Design of An Active Noise Reduction System (Mechanical Engineering)

Students:Mohammed Saber Bou-said 200106411Khaled Ahmad Ashoor 200001533

Advisor: Dr. Farag K. Omar

UNITED ARAB EMIRATES UNIVERSITYCollege of EngineeringGraduation Projects Unit

PreviewNoise to be reduced to an acceptable level in a desired area.Designing an ANC system that contains Microphones:MicrophonesSpeakersProcessorGPII: produce a working prototype of our designed system.

ContentTheorySteps performed in GPISteps performed in GPII:Case studyComponents SpecificationsAlternatives for ProcessingSystem IntegrationSystem testingSystem development based on the testing feedback

Theory: ANC (general)Introduction, benefits

Theory of noise canceling by wave superposition

Applications of active noise control: HeadsetsIndustrial fansAC ducts

Theory: ANC (Technical)The different techniques of Active Control Main components of ANC systems

Theory: ApplicationBedroom or officeA fan producing undesirable noiseNoise cancellation through ANC

GPI: SummaryLiterature review: Background InformationDefining application propertiesApplication SelectionProperties of Noise, Area, FansDefining constraints and limitationsComparing alternatives: Components and placementDesign & simulation: Room ModelingEvaluation of the possibility of noise reduction at users area

Case StudyA student from electrical engineering made a project of a sound recorder Part of this project was interesting for our project.Helps to define the main components of the processing part of the system.

CaseProject during industrial trainingstoring sound taken by a microphone into a memoryplaying it through headphones when playback mode selectedA/D after Microphone, D/A before speakerMicroprocessor and program in between

Buffers & processingBuffers may be used after taking original noise and after processingThis is better than using a DAC and PC:High speed of processingLow probability of interruptionFast processing:To avoid adding another delayTo ensure a good response time for the system

Components SpecificationsComponents:MicrophoneSpeakerA/D & D/AProcessor

Specifications depending mainly on noise properties

Some types of noise recorded and evaluated

Kitchen Fan NoiseMain frequencies: 21.9, 41.9, 62.9, 83.8, 104.22, 125.8, 145.8, 167.5, 184.5, 209.3, 228.9, 251.5, 272.4HzConsiderable harmonics up to 300 Hz Range of frequency for this noise: [20,300].

Office Fan NoiseMajor frequencies: 16.7, 22.5, 45.2, 67.7, 89.9, 113, 134.8, 157.7The range of frequency for this noise: [15, 250]

System Specifications: Mic.Frequency range: [ 15, 1500]Output suitable for the processor, mostly [-5, 5V]Microphone called "tie-clip microphone"Speaker compatible with these specifications

Digital Signal ProcessorMaximum frequency 500HzSampling frequency must be at least 3 KS/s Continuous Data taking

ProcessorBasic wave: f=20Hz, T=1/20= 0.05s= 50msHarmonics: f=500Hz, T=1/500= 0.002s= 2msDelay step: 0.5ms, up to 25ms"Digital Delay Line containing A/D and D/A converters

Single Chip Digital Delay IC

Processing MethodsA stand alone microprocessor chip with all required input output circuitsA digital delay chip integrated with DAC and controlled by LabViewA PCI card and LabView VIA PC sound card with a LabView VI

Alternative No.2

Alternative No.3 (DAQ & LabView)Installing LabView on the PCInstalling Card Drivers on the PCAssembling the DAQ inside the PCConfiguring & testing through provided utility program. Two tests :Analog input testAnalog output test

Analog Input & Analog Output:LabView VIfunction generator with the DAQ through the input channel.Input is processed by the VI To oscilloscope through AO channel.

Sinusoidal WaveSinusoidal sound wave generated by function generatorProcess: multiplication by -1Output through AO channel to speakerPhysical delay by moving actuator

Results

Wave Delay Control VI

Operation with Real NoiseA fan noise recorded 10 minutes, then played from a separate PC through a speaker. ------->source Actuators placed near the source, as well as the reference microphoneBasic microphone sensing noiseThe delay tuned from the LabView VI user interfaceSound pressure level monitored using a SPL meter placed at 3meters from the source.

Mic.

Band Filter

DAQ

Processor ( LabView)

Ability to add gain (instead of amplifier)Speaker

Results

ConclusionEngineering design projects Procedure followed.Noise reduction practically possible using wave superposition.Difficulties: lower expectationcomplete prototype of an active noise reduction system built, including:Reference microphones to collect noise data.Signal processing electronic circuits (amplifier, low-pass filter, etc)Configured data acquisition system (Data acquisition card, PC and software code)Output signal processing circuit.Output speakerSound level meter to measure noise level at and around the user's location.

Thanks for Listening