Royal River Sound Test –January/February 2009
Sound tests were conducted on the Royal River in the Boundary Waters Canoe Area
Wilderness on 3 separate occasions during January and February of 2009. The purpose
was to measure the decibel level in the wilderness of a snowmobile’s engine running
outside the wilderness. Following is a summary of the methods and equipment used, and
a summary of the results.
Parameters of the Sound Test
1. Three sites were chosen to produce the sound of a snowmobile’s engine running
at different speeds. One snowmobile was placed on Little John Lake running at a
speed of 15-25 miles per hour. Another snowmobile was placed on North Fowl
Lake running at a speed of approximately 40 miles per hour. The third site was
on the proposed South Fowl Lake snowmobile trail. Since a snowmobile could
not get to this location, a recording of a snowmobile running at 5-10 miles an hour
was used.
2. Nine listening points were chosen along the Royal River. These points were
chosen in relation to the terrain along the river. Sound points were taken in open
bogs, open lakes, where ridges changed direction, and in closed canopy forest.
These points also corresponded to the travel route someone would use on their
way from John Lake to North Fowl Lake.
3. Each sound point had 4 tests conducted, each test being a 2 minute recording of
decibel levels. Test one was the ambient noise of the Royal River with no
snowmobiles running. Test two was the running of the snowmobile on Little John
Lake. Test three was the playing of the recording of a snowmobile from the
proposed snowmobile trail(the location of the recording was a point south of
Royal Lake). Test four was the running of the snowmobile on North Fowl Lake.
4. Weather readings, general terrain, and times of each test were recorded on a data
sheet for the nine sound points. Photos were also taken at each point
corresponding to the 4 cardinal directions.
Equipment Used
1. A Dell AXIM personal data recorder was used to record the sound of a
snowmobile running at approximately 5-10 miles per hour. At 50 feet the
recording produced a sound level of 72-74 decibels.
2. The data recorder was connected to a Galls Streetthunder bullhorn. Eight C
batteries power the bullhorn.
3. A Ski-Doo Skandic 550 produced the recorded sound.
4. Two Ski-Doo Skandic 550’s were used, one on North Fowl Lake and one on
Little John Lake.
5. A Kestrel Mobile Weather Station recorded weather readings.
6. An EXTECH HD600 Digital Datalogging Sound Level Meter on a 4 foot tripod
recorded the decibel levels on the Royal River.
Summary of the Tests
1. On January 28th six Forest Service personnel attempted to gather data at all nine
sounding points. Due to cold weather and dead batteries in the Dell data recorder,
only Sound Points one and two were surveyed(refer to map).
2. On January 30th two Forest Service personnel surveyed Sound Points six and
seven. Only the ambient sounds of the Royal River and the recording of a
snowmobile on the proposed trail were sampled.
3. On February 5th six Forest Service personnel surveyed eight sound points on the
Royal River. These were points three through ten(refer to map). Four recordings
of decibel levels were conducted at Points 3 and 4. At Points 5 through 10 three
recordings for decibel levels were sampled(the snowmobile on Little John was not
recorded at these points).
Summary of Test Results
1. The highest decibel level recorded for the snowmobile on Little John Lake was at
Sound Point one. It was approximately 55 decibels at 300 meters.
2. The highest decibel level recorded for the snowmobile recording on the proposed
snowmobile trail was at Sound Point 7. It was approximately 45 decibels at 400
meters.
3. The highest decibel level recorded for the snowmobile on North Fowl Lake was at
Sound Point 10. It was approximately 55 decibels at 200 meters.
4. Ambient decibel level varied between 39 and 41 decibels at most Sound Points.
General Thoughts on the Test
1. The Royal River is difficult to snowshoe. Open water and thin ice prevented
Forest Service personnel from sampling the entire river, especially the area
between points 2 and 3(refer to map). One Forest Service employee broke
through the ice on the river near Sound Point 3.
2. There were no human tracks or snowmobile tracks on the entire river.
3. Throughout the tests on February 5th a road grader could be heard on the
Arrowhead Trail, but was not loud enough to be recorded on the Decibel Meter.
Snowmobiles on Mcfarland Lake could also be heard throughout the tests, but
were not loud enough to be recorded on the Decibel Meter.
4. Snowmobiles could be heard on the Fowl Lakes throughout the tests, but were not
loud enough to be recorded on the Decibel Meter.
Sound Recordings
Enclosed is a series of sound graphs from each sounding point(refer to map). Following
is a summation of what we recorded.
1. Only Point 1 recorded the snowmobile on Little John Lake. The graph spiked at
55 decibels at 300 meters, with ambient decibels at 36.6.
2. Only Points 5 and 6 recorded the snowmobile recording from the proposed trail
site(refer to map). Sound Point 5’s maximum decibel was 44.1 at 440 meters,
where as the ambient sound was 40.1. At Sound Point 6, the maximum decibel
was 44.8 at 400 meters, with ambient decibels at 39.5.
3. Only Point 10 recorded the snowmobile noise on North Fowl Lake. Maximum
decibels were 54.3 at 200 meters, with ambient decibels at 39 decibels.
Participating U.S. Forest Service Personnel
Tom Kaffine Pete Lindgren Heather Fox Ryan Blaisdell Harvey Sobieck
Rich Kujawa Sue Abrahamsen Rob Bryers Ike Heruth
Sound point 7 Royal Lake 01/30/2009
Tom Kaffine at Sound point 7. Sub-Zero Temps. 01/30/2009
Sound point 8 02/05/2009. Arrow is approximate location of recorded snowmobile
sound (proposed trail).
Little John Lake. Area of operation for snowmobile running 15-20mph. 01/28/2009
North Fowl Lake area of operation for snowmobile 40-50mph. 02/05/2009
Photo from trail recording broadcast point (propose trail). Looking South toward Royal
River. 02/05/2009
Royal River looking NorthWest Sound point 5. Notice dark color of ice indicating
unsafe ice. Temperatures up to this point have been sustained well below freezing.
01/30/2009
Royal River looking west toward John Lake. 01/28/2009
Sound Point 1. Background. 01/28/2009 1008. Decibel spike was caused by squirrel.
Average dba: 37.55
Sound Point 1 Little John snowmobile. 01/28/2009 1012. Decibel spikes 44dba
maximum caused by snowmobile on Little John.
Sound Point 1 Trail Recording. 01/28/2009 1016. Decibel spikes are wind gusts.
Recording not audible. Average dba: 40.7
Sound Point 1 North Fowl Lake Snowmobile. 01/28/2009 1020. Decibel spike is wind
gust. Snowmobile is not audible. Average dba: 38.1
Sound Point 2 Background. 01/28/2009 1045. Running water ambient noise.
Max dba: 44.1
Sound Point 2 Little John Snowmobile. 01/28/2009 1048. Snowmobile not audible.
Max dba:44.7
Sound Point 2 Trail Recording. 01/28/2009 1051. Recording not audible.
Max dba: 44.4
Sound Point 2 North Fowl Snowmobile. 01/28/2009 1054. Snowmobile not audible.
Max dba:44.8
Sound Point 3 Background. 02/05/2009 0926. Average dba: 39
Sound Point 3 Trail Recording. 02/05/2009 0932. Volume on recording set to high.
Average dba: 41
Sound Point 3 North Fowl Snowmobile. 02/05/2009 0935. Decibel spikes were wind
gusts. Could hear snowmobile but did not register. Average dba: 40.7
Sound Point 4 Background. 02/05/2009 0952. Average dba: 41.4
Sound Point 4 Little John Snowmobile. 02/05/2009 0955. Snowmobile audible but did
not register. Average dba: 41
Sound Point 4 Trail Recording. 02/05/2009 1004. Decibel spikes caused by wind gusts.
Average dba: 42.4
Sound Point 4 North Fowl Snowmobile. 02/05/2009 1007. Snowmobile audible but did
not register. Decibel spikes are wind gusts. Average dba: 40.1
Sound Point 5 Background. 01/30/2009 1041. Average dba 37.4
Sound Point 5 Trail Recording. 01/30/2009 1059. Decibel spike is trail recording.
Max. dba: 44.1 Average dba: 40.3
Sound Point 5.1 Background. 02/05/2009 1022. Large sustained wind caused spikes.
Average dba: 45
Sound Point 5.1 Little John. 02/05/2009 1028. Decibel spikes caused by wind. Could
here snowmobile but it did not register. Average dba: 45.7
Sound Point 5.1 Trail Recording. 02/05/2009 1032. Spikes caused by sustained wind
gust. Decibel level for snowmobile no wind was visually recorded as 43dba.
Sound Point 5.1 North Fowl Snowmobile. 02/05/2009 1036. Decibel spikes caused by
wind gusts. Could barely hear snowmobile. Average dba: 42.8
Sound Point 6 Background. 01/30/2009 1119. Average dba: 38.3
Sound Point 6 Trail Recording. 01/30/2009 1123. Trail recording very clear. Recording
spiked at 40.7dba. Average dba: 39.6
Sound Point 6.1 Background. 02/05/2009 1048. Blocked wind from data logger.
Average dba: 39.4
Sound Point 6.1 Trail Recording. 02/05/2009 1052. Blocked wind from data logger.
Peak recording dba 44.8. Average dba: 42.5
Sound Point 6.1 North Fowl Snowmobile. 02/05/2009 1056. Could barely hear
snowmobile. Average dba: 39.6
Sound Point 7 Background. 02/05/2009 1109. Average dba: 39
Sound Point 7 Trail Recording. 02/05/2009 1113. Large spike was caused by a sniffle.
Recording audible. Average dba: 41.5
Sound Point 7 North Fowl Snowmobile. 02/05/2009 1117. Could hear snowmobile but
did not register. Max. dba: 39
Sound Point 8 Background. 02/05/2009 1133. Spike caused by a sniffle.
Average dba: 39.1
Sound Point 8 Trail Recording. 02/05/2009 1137. Could hear recording but did not
register. Average dba: 38.95
Sound Point 8 North Fowl Snowmobile. 02/05/2009 1141. Could not hear snowmobile.
Average dba: 38.9
Sound Point 9 Background. 02/05/2009 1200. Could hear water in rapids and
mechanical noise from McFarland Lake area. Average dba: 40.7
Sound Point 9 Trail Recording. 02/05/2009 1204. Recording faintly heard but did not
register. Average dba: 40.8
Sound Point 9 North Fowl Snowmobile. 02/05/2009 1208. Could here snowmobile
clearly. Average dba: 40.6
Sound Point 10 Background. 02/05/2009 1244. Decibel spike was caused by a sniffle.
Average dba: 37.7
Sound Point 10 Trail Recording. 05/05/2009 1248. Could barely hear recording.
Average dba: 37.8
Sound Point 10 North Fowl Snowmobile. 02/05/2009 1253. Maximum dba: 54.3
caused by snowmobile. Average dba: 41.5