AVR Bass setting anomaly?

[Gordon Palmer]

I was running sweeps of my fronts+sub and centre+sub both XO at 120hz
I noticed the 15-120hz range was the same shape curve in both (as expected) but the centre channel was 5db lower.
Beyond 120hz the levels match out to 15Khz
I then checked the surrounds and they are also 5db lower than fronts in the bass range.
Its a Yamaha AVR and I wondered if this is normal?
If not, am I losing something from my sound?

 

[John Mulcahy]

If you send signals to both left and right bass limited speakers there will be bass redirection from each to the sub output, so the sub level would be 6 dB higher than if you measure with a test signal going to one channel, such as the centre or either front speaker on its own.

 

[Gordon Palmer]

Ah yes, of course, silly me
Thanks