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Boult Audio K40 specifications and in-depth review

Boult Audio K40

Manufacturer: Boult Audio

The Boult Audio K40 are true wireless earbuds designed for everyday use, combining a lightweight in-ear fit with a cable-free listening experience. Built around a 13 mm driver unit, they cover the standard 20 Hz to 20,000 Hz frequency range and incorporate passive noise isolation to help reduce ambient sound during use. The earbuds carry an IPX5 rating, making them resistant to sweat and light moisture.

On the connectivity side, the K40 use Bluetooth 5.3 with AAC codec support and deliver a stated audio latency of 45 ms over a maximum wireless range of 10 metres. The earbuds themselves offer 8 hours of playback, while the included charging case extends total usage to 40 hours; USB Type-C charging is supported, and fast charging is available. A quad-microphone setup with noise-canceling capability handles calls and voice input, and onboard controls are accessible directly on the earbuds. The package also includes a travel bag, and the product comes with a one-year warranty.

Pros
  • The charging case extends total battery capacity to 40 hours, making extended use between full recharges practical
  • Fast charging support helps reduce downtime when the battery runs low
  • Four microphones with noise cancellation improve call clarity in noisy environments
  • Bluetooth 5.3 with AAC codec support provides a stable and reasonably capable wireless connection
  • A travel bag is included in the box, adding convenience for portability
  • IPX5 sweat resistance makes the earbuds suitable for physical activity
Cons
  • No active noise cancellation, which limits the ability to block out persistent ambient sound
  • Wireless charging is not supported, requiring a cable every time the case needs to be recharged
  • No fast pairing or NFC pairing, making the initial connection process less convenient
  • Advanced audio codecs such as LDAC, aptX, and aptX HD are absent, limiting high-resolution audio transmission options
  • There is no ambient sound mode, so users cannot let in environmental audio without removing the earbuds
  • The maximum Bluetooth range of 10 metres is relatively modest for wireless use
Who is this for?

The Boult Audio K40 suits users who want a straightforward pair of true wireless earbuds for daily commutes, casual listening, and fitness use. The IPX5 sweat resistance makes them a practical option for workouts, while the 40-hour combined battery capacity accommodates extended use across multiple days without frequent recharging. The four-microphone setup with noise-canceling capability also makes them a reasonable choice for those who frequently take calls or participate in voice-based communication on the go. The inclusion of fast charging further benefits users with unpredictable schedules who need a quick top-up between sessions.

Who is this NOT for?

Users seeking an immersive, distraction-free listening environment will find the absence of active noise cancellation a notable limitation, particularly in loud or crowded settings. Audiophiles or those prioritising high-resolution audio transmission will be underserved by the lack of advanced codecs such as LDAC, aptX HD, or aptX Adaptive. Additionally, the 10-metre Bluetooth range and absence of wireless charging may frustrate users who expect greater flexibility in how and where they use and charge their earbuds, especially in larger spaces or smart charging setups.

Design:

Fit In-ear
Ingress Protection (IP) rating IPX5
water resistance Sweat resistant
has no wires or cables ✓
are neckband earbuds ✕
wingtips included ✕
has stereo speakers ✓

The Boult Audio K40 adopt an in-ear fit and operate as fully true wireless earbuds, meaning there are no cables or wires involved. They feature stereo speakers but do not include wingtips or a neckband design. For protection against moisture, the earbuds carry an IPX5 rating, classifying them as sweat resistant and suitable for use during physical activity.

Sound quality:

has active noise cancellation (ANC) ✕
has passive noise reduction ✓
driver unit size 13 mm
lowest frequency 20 Hz
highest frequency 20000 Hz
has a neodymium magnet ✕

The Boult Audio K40 use a 13 mm driver unit and cover a frequency range of 20 Hz to 20,000 Hz. While the earbuds do not feature active noise cancellation or a neodymium magnet, they do offer passive noise reduction, which helps attenuate ambient sound through the physical seal of the in-ear fit.

Power:

Battery life 8 hours
Battery life of charging case 40 hours
charge time 1.5 hours
has wireless charging ✕
has a battery level indicator ✓
has a rechargeable battery ✓

The Boult Audio K40 offer 8 hours of battery life per charge, with the accompanying charging case extending total playback capacity to 40 hours. The earbuds have a rechargeable battery and take 1.5 hours to fully charge, though wireless charging is not supported. A battery level indicator is included, allowing users to monitor remaining charge during use.

Connectivity:

has fast pairing ✕
Has USB Type-C ✓
Bluetooth version 5.3
has LDAC ✕
has LDHC ✕
has aptX Adaptive ✕
has aptX Low Latency ✕
has aptX HD ✕
has aptX ✕
has aptX Lossless ✕
audio latency 45 ms
has aptX Voice ✕
maximum Bluetooth range 10 m
supports Bluetooth pairing using NFC ✕
Can be used wirelessly ✓
has AAC ✓

The Boult Audio K40 connect wirelessly via Bluetooth 5.3 and support the AAC codec, though advanced codecs such as LDAC, LDHC, aptX, aptX HD, aptX Adaptive, aptX Low Latency, aptX Lossless, and aptX Voice are not available. The maximum Bluetooth range reaches 10 metres, and audio latency is stated at 45 ms. Fast pairing and NFC-based pairing are not supported. The charging case uses USB Type-C for wired charging, keeping the connection standard current and widely compatible.

Features:

has ambient sound mode ✕
has in/on-ear detection ✕
has find device feature ✕
Supports fast charging ✓
has a mute function ✓
can be used as a headset ✓
control panel placed on a device ✓
warranty period 1 years
Has voice prompts ✓
travel bag is included ✓
Has an in-line control panel ✕
Has a temperature sensor ✕

The Boult Audio K40 support fast charging and can function as a headset, with controls accessible directly on the earbuds; there is no in-line control panel. A mute function and voice prompts are both included, while ambient sound mode, in/on-ear detection, a find device feature, and a body temperature sensor are absent. A travel bag is provided in the box for portability, and the earbuds are backed by a one-year warranty.

Microphone:

number of microphones 4
has a noise-canceling microphone ✓

The Boult Audio K40 feature a quad-microphone setup with noise-canceling capability, designed to help reduce background noise during calls and voice interactions.

Final Verdict

The Boult Audio K40 present a competent set of true wireless earbuds aimed at everyday users who prioritise practicality over audiophile-grade performance. With a 40-hour combined battery life, fast charging support, IPX5 sweat resistance, and a four-microphone noise-canceling setup, the earbuds cover the fundamentals well for commuting, casual listening, and active use. However, the absence of active noise cancellation and high-resolution codec support signals that these earbuds are positioned for general use rather than critical or immersive listening. For users whose needs align with those boundaries, the Boult Audio K40 deliver a reliable and well-rounded feature set that holds up in daily scenarios.

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