Gear note: For this review I used an HRT HeadStreamer DAC/Amp connected to a PC using Foobar2000 to play FLAC-format music tracks, and also an iStreamer DAC connected to an iPhone4s and pre-assembled Objective2 by JDS headphone amp to play 320k CBR MP3 conversions of my FLAC tracks. The FLAC tracks range from 44 to 96 khz depending on their source.
Based on use with the headphone amp and using the iPhone sans amp, the H/K CL's efficiency is greater than average for this type of headphone. Testing with an iPod Nano (touchscreen variety) and average-volume tracks that are lower in volume than what Amazon or iTunes typically sells, I can still get volume well above loud, and loud for me is pretty loud.
Getting to the sound first, the Harman/Kardon CL is treble shy, and so I used Treble Booster EQ on the iPhone and the equivalent EQ setting in Foobar. This review is based entirely on that EQ'd sound since I found that even with that EQ setting, the treble still did not come up to the level that my other headphones have - Philips L1, ATH M50, Shure 1840 to name a few. Compared to my B&W P5 and Bose OE2 headphones, the treble of the H/K CL is lower than the P5 and slightly greater than the OE2. All of the following comments are based on the EQ'd sound, and the H/K CL's sound is high fidelity. The highs have no tendency to be sharp, edgy or sibilant. It's interesting to note that the H/K CL, B&W P5 and Bose OE2 all have the same basic earpad design.
The mids are very good, and whether anyone would perceive them as slightly forward or recessed will depend on the recording itself, since there is no significant midrange peak or dip that I can detect. The bass is not as strong as the ATH M50, but the M50 sound is slightly emphasized in the upper bass and moreso in the lower bass. While I like the M50's bass better than the so-called neutral bass of the Sennheiser HD800 for example, the H/K CL's bass is much closer to the neutral variety, but it's not shy in any sense of the term - it goes all the way down without rolling off.
I don't know how many reviewers rate the overall sound quality of their headphones according to their price, but it's reasonable to assume that some of them do. I don't exactly do that, but I would like to point out that the lower the price of a hi-fi headphone the less likely that the drivers will be precisely matched, or that all of the samples of that headphone model will sound alike with very small variances. In the case of the H/K CL, looking very close at the build quality and finish, it looks good enough to suggest that the drivers and other internals are probably spec'd very closely as well. With approximately 20 hours of play time so far, I don't hear any major changes in the sound.
The H/K CL is a supraaural (on ear) closed-back headphone. The cable is single-sided and detachable, disconnecting at the earcup. The stereo miniplug has the Apple i-device configuration, and where my Objective2 amp doesn't make a secure connection with some of those, the H/K CL cable works perfectly. The end that plugs into the left earcup is a 2.5 mm stereo sub-mini plug. The cord is 2.5 mm thick and looks fairly durable. It's much thicker than the B&W P5's cord, which is comforting to know. If you needed a replacement cable and couldn't get the H/K CL cable right away, any cable with a 2.5 mm stereo plug on one end and 3.5 mm stereo plug on the other end should work as well, without the Apple controls of course. There is no 6.5 mm (1/4 inch) adapter plug supplied with the H/K CL.
Construction is all metal with an inner/outer headband design, where the inner headband is leather padded. Two outer headbands are supplied and the smaller of the two is mounted on the headphone by default. I switched to the larger headband, even though the smaller headband worked well by pulling the earcups down further. There are no slider or click-stop adjustments on the headband, so the fit is accomplished by placing the padded inner headband on top of your head and pulling the earcups down. I've had other headphones that work this way, but none of those were as instantly-fitting or as comfortable as the H/K CL. The clamping force is lighter than average for a closed-back headphone, and while I don't feel any excess warmth wearing it indoors, it may get slightly warm outdoors on a hot day.
The H/K CL is slightly larger than the B&W P5, but that alone would not be a factor in portability - i.e. the ability to pull the earcups down on a headphone and wear it around your neck all day when not in use. Since the earcups on the H/K CL pull down by stretching, they return to the retracted position when worn around the neck. This particular arrangement may not be satisfactory for some people but I get along with it. The earcups fold flat and sit right on my collar bones which doesn't bother me, but your experience may be different. The earcup rotation is excellent either direction so getting a good fit on different head sizes and shapes should not be a problem.
Walking around with the headphone on, it didn't have any tendency to shift on my head, but leaning forward or making other moves will cause it to shift unless your hair blocks it from moving. The H/K CL comes with a soft plastic carry pouch which would protect it from dust, but I would prefer a rigid compact carrycase for use in airline luggage etc. The H/K CL's isolation is moderate - high frequencies are attenuated well, but mids are suppressed less than 10 db from what I can tell. Leakage is very low so use in a corporate cubicle would be no problem even at fairly high volumes.
Now that I've covered the basics and the sound, it's time to describe how the H/K CL sounds with a variety of music that's available on CD's or as high-quality downloads from Internet music stores. I've used the following examples in other reviews, so these will serve as good test tracks for this review and the results can also be compared to the results noted in the other reviews.
Bauhaus - Bela Lugosi's Dead (~1980): Strong midrange sound effects - this is a good worst-case test for resonant-type sounds in the most sensitive midrange area. Handled very well by the H/K CL.
Beethoven Symphony 9, Solti/CSO (1972): Good overall sound although the H/K CL reproduces the triangles, bells and other high-frequency instruments with less detail than my other more expensive headphones. Of special note for this headphone are the bass impacts beginning around 10:30 of the fourth movement. It's a good headphone that has such a strong, solid deep bass impact yet no significant mid or upper bass emphasis.
Blues Project - Caress Me Baby (1966): Rarely mentioned, but one of the greatest white blues recordings ever. The loud piercing guitar sound at 0:41 into the track is a good test for distortion or other problems. Handled well here.
Boz Scaggs - Lowdown (1976): Good sound quality - this is a great test for any nasality in the midrange. Handled well by the H/K CL.
Buffalo Springfield - Kind Woman (~1968): A Richie Furay song entirely, rarely mentioned, but one of the best sounding rock ballads ever. This will sound good on most headphones, but it's very good with the H/K CL.
Cat Stevens - Morning Has Broken (early 70's): A near-perfect test for overall sound - this track will separate the best sounding headphones from the lesser quality types. Nothing specific, except that almost any deviation from perfect reproduction will stand out with this track. Sounds good with the H/K CL.
Catherine Wheel - Black Metallic (~1991): Goth with industrial overtones - I like this since it's a great music composition and the sound effects are smoothly integrated into the mix. This may sound distorted or mushy with some headphones, but the H/K CL renders the deliberate instrumental distortions clearly.
Def Leppard - Bringin' On The Heartbreak (1981): MTV goth/pop/metal at its best - good ambience and high energy - the better headphones will separate the details and make for a good experience. Lesser quality and the details tend to mush together. Sounds very good with the H/K CL.
J.S. Bach - E. Power Biggs Plays Bach in the Thomaskirche (~1970): Recorded on a tracker organ in East Germany, the tracks on this recording have the authentic baroque sound that Bach composed for, albeit the bellows are operated by motor today. The H/K CL plays the tones seamlessly through the upper limits of the organ, which cover nearly the full range of human hearing. Of special note are the pedal notes - tracker organs have low-pressure pipes and don't typically produce the kind of impact around 20-35 hz that modern organs do. A headphone that's lacking even a little in the low bass will sound especially bass-shy with this type of organ, but the H/K CL delivers the full experience of this music.
Jamming With Edward - It Hurts Me Too (1969): Intended originally as a test to fill studio down time and set recording levels etc., this was released a few years later for hardcore Rolling Stones fans. Although not as good technically in every aspect as the Chess studio recordings of 1964, and in spite of the non-serious vocals by Mick Jagger, this rates very high on my list of white blues recordings, and sounds absolutely delicious with the H/K CL.
Jimmy Smith - Basin Street Blues (early 60's): This track has some loud crescendos of brass and other instruments that don't sound clean and musical on some headphones. The H/K CL provides good reproduction. Listen particularly to the second crescendo at 15 seconds in, for maximum detail effect.
Ladytron - Destroy Everything You Touch (~2009): Featured in The September Issue, this song has heavy overdub and will sound a bit muddy on some headphones. Sounds OK with the H/K CL.
Milt Jackson/Wes Montgomery - Delilah (Take 3) (1962): The vibraphone is heavily dependent on harmonics to sound right, and the H/K CL plays it very well.
Pink Floyd/Dark Side of the Moon - Speak To Me (1973): Strong deep bass impacts will be heard and felt here.
Rolling Stones - Stray Cat Blues (1968): Dirty, gritty blues that very few white artists could match. On some headphones the vocals and guitar lack the edge and fall more-or-less flat. If you're a really good person, playing this song will probably make you feel nervous and uneasy.
Tony Bennett - I Left My Heart In San Francisco (1962): Frank Sinatra's favorite singer. Highest recommendation. With some of the best headphones, the sibilants on this recording are very strong, but they're not an issue with the H/K CL.