This chart shows you the degree of permissible background noise for different headphone types.
| Type |
Supra-Aural Headphone |
Circumaural Headphone |
Insert Earphones |
| Reference |
OSHA Appendix D |
ANSI S3.1 |
See note 3 below |
ANSI S3.1 |
| Transducer |
TDH-39/49 & DD45 |
DD450 |
DD65 V2 |
ER-3A & IP30 |
| 125 Hz |
- |
49 |
57 |
50 |
78 |
| 250 Hz |
- |
35 |
46 |
46 |
64 |
| 500 Hz |
40 |
21 |
38 |
41 |
50 |
| 1000 Hz |
40 |
26 |
43 |
46 |
47 |
| 2000 Hz |
47 |
34 |
49 |
61 |
49 |
| 4000 Hz |
57 |
37 |
61 |
59 |
50 |
| 8000 Hz |
62 |
37 |
58 |
60 |
56 |
| Notes |
|
- OSHA 1910.95 Appendix D is based in political compromise rather than good science. Note that for Supra-aural headphones, OSHA permits far more ambient noise than the science-based ANSI standard. 1910.95 does not address MPANLs for circumaural or insert earphones.
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- ANSI S3.1 - 1999 (R2018) Maximum Permissible Ambient Noise Levels in Audiometric Test Rooms; Table 1 for the audiometric testing range 500 to 8000 Hz provides MPANLs for supra-aural and insert earphones.
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- MPANLs for circumaural headphones are not provided in any standard. Rather, they are calculated values based on:
|
| |
1. Ambient noise reduction of DD450 and DD65 V2 headphones indicated on the manufacturer's datasheets (Radioear) |
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2. Ambient noise reduction of the TDH-50 supra-aural headphone based on "The Acoustic Test Environment for Hearing Testing" Margolis & Madsen, J Am Acad Audiol 26: 1-8 (2015) |
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3. MPANL for the TDH-50 per the reference above |
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4. MPANL for circumaurals calculated by adding the difference between 1 and 2 to the MPANL values in 3 |
| Analysis |
- Note the sizeable difference for Supra-aural headphones between what OSHA permits and what the ANSI standard permits. OSHA permits far too much background noise when using Supra-aural headphones which provide poor noise reduction, especially poor low-frequency noise reduction.
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- For psychoacoustic reasons, higher-frequency noise is generally not as compromising to test accuracy as lower-frequency noise. HVAC noise, the rumble of passing vehicles, low-frequency vibration from machinery - these are the main sources of concern.
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- The values for both circumaural headphones are considerably larger at all frequencies than for supra-aurals, especially in the 250 - 2000 Hz range. Circumaurals provide more noise reduction than supra-aurals permitting circumaurals to be used in a noisier environment.
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- At the critical frequencies of 125 through 500 Hz insert earphones provide significantly greater noise reduction than circumaurals. The circumaural advantage in the higher frequencies is not important as higher-frequency noise is generally not an issue.
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- The noise reduction provided by circumaurals and insert earphones is comparable to a single-wall sound booth, the type of booth commonly used for OSHA/MSHA testing.
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- With any headphone, it is important to minimize audio and visual distraction. No headphone or single-wall sound booth can overcome this.
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