I know someone with a handsfree BlueAnt Bluetooth car-kit and they find it extremely useful. And it is a lot easier to install (it just clips onto the visor) than to put in a whole new stereo. Plus, it is portable, so you can use it indoors if you want to.
A boombox is a portable stereo; so a stereo is portable and a boombox is not.
There are many portable stereo recorders currently available. One of the best selling brands of portable stereo recorders is Tascam's DR07mkII Portable Digital Recorder.
The electric energy in a portable stereo is in the batteries. The batteries are what supplies the power to the stereo and in turn makes it work and produce the sound.
In a portable stereo, electrical energy from the batteries is converted into sound energy through the speakers when music is played.
A portable stereo recorder allows for brilliant stereo recording in a very small design. Stereo recorders allow for much higher quality recordings then regular digital recorders.
The Walkman!
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Ghetto blaster
The personal stereo is also known as a Walkman. This portable personal stereo player was invented by Andreas Pavel.
The manual for the LG800G shows describes a "handsfree or stereo earphone connector." It requires a (larger than some) 3.5mm male plug.
The first portable stereo was not sold in America. The Stereobelt was invented in 1972 by Andreas Pavel. The Stereobelt is the ancestor of the Sony Walkman.