When creating the KOSS BT539i, the main emphasis was placed on compactness, namely: miniature D-shaped cups, thin headband and minimal weight. The light body looks boring, since the main plastic is dark gray, the soft inserts are lighter, and the ear pads, on the contrary, are almost black. The quality of materials and workmanship pleases, the test is far from a new sample, and the neatness is completely preserved.
Successful ergonomics are an absolute feature of the KOSS BT539i: no matter how much you shake your head, the headphones stay in place. This is the merit of a tight hold and a low weight at 172 grams. The D-shaped ear cups fit precisely to the contour of the ear and provide optimal hold. The leatherette ear cushions are durable and practical. But hours-long gatherings are questionable, since the thin headband still begins to press on the top of the head.
Connecting KOSS BT539i to the device is simplified as much as possible, just select the headset in the Bluetooth settings. The signal strength allows you to leave your smartphone in the middle room and move around the apartment without interference, which came in handy for me during cleaning. The audio in the video is perfectly synchronized.
On the right earcup are five physical buttons that work when connected wirelessly. In the center – a multifunctional key to enable / disable, pause delivery and answer a call; the rest adjust the volume and switch tracks. Headphones do not create a second level, but adjust the system volume. Large spacing between buttons and visible notches help you navigate blindly. The only gripe – loud clicks when triggered are given to the right ear.
Alternatively, you can use the wired AUX connection, with a 3.5mm jack on the right earcup. In this mode, button control and built-in microphone are not available. The set includes a simple wire with straight plugs in a rubberized blue sheath.
Sound and microphone
When using Bluetooth, the built-in DAC is responsible for sound processing, so this particular mode should be considered optimal, while paired with AUX, the character largely depends on the source. The sound is smooth, that is, without noticeable frequency distortions. Only in music filled with instruments can one notice a lack of highs, but this is corrected by an equalizer. The trademark relaxedness of KOSS, creating a feeling of a concert hall on the ears, is present! The manufacturer only discloses data on a closed acoustic circuit. The diameter of the installed emitters is kept secret, but according to my measurements, it is 40 millimeters.
At the bottom of the right earcup is the only microphone for headset mode. Its opening is far from the mouth and picks up all the surrounding noise, so with the KOSS BT539i you can only answer a call in a quiet room. On a windy street, the interlocutor begins to complain about poor intelligibility.
built-in 230 mAh battery;
declared operating time: up to 12 hours of continuous listening to music;
real time: 15 hours of continuous music and podcast playback at medium volume;
charging via microUSB.
Real testing at medium volume gave 15 hours of battery life, which is a third more than the stated time. The status bar does not display the remaining charge level. The only way to know the battery status is with audible alerts and red light blinking when low. The first warning appears half an hour before discharge.
Charging via microUSB on the right earcup. A full charge takes about 30 minutes, after which the indicator turns blue.
Simple and unpretentious wireless headphones for every day, just such a characteristic can be given to the KOSS BT539i . I was especially impressed by the durability, the tested sample retained the state of the new headphones after 2-3 years of careless use by reviewers. The sound is balanced, the wireless connection works smoothly, and the battery is easy to stretch for a week of use.