ITU-T Recommendations

This Recommendation “Safe Listening Guidelines for Personal Sound Amplifiers (PSAs)” complements recommendation ITU-T H.870 “Guidelines for safe listening devices/systems”.
There is currently no international standard for Personal Sound Amplifiers (PSAs), which is needed to ensure these devices are safe for the user and do not further damage the users hearing, since they are freely available to anyone.

Personal Sound Amplifiers (PSAs) are non-medical devices, intended for people with normal hearing and (a) can have a design physically comparable to hearing aids, in which case it is called Personal Sound Amplification Product (PSAP) or (b) can also simply be an app on any smartphone or other device, in which case it is called Personal Sound Amplification App (PSAA).

As is defined in H.870, the sound exposure should be limited to an accumulated dose (100 % CSD) over 7 days of in total 1.6 Pa2h which corresponds to 80 dBA for 40 hours to prevent noise induced hearing loss. When the 100% CSD is reached, the sound level should suddenly drop, and the user will get the suggestion to lower the sound level, since the weekly sound listening dose is exceeded.

When PSAPs and PSAAs do not have the capacity to measure CSD, the output level of the device needs to be permanently limited to 95 dBA, so that the user is unlikely to use the device at a level higher than 80 dBA, since the dynamic range of speech has a crest factor of 12 to 17 dB.

The U.S. Food and Drug Administration has carried out considerable work on these devices and their work has been referenced in this document.