2024 Prius Limited. How do you bridge front and rear speakers?

As we all know, there is virtually no bass coming out from the head unit to the rear speakers. Of course there is plenty of bass from the front speakers.

Any thoughts or instructions or a harness that can bridge rear and front speakers?

I know this will eliminate any fade adjustments. But left and right balance would still be adjustable.

I'm not looking for a subwoofer as I wish to keep this somewhat simple.

Thanks!

 

Yes, the 8 speaker JBL System.