Yealink SIP-T2 SERIES Administrator's Manual page 815

Parameter
Web User Interface:
Features->Audio->Handset Send Volume (-50~50)
Phone User Interface:
None
voice.headset_send
Description:
Configures the sending volume of the headset.
Note: It is not applicable to CP860 IP phones. We recommend that you modify this
parameter cautiously. An unreasonable value may render the voice quality bad. If
you change this parameter, the IP phone will reboot to make the change take
effect.
Web User Interface:
Features->Audio->Headset Send Volume (-50~50)
Phone User Interface:
None
To configure sending volume via web user interface:
1. Click on Features->Audio.
2. Enter the desired value in the Headset Send Volume (-50~50) field.
3. Enter the desired value in the Handset Send Volume (-50~50) field.
4. Enter the desired value in the Handfree Send Volume (-50~50) field.
5. Click Confirm to accept the change.
A dialog box pops up to prompt that the settings will take effect after a reboot.
6. Click OK to reboot the phone.
Permitted Values
Integer from -50 to 50
Configuring Audio Features
Default
0
793