Telling the difference between good and bad quality earphones involves evaluating sound quality from measurement and calibration testing. Good headphones should provide clear, balanced sound with good bass, mids, and highs as well as no distortion at high volumes. ANSI ASA S3.7-2016 (R2020): Method For Measurement And Calibration Of Earphones covers the measurement and calibration of earphones and receivers that use couplers or ear simulators.
Calibration of Earphones
Calibration is done to identify the output voltage of the earphone amplifier that corresponds to a certain sound pressure level (SPL) at the output of the headphones. This nominal sound pressure level (a value that expresses how headphones convert the supplied electrical power into the sound pressure) is maintained as long as the output voltage of the headphone amplifier is not changed. A higher nominal sound pressure level typically means that the headphones sound louder. The electrical impedance is also critical to measurement as it makes the difference about being able to play sounds at a low or full volume.
When calibrating earphones, the actual sound pressure level (in dB) is measured during calibration using an artificial ear (coupler or ear simulator) and a sound level meter. Artificial ears are also used to provide an acoustic impedance approximating the median adult human ear and equivalent sound pressure at the eardrum. After calibration, the corresponding voltage is measured using a voltage meter. Ultimately, the calibration of earphones assures accuracy, standardization, and repeatability in measurements.
What Is ANSI ASA S3.7?
ANSI ASA S3.7-2016 (R2020) describes test methods and procedures for the measurement and calibration of earphones and receivers using couplers or ear simulators. The American National Standard provides guidance for the selection of the appropriate coupler or ear simulator for a given earphone and application. It describes methods for measurement of calibrated frequency response, input-output linearity, electrical impedance, harmonic distortion, and non-linear distortion.
This standard only considers electroacoustic response. The electroacoustic test methods described in ANSI ASA S3.7-2016 (R2020) are primarily for use with circumaural (over-the-ear), supra-aural (against-the-ear) and insert (ear-canal) type earphones, but they may be applied to other types as well. Although these methods are generally applicable to earphones for all uses, the most common application of these methods are for earphones intended for hearing aids and audiometric testing and for receivers or other electroacoustic transducers intended for use in an earphone.
In all cases, connection to the device under test is analog electrical; digital, USB, or wireless systems are not considered in ANSI ASA S3.7-2016 (R2020). However, the results of the tests in this standard may be used as the basis for establishing performance tolerances. For additional requirements and tests for earphones for consumer audio applications, reference is made to IEC 60268-7.
How Are Headphones Measured?
ANSI ASA S3.7-2016 (R2020) specifies that the elements of an electroacoustic system used to measure the response of an earphone or receiver are as follows:
- Earphone Under Test
- Coupler or Ear Simulator
- Standard Pressure Microphone
- Microphone Preamp & Power Supply
The generator may include or be followed by an amplifier in order to obtain sufficient signal level. The microphone drives a calibrated output indicator, such as an analyzer or meter which indicates sound pressure at the diaphragm of the microphone. The meter or analyzer typically incorporates selective filtering to improve measurement signal to noise and to enable the measurement of harmonic distortion components; they are used to measure the microphone output as well as to measure the voltage or the current to the earphone or receiver under test.
Headphones VS Earbuds
Both headphones and earbuds deliver sound to your ears and can connect to audio devices wirelessly or with a wired connection, but there are subtle differences between these devices. The main difference is that headphones sit outside of your ears; whereas, earbuds are compact drivers that fit within each ear. The sound quality is another major difference as earbuds tend to have poorer sound quality than headphones because they have smaller drivers. Since headphones have larger drivers, they reproduce sound with greater accuracy, which generally results in headphones having a better bass response and overall sound quality than earbuds. Lastly, the size of earbuds versus headphones can vary greatly as earbuds are small and lightweight while headphones are larger and bulkier.
ANSI ASA S3.7-2016 (R2020): Method For Measurement And Calibration Of Earphones is available on the ANSI Webstore.