Amazon has unveiled two new versions of its popular Echo smart home speaker. The new Echo Dot is a $90 hub that can be connected to existing home audio systems, replicating the functions of the original Echo but not including the speaker housed inside its tall cylindrical housing. The Amazon Tap is a $130 portable version of the Echo, battery-powered and requiring a push-to-talk button in order to query the Alexa assistant. The push-to-talk is the tradeoff for a decent battery life, as keeping the original Echo’s omnidirectional microphone array powered on and always listening is too power-intensive for a portable device – which has instead opted for a single microphone. While an always-on listening device like the other two…