The JBL D120 is a 12-inch full-range speaker adapted for instrument amplifiers in the early 1960s. It is made of an all paper cone and surround and is distinguished in its Fender amp version by its orange basket. The D120 has a distinctive sound made famous by artists as varied as Dick Dale and Duane Allman and is known as one of the best guitar amp speakers ever made.
Improved Voice Coil
This is an alteration of the preceding model D130F to allow more tolerance in mounting. The widened gap results in less than 1 dB loss in speaker efficiency, but improves the ability of the D120 to resist warping when the speaker is attached too tightly to the cabinet.
Aluminium Dome Cap
The aluminium dome cap is originally used simply for cosmetic reasons. Over time, however, it was discovered that it produced a slight amount in top end response of bass frequencies.
Up until the development of improved materials in the 1970s, alnico magnets were considered a lightweight, yet powerful JBL magnet material. Alnico, as the name indicates, is an alloy of aluminium, nickel, cobalt and copper. Aluminium and copper particularly covered the reproduction of a wide range of musical frequencies.
Viscous Damped Surrounds
JBL developed a high viscosity coating to add to the its Hi-Fi line of speakers. The coating reduces woofer ringing. It was applied to guitar amp speakers to prevent the drying out of surrounds that temperature variations would wreak on them.
The distinctive orange baskets (seen clearly on the backs of the speakers) are part of the distinction that went into the OEM D120s sold to Fender. Fender Amps were the largest single buyer D120 component loudspeakers, and this led to the designation D120F.