Loudspeakers

I discuss the original 770 in our boxout so we see that, over 40 years later, the 'new' 770 is almost exactly the same size but heavier, slightly more sensitive, offers improved extension while still being an easy drive for most amplifiers. Specifically, the minimum impedance is a relatively high 5.8ohm/4.9kHz while the toughest EPDR of 3.0ohm occurs at 3.3kHz, ensuring the 770 is 'friendlier' than average. There are suggestions of 'color' from the 770, however, its forward response [see Graph 1, below], measured on the tweeter axis, shows a mild ~1dB bump around 1kHz (possibly a cone/surround mistermination) associated with a resonance on the CSD waterfall [Graph 2] and on the nearfield of the 200mm polypropylene woofer. The same is true of the series of undulations from 2-5kHz, just prior to the 4dB presence band dip at 6-7kHz, pushing up the response errors to ±3.9dB and ±3.8dB, respectively (re. 200Hz-20kHz).

Otherwise, pair matching is a good 1.5dB while the overall response trend is flat or slightly downturned up to ~6kHz – and further emphasised by the magnetically-attached grille [blue trace, Graph 1] – prior to an upturn in treble of +3dB/18kHz. The polyester dome tweeter hangs on to a respectable 34kHz (–6dB re. 10kHz). The bass/mid unit has a 50Hz-500Hz bandpass (–6dB) supplemented by the low 27Hz tuning of its flared reflex port to deliver a very impressive 34Hz bass extension [–6dB re. 200Hz]. By way of payback, while the 1kHz response 'bump' lifts sensitivity to 87.2dB at this reference frequency, the 500Hz-8kHz average is a more representative 85.5dB, somewhat short of the 88dB claimed by IAG's Mission. PM