The project I'm working on is going to use a LiPo Battery to run a Raspberry Pi, Arduino, and some LED's. I currently have all of that working. One final thing I want to do is have a "Speaker" plugged into the Raspberry Pi. I went to the local electronics store and got a little battery operated speaker thingy that has a 3.5mm audio jack. The speaker runs off of two AAA batteries. I would like to wire it up so that the speaker runs off of the lipo battery instead of AAA. That way when I connect/disconnect the battery the whole system turns on and off as one.
My question is what resistor would I need to appropriately power the device? Two AAA batteries only put out 3v but my power source is 5v. I don't really know how much current the device needs though so I don't know how to calculate a resistor.
EDIT: Did a little search on the internet and found a link to the product description: http://www.radioshack.com.eg/en/auvio-universal-speaker-for-media-players-40-036 That is the item I have. Due to complexity, budget, and size constraints I am unwilling to add another voltage regulator to the system. The battery I have is a 7.4v LiPo battery running through a BEC that is set to the default (5.1v). If I can use the power source directly great. If not then I'll have to just omit the sound feature of the project which will make it significantly simpler because the only reason for the Raspberry Pi is to provide sound.
EDIT 2: This is my BEC: http://www.quadrocopter.com/Battery-Eliminator-Circuit-BEC_p_625.html