Isolation Sand Boxes

My guess is less vibration? DO I WIN!!!

it sounds quieter because you're so chuffed with yourself for building them, that the sound just had to be better!
on a more serious note, maybe your cd player sounds quieter because you blew out your hearing using the power saw cutting all that mdf.
how come the big ticket audio reviewers never mention these possibilities?!
cheers
tom

Is it because you put the sand in one of the boxes while the CD player was in the box?

On a more serious note, and assuming you have placed the CD player on the sand (be careful with that) or a non-resonant platform on the sand, my observation is that Glen does win. You are doing a superior job of isolating the CDP from its environment and in damping the vibrations eminating from the CDP itself. When I placed my SACD player on an Isobase (an isolation platform manufactured by one of our NJ Audio Society members which uses a small, silicone and air filled innertube in a base with a lead and sand mixture) I would swear to you that the player's volume level increased 2 db. Lowered noise floor, who knows? But very effective.

You will undoubtedly change the sound by putting a CD player on a sand-box. Whether or not it is an improvement depends on how bad the previous support was. Now that you have discovered how important vibration control is, you will hopefully look at some alternatives to sand-boxes.