Bluetooth BT40 in a T48G - how to increase microphone gain

[Yealink_Peter]

Hi,

For bluetooth, you should change the value on "voice.headset_send=", not on "voice.handfree_send=", the default value is 1, you can set 10 or other value as you like.
Additional, this option can only be changed via auto provision, can't change via import the changed cfg file. More information about auto provision, you can refer to this guide:Yealink SIP-T2 Series T4 Series IP Phones Auto Provisioning Guide V73_40
If you have increased the headset sending volume but issue persist, suggest swap another compatible headset to test, this link shows the tested compatible list of headset with Yealink.
Tested headset list compatible with BT40

Thank you.
Regards,
Peter