Sound Pressure Level Reduction Tests

Sunday, 26 August 2007

The following is a copy of a preliminary report provided to the board of directors via e-mail on Friday, 29 June 2007.

We installed a noise reduction material (2 inch thick melamine foam panels) on the walls, ceiling and front (north) face of shooting position #1 on the 100 yard line during the work party on 23 June 2007.  We had enough extra material that we also put it on the north face (above the shooting position, but below the eave, facing the first baffle) of shooting position #2.  The material was installed to test two conditions:

1. Would noise reduction material make the 100 yard range more usable for the shooter?  (For those of you who have not used the 100 yard range, it can get very loud, sometimes uncomfortably loud, inside a shooting position when a high-powered rifle is fired.)
2. Would noise reduction material inside a shooting position do anything to reduce the sound of gunfire at other locations on and off the range?

This is a preliminary report of our test results.

Jim Burdett and Richard Phaneuf fired four different types of ammunition from three different firearms:

1. A .30-06 rifle
2. A lever action carbine in .454 Casull
3. A level action carbine in .45 Long Colt (.45LC)
4. A Thomson/Center pistol (14 inch barrel) in .223 Remington

Shots were fired from shooting positions 1, 2, and 4 on the 100 yard range to correspond to the two sets of insulation noted above, and from a shooting position with no insulation, and not adjacent to a bay with any insulation.

Sound pressure levels were recorded at five different locations:

1. At the old 300 yard line shooting positions, 200 yards south of the 100 yard firing line.
2. At the 100 yard firing line, 10 feet south of the shooting position (just south of the south eave of the roof).
3. In the shooting position, three feet to the right of the shooter, even with the trigger of the firearm.
4. At the 100 yard target for that shooting position.
5. At the northwest corner of 13th Avenue and Teakwood Street, which is about 700 yards NNW of the 100 yard shooting positions (675 yards north, 200 yards west).

The tables appended below record the A-weighted measurements made with the club’s sound level meter.  Some measurements were limited by the amount of ammunition available.

The following two paragraphs are a very brief overview of sound pressure levels to help interpret the data in the spreadsheet.

It is worth noting that the sound levels are measured in decibels (dB, tenths of Bels) on an A-weighted scale.  This measures the level of sound intensity above the minimum which can be perceived by a human, weighted by the frequencies over the ranges to which the human ear responds, so that a measurement of intensity in one frequency will be perceived to be the same level of intensity in another frequency.  Decibels are measured on a logarithmic (base 10) scale.  Each increase of 1 Bel corresponds to an increase in sound intensity of a factor of 10.  So going from 40dB (40 tenths of a Bel, or 4 Bels) to 60dB is an increase of 2 Bels, or a 100 times (10*10) increase in sound intensity.  A person’s perception of loudness, though, is not directly related to an increase in the intensity of sound.  As a rough rule of thumb, an increase of 10dB in sound pressure level at the same frequency is perceived to be about twice as loud.  For more information, see http://www.campanellaacoustics.com/faq.htm, a site referred to by the Acoustical Society of America web site (http://asa.aip.org/).

A soft whisper at five meters is about 30dB, while a normal conversation is 60 to 65dB.  An open field (wind in tall grass or leaves, birds, etc.) is about 35dB.  Busy traffic along Highway 99E is about 70dB at 50 feet from the road.  Traffic along 13th Avenue, measured from the sidewalk, is 70 to 85dB.  A vacuum cleaner is about 80dB.  The threshold of pain is between 120 and 130dB.  A .338 Winchester Magnum was measured at 126.1dB in one of the 100 yard shooting positions.

The preliminary conclusions, based upon this tiny test, are:

1. The noise reduction material seems to reduce the loudness by about a third between station 1 and either of the other two, and it reduces the muzzle blast felt by the shooter by at least half.
2. The noise reduction material in the shooting station has no effect on the level of the sound pressure outside the shooting line.

We need to expand this test by recording more shots from each of the positions to eliminate the effect of any extraneous noise that may have been measured, and to include measurements from Alder Creek Road, and the southeast corner of Tofte Farms.  We also need to test more powerful rifles to determine whether the noise reduction material is more or less effective with more powerful muzzle blasts.  We also need to try the effect of covering the south faces of the baffles with some less reflective material than plain plywood - perhaps outdoor carpet, or something similar.  When we get done we will have some idea of the cost and effectiveness of man-made materials in reducing sound from the ranges, and we can determine what, if anything, we want to do.

Firearm:  .30-06 rifle, Station 1

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	71.7	70.4	69.7
100 yd line	94.4	94.5	94.1
Shooting Pos	94.2	93.1	83.7
100 yd targets	90.0	91.9	92.0
13th Ave	57.1	53.0	52.9

Firearm:  .30-06 rifle, Station 2

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	68.3	68.5	68.7
100 yd line	95.3	95.4	95.3
Shooting Pos	89.7	89.5	89.5
100 yd targets	91.7	91.4	91.4
13th Ave	53.5	51.6	N/A

Firearm:  .30-06 rifle, Station 4

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	68.2	68.2	68.4
100 yd line	95.3	95.1	95.3
Shooting Pos	87.2	87.7	87.5
100 yd targets	90.2	89.2	N/A
13th Ave	56.0	53.1	N/A

Firearm:  .454 Casull carbine, Station 1

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	71.9	71.0	N/A
100 yd line	87.9	90.1	N/A
Shooting Pos	83.1	80.7	N/A
100 yd targets	93.7	94.1	N/A
13th Ave	51.8	55.0	N/A

Firearm:  .454 Casull carbine, Station 2

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	71.9	71.0	N/A
100 yd line	94.7	95.1	N/A
Shooting Pos	90.1	89.8	N/A
100 yd targets	89.2	92.4	N/A
13th Ave	59.5	58.2	N/A

Firearm:  .454 Casull carbine, Station 4

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	71.3	71.4	N/A
100 yd line	95.1	95.2	N/A
Shooting Pos	86.8	88.0	N/A
100 yd targets	92.0	92.4	N/A
13th Ave	58.7	57.6	N/A

Firearm:  .45LC carbine, Station 1

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	66.0	65.9	N/A
100 yd line	N/A	N/A	N/A
Shooting Pos	N/A	N/A	N/A
100 yd targets	N/A	N/A	N/A
13th Ave	52.1	53.3	N/A

Firearm:  .45LC carbine, Station 2

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	66.1	66.1	N/A
100 yd line	N/A	N/A	N/A
Shooting Pos	N/A	N/A	N/A
100 yd targets	N/A	N/A	N/A
13th Ave	52.4	56.4	N/A

Firearm:  .45LC carbine, Station 4

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	65.7	65.7	N/A
100 yd line	N/A	N/A	N/A
Shooting Pos	N/A	N/A	N/A
100 yd targets	N/A	N/A	N/A
13th Ave	49.1	50.7	N/A

Firearm:  .223 Remington T/C pistol, Station 1

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	66.0	65.6	N/A
100 yd line	94.3	94.2	N/A
Shooting Pos	82.1	81.8	N/A
100 yd targets	89.9	89.7	N/A
13th Ave	52.1	51.6	N/A

Firearm:  .223 Remington T/C pistol, Station 2

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	66.4	66.2	N/A
100 yd line	95.6	95.5	N/A
Shooting Pos	89.6	89.3	N/A
100 yd targets	82.8	90.3	N/A
13th Ave	53.4	55.8	N/A

Firearm:  .223 Remington T/C pistol, Station 4

Meas. Pos.	Shot 1	Shot 2	Shot 3
300 yd line	66.4	66.4	N/A
100 yd line	95.4	95.6	N/A
Shooting Pos	90.1	88.8	N/A
100 yd targets	85.2	87.3	N/A
13th Ave	47.3	49.9	N/A