Best bang for buck improvement to speakers

I thought this was worth sharing - This winter I replaced the stereo and now have Inifinity Kappa speakers in the doors - and then last week I sound proofed both driver and passenger door with one layer each of Noico butyl mat and closed cell foam mats, which improved the audio sound.

But the next day I received the speaker baffles I'd ordered, a couple days late, so I had to go back and pull the door panels again and install these baffles behind and around the speaker cavities. They cost around $15 for each pair and made a substantial noticeable improvement in the quality of sound. Remarkable really. I highly recommend them whether you have the stock speakers still or have upgraded your system. They are called stinger roadkill, and are made for 5.25" 6.5" 6x8 and 6x9. Here's a picture.