DE4408278A1 - Extractor hood with at least partial cancellation of the fan noise - Google Patents

Description

The invention relates to an extractor hood with little least partial cancellation of the fan noise, with at least one built-in fan in a flow duct that connects the suction area to the fan. In addition, advantageous methods of implementation the sound extinction specified for extractor hoods.

Extractor hoods for extracting cooking and bra There are many vapors in the stove area Executions known. The filter surface is che by a fan or by a pair of fans sucked air mixed with cooking fumes either around air operation returned to the room or in the exhaust air drifted out through a duct. For Achieving a sufficient suction effect is a a correspondingly high fan output is required. There  the impeller diameter of the fans used with regard limited to the limited overall dimensions that must be to achieve the desired funding high fan speeds required, which at radial fans reach up to 2900 rpm.

Therefore, a clearly prominent one arises in operation Fan noise, depending on the type of fan used has complex frequency and amplitude spectrum that turns out of a broadband flow noise and turns number-specific, harmonious components. Experience has shown that the noise amplitudes are in the range the blading of the fan wheel greatest because there the greatest speed gradients and connected with it pressure fluctuations occur. Because of the large, open suction area in the suction area where the sound permeable grease filters are arranged, are possible sound insulation by using sound absorbers insulating coatings are severely restricted. In addition come restrictions regarding the frequency range, Fire protection regulations and the requirement that in all keep common porous sound absorber surfaces clean. On Because of these circumstances, especially in the mostly available as a higher option Power levels of the fan, the resulting fan noise is particularly annoying.

The physical principle has been around for a long time the "active sound compensation", d. H. at least Partial cancellation of noise by the cover an opposite phase signal, sometimes called "Antisound" is known.  

The publications D. Gucking, Active Noise Control - Achievements, Problems and Perspectives, IEICEJ Technical Report Vol. 91, No. 1 (April 12, 1991), pages 1-10, Paper No. EA 91-1 and D. Gucking, Active Noise Control
- A Review Based on Patent Specifications, Proceedings of the International Noise and Vibration Control Conference, May 13 - June 3, 1993, St. Petersburg, Russia, Vol. 2, pages 153-158. From these publications it is known to record the noise to be compensated by means of a reference microphone and to calculate a compensation noise from it, which is superimposed on the noise by means of a sound source, whereby the noise is at least partially extinguished. The replacement of the reference microphone with a synchronization sensor is also mentioned in the first publication.

It is also known that because of the approximately logarith mix relationship between the sound pressure and the The sensation of loudness of human hearing compensated sound field very exactly equal in amplitude and must be in phase opposition and the directions of propagation of the noise and the compensation sound field have to vote. Furthermore, transient transmission characteristics of the sound propagation distance be viewed.

The high demands on accuracy and speed signal processing led to the fact that only in industrial applications using adap tive digital filter with simple acoustically Systems became known.  

Such an application, which ent the state of the art speaks, is the compensation of predominantly low frequencies noise in a straight ventilation duct, the one approximately one-dimensional sound propagation possible light and an approximately linear transmission charac has the same characteristics for all noise components is. A corresponding arrangement can be from a tube stand in which both the sound and the air current spreads. The direction of flow is Air for sound compensation in principle not from Be interpretation.

It is also known to improve sound compensation a correction of the compensation sound by Auf the residual sound remaining during the superimposition by means of an error microphone, the Error microphone to the signal processing unit retroactively. With an arrangement corresponding to the above Example is the reference microphone in the tube in the area of the sound inlet arranged to pick up the noise net. In the direction of sound propagation is in one defined distance from an electroacoustic transducer Generation of the compensation sound field. The distance between between the reference microphone and the speaker essentially from the condition that during the Sound propagation time between the reference microphone and the Loudspeaker all necessary calculations of the signal ver unit of work taking into account all ver delays and phase shifts have been completed must, so that the compensation sound field through the Loudspeakers in phase with the interference sound can be generated. The one after the compensation residual sound is measured using an error micro Phons recorded that in the direction of sound propagation  ter the speaker or at least at the same distance How this is arranged and the tax variable for Readjustment of the signal processing unit delivers.

Essential components of the signal processing unit are usually one or more digital filters, their filters coefficients can be adapted so that the for Noise compensation required to replicate the Sound transmission path taking into account the Feedback effects between loudspeaker and reference microphone always optimal, for example according to the method the smallest sum of squares is. There is one Variety of algorithms according to which the required Calculations are carried out, for example by means of a micro or signal processor.

From the above-mentioned prior art documents and US-PS 5 206 911 is an arrangement for sturgeon sound compensation known, which is only an error microphone needed. This assumes that the noise is a ge has predictability or quasi-periodicity. He can, for example, at least become a considerable one Share from a few individual, discrete frequency shares assemble or with an operating parameter of the sturgeon sound generator, such as the speed, be correlated.

For many applications of active sound compensation the known principle proves to be inapplicable because the physical requirements regarding the egg properties of the sound field are not given or the required to calculate the compensation sound field che computing capacity of the signal processing unit un feasible high costs. Especially for the Present, novel application in an extractor hood  hood designed for installation in kitchen wall cabinets hen, the conditions regarding the acoustic properties of the flow channel, which also must allow sufficient air flow than for the active sound compensation unsuitable as well as the sound signal processing considered too expensive tet.

The invention takes into account the state of the Technology from the task, an extractor hood to train the hood so that by using a host economically acceptable costs an at least partial extinction of the fan generated noise is achieved.

The solution according to the invention consists in a Extractor hood with at least one built-in fan and a flow channel that connects the suction area with the Fan connects to provide a reference microphone for recording the noise to be compensated for in the air ters, as well as at least one sound source and one error microphone that is in the intake area of the extractor hood is ordered, and one with the reference microphone, the Sound source and the signal associated with the error microphone processing unit, which from the input signal serving signals of the reference microphone and the error microphones an output signal fed to the sound source nal for at least partial cancellation of the noise generated, are provided. This can advantageously be pre- hen be that the air sucked in by the fan through a flow channel is led, the one the channel length-increasing detour. Under the Be handle "detour" should extend the Flow channel opposite the shortest connection linear education can be understood.  

It can also be conveniently provided that the Noise cancellation, preferably by signal processing processing unit only for tonal frequencies or quasiperi odic noises is performed. Furthermore, before provision may be made for the interference to occur deletion preferably by means of signal processing only for frequencies below 2000 Hz, preferred is only carried out below 1500 Hz. An analysis of the noise from fans gives maxima of the signal ampli tuden at frequencies below 2000 Hz, in preference cases below 1500 Hz. In this frequency range Sounds from human hearing become rich as special who felt uncomfortable. To avoid unnecessary costly signal processing can therefore the signal processing for noise cancellation Frequencies below 2000 Hz, preferably below 1500 Hz can be limited. The above these frequencies Incident noise components can advantageously be additional Lich by means of passive sound absorbers, which in principle high frequencies better than at low for sound absorption tion are suppressed.

Especially with predominantly tonal frequencies or qua Siperiodic noise can be useful for training be taken so that instead of the reference microphone a synchronization sensor for synchronization on the Noise generated by the fan is provided.

This is particularly advantageous if a fan type is selected, the noise of which is less broadband spectrum rather than tonal frequencies. Radial fans have proven to be such fans, ins especially if they have backward curved blades and ge possibly have a special housing geometry.  

Surprisingly, it has been shown that on this basis with extractor hoods an effective noise control compensation of the fan noise with a reasonable Expense, especially with regard to the signal processing unit, can be achieved.

The active sound compensation can be in an extractor hood hood are provided, in which the flow channel in the we is substantially rectilinear, for example in Form of a vertically ascending, tubular exhaust air box nals. Depending on the application, the rapid sound propagation with smaller, inexpensive relatively high signal processing speeds Exhaust duct lengths result. Cheaper in the sense of a Compact design and the resulting installation possible in standard wall cabinets, for example with egg ner extension kitchen, therefore appears a long enough Detour in the housing of the extractor hood. It can it may be advantageous to make the flow channel U-shaped, L-shaped mig, C-shaped, helical, helical or spiral to form. It should be noted that on the one hand the flow resistance is kept small and others the acoustic properties of the flow channel as well as possible to the conditions outlined above as well as with regard to the one-dimensionality of the sound field linearity and causality are approximated.

Furthermore, the Ge noise reduction through passive, constructive measures be supported. For this purpose, it can be advantageous that the flow channel at least in sections formed wall surfaces that the intensity of Sound reflections reduced transverse to the direction of flow becomes. For this it appears advantageous to the wall surfaces  the flow channel while largely avoiding parallel wall surface sections, as for example with a rectangular or circular cross-section to train. The wall surfaces of the flow channel can also expediently irregular surface changes changes, for example grains, or sound absorption Rende coatings have.

In a further training, it can also be advantageous be acoustic in two or more flow channels to subdivide decoupled subchannels. These Subchannels are expediently formed by air baffles det, which are advantageously performed so that flow ab solutions are reduced or avoided. Another advantageous peculiarity can be that the Flow channel or the sub-channels or the interior of the Extractor hood is provided with sound absorbers.

It may also be advantageous to have two sided or double-sided radial fans next to or are arranged one behind the other and that the two Radial fans are housed in volute casings, which as air guiding elements for the air flow in the interior of the Extractor hood are designed. After all, it can be advantageous that the interior of the hood hood is part of the exhaust air duct.

Other advantageous features and special features result from the following examples of Dunstab hoods with active sound compensation based on the Representation in the drawings below be are written and explained. Show it.  

Fig. 1 shows a longitudinal section through an extractor hood seen from the front with a rectilinear flow channel;

2 shows a longitudinal section through a front die hene hood with detour guide of the flow channel.

Fig. 3 is a front view of a fume extractor hood with two juxtaposed fans;

Fig. 4 is a sectional view of a view seen from the side hood according to Fig. 3;

Figure 5 shows an alternative embodiment of an extractor hood with two fans arranged side by side.

Fig. 6 shows a section through a view seen from the side hood according to Fig. 5.

In the principle view of FIG. 1, 1 detects a Ansaugschirm an extractor hood for Abluftbe shoot, which on its suction opening a filter plate 2. At the intake screen 1 is a straight line rising flow channel 3 , which mün det at its upper end in a housing 5 of a radial fan 4 .

In the area of the noise source, ie the radial fan 4, there is a reference microphone 7 and in the intake area of the extractor hood, a sounder 8 and an error microphone 9 are arranged. The measured variables of the reference microphone 9 are fed to a signal processing unit 6 as input variables. The output variable of the signal processing unit 6 feeds the sound generator 8 . It can be seen the relatively large length of the rectilinear flow channel 3 , the accommodation of z. B. may encounter difficulties in cupboards of fitted kitchens.

Therefore, in the exemplary embodiment in FIG. 2, a route is provided by a curved design of the flow channel 10 . The left, vertical leg 11 opens to the intake screen 1 of the extractor hood, while the right vertical leg 12 forms an outlet to the fan housing 5 of the radial fan 4 .

The signal processing unit 6 , like the sound source 8 , can be accommodated in the free inner space 13 enclosed by the detour of the air duct 10 . This training z. B. A placement of the exhaust air duct in a wall cupboard of a kitchen extension possible.

In the embodiment according to FIG. 3, which is shown for clarification in FIG. 4 from the side, two radial fans 14 and 15 arranged next to one another are provided. The two fan housings 16 and 17 open into a common exhaust outlet 18 . The initially vertically rising flow channel 19 from the suction screen 1 goes backwards into a connecting space 20 of the two fan housings 16 , 17 . The reference microphone 7 is located at the wall-side end of a connected to the vertical constricting on stei part of the exhaust air duct 19 horizontal transition piece 21st

In the embodiment of Fig. 5, which is shown for clarity in Fig. 6 from the side of the flow channel 19 opens rearwardly in the two Lüfterge housing 16, 17 of the two radial fans 14, 15 and the Since they share Lüfterauslaß 22 is provided with an outlet port 23 connected.

The individual parts not mentioned correspond to those of the embodiment according to Fig. 1. The sound source 8 can be ge be geous from one or more speakers.

In a simplified version of an extractor hood with the features described above, ge possibly advantageous instead of a reference microphone and error microphone only a single microphone expedient be used in the area of the error microphone.

Claims (28)

1. extractor hood with at least partial extinguishing of the fan noise with at least one built-in fan ( 4 ; 14 , 15 ) and a flow channel ( 3 ; 10 ; 19 ) which connects the suction area ( 1 ) to the fan ( 4 ; 14 , 15 ), with a reference microphone ( 7 ) for recording the noise from the fan to be compensated ( 4 ; 14 , 15 ), with at least one sound source ( 8 ) and an error microphone ( 9 ), which is in the direction of flow behind the sound source ( 8 ) in the suction area of the extractor hood is arranged and with a with the reference microphone ( 7 ), the sound source ( 8 ) and the error microphone ( 9 ) connected signal processing unit ( 6 ), which from the input signal as the input signals of the reference microphone ( 7 ) and the error microphone ( 9 ) the sound source ( 8 ) supplied output signal for at least partially extinguishing the noise generated. 2. Extractor hood according to claim 1, in which a to increase the channel length of the flow channel To guide ( 10 , 19 ) is provided. 3. Extractor hood according to claim 2, in which instead of the reference microphone ( 7 ) a synchronization sensor for synchronization with the noise generated by the fan ( 4 ; 14 , 15 ) is provided. 4. Extractor hood according to claim 2, wherein the Flow channel U-shaped, L-shaped, C-shaped, spiral shaped, helical or helical is. 5. Extractor hood according to claim 2, in which the Detour of the flow channel essentially with has interconnected rectilinear sections. 6. Extractor hood according to claim 2, wherein the fan ( 4 ; 14 , 15 ) is a radial fan. 7. Extractor hood according to claim 2, wherein the impeller of the fan ( 4 ; 14 , 15 ) is provided with backward curved blades. 8. Extractor hood according to claim 2, wherein the flow channel ( 3 ; 10 ; 19 ) at least in sections has wall surfaces designed in such a way that the intensity of sound reflections across the flow direction is reduced. 9. Extractor hood according to claim 8, in which the flow channel ( 3 ; 10 ; 19 ) is coated at least in sections with sound-absorbing materials. 10. Extractor hood according to claim 8, in which the flow channel ( 3 ; 10 ; 19 ) is provided at least in sections with irregular surface changes. 11. Extractor hood according to claim 8, in which the wall surfaces of the flow channel ( 3 ; 10 ; 19 ) are cut while largely avoiding parallel wall surface sections. 12. Extractor hood according to claim 8, wherein the flow channel ( 3 ; 10 ; 19 ) is divided into two or more acoustically decoupled sub-channels. 13. Extractor hood according to claim 12, wherein the Sub-channels are formed by air baffles. 14. Extractor hood according to claim 12, wherein the Sub-channels are formed by concentric tubes. 15. Extractor hood according to claim 13, wherein the Air baffles to avoid flow separation are designed. 16. Extractor hood according to claim 2 or 12, in which the flow channel ( 3 ; 10 ; 19 ) and / or the partial channels and / or the interior of the extractor hood are provided with perforated, plate or membrane absorbers. 17. Extractor hood according to claim 2 or 12, in which the flow channel ( 3 ; 10 ; 19 ) and / or the partial channels and / or the interior of the extractor hood are provided with sound-absorbing materials. 18. Extractor hood according to claim 2, in which two single-sided or double-sided suction radial fans ( 14 , 15 ) are arranged side by side or one behind the other and in which the two radial fans ( 14 , 15 ) are housed in spiral housings ( 16 , 17 ), which act as air guiding elements the extractor hood are designed. 19. Extractor hood according to claim 2, in which a Single-sided or double-sided radial fan is housed in a volute casing, which as Air guiding element for the air duct of the extractor hood hood is formed. 20. Extractor hood according to claim 2, wherein the Part of the interior of the extractor hood Exhaust air flow represents. 21. Extractor hood according to claim 3, wherein the synchronization sensor is a position sensor measuring the angular position of the impeller of the fan ( 4 ; 14 , 15 ). 22. Extractor hood according to claim 3, wherein the synchronization sensor is a pressure sensor that measures the pressure fluctuations generated by the fan ( 4 ; 14 , 15 ). 23. Extractor hood according to claim 3, wherein the synchronization sensor is a frequency sensor measuring the blade frequency of the fan ( 4 ; 14 , 15 ). 24. Extractor hood according to claim 3, wherein the synchronization sensor is a speed sensor measuring the speed of the fan ( 4 ; 14 , 15 ). 25. Extractor hood according to claim 1 or 2, in which instead of the reference microphone ( 7 ) and error microphone ( 9 ) only one error microphone ( 9 ) is provided. 26. A method for at least partially canceling the fan noise in an extractor hood with at least one built-in fan ( 4 ; 14 , 15 ) and a flow channel ( 3 ; 10 ; 19 ) that connects the suction area ( 1 ) with the fan ( 4 ; 14 , 15 ) connects, with a reference microphone ( 7 ) for recording the noise to be compensated for by the fan ( 4 ; 14 , 15 ) with at least one sound source ( 8 ) and an error microphone ( 9 ) which is in the direction of flow behind the sound source ( 8 ) is disposed intake of the extractor hood, and with a with the reference microphone (7), the sound source (8) and the error microphone (9) verbun which signal processing unit (6) consisting of the compounds serving as input signals signals from the reference microphone (7) and the error microphone ( 9 ) an output signal supplied to the sound source ( 8 ) for we at least partially canceling out the noise, it produces, in particular in an extractor hood according to Ans pruch 2 and / or 25, in which the noise cancellation by means of the signal processing unit ( 6 ) is carried out only for tonal frequencies or quasi-periodic noises. 27. Method for at least partially canceling the fan noise in an extractor hood with at least one built-in fan ( 4 ; 14 , 15 ) and a flow channel ( 3 ; 10 ; 19 ) which connects the suction area ( 1 ) with the fan ( 4 ; 14 , 15 ) connects and with a reference microphone ( 7 ) for recording the noise to be compensated by the fan ( 4 ; 14 , 15 ), with at least one sound source ( 8 ) and an error microphone ( 9 ), which is downstream of the sound source ( 8 ) is arranged in the suction area of the extractor hood and with one of the reference microphone ( 7 ), the sound source ( 8 ) and the error microphone ( 9 ) verbun those signal processing unit ( 6 ), which from the signals serving as input signals of the reference microphone ( 7 ) and the Error microphones ( 9 ) an output signal supplied to the sound source ( 8 ) for we at least partially canceling out the noise, it produces, especially in the case of an extractor hood Claim 2 and / or 25, in which the noise cancellation is carried out only for frequencies below 2000 Hz. 28. The method of claim 27, wherein the sturgeon sound cancellation only below 1500 Hz leads.