AKG D-321
A vocal mic built to survive a seven-foot drop onto a hard floor - and the transducer inside is the strangest part.
Overview
Pick up a D-321 and the first thing you notice is the housing. It's die-cast zinc alloy, painted a non-reflective dark grey, and it has the heft of something made for road duty. The spec sheet claims it will take a compressive stress in excess of 1000 lbs. and survive a 7 ft. drop. Most vocal microphones don't advertise that, and it explains why the D-321 turns up in working collections decades after it left the factory.
The transducer is where the D-321 gets unusual. AKG's own literature describes a magnet suspended on an elastic element instead of rigidly fixed, with the diaphragm tuned to the same resonance frequencies. A mechanical shock excites both magnet and diaphragm in phase, so neither produces an output signal. No rumble, no handling thump. Airborne sound moves only the diaphragm while the magnet stays put, so full sensitivity is preserved. Light tapping on the body reportedly produces no electrical output at all. Whether the system is worth the complexity is a fair debate, but it's the reason collectors pull these apart to look inside.
The D-321 is a hypercardioid dynamic vocal microphone. The pattern is tighter than cardioid, which means better rejection of stage wash and monitor bleed. The cost is a more pronounced rear lobe that will punish careless monitor placement. The diaphragm is tuned for the human voice, and AKG's documentation highlights proximity effect as a deliberate tool, particularly in the 150-200 Hz region. Work the grille close and the low end thickens. Back off and it cleans up. That's standard behavior for a directional dynamic, but the D-321's tuning makes the effect usable rather than muddy.
Frequency range is quoted at 40 Hz to 20 kHz with sensitivity at 1 kHz listed as -57dBV. Contemporary listings for AKG's microphone line in Mix Magazine (October 1985, p.126) cite a cardioid polar pattern with a 50-18,000 Hz frequency response and 200-ohm nominal output impedance. Read those numbers with a raised eyebrow. A 40 Hz - 20 kHz figure on a dynamic vocal mic is optimistic, and the sensitivity is on the low side, so the D-321 wants a preamp with real gain rather than a budget interface input. Starve it and it sounds thin and lifeless.
A patented built-in XLR connector secures the mating cable, so there's no dangling connector to stress, and a captive locking screw holds the cable in place. AKG's copy notes the housing allows a full 360° cable swing without launching the connector. Two shock-absorbing baskets protect the transducer element, and there's a dual windscreen/pop filter up top. The mic ships with an SA-41 stand adaptor and a vinyl case. A D-321S variant adds an on/off switch.
AKG also built the D-321 into its Wireless Modular System line, alongside the D330, C535 and CK67. Those systems use LN compander circuitry, selectable carrier frequencies, twin antenna receivers and automatic best-signal selection. That's useful if you find a transmitter body and wonder what capsule family it belongs to, though the wired D-321 is the version most collectors encounter.
In the AKG dynamic lineup, the D-321's hypercardioid pattern and road-hardened construction set it apart from the cardioid D-190E and the large-diaphragm D-112. Those two do different jobs: the D-112 on bass instruments and kick, the D-190E as a general-purpose cardioid. The D-321 is the vocalist's tool. Its -57dBV sensitivity is lower than the D-112's -55dBV and the D-190E's -53dBV, which matters if you're swapping between them on the same preamp.
Expect cosmetic wear on the dark grey finish and check that the captive cable screw is present and threads cleanly. It's a small part that's easy to lose and annoying to replace. Verify the capsule hasn't been crushed or the baskets deformed. The shock-mount system is tough but not indestructible, and a mic dropped hard enough to deform the housing may have a compromised suspension. Given the design's tolerance for abuse, most surviving examples should still function, but test before you buy.
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