Sennheiser PXC 550 vs 66 Audio BTS Pro

The feature works really well in preventing outside noise from intruding into your music listening experience. Also, there are very little to no reports of a feeling of pressure in the ears when the feature is active.

The sound tuning of these headphones is focused on the lower frequencies. The bass is quite powerful with good sub-bass extension. Users who listen to a lot of hip-hop, dance and bass-heavy music will certainly enjoy the oomph that these headphones can give. The mids sound natural and smooth, yet the lower regions of these frequencies can be overwhelmed by the powerful bass. The highs are crisp and clear though, which prevents the sound from getting too muddy.

Soft foam and leather are used in the interior and exterior of the ear pads respectively which makes them feel really soft and smooth on the head. The same material choices can be found in the headband.

The Smart Pause feature detects if you are removing or putting on your headphones. These gestures will trigger the music to pause or play automatically.

When in wireless mode, you do not need to use buttons in order to control the functions of the headphones. The right ear cup lets you control the headphones through touch gestures. You can swipe left or right for next or previous track, swipe up or down to increase or decrease the volume or tap on the ear cup to pause or play track as well as answer or end calls.

You can set just how much noise is cancelled by the headphones, from maximum active noise cancelling, to an ambient mode which allows some sound into the headphones. You can also turn the feature off entirely.

These headphones are quite effective at preventing sound leakage, and also passively block out noise really well. This is achieved by the closed ear cup design along with the effective seal from the leather-surfaced ear pads.

You can twist the ear cups and then fold them into the headband for a smaller, more travel friendly size. In this state, it should take up a lot less space inside your bag for less hassle when used on the go.

Sennheiser offers the CapTune smartphone app which allows users to see the battery level of the headphones, adjust the headphones' EQ, and control other functions.

The case is made from a tough fabric material which should protect the headphones from minor bumps and scratches.

The BTS Pro is quite robust and can withstand some minor splashes of sweat or rain as these are sweat-proof. They are not completely water-proof though, so you should not get them soaking wet.

There is good detail in the highs and the mids can also be heard clearly with very little muddiness. The lower frequencies are boosted, resulting in a good level of depth and power to each bass thump.

The BTS Pro ear cups sit on the ears with hooks keeping them in place. The flexible connecting band provides good clamping force and can adjust to your head size with continued use. Combined with cushioning on the cups, these are comfortable to wear and will stay in place.

Bluetooth connectivity allows the BTS Pro to connect with smartphones and compatible music players wirelessly, so cables won't be an issue.

66 Audio's Motion Control iOS App gives users added functionality, including EQ control and presets selection, battery status indicator, and even headphone position tracking. These features can improve the listening experience and also minimize the chances of you losing these headphones.

With up to 40 hours of playback time at full charge, it's more than enough for most listening sessions. You won't have to charge these frequently.

A hard shell carrying case is included, which can protect the headphones from minor impact and also make transport much easier. The case also has good aesthetics.

They are easy to bring on the go as the ear cups can be folded into the headband. This further reduces the already slim and compact size, making them easy to chuck into a bag when on the go.

The right ear cup of the BTS Pro features buttons for controlling headphone features. You can play/pause tracks, increase/decrease volume as well as answer/end calls by pressing the corresponding buttons, negating the need to pull out your phone to do so.

You do not need to take the BTS Pro off in order to answer incoming calls. There is a built-in microphone which allows you to easily take or make calls in the middle of your run or workout.