Yeah I use these regularly and never notice any volume differences. They're not designed to sound proof you voice, they're designed to stop the mic picking up reflections making your audio quality higher
They're more to help you obtain a good recording sound, they don't really insulate at all...

Gibson 2005 Les Paul Standard
Fender Road Worn Strat w/ Noiseless pickups
Marshall JCM 2000 401C
Marshall Vintage Modern 2266
Marshall 1960A cab (Dave Hill from Slade's old cab)
Ibanez TS9DX
EHX Little Big Muff
Freshman Acoustic
tape a bunch of egg cartons to the inside of a closet and sing in that, egg cartons trap air which stops sound transfer which is all insulation does for sound

As ProphetToJables said your option are for recording quality, sound waves move in all directions so your options will to very little, if anything, to diminish it

EDIT: hah ya you're right guy, its just long and borin to explain, but thats why soundproofing insulations and drywalls are denser, but you're supposed to hang a heavy blanket over the cartons, forget to mention that, but ive tried it and used it and works pretty well, not for a drum kit or anything, but just singing you're more then set
Last edited by Acou97 at Mar 22, 2013,
Egg cartons are practically useless for soundPROOFING. They don't have enough mass, and they can't be decoupled from the surface that you would think you'd want to attach them to. Soundproofing involves having a mass + an air space (or insulation) + mass, where the greater the mass and the greater the airspace, the better. Soundproofing is expensive and complicated - no two ways about it. It starts with the construction of your space.

Once the space is built, what you are doing is sound TREATMENT. This is where you control reflections, etc. At this point, soundproofing is not really an option.

Could I get some more talent in the monitors, please?

I know it sounds crazy, but try to learn to inhale your voice. www.thebelcantotechnique.com

Chris is the king of relating music things to other objects in real life.