L-1 Acoustic Emissions

On 12-15-2003 an initial sound reading was made. The machine is in its raw state in that no adjustments have been made since it first became operational. The machine has many struts and supports that will eventually be covered with airfoil shapes, but which for now are round and rectangular. There are holes which are not capped, and corners not filleted. All these things will contribute to the noise produced. No sound absorbing material has been used. There is great potential for noise reduction by adding absorbent material and covering the struts, etc. This will be done later after a thorough evaluation. Air moving through the net produces some of the noise. Still, the machine is very quiet. Most competing designs are 20-30 db louder.

These initial measurements were made with a "Radio Shack 33-2055 A" Sound Meter. It is not very accurate, but it is readily available and inexpensive, so it will be easy to compare our facility with others. These measurements were taken from a single location, about three feet above the net walkway, at the southeast corner of the net. This is approximately 29-3/4 feet from the edge of the jet, or 36 feet from the center of the jet. This is approximately 7 feet above the exit and so is fully exposed to the audio emissions. The readings were taken at about 74% of maximum RPM, or approximately 100 MPH and include readings with both A and C weighting. The temperature was approximately 50 degrees F.

     Condition                             A Weighting               C Weighting

  No power (Ambient)                     55 db                           56 db

  No power, Trucks passing             70 db                           70 db

  74% maximum RPM, no flier        90 db                          92 db

  74% maximum RPM with flier       92 db                           94 db

These images show the meter in position just before the measurements were taken.

These are merely preliminary rough measurements. A Phonic PAA2 portable 1/3 octave analyzer has been purchased. [ www.phonic.com ] Soon a complete series of measurements will be taken at many locations around the machine, and at several different power settings. These will be published when they become available.