Hardware and software – listing
The following hardware and software is used in performing and post-processing Headphone Test Lab's measurements, and creating the SVG results files.


Artificial Ear
GRAS RA0150 cheek simulator plate
GRAS KB5001 large left anthropometric pinna (Shore 00-35)
GRAS KB5000 large right anthropometric pinna (Shore 00-35)
GRAS RA0307 conversion kit
GRAS RA0402 high resolution ear simulator
GRAS 40AO pre-polarised half-inch microphone capsule
GRAS RA0001 right-angle adaptor
GRAS 26CB preamplifier
(In preparation) low 1/f noise impedance converter for the 40AO
GRAS 12AL constant current power supply
GRAS RA0080 preamplifier input adaptor (for system testing)

Artificial head
Custom-built from laminated 12mm and 18mm MDF sheet with optional spring support for isolation from external vibration, natural frequency ~6Hz (KH)

Stand for artificial head
Pillar stand constructed from 4-inch × 2-inch rectangular aluminium extrusion, filled with marble flour for resonance suppression. Bottom plate attaches to the Outline turntable, see below. The artificial head can be decoupled from the top plate using coil springs, resonance frequency ~6Hz (KH)

Microphone (sound emission measurement)
Røde NT2-A, calibrated by reference to a GRAS 40BE/26CB/12AL, used with a Røde SM6 shock mount for isolation from external vibration

Headphone amplifier (frequency response measurements)
Lehmann Black Cube Linear

Headphone amplifier (distortion measurements)
Custom-built, battery-powered (4× PP3), mono, ultra-low distortion design using a TI LME49860 op-amp and LME49600 unity-gain buffer, with servo circuit to remove DC output offset (KH)

Microphone preamplifier (frequency response measurements)
Custom-built, battery-powered (2× PP3) mono, low distortion design using a TI LME49720 dual op-amp (KH)

Microphone preamplifier (distortion measurements)
Custom-built, battery-powered (4× PP3), mono, ultra-low distortion design utilising a TI LME49710 op-amp (KH)

Microphone preamplifier (sound emission measurement)
Custom-built, mains-powered, mono, low distortion, balanced design with phantom powering, using Analogue Devices AD797 op-amps (KH)

Sound card
M-Audio Audiophile 192

Bluetooth transmitters
Avantree Oasis Plus (codecs: SBC, aptX, aptX HD, aptX Low Latency)
MEE Audio Connect (codecs: SBC, aptX, aptX Low Latency) 

Loudspeaker for isolation measurements
(In preparation) Custom-built, three-facet, eighth-of-a-sphere, corner-located design using three KEF Ci132CR Uni-Q arrays (KH)

Turntable for isolation measurements
Outline ST1 with ET1 controller

USB interface for the Outline ET1
Custom-built using a Numato 8-channel USB GPIO module (KH)

Test stand for measuring insert headphones
Custom-built using 3mm shock cord to provide vibration isolation for the GRAS RA0402 ear simulator (KH)

Test stand for head clamping force measurement
Custom-built using a Zemic L6D 3kg class C3 load cell and Leo Bodnar load cell amplifier board, calibrated using a G&G M2 500g precision mass (KH)

Right channel isolation box for crosstalk measurements
Custom-built (KH)

Impedance measurement box
Custom-built using a 102 ohms 0.1% 1W series resistor (KH)

Weighing scales
Tree HRB 3001 precision electronic balance (0-3kg, 0.1g resolution, accuracy ±3d)

AC millivoltmeter (for setting signal level)
Uni-T UT632 (4-bit display, accuracy ±(0.5%+15))


Impulse response measurement
ARTA Labs Audio Real Time Analysis (ARTA), v1.7.0 or later, used in two-channel mode to eliminate the effect of source frequency response

Impulse response measurement (Bluetooth)
Custom-written code (KH)

Impedance measurement
Custom-written code (KH)

Isolation measurement
Custom-written code (KH)

Nonlinear distortion measurement
(In preparation) Custom-written code (KH)

Sound emission measurement
Custom-written code (KH)

Measurement post-processing
Custom-written code (KH)

SVG table/graph creation
Custom-written code (KH)


Thanks to:

  • GRAS Sound & Vibration A/S for long-term loan of the RA0402.
  • Sean Olive and Todd Welti of Harman International for details of the Harman target responses.
  • Peter Selinger for potrace v1.15, used to convert the Headphone Test Lab logo to SVG.
  • The developers of Inkscape, which was invaluable for converting supporting diagrams to SVG.
The custom-built headphone amplifier is based on a circuit in TI’s LME49610 datasheet.
The microphone amplifier for the sound emission measurement is based on mic amp and power supply kits from www.diy-tubes.com.
The Lehmann Black Cube Linear is a review sample.
All other commercial hardware and software is owned/licensed by KH.