Abstract: A device for insertion into an ear canal of a mammalian subject, including a body, a first adjustable acousto-mechanical portion, a second adjustable acousto-mechanical portion and an adjustment arrangement. The body has at least one sound path extending therethrough. The first adjustable acousto-mechanical portion incudes an adjustable channel forming at least part of the sound path, and the second adjustable acousto-mechanical portion includes an adjustable membrane. The second adjustable acouto-mechanical portion is arranged acoustically in series with the first adjustable acousto-mechanical portion. The adjustment arrangement is configured for simultaneously adjusting the first and second adjustable acousto-mechanical portions to alter an acoustic response of the at least one sound path.