Telecommunications Industry Association TR41.7.1-07-08-003-L-MR-AcousticLimits
Document Cover Sheet
Project NumberDocument Title / Proposal for Revised Acoustic Limits in UL60950-1
Source / UL and Plantronics
Contact / Randy Ivans – UL Inc
/ Allen Woo
Distribution / TR-41.7.1
Intended Purpose of Document
(Select one) / For Incorporation Into TIA Publication
For Information
X / For discussion and the development of a formal proposal to UL.
The document to which this cover statement is attached is submitted to a Formulating Group or sub-element thereof of the Telecommunications Industry Association (TIA) in accordance with the provisions of Sections 6.4.1–6.4.6 inclusive of the TIA Engineering Manual dated March 2005, all of which provisions are hereby incorporated by reference.
Abstract
This contribution introduces revised limits for the acoustic tests in UL60950-1 and provides background and rationale for the original, existing and proposed requirements.
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TR41.7.1-07-08-003-L-MR-AcousticLimits
Background and Rational to revise Acoustic Limits in UL60950-1
PEAK LIMITS
v Current limits in UL60950
Compliance is checked by following the methods described in NAD.3.1 or NAD.3.2. During the above tests, the peak acoustic pressure level measured in the artificial ear or coupler shall not exceed 136 dB (relative to 20 µPa) at ear reference point (ERP).
This 136 dB limit at ERP does not agree with the OSHA regulations from which it was derived.
v ORIGINAL LIMIT
140 dB
IEC 318 Coupler which Measures at ERP
v WHAT WE WANT
140 dB limit at free field
Translate all measurements to diffuse free field which aligns with the measurement methods of is the OSHA regulation and also aligns with ETSI measurement methods and.
v ORIGINAL RATIONALE FOR LIMIT
See EIA report to UL November 1984.
The original limit was 140dB based on the OSHA limit of 140 measured in the free open field [1]. This was identified as conservative. See EIA report to UL November 1984.
v Where Current Limits Came From
When the limit was introduced into UL 1459 the 140 was used but translating the measured value from the ERP (where the measurement is actually made with the 318 coupler) to the open free field (where the requirement came from) was overlooked. The error was further made worse when the in-ear coupler (Type 2 coupler) was added for insert earphones which measures at the DRP. There was never an attempt to translate measurements made with either coupler (which are different from each other, one ERP, one DRP) to the free field as specified by the OSAH requirements. FIND REFERENCE FOR INITIAL INSERT EARPHONE RQMTS
In researching the change to 136 dB, we found the following regarding when the change was made and why.
In July 28, 1995, (more than 10 years after the original requirements were established) UL published a "Working Document for the Standard for Safety of Information Technology Equipment, Including Electrical Business Equipment; CSA C22.2 No. 950 * UL1950 - Third Edition. In it under deviation No. 317 the original 140 dB limit was still included, with the source document coming from the TIA which was essentially the UL1459 requirements, 140 dB using the two different couplers. There was an associated note that stated:
"This deviation is contained in the IEC proposal mentioned in deviation No. 316. At the October 1993 meeting, it was decided to replace this deviation with the revised proposal being pursued through the IEC. See deviation No. 317a."
Deviation No. 317a included the text from an IEC proposal on acoustic limiting that contained the 136 dB limit. It appears that the change was made to the proposed UL1950 to try and harmonize with anticipated requirements for IEC 950. Even though the IEC never adopted acoustic requirements, the 136 dB stuck for UL1950 and later UL60950.
Regarding the current requirements in UL60950-1 that do mention the ERP, since the original requirements in UL1459, UL1950 or UL60950 did not mention free field, ERP or DRP, and the original reference ear coupler was the 318 (Type 1), it was natural to assume that the measurement and limit was at the ERP (Type 1 is referenced at ERP) and this is what was included into the current UL60950-1 requirement.
ADD ETSI REQUIREMENTS
Add definition of “Diffuse Field”
open-field: where the sound or noise sources are at a distance from a person's ear
NOTE: The sound or noise environment can be a combination of more acoustic fields, i.e. free, partially reflected, diffused and reverberant fields.
LONG DURATION
v CURRENT REQUIREMENT
Compliance is checked by following methods specified in NAD.4.1 or NAD.4.2. During the above tests, the maximum steady-state A-weighted sound pressure coming from the earpiece or receiver shall not exceed 125 dBA for handsets, 118 dBA for headsets, and 121 dBA for insert earphones.
v WHAT WE WANT
125 dB for handsets
118 dB for hands free headsets (e.g. over the ear, in-ear, insert earphones) and insert earphones
Reference all measurements to the ERP
v ORIGINAL REQUIREMENTS
125dB
IEC 318 Coupler (Type 1) which measures at the ERP.
Hand Held Only
v ORIGINAL RATIONALE
See:
v LATER REQUIREMENTS
December 14, 1987 UL1459 Meeting report on revised requirements.
This added 118 dB for headsets based on a longer than 2 second exposure since it takes a user longer to remove a headset that to pull a handset away in the event of a loud noise. This was still measured using the IEC 318 coupler which measures at the ERP.
It also added a limit of 121 dB for insert earphones which was derived at the time from the 118 dB limit translated to a measurement made with an insert earpiece coupler, at the DRP.
Using a single coupler (Type 3.3 from IEEE269) for on-ear and insert ear couplers invalidates the different requirements for insert ear pieces and on-ear headsets when all of the measurements are referenced back to the ERP. Although different couplers are still allowed where appropriate IEEE 269 instructs that all of the measurements, regardless of the coupler used, should be referenced back to the ERP.
Although the difference in the requirements for handsets and headsets (based on time of exposure) remain valid, because of the variations of headphones, earpieces, etc, it is also no longer valid or practical to base the requirements on the type of earpiece or coupler used.
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[1] OSHA does not specifically identify the 140 dB limit as “free field”, “open field” or “diffuse field”. However, their measurement method describes actual noise exposure received by a person in an "open-field" environment. An "open-field" environment is an environment where the sound or noise sources are at a distance from a person's ear. The sound or noise environment can be a combination of more acoustic fields, i.e. free, partially reflected, diffused and reverberant fields. For measurement purposes it is not possible to recreate a true “open field” environment. A diffuse field measurement is considered the closest representation of an open field environment.