A Φ100mm ferrite magnet is used in the magnetic circuit to ensure sufficient magnetic flux density. The pole section is covered with a copper cap to reduce current distortion. This enables powerful music reproduction.
• Highly rigid aluminum die-cast frame A highly rigid aluminum die-cast frame is used to support the large ferrite magnetic circuit and to prevent unwanted vibrations from being transmitted to the enclosure. *Frame outline: Φ128mm, Mounting hole pitch: Φ115mm, Baffle aperture: Φ102 to Φ103mm
• Mechanical 2 way center cap The center cap is directly connected to the voice coil bobbin in order to extend the high frequencies to over 20 kHz.
• Gold plated terminal The input terminal is a low-loss, gold-plated fastener, specifically the #205, which ensures a stable speaker connection and minimizes sound deterioration.
• Manufactured in Japan This re-release model reproduces the specifications of the previous release from December 2015, now with Japanese domestic production.

A folded horn enclosure will deliver the best performance.  Use the QR code on the inside flap of the box to see the complete manual.  Here is PDF link to that information.

Can also be used in the BK12m folded horn kit.

Sealed box of 0.05 cubic feet for an F3 of 190Hz

Vented box of 0.15 cubic feet with 1.5" diameter vent by 4" long for an F3 of 84Hz

Vented box of 0.20 cubic feet with 1.5" diameter vent by 3" long for an F3 of 74Hz














Frequency response graph from the folded horn enclosure.



This is an example of the FE108-Sol in a back-loaded horn enclosure. Proceed with assembly according to the assembly order.
When assembling the Middle plate, draw positioning lines on the Side panels in advance to align them. When bonding boards
together, it is recommended to use an additional amount of adhesive to prevent gaps. Sound absorbing material should be placed
on the Middle plate #9 in the air chamber. Use wool (recommended) or felt as sound absorbing material.