As I understand it, the HD 530 (which I have and use all the time as my main headphone) is closer to the HD 600 than to the HD 595. There is no exact comparison, but genealogically, the series is HD 540, HD 530 (a later, somewhat cheaper, but also in many people's view better can), HD 560. Then there is a discontinuity, with substantial modification for improved bass, in the HD 580, HD 600, and (warmest of all) HD 650. Some purists object to these last three (thus the preference among them for AKG or Beyerdyamic); others modify them by adding Cardas or other aftermarket cable, which improves clarity and brightness.
The HD 530 is not the sharpest at the very high tones, not the deepest, and not the deepest soundstage. I have not heard the HD 540 and HD 560; (I believe (from other reviews) they are more treble-tilted than the HD 530.) These older Sennheisers are, however, wonderful in tone. (Try Bach's Cello Suites.) If you listen to classical or jazz, and especially if you listen to instrumental or voice solo or small ensembles, the 530 (or 560) is a superb choice and -- when you come across one in good condition -- a fantastic bargain. (It is not quite so nimble with a large orchestra, especially if you like to listen analytically.) The HD 530 must have a decent -- and powerful -- amplifier to sound like anything at all. Not only is this a 300 ohm impedance headphone; it is a relatively inefficient headphone (94 dB at 1KHz). I have an Onkyo rig whose integrated amp has very nice headphone output, at least for the 530. (A Sennheiser Lucas -- admittedly not a very reputable amp, is muddy and dull -- but can drive the 32 ohm impedance HD 448s with great clarity. The Lucas was designed for the HD 580, which is also 300 ohm impedance. Possibly the vintage Sennheisers just need an even more powerful amp than the 580/600/650.)
The HD 530 was apparently originally marketed for jazz -- perhaps a way of saving a niche for the more expensive and earlier HD 540. I have not heard the HD 540 or HD 560, but I've seen someone perhaps unfairly describe the 540 as shrill. No one could possibly say that about the 530. Actually, the highs are a bit rolled off. You don't even notice it listening only to the 530, but when you come back to it just after listening to a headphone with very extended and successful treble, it takes a moment to adjust. It's like turning down the intensity of the color settings on your camera. Actually, the slightly muted settings can make for subtlety, and the HD 530 is excellent at nuance. A quartet is really a conversation, and with the HD 530 that's just what you hear -- not so much an event in a concert hall (the 530 is an intimate not a spatial headphone) but four voices rendered with beautiful articulation. If the 530 was for jazz, perhaps Sennheiser designed it for the saxaphone: it's to die for in that register. As a classical listener, I especially love it for Bach's use of baroque cello, Mozart's Clarinet Quintet, or a Beethoven quartet; piano solo is also marvelous. Vocals from baritone to mezzo soprano are also simply outstanding. As for bass: the punch isn't formidable; and I think it's the absence of this which allowed Sennheiser in this case to avoid the famous "veil," which I believe was a side effect of adding much more powerful bass with the HD 580/600/650. Used for its strengths -- chamber music other than the highest notes on flute and violin -- the HD 530 would be very hard to surpass or even match in any headphone. Beyond that (in symphonies or violin concertos) it is still a refined if noticeably dated performer. (If you don't listen chiefly to classical music or jazz, this isn't your headphone.)
PS: As I'm becoming a more sophisticated listener: I do note some distortion in the HD 530 at extreme moments -- for example, in the right channel, in the opening bars of Beethoven's 5th in the Carlos Kleiber recording. Or this may just be the placement of the microphones on that recording. Also (and this has nothing to do with the HD 530), the Lucas has its limits as a music amp. In any case, the main point of my review stands: the HD 530, well amped, is lovely for classical chamber music.
For a discussion of the tonal superiority ("
Klangfarbentreue und Transparenz") of the HD 530 and HD 560 to the HD 580/600 series, see the German Hi-Fi Forum:
http://www.hifi-forum.de/viewthread-110-312.html
[Added December 2010] I just acquired some HD 560s, which I found on Ebay. These are unquestionably even better than the HD 530s. They are, however, very similar. I suspect they have the same driver, but the casing for the HD 560 creates a more natural sense of space. But the HD 530 is itself an exquisite headphone. At their respective recent price points on Ebay, they are both great buys. I also bought a Purity Audio K.I.C.A.S. amp and a Musical Fidelity V-DAC. I cannot believe what I am hearing. What marvelous choices, which I owe to reviews on Head-Fi. I mention that here just to say that these old Sennheisers are fine headphones that respond to a good source. My statement above that they "aren't the sharpest or the fastest" may have been more a reflection of the amps I was using. The K.I.C.A.S. gets a very crisp response out of them.]
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