Key words: Acoustic microclimate, acoustics, sound, noise, sources of noise, biological effects of noise, anti-noise

ACOUSTICS MICROCLIMATE

The acoustic microclimate is an important component of the indoor environment characterized by a large number of sound sources with a wide range of frequencies.

Acoustics is a branch of physics dealing with the study of sound - the study of the mechanical vibrations and waves in flexible environments, its creation, dissemination and action.

Sound is mechanical waves in a fabric environment that is capable of producing an auditory sensation.

An audible sound is capable of producing a sound sensation. It is noise whose frequency spectrum is located in one-third octave frequency bands with medium frequency of 20 Hz to 20,000 Hz.

Infrasound is a sound whose frequency range is in the third octave bands with a mean frequency of 1 Hz to 20 Hz.

Ultrasound is a sound with a higher frequency than audible sound. Its average frequency is 25,000 to 40,000 Hz.

Noise is any unwanted sound that adversely affects the well-being of a person, causes an unpleasant, disturbing feeling, endangering his health.

In our population, the noise load is caused by an average of about 40% of the work environment and 60% of the outside work environment.

Noise is either penetrated from the outside through the building envelope, or the noise is generated directly inside the building. From its source, the noise is transmitted either by air only, or transmitted by building structures and then by air.

In terms of reflection, we recognize the direct waves and the reflected waves.

In terms of the time course, it is recognized:

• Stabilized noise at a given location does not change over time by more than 5 dB
• Variable noise varies over time by more than 5 dB in time
• Intermittent noise is noise, which suddenly changes the sound pressure level or the sound level, which is steady during the noisy interval
• Pulse noise is generated by individual sound pulses with a duration of up to 200 ms or a sequence of pulses successive at intervals longer than 10 ms

BIOLOGICAL EFFECTS OF NOISE

Acoustic flows act on the subject by acoustic pressure, which does not depend on the frequency of acoustic waves, but on their amplitude given by the magnitude of the source.

An acoustic pressure of 20.10-6 Pa characterizes the weakest sound recorded by undamaged human hearing. Human hearing is also able to withstand acoustic pressures more than a million times larger, that is a pain threshold of 200 Pa.  In practice, this would mean working from tens to tens of millions of Pa, so the logarithm of these values, the so-called sound pressure level, was chosen. This adjustment narrows the range from 20 to 200,000,000 mPa to a range of 0 to 120 dB:

• L < 20 dB(A) - deep silence, adverse effect on psyche
• L 85 dB(A) – results in permanent hearing loss
• L = 130 dB (A) - threshold of pain
• L 160 dB (A) - the human drum breaks

The persistent effect of noise on the human organism is of three kinds:

• Effect on hearing organs - Harmfulness of hearing effects depends on sound level and frequency waves. The more energy is concentrated in the higher frequencies, the lower the noise level is
• Effect on the vegetative nervous system - Reactions are dependent on the subjective perception of the individual
• Effect on human psyche - It is the most complex of effects. Neuroscientists may aggravate the nervous system lability, which is manifested by irritability, insomnia, headaches, memory impairment

OPTIMIZATION OF ACOUSTIC MICROCLIMATE

Noise maps express the burden of the population. Maps are geared to land use in spatial planning and strategy development.

Optimization of acoustic microclimate can be done in two basic ways - interference to the source of noise or interference in the field of transmission.

The most effective way to improve acoustic comfort is to remove or replace the source. Consideration is also given to organizational measures to limit major sources or transport them to better acoustically isolated places (covers or dampers).

Optimization of acoustic comfort by intervention in the field of transmission can be done by installing barriers, increasing absorption and decreasing the reflectivity of the walls and ceilings or so called anti-noise. The principle of anti-noise method is based on the principle of the propagation of airborne pressure waves. Anti-noise is a mirror image of these waves but phase shifted precisely by 180 °. Encounters two waves to each other, interference occurs destructive (waves cancel each other out). Currently, more theoretical possibility.