This HCI helmet is designed with a partial vacuum in it. The vacuum will stop the input from infrasound and ultrasound. Make it into a true vacuum yourself with one of those vegetable bag units. They commmunicate thru the back of the head with a small beam of ultrasound and out the front right eye. If you wear glasses,the glasses will fog up with the moisture from your right eye. After a few years your right eye sight is compromised from the constant flow of ultrasound(20megahertz or so). They use this technique to see thru the lens of you own eye and other readings. Really!