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Author: Zarina Bhimani. Reprinted from the June 2016 issue of Voice Coil.
In this article we discuss how review website Reviewed.com uses SoundCheck to evaluate headphones.
Linear motors (also known as linear vibrators or linear resonant actuators) have become increasingly popular in handheld devices such as phones and tablets for providing haptic feedback to the device’s user. The performance characteristics of these devices can now be tested using your SoundCheck system – the same software you are familiar with from your audio tests! The main difference between linear motor testing and audio testing is that an accelerometer (rather than a microphone) is used to measure the performance of the device under test.
A linear motor is designed to have a strong resonant frequency across a narrow frequency bandwidth; the motor is then operated at its resonant frequency to produce maximum output (vibration) while having minimal power demands on the portable device. The strength of the vibration is controlled by adjusting the magnitude of the AC signal input to the motor. In this sequence, first a sine sweep is applied to the device to calculate the resonant frequency, impedance and related values, and then a single tone at resonance is applied to measure characteristics such as rise and fall time.
It is well-known that the frequency response of loudspeakers and headphones has a dramatic impact on sound quality and listener preference, but what role does distortion have on perceived sound quality? To answer this question, five popular headphones with varying degrees of distortion were selected and equalized to the same frequency response. Trained listeners compared them subjectively using music as the test signal, and the distortion of each headphone was measured objectively using a well-known commercial audio test system. The correlation between subjective listener preference and objective distortion measurement is discussed.
Authors: Steve Temme, Sean E. Olive*, Steve Tatarunis, Todd Welti*, and Elisabeth McMullin* *Harman International
Presented at the 137th AES Conference, Los Angeles 2014
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.
This sequence allows you to test devices without an analog input such as tablets, cellphones and MP3 players. A stimulus WAV file is created in SoundCheck, and copied to the device under test, where it is played and the response recorded in SoundCheck as if the stimulus were played directly from SoundCheck. The stimulus WAV file to be used on the device under test (DUT) may be customized in the stimulus step.
Note that this sequence uses the level-based trigger available in SoundCheck 16.0 and earlier. If you are using version 16.1 or later, please see the frequency-trigger based sequence which takes advantage of new functionality to offer more robust triggering.
This 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.
This sequence performs two of the measurements from the ANSI hearing aid test standard S3.22-1996. The first part, in accordance with section 6.7 of the standard, helps the user set the reference test gain for the hearing aid, which is used for multiple measurements in the standard. The second part, from section 6.12, tests the equivalent input noise (EIN) of the device.
The Hearing Aid Standard suite of sequences contains all the major tests from ANSI S3.22 and IEC 60318-7, as well as some of the additional ‘Annex C’ sequences from the 2003 ANSI standard. Each test, as outlined in the standards, is contained in a single test sequence. These sequences can each be run independently. There are also several full test sequences, which call up the required individual tests to run a complete standard test suite.