User Guide

PAMS
Technical Documentation
NME–3
Technical Information
Page 21
Issue 1 10/99
Handsfree Loudspeaker
According to VDA at has to be suitable to drive 4W Loudspeakers with a
maximumpower of 5W. When checking the offical requirements for the
response of the loudspeakerpart, we see that we need to have at 1,5W
Audiopower , if the sensitivity is as specified in CD949 acoustical
components. We are using a bridged Audio Amp. The requirements for
the Loudspeaker are shown below:
Table 8. Loudspeakeroutput
Parameter Value Note
Loadimpedance 3W– 5W
Power at 1% THD 1,5W
minimum drive capacitance 10 nF
Frequency response 300 Hz – 6,8 kHz
Total Powersupply rejection ra-
tio
> 60 dB
Handsfree Microphone
Specification for microphone input
First stage in the CD949 microphone path is an active microphone. This is
needed to get a good signal to noise ration on the long cable between
microphone and CD949 radio unit. The electrical specification for the
microphone (according VDA) could be seen in the table below.
1. 8V Biasvoltage
2. only two Pins
3. 10 kW minimum load
4. at P=74dB,1 khz and 30cm distance it has to deliver 190 mV-
PP
with a distortion of less then 1%
5. more then 15 dB dynamic range
6. Flat frequency response from 300 Hz to 4 khz +– 1 dB
7. signal to Noise ratio of more then 50 dB at 1% distortion limit
8. mountable on sunscreen and at chassis of the Car
9. Possibility to drive 7m microphone cable
To interface this microphone, the CD949 radio unit has a low noise power
supply The input stage of CD949 has to have an input impedance of >20
kW.