After trying lots of noise cancelling (NC) headphones, Philips SHB9850NC stands out as the satisfactory pair - comfortable, effective NC and good sound for less than $200 (got mine for $82 during the holidays).
However, ever since I put them on, I felt too much bass. I took off the ear cups to see what I can do about that:
The first thing I noticed: the large oval foam rings are off their supposed tracks. I tear carefully them up and put them back on the tracks. This correction should give better seals which is important for noise isolation.
I then removed the two white round tapes to reveal the two small holes.
These two holes release resonance and thus reduce booming bass. Now they sound like monitor type headphones without excessive bass. If you want a little more bass after fully opening the holes, then you may try to block partially the holes, or use a mask tape with a tiny hole. The larger the hole, the less bass and less efficiency of NC. I used a 1/32" - 3/64" drill bit.
Or insert a tiny piece of foam into the hole to reduce bass but without letting treble out to degrade NC and sound quality:
I like this foam tweak the most - very clean and sweet sound.
Also insert a little bit of foam into the two Mic holes to avoid wind noise while running or riding a bike etc.:
One more tweak you must do is to insert some foam into the ear cups. Not only far more comfortable, better sound stage too!
You can have lots of fun with these tiny holes and some foam!
The clapping force is still too much, not comfortable after an hour or two; so I bend the headband like this:
Don't worry, you cannot break it because the headband is made of steal (but grab and bend the top part only, or you may break the two plastic seats that connect the top and lower segments):
Now this Philips is perfect, except just one thing - the stupid touch panel. To let the touch to work is like to win the Lottery.
Some notes on NC headphones
I tried more than 10 pairs of NC headphones and earbuds. The top Audio-Technica (priced at $200) have four microphones like this Philips for effective NC, but the speakers in them are bad sounding. They sound very poor when NC is turned off; Bose is the same. The Sennheiser PXC 550 is the only perfect NC headphones, but they cost $400, insane. For only $82 during this Black Friday, this Philips is currently the only choice if you don't want to pay a leg or arm for a good pair of NC headphones.