National Physical Laboratory

Acoustic calibration and testing at simulated ocean conditions (in the NPL Acoustic Pressure Vessel)

Acoustic Pressure Vessel Integrity testing of marine components Acoustic properties of materials 

The increasing level of man-made sound in the ocean (whether deliberately generated or not) has led to concern over marine noise pollution. In particular, exposure of marine life to underwater man-made noise is of growing concern as the effects of this exposure begin to be understood. NPL provides guidance and expertise in the measurement and assessment of underwater radiated noise and conducts noise surveys in collaboration with academic partners.

For more information on the Acoustic Pressure Vessel (APV), contact Stephen Robinson

The APV is designed for free-field testing of underwater acoustic transducers under simulated ocean conditions, providing a cost-effective alternative to sea-trials.

Features of the facility include:

  • simulation of ocean depths of up to 687 m [6,895 kPa or 1000 psi]
  • water temperature may be controlled within the range 2 ºC to 35 ºC
  • steel vessel 2.5 m in diameter and 7.6 m long
  • operating frequency range from a few kHz to 1 MHz
  • walls and ends are lined with acoustically absorbing wedges to reduce reverberation and allow the use of high pulse repetition rates
  • filled under vacuum to minimise air bubbles
  • two access ports - large port is 0.84 m in diameter with a rotator shaft allowing rotation of devices weighing up to 350 kg
  • High-pressure pumps provide pressurisation from ambient atmospheric pressure to 6.9 MPa with a rate which is variable from 35 kPa per minute to 1.5 MPa per min
  • supported on four air-filled anti-vibration mounts to provide isolation from ground-borne vibrations and achieve a low ambient noise level
  • pneumatic lid actuators enable rapid access to APV to replace transducers, etc

Versatile computer control system provides:

  • pre-programmed sequences for standard operations to improve operating time sequences and efficiencies – for standard operations such as filling under vacuum, changing pressure, pressure cycling, changing temperature
  • real time indications of pressures, temperatures, flow rates at all critical points in the system
  • trend plots showing history of pressure and temperature variation (trend data is exportable in bitmap form for use in reports, etc.)

APV Specifications

Feature Description
Frequency Range 2 kHz to 500 kHz for sensitivity, 2 kHz to 1 MHz for directional response and electrical impedance
Free Volume Provided
by Acoustic Lining
1.93 m diameter and 4.0 m long
External Dimensions 2.5 m diameter and 7.6 m long
Access Ports Two ports 2.4 m apart: one port having access diameter 0.84 m and the other 0.50 m
Measurement Distance One fixed stage and one moveable to give distance range 0.8 m to 2.5 m. Rotation of main shaft through 360°. Rotating the device mounted on the moveable carriage by ±30°
Device Handling Overhead crane with continuous fine control of speed, comprehensive safe support system for large lid during device monitoring procedures, and a versatile lifting platform to aid device attachment
Maximum Weight For devices under test 350 kg
Hydrostatic Pressure 20 kPa to 6895 kPa, normal rate of change variable from 35 kPa per minute to 1500 kPa per minute (5 psi to 220 psi per minute)
Temperature 2 °C to 35 °C
Cable Specifications Electrical lead-through to take cable from 5 mm to 20 mm diameter and connectors up to 38 mm diameter
Signal Power Analogue Associates MA 5000VZ amplifier (5 kW, DC to 25 kHz); Brüel & Kjær 2713 100 W amplifier (DC to 200 kHz); Krohn-Hite 7500 75 W amplifier (DC to 1 MHz); ENI 240L 200 W amplifier (20 kHz to 10 MHz)
Pre-soak Facility Pre-conditioning of the temperature of devices of size up to approx. 1 m using pre-soak tank independently controlled from the main pressure vessel facility
Device Mounting Full information on the device/flange mounting arrangements is available on request


NPL provides a unique a range of facilities and measurement services to meet the individual measurement needs of the customer. The following services are offered over the full range of operating conditions of the APV: temperature range from 2 °C to 35 °C and at simulated ocean depths of up to 687 m (6.8 MPa or 1000 psi).

Services for test and calibration at simulated ocean conditions using the APV:

  • Free-field testing of underwater acoustic transducers and hydrophones over the frequency range from a few kHz to 1 MHz.
  • Evaluation of the acoustic properties of panel materials including echo reduction, transmission loss, etc. The operating frequency range is from approximately 1 kHz to 100 kHz for a maximum panel size of 0.8 m wide by 0.9 m high.
  • Free-field testing of underwater acoustic transducers and sonars including transmit and receive sensitivity, electrical impedance, directional response, etc. The operating frequency range of the test chamber is from a few kHz to 1 MHz.

Our experienced team of scientific staff offer a flexible cost-effective approach to test work with a choice of service arrangements:

  • Fixed price - Calibration and tests undertaken by NPL staff on customer devices to a schedule agreed with the customer, with results presented in a report.
  • Day rates - Calibration and tests undertaken by NPL staff in collaboration with customer staff on customer devices to a schedule agreed with the customer.
  • Facility hire rates - Hire of facility by customer including NPL staff trained to use the facility.

Other options may also be considered.

Download Underwater Acoustics Pressure Vessel flyer Adobe pdf file


Customer Services tel: +44 20 8943 8631

Last Updated: 29 Mar 2012
Created: 6 Jun 2007


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