As one of its daily deals, Best Buy offers the Harman Kardon Invoke Bluetooth Speaker with Cortana in Graphite or Pearl Silver for $49.99 with free shipping. That's $50 under our June mention and the lowest price we've seen. (It's the best today by $50.) It features three woofers, three tweeters, two passive radiators, Cortana voice control, and a frequency response of 60Hz to 20kHz.