Hydrophones - Underwater Microphones

Hydrophones / Underwater Microphones

Brüel & Kjær hydrophones are individually calibrated, waterborne‐sound transducers. The instruments deliver a flat frequency response and are omnidirectional over a wide frequency range. All hydrophones are built with a shielded-element construction; completely waterproof, corrosion-resistant, and are able to withstand high levels of salinity. The instruments provide unrivaled depth, range, and precision when measuring sound in the lab and in ocean research.

Hydrophone Specifications
  • Spherical hydrophone Type  8105

    TYPE 8105

    Spherical Hydrophone

    Spherical hydrophone with rugged construction capable of withstanding pressures of up to 9.8 MPa (100 atm; 1000 m (3250 ft) ocean depth) and featuring exceptional directional characteristics.

  • Hydrophone Type 8106

    TYPE 8106

    Low-Noise Hydrophone with Preamplifier

    Hydrophone Type 8106 features a built-in, thick-film, and low noise, 10 dB preamplifier, delivering signal conditioning for transmission over very long distances. This makes Hydrophone Type 8106 suitable for underwater sound measurements down to 1000 meters depth. 

  • Miniature hydrophone Type 8103

    TYPE 8103

    Miniature Hydrophone 

    Miniature Hydrophone Type 8103 is a small piezoelectric transducer designed for high-frequency laboratory and industrial use. The instrument is particularly useful in the acoustic study of marine animals or for cavitation measurement.

  • Standard measuring hydrophone Type 8104

    TYPE 8104

    Calibration Standard Hydrophone

    A wide-range general purpose hydrophone that can also be used as a sound transmitter, making it ideal for calibration purpose. The hydrophone is supplied with 10 m waterblocked low-noise shielded cable to MIL-C-915 with BNC plug.

Hydrophones / Underwater Microphones


Brüel & Kjær hydrophones are piezoelectric transducers, designed to be used underwater for recording or listening to underwater sound.

The ceramic piezoelectric sensing element and its internal supporting structure are permanently bonded into sound-transparent, lead-free, nitrile butadiene rubber. Support structures are made from metal alloys that are extremely resistant to corrosion in virtually all hostile environments and have very good anti-fouling properties when immersed in seawater.

The internal support is mechanically and electrically isolated from the metal housing, being coupled only by synthetic rubber. This provides vibration isolation of the sensing element.


Each Brüel & Kjær hydrophone is submitted to an extensive aging and temperature stabilizing procedure before being individually calibrated. Individual calibration data and frequency response curves are supplied with each hydrophone.

The receiving sensitivity calibration of the hydrophones is traceable to international standards.


The frequency response of the four hydrophone types is shown here:

Frequency ResponseFrequency response measurements are made in a water tank in free-field conditions using a Brüel & Kjær PULSE™ calibration system. 


B&K Hydrophones deliver great omnidirectional sound measurements. The individual hydrophone directivity patterns in water, are shown here:


Hydrophone dispersion

The polar directivity patterns were measured in free-field conditions achieved using gating techniques in a water tank. This requires a standard hydrophone as a projector and the unknown hydrophone as the receiver.



Type 8103

Type 8104

Type 8105

Type 8106


-211 dB re 1 V/μPa

+/- 2dB

-205 dB re 1 V/μPa

+/- 3 dB

-205 dB re 1 V/μPa

+/- 2 dB

-173 dB re 1 V/μPa

+/- 3 dB

Nominal Voltage Sensitivity

29 μV/Pa

56 μV/Pa

2.24 mV/Pa

Nominal Charge Sensitivity*

0.1 pC/Pa

0.44 pC/Pa

0.41 pC/Pa


Capacitance* (incl. standard cable)

3700 pF

7800 pF

7250 pF


Frequency Response* (re 250 Hz) Continuous is valid with integral cable

0.1 Hz to 20 kHz

+1/–1.5 dB

0.1 Hz to 10 kHz

+/-1.5 dB

0.1 Hz to 100 kHz

+1/-6.5 dB

10 Hz to 10 kHz

+0.5/-3.0 dB

Length up to:

0.1 Hz to 100 kHz

+1.5/-6.0 dB

0.1 Hz to 80 kHz

+/-4.0 dB

0.1 Hz to 160 kHz

+3.5/-10.0 dB

7 Hz to 30 kHz

+0.5/-6.0 dB


0.1 Hz to 180 kHz

+3.5/-12.5 dB

0.1 Hz to 120 kHz

+4/-12.0 dB


3 Hz to 80 kHz

+6/-10.0 dB

Horizontal Directivity †

(Radial, XY Plane)

+/- 2 dB at 100 kHz

+/- 2 dB at 20 kHz

Vertical Directivity

(axial, xz plane):

+/-4 dB at 100 kHz

+/-2 dB at 50 kHz

+/-2 dB over 270° at

80 kHz

+/-2.5 dB at 100 kHz

+/-3 dB at 20 kHz

Leakage Resistance* (at 20 °C)

>2500 MΩ


Operating Temperature Range:

Short-term Continuous (-1 hr operation):

-30 to +120 °C

-30 to +80 °C

-10 to +60 °C

Sensitivity Change with temperature:

Charge Voltage:


0 to +0.03 dB/°C

0 to -0.03 dB/°C


0 to +0.03 dB/°C

0 to -0.04 dB/ °C


0 to +0.03 dB/°C

0 to -0.03 dB/°C


0 to +0.01 dB/°C

Max. Operating Static Pressure:

252 dB

= 4 x 106 Pa
= 40 atm
= 400 m ocean depth

260 dB

= 9.8 x 106Pa 
= 100 atm
= 1000 m depth


Sensitivity Change (Static Pressure):

0 to –3 × 10–7 dB/Pa
(0 to -0.03 dB/atm)

0 to 1 × 10–7 dB/Pa

0 to 0.01 dB/atm