First, although K240 phones old and new surround your ears, they are vented.  Ambient noise is not reduced greatly as a result, but this design improves sound quality.

I have used the 600 ohm K240M phones since 1986.  The new K240S are 55 ohms making them far more compatible with todays lower voltage gear.  Even better, this new design gives deep bass response that I never thought was possible from phones.  Even a 32 foot bombarde pipe organ stop sounds quite real, although you will not feel the room shake.  Listening to a signal generator through these new K240S phones gives an impression of powerful bass down to at least 40 Hz.  The old K240M drops off below 100 Hz.  A slight dip in the midrange(K240M) has been filled in, making the K240S more true sounding.

Both the new and old versions reproduce operatic voices without increased "ping" which can be very abrasive.  Years ago I started using phones to judge voices on choral recordings, resorting to speakers only to judge the organ sound.  Speakers can make some beautiful voices sound nasty.  Producer John Culshaw documented this in one of his books on recording the Wagner Ring.

The open air design minimizes ear sweating while giving a more open perspective.  "In your head" effects are greatly suppressed compared to many sealed type phones.  When watching opera DVD I find no conflict between the phone perspective and the TV screen on DVD that are well mixed.  Orchestral sound is excellent, as is piano.  To my ears, these phones give a perspective and tonal balance that is very close to what I hear at Boston Symphony Hall, when I sit in the second balcony front.  These seats overhang the stage.  When I sing in a choir, the live perspective is even closer to what the phones produce, provided my position on stage is fairly central.  This is, in my opinion, a valid sound perspective, even if it is quite different from the tenth row center sound I aim for when I build speakers.  Non performers sometimes have trouble accepting this close a perspective at first, only because it is not familiar.  Many other phones give a perspective that is too close for comfort, a good reason to avoid the low end.

It is good to bear in mind that individual ears are unique in shape and that phones are designed to work on a "standard ear" made with an average shape.  Phones will give different response curves depending on how your ear pinnae and canal differs from that "laboratory standard ear" shape.

People with small heads will have trouble keeping the phones on.  It is unfortunate that although this problem has been known for years, nothing has been done to correct this.

AKG did not change any parts that touch your ears and head, a very wise move.  Some parts are interchangeble, as they have the same stock number on AKG parts lists.  Unfortunately AKG has of late been hard to deal with, making part purchases difficult.

Consider buying the K 240 studio phones in the MK II version as you get a spare cord and spare ear pads with a velvet like feel. Having these extra parts on hand is worth the extra cost and makes this four star item a 5 star item.
First, although K240 phones old and new surround your ears, they are vented. Ambient noise is not reduced greatly as a result, but this design improves sound quality. I have used the 600 ohm K240M phones since 1986. The new K240S are 55 ohms making them far more compatible with todays lower voltage gear. Even better, this new design gives deep bass response that I never thought was possible from phones. Even a 32 foot bombarde pipe organ stop sounds quite real, although you will not feel the room shake. Listening to a signal generator through these new K240S phones gives an impression of powerful bass down to at least 40 Hz. The old K240M drops off below 100 Hz. A slight dip in the midrange(K240M) has been filled in, making the K240S more true sounding. Both the new and old versions reproduce operatic voices without increased "ping" which can be very abrasive. Years ago I started using phones to judge voices on choral recordings, resorting to speakers only to judge the organ sound. Speakers can make some beautiful voices sound nasty. Producer John Culshaw documented this in one of his books on recording the Wagner Ring. The open air design minimizes ear sweating while giving a more open perspective. "In your head" effects are greatly suppressed compared to many sealed type phones. When watching opera DVD I find no conflict between the phone perspective and the TV screen on DVD that are well mixed. Orchestral sound is excellent, as is piano. To my ears, these phones give a perspective and tonal balance that is very close to what I hear at Boston Symphony Hall, when I sit in the second balcony front. These seats overhang the stage. When I sing in a choir, the live perspective is even closer to what the phones produce, provided my position on stage is fairly central. This is, in my opinion, a valid sound perspective, even if it is quite different from the tenth row center sound I aim for when I build speakers. Non performers sometimes have trouble accepting this close a perspective at first, only because it is not familiar. Many other phones give a perspective that is too close for comfort, a good reason to avoid the low end. It is good to bear in mind that individual ears are unique in shape and that phones are designed to work on a "standard ear" made with an average shape. Phones will give different response curves depending on how your ear pinnae and canal differs from that "laboratory standard ear" shape. People with small heads will have trouble keeping the phones on. It is unfortunate that although this problem has been known for years, nothing has been done to correct this. AKG did not change any parts that touch your ears and head, a very wise move. Some parts are interchangeble, as they have the same stock number on AKG parts lists. Unfortunately AKG has of late been hard to deal with, making part purchases difficult. Consider buying the K 240 studio phones in the MK II version as you get a spare cord and spare ear pads with a velvet like feel. Having these extra parts on hand is worth the extra cost and makes this four star item a 5 star item.