low volume: speakers or receiver dead?

[papaschtroumpf]

over the years my Sony 5.1 receiver has been sounding lower and lower volume.
I used to crank the volume to the 20's to get sound filling the room, not I have to turn the volume know to be the high 40s.

How do I know if the speakers or the receiver are bad?
I just got a new HD TV and will need a receiver for it, just not sure if I need to buy new speakers too (or an HTIB system)

 

[Howard]

If all the speakers are getting quieter, it's probably the receiver.

 

[papaschtroumpf]

good point, thanks