Acoustic Panels — Buy or Rent

The Theory Two 2" panels, closed vs. open back, each hit by the same three frequency bands, all three firing together on each loop rather than taking turns. High frequency is absorbed right at the front face in both panels — the backing doesn't change anything up there. Mid and low frequency behave very differently: in the closed panel they reflect almost immediately off the panel's own solid back and exit only partly faded, back into the room. In the open-back panel, with the frame open and an air gap to the real wall, the same waves travel all the way to the wall before reflecting — crossing the absorptive core twice end to end instead of once. Low frequency still exits, badly faded; mid frequency is shown fully spent by the time it crosses back — it fades out right at the core, never re-emerging into the room at all.

What the outside sources actually say: ATS Acoustics' own write-up on open-back bass traps explains that fabric backs "instead of wood… so the air gap can work" create "a node at the wall," placing the absorbent material closer to an "anti-node… at low frequencies," and recommends mounting "across a corner or with an air gap behind the panel" for best low-frequency results. GIK Acoustics' own mounting guide separately states that "leaving a small air gap (2–4in) behind the panel can increase low-frequency performance." Neither source publishes test data or an NRC number for this specific comparison, and neither one draws a closed-vs-open-back picture like the one above — so the fade amounts and the three-band split drawn here are our own illustrative interpretation, not measured or sourced directly from either company.

Sources: ATS Acoustics, "Open Back Bass Traps" · GIK Acoustics, "How to Hang Acoustic Panels"