I have been reading and chatting with folks about stereo upgrades and mine is nearly done. I have read many people say that the rear speaker change has not done much for them. I just changed mine out and the difference was huge. I took the advice of one member and dynomated the rear wall and under the seats to get rid of some of the engine vibration.(big change). I also dynomatted the rear plastic shelf piecemon the back side for subwoofer vibration. I noticed the rear foam did not leave much airspace for the speakers. Most speakers go in doors or other larger air spaced areas. I removed the foam directly behind the rear speakers a little wider than the speaker hole width. I did not take pics, but admittedly did not do it neatly. I also did not try my new speakers with the foam for comparison. I put in alpine type r speakers and a pdx-v9 amp. The sound is clean and rich. At half volume and 65 miles per hour there is no wind noise with the top off and pure clean sound.
For good measure I added the carbon sub box and a kicker rt sub. The sub is decent, but not like my old jl-10w6. I had to also Dynomat the interior of the sub box as it caused initial rattling. I really hate the front right passenger seat bolt and hope I never have to pull it again. I'm sure You all know what I mean.
I just need to get some fronts to balance out the sound field.
Anyhow if your rears sound flat, the foam behind them may be why.
For good measure I added the carbon sub box and a kicker rt sub. The sub is decent, but not like my old jl-10w6. I had to also Dynomat the interior of the sub box as it caused initial rattling. I really hate the front right passenger seat bolt and hope I never have to pull it again. I'm sure You all know what I mean.
I just need to get some fronts to balance out the sound field.
Anyhow if your rears sound flat, the foam behind them may be why.