Bass traps are designed to absorb low frequency energy in our listening, home theater, and professional recording studios. There are two major types of bass traps currently on the market: membrane and diaphragmatic.
The first type of bass trap you will see companies offer is a membrane type absorber. This is a box or cavity that is a certain depth that also has a membrane or cover stretched over the absorber itself. The membrane is cosmetic and is used to cover the contents of the absorber which is usually some type of construction, insulation type, material. The unit itself is constructed of light weight materials. The performance of a membrane absorber is determined by the depth,size, and insulation type material used inside the absorber.
The second type of bass absorber used today is a diaphragmatic absorber that has a face that moves in response to sound pressure exerted upon it. It moves like a speaker cone with a back and forth motion. It movement is not as pronounced as a speaker cone, but it does move in response to low frequency pressure. Inside the diaphragmatic absorber, we can find fiberglass insulation type materials or specially designed materials that lower the pressure level inside the cabinet itself. The cabinet is made to be very rigid to encourage the diaphragmatic face to “move” without the cabinet itself moving.
Membrane type low frequency absorbers are light weight. They are not designed to go down to the lower frequency range even though the manufacturers claim they do. Diaphragmatic absorbers are heavy, but absorb much lower frequencies at greater rates and levels.