Measuring Dynamic HD Drivers for Hi-Res Audio
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                                Measuring Dynamic HD Drivers for Hi-Res Audio Earphones & Headphone
                     More and more consumers are looking to Hi-Res source material and playback
           devices for a premium listening experience. Special Provide the correct Hi-Res test methods  
                                for the high frequency bandwidth necessary to demonstrate
 

                                      Hi-Res Audio capability in earphones & headphone.
                                                                                                         
                                                                                             Issue by: Billy Chen, Hugo Hsu
                                                                                    IEA Electro-Acoustic Technology Co., Ltd.
                                                                                                          www.iea.com.tw
                                                                                              billy@iea.com.tw

The Hi-Res Audio initiative was originally created by the Japan Audio Society (JAS). More recently, the Consumer Electronics Association (CEA) has indorsed
the initiative and obtained the right for its members to use the Hi-Res Audio logo, giving the initiative global influence. As a result, manufacturers of consumer
arphones & headphones are increasingly looking to Hi-Res Audio as a way to differentiate their offering.
Hi-Res Audio is a set of performance standards for both digital and analog audio devices.  For analog devices a demonstrated capability to 40kHz is required,
though in the case of earphones the measurement methods are left to the manufacturer. For in-ear earphones the standard method for measuring frequency
response is not capable of detecting output to 40kHz. Therefore new measurement methods are needed. This white paper describes one such method and shows
how Dynamic drivers can be used to create Hi-Res Audio Earphones & Headphone.
 
Measurement Method for Dynamic Speaker Drivers
Components for in-ear earphones are typically measured using an acoustic coupler, most commonly the IEC 60318-4, or “IEC-60711,” coupler. 
(Figure 1) Available standard 711 couplers do not support driver frequency response measurements above about 8 kHz ~ 12 KHz due to their
resonant frequency, and are therefore unsuitable for checking performance for Hi-Res Audio. 
                          
                                 Figure 1: GRAS RA-0045 IEC-711 Typical Coupler Frequency Response

An alternative method was developed by IEA to measure the frequency response of HD dynamic drivers to 40kHz above. 
To avoid coupler resonance effects the component frequency response is measured through free air. 
An IEC-60258-5 (Figure 2) 1/4 quarter size baffle ~12mm thick is used to provide a consistent fixture for the device under test. (Figure 3)

                        
                                        Figure 2: IEC-60268-5                                     Figure 3: IEA Test Baffle

A variable hole is drilled in the near to center of the baffle issue by IEC-60268-5 relative position. Choosing the right microphone is very important,
especially in the near field must using pressure-field microphone for high frequency range can be extended. A quarter inch diameter reference
microphone use comparison GRAS 46BP Pressure Field type and GRAS 46BF free field microphone in the same near field test. (Figure 4)

                         
                        
                                         Figure 4: Comparison GRAS Type 46BP and 46BF in near field test


Measuring distance range 5~10mm from the sound opening in the baffle and at a 180 degree angle. 
5~10mm is chosen as the spacing because it provides good signal to noise at typical earphone drive levels and is also
a fair approximation of the distance from an in-ear speaker component to a user’s ear canal. (Figure 5)
 
Experiments can be learned through the use of near-field test is recommended to use a pressure field microphones (as like GRAS 46BP),
if the test distance is greater than 2 times the diameter of the DUT speaker to recommend the use of free-field microphone (as like GRAS 46BF).
                           
                             Figure 5: GRAS 46BP Microphone positioning for Hi-Res Audio measurement

Test level will be 1mW or 100mVrms, a typical drive level in a portable music player or smartphone, is chosen as the test voltage. 
Figures 6 and 7 show the measurement set-up. Note that dynamic drivers are designed to be very small 6~50mm and to deliver
a pleasing audio response into a sealed hole. In free air the bass output will by design be much lower. Therefore the free air measurement
is valid only for high frequencies. Of course the midrange and bass response of either drivers or assembled earphones is easily measured
 by standard techniques.
                                              
                               

Measurement Results
For this white paper SONY MDR-1A Dynamic drivers were measured.
                                            



                                            

As shown by Figure 8 and (Graph 1) SONY Hi-Res HD Dynamic drivers demonstrate output to 40kHz were in the test baffle
and KEMAR head and torso test frequency response curve, (Graph 2) The Phase Response curve, The phase frequency it can clearly know
the phase crossover point is transfer frequency at 2KHz can be a combination of both the frequency response curve (Graph 3),
therefore suitable for use in creating Hi-Res Audio earphones & headphone. IEA engineers can assist in the acoustic tuning
of earphones using HD dynamic drivers to achieve Hi-Res Audio performance.


IEA Hi-Res Test Equipment’s List:
                                     
                                                          
Conclusion

The demand for Hi-Res music is increasing, and with it, products to take full advantage of the increased fidelity. The Consumer Electronics Association expects that shoppers will look for the Hi-Res Audio logo when choosing listening devices. For earphones, the logo may be displayed on products with demonstrated output to 40kHz and more. Using measurement techniques devised by IEA, this capability maybe proved in both individual IEA measuring technical and in finished earphones. In particular.
 
About the Author:
Billy Chen is AES from 1991 (Member of Audio Engineering Society), Specialty work for IEA Electro-Acoustic Technology Co., Ltd.
He can be reached at billy@iea.com.tw IEA is a global supplier of advanced Electro-Acoustic test & measurement in Taiwan & China
Specialty electro-acoustic transducer components solutions, including smart phone, tablet, headphone, medical application.
Local in Taipei, TAIWAN www.iea.com.tw

 
REFERENCES
[1] Japan Audio Society (JAS) http://www.cta.tech/News/News-Releases/Press-Releases/2014/CEA-and-Japan-Audio-Society-to-Collaborate-on-Hi-R.aspx
[2] Japan Audio Society (JAS)http://www.jas-audio.or.jp/
[3] Audiomatica, “CLIO 11 user's manual”, www.audiomatica.com, 2013
[4] GRAS, http://www.gras.dk/
[5] Hi-Res Test & Measurement Application http://www.iea.com.tw/
[6] IEC-60268-5 Sound system equipment - Part 5: Loudspeaker
[8] IEC 60318-4:2010 Electroacoustics - Simulators of human head and ear - Part 4: Occluded-ear simulator for the measurement of earphones coupled to the ear by means of ear inserts.
[9] Loudspeaker and Headphone Handbook 3rd Edition by John Borwick (Editor)
[10] SONY MDR-1A
        http://www.sony.com/electronics/headband-headphones/mdr-1a