Low Noise, Low Distortion and Flat Response for Loudspeaker, Headphone and Microphone Measurement

APx1701 Transducer Test Interface

The APx1701 Transducer Test Interface is an APx accessory device that integrates instrument-grade amplifiers and microphone power supplies for designers and production test engineers seeking clear insight into the behavior of their electroacoustic devices.

Primarily designed for electroacoustic testing, the system drives loudspeakers and headphones with dedicated power amplifiers, enables impedance measurements, and provides power to measurement microphones and microphones under test. Its functions are integrated with the APx500 audio measurement software and a connected APx analyzer. It requires a B Series or legacy APx analyzer and is supported by APx500 audio measurement software version 4.3 or later.



Quiet, Clean and Flat – A New Standard in Amplifier Performance

With an industry-leading signal-to-noise ratio (SNR) of 134 dB, the APx1701 provides 20 dB of fixed-gain amplification from DC to 100 kHz. In the frequency range of 10 Hz to 20 kHz, the APx1701’s residual THD+N is ≤ -100 dB (80 kHz BW), and frequency response is ±0.08 dB (DC-coupled). The system’s power amplifiers are configured as two independent channels, with power ratings up to 100 W for a single channel into 8 Ω. Voltage taps across integrated current-sense resistors in the amplifier outputs enable easy impedance measurements.

For microphones, either as measurement mics or as the device under test (DUT), the APx1701 is equipped with pairs of balanced and unbalanced microphone inputs. The balanced inputs include switchable +48 V phantom power, while the unbalanced inputs support switchable CCP (Constant Current Power) and are TEDS-capable (Transducer Electronic datasheet).

Integrated Analog, Digital and Electro-Acoustic Testing

The increasing complexity of audio devices (wireless Bluetooth speakers or active noise-canceling headphones, for example) is driving ever-more complicated test scenarios, especially if engineers have to repeatedly switch measurement instruments.

As an electroacoustic test accessory, the APx1701 is directly integrated with APx500 audio measurement software and, when paired with any B Series or legacy APx analyzer, provides an integrated platform capable of evaluating the performance of electroacoustic devices as well as their analog and digital components.

Calibrated Instrumentation

Whether in the lab characterizing a design’s performance or conducting QA-testing on the production line to ensure products meet their specifications, confidence in the resulting measurements is key.

Like the APx500 Series audio analyzers it is designed to complement, the APx1701 is a calibrated instrument under ISO / IEC 17025:2005 and all new units ship with an Accredited Calibration. Calibration provides documented and traceable verification that instruments meet or exceed all of their published specifications.



APx1701 accessory cable kit (CAB-1701)
This kit provides additional cables to support additional test scenarios. Includes:

  • 2 BNC-BNC cables (14 in; 36 cm)
  • 1 XLRF to XLRM cable – blue (2 ft; 61 cm)
  • 1 XLRF to XLRM cable – red (2 ft; 61 cm)
  • 1 SpeakON to BNC loopback cable with 100 Ohm to ground (2 ft; 61 cm)

APx1701 self-test fixture kit (SLFT-KIT-1701)
Provides load box and cabling to support performance self-testing of APx1701. Includes:

  • Load box with 2 x 5 W, 8 ohm loads
  • 1 SpeakON-SpeakON cable (3 ft; 91 cm)
  • 2 BNC-BNC cables (3 ft; 91 cm)
  • 2 BNC-BNC cables (14 in; 36 cm)
  • 2 XLRF to XLRM cables – blue (2 ft; 61 cm), 2 XLRF to XLRM cables – red (2 ft; 61 cm)
  • Instructions

SpeakON-to-BNCThis is our off-the-shelf cable designed for easy connection of a GRAS mouth simulator to the APx517 B series acoustic analyzer, or to connect a mouth simulator to an APx1701 when connected to any of our other APx5XX analyzers. The cable comes in two and five meter lengths.

  • CAB-SPK-MS-2M:Two-meter SpeakON-to-BNC cable
  • CAB-SPK-MS-5M: Five-meter SpeakON-to-BNC cable


Listed below are APx500 software options related to electroacoustic and perceptual audio testing. These are options intended for B Series or legacy APx analyzers (not the APx1701).

For B Series APx analyzers and legacy APx analyzers running version 5.0 software, software option licenses are electronically activated and are tied to a specific analyzer via serial number. For legacy APx analyzers running APx software version 4.6 or earlier, software option licenses are enabled by “iButtons” that mount on the rear of the instrument.

Electroacoustic Production Test (SW-SPK-PT)
The SW-SPK-PT option enables high-speed production test of electro-acoustic devices, providing key loudspeaker measurements in a single one-second sweep. Results include Rub & Buzz detection, essential Thiele-Small parameters, and impedance magnitude and phase. A proprietary modulated noise measurement is also provided to aid in detecting enclosure air leaks.

Electroacoustic R&D (SW-SPK-RD)
The SW-SPK-RD option delivers a complete suite of measurements and results tailored to the needs of designers and engineers developing electro-acoustic audio products. It includes key measurements and results such as complete Thiele-Small characterization; time-gated, quasi-anechoic Acoustic Response; Impedance analysis; plus the Loudspeaker Production Test measurements.

Perceptual Audio Test: POLQA (SW-POLQA-2)
Perceptual audio measurement returns a subjective assessment of speech quality using the next-generation POLQA algorithm for wide-band speech devices or devices with acoustic coupling. (Successor to PESQ with support for HD Voice, 3G, 4G/LTE and VoIP technologies)

Speech Intelligibility: ABC-MRT Measurement (SW-ABC-MRT)
The APx ABC-MRT plugin is a software option for APx500 audio measurement software that provides speech intelligibility measurement based upon the ABC-MRT speech processing algorithm developed by the Institute for Telecommunication Sciences (ITS) of the United States National Telecommunications and Information Administration (NTIA).

Speech Intelligibility: Speech Transmission Index (SW-STI)
SW-STI is a plug-in for conducting Speech Transmission Index (STI) measurements using the STIPA method.

Specifications & Requirements


  • Power Ratings
    100 W (1 channel into 8 Ω)
    60 W (1 channel into 4 Ω)
    30 Vrms (2 channels into ≥15 Ω)
  • Frequency Range
    DC to 100 kHz
  • Frequency Response
    ±0.08 dB (10 Hz to 20 kHz, DC-coupled)
    ±0.30 dB (20 kHz to 50 kHz)
    ±0.80 dB (50 kHz to 100 kHz)
  • Voltage Gain
    20.0 dB [x10]
  • Residual Noise
    ≤7.5 µVrms (22 kHz BW)
    ≤13 µVrms (80 kHz BW)
  • Signal-to-Noise Ratio
    ≈134 dB (ref 30 Vrms output)
  • Output Impedance
    ≈0.13 Ω (0.1 Ω current sense resistor in series with the – output terminal)
  • Residual THD+N
    ≤ –100 dB, 10 Hz to 20 kHz (80 kHz BW)


  • Configuration
    Balanced and Unbalanced (2 each)
  • Balanced Mic Inputs
    2 female XLR
    Switchable +48 V phantom power
  • Unbalanced Mic Inputs
    2 BNC
    Switchable CCP (4 mA, +24 V)
  • Maximum Input
    10 Vpk Balanced
    5 Vpk Unbalanced
  • Residual Noise
    Determined by analyzer; inputs passively switched
  • Input Crosstalk
    ≤ –78 dB + 1 µV to 20 kHz