I used to use an app called dB Volume. I found it worker better for me as it has a "slow response" option, so your dB readings are constant instead of jumping around.
Hopefully your centre is ok and its just a measurement issue, because as taibanl says, the centre should be louder than your doors.
2008 E92 335D SE
2010 E90 320D SE
1994 E36 318I SE
1996 E36 316I SE