Audio Visual Design Guidelines

Electroacoustics

10 views November 19, 2019 aetm 0

The electroacoustic implementation for any space includes design and configuration of active systems for the amplified reproduction of audio. Particularly in cinemas, performance venues and similarly critical spaces the required electroacoustic performance may heavily influence the physical acoustics.

In particular, we are seeking to

  • Provide audible speech and programme sound to all listeners (SPL, uniformity)
  • Maximise speech intelligibility (STI)
  • Achieve an acceptable frequency response by control any peaks or troughs that might cause discomfort

The designer will apply their professional judgement to shortlist appropriate components for the sound system based on the physical environments, the loudspeaker’s technical parameters and the designer’s subjective opinion on its voicing. An institution’s equipment or supplier preferences will influence shortlisting, but designers must always consider what is most appropriate for each space.

In larger spaces and those able to be linked or divided, speakers must be logically zoned. The simplest zoning may be for adjacent, linkable spaces, though in large spaces the audio feeding each zone may be delayed slightly to reduce late arrivals and improve intelligibility. In complex spaces, an audio DSP affords designers the capability to change level, equalisation, delay and dynamics instantaneously to cater for each possible room configuration.

Industry-standard tools and calculation methods should always be employed to refine each design, including:

  • Nomination of safe sound pressure levels, especially for extended listening
  • Calculation of the electrical power required (EPR) by the selected speakers to achieve the performance target
  • Calculation of the room’s stability (resistance to feedback) based on the needed acoustic gain (NAG), the potential acoustic gain (PAG) and the number of microphones required
  • Spacing of ceiling loudspeakers to achieve the desired uniformity based on their dispersion and sensitivity and the height of the ceilings
  • Calculation of audio delays to each zone to better synchronise arrivals or appropriately time-align different components

It may be appropriate to commission a detailed electroacoustic model to predict the coverage (SPL and uniformity) of amplified systems and/or unamplified speech in certain spaces, and to predict the intelligibility that may be achieved with the nominated system, room geometry and intended surface treatments. 

These models are prepared by specialists using an electroacoustic simulation program. A number of programs are available, and each targets a different market. 

  • Institutions will most commonly encounter AFMG’s Electro Acoustic Simulation for Engineers (EASE) as it is accessible to – and can be afforded by – the majority of professional audio contractors. Most manufacturers release EASE data for their loudspeakers (including line arrays) so they can be accurately modelled. Institutions should consider the availability of an infra-red module for EASE which will also permit modelling of some infra-red assistive listening systems to increase confidence that the system will meet Code.
  • Acousticians and sound system designers working on more complex spaces may prefer a specialist program such as Odeon which provides more comprehensive tools for acoustic analysis. Odeon also has the capability to model a wide range of speakers, though not all manufacturers can provide their data in the required common loudspeaker format (CLF).
  • Many specialist and DSP-steerable loudspeakers can only be modelled in proprietary tools provided by the manufacturer.

Members should remember that any model is used to validate and fine-tune the design. First principles calculations and the designer’s experience must still inform the type, location and power requirements of speakers. 

The level of detail in the model and the accuracy of surface material parameters directly affect the accuracy of the prediction, and the designer and modeller should agree the appropriate level of detail for each project.

Modelling is labour intensive and will be expensive in complex spaces. As discussed previously it cannot be assumed to be included in a standard AV or Acoustics consultant’s commission.

Was this helpful?