For my prototype I am using an array of hc-sr04's coupled with a pressure feedback array. Having researched the easier option of vibration feedback the risk of a forehead equivalent of 'vibration white finger' would damage the heads sensitivity and render any such device useless. Vibrations would interfere with the users hearing and any bulk or weight would be uncomfortable for long periods. The reason for the sr04s rather than a kinect type sensor is range, cost and openness. I want this to be a $20 device although I am not opposed to the possibility of a more advanced model later. Drawings and updates to come. Also worth mentioning, I need people in south Wales to try out prototypes as I build them.