This Recommendation has been updated from Recommendation P.37, Coupling Hearing Aids to Telephone sets.
Clause 4 covers inductive coupling and is technically similar to the original Recommendation P.37. Clause 4 however now includes the relevant figures that were previously referred out to other Recommendations. It presents recommended levels and frequency characteristics for the inductive field at the telephone earphone relative to a sound level presented at the same earphone.
Clause 5 covers additional amplification that may be provided for the benefit of hearing impaired users, and only editorial changes have been made to the text originally contained in Recommendation P.37. Limits for the additional amplification and range of volume control are given. Frequency response is also covered.
Clause 6 introduces the possibility of electrical coupling of a telephone set to a hearing aid. It is compatible with IEC Publication 118 Part 6, which covers the characteristics of hearing aid electrical input circuits. The electrical output level relative to the sound level in the same telephone’s earphone is given in this Recommendation, together with frequency response, source impedance and maximum output level.
Technically this Recommendation is compatible with similar documents recently drafted within ETSI covering the same subjects.