ANC headphones are great for low-frequency (bass) sounds. But with cheap headphones I find I can still hear speech. I think new housing uses mass loaded vinyl to prevent high frequency sounds from passing through walls - perhaps heavy, 1lb or 1kg headphones with ANC are the solution for experiencing real silence in e.g. a busy workspace? Does anyone have an idea if material weight or density is a big factor in sound insulation? Along with air-tight sealing.