The purpose of this report was to investigate how an intake for a battery-powered leaf blowershould be designed to reduce sound emissions. A reduced sound emission improves both theworking environment for the user but also reduces disturbances to the surroundings. The workbegan with a market analysis of different leaf blowers’ intakes. Other industries and differenttypes of noise reduction systems were also investigated. The market analysis stated that animplementation of Helmholtz resonators in an intake has great potential to reduce the tonalsound that a battery-powered leaf blower emits. As the sound image of a battery-powered leafblower is very tonal, the idea with resonators was to reduce the tonal spikes to achieve a lowersound level. If the work could prove that the resonators provide a high effect in the area aroundthe tonal sound spikes, then with some optimization, the resonators could be adapted and lowerthe sound equally at these frequencies. The work then progressed with testing whetherresonators work effectively. The result of the test showed that resonators can dampenfrequencies with high power, which led to the work continuing with a Concept Generation. The concept generation resulted in four different concepts that all had different placements andimplementations of resonators in the intake. These concepts were tested again and comparedto a reference that did not have any sound dampening features. From this test, two conceptsperformed at a high level, which were Back Cone and Big and Large, and these were furtherdeveloped. Further development produced four different variants of Big and Large. These werevariants with different numbers of resonators. Back Cone was produced in three differentvariants with different sizes of resonators. The purpose of these variants was to investigate howthe size and number of resonators affect the sound dampening ability. These variants weretested according to ISO-22868:2021. The final test revealed that four prototypes achieve therequired value for sound minimization. However, several external parameters emerged that affected the test results. One parameter was likely a floor reflex between the leaf blower and themicrophone directly behind the intake. The influence of the external parameters leads to thecredibility of the test results being unclear and thus these prototypes cannot be approved. During the same test, a speaker was used as the sound source instead of the fan. In this test, itappears the same four prototypes achieve a sound-minimizing effect that achieves the requiredeffect in the same range as in the tests with a fan as a sound source. Even in this test, there wereseveral external parameters that affected the result and therefore the prototypes could not beapproved with certainty according to the requirements specification. The project can be summed up by stating that resonators have great potential to reduce thetonal sound that a battery-powered leaf blower generates. The project has also shown howdifferent placements of resonators affect the sound dampening effect. During test two, a prototype emerged that can be approved according to the requirement specification as itperformed 17,5 dB maximum sound dampening effect right above the tonal frequency and sixdB at the right frequency. The project cannot determine with certainty if the variants of intakeused in the final tests meet the requirement specification due to the external parameters thataffected the results. However, the project can state that the resonators have achieved an effectin all tests. The maximum effect achieved was analysed in test one and was 27 dB soundminimization. The project ends by proposing further work such as investigating how an intakewith resonators should be designed to be manufactured in mass production. The influence ofthe thickness of the intakes surface boundary layer on the effect of the resonator should also beexamined, as well as the distance of the resonator to the fan and the outer edge of the intakeshould be examined together with the several other points presented in the chapter Discussions.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:hj-65383 |
| Date | January 2024 |
| Creators | Appell, Albin, Sandqvist, Jesper |
| Publisher | Jönköping University, Tekniska Högskolan |
| Source Sets | DiVA Archive at Upsalla University |
| Language | Swedish |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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