Men’s sense of   hearing   acts in an useful frequencies interval useful to its  acoustic equilibrium, functional to the integration with the other four   senses. Under the limits of the 20 Hertz and above that, on the average 18.000 Hertz, the eardrum membrane is longer reached by any aerial noise. In the specific contemporary acoustic field if the very high frequencies are not caught even if produced and however with small energy, the low frequencies on the contrary are responsible for notable and notably measurably caught deformations.

In particular, the defined  infrasonich waves, are not eptible by the human auditive system (external ear- inside ear cerebral cortex) but, they are absorbed  by the whole rest of the body. These waves are also produced by loudspeaker systems for Surround and they create a distorsion of the sonar field throughmodalresonances   caused by  the spatial dimensions of the indoor spaces  they are released, and a  deafness physical perception because of resonances of soft biological hollow of the human body.

If, in the first case, to high levels of sonorous pressure and with spaces notably dilated, the effect can create a glut of the timpanic  system with the effect to feel with notable attenuation any other sound, in the second case it is had a vibrational effect that stimulates the vestibolari receptors and the connections with the neurovegetative centers determining diffused discomfort. To such intention we propose the following chart where some infrasonic frequencies common are listed: 


0.1 – 0.01 Hertz : Northern aurora, solar wind

1 - 2 Hertz : Naval transport

15 - 20 Hertz : Wind in the cavern

30 - 40 Hertz : Jet engine

The effects of the very low frequency waves and at strong power, may cause what follows:

7 Hertz : Alpha Rhythm (frequency of the celebral mass ) the intense exposure provokes intellettual inhibition, neurologich interfereces, the death.

12 Hertz : Nausea and vomiting  for many days.

43 Hertz : Visual diminution, loss of the spatial orientation, loss of equilibrium, miscoordination.

60 Hertz : Coughing and strong pressure on the sternum, excessive salivation, abdominal pain.

100 Hertz : Irritation, nausea, respiratory dysfunction.


These effects, introduce the importance of the concept of absorption to low frequency that is one of the expressions of quality concerning the acoustic answer of an space solicited by a sound to wide gang. Even if the levels above mentioned  are almost never reached and however with very reduced energy, the frequencies up to 300 Hertz are studied with attention in how much their increas or their attenuation are the cause of the bad result of a control room  acoustic planning.

Slightly simpler is the study of the dominion of the middle high frequencies. The vibrational energetic content  is less powerful but more directional. In fact   we enter   a field where the guides of propagation of the frequencies can be compared to beam rays that departing from the reasonably directs source in the acoustic space with narrow bundles, opposite to the low frequency waves   that, with strong energy, have a spherical diffusion from the origin.

On these considerations it founds the philosophy of project SAE (Stealth Acoustic Environment) developed by Giuseppe Zappata with which the space of a control room, around the listening point of the sound engineer,  built upthrough angular profiles of reentry that trap the flows of acoustic energy.

These highly strikly stratifications of materials with porous structures (microsorbers) able to notably reduce the speed of the vibrations of the air around its state of equilibrium (Photo 1). The residual echoes not turned into heat by the friction of the porous material with the molecules of air, will dispersin all the directions, eliminating the part of acoustic energy that would return around to the some point of principal listening.

Photo 1	Photo 2	Photo 3

The technical stealth, been  born and applied in   military defense and in particular  for airplanes and ships (photo 2 and 3) it enable these to offer a low radar return, dispersing and absorbing the incidental radiations through forms and particular materials (Photo 4).

The engineers are alwaysable to create aereodinamically optimized forms with the purpose to limit the solicitations of the air on the structures (Photo 5).

Also in the acoustic field the "form" establishes the quantity and quality of the vibrational waves that return back from the walls of a confined space and therefore, dispersing and attenuating the energy of return is gotten a low acoustic "marking" that corresponds to a negligible contribution of the resonances suitable for of the environment in practical terms (Photo 6). 

Photo 4	Photo 5	Photo 6