Loudspeaker cabinet characterization using particle-velocity
Loudspeaker cabinet design pursues to provide the appropriate acoustic loading for the drive units while ensuring a good performance of the complete system. The vibrations induced by the driver frame and moving air mass within the enclosure should be therefore controlled in order to minimize the radiation from the cabinet itself. There are several methods to capture and visualize the vibro-acoustic behaviour of a radiating sound source, but often they are tedious or impractical. Nearfield acoustic holography (NAH), for instance, uses an inverse approach to predict the surface displacement of a vibrating object based upon acoustic measurements, traditionally performed with pressure microphones. However, the complex analytical models required to back-propagate the acquired data are fairly sensible to the acoustic environment and complex source nature. Thus, NAH is not suitable for every measurement case. In contrast, direct sound field visualization offers a more flexible approach to display sound phenomena. Sound maps are excellent tools for building understanding about a wide range of specific problems. Novel scanning methods have been recently introduced to accurately map stationary sound fields in an efficient way. In the previous literature, sound pressure, particle velocity, intensity, sound absorption and acoustic impedance have been measured with a new scanning method developed by Microflown Technologies called “Scan & Paint”. This methodology is based upon the acquisition of acoustic data by manually moving a P-U probe (pressure-particle velocity sensors) across a sound field whilst filming the event with a camera. It is then possible to visualize sound variations across the space in terms of any acoustic quantity. This efficient measurement method allows us to display the sound field and also assess the dynamic behaviour of the enclosure via particle velocity. In addition, the pressure contribution from the different cabinet sides can be calculated by applying transfer path analysis to the acquired data. The measurement methods presented in this paper provide novel approaches for enhancing a cabinet design in a fast and efficient way. The main advantages of the proposed procedure are linked to the use of a single scanning probe. Results from direct sound visualization, intensity vector field investigation, operational deflections shapes and panel noise contribution analysis are presented throughout the following sections.
Fernandez Comesana, D., Grosso, A. and Holland, K.R., 2013. Loudspeaker cabinet characterization using a particle-velocity based scanning method. In German Annual Conference on Acoustics.