Headphones — Koss BT115i Bluetooth

The BT115i is a Bluetooth earbud from Koss, the Milwaukee firm John C. Koss started in 1953 and best known for introducing the stereo headphone to the consumer market. The BT115i is one of Koss's simple, affordable Bluetooth models, released in 2019, with its two earpieces linked by a short cable that carries the controls and battery, intended for everyday listening and calls with a phone, tablet or laptop.

Key specs that matter

Moving-coil drivers sit in sealed earpieces, rated from 18Hz to 20kHz with 110dB SPL sensitivity. Connection is by Bluetooth 4.2, and its rechargeable Li-ion cell runs for over six hours of playback. An in-line microphone and three-button remote handle play/pause, track control, volume and answering or ending calls. The earbuds are sweat-resistant, have angled nozzles and come with small, medium and large ear cushions and a cable-management clip. The package weighs about 152g, and Koss gives a one-year limited warranty.

Engineering and use context

A dynamic driver uses a small cone moved by a voice coil in a magnetic field, the same principle as a full-size loudspeaker, and in a sealed in-ear design it relies on the seal between ear tip and ear canal to reproduce bass. That is why the fit of the tips matters so much - supplying three cushion sizes lets the wearer find the size that seals properly, which both extends the low-frequency response and blocks outside noise. The angled nozzle points the sound bore along the ear canal and helps the earpiece sit securely, so it holds its seal during movement. High sensitivity means the drivers reach high levels from the small built-in amplifier, conserving battery power. Linking the two earbuds with a cable, rather than making them fully independent, lets the battery and electronics sit in the cable housing, keeping each earpiece small and removing the need for a charging case. The Bluetooth link pairs with any modern phone, tablet or computer. The in-line remote places the controls where they are easy to reach without taking out the phone, and the clip reduces cable noise transmitted through the wire when the wearer moves. Sweat resistance protects the electronics during exercise.

Pairing

The BT115i connects to any Bluetooth device for music, podcasts and calls. Its sealed fit suits commuting and outdoor use, where isolation from surrounding noise lets it play at moderate volume.

Alternatives

Koss's own BT232i uses a similar Bluetooth platform with SportClip ear hooks for a more secure fit during exercise.