Sony MDR-24
A cheap open-back headphone that a DIY amplifier builder reached for when he wanted to hear what his circuit actually sounded like.
Overview
The Sony MDR-24 survives less as a catalog entry than as a footnote in someone else's listening test. The clearest portrait comes from a DIY amplifier project in Audio Express (June 2003, p.36-37). The builder assembled a small capacitor-coupled headphone amp and then needed something to listen through. Alongside a Sansui SS-2 and a Best SH-50BV, he pulled out a Sony MDR-24, measured at 32Ω, and called it a "good-sounding pair." That 32Ω figure is the one hard electrical spec that survives in the record. It is low-impedance territory, the kind portable gear and simple solid-state amps are built to drive, which is presumably why it ended up in a test bench's headphone rotation.
The praise was specific. In the same Audio Express piece (June 2003, p.37), the reviewer called the headphone an open system and reported that with it "a very high sound quality was achieved (surprisingly high for such a cheap item)." So a budget Sony surprised someone who was actively measuring and listening to the amplifier feeding it. The same writeup noted the MDR-24 handled the amplifier's low-impedance damping better than the vintage closed-back alternatives on hand, whose bass came across as less controlled.
The open design had a downside, and the same review shows it. With the MDR-24 in place, the reviewer heard occasional hardness in the amp's sound. He was careful to say it was hard to pin on the headphone, the recording or the circuit's electrolytic output coupling capacitor. That kind of ambiguity is typical of open-back headphones used as evaluation tools. They leak and they don't isolate, so what you hear is partly the room and partly everything upstream. Expect no isolation, a light clamp, and a sound that flatters simple amplification rather than punishing it.
Collectors should temper expectations. The MDR-24 was a cheap item when new, and the surviving documentation treats it as a working tool. There is no confirmed production run, no original list price, and no published frequency response or sensitivity figure in the sources available here. What remains is a 32Ω open-back headphone that a builder kept on his bench because it told him the truth about his circuit.
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