Sennheiser HD-490
A 70-ohm open-air headphone pitched at the Walkman crowd and, by Sennheiser's own catalog copy, the cream of the 400 series.
Overview
Sennheiser put the HD-490 at the top of its 400-series open-air line, and the distributor literature says so bluntly. One catalog calls it "cream of the 400 series." Another says it employs "all of the technology of Sennheiser's more expensive models." The second phrase tells you more. The HD-490 was not a cost-reduced flagship. It was a hand-me-down of the good stuff: neodymium-ferrous magnets, aluminum voice coils and field-replaceable parts, the same building blocks Sennheiser used further up the range, packed into a low-impedance format for portable listening.
The electrical spec is the whole story here. At 70 ohms, the HD-490 sits far below the 600-ohm loads that dominated Sennheiser's studio-oriented open-air models. The catalogs are explicit about why: this is a headphone for "on-location monitoring" or for listeners who "prefer portable walkman-style listening." A 600-ohm phone wants voltage behind it. A 70-ohm phone will make sound out of a weak portable output. The same distributor copy bills the HD-490 as "Sennheiser's finest low impedance headphone," which is a marketing claim and not a measurement, but it shows which buyer the model was drawn for.
The driver construction gets more specific than catalog copy usually does. Sennheiser's literature credits "triple-wound aluminum voice coils" for better low- and high-end reproduction, the idea being that the extra winding geometry buys extension at both extremes instead of a midrange-focused compromise. Whether the triple winding is the cause or just the marketing hook, the published frequency response backs up the intent: 18 Hz to 22 kHz, a wide figure for an open supra-aural design of this generation. The catalogs also call the HD-490 "digitally compatible," period shorthand for a phone whose response reaches high enough not to roll off the top of the CD band.
Sensitivity is quoted at 94 dB SPL at 1 mW/1 kHz, with total harmonic distortion under 1% at 94 dB SPL. That pairing is sensible, since the distortion figure holds at a realistic listening level and not only at a whisper. Weight without cable is listed at 4.8 ounces. The trade-off is the familiar one for open designs: isolation is essentially nil, and nearby conversation comes through about as clearly as the music does.
The cable is a 10-foot stranded-steel cord ending in a stereo mini plug with a 1/4-inch phone adapter. The catalogs note that replacement cushions, drivers and cables are available for the model. Sennheiser's distributor network was explicitly stocking spares for the HD-490 alongside the rest of the line.
Pricing in the surviving distributor literature is inconsistent, as you'd expect from dealer catalogs printed at different moments. One lists the HD-490 at $102.00. Another shows a manufacturer's list of $129.00. A third quotes an "E.I. Price" of $78.95, with a second figure of $104.95 elsewhere on the same page. Treat the $129 manufacturer's list as the anchor and read the lower numbers as dealer or jobber pricing. The spread is a discount structure, not a contradiction about what the headphone was.
Period reception is thin in the archive, but what survives is favorable. HiFI-Stereo (July 1991, p.42) tested the German-made phones and found the sound well balanced and free of obvious colorations, with more than enough available volume whether driven from a home music system or a personal portable. The same report noted the replaceable foam cushions and normal-size earpieces. It also observed that above several kilohertz, headphone response is shaped as much by the individual listener's ear as by the driver.
What the HD-490 is, then, is a document of a specific moment: Sennheiser taking the materials and construction of its serious studio headphones and re-tuning them for a low-impedance, portable-first world. The 70-ohm load, the 18 Hz–22 kHz window, the 4.8-ounce frame, the replaceable everything — those numbers describe a headphone designed to be used hard and kept running.
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