Hair dryer with low noise impact Description Field of the invention The invention relates to an innovative hair dryer suitable for simplifying the profession of a generic hairdresser, reducing the acoustic impact and the vibrations commonly produced by any type of hair dryer present on the market; the hair dryer object of the invention is further lightened and optimized. Prior art The hair dryer is a small electromechanical appliance that generates a jet of hot air in order to dry the hair, i.e. to disperse the humidity it contains into the air. The jet of hot air is commonly produced by an electric motor which rotates a fan. This fan draws in and moves the air, directing it to an electrical heating resistor. The resistor consists of a twisted nickel-chrome wire wound on a heat resistant support, in which the drawn in air is heated and then blown out. The power of the resistor normally ranges from 700 to 2400 W. The motor can be a permanent magnet DC motor or a single-phase AC motor. The flow rate of air generated by the fan is normally around 40-50 m³/h. The heating resistance is protected by a thermostat and the air temperature at the outlet is around 70-80 °C. Often the hair dryer has a series of settings that allow you to determine the intensity and temperature of the air jet. In addition to common use, the hair dryer is a tool used by hairdressers to create particular hairstyles and to give shape to hair. Used together with a brush and comb, it can change the direction and the wave of an area of the hairstyle. In addition to regulating the intensity of the flow and heat, hair dryers with additional functions are found on the market, one of which is the presence of an ionizer. The ionizer, coupled to a resistance, releases negative ions which have the power to divide the drops of water present on wet hair into many micro-drops allowing for faster drying, it also prevents the formation of electrostatic charges thus making the hair more shiny and less frizz. Over the years, the way of drying hair aimed at the final style has become much easier, thanks to the technologies applied to the beauty sector which have made the use of the hair dryer practical and manageable. However, there are some critical issues that have not yet been overcome. First of all the critical points is undoubtedly the noise which, combined with the vibrations produced by the electric motor, jeopardizes the work of the professional in the long term. Despite this, even the weight, in itself significantly decreased today, means that prolonged use for several hours causes tendonitis capable of jeopardizing the health of the arms of professionals. The previously registered inventions have not yet remedied the drawbacks highlighted, such as the patent CN202436385, released on September 19, 2012, which describes a ventilation system inside the hair dryer that can be less disturbed and turbulent, reducing noise; said invention does not consider either the reduction of weights or the reduction of vibrations and obtains a mediocre acoustic result compared to the invention object of the present patent application. The object of the patent is therefore to claim the creation of a hair dryer capable of minimizing noise and vibrations, facilitating the work of professionals who have to handle said hair dryer every day. Description of the invention According to the present invention, a hair dryer with low noise impact is provided which effectively solves the aforementioned drawbacks. The innovative device allows the professional to operate his/her profession in the long term, without affecting his/her health. Thanks to the technologies applied to the subject hair dryer, a device is supplied with a decidedly lower mass than that of the competitors. Said hair dryer undoubtedly contributes to the technological development carried out in the small household appliances sector thanks to the reduction of the acoustic impact and vibrations, common to all household appliances. The hair dryer object of the present invention is therefore easy to handle and light, easy to use for the majority of professionals in the beauty sector. Another important advantage of the hair dryer of the present invention is the substantial reduction, close to zeroing, of the need for maintenance interventions (and expenses). An external rigid housing is essential to include, inside it, the plurality of electronic and mechanical components suitable for regulating the flow of air emitted; said external housing is furthermore adapted to facilitate gripping of the entire hair dryer by any professional. By way of non-limiting example, said housing has a plurality of engageable joints suited to hold together the entire rigid structure and ensure at the same time the possibility to easily open the housing in order to examine and possibly replace its inner components. The air flow, necessary for the hair dryer to perform its function, is advantageously supplied by an external compressor, installed in a room different from the one where the hairdresser who uses said hair dryer works; said compressor has the purpose of maintaining pressure in an air circuit outside the room where the professional works. In one embodiment thereof, said air flow is provided by a plurality of compressed air cylinders, in the event of an emergency in which there is no electricity inside the professional's premises. A wall socket is advantageously installed on the internal side of the room where the professional works, and is adapted to put the air circuit supplied by the compressor in communication with the hair dryer; said wall socket can further comprise a common electric socket to simplify the power supply circuit of said hair dryer. In one embodiment thereof, said wall socket comprises an air filter in order to be able to further purify said air flow before it enters into circulation through the subject hair dryer. In order to connect said hair dryer to the air circuit, an air duct made of plastic material is used, having a terminal adapted to engage with said wall outlet. A further duct is enclosed in said rigid housing, having an outlet cross-section greater than its inlet cross-section, for decreasing the pressure of the flow coming from the compressor. A plurality of electric resistances are instead enclosed within the housing, downstream of the duct, and are adapted to give off heat to the air flow traversing said electric resistances before it reaches the client’s hairs. An electrical connector connected to the hair dryer by means of a common electric cable is adapted to electrically supply and consequently heat said electrical resistances. To rebalance the composition of the ions in closed environments, a sufficient supply of negative ions is provided for the purpose of purifying the emitted air, using a negative ion generator included inside said housing. An air flow switch coming from the external compressor is instead installed laterally to said housing, in order to modulate said air flow during use; the switch is further adapted to stop the flow to disconnect the hair dryer from the wall socket. The outlet temperature of the hair dryer can be easily customized by exploiting the regulator installed on said housing, adapted to act on the overheating of said electrical resistances. In one embodiment of the present invention, the air duct, used to transfer the compressed air from the compressor to the hair dryer, comprises two internal chambers each adapted to accommodate a different air flow; the first houses a warm air flow and the second a cold air flow. The presence of an air duct comprising two chambers eliminates the presence of electrical resistances inside the housing, guaranteeing even lower weights and dimensions. By way of non-limiting example, said temperature regulator, if associated with the air duct with two distinct chambers, is adapted to mix the right amount of air in order to obtain the desired temperature, dosing the right percentage of cold air and hot air included within said air duct. The advantages offered by the present invention are clear in the light of the above description and will be even apparent from the accompanying figure and the detailed description. Description of the figures The invention will hereinafter be described in at least a preferred embodiment thereof by way of non-limiting example with the aid of the accompanying figure, in which: - FIGURE 1 shows a generic diagram where the operating system of the hair dryer 10 object of the present invention is simplified. The air flow is generated by a compressor 21, located in a room outside the salon where the professional works. By using a sophisticated wall socket 19, it is possible to put the external air circuit 20 in communication with the air duct 18, adapted to supply the hair dryer 10. The heat of the flow is always managed by a temperature regulator 15 adapted to control a plurality of electric resistances 12. Current is supplied to said hair dryer 10 by means of an electric cable 16 and an electrical connector 17. A duct 13 is used to decrease the pressure of the flow before introducing the air into the salon. All the components included in the hair dryer 10 are contained within a rigid and compact housing 22. Detailed description of the invention The present invention will now be described purely by way of non-limiting or binding example with the aid of the figure, which illustrates some embodiments relative to the present inventive concept. With reference to FIG. 1, a typical example of use of the hair dryer 10 object of the invention is shown. Thanks to the use of a compressor 21 external to the room where said hair dryer 10 is used, the noises and vibrations previously due to the presence of an electric motor which fed a fan adapted to manage the air flow are reduced. Thanks to the reduction of vibrations and noises, the hair dryer 10 object of the invention is more practical and easier to handle, thanks also to the use of a rigid external housing 22 adapted to include inside all the components necessary for the management of the air flow. The compressor 21 is adapted to keep the external air circuit 20 under pressure, until it reaches the wall socket 19. Said wall socket 19 is installed inside the room where the professional works and is adapted to house the terminal of the air duct 18 and furthermore the electrical connector 17 of the hair dryer 10. Said air duct 18 allows the flow of air inside the hair dryer 10, further reducing the pressure by means of a duct 13 having the outlet section larger than the inlet section. The speed of the flow is managed by a switch 14, installed laterally to said housing 22. A plurality of electric resistors 12 are installed downstream of the duct 13, in order to supply heat to the flow, by regulating a suitable temperature regulator 15. The electric resistors 12 are powered by the current carried by the electric cable 16. A negative ion generator 11 is further included inside said housing 22 in order to purify the air before introducing it into the salon. Finally, it is clear that modifications, additions or variants may be made to the invention described thus far which are apparent to those skilled in the art, without departing from the scope of protection that is provided by the appended claims.