Headphones - CJS Labs

Headphones - CJS Labs

26‐Jan‐17 Headphones Electroacoustic Design and Verification  Christopher J. Struck CJS Labs San Francisco, CA – USA © Copyright CJS Labs 2017 – San...

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26‐Jan‐17

Headphones Electroacoustic Design and Verification 

Christopher J. Struck CJS Labs San Francisco, CA – USA © Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Overview • • • • •

The Insertion Gain Concept Orthotelephonic, Free & Diffuse Field Responses Acoustic Impedance Couplers, Ear Simulators & Manikins Electroacoustic Measurements as per IEC 60268‐7  &  ANSI/ASA S3.7‐2016 – Electrical Impedance – Frequency Response • Free‐ and Diffuse Field Corrected Response • L‐R Tracking

– Non‐Linear Distortion • Harmonic, Difference Frequency, Intermodulation

– Crosstalk – Noise Isolation • Noise‐canceling Headphones

– Maximum Voltage & Maximum Output © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

1

The Insertion Gain Concept A: Loudspeaker Response Free Field B: Loudspeaker Response At Ear Drum C: Earphone Response at Ear Drum 30

C

D: Insertion Gain = C - B [in dB]

[dB]

20

10

D

B

0

A -10 100

1000

10000

Frequency [Hz]

The target is a “flat” Insertion Gain! © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Orthotelephonic Reference

Acoustic transfer function intended to represent a typical conversation 0

p ERP pMRP

-10 dB -20

-30

Including distance attenuation and obstacle effect of the head

-40 100

1000

10000 Frequency [Hz]

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

2

Components of the Orthotelephonic Response 30

“Obstacle Effect” of Head (& Torso)

To Ear Entrance Ear Entrance To Ear Drum

20 dB

To Ear Drum (DRP)

Helmholtz Resonance of Ear Canal

10

0

-10 100

1000

10000 Frequency [Hz]

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Head Related Transfer Functions 30

20

dB

10

0

-10

-20 20

200

2000

20000

Frequency [Hz]

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

3

Free & Diffuse Field Responses (at DRP)

IEEE 1652

20

Free Field, 0° Az., 0° El.

15

Diffuse Field

dB

10

5

0

-5 20

200

2000

20000

Frequency [Hz] © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Outer Ear & Pinna

Helix

Fossa Darwin’s Tubercle

Crus of Helix Anti-Helix Concha

{

Cymba Cavum

Tragus Canal Anti-Tragus Lobe

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

4

Acoustical Impedance of Headphones High Acoustic  Impedance

Low Acoustic Impedance

(Sealed)

(Open)

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

The Effect of Leakage on Response Sealed dB

f

With Leak dB

f

Loss of low frequencies!

…assuming a high acoustic impedance source © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

5

Acoustic Impedance  Thévenin Equivalent U + -

p

Norton Equivalent

Z

U

Z

ZA 

+

ZS

ZS

Ohm’s Law

p

p U

[ N·s/m5 (mks acoustic ohms)]

Low ZS Pressure Source

High ZS Volume Velocity Source

IMPEDANCE x f OF OCCLUDED EAR

EQUIVALENT VOLUME OF EAR

40

|Z|·f dB

100

30

Measured

20

Transfer

10

log V [cm3]

1

10

0.1

0

0.001

100

200

500

1k

2k

5k

10k

20k

Frequency [Hz]



ZA · f

Sealed w/ Leak or Vent 100

200

500

1k

1 / VEquivalent

2k

5k

10k

20k

Frequency [Hz]

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Earphone Types Circumaural

Supra-aural

Supra-concha Intra-concha

Insert

© Copyright CJS Labs 2014 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

6

Acoustic Couplers • Couples measurement microphone to earphone receiver • Approximates (simplified) acoustic load of ear

A Brief History of some Legacy Couplers: NBS 9A (6cc) Coupler ca. 1950 (standardized ca. 1961) Audiometer Calibration

2cc Coupler

Braun Coupler

1945 (standardized 1961)

ca. 1953

Hearing Aid & Insert Earphone QC/QA

(DIN standard ca.1968) Telephone Handset Testing (Legacy)

NOTE: No “reference point”, per se

© Copyright CJS Labs 2014 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Artificial Ear IEC 60318‐1 (ITU‐T Type 1) ca. 1962‐68 (standardized 1973) Acoustic |Z| x f at ERP*

* Ear Reference Point or Concha bottom

• Audiometer Calibration • Telephone Handset Testing (Legacy) © Copyright CJS Labs 2014 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

7

Zwislocki Coupler (Legacy)

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

IEC 60318‐4 Ear Simulator (formerly IEC 711)

also ANSI S3.25-2009

Measurement Microphone Diaphragm is at DRP! © Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

8

IEC 60318‐4 (formerly 711) Ear Simulator Acoustic Transfer Impedance 40

also ANSI S3.25-2009 30

20

10

0

-10 20

50

100

200

500

1k

2k

5k

10k

20k

Frequency [Hz] © Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Ear & Cheek Simulator • Uses IEC 60318‐4 (711) Ear • No Crosstalk or Insertion Response Testing • Cannot utilize actual headband force • Retaining force arm may occlude some open‐back designs • Serial Testing of L & R requires pinna substitution

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

9

QC Test Fixture • Can be configured with IEC 60318‐4 Ear Simulators • Crosstalk, Isolation & Insertion Response Test results may differ from manikin tests • Positioning may be more consistent but less realistic than manikin • Optimized for QC/QA

© Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Brüel & Kjær Head And Torso Simulator • • • •

IEC 60318-4 (formerly 711) Ear Simulators Anatomical Pinnæ Fulfills IEC 60318-7, ANSI S3.36, and ITU-T Rec. P.58 Mouth Simulator for headset testing

© Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

10

g.r.a.s. KEMAR Manikin • • • •

IEC 60318-4 (formerly 711) Ear Simulators Anatomical Pinnæ Fulfills IEC 60318-7 and ANSI S3.36 Optional mouth simulator for headset testing

© Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Pinna Simulators ITU‐T Rec. P. 57 Type 3 (all fitted to IEC 711 Ear) ca. 1996 Type 3.2

Type 3.4

Type 3.3

Type 1 (IEC 60318-1/2) (Legacy)

Sealed High Z Telephones Audiometer Calibration

Type 2 (IEC 60318-4) Occluded Ear (no pinna)

Insert Earphones

Type 3.2 High Leak / Low Leak

Hard Earcap Telephones

Type 3.3 Soft Anatomical (HATS)

All Types. Most Realistic.

Type 3.4 Simplified Soft Anatomical

Handset Telephones Binaural Recording

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

11

Basic Test System Headphones Under Test

Analyzer Headphone Amplifier

Signal Generator

Microphone Preamp(s)

or Interface Post-Process IEC 60318-7 Manikin with Ear Simulators

adapted from IEC 60268-7

© Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Electrical Impedance +

I

VS VG

+

-

-

+ R

VG – VS GND

For R << 0.1 |ZMIN(f)| (typically 0.1  ): Z( f ) 

VS ( f ) R VG ( f )  VS ( f )

© Copyright CJS Labs 2014 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

12

Electrical Impedance • Low Voltage (LINEAR!) • R40 40th decade (1/12 octave) stepped sine • Can also measure phase, if desired • Measured with headphones on manikin! • For ‘standard’ impedances (e.g., 16, 32, etc.), RDC is often a good indicator of ZMIN & Z0 !

ZMIN  0.8 Z0 ! Z0  1.25 ZMIN

Frequency Response: MAGNITUDE 75

50

 25

0 20

200

2k

20k Frequency [Hz] © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Source Output Impedance • IEC 60268‐7 Specification: ZOUT = 120  • Actual headphone amplifiers vary from < 1 to > 100   Recommend measuring at both 120  AND 1 

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

13

Test Conditions ‐ 1 • Characteristic Voltage: The sinusoidal voltage at 500 Hz (or IEC 60268‐1 simulated program signal*), applied through the rated source impedance (120 ohms), to obtain a sound pressure level of 94 dB SPL in the ear simulator (with or without A‐Weighting). – NOTE: Some devices for portable music players may not be capable of producing 94 dBSPL!

• Rated Source Voltage: Maximum specified RMS voltage which should be applied to the headphone through the rated source impedance, during the reproduction of normal program signals. NOTE: For headphones complying with IEC 61938, Rated Source Voltage = 5 V. Preferably, should not exceed the Characteristic Voltage by more than 15 dB. * Only applicable to systems with integral signal processing for IEC 60268‐7. Required  for EN 50332.

© Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Test Conditions ‐ 2 • Working Sound Pressure Level: SPL resulting from a sinusoidal voltage (single figure at 500 Hz or simulated program signal) through the rated source impedance (120 ohms), across the input connector of the headphone, at a level such that would cause 1 mW to be dissipated in a pure resistance equal to the rated impedance of the headphone. Voltages for 1 mW for Nominal Impedance, Z0 : 16  : 126 mV  20  : 141 mV   25  : 158 mV   32  : 179 mV   40  : 200 mV   50  : 224 mV  

60  : 245 mV          250  : 500 mV     80  : 283 mV  300  : 548 mV   100  : 316 mV  400  : 632 mV   120  : 346 mV  500  : 707 mV   160  : 400 mV     600 : 775 mV   200  : 447 mV

• Maximum Sound Pressure Level: SPL produced in the ear simulator when the headphone is supplied with a sinusoidal voltage of the Rated Maximum Voltage at 500 Hz (see also EN 50332).

Ohm's Law V  IR, P  VI P

V2 V2  R Z0

V 2  PZ 0 V  PZ 0  0.001 Z 0 V  0.0316 Z 0

© Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

14

26‐Jan‐17

Frequency Response 1 mW Input 110 Left Right 100

dB SPL

90

• Ear Simulator(s) must be calibrated! • R40 (1/12 octave) stepped sine, 1 mW (or 94 dBSPL) • Can also be plotted as a calibrated transfer function in dB Pa/V as per ANSI S3.7-2016

80

70

60 20

200

2k

Frequency [Hz]

20k

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Positioning Errors & Test Repeatability 100

90

80 dB

Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Average

70

60

Circumaural, Supra‐aural, Supra‐concha, Intra‐concha devices 50 20

200

2000

20000

Frequency [Hz]



Test/Re‐Test: dB Average of 5 re‐positions: – – – –

Complete removal and re‐installation! Reject re‐positions > ± 2 dB (500Hz – 5 kHz) Check low frequency response for leakage Report Average & Max 

© Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

15

Coupling Sealed Insert Earphones Insert Earphone Airtight Seal & Support for Earphone (putty)

Ear Simulator Tip of Insert should be flush with cavity wall

© Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Diffuse & Free Field Corrected Response DIFFUSE: HDFC (f) = H (f) – HDiffuse (f)

[in dB]

FREE FIELD: HFFC (f) = H (f) – HFF 0°,0° (f)

[in dB]

110

Diffuse Corrected Response dB SPL for 1 mW

105

Free Field Corrected Response

100

This is the Insertion Gain!

95

90

85 100

1000

Frequency [Hz]

10000

• Maps to perceived response • Simplifies visualization and tolerance application • Important range: 300 Hz – 8 kHz © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

16

Measured Responses at DRP 100

90

90 dB

110

100

dB

110

80

80

Circumaural

70

Supra-aural

70

60

60 10

100

1000

10000

100000

10

100

Frequency [Hz]

1000

10000

100000

10000

100000

Frequency [Hz]

120

70

110

60

100

dB

dB

80

90

50

Intra-concha

40

Insert

80

70

30 100

1000

10000

10

100000

100

1000 Frequency [Hz]

Frequency [Hz]

© Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Resulting Insertion Gain Diffuse Field Corrected Response Free Field Corrected Response

Circumaural

Supra-aural

20

Intra-concha

Insert

10

0 dB

10

-10

-20

-30 100

1000

10000

Frequency [Hz]

© Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

17

Left-Right Tracking L & R Responses are 1/3 octave power averaged in each band: In each 1/3 octave band: N

L(f) = 10log10

 10 N 1

Li /10

i=1

10

HL-R (f) = HLeft (f) - HRight (f) [in dB] dB

5

0

Polarity must also be tested!

-5

-10 100

1000

10000 Frequency [Hz]

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Polarity Test Methods • Low Frequency Phase comparison – (f) asymptotes toward 0° or 180°

• HL(f) + HR(f) complex summation – Magnitude: +6 dB or noise floor – Change in shape of Lissajous figure

• Time Domain Pulse – Positive or negative going waveform

© Copyright CJS Labs 2014 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

18

250 Hz 500 Hz 1 kHz 2 kHz 4 kHz 8 kHz Distortions

120 110 100

Input vs. Output Earphone Response • Traditional measure of linearity • Step size: 1 dB • Tested at multiple frequencies, but limited frequency information • Linear is at 45° for correct aspect ratio

80

• Upper “knee” point shows linearity limit

70 60

• Total Distortion is the power sum of the 2nd & 3rd Harmonics

50 40 30 20 -60

-50

-40

-30

-20

-10

0

10

20

30

40

Input [dB V] © Copyright CJS Labs 2014 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Harmonic Distortion at Rated Voltage 100

80

60 dB SPL

Output [dB SPL]

90

40

Fundamental 2nd Harm. 3rd Harm.

20

0 20

200

Frequency [Hz]

2k

20k

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

19

THD vs. Frequency 0 N

THD 

-20

dB

A n2 N

2 n

 An2

10 %

n 1

-40

1%

-60

0.1 %

-80

0.01 % 20

200

2k

Frequency [Hz]

20k

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Intermodulation Distortion 3rd: f1 + 2f2

f1

2nd: f1 + f2

-2nd: f1 – f2

10 dB/div

-3rd: f1 – 2f2

f2

Relative Frequency

• • • •

f2 low frequency fixed tone at -1.9 dB re: Rated Voltage at 70 Hz f1 tone at -14 dB (4:1) at 600 Hz OR stepped or swept f2 is the frequency interval between distortion products IM products follow f1 as a group

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

20

f

f2

f1

3rd: 2f1 – f2

-2nd: f1 – f2

dB

-3rd: 2f2 – f1

Difference Frequency Distortion

f

Relative Frequency

• f1 & f2 each at -6 dB re: Rated Voltage, stepped or swept. • f = f1 – f2 = 80 Hz • f is the frequency interval between distortion products • Odd-order products follow as a group with f1 & f2 . Even order products fixed. © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Distortion Measurements in Band Limited Systems Harmonic Distortion

f1 dB

– Most Harmonics above passband – Does not excite higher order non-linearities

Intermodulation Dist.

Frequency

f2

f1

dB

– f2 below passband OR IM products outside passband Frequency

Difference Frequency Dist. – Odd-order products within passband – Even-order products may be inside or outside passband

f2 f1 dB

Frequency

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

21

Diff. Freq. vs. Harmonic Distortion Harmonic Distortion

120

Fundamental 2nd Harmonic 3rd Harmonic 4th Harmonic

100

dB SPL 80

Effective cutoff: fMAX / N where N = Harmonic order Underestimates distortion at high frequencies

60 40 100

200

500

1k

2k

5k

10k

Difference Frequency Distortion 120

Fundamental 3rd Order DF -3rd Order DF -2nd Order DF

 f = 80 Hz

100

dB SPL 80

No inherent high frequency cutoff! Realistic estimate of high frequency distortion

60 40 100

200

500

1k

2k

5k

10k

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Crosstalk

In each 1/3 octave band: N

• Requires 2 Ear Simulators • Measurement S/N is poor:

L(f) = 10log10

 10

Li /10

i=1

– Use 94 dB SPL sinusoidal test signal – Convert to 1/3 octave as power summation* – Check background noise level (  -10 dB in each band!) 120

• Can measure sequentially – But best measured simultaneously Right (w/signal)

dB SPL

110

Left (other ear)

100

90

80

70 100

200

400

800

1600

3150

6300

12500

Frequency [Hz]

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

22

Crosstalk CL-R (f) = GL/R (f) – GR/R (f) [in dB] CR-L (f) = GL/R (f) – GR/R (f) [in dB]

for signal applied to RIGHT Ear for signal applied to LEFT Ear

0

Only applies to Active Systems with signal processing! -10

dB

-20

-30

Left/Right -40

Right/Left -50 100

1000 Frequency [Hz] © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

10000

Noise Isolation

Diffuse Noise Field • Reverberant Room and/or Uncorrelated Sources • 90 dB SPL at Test Point © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

23

Noise Isolation ‐ 1 100 Calibration

dB SPL

90

80

70

60

50 100

160

250

400

630

1000

1600

2500

4000

6300 10000

Frequency [Hz]

90 dBSPL Pink Noise w/ Real-time Filter Analysis OR FFT + 1/3 Octave Synthesis © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Noise Isolation ‐ 2 Open Ear Response 110

dB SPL

100

90

80

70

60 100

200

400

800

1600

3150

6300

12500

Frequency [Hz]

90 dBSPL Pink Noise w/ Real-time Filter Analysis OR FFT + 1/3 Octave Synthesis © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

24

Noise Isolation ‐ 3 G 1 (f) Noise Cancelation OFF! 110

dB SPL

100

90

80

70

60 100

200

400

800

1600

3150

6300

12500

Frequency [Hz]

90 dBSPL Pink Noise w/ Real-time Filter Analysis OR FFT + 1/3 Octave Synthesis © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Noise Isolation ‐ 4 G 2 (f) Noise Cancelation ON! 110

dB SPL

100

90

80

70

60 100

200

400

800

1600

3150

6300

12500

Frequency [Hz]

90 dBSPL Pink Noise w/ Real-time Filter Analysis OR FFT + 1/3 Octave Synthesis © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

25

Noise Isolation LPassive (f) = GNR-OFF (f) – GOpen Ear (f)

[in dB]

LActive + Passive (f) = GNR-ON (f) – GOpen Ear (f) LActive (f) = LActive + Passive (f) – LPassive (f)

[in dB] [in dB]

10 0 dB

-10 -20 Passive Attenuation

-30

Active + Passive Attenuation Active Attenuation Only

-40 100

1000

10000 Frequency [Hz]

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

IEC 60268‐1 Simulated Program Spectrum 10

[dB]

0

-10

Filtered Pink Noise*

-20

-30

*Crest factor limited to 2:1 (6 dB) – EN 50332 -40 10

100

1000

10000

100000

Frequency [Hz]

© Copyright CJS Labs 2017 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

26

EN 50332 Maximum Output EN 50332-1: System

EN 50332-2: Player

EN 50332-2: Earphones

IEC Program  Noise Input   at ‐10 dBFS

IEC Program  Noise Input

Input ‐ Adjust Level 

Measure SPL  Spectrum in  HATS Ear (30s)

Correct  Spectrum to  Free Field

Calculate A‐ Weighted Level

IEC Program Noise

Max Input Level

Measure Voltage  at Headphone  Jack (30s)

Measure SPL  Spectrum in  HATS Ear (30s)

Correct  Spectrum to  Free Field

Calculate Overall  Voltage Level A‐Weighted  Level =

NO

94 dB SPL ?

Output Limit:  < 150 mV ? YES

Output Limit:

Input Limit:  

<100 dB SPL(A)?

> 75 mV ?

© Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

Maximum Voltage • Maximum RMS voltage of the IEC 60268‐1 program noise signal, limited to a crest factor between 1.8 and 2.2, through the rated source impedance, which the headphone can tolerate without permanent damage* • Rated Long‐Term Maximum Voltage: – Signal applied for 10 periods of 60s ON, 120s OFF – *No change in specs after 4 hours of rest/storage • Rated Maximum Permanent Noise Source Voltage: – Signal applied continuously for 100 hours! – *No change in specs after 24 hours of rest/storage

NOTE: THIS IS A DESTRUCTIVE TEST! © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

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A Minimum Test Suite • L & R Frequency Response1 – Show Mean and all re-position trials

• Left-Right Tracking • L & R Harmonic Distortion2 • Free and Diffuse Field corrected responses 1Test

level, and nominal electrical impedance (if applicable) should also be reported 2-tone distortion test capability is not available.

2Assumes

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Headphone Test System to Earphone L & R Headphone Amp

PC with Measurement SW

Pistonphone USB from Headphone Multi-Channel D/A & A/D

Interface

SPDIF

(comprises Generator & Analyzer)

Bluetooth Interface

Microphone Power Supplies

HATS

from Ear Simulators

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Conclusion (1) • Insertion Gain • A FLAT INSERTION GAIN is the target! • This is ‘corrected’ from the measured response at DRP.

• Acoustic Impedance • Low Acoustic Z = Open • High Acoustic Z = Sealed

• Test System and Tests • • • • •

Requires a manikin equipped with calibrated ear simulator(s) Sine AND Noise stimuli may be required FFT Data requires 1/3 octave synthesis (power averaging) Most post-processing is simple dB subtraction Present data using the IEC 60263 preferred aspect ratio: – 10, 25, or 50 dB = 1 decade

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Conclusion (2) Vis-à-vis IEC 60268-7 {Ed. 3.0} 2010-1: • 120 amplifier ZOUT not representative in many cases • Average of 5 trials can mitigate positioning errors • Free & Diffuse Field responses provide useful estimates (bounds) of perceived response, i.e., the insertion gain • Left-Right Tracking in 1/3 octaves correlates to loudness match. Polarity is also important! • I/O response reveals range of linearity vs. input level • 2-Tone distortion tests are a realistic indicator of nonlinearity in band-limited systems • ANSI/ASA S3.7-2016 incorporates most of these refinements © Copyright CJS Labs 2016 – San Francisco, CA USA www.cjs-labs.com Email: [email protected]

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References • • • • • • • • • • • • • • •

C. J. Struck, “Refinements in the Electroacoustic Testing of Headphones”, proceedings of the Audio Engineering Society International Conference on Headphone Technology – Aalborg, Denmark (2016  August 24–26). IEC 60268‐7 – Sound System Equipment. Part 7: Headphones ANSI/ASA S3.7‐2016 – Earphone Measurement and Calibration IEC 60268‐1 – Sound System Equipment. Part 1: General ANSI/ASA S3.25‐2009 – Occluded Ear Simulator IEC 60318‐4 – Occluded Ear Simulator (formerly IEC 711). IEC 60118‐7 Electroacoustics – Simulators of human head and ear – Part 7: Head and torso simulator for the measurement of hearing aids IEEE Standard 1652‐2016 “IEEE Standard for Translating Head and Torso Simulator Measurements from  Eardrum to Other Acoustic Reference Points” ISO 4869‐3: 2007 – Acoustics – Hearing protectors ‐‐ Part 3: Measurement of insertion loss of ear‐muff type protectors using an acoustic test fixture European Standard EN50332‐1 (2000), “Sound system equipment: Headphones and earphones associated  with portable audio equipment. Maximum sound pressure level measurement methodology and limit considerations. Part 1: General method for “one package equipment” European Standard EN50332‐2 (2003), “Sound system equipment: Headphones and earphones associated  with portable audio equipment. Maximum sound pressure level measurement methodology and limit considerations. Part 2: Matching of sets with headphones if either or both are offered separately”. BS EN 62368‐1:2014 Audio/video, information and communication technology equipment. Safety  requirements J. Borwick, Loudspeaker and Headphone Handbook 3rd Ed. 2001 Møller, H. et al, “Design Criteria for Headphones” J. Audio Eng. Soc.,  Vol. 43, No. 4 – April 1995. Burkhard, M.D., editor, “Manikin Measurements”, Industrial Research Products, Inc., Elk Grove Village,  Illinois, U.S.A. (1978) – available as a PDF from G.R.A.S., Denmark

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