*** Sound Sweep in the Woods - Field Tips *** Night Search Sound Sweeps: A night grid-search seems like a pretty good idea when the nights are getting longer. If you are planning to do the Sound Sweep? There are a few obvious suggestions, like take a spare set of headlamp batteries. I would reccomend that you place four or five people out as subjects and see if they can be found i.e. what your real POD is. If you have GPS units you could give one to each subject to help them find their own way out, - its actually posible for a volunteer 'subject' to get lost in the woods at night! These subjects MUST also have whistles, and preferably a radio, again just in case they really do get lost. To mark the wide searcher spacings along the baseline small lightsticks can be helpful, a second set can also be used by the searcher when they have to deviate off their track to investigate sounds, it give them an easy to find returning point. You may also wish to have a fail-safe meeting point for any searchers who's radios go out of commission. You should also have each searcher radio into base at the moment that they actually go into the search area and log that time, location and direction of travel on the map. - Its easy with large numbers of searchers moving separately to briefly 'forget' about some of them, especially if their radios die. Supply each searcher with a map of the search area and their intended route. Try and enforce quietness on the entire search (its actually a listening search). On the first few Sound Sweep practises the teams area little uncoordinated in making there whistle blasts truly simultaneous, rather like a poor orchestra. Ask them to play close attention to getting their whistle-blasts to be simultaneous, as a late blast can mask a human voice relying for help. After a while they getthe hang of it and it sounds much more professional. Re: Whistles (Andy Hiltz) Keywords: sound, whistles Date: Sun, 22 Jun 1997 19:10:35 GMT From: Del Morris The value of sound and accoustics that we have transformed into the Whistle Stop tactic can be used in reverse to assist the victim to be heard/found faster. Maybe this will help. WHISTLE STOP The controlled use of sound during searches for a responsive subject is a stratagem that should be a practice of every SAR Team. At a "Sound Sweep" exercise, we were debriefing our "victims" and our searchers, graphing/mapping the time and location of each "whistle blast" and the victim's perception of 'direction from where the sound was coming from'. We discovered that the distance of sound travel and perception of sound direction was so variable that it deserved further study. After some additional field testing and research in acoustics, I offer the following suggestions: 1] Shift to lower frequency whistles 2000-3000 Hz or fog horns (marine supply) Plastic horns(sports events) Compressed air horns (marine supply). The higher frequencies are "absorbed" by humidity and vegetation. The lower frequencies will more readily bend around vegetation and rocks. 2] "Whistle Stops" can be done during the normal course of a Team Assignment when ever you are "inline" a drainage , contact SAR Base and request a "WHISTLE STOP". SAR Comm. will then orchestrate a "Whistle Stop" by contacting all Teams, giving any team time to get "inline" with other drainages, and doing a count down ( 3...2...1) to blast" just like the "sound sweep". Followed by that all important ... LISTENING PERIOD. 3] Teams that are on ridges will be at a disadvantage. Their whistles will be difficult for the subject to discern direction of the team. The subjects return whistle blows or yells for help will be equally difficult for the team to accurately determine the location of the subject. 4] Teams that are at the bottom (below the subject) of a drainage will a)have the best chance of hearing the subject in the drainage and b) have the most accurate direction of where the subject is. They will hear the subject better than the subject will hear them. 5] Teams that are at the top (above the subject) of a drainage will a)have the best chance of the subject in the drainage hearing them and b) have the second most accurate direction of where the subject is. The subject will hear them better than they will hear the subject. 6] Frequency is more important than additional decibels. 3 -110db whistles does not equal 330db. The combined decibel level is only about 117db. Sound level does not build exponentially. Some frequencies "blown" side by side can actually cancel each other do some degree. DISTANCE was greatly increased with the lower frequencies of sound (yelling was heard a lot further than a whistle). The lower feqs are not gobbled up as readily by vegetation and the moisture in the air. I reference the use of low freqs in Fog Horns. Our "victims" all heard "yelling" before they heard a discernible "whistle" at a time when the "yelling" teams were further away. Whistles seemed to be blended with the crickets and other background noises. DIRECTION or the perception of direction was more accurate when teams were "blowing" or yelling while inline with the drainage where the victim was. Blows that were blown by teams that were on the sides of hills or tops of ridges ... the victims found the sound very difficult discerning from "forest" noise and on the whole ...non-directional. Sound seems to carry better up hill than down hill, better with the wind than against. WHISTLE STOP can be used during any "phase" of a search for a responsive subject. Hasty teams running trails, dog teams doing area searches, etc. ... WHISTLE STOP is a more effective use of person power. A comparison could be made between "closed grid" search lines (Sound Sweep) and "open grid" purposeful wandering (WHISTLE STOP) searching methods. Del Morris Sonoma County (CA) SAR Unit dlmorris@concentric.net -----------------------------