If you are looking for an inexpensive bluetooth speaker that you won't worry about taking to the beach or other places it is at risk of harm, the $30 Genius SP-925BT is not a bad choice.  It features two 50mm speakers and a passive sub-woofer, with a 1500mAh battery.  In addition to Bluetooth 4 connectivity there is also a 3.5mm jack to connect devices without a radio.  Modders Inc tried a variety of audio sources and found the quality and volume perfect for sharing you music with a crowd of people.

"Bluetooth technology is rendering wires passé in a world where using a mobile phone is an essential part of daily life. Staying connected no longer requires continuous tethering of devices to cables, so why shouldn’t audio listening enjoy the same freedom as well?"

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Audio Corner