What's up with this?

[Tbsh 10+ year member]

Okay well awhile ago I took out my headliner in my blazer to deaden it and I never put the headliner back in after I finished it. So, after I was done with that I hooked all my equipment back up to hear how it sounded and I completely lost the lows like

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[Jepalan]

You are mistaken. The headliner did not make a difference.

 

[subzero 5,000+ posts]

Because the headliner absorbed the reflections and cleared out any reflections. With out the headliner, the sound bounced, reflected around causing cancellation. Same effect with rolling down windows, but windows also has a cabin pressure effect in addition to.