Eastern Branch

Acoustics With Lasers

Presentation By

Ben Piper

National Physical Laboratory

Tuesday 31st March 2015 at 7pm

The Weston Homes Community Stadium

United Way, Colchester, Essex, CO4 5UP

(See below for directions)

Lasers are used in a variety of acoustical applications and are integrated into systems measuring displacement, velocity and pressure. This presentation will detail two methods, currently being researched at NPL, which make use of lasers to measure particular properties of airborne sound.

The first is a method for measuring free field acoustic particle velocity in an absolute fashion using photon correlation spectroscopy. Essentially, this is a measurement of the oscillation of particles in the air due to a propagating sound-field. This technique could provide a new standard for the free-field calibration of microphones by allowing the direct measurement of the Pascal at a single point within an anechoic chamber which can be used to obtain the sensitivity of a microphone placed at the same point. The latest results show that measurements can be made up to 20 kHz and with various different microphone types.

The second method makes use of a scanning laser vibrometer to exploit the acousto-optic effect. This technique can give spatially detailed information about the sound radiating from a sound source or the interaction between a surface and an incident sound wave. This method can be used to explore how sound diffracts around a loudspeaker cabinet, the effect of a loudspeaker crossover circuit or how sound is reflected from a diffusing or absorbing surface.

CPD Certificates will be available.  

There is no need to book places for this event.  Please direct any questions about the meeting to Hugo Cass, Secretary Eastern Branch

 [Tel. 07970 807526]     [E-mail: info@ammonite-acoustics.co.uk]  

For all Regional Branch activities please refer to the IOA website at: www.ioa.org.uk

 Directions to the Weston Homes Community Stadium

Postcode for satnav users is CO4 5UP

Driving From London:

Take the A12 towards Chelmsford off M25 and follow A12 beyond Chelmsford towards Colchester
Do not take any of the early exits off the A12 signed Colchester Central but instead carry on to the new Junction 28 (signposted for the Hospital), which takes you directly into the stadium site.

Having turned off onto the slip road, turn right at the first roundabout. Go across the bridge and then go straight over the second roundabout, before turning right into United Way from the third roundabout. You are now at the stadium

Driving From Ipswich:

Take the A12 from Ipswich towards Colchester

Turn off at the new Junction 28, signposted for the Hospital

Turn left at the first roundabout. Turn right into United Way from the second roundabout. You are now at the stadium

Train / Bus:

Take Greater Anglia train to Colchester North Station

First Group buses from North Station to stadium include: No 65