3results about How to "Sound absorption frequency bandwidth" patented technology

The invention discloses a helicopter ducted tail rotor noise reduction lining for low-frequency line spectrum noise suppression, and belongs to the technical field of helicopter ducted tail rotor noise reduction. Ducted tail rotor noise belongs to multi-line spectrum harmonic noise, and noise energy is reduced along with increase of frequency, that is, the noise energy is concentrated in first two-order harmonic waves. And on the other hand, the ducted tail rotor is low in rotating speed and small in blade number, so that the noise frequency is low. The micro-perforated plate composite folding back cavity is used as the sound absorption unit, and two sound absorption resonance frequencies of the sound absorption unit coincide with the first two orders of harmonic noise of the tail rotor through parameter design, so that the thickness of the whole sound absorption unit is reduced, and meanwhile, the low-frequency multi-line-spectrum noise reduction performance is achieved; the weight cost is reduced, and the tail rotor noise is effectively restrained.

The present invention discloses a muffler device suitable for an integrated stove, comprising a first muffler sheet arranged on both sides of an air inlet of the integrated stove, a second muffler sheet arranged on both sides of a volute of a fan of the integrated stove, and a third muffler sheet arranged at a back plate in a fan compartment of the integrated stove. The upper parts of the first muffler sheet and the second muffler sheet both adopt a micro-perforated plate resonance sound absorption structure with a built-in multi-slit resonance cavity, and the lower part of the second muffler sheet and the third muffler sheet both adopt a micro-perforated plate resonance sound absorption structure. The present invention makes full use of the oil fume air inlet of the integrated stove and the space of the fan compartment, while achieving efficient muffler, maintaining the original oil fume absorption effect of the integrated stove, being resistant to high temperatures, easy to clean, and having good commercial application prospects.