Testing With Hemi-Anechoic Chambers
January 9, 2020 | Anechoic, Testing
Audio testing facilities come in a number of different forms. Most of these involve an anechoic chamber of some kind. These are used to isolate the test item from ambient sounds, but there are different types of anechoic chambers too, with both fully and hemi-anechoic chambers in use.
What Is an Anechoic Chamber?
At its simplest, an anechoic chamber is a space that is lined with sound-absorbing material. This eliminates echo and thus provides a controlled testing environment. Full anechoic chambers are lined on all surfaces.
However, hemi-anechoic chambers have only the walls and ceiling lined, leaving the floor flat. The name comes from the fact that the testing field area is a ‘hemisphere’. This still allows accurate measurements to be taken. There are other advantages too – for example, it’s easier to move objects to be tested in and of the chamber if there’s a flat floor. In full anechoic chambers there would be a need to cover and protect any wedges on the floor when moving objects around.
How Are They Used?
This type of chamber is commonly used in testing machinery and vehicles in order to pinpoint sources of noise and vibration. The walls and roof of the chamber are lined with sound-absorbent wedges, and a movable microphone array is then used to measure sound at different points. Microphones positioned at the sides can also be ‘pulsed’ in order to simulate how sound might be created by a moving vehicle.
Design Issues
When creating hemi chambers, there are many different factors that need to be taken into account. Often these are used to test engines, so a ventilation system that is capable of bringing in air and removing fumes is essential, but it needs to run silently. It’s necessary to control heat and humidity inside the camber in order to guarantee consistency of results, so this too needs to be done in a way that doesn’t generate extra sound.
Of course, engineers need to be able to monitor what is happening inside the chamber. There must be provision for this while also ensuring that the routes for any cables attached to monitoring equipment do not permit the transmission of unwanted noise. This can be dealt with using removable floors, allowing cable access from below without disrupting the test chamber environment.
As well as ventilation and climate control, here at IAC we can provide all of the items needed to successfully create hemi-anechoic chambers. These include acoustic doors, available in single or dual leaf forms as well as sliding types, and wedge baskets to allow accurate positioning and fixing of the sound-absorbing material. We can supply vibration isolation systems too in order to ensure accurate testing of machinery.