Tag Archive for: standards

100 Things #35: AES75 (M-Noise) Measurement of Max SPL for Loudspeakers

The AES75 standard details a method for measuring maximum linear sound levels of a loudspeaker system or driver using M-Noise, a test signal specifically developed to emulate the dynamic characteristics of music. Our pre-written test sequence automates this measurement to the new AES 75 standard for Maximum SPL, removing subjectivity, increasing reliability, and saving time.

Automated AES75 Measurements in SoundCheck

More Resources for Measurement to AES75

Would you like to try this yourself? If you already have SoundCheck, you can download the AES75 (M-Noise) test sequence. Please note that you will need the waveform filter (part # 2032) and transfer function (part # 2021) modules installed on your SoundCheck system.

Get a copy of the AES75 Standard.

 

Video Script: Automate Measurements Using M-Noise with SoundCheck

Our pre-written test sequence automates measurement to the new AES 75 standard for Maximum SPL, removing subjectivity, increasing reliability, and saving time.

This standard details a method for measuring maximum linear sound levels of a loudspeaker system or driver using M-Noise, a test signal specifically developed to emulate the dynamic characteristics of music. Clearly defined limits for linear frequency response and coherence determine the Max SPL level and remove any measurement ambiguity.

Implementing the standard manually relies on an operator’s subjective judgment of real time spectrum analyzer data. It also requires multiple iterations of a measurement, therefore is labor intensive.

Our test sequence is fully automated. We use the same test signal and calculations outlined in the standard, but automated analysis steps objectively calculate the measurements and drive the next steps in the procedure.

Let’s take a look.

Here, you can see we are using the freely available M-Noise test signal introduced by Meyer Sound. This stimulus features a relatively constant peak level as a function of frequency, but a diminishing RMS level with increasing frequency.

First, we use a test signal approximately 20dB below our expected Max SPL to obtain a provisional linear frequency response, linearity, coherence and signal to noise ratio. We then increase the test level by 3dB, and compare the results to the initial value. The results must be within +/- 1dB, have a coherence of at least 97% and a signal to noise ratio 15dB or higher so that we know we are operating in the speaker’s linear region and our signal to noise ratio is sufficient for accurate measurements.

Next we automatically increase the test level by 3dB and compare it to the initial results, normalized to the current test level. Multiple measurement iterations take place until one of the ‘stop’ conditions is reached. These conditions are either:

  • the live measurement differs from the linear frequency response by at least 2 dB over at least two octaves
  • the live measurement differs from the linear frequency response by at least 3 dB anywhere, or
  • the Coherence Reduction Target is met –  this means the signal to noise ratio is 10dB or less and/or the coherence is 91% or less.

When one of these limits is reached, the sequence then reduces the test level to the last level that passed and repeats the measurements in 1dB increments to find the precise Level at which the response deviates from the base level.

Once this level is established, the device enters a burn-in process, where the M Noise stimulus is played through the DUT for five minutes and fifty-three seconds and again compared to the initial result. This long duration measurement is also used to generate peak, rms and A weighted RMS sound levels. If the response curve remains consistent, this curve is the Max SPL curve according to the standard. If it is not within the acceptable limits, the device is cooled down and the tests repeated with a longer stimulus duration.

All the operator needs to do is enter any stimulus limits based on the operating range of the DUT into the sequence before starting, then return when the test is complete.

As well as saving time, SoundCheck mathematically calculates the data in analysis steps within the sequence, which avoids the subjectivity of relying on operator interpretation of real-time spectrum analyzer outputs. This increases repeatability and confidence in the results. This sequence is available free of charge on our website. Check it out!

 

 

 

TIA 920-B Sequence for Measurement of Narrowband and Wideband Digital Phones

TIA 920-B is a comprehensive US dual-bandwidth standard that applies to both narrowband (NB) and wideband (WB) devices. It also allows a choice between Free Field (FF) and Diffuse Field (DF) as the Listener Reference Point (LRP). These sequences measure digital communications devices with handset features according to TIA-920.110-B, speakerphones according to TIA-920.120-B, and headsets according to TIA-920.130-B.

This module is a large, structured set of sequences and subsequences which perform all the measurements. Curves and values are shown on the screen, and tolerance checks are performed. Data is saved to a pre-formatted Excel test report that includes all measurements on any one device. Completely prompted sequences for calibration of all the transducers are included. After a one-time setup with a sound card and other user-specific interfaces, the sequences are automatic. They run by simply selecting, pressing start, and following prompts where user interaction with the device under test is required. The sequence works with approved sound cards for connection to the transducers. Windows audio devices such as USB headsets work directly with SoundCheck®. VoIP softphones also work with SoundCheck, by means of a recommended third-party Windows audio application.

The current release of these sequences is compatible with SoundCheck version 20. It includes new sequences to test speakerphone or headset devices that connect to a server, using the “open loop” method.

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IEC-60268-7 Headphone Sequences

IEC-60268-7: Sound System Equipment – Part 7: Headphones and Earphones is an international standard intended to characterize the performance of headphones and earphones. The standard itself is a lengthy document, 9 Sections and 3 Annexes covering 46 printed pages. These SoundCheck sequences focus on the electro-acoustic tests which are detailed in Section 8 “Characteristics to be specified and their method of measurement”.

Five separate sequences are provided, each designed to measure specific characteristics. This approach provides the user with the flexibility to measure all or some of the characteristics of their headphone.

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EN 50332-1 – Max. SPL of Portable Audio Devices

EN-50332_1 screenshotThis sequence follows the test standard detailed in EN50332-1 (2013) for measuring the maximum sound pressure for portable music players and the earphones/headphones they are bundled with. The test involves loading a weighted pink noise stimulus file (as specified by IEC 268) onto the portable device and playing it through the earphones at the player’s maximum volume.

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ANSI S3.22 Hearing Aid Test Sequences

These sequences include all the tests from ANSI S3.22:2014 as well as some of the additional ‘Annex C’ tests from the 2014 ANSI standard. This guide describes the basic functionality of each sequence and details the process of hardware setup and calibration.

Each test, as outlined in the standards, is contained in a single test sequence and can be run independently. The ‘— HA ANSI S3.22_2014 Product Test — master sequence’, calls all the required individual test sequences to run a complete standard test suite. It also creates or recalls a limits file according to the definitions in ANSI S3.22:2014 and assists in setting the correct Reference Test Setting for the device being tested. The name of the master sequence is bracketed by dashes to separate it from the individual test sequences.

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Hearing Aid Compatibility to TIA 1083 and FCC Part 68.316

These two test sequences are designed to test the hearing aid compatibility of a telephone according to the TIA 1083 and FCC Part 68.316 standards. These sequences, which rely on the user having radial and axial HAC probes, play the appropriate test signals, measure the response and compare them to the limits in the standard. These pre-written sequences enable the user to immediately test to the relevant standards, and can be fully modified to meet any custom testing needs if desired.

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