NCJ Number
218442
Date Published
January 2007
Length
6 pages
Annotation
This article reports on an acoustic analysis designed to determine whether the five "ping" sounds recorded through an open phone line in the 911 call from a homicide scene were caused by an assault on the victim with an aluminum baseball bat found at the scene.
Abstract
The examination showed that the resonant frequency of the crime-scene bat was generally consistent with the 911 "ping" recordings. The sound when an aluminum bat hits a hard object is produced by the bat's oscillation upon striking the object, which produces a specific vibration called the fundamental frequency (FF) and a series of harmonic, or nearly harmonic, overtones. The FF range for test bat one was 2062.50 to 2075.00 Hz; for test bat two, 2837.50 to 2850.00 Hz; and for the evidence bat, 2237.50 to 2250.00 Hz. The accuracy for all tests was within 6.25 Hz. The speed-corrected FF values of the "ping" sounds on the 911 recording had a fairly wide range of 2222.66 to 2306.14 Hz. Only the "ping" events at 100.10 and 110.70 seconds fell within the FF range of the evidence bat tests. The listed variances between the tested resonant values of the evidence baseball bat and the five recorded "ping" sounds could be due to a number of factors, including how the bat was held during the incident compared with the testing and the possibility that some of the "ping" sounds originated from different sources. Laboratory comparisons were made between the submitted bat, two other test bats, and the 911 recording, using narrow-band spectrum analysis. This article includes a discussion of relevant acoustic theory and describes test procedures, along with results. 4 tables and 6 references