technology

Discover the new digital “semi-anechoic” type audio measurement chamber

The semi-anechoic measurement chamber benefits from a floor separated from the ground to avoid structure-borne transmissions. The walls and ceilings are covered with special absorbent materials.

© Guillaume du Mesgnil d’Engente / Digital

The summer of 2022 marked a turning point for Digital, with major developments for our laboratories. Among them, the Audio lab has seen its design completely changed thanks to the construction of a semi-anechoic type measurement chamber.

Sanctuarize audio measurements

In order to better understand why this new feature constitutes a major change for Digital, and so for the tests delivered to our readers, let’s go back a bit. As we explained in our previous article on the new Image & Sound laboratory, the two entities were previously separate.

The Image & Sound lab where the remote test equipment useful for measurements in the semi-anechoic chamber is positioned.

The Image & Sound lab where the remote test equipment useful for measurements in the semi-anechoic chamber is positioned.

© Guillaume du Mesgnil d’Engente / Digital

The Image lab managed televisions, video projectors and other monitors while the Sound lab evolved in parallel. We tested the speakers, wireless headphones, but also the audio part of a television. From now on, this operation is over with the pooling of the Image laboratory and the Sound laboratory.

The new Image & Sound lab enables tests to be carried out on the image or even on the electrical consumption of products. It also allows testing of consoles or video games and even accommodates a 3D printer. Above all, it makes it possible to have a perceptual analysis of audio equipment thanks to its design in the form of an auditorium. Finally, the new space integrates our audio measurement equipment, which is now separated from the space where the audio tests are carried out.

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Our measurement microphone ready for action.

Our measurement microphone ready for action.

© Guillaume du Mesgnil d’Engente / Digital

A semi-anechoic chamber with Digital

This great first for our newsroom marks the largest investment ever made by Digital in its laboratories with the arrival of a semi-anechoic chamber. Thanks to it, the audio measurements are protected for the best possible precision, instead of being carried out in a laboratory mixing work and test spaces.

A measurement microphone is required for a speaker test while the Rick dummy replaces it for a headphone test.

A measurement microphone is required for a speaker test while the Rick dummy replaces it for a headphone test.

© Guillaume du Mesgnil d’Engente / Digital

But then, what is a semi-anechoic type measuring chamber? Also called anechoic room, this place must meet certain acoustic characteristics to carry out the tests in the best possible conditions. Indeed, testing and measuring the audio part of a product requires taking two main elements into account.

Two objectives: isolate and absorb

On the one hand, the audio measurements must not be disturbed by the exterior in order to measure only the performance of the product. Then, the measures must only represent the direct performance, without the room exerting an influence. Reverberations must therefore be limited.

Our claustrophobic friends may not lock themselves in such a room...

Our claustrophobic friends may not lock themselves in such a room…

© Guillaume du Mesgnil d’Engente / Digital

This is where the anechoic chamber comes into play. It responds to a “box within a box” design that we mentioned in 2016 for the construction of our previous laboratory. The external envelope makes it possible to isolate the anechoic room from extraneous sound nuisances and to reduce background noise.

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For its part, the inner part of the anechoic chamber must absorb the sound waves emitted by the product as much as possible, without reverberation. The chamber must thus reproduce the conditions of free field, as if the object were magically positioned in a complete vacuum. The semi-anechoic chamber incorporates these characteristics, but has a floor and therefore reproduces semi-free field conditions.

Ventilation, lighting and an electrical network isolated from the general supply circuit of the building; a luminous panel makes it possible to see from the outside if a test is in progress.

Ventilation, lighting and an electrical network isolated from the general supply circuit of the building; a luminous panel makes it possible to see from the outside if a test is in progress.

© Guillaume du Mesgnil d’Engente / Digital

Surface stresses

The room is built using absorbing dihedrals, melamine polygons distributed on the walls of the room which allow the waves to be absorbed according to their size. The more it is necessary to reduce the undesirable effects of low frequencies, the larger the wedges must be.

Depending on our constraints, particularly related to the available area, it is difficult to use conventional construction. We therefore chose to use a solution based on a compact broadband absorber. Thanks to a multilayer design consisting of a metal plate and dissipative materials, good performance can be achieved over the entire spectrum while limiting the thickness of the walls. Useful floor space is thus preserved as much as possible. The icing on the cake, the modules benefit from perforated metal protection allowing better resistance over time against corners that are generally too fragile.

A double door system is provided. The interior door also benefits from absorbent panels.

A double door system is provided. The interior door also benefits from absorbent panels.

© Guillaume du Mesgnil d’Engente / Digital

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Laboratories at the heart of the tests

For our tests, the progress compared to our old laboratory is major. Measuring the sound level of a computer’s ventilation or the performance of a soundbar now allows a level of precision and reliability never before achieved on Digital. Of course, Rick, our measurement dummy dedicated to headphones and earphones, stays in the game and also takes his place in the semi-anechoic chamber so that the test is carried out in the best conditions.

The Rick measurement dummy takes place in the anechoic chamber for testing headphones or earphones. In the background, part of the remote equipment necessary for the measurements.

The Rick measurement dummy takes place in the anechoic chamber for testing headphones or earphones. In the background, part of the remote equipment necessary for the measurements.

© Guillaume du Mesgnil d’Engente / Digital

Thanks to the synergy of the two Image and Sound laboratories and the construction of a separate semi-anechoic chamber, the image and sound tests take the path of modernity and the rationalization of spaces, all carried by the requirement that characterizes us. A path already taken by the Photo lab and the Home lab. A set of premises equipped with state-of-the-art equipment which makes it possible to provide readers with Digital nearly 1,000 tests each year, with ever greater rigor and ambition.

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