First introduced in 2019, M-Noise was developed as a means for determining the maximum linear output levels of loudspeaker systems when used in music reinforcement applications. To assure consistent repeatability, a test procedure was developed that specified test parameters and described requirements for associated microphones, signal generators and analyzers.
AES75 details a procedure for measuring maximum linear sound levels of a loudspeaker system or individual driver using the M-Noise test signal. Mathematically derived from analysis of hundreds of music selections spanning all genres, M-Noise uniquely exhibits a crest factor characteristic of music program signals. The specified test procedure determines maximum linear sound levels by incrementally increasing playback levels until reaching a stop condition: an unacceptable change in the transfer function’s magnitude or coherence. Specific procedural steps are outlined to accommodate both self-powered and externally powered loudspeakers.
Use of the AES75 procedure will eliminate uncertainties caused by published loudspeaker data that state a maximum SPL output but often are ambiguous regarding the test signal used or other relevant test parameters.
AES75 is the result of extensive work by the AES Standards Committee’s SC-04-03-A Task Group, co-chaired by Merlijn van Veen (senior technical support and education specialist at Meyer Sound) and Roger Schwenke, Ph.D. (Meyer Sound senior scientist and innovation steward).
"The work of the drafting group was deliberate and thoughtful as they carefully refined the standard," says AES Standards chair Bruce Olson. "AES75 will no doubt join the most impactful standards that the Society has published in its long history of providing the audio industry with critical tools for analyzing the performance of audio equipment and ensuring interoperability."
Predictive evaluation of loudspeaker performance based on published specifications has traditionally been challenging due to inconsistencies in both measurement procedures and in how measured parameters are reported. "Until now," explains Schwenke, "reading an SPL number on a datasheet often inspired more questions than answers regarding test signals used and procedures for measurement. Most important to the end user is how the loudspeaker will perform with typical audio signals and whether the numbers can be compared apples-to-apples with numbers from one datasheet to another."
"AES75 addresses these issues," Schwenke continues, "by providing a detailed procedure as well as a specific test signal, M-Noise, whose RMS and peak levels as functions of frequency have been shown to better represent typical program material. Furthermore, AES75 is designed to be independently verifiable, using analyzers and microphones typically used by audio professionals. By being independently verifiable, AES75 provides system specifiers and users a much more enforceable metric to use in quotes and architectural specs."
The M-Noise test signal is based on Meyer Sound’s analysis of hundreds of music selections spanning all genres. The procedures documented in AES75 provide measurement of maximum linear sound levels by incrementally increasing playback levels until the magnitude or coherence of a loudspeaker’s acoustic reproduction of the M-Noise test signal reaches an unacceptable state. The AES75 test procedures cover performance measurements of both self-powered and externally powered loudspeakers.
Credit for the development of AES75 is owed to the large task group, AES’s standards management and to Meyer Sound’s original work, shares van Veen. "The chairs would like to acknowledge the nearly 80 task group members who represent all market verticals such as, but not limited to, automotive, consumer electronics, pro audio, post-production, and cinema," he says. "For more than two years — during a pandemic — we met more than 50 times, every other week, which is extraordinary given the circumstances! Special recognition goes to the AES, Bruce Olson, Richard Cabot [AES standards manager], and Steve Hutt [recent co-chair AES Technical Council], as well as the SC-04-03 parent committee we report to for their continued support and guidance. Finally, the chairs would like express gratitude to John and Helen Meyer and Meyer Sound where M-Noise and its former companion procedure originated."
Meyer Sound also welcomed the adoption and publication of the AES75-2022 Standard. The company recognizes that the new standard, which includes the M-Noise test signal and an independently verifiable test procedure, marks a long-awaited breakthrough in the analysis and objective comparison of loudspeaker output levels.
"Having a common and clearly defined test procedure coupled with a test signal that reflects real-world applications is of enormous benefit to audio professionals," says John Meyer, president and CEO of Meyer Sound. "It not only allows users to verify the performance limits of their current systems, but also lets them make meaningful, apples-to-apples comparisons of published data for different loudspeakers.”
More information about AES75-2022 “AES standard for acoustics - Measuring loudspeaker maximum linear sound levels using noise” can be found in the Audio Engineering Society’s Standards News Blog (https://www.aes.org/standards/blog/). The AES75 standard as well as the M-Noise signals and coherence test tracks are also available for download in the links below.
AES75-2022 Standard
Download M-Noise and coherence test tracks.
www.aes.org
