Pros: Overall accurate, enjoyable sound, light weight, quality fit and finish, durability, easy to drive
Cons: Diffuse low bass, rolled-off top end, flat soundstage
The Sennheiser Expression series was an inexpensive, lightweight entry-level lineup of open, supra-aural (on-ear) headphones from the early 1990s comprising the HD 320 / 330 / 340 models. The headphones were designed for home listening and they were based on the same design, with different-colored exterior foam and plastic housings to distinguish each model (bright red foam, grey angled plastic grill, grey circular-holed grill, respectively).
This was my first "good" headphone, purchased from a musical instrument store in 1994. Until then, I had been using stock earbuds and on-ear headphones from my Panasonic portable cassette player, CD player, and various Koss earbuds. I made a huge leap in audio quality with the combination of compact disc technology and Sennheiser quality at home and on the go.
Speaking of mobile use, I wouldn't recommend this series of headphones for listening on the street. The combination of a light clamping pressure, a long cord, and a somewhat wobbly fit on my head meant that it was safer to wear them in a stationary position. If you have a small head, the rigid gray plastic arc over your head looks a bit bulky and ridiculous – it's fine on medium and larger-sized heads.
The HD 320 had what I considered to be deep, powerful bass and musicality. Its generally neutral presentation worked with every genre, though I didn't listen to much classical or jazz back then.
* Note: I have based my ratings on contemporary headphone performance. I owned a pair of HD 320 for 10 years and listened to them from a variety of sources (cassette, radio, compact disc) but not from a dedicated headphone amplifier. The adjustable plastic head strap broke, which forced me to retire the headphones from active use – replacement straps are still available.
Specifications (from HD 340 manual):
Frequency response: 16 - 23,000 Hz
Acoustic principle: dynamic, "open-aire"
Frequency curve: diffuse-field loudness equalization
Nominal impedance: 100 Ω
Sensitivity at 1 kHz: 94 dB ± 2dB
Power handling capability: 0.1 W as per DIN 45580
THD (as per DIN 45500): < 0,7%
Sound coupling to the ear: circumaural
Headphone caliper pressure: approx. 2.5 N
Weight (without cable): xxx g
Plug: 3.5 / 6.3 mm ⌀ stereo jack
Connecting cable: OFC signa cable, 3 m
Cardigans – First Band on the Moon
Cocteau Twins – Heaven or Las Vegas
Jane Monheit – Taking A Chance On Love
LTJ Bukem – Some Blue Notes of Drum 'N' Bass
Moloko – Catalogue
Neko Case & Her Boyfriends – The Virginian
Orbital – In Sides
Pizzicato Five – Happy End of the World
The Prodigy – Music for the Jilted Generation
Sky – Piece of Paradise