Nothing lasts forever so, when your old, trusty set of headphones finally kicks the bucket, it means going back to the drawing board and unearth a new set of cans! This is, of course, easier said than done since there is literary bucket-loads of headphones to choose from, including Sennheiser's latest ANC headphones - the HD 450BT - which come with all the bells and whistles you could ever need!
The Sennheiser HD 450BT Wireless is entirely made of dense (non-creaky) quality plastic, including the earcup yoke, adjusting band and folding mechanism hinge. The earcups cannot be rotated flush against a surface but the earcups have a good amount of swivel (left to right) and excellent tilt adjustment, up to 30 degrees to accommodate an odd shape head. The overall footprint of the HD 450BT Wireless headset is very slender in design and well proportioned compared to most over-ear headphones. The HD 450BT Wireless don't stick out, which is perfect if you're looking for a pair of non-bulky wireless headphones.
The HD 450BT Wireless earpads can be removed and interchanged with other Sennheiser earpads, including the HD1, Momentum 2.0 and the HD 4.50 BTNC. The HD 450BT Wireless earpads are made of memory foam and protein leather material, which provide excellent cushioning. Provided that your ears aren't too large nor do they protrude, you will find the earpads provide supreme comfort, thanks to their thick foam padding (1.5cm thick) and isolation with virtually no sound-leakage at max volume.
You can easily use the HD 450BT Wireless for listening to music or watching TV while sitting next to someone or laying in bed without disturbing them. The HD 450BT Wireless earpads can also be replaced with third party velour ones, which you may end up doing since the earpads that ship with the HD 450BT Wireless headset can get really hot after long usage.
Gold beige accents can be found on the earpad fabric material and sides of the headband, including Sennheiser's laser etched branding. Despite being marketed as over-ear, the HD 450BT Wireless earpads have an oval shape with a very narrow oval opening hole that look almost on-ear. The inner dimensions of the earpads are 6cm high and 3cm wide (at the widest part). The outer dimensions are 9cm high and 7.5cm wide. The earcup depth is 2cm.
There are several control buttons on the right earcup, including a small volume rocker and a small joystick-like toggle switch which rocks forward and back to skip tracks and handle calls (answer/reject/hold). This toggle switch is also a push button and when pushed, it play/pauses the audio. The tiny bump on the volume button rocker allows the finger to grip securely onto the rocker button.
The HD 450BT headset has 32mm size drivers, which are highly sensitive (108dB) and generate a lot of volume sound without any apparent distortion at high volume. The volume adjustment is incremental but, it generates an audible beep every time you turn the volume up and down. The beep isn't overly loud but it usually works best when headphones generate a beep when reaching max volume so, you know when to stop pressing the button.
With just 32mm drivers, the HD 450BT Wireless are technically comparable to on-ear headphones, not over the ear headphones, which usually tend to integrate 40mm or 50mm drivers as a standard. A large driver size does provide a more boomy bass and better sound immersion, especially when equipped with 7.1 surround sound. There is no surround sound built-in to the HD 450BT Wireless but, it more than makes up for it by having superb passive isolation. Because sound leakage is so reduced, the sound waves bounce inside the earcup, producing a 3D-like effect that makes stereo reproduction wide. Activating noise cancellation (ANC)also increases bass response.
While the HD 450BT aren't probably as good for gaming as the GSP 601 headset, the aptX LL support and wired mode makes the HD 450BT perfect for wireless and wired gaming as long as the phone or computer Bluetooth chip supports aptX-LL. There is no seamless switching between wired and wireless; hence when the HD 450BT is connected via bluetooth and you plug in the headphone cable, the headset powers off. 
With some headphones, you can keep the bluetooth connection while in wired mode, which is convenient but, the HD 450BT headset auxiliary port is passive; hence it does not require power, which means you can use the HD 450BT headset like a regular pair of wired headphones without using up any battery. It's also worth pointing out that you cannot stream wireless audio while the headset is charging.
The power button also controls the ANC and bluetooth pairing activation.