Loss of bass & full spectrum sound

I've now rung Yamaha and some service centres. They are inclinded to think that the problem we are both descibing is more so the speakers/drivers are the issue.... not the amp. I really hope my speakers are ok... and an amp replacement will fix the issue... but it sounds unlikely. The amp I just bought is the Yamaha RN803D by the way...

Hi @fishing716 
I'm just wondering if you ever solved this problem. 9 years later I hope so! Anyway, I was searching the internet for any insights on this. I seem to be experiencing exactly the loss of bass that you've described. The Bass sounds hollow and thin. But the first few days of owning the amp, I was blown away by the clarity of sound. Music had amazing bass & clarity even at low volumes. Now I get nothing like it. The amp will still play loud, and I do get bass frequencies, but everything sounds very average now.  Anyway, if you found a solution, I'd love to hear it. I'm going to call my supplier tomorrow and explain the problem. I've never experienced an amp sounding so good one day, then just so so the next.

@kennesawjet Inteseting. Yeah I have been trouble shooting this amp/speakers for a few days now. I took all the speakers out the other day and ran a multimeter through them to check the resistance. All speakers were getting a healthy reading. Then I took my amp into an authorised Yamaha specialist, and they ran some tests on the amp.  I have the Yamaha RN803D.  Here's the video & test results...

Anyway, to sumarise. It was getting 28V output at 1khz. When they switched the frequency to 10hz (bass), it was only outputting 16V.  I was told that's much lower bass output than it should be. Almost half the bass output is gone!!