Audio-Technica AT-9400
Fifty dollars bought a genuine one-point stereo condenser in 1987 — and a laboratory surprise that beat the spec sheet.
Overview
The AT-9400 is a one-point stereo microphone: twin unidirectional electret condenser elements sharing a single high-impact plastic case, angled 120 degrees apart, feeding twin mini-phone plugs through a permanently attached cable. Audio-Technica pitched it at cassette deck owners who wanted stereo ambience without buying two microphones and a stand — the kind of buyer recording a choir concert, a wedding, or a conference. At a suggested $49.95, it cost about $25 per channel, which is the sort of number that usually signals disposable consumer gear. The lab results told a different story.
The published specs are modest on paper: 60 Hz to 17 kHz, 1.5 kilohms per channel, -53 dB sensitivity referenced to 1 mW per 10 dynes/cm². The microphone runs on a single internal AA cell, ships with a swivel mount threaded 5/8-inch-27, and measures 8 7/16 inches long with a head roughly 2 1/4 by 1 1/2 inches. It weighs 7.1 ounces — 201 grams — which is light enough to sit on a desk stand without complaint but heavy enough that the plastic body feels like a real object rather than a toy. The cable runs 9 feet 10 inches, and the whole package includes a slip-on desk stand and the AA battery.
What makes the AT-9400 interesting is what happened when it was actually measured. Audio (November 1987, p.132) ran it through a full equipment profile and found the axial response rising smoothly from 40 Hz to 19 kHz — a range that beats the published spec at both ends. That is not a common outcome for budget microphones, and it is the single best argument for the AT-9400 as a used purchase today.
The capsule layout deserves attention because it explains the sound. The two cardioid electret elements sit with coincident horizontal axes, only about an inch apart, rather than on the common vertical axis most professional stereo microphones use. Audio (November 1987, p.136) noted that this arrangement is genuinely good: the elements are close enough together that the stereo image stays coherent, and the axial pickup direction makes the microphone easy to aim. The 120-degree angle between capsules is a sensible fixed choice for amateur use — wide enough for a real stereo spread, narrow enough to keep rear reflections and room noise out of the recording. The reviewer measured a 120-degree included angle between the capsules by backlighting the wire cage, since Audio-Technica supplied no documentation on capsule orientation.
That missing documentation is one of the real frustrations. Units arrived in lightweight cardboard boxes with only brief data printed on the outside — no instruction sheet at all. Audio (November 1987, p.136) argued that a detailed instruction sheet would have cost Audio-Technica almost nothing and helped the user considerably, and that judgment holds up. Owners report having to work out the 120-degree pickup window and the correct on/off switch orientation (facing up) by trial and error.
The measured impedance came in at 920 ohms per channel — well below the rated 1.5 kilohms, and consistent across both samples tested. That is high compared to the 150-ohm ratings typical of professional microphones, but it means the AT-9400 does not load down the inputs of typical cassette recorders, which is exactly the equipment it was built for. The unbalanced output means long cable runs are a bad idea; a 30-foot shielded twisted-pair extension worked cleanly in testing, but the reviewer explicitly advised against going longer on any unbalanced microphone.
Handling noise is the practical weakness. The one-piece plastic body is neither shock-mounted nor insulated, so any recording made while touching the microphone will pick up the handling. The AT-9400 needs a stand or a desk mount — it is not a handheld. The all-plastic casing is appropriate for the price, and the cable and connectors are of genuinely good quality despite it.
In use, the microphone behaves like a proper stereo tool. Audio (November 1987, p.136) recorded a cappella choral work with it and found the pickup clear and clean, with a good stereo spread and adequate rejection of side and rear noise and unwanted ambience. As an ambient microphone on a rock session, though, the gain had to be pushed high enough that hiss became a problem — the reviewer noted that careful attention to miking distance and source levels avoids it, but it is a real limitation for quiet sources at distance. For classical orchestral work, some equalization may be wanted; the reviewer suggested the microphone suits organ well but benefits from a graphic EQ on orchestra, using the published axial curves as a guide. The rising high-frequency response that flatters muddy pop vocals will also brighten a naturally dark hall, and the bass roll-off that helps in small boomy rooms will thin out a large ensemble.
The vertical-plane behavior is worth knowing. Only the left capsule was tested vertically, and rejection at 120 degrees in that plane is poor — apparently traded for the extra rejection measured horizontally. The rectangular cage cross-section means vertical and horizontal responses do not match, which matters if the microphone is ever tilted rather than kept level. The L+R summed response stayed essentially flat with no deep nulls up to 19 kHz, so mono compatibility is not a concern.
Collectors and recordists hunting one today should expect the obvious: check that the AA compartment is clean, confirm both channels are live through the twin mini-plugs, and test for capsule cage damage given the exposed wire grille. The swivel mount and the 1/4-inch plug adaptors are frequently separated from the microphone on the used market, so a complete example is worth more than a bare one. The AT-9400 was sold as a low-cost accessory, not a prestige item, and surviving examples turn up cheaply — which is precisely why it remains a sensible first stereo microphone for anyone recording to cassette or to a modern portable recorder through the mini-plug inputs.
It is not a professional tool and was never meant to be. What it is: a genuinely competent coincident stereo condenser that measured better than its own spec sheet, sold for the price of a decent dinner, and let a generation of home recordists capture real stereo perspective without a mixing board. That is a more interesting legacy than most budget microphones manage.
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