naes14

One warning. With this set up you will need a mic pre amp if you are planning on using those little electret mics. the pre amp will boost the signal enough for this thing to then play sound. However this works great as is with an MP3 player.

This is what I bought for my experimentation in external amplification I like the modular aspect of it plus the price is great. http://www.allelectronics.com/make-a-store/item/AMP-5/MINI-STEREO-AUDIO-AMPLIFIER-W/SPEAKERS/1.html

How long the fan will run depends on the battery's mAh the greater the number for the milliampere-hour the longer the fan will run. A higher Voltage usually means more power can be utilized and the fans ability to move air is increased however this can increase the sound because moving air is not quiet. Think about the difference in sound when you blast A/C in your car instead of setting the A/C fans to the lowest setting. These ideas will also help decide what battery combos to use as wiring batteries in series increases the V (keeps mAh the same) while wiring in parallel increases the mAh (keeps V the same) P.S. Expect between 400 and 600 mAh from a single standard alkaline 9v battery.