noise reduction efficiency of helmholtz resonator in simulated channel of hvac system

abstract background: given the fact of irrecoverable consequences of noise in industrial societies and the environment, acoustic filter (silencer) is an instrument which obstacles the transmission of sound waves. a sort of this silencer is helmholtz resonator (branch amplifier) which comes to sound appropriate for low and below 200 hz frequencies in fan and channel noise. the purpose of this article is investigating the efficiency of designing resonator in decreasing low noises. methods: this is an experimental study. the designed helmholtz resonator was installed in a channel analogous to ventilation channel. through using matlab software, there were produced signals at very low frequencies of 250-500 hz and transmitted through a channel by means of a speaker. afterwards, comparing the sound pressure level before and after (existence of) helmholtz resonator, the rate of decreased sound in various frequencies was considered and then the matlab software was used to process intra-channel signals and to prepare sound algorithm in the channel. findings: the most decrease of sound in the frequency of 125 hz among helmholtz resonators befalls when there is chamber diameter of 63 millimeters and resonator's 1cm-caliber. the decrease of sound was at its pinnacle at the frequency of 125 hz and at its nadir at the frequency of 500 hz.  given the fact of already conducted measurements at the frequency of 125 hz, forthwith the increase of sound through resonators and also increase in diameter of resonator's mouth, the rate of sound resonance will be decreased. conclusion: this research showed that the designed and installed-in-channel helmholtz resonators at a certain frequency of low-frequency sound demonstrated the soundest decrease. this very decrease was more obvious in smaller resonators. additionally, the increase in the helmholtz resonators' chamber volume and their neck's pass area are negatively associated with the rate of sound resonance. as a result, determining the effective frequency range of the helmholtz resonator, this very kind of resonator could be applied as an effective and efficient instrument of removing or decreasing noise. key words: noise reduction, silencer, helmholtz resonator