Kleer assumes that you'll spend most of your time listening to these headphones wirelessly, so both the dongle and the headset come with rechargeable batteries. The AC charger in the box is fitted with a detachable USB cord on the male side for sourcing power through a computer, but SMS only includes one power set so you need to buy another USB cord if you want to charge the headphones and the dongle at the same time.
Alternatively, if you run out of juice and don't have a port to plug into, you can listen using a hardwired connection through the port on the bottom of the left earcup, and SMS Audio does provide a matching blue cable with a single-button remote installed so you can keep your audio player in a bag.
The two earcups house most of the controls you need to equalize your music, including volume and track navigation on the right side and a bass-boost button on the left. Unfortunately, since the dongle can't connect natively to the music player on your smartphone, you won't be able to use the track reverse and forward buttons unless you purchase the USB Wireless Transmitter, sold separately in the SMS Audio Web store for $80.
Headphones that operate on a wireless signal are typically interrupted by static noise from other wireless devices (telephones, microwaves, Wi-Fi network routers) on the same channel, but the Kleer technology built into the Sync headphones automatically cycles through 16 channels to find the most reliable source without interrupting the music.
The headphones never cut out in my time testing the headphones, and they also power themselves off after 5 minutes of latency to preserve battery life--same goes with the wireless adapter.
Kleer's lack of audio compression means they sound distinctively clearer than Bluetooth headphones, and a panel of my coworkers had a tough time distinguishing between a Kleer signal and a wired connection. Spatial detail and vocals are crisp and more realistic than Bluetooth's distorted tones, and the extra bass boost on the side adds body to songs that need an extra push on the low end. Using a wired connection to compare them with Ludacris' SL300s and the Beats by Dr. Dre, the Syncs have a similarly artificial frequency response with an emphasis on bass that appeals to fans of modern, beat-driven tunes.
The headphones perform adequately in noisy environments but are limited by their lack of active noise cancellation. In other words, while the Beats by Dre and the Ludacris SL300s use power to eliminate lower frequencies and selective ambient noise like the roar of an airplane engine, the Sync headphones rely on padded insulation and volume levels to filter out sound.
Additionally, the limited angular movement of the earcups in relation to the obtuse curve of the headband creates a loose seal that leaks your music to everyone sitting around you, so be cautious not to embarrass yourself blasting songs you may not want broadcast to your neighbors.
The SMS Audio Sync by 50 headphones are a trendy fashion accessory while resting on your shoulders, but their flimsy plastic housing makes me question long-term reliability. The decision to choose Kleer wireless technology over simple Bluetooth extends its utility as a home theater headset and draws the attention of audiophiles who appreciate lossless quality, but SMS needs to lower the inflated price tag and re-evaluate the hardware design before I can recommend these to active listeners.