I wanted to get a pair of ATH-M40X after reading all the rave reviews, but went for M30X to save money for my birthday. So, on the big day i ordered pizzas and coke. After passing flat coke to my mortal enemies (teacher and some dumb nuts) and saving the extra cheese pizza for my friends, we decided to party.
Unfortunately, a friend met with an accident (he is alright now), so i called off the plan because I didn't want a hospitalized virgin's evil eye on my birthday and also because i felt bad for him. So, as i was contemplating on the harsh realities of life and pondering incessantly over how i have wasted most of my life chasing material joys albeit watching Johnnh Bravo on Amzon prime. Then the delivery guy came.
i savagely unboxed them with my teeth (or a cutter).On comparing it to my friend's pro 280, M30x are more musical and outright enjoyable. I was under the impression of M30x being a bit muddy and less bassy but i was wrong.
pros-1 have listened to beats solo,sennheiser pro 280(sounds too critical)and Sony xb450 for extended period of time and none of them comes even close to M30x.
2)Lightweight and comfortable.
3) Very cheap for the kind of sound they offer.
Cons-1) High impedance, Get it if your device has a solid DAC and amp. They sound muddy on Oneplus 2 but sound great on HTC 10.
2) Slightly warm sound signature, not a con but putting it out.
3) Sound stage is not expansive. It's not bad by any means.
Summing it up:
1) Highs-8.5/10 (better than the high i was supposed to have at the pub).
2)Mids-9/10
3)Bass-8.5/10 (not boomy like beats but punchy and controlled)
The added functionality of M40X with replaceable cable and lesser impedance to drive are attractive features. If you have the dough then for the M40x.
If you want something under 5k then M30x is your best bet. And don't think that you are compromising on sound quality. These just sound so right! I would pick them over pro280 (which is for 4k on amazon), beats and Sony
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Thu...

Awesome headphones.....ath m30x worth money....thnx headphone zone....received on time....excellent sound....thumbs up....:)

Before upgrading to a studio monitoring style headphones, I was used to bass heavy headphones and trust me, these headphones won't disappoint you at all if you have already changed your mindset to listening to much more balanced sounding headphones. Lows, mids and highs are nicely balanced . There is enough amount of low end for a bass lover. Though, the mids are a bit muddy in the 400-1 kHz range. Genres like rock might not sound great as you won't enjoy the snares and guitars. But, for those listening to electronic music, these are perfect for the price point. I do some casual DJing too and these can be a little bulky and uncomfortable (not a problem for me). For longer usage, oh man, these things do get sweaty. There is absolutely no sound leakage even at the maximum volume and they do cancel external noise but to some extent. All in all, they can fulfil my purpose of producing electronic music and DJing. And yeah the 15Hz sinewave on these sounds unbelievably crazy.

Seriously good they are. In this price range you won't find any better.
You won't hear those cheap booms, but clear music.

I had been using Apple and Creative earphones all my life. And then, I got these.

The difference in listening experience is so huge that you will wonder why you didn't get these headphones so long ago. Its like you have been driving a Maruti 800 and then suddenly, someone handed you a Ferrari. Audio Technica Headphones are that good. With these headphones, you literally feel the music. It's just pure, unadulterated sound.

If you got four grand to spare, buy these headphones. The best buying decision I ever made.

Audio-Technica - ATH-M30x