Etymotic Research hf2 & hf5 in-ear headphones
Conventional audiophile thinking would have Mead Killion, PhD, who founded Etymotic Research in 1983, introducing a new flagship model to take advantage of the new price paradigm. But Killion isn't so much an audiophile as an audiologist, with multiple patents on hearing aids and hearing-aid amplifiers to his credit. Instead of going for a top-this product, he decided to top himself by getting the performance of his classic ER-4 model in a better form and at a cheaper price.
Etymotic's hf5 lists for $149, the hf2 for $179. Both offer what Killion claims is virtually identical performance to the ER-4 and to one anotherthe difference between the newer models is the presence on the hf2 of an inline microphone that makes it compatible with an Apple iPhone.
The biggest difference between the ER-4 and the hf2 and '5 is that the individual driver modules of the ER-4 are replaceable, whereas they're molded to the cable in the newer models. The ER-4's replaceable modules allow for precise matching of the drive-units; the hf2's and hf5's modules are matched within 2dB over the entire range.
There are other differences. The ER-4's cable was quite stiff, making it microphonic, which could be distracting when listening on the move. The hf2 and hf5 have more supple cables whose microphony is very low, if not nonexistent. The cord terminates in a molded, reinforced, 3.5mm plug. The plug for the hf2 is angled, which is more convenient than the straight-out plug employed on the hf5 and many other portable headsets (footnote 1) (a response to Apple's ham-handed inset headphone jack on the original iPhone and iPod Touch).
As in other iPhone-compatible headsets, the microphone in the hf2 is spaced at about mouth distance from the right driver and includes a small button that lets the user pause the player to use the phone. Not using it on an iPhone? No problemit'll pause your iPod, too, as well as let you skip to the next track. I found this feature far more useful with my iPod Touch than I had anticipated, especially as its Start/Stop and Skip functions worked even when the player's own controls were locked. The hf2's microphone and control features mean it differs in another way from the hf5: Its minijack has four contacts rather than the conventional three-segment stereo model.
Other vital stats: Both models have a single balanced-armature driver (as does the ER-4S), a nominal impedance of 16 ohms, and employ user-replaceable filters to achieve their final response curves. That's rightthose tiny little filters inside the hf2s and hf5s do more than keep earwax out of the transducers; they're part of Etymotic's EQ strategy.
Etymotic bills the ER-4, hf2, and hf5 as being diffuse-field-response dynamic transducers, which requires a bit of explanation. As explained by Keith Howard in the August 2008 issue of Stereophile, one standard for headphone (and hearing-aid) response is free-field equalization, which mimics the on-axis frequency response of a loudspeaker in an anechoic chamber. Diffuse-field equalization mimics the flat frequency response of a speaker in a reverberant room, where the sound arrives at the ear from all directions (hence diffuse-field). Neither frequency response is truly flat, but the goal is to mimic flatness at the eardrum. This difference in design and listening philosophies accounts for some of the measured differences among highly respected headphone models (there's also a flat-EQ school of headphone thought). Suffice it to say that Mead Killion is a proponent of the diffuse-field philosophy, and was a co-author of a pioneering paper on the subject (footnote 2).
Footnote 1: My preference is for a right-angle plug, which places less mechanical strain on the player's jack when pushed from the side.John Atkinson
Footnote 2: Mead C. Killion, Elliott H. Berger, and Richard A. Nuss, "Diffuse field response of the ear," J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S75-S75 (May 1987). See http://dx.doi.org/10.1121/1.2024388.