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.  The sound sources have proved to be very versatile and their application is not confined to road vehicles.

 

High Frequency Omnidirectional Sound Source, MkIII

The high frequency sound source, photo

The high frequency source

The high-frequency sound source provides near omni-directional radiation up to 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 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 34 mm diameter, 3 metre long flexible hose allowing the source to be positioned in relatively confined locations. The source will produce a consistent calibrated output level which is largely unaffected by the routing of the tube, as long as care is taken to avoid crushing the hose.

The orifice contains a small microphone that is connected to a preamplifier in the base of the driver unit, the output from which is available on a BNC socket on the sound source. The microphone system produces an approximation to the free-field sound pressure level at 1 metre and 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.

 

Table 1 - Outline Specification for the
High Frequency Sound Source

One-third octave band 
Sound Pressure Level at 1 metre 
 54 dB at 300 Hz
 > 81 dB 2 000 - 10 000 Hz
Omni-directionality   ± 1 dB:  < 2 000 Hz
 ± 2 dB:  2 000 Hz - 6 300 Hz

Download specification for the High-Frequency Sound Source and Noise Source Power Unit

 

Low Frequency Sound Source, MkII

 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 vibro-acoustic 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.

 

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

Download specification for the Low-Frequency Sound Source

 

Noise Source Power Unit MkIV

The Noise Source Power Unit is a combined white/pink noise signal generator and power amplifier designed to drive a number of different sound sources.  It will drive the Low-Frequency Omni-directional Sound Source that covers the range 20 Hz to 500 Hz and the High-Frequency Omni-directional Sound Source that covers the range 200 Hz to 10 kHz. The unit will also drive the Tailpipe and Intake Noise Simulator (TINS). The Noise Source Power Unit is a stable, calibrated device that produces a consistent and repeatable acoustic output from the various sound sources.

Filters within the Noise Source Power Unit are selected automatically when a sound source is connected, as each source has its own unique connector which is recognised by the Power Unit.

The Power Unit contains a digital signal processor, a Class D audio amplifier, and a power supply. The processor produces white noise, pink noise or a swept sine wave, or will accept and process an external input signal.

 

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 Noise Source Power Unit and is individually calibrated. 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