we have four kid , the oldest be 4 yo , so sound machine be common in my house . here 's how I would rank the one we use currently : 1 . sharper image ec-b100 -lrb- ~ $ 40 -rrb- . pro : 20 sound , by far the best for low -lrb- bass sound -rrb- , ac power . con : Big , expensive . 2 . White Noise app for iphone\/ipod -lrb- Free for Lite version -rrb- . pro : sound ok , cheap . con : only 10 sound , need smartphone , need to be charge or plug in . 3 . Sleep Aid app for iphone\/ipod -lrb- $ 0.99 -rrb- . pro : sound ok , cheap . con : only a few sound , need smartphone , need to be charge or plug in . 4 .  Conair SU7 Sound therapy and relaxation clock radio  pro : good value , compact unit , ac power . con : sound fair compare with app , terrible when compare with sharper image , only 10 sound . - recommendation - it be not cheap but it be a really good sound machine . if you be look for a physical machine and want value , go with the Conair ; otherwise , spend the extra money and get this . - SPECIAL note if you have kid - we do not use any of these for the alarm clock feature . if you be use this for kid , I highly recommend this  american innovative teach I Time ! talk Alarm clock and nightlight