Acoustic_shock_memo_en
mPD/DD/HSD-ATD
Audio & Acoustic Group
Auteur Stéphane Dufossé (translated by Nicolas PAILLUSSEAU, 2008/08/20)
Ref mPD/DD/HSD-ATD/SD/173.03
Date19/06/2003
Prevention of occurrence of excessive acoustic pressure
with ALCATEL telephone receivers.
Results obtained on OT311.
1. Introduction : ITU-T P.360 Recommendation
This Recommendation proposes limits to the acoustic pressure generated by the handset and headset earphones and some guidance on how to measure it.
It also provides guidance on how to assess acoustic sound exposure of telephone users.
It also includes some guidance to avoid speech degradation due to the use of devices implemented in the terminal to prevent the occurrence of excessive acoustic pressure.
This recommendation indicates that the measured acoustic level on a handset, with a normalized equipment, shall not exceed +46dBPa (140dBspl) for very short sound impulse (less than 80ms), and +31dBPa A weighting (125dBsplA) for longer sound impulse (measured with slow integration time) The level of +31dBPa is based on the calculation provided by European directive 86/188/EEC, it sets the user exposition time to 2s.
2. Alcatel Strategy in order to prevent excessive acoustic pressure on melodies ( ringtone /
buzzer)
Alcatel strategy objective is to pass the P.360 recommendation, and always have less than +31dBPa(A) during the first 2 seconds of a ringtone when there is an income call.
2 seconds is usually the time that is considered to be more than enough for user to realize he’s getting an incoming call and he should put the handset far from his ear.
A few remarks concerning the measurements :
a. The ear that we used is Artificial Ear Type 3.2 (standard normative equipment). This Ear is often used in the mobile phones certification. (cf 3GPP certification 26-131 and 26-132). There are also HATS ear types, (Type 3.3 and Type 3.4) but these ears have more leakage and it decrease the measured acoustic power. Another advantage of Ear Type 3.2 is that it is wideband, and peaks can be measured above 4kHz.
b. This ear is applied with no leakage on the receiver hole area by using “acoustic paste”, which gives the worse conditions as possible. It is the acoustic pressure that the user could hear if he applied the handset really very tight to his ear, which is not a realistic use-case. (cf picture below) An important thing is the “Progressive Melody” strategy that Alcatel is using :
When there is an incoming call, the melody step level is increased step by step.
For example, on OT311, the step level is increased every second (cf document ? paramètres techniques du BF3 ?). The 31dBPa(A) sound level is generally obtained after the 4th step (after 4 seconds).
This strategy is usefull when the user is just starting an outcoming call, and at the same time receiving an incoming call.
3. Measurement results (done on OT311)
Measurements done on OT311 with Type 3.2 Artificial Ear, applied with no leakage (cf picture below)
“Slow” integration Time (cf rec P.360)
A weighting (P360)
Melody menu tuned on Maximal Melody level
Measurement done when incoming call occur.
Number of steps before 31dBPa(A) is measured :
Melody Step Melody Step Melody Step
Bass 4 Swift 4 Alert 4
Escape 3 Chimes High 7 Ring 6
Flutebox 3 Chimes Low 5 Latinos 3
Dring 5 Ding 3 Fanfar 5
Claps 4 Tada 5 Stadium 3
Bhrams 3 Notify 5 Dring 4
Mozart 4 Chord High 4 Bip Bip 5
Vivaldi 4 Chord Low 4 Asia 3
Schubert 3
END OF DOCUMENT