In recent years, wireless audio has become more commonplace and even the norm in many of our everyday products. The use of network audio, which does not use conventional media sources such as compact discs (CDs), is also expanding due to the increase in sound source data from high-resolution audio and subscription-based music distribution services. New audio usage is often centered on smartphone-based services that provide audio through the smartphone to speakers and earbuds [earphones, earpods, etc.] via Bluetooth connectivity. These two use cases for audio output have come to dominate.
The recent mass implementation of True Wireless Stereo (TWS) within earbuds, with their comfortable cable-free non-tangling fit, has yielded vastly improved sound quality over traditional Bluetooth audio technology. TWS also comes with the ability to cancel external noise (isolation) which results in quieter playback. This feature allows users to use TWS-based devices without concerns of the sound being “broadcasted” to surrounding areas.
Additionally, Bluetooth connected speakers, which also do not require cables for signal transmission, allow for unfettered placement of playback devices and speakers. These mobile speakers, with their built-in amplifiers, can operate on battery power and be completely portable.
Bluetooth enabled audio devices are easy to use, easy to connect to and have many advantages. However, since they require a wireless signal, they can be susceptible to problems that do not occur with cable-connected audio devices.
This article describes phenomena that can cause problems within Bluetooth audio designs and will provide examples of potential countermeasures.

Class-D amplifiers, which are used in devices such as smartphones and audio equipment, have the advantages of being compact and highly efficient, but crucially require countermeasures against noise generated by their high-speed switching. TDK has an extensive lineup of products which can provide effective noise countermeasures while ensuring high sound quality and without affecting signals. This article describes the applications and effectiveness of these products in speaker lines for various devices which use Class-D amplifiers.