IP ratings: IPX4, IP67 and IP68

IP codes come from the international standard IEC 60529. The first digit rates protection against solids such as dust, and the second rates protection against water. An X means that part was not rated, so IPX4 says nothing about dust.

Water ratings are not automatically cumulative: according to the IEC 60529 definitions, a device rated IPX7 is not necessarily compliant with IPX5 or IPX6 (water jets). Devices that pass both are listed with both ratings, such as IPX5/IPX7. Standard testing uses fresh water, so a rating does not promise protection from salt water, chlorine or other liquids. Apple, for example, says water and dust resistance are not permanent and can decrease with normal wear, and that liquid damage is not covered under its warranty.

  • IPX4: water splashing from any direction should have no harmful effect. Fine for sweat and rain.
  • IP5x: dust can get in, but not enough to interfere with operation. IP6x: dust-tight.
  • IPx7: protected during immersion up to 1 meter for 30 minutes.
  • IPx8: suitable for continuous immersion under conditions the manufacturer specifies. Look for the stated depth and time; Apple lists IP68 at up to 6 meters for 30 minutes on iPhone 12 and later, for example.

Noise cancelling claims: treat dB numbers with care

Listings often advertise noise cancelling as a number of decibels, but a bare dB figure does not say how it was measured, at which frequencies, or whether it includes the passive blocking from the ear tips or cushions. An international standard for measuring active noise cancelling, IEC 60268-24, was published in 2023, and the US adopted it as ANSI/CTA-6015 in January 2026. A listing that does not name its method may not be comparable with another brand's number.

The more reliable comparison is a review that tests several models the same way, ideally with noise cancelling switched on and off. Pay attention to the kinds of noise you deal with most, such as engine rumble on a commute or voices in an office.

Battery-life claims: read the footnote

Battery figures depend on the test conditions. Apple's specs for AirPods Pro 3, for example, list up to 8 hours of listening on a single charge with Active Noise Cancellation on and up to 24 hours with the charging case, measured at 50% volume with a set playlist, and note that results vary with settings and use.

When comparing a cheaper pair, make sure both numbers describe the same thing.

  • Per charge or total with the case?
  • With noise cancelling on or off?
  • At what volume, and with which features enabled?

Bluetooth codecs and multipoint

A codec is the format used to compress and send audio over Bluetooth, and What Hi-Fi notes that both the phone and the headphones must support a codec to use it. SBC is built into the standard Bluetooth audio profile, so every Bluetooth audio device supports it. iPhones support AAC and SBC, so headphones advertising LDAC or aptX gain nothing from those codecs on an iPhone. LC3, part of Bluetooth LE Audio, is designed for efficiency; the Bluetooth SIG cites better quality than SBC even at a 50% lower bit rate, but both devices need LE Audio support.

Multipoint lets one headset stay connected to two source devices at once, such as a laptop and a phone. SoundGuys notes that support varies by model: some allow only a phone and a computer, others two phones. Trusted Reviews adds that most multipoint headphones play media from one source at a time.

Vacuum suction: Pa vs AW

Vacuum specs mix units that measure different things. Suction in pascals (Pa) is the maximum pressure difference the motor can create. Air watts (AW) measure output power at the cleaning end, combining airflow and pressure; ASTM International defines the airwatt from airflow and pressure. Input power in watts only shows how much electricity the vacuum uses and, as the Wikipedia overview of vacuum cleaners puts it, does not indicate cleaning effectiveness.

Pa and AW cannot be converted into each other without airflow data, so compare like with like: AW against AW, Pa against Pa. Check whether a figure is for the highest boost mode or the standard mode you will use most.

mAh: battery capacity needs a voltage

Milliamp-hours (mAh) measure charge, not energy. TP-Link explains that energy in watt-hours equals amp-hours times voltage: a 10,400 mAh lithium-ion power bank at about 3.7 V holds roughly 38 Wh. Because the output to your phone is converted to 5 V, that becomes about 7,696 mAh in theory, and conversion losses reduce it further.

In practice, mAh is a fair comparison only between similar devices. Between a power bank and a phone, or two products with different voltages, compare watt-hours.

Display refresh rate

Refresh rate, in hertz (Hz), is how many times per second a screen draws a new image. A 120 Hz screen should look smoother than a 60 Hz or 90 Hz one in scrolling and games, but What Hi-Fi notes that refreshing more often uses more power. Adaptive displays, such as Apple's ProMotion, raise or lower the rate to match the content, which reduces that cost.

For video, What Hi-Fi notes that most films are traditionally shot at 24 frames per second, so a higher refresh rate matters most for scrolling, animations and games that run at high frame rates.