Measurement of Airborne Noise Emitted by Information Technology and Telecommunications Equipment
ISO 7779 Principally a Standard for Acousticians
ISO 7779, intended only for noise measurement, is often also used for noise declaration of information technology (IT) and telecommunications equipment. Those who do this leave out the fact that IT noise should be declared using the ISO 9296 standard. ISO 9296 is the international standard for noise declaration of information technology equipment. The reason for this mix-up of standards is sometimes simply a lack of knowledge, but sometimes due to a temptation to mislead customers to believe that noise figures are better than they actually are.
Note that you also can be sure that you are subject to misleading if a manufacturer or seller only states a dB or B figure without mentioning any standard at all; such as is most common these days. Those figures are as relative as the notions "quiet" and "almost silent", but since most people will judge figures as an objective truth, will they be much less honest than just simple telling "our product is very quiet" or "our product is almost silent".
ISO 9296 mathematically corrects ISO 7779 raw data for uncertainty in both measurement and production. ISO 9296 specifies a statistical maximum sound power level: LWAd. Many manufacturers and sellers used to dislike the intelligent ISO 9296 feature that corrects for uncertainty - this because ISO 9296 values become about 0.3 - 0.4 B (bel) above the average sound power level (LWA) according to ISO 7779.
The part of ISO 7779 that can be of interest for non-acousticians, is the one about operating modes. The two most well-known operating modes for personal computers, for example, are the Operating and Idling ones. ISO 7779, but not ISO 9296, defines these operating modes for information technology and telecommunications equipment. Noise declarations according to ISO 9296 must include the declared operating modes.
ISO 9296 is the Meeting Point
Few people, except of acousticians, need to know the details about noise measurement standards, but most sound conscious purchasers, purchasing managers, procurement offices, and manufacturers and sellers will benefit of understanding the interfaces where acousticians make product noise data comparable. These interfaces are named noise declaration standards. In this world of global trade, it is most natural to avoid national, and use international noise declaration standards.
This means that ISO 9296 is the meeting point where we communicate IT noise data.
ISO 7779 is Based on the ECMA-74 Standard
ISO 7779 is based on the ECMA-74 standard - The ECMA standard is more frequently updated.
National Instruments® explains:
"A note about ECMA, ISO and ANSI test code standards and declaration standards for ITTE (information technology and telecommunications) equipment – Many of the ITTE test codes are published by ECMA, ISO and ANSI. The current process is that new or revised standards are developed as a part of the ECMA process, as ECMA standards can be adopted quickly. The ECMA standards are then submitted to ISO for approval as an ISO standard and then submitted to ANSI for adoption as a consensus international standard. When the entire process is completed, the ECMA, ISO and ANSI standards become equivalent."
Download ISO 7779 and ECMA-74 Here
Those who want to get a glance on what's included in ISO 7779 can download a copy of ECMA-74 from ECMA International, free of charge.
You can buy ISO 7779 from ISO, or from your national standards office.
In the article What is a "Silent" Computer? Mike Chin at Silent PC Review concludes: "By focusing only on sound power and a single half meter SPL measurement, ISO 7779 manages to ignore the sound quality aspects so important to human perception, leaving only a machine-language definition of overall noise. The fact that so few companies actually use this standard and its results for promotion is actually something of a relief. It would only lead to greater confusion and consumer dismay."
Quality and technical issues related to traceable measurements of acoustic noise emissions of computer and business equipment - By Jeff G. Schmitt, P.E. JGS Consulting.
Noise effects of cooling fans and its measurement - by Ian McLeod, Engineering Director, Papst plc.
International Standard ISO 7779:1999 (E) -- Measurement of airborne noise emitted by information technology and telecommunications equipment.
International Standard ISO 9296:1988 (E) "Acoustics -- Declared noise emission values of computer and business equipment".
Standard ECMA-74 -- Measurement of Airborne Noise Emitted by Information Technology and Telecommunications Equipment. 8th edition (December 2003).