Headphones are available with high or low impedance (typically measured at 1 kHz). Low-impedance headphones are in the range 16 to 32 ohms and high-impedance headphones are about 100-600 ohms. As the impedance of a pair of headphones increases, more voltage (at a given current) is required to drive it, and the loudness of the headphones for a given voltage decreases. In recent years, impedance of newer headphones has generally decreased to accommodate lower voltages available on battery powered CMOS-based portable electronics. This has resulted in headphones that can be more efficiently driven by battery-powered electronics. Consequently, newer amplifiers are based on designs with relatively low output impedance.
Released in 2017, the Bose QuietComfort 35 (Series I) are essentially the exact same headphones as the Series II. They have the same design, feel, sound quality and noise-canceling skills. The difference is that the Series I don’t have Google Assistant built-in and a dedicated button on the left ear cup to activate it. If you don’t care about talking to a virtual assistant while wearing your headphones, which allows you to play/pause music or skip tracks via a verbal command, then Series I or Series II shouldn’t matter to you. The catch is that the Series I is more difficult to find online and they aren’t usually that much cheaper than the Series II.
Until now, the best true-wireless earbud features like noise cancellation or hands-free access to voice assistants were something you could only have if you spent well over $200. So when Amazon introduced its Echo Buds for just $130 with onboard Bose active noise reduction, IPX4 water-resistance, hands-free Alexa access, and a customizable fit, our only question was: Do they sound good?
Earbuds have small speakers that rest on the ear canal of the wearer. These are usually much less expensive than on-ear and over-ear headphones and reproduce the sound well. However, outside sounds, such as traffic or power tools, can get past the earbuds and interfere with your enjoyment. Earbuds also don't stay in place very well if the wearer is moving much, such as exercising. These also are lower fidelity than on-ear and over-ear headphones.