ELECTRO-VOICE MODEL 668 DYNAMIC CARDIOID BOOM MICROPHONE
Widely used in motion picture and television sound recording -- features a windscreen fabricated from AcoustifoamTM.
This unique '"open-pore" polyurethane material, developed for Electro-Voice by the Foam Division, Scott Paper Company, slows down air velocity to eliminate wind blast, keeps air-borne dirt particles away from microphone and protects against shock damage.
Polyurethane windscreen is used on a number of E-V professional model microphones.
Producers of TV and movie westerns no longer have problems with desert winds blotting out the sound of the hero's voice as he inquires, "Which way'd they go?"
A special windscreen made from an "open-pore" polyurethane foam is an integral part of a number of professional model microphones manufactured by Electro-Voice, Inc., Buchanan, Michigan.
The windscreen slows down the velocity of air entering the microphone from wind or fast movement of the microphone and prevents distortion of sound. Called Acoustifoam(TM), the porous material is manufactured by the Foam Division, Scott Paper Company.
The material does not affect frequency response or the polar pattern of microphones, according to L. R. Burroughs, Electro-Voice vice president, Broadcasting and Recording Equipment.
Acoustifoam was specified for windscreen use in Electro-Voice microphones after a two-year search for a material to replace silk cloth. Most of the materials tested, including all types of cloth, usually produced sounds of their own when wind passed over their surfaces, Mr. Burroughs said.
Cloth materials, such as silk, had to be stretched over a supporting frame. The resulting rigid surface often was tuned to a frequency audible to the microphone it surrounded.
In addition, turbulence caused by wind passing over the surface created a disturbing noise.
Cloth which was dense enough to materially reduce wind blast created a cavity around the microphone, seriously altering its directivity. Acoustifoam proved to be the ideal material, Mr. Burroughs reports.
Combining the unique polyurethane windscreen and an external filter eliminates almost all microphone pickup of windscreen surface noise. Due to the soft, low-resonant quality of the foam, a large percentage of surface noise is held below 100 cps.
Use of an Electro-Voice model 513 filter eliminates response below 100 cps. The material is also effective in control of noise caused by wind striking the diaphragm.
Acoustifoam is a porous ester-type polyurethane foam which has no exterior surface membranes to block passage of sound.
With 97 per cent of its volume consisting of air space, the foam is made of thousands of interconnecting strands which break up the air stream substantially reducing velocity.
Windscreens made of Acoustifoam have operated effectively in outdoor wind velocities up to 40 MPH.
Wind blast is reduced up to 80 per cent.
In addition to acoustical benefits, the polyurethane windscreens protect sensitive microphones against air-borne dust and other particles.
Dust, which collects on the interior strands of the material, may be removed by washing the windscreen under running water.
If severely soiled, the foam may be washed in a mild soap.
Excess water is squeezed out. Two layers of polyurethane foam are used in Electro-Voice windscreens; a smooth-textured outer layer with 60 pores per lineal inch (ppi) and a rough-textured inner layer of 40 ppi.
This double layer of foam not only provides efficient wind blast control, but also helps protect microphones against mechanical shock damage.
Acoustifoam windscreens are an integral part of the Model 668 boom microphone, which was used on the podium at both recent national political conventions, and the seven-foot-long Model 643, the most directional microphone available.
Windscreens are also available for installation on many other professional Electro-Voice microphones.
Because of its contributions to sound recording, Electro-Voice earned the first Academy Award "Oscar" for microphone design in 22 years.
Stevenson and Lawyer, Grand Rapids, Mich., fabricates the windscreens to Electro-Voice specifications. Additional information may be obtained from Foam Division, Scott Paper Company, Chester, Pa.
Original Caption by Science Service
Additional Information - what is the Oscar Achievement ... April 8, 1963 Academy Awards, Santa Monica Civic Auditorium, Santa Monica, California; Host: Frank Sinatra - Electro-Voice, Inc. - - For a highly directional dynamic line microphone
... background of:
Technical Achievement Award