I bought these when my Klipsch S4i started dying (volume is cutting out on the left channel). Fair enough – 7+ years is a long service life for a pair of inexpensive earbuds. My first priority was compatibility with my 3G iPod Shuffle, which needs a 3-button remote to operate. The second was to get a sonic upgrade – I thought 8 years was a long time for headphone technology to improve. The third priority was form factor – I loved how small the Klipsch S4i and the iPod Shuffle were together, so I didn't consider non-earbud headphones for replacements.

There aren't a lot of "value/quality" earbuds left in the market. I paid about $80 for the Klipsch S4i in 2009 and Klipsch don't seem to make iOS (3-button) products in that price range any more – online reviews describe the descendant Klipsch S6i as bass monsters, which is too far from neutral for me. I can't afford to buy expensive earbuds because of the high probability of damage/theft with portable use. Klipsch and the other manufacturers (Sony, Sennheiser, Grado, Shure, etc.) offer mid/high-end earbuds and IEMs for hundreds of dollars, but nothing much good below $150. Other headphones I considered: Jays q-Jays (not available in Canada), Klipsch x6i, Beyerdynamic Byron (not available yet), Etymotic hf5 (no remote), Koss IL200k KTC, Shure SE215m+, and V-Moda Zn.

The M2 headphones should be easy to drive from any device with an impedance rating of 18 Ω and a SPL of 118 dB (1kHz/1Vrms). They have dynamic drivers where other manufacturers use single-driver balanced armatures. I am using the 3G iPod Shuffle and Panasonic SL-CT820 portable CD player as sources.

More specs here: http://en-ca.sennheiser.com/hd1-headphones-in-ear-with-mic

* Note: I think Sennheiser is in the process of rebranding the Momentum In-Ear (M2 IEi) headphones as HD 1 In-Ear – specifications and design appear to be identical.


Physical Appearance
The M2 comes in a nice zippered carrying case and it has 4 sizes of silicone ear adapters (XS, S, M, L). The earbuds are lightweight – not as heavy as the "stainless steel sound funnels" might lead you to believe. I bought the Black Chrome variant, which matches nicely with my equipment. The in-line microphone/controls are on the right headphone cable and they are easy to operate. The headphone plug is a slim L-shaped connector that should work in most 3.5mm jacks. The "elliptical" (flat) cables are tangle-free and not particularly microphonic – the cable is slightly long so tuck it away to prevent catching it accidentally. There is no shirt clip included with these headphones.

Comfort
The silicone ear adapters had a good seal, but they were hurting my ears after an hour (the medium size is slightly too big for me, small is too small and doesn't seal properly) – Sennheiser's circular-shaped ear adapters aren't as comfortable as Klipsch's oval ear tips. I switched them with Comply Foam Tips and now I'm able to keep them in for hours. Initially, I was hooking the cable over my ears like I did with the Klipsch (uncomfortable), but the M2 stay in without a problem with the cable running straight down – you just have to rotate them a bit until the angled enclosure lines up with your ear canal.

Isolation
Sound isolation is moderate with either type of tip (silicone or foam). The M2 aren't as quiet as full IEM designs, but they are fine for listening in medium-loud environments.

Sound Quality
Extended highs, rich bass – the Momentums have a pleasant frequency response, but I wouldn't call them reference-quality. Treble tuning is noticeably increased without being painfully bright – I noticed higher-pitched instruments and effects jumping out at me where they were previously lost in the mix with the Klipsch headphones. Bass doesn't extend to subterranean depths, but it is slightly boosted. The Comply tips seem to be less overtly bassy than the silicone tips, which is a good thing. The coloration doesn't seem to affect well-recorded acoustic instruments or vocals much. Some reviews mention a slightly-recessed midrange, but I'm not hearing that on my equipment.

Overall, the Momentum are more lively-sounding where the Klipsch were dull. Resolution is moderate – I'm not getting the same detail I'd hear on my home equipment (Arcam FMJ CD36 + Headsave Classic OPA627x3 + Grado HP-2), but they are smoother and more pleasant-sounding than my Koss Sportapros. Compared to my Alessandro MS-1 headphones, they're missing a bit of that midrange magic, but they are surprisingly close. I'll update this section as the headphones burn in. I'm not expecting them to change much.


Recommended Listening
Bran Van 3000 – The Garden
Chromeo – White Women
Groove Armada – Vertigo
Kylie Minogue – Body Language
Jane Monheit – Home
Röyksopp – Melody A.M.
St. Vincent – Strange Mercy
Matthew Sweet – Girlfriend
Various Artists – Songs from the Cool World
The White Stripes – De Stilj

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
 
Additional info: http://www.radiomuseum.org/r/sennheiser_stereo_headphones_hd_320h.html
 
DIY audio measurements: https://diyaudioheaven.wordpress.com/headphones/measurements/brands-s-se/
 
Replacement strap and jack adapter: http://headphonespares.sennheiser.co.uk/hifi-tv-headphones/hd-340m52LJs_jT6xHyVQrdcy9g
 
Replacement earpads appear to be discontinued
 
 
Recommended Listening
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

Introduction
First, the set of headphones I am reviewing is 12 years old (predating the "i" and "e" series drivers and larger cups) and I listen to them almost every day, so they've had plenty of burn-in. I recommend listening to them for a few weeks at least before making any sonic judgments – mine took at least a few months to settle into their final sound. They sounded pretty rough and underwhelming when I received them from Alessandro. For reference, I listened to a set of Sennheiser HD 320 headphones for about 10 years before switching to these, and I also listen to a set of Joseph Grado HP-2 headphones in my home rig.

Fit
These headphones fit closely to your head (aside from the protruding pivot rods). This was a big deal for me, with my small-medium size head. A lot of the high-end headphones look huge and unwieldy on my head (for example, my old Sennheisers had a plastic arch that went several inches above my head) and some were close to falling off my head at the smallest size adjustment. The other thing to mention about fit is getting the right position for the drivers over your ears. Since each person's anatomy differs, experiment with placement (forward, backward, up and down) until you get an optimum sound and comfortable fit. This is easiest to try with comfy pads – flat pads and bowls are less forgiving.

Open Design
This is a love it or hate it part of the design. Open headphones generally have a more accurate sound presentation than closed headphones (other than at the very high end), but at the expense of zero isolation. You can hear almost everything that is going on around you, and if you listen at high volumes, other people will be forced to listen to your music. Sensitivity is reasonably high, so you won't have to turn your volume up too far.

Looks and Build Quality
I've had people compliment me on my headphones – they look like the kind of headphones people used in the earlier half of the twentieth century (e.g., phone operators, studio engineers, or aviators). Build quality, materials, and finish are not particularly impressive. They do look like headphones hand built in Brooklyn. People usually cite the mold flash marks on the plastic or excess hot glue around the drivers when they criticize Grados. They are not fashionable or stylish headphones, but I put sound quality first.

Treble, Midrange, Bass
Treble is sweet and well extended at safe listening volumes. It certainly doesn't have the harshness that some people complain about with regular Grados. You can hear cymbals and brass easily without any kind of added glare or emphasis. Overall, the treble and bass are well balanced, neither overwhelm the sound of music and I find the Alessandro MS-1 more forgiving with badly-recorded or lo-fi recordings than some reference headphones. Detail retrieval is moderate. The midrange, in particular, is smooth and beguiling, inviting you to re-listen to all your recordings. Bass is well articulated, but it doesn't go to subterranean depths like more expensive headphones. With a clean, powerful amplifier, particularly one that supplies plenty of current, you can get slightly deeper bass and a more dynamic sound, but the MS-1 can be driven by most portable players with a reasonable output stage (i.e., they benefit from, but don't require a separate amp).

Attack, Decay, and Transient Response
The MS-1 sounds "fast" in that it makes more flawed headphones sound slow or boomy. More accurately, they are naturalistic, while the "fun" is lost in translation with some other headphones. Compare the sound of recordings on the MS-1 to live music and you'll see that they hold up well. The sound of strings being plucked and their resonance in the instrument body, the low boom of a kick drum, or reverb in a guitar amplifier corresponds to what you hear from real instruments. Male and female vocals are balanced, without hints of chestiness, shrillness, or sibilance other than what was recorded.

Soundstage
The traditional Grado weakness. Performers sound very close to you and they seem tightly spaced together – these aren't headphones with holographic imaging that allows you to mentally map the placement of individual musicians on stage. They're great with intimate recordings in genres like jazz, blues, or rock, but less impressive with large-scale symphonic performances or ambient mixes. You also won't get a lot of front-back or up-down auditory cues – the sound is very directly in your ears. They do have the advantage of on-ear headphones in that the drivers fire against your pinnae (your outer ear) rather than into your ear canal, providing a more natural acoustic signature.

Comfort
All the plastic-bodied Grado and Alessandro headphones are lightweight. Some people find the stock "comfy" pads (now called the S-cushion by Grado) scratchy when they are new, but they soften over time to a silky finish. My headphones are completely stock – I don't notice the plastic headband at the top very much – some people replace it with a leather one. The fit is a bit tight on your ears at first, and Grado used to recommend bending the metal headband out to fit if you have a larger head. Don't bend the band out too far or the headphones will be too loose and you will lose bass response. The drivers swivel to lay flat, but they aren't particularly comfortable to wear around your neck because the plastic headband is stiff – just take them off if you're not listening to them. I have seen some people wearing Grados on the street and apparently some people even jog with them, but I wouldn't recommend it. The headphone cable is relatively thick, heavy, and long (not too microphonic, though) and although the stock clamping force is tight, they're not really meant for active use. Also, if you are wearing static-prone clothing like a wool sweater or coat, you can get a small shock from them, particularly in the winter.

Durability
Well, they've survived 12 years, including some not-so-gentle time spent in my various bags. The plastic cable at the Y-connection has split, which I've fixed with electrical tape, and one of the rods is getting loose at the cup end (I plan to repair it with some epoxy). The first thing to wear is the silver paint on the lettering – it's cheap and easy to fix but I haven't bothered. The plastic headband is in perfect shape and the driver cups likewise. I recommend using the Alessandro MS-1 at home or at your desk... they're not really designed for portable use, being somewhat bulky compared to earbuds and in-ear phones (or even newer lightweight on-ear designs) and, though tough, can be broken at their weak points (particularly where the sliding metal rods go into the plastic cup swivels). Grado seems to do a good job repairing their headphones, but shipping might be pricey for international customers.

Pad Rolling
One of the great things about Grado headphones is the variety of foam cushions you can use to replace the stock Grado S (comfy) pads. The most commonly used replacements are the Grado L (bowl) pads, Grado G (bagel) pads, TTVJ flat pads, TTVJ deluxe flat pads, and the quarter-modded Sennheiser 414 pads. After testing a few of these, I recommend upgrading to the TTVJ flat pads. They increase overall transparency by removing the slightly absorbent barrier of the stock pads over the drivers and they use a denser foam to focus the sound. The flat pads are firmer than comfy pads at first but they break in over a period of days. Do not underestimate the effect of pads on Grado headphones' sound.

Value
These headphones are a killer value at $100 USD. Most headphones in this price range come with serious sonic compromises – these headphones compete with products far above their price.


Recommended Listening
Alison Krauss & Union Station: Live
Beck – Midnight Vultures
Blur – Blur
Feist – Let It Die
Goldfrapp – Head First
The Grassy Knoll – Positive
Hilary Gardner – The Great City
My Life with the Thrill Kill Kult – 13 Above the Night
Roxy Music – Avalon
Shivaree – Who's Got Trouble?
Shpongle – Nothing Lasts... But Nothing Is Lost
Various Artists – Verve Unmixed, Vol. 1-4