4
1
2
3
Frequency [Hz]
125
250
500
1000 2000
3150
4000
6300
8000
NRR
CSA
Class
MT7H7A4600-NA
Head band
Mean Attenuation [dB]
17.8
23.0
32.1
36.2
35.1
39.0
38.7
38.3
36.5
25
A
Standard Deviation [dB]
4.4
3.2
2.8
3.0
2.4
3.8
3.0
3.5
3.9
MT7H7B4600-NA
Neck band
Mean Attenuation [dB]
18.9
25.9
35.2
37.0
34.9
40.6
39.9
39.7
39.7
26
A
Standard Deviation [dB]
5.2
3.2
3.3
2.9
2.5
3.6
3.0
2.3
2.5
MT7H7P3E4600-NA
Helmet attachment
Mean Attenuation [dB]
19.4
24.3
33.6
35.5
34.1
38.5
38.0
35.8
35.7
25
A
Standard Deviation [dB]
3.4
3.3
3.8
1.7
2.6
3.6
3.1
5.4
5.4
(K) Attenuation
The NRR calculated from these laboratory-based attenuation data is 25 in the over the head and hard hat attached versions and
26 when worn behind the head.
The NRRs may overestimate the hearing protection provided during typical use due to variation in earmuff fit, earmuff fitting skill
and motivation of the user. 3M recommends reducing the NRR by 50% for estimating the amount of noise reuction provided.
The level of noise entering a person’s ear. when a hearing protector is worn as directed, is closely approximated by the difference
between the A-weighted environmental noise level and the NRR.
Example:
1. The environmental noise level as measured at the ear is 92 dBA.
2. The NRR is 25 decibels (dB).
3. The level of noise entering the ear is approximately equal to 67 dBA.
Caution: For noise environments dominated by frequencies below 500 Hz, the C-weighted environmental noise level
should be used.
Although hearing protectors can be recommended for protection against the harmful effects of impulsive noise, the
noise reduction rating (NRR) is based on the attenuation of continuous noise and may not be an accurate indicator of
the protection attainable against impulsive noise such as gunfire.
Improper fit of this device will reduce its effectiveness in attenuating noise. Consult the fitting instructions for proper fit
.
ANSI S3.19-1974
1
.
67.0
8.
88.5
15.
110.9
22.
141.3
29.
179.9
36.
233.6
2.
71.9
9.
91.5
16.
114.8
23.
146.2
30.
186.2
37.
241.8
3.
74.4
10.
94.8
17.
118.8
24.
151.4
31.
192.8
38.
250.3
4.
77.0
11.
97.4
18.
123.0
25.
156.7
32.
203.5
5.
79.7
12.
100.0
19.
127.3
26.
162.2
33.
210.7
6.
82.5
13.
103.5
20.
131.8
27.
167.9
34.
218.1
7.
85.4
14.
107.2
21.
136.5
28.
173.8
35.
225.7
(I) CTCSS (Continuous Tone Coded Squelch System)
(J)