EMT BX-20
A studio reverb that fewer people realize wasn't built by EMT at all. The documentation trail is a mess of misattribution.
Overview
The first thing a collector needs to know about the "EMT BX-20" is that the name is a trap. The BX-20 was an AKG product, a stereo spring reverberation unit. It turns up in period documents as the AKG BX20, the AKG BX-20, and sometimes, thanks to sloppy catalog copy, under EMT, because it sat in the same studio racks as the EMT 140 plates and EMT 240 gold foils. Anyone searching for an "EMT BX-20" today is almost certainly looking for the AKG unit. The archive treats the identification as unresolved pending better documentation. That ambiguity shapes how this gear is bought, sold, and argued about.
The clearest contemporary description comes from a 1972 trade demonstration report. According to Studio Sound (January 1972, p.52), the BX20 was a stereo spring reverberation unit with a decay time of 2 to 4.5 seconds, independent control of each channel, and channel separation better than 60 dB measured to DIN 45405. A decay of 2 to 4.5 seconds is long for a spring device. Independent per-channel control put it in a different class from the mono spring tanks in cheaper studios. The same report described a single-point pendulum mounting system giving a remarkable degree of insulation against external vibration. It was claimed to avoid feedback even in the immediate vicinity of monitor loudspeakers at up to 100 dB SPL. Spring reverbs pick up footfalls, door slams, and bass cabinets, and the pendulum mount was AKG's answer.
Price, per that same 1972 report, was £975 including the remote control unit. That is a serious figure for the era. This was a professional studio tool, not a budget spring tank. The remote control unit implies the reverberation chassis could sit away from the console. Studio Sound (June 1973, p.52) reviewed the BX20 in depth and observed that it could be mounted in a studio console located at practically any distance from the reverberation unit, since the control signals were DC and therefore unlikely to pick up interference over the run. In practice the noisy, vibration-sensitive spring chassis could live in a machine room while the engineer worked the controls at the desk.
For period testimony on the sound, there is a working producer interviewed in Recording Engineer/Producer. He singled out the AKG BX20 as a favorite and praised a good example as a very warm echo that doesn't sound "springy" at all. He also conceded that there was a big difference between individual units and that you needed a good one. Spring reverbs vary unit to unit, and the BX20's reputation rests on the good ones. The same interview called the EMT 240 gold foils sometimes a little noisy and expressed love for the old EMT 140 plate. That helps explain why the BX20 got filed mentally alongside EMT gear even though AKG built it. Studios ran them side by side, and the BX20 held its own against plate reverbs costing far more.
Period studio inventories document the unit in professional rooms repeatedly. A facility profile in Mix (April 1980, p.28) lists an AKG BX20 reverb alongside EMT 250 and 251 digital units, a pair of EMT 140 plates, and a Lexicon 224. That is a late-1970s room where the BX20 was the analog spring option in a rack otherwise dominated by plates and early digital. A separate used-equipment listing from the same era prices an AKG BX-20 Echo Chamber at $2,600 and a BX10 at $1,500, with EMT 140S plates at $4,000. That puts the BX20 at roughly two-thirds the cost of a plate on the used market, and well above the smaller BX10. Another dealer listing shows a BX20 at $2,500. These are period asking prices, not current market values.
The documentation does not establish production years, total units built, or a definitive statement of who manufactured what under which name. The "EMT BX-20" designation appears to be a cataloging artifact rather than a factory model, and the archive flags the identity as unresolved. Buyers should check the badge on the actual unit before treating any listing as an EMT product, since an AKG BX20 will carry AKG markings. The engineering is well attested: a stereo spring system with 2 to 4.5 second decay, better than 60 dB channel separation, independent channel control, and that pendulum mount. The period accounts suggest a good unit was never guaranteed.
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