Electroacoustics Preview: an analysis of its value

Locations with bad acoustics: The Villa Galli case study
21 Gennaio 2019
Acoustic preview

The acoustic prediction allows you to “see” the sound of a PA system, which would otherwise be difficult to explain in word. It is a powerful tool for communicating with everyone involved in the installation, especially with those who have no direct experience with sound; even before calling riggers and technicians.

The electroacoustic prediction software simulate the performance of an audio system and the transmission of sound in the environment. There are two types of simulators: those specific to PA loudspeaker manufacturers and those of third parties, extended to multiple manufacturers. Many software also generate data for mounting and hanging the speakers. The simulation has only spread widely in the last decade with the surge in the computing power of computer CPUs. Today it can be modeled both in three and in two dimensions.

Define the objectives of the acoustic prediction

Simulating will help us evaluate different options and carry out a pre-eliminate optimization, but it will not teach us how to design a PA system. In fact, prediction is a means for the real objectives of “sound reinforcement”:

  • obtain a homogeneous coverage on the horizontal and vertical plane
  • move the sound image on stage
  • compare the required sound pressure level with that allowed by the PA
  • “Dirty” the stage, walls and ceiling as little as possible
  • maximize the intelligibility, dynamic range and reliability of the system
  • minimize distortion and background noise values.

I software di previsione elettroacustica consento di scegliere la tipologia e quantità dei diffusori, impostare livelli e ritardi dei sistemi main, front-fill, delay, in-fill e out-fill, oltre all’inclinazione verticale e orizzontale dei line array e dei point source. Questo permetterà di:

  • quickly compare multiple solutions for the project
  • be very precise
  • minimize interference between speakers
  • make all the material work safely
  • save time during installation and calibration
  • foresee variations and trade-offs in speaker positions
  • compensate for the lack of adequate equipment for testing .

Search for information about the project

At this point you need to know the details of the work you are going to do:

  • Customer needs (sound pressure level, low frequency headroom, opening or closing of seats according to the amount of audience)
  • Type of event (speech amplification, A/V contributions, live music concert,…)
  • Resources for site inspections
  • Availability of CAD plans and pre-visualization of the technical set-up.

The most common objective of acoustic prediction is uniform coverage in the vertical plane. Make sure that your software, in 2D mode, displays the result at the height of the receivers and not at the height of the speakers. This means that it works in 3D, even if the display is in 2D. Here’s what you need to draw:

  • Plans and heights of the location, balconies, ceiling and rear walls
  • Speaker (the main must be placed at the zero point in the section view)
  • Alternative positions for the speakers
  • Direction
  • Reflective surfaces (if the software allows it, also the type of material)
  • Variable configurations, such as orchestra pit, movable walls, motorized led walls,…

If you have a CAD of the location, make sure on site that the measurements match. Especially the heights. I use a Leica Disto, or a Bushnell if there is too much light.
Also check that the temperature and humidity of the air are not totally different from those set on the software. I use HTC-1.

Build the sound system

If you haven’t yet defined the amount of speakers for the suspended line array, start with an appropriate number for your purpose and have the software process the angles between the speakers with the auto-splay function. If the result is a set of wide, slightly growing angles from the top to the bottom speaker, you should add more to the array.

Divide the whole area, with the section view, into similar segments and keep as a reference the final result of homogeneity on the high frequencies. The shorter the segments, the higher the dB SPL value that the PA can reach. At the same time, the smaller the sound pressure drop as we move away from it. An array resting on the stage will have lower homogeneity than a suspended array. In particularly “difficult” locations, you can increase the directionality of the low frequencies by increasing the length of the array, that is, adding more speakers to it.

A good starting point will be a 6 dB drop in the last session, with the first reference row. The more we add speakers to the array, the more we will have the possibility to lower this value. However, reaching a hypothetical 0 dB will be unnatural, because we are used to an increase in volume as we approach the source. For some outdoor applications, we may need a significant drop towards the back rows to prevent noise pollution problems on neighboring homes.

Use the analyzers

Starting from an acoustic prediction, analysis and measurement software such as Rational Acoustics Smaart, AFMG SysTune, AFMG SysTune or SATlive can be used as tools to verify the simulation.

Calibrating a PA without having done a project won’t buy us time. On the contrary, it will be known exactly where:

  • position the measurement microphone to check the alignment of the front-fills or delays with respect to the main
  • check uniform coverage of in-fill and out-fill
  • immediately understand if there is an assembly or setup problem.

Modifying the project data – because for example the PA is physically to be moved – will take us less time than starting from scratch and with only the help of the analysis software. Then, with field measurements, the theories of predictions will be tested. If you have no way of carrying out checks and measurements, insert the data found with the forecast on the machines: you will still have an excellent starting point.

Progetto audio

L’Acoustics Soundvision

The preview is a model, not reality

The electroacoustic preview cannot be perfect, but this is not the important thing. The acoustic effects related to the transmission of sound such as refraction, diffusion, diffraction, resonance, are difficult to calculate. The air temperature, humidity and wind also play their part. In addition, the accuracy decreases with increasing distance.

The PA can be considered as a large lamp: you need to know how to aim it to illuminate the audience. The latter will act as an absorbent surface, and much of the effect of the environment will disappear. In particularly unfavorable and reverberating places – such as sports halls – the problem will remain. But we will be able to understand how the walls adjacent to the audio system and the public will behave, finding the best compromise on pointing.

If you know its limitations, you can interpret the results. The usability of the software will be limited if your knowledge of acoustics and electroacoustics is limited. I believe that without foresight, an experienced technician will design a better PA than a novice who uses software. But a professional who fully exploits the potential of these tools will have unparalleled results.