Omni-directional sound sources

The Automotive and Marine section of ISVR Consulting has developed two near omni-directional sound sources specifically for the measurement of road vehicle airborne and structure borne transfer functions.  The sound sources are driven by a custom-built signal generator and amplifier unit.  Full details are given below.  A brochure giving the same information is available for download in Acrobat (pdf) format.  The sound sources have proved to be very versatile and their application is not confined to road vehicles.

High Frequency Sound Source

The high frequency sound source, photo

The high frequency source

The high frequency sound source provides near omni-directional radiation up to around 8  kHz. It was designed specifically for the measurement of road vehicle airborne transfer functions where it provides sufficient acoustic energy to enable P/Q functions to be reliably measured above around 200 Hz using both direct and reciprocal methods.

The high frequency sound source consists of a horn driver unit, which is connected to a radiating orifice via a 3 metre long flexible tube. This allows the source to be positioned in relatively confined locations. The source should produce a consistent calibrated output level which is largely unaffected by the routing of the tube.

The orifice contains a small microphone that is connected to a preamplifier in the base of the driver unit. The output from this is available on a BNC socket on the base of the sound source. The microphone system produces an approximation to the sources free field 1 m sound pressure level. This provides a reliable integrity check of the complete sound source system as well as allowing real time acoustic transfer functions to be measured. Although originally developed for automotive applications, this versatile high frequency source is increasingly being used in far wider fields such as marine and general machinery noise control. Each source is individually built to a client's specification, but an outline specification of a typical source is given in Table 1.

 

Table 1 - Outline Specification for the
High Frequency Sound Source

One-third octave band Sound Pressure Level at 1 metre   55 dB at 200 Hz
 85 dB at 3 150 Hz
Omni-directionality   ± 1 dB:  < 2 000 Hz
 ± 2 dB:  2 000 Hz - 10 000 Hz

 

Low Frequency Sound Source

 Low Frequency sound source

The low frequency source

The low frequency sound source provides near omni-directional radiation from 30 Hz to 300 Hz. It was designed specifically for the measurement of road vehicle structure borne transfer functions where it provides sufficient acoustic energy to enable P/F functions to be reliably determined using reciprocal methods.

The device consists of a 200 mm driver unit connected via a composite reverse cone to an 80 mm diameter-radiating orifice.

A small probe microphone is mounted centrally in the radiating orifice, allowing an estimation of volume velocity to be monitored in real time. The signal for the probe is conditioned by electronics mounted in the base of the device. Each source is individually built to a client’s specification, but an outline specification of a typical source is given in Table 2.

 

Table 2 - Outline Specification for the
Low Frequency Sound Source

Frequency range   ≈ 30 Hz to 300 Hz
One-third octave band Sound Pressure Level at 1 metre   70 dB at 30 Hz
 90 dB at 200 Hz
Overall diameter   240 mm
Overall height   430 mm
Radiating orifice diameter   80 mm

 

Signal Generator and Amplifier Unit

Each of the high frequency and low frequency units are powered by the same design of signal generator and amplifier unit. Coded cable connections ensure the correct filters in the electronics are selected for the two different sources.

The power unit incorporates both a white and pink noise generator as well as an external signal input. The power amplifier is a nominal 150 watt VFET device with a 60 dB gain range in 6 dB steps.

 

Delivery

The sources are made to order and an estimated delivery date will be given on request. Typically delivery is between 6 and 8 weeks from receipt of order.

 

Costs

Each sound source is supplied complete with a signal generator and amplifier unit. Contact us by email, post or phone for up-to-date prices and delivery details.

 

Contact

For further information regarding facilities and capabilities please contact us