Problem
Repetitive reflections from hard parallel surfaces produce flutter echoes that are perceived as timbre coloration and degrade sound quality and speech intelligibility. Absorptive surfaces are often used to control this annoying problem, with the unfortunate side effect of making the room too “dead”.

Solution
FlutterFree is the first acoustical hardwood molding that controls flutter echo by diffusion, maintaining the natural ambiance of the room. When adjacent panels are spaced and mounted with an air cavity, low frequency absorption can also be achieved.

Absorption 1
When FlutterFree panels are mounted 1/16" apart, the graph can be used to determine the spacing from the mounting wall for the desired absorption frequency. For example, to achieve bass absorption at 100 Hz, follow the vertical 100 Hz frequency line until it intersects the leftward sloping fractional open area line. Follow the horizontal line to the 8" intersection point.

Absorption 2
The absorption coefficient data on the left is for non-slotted FlutterFree in a Hemlholtz mounting. Surface mount refers to a C mounting with fiberglass on the boundary. The Cavity mount refers to a D mounting with a cavity depth of 3.5" (89 mm). The spacing between FlutterFree strips is 0.063" with a fractional open area of 0.015.

Absorption 3
The absorption coefficient data on the left is for slotted Flutterfree and was measured without any spacing between the FlutterFree planks. Surface mount refers to a C mounting with fiberglass on the boundary. The Cavity mount refers to a D mounting with a cavity depth of 3.5" (89 mm). For extended low frequency absorption the FlutterFree Helmholtz mounting may be used in conjunction with the slotted planks.

Diffusion
The graph illustrates how FlutterFree® provides useful diffusion above the diffraction limit of roughly 3400 Hz compared to a flat reflective surface. The chart represents the mean diffusion coefficient, which is the normalized standard deviation of the 1/3 octave polar responses for angles of incidence between 0° and 90°.

FlutterFree strips are molded on a 5 head wood molder from hardwood that is kiln dried to 6-8% moisture content.

FlutterFree strips can either be nailed, screwed or glued directly to a wall surface or mounted with a rear air cavity for low frequency absorption. In this Helmholtz mounting, a semi rigid fiberglass panel is mounted 1/4" behind the FlutterFree strips.

To standardize and maintain the proper spacing, lamella biscuits are included. When used as wall panels, a hardwood frame—not supplied—is suggested.