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18 Modular Add-On for Headphones to add Noise-Cancelling
Harrison Qu
Tanishq Dubey
Yu Wang
Dongwei Shi design_document0.pdf
design_document0.pdf
design_document0.pdf
final_paper0.pdf
proposal0.pdf
- Tanishq Dubey (tdubey3)

- Harrison Qu (hqu5)

- Yu "Benson" Wang (yuwang15)

Problem statement:

There is a burgeoning market for wireless, active-noise cancelling headphones, however, currently, headphones that have these features are very expensive. This leads to a void in the market for cheap noise cancelling headphones that offer good performance. In addition, many already own headphones without advanced features such as noise cancelling and cannot justify paying high prices just for a single feature.

Background Information:

Currently the headphone market is divided into two distinct segments: general consumer grade headphones that cost than or equal to $150, and high end “audiophile” headphones that include the latest features and cost $200 and upwards (some headphones, such as the Sennheiser HD 800 model, can cost $1200 dollars!). Due to the recent removal of the 3.5mm headphones connection as a commodity in mobile devices, bluetooth audio has gone from being a luxury product to being priced with regular consumer headphones. Noise canceling technology, however, has remained at the upper range of the market and is still considered a luxury feature. In fact, simply adding noise cancelling to headsets can raise the price by $100, for example:

https://www.amazon.com/Bose-SoundLink-around-ear-wireless-headphones/dp/B0117RGG8E/ref=sr_1_6?s=aht&ie=UTF8&qid=1504991769&sr=1-6 ($230)

https://www.amazon.com/Bose-QuietComfort-Wireless-Headphones-Cancelling/dp/B01E3SNO1G/ref=sr_1_1?s=aht&ie=UTF8&qid=1504991769&sr=1-1 ($330)

Solution:

We will to make an add-on to headphones, attached to the line-in, that modifies a headphone to be noise-cancelling. We will also attach an amplifier and an app alongside the hardware for noise-cancelling variability, frequency adjustment, volume control. By doing this, it will not only be user-customizable, but also cost-efficient. Our goal is a modular device that is capable of removing 50% of background noise, while maintaining 30% of the cost of popular noise cancelling headsets (it should be noted that this cost takes into account the cost of the module and a set of non-noise cancelling consumer grade headphones). We understand that headphones are made differently, so we’ll also make an application that syncs frequency levels and noise-cancelling levels with the headphone. As previously stated, the goal of this project is not to improve upon noise cancelling, but rather create noise cancelling for the masses.


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Functional Overview:

Control Circuit

The control circuit is made up of 2 components, the bluetooth module and the ATMega control, which work together to give wireless control of the noise cancelling circuit via an app that runs on a smartphone. The Bluetooth module communicates with the smartphone running the app so that parameters such as “microphone level”, “microphone mix level”, and “output amp level” can be controlled, allowing for fine-tuning of the NC circuit by the user based on the location/environment they are in. However, the bluetooth module is useless without the ATMega controller, which is used to convert the packets received by the bluetooth controller into actions taken by the NC circuit, effectively acting as a translator between the bluetooth module and the circuit itself.

Noise Cancelling (NC) Circuit:

The noise cancelling circuit is made up of four distinct components that act in a pipeline fashion to produce an output that is noise cancelled audio playing through the user's headphones. The first component is the microphone amp circuit, which takes in the signal from the microphones mounted on the sides of the headphones and amplifies said signal. This is done because the signal from the microphone may not be strong enough to be mixed into the incoming audio signal from the user’s audio source. The second component is the Inverting circuit. This circuit takes input from the microphones attached to the headphones and inverts the signal. This contributes to the noise-cancelling attribute of the headphones as this step is crucial in cancelling external sound waves. The third stage in the pipeline is the mixing circuit. The mixing circuit takes the inverted microphone signal and adds the user’s input audio signal to it. This effectively creates a noise cancelled version of the user’s audio. In addition, if there is no audio coming from the user, then the circuit simply acts as a active noise cancelling headset, still providing silence to the user. The final stage in the pipeline is the output amp. This outputs an amplified version of the noise cancelled signal so that the user can control the output volume from the module itself. The digital potentiometers exist to allow for a control interface between the control circuit and the NC circuit. This allows for wireless control of the NC circuit.

Circuit Power:

The NC module is made to be powered by a battery, so it can be portable and operate anywhere. This means that two things are required. Firstly, a battery is required to provide power to the entire circuit when it is portable, ideally for extended periods of time. Secondly, a voltage regulation circuit is needed. This circuit will play a twofold role. First, it will regulate voltage between the battery and the NC and control circuits to acceptable levels. Second, it will act as the charging circuit for the battery and will prevent back current to the NC and control circuits while also regulating the charging of the battery.

Smartphone App

The smartphone app will be used to control and fine tune the noise canceling of the headphones. This is done by connecting the headphones to the app via bluetooth and then being able to regulate the NC circuit via sliders in the app. The fine tuning of the NC circuit is required because a modular NC unit cannot automatically acclimate to the requirements of the user, the environment the NC module is being used in, and also the placement of the microphones on the headset itself.

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Critical Design Decisions:

Frequency Response: Noise cancelling does not cancel out all frequencies. Top of the line headphones have trouble cancelling out anything about 2.5KHz, simply due to the difficulty of that topic. However, they achieve good results by cancelling out lower frequencies (50Hz to 1Khz) in which most background noise is made. Again, we are not claiming to match the performance of the top of the line headphones, because we know we cannot, but instead are reaching at least 50% of their performance, which will be more than sufficient for everyday activities. Most headphones, especially the market we are targeting, mid-range consumer headphones, as stated in our proposal, can handle producing frequencies from 40Hz to 15kHz, and thus should not be a problem to replicate our NC signal on the headsets we are targeting.

Microphone Placement: We are placing the microphones externally on the headphones, which is not an uncommon design, known as Feed-Forward ANC, for a few reasons. Firstly, this is meant to be designed as a consumer add-on to regular headphones, which means that the user should be able to easily mount the microphones to the headphones, ideally through some simple adhesive. Shape and distance from the speaker was also mentioned, and we have thought about this with microphone placement. The external placement of the microphone is done so that our circuit has time to create the NC signal, whose phase with the speaker can be adjusted through an all pass filter.


Other Notes: The bluetooth components can be removed for manual controls if needed due to time constraints.


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Diagrams:

Block Diagram:
https://docs.google.com/drawings/d/1AiGq-65086qo_2F51qC4Sr7ae5TG2Kho-xoQhbYoBQ8/edit?usp=sharing

Circuit Diagram:
https://drive.google.com/open?id=0B4-oirNpdS2kSGExY2F5aFNVbGc


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Previous Literature:

https://ese.wustl.edu/ContentFiles/Research/UndergraduateResearch/CompletedProjects/WebPages/sp09/ShizhangWu/NCH.pdf

http://www-personal.umich.edu/~gowtham/bellala_EECS452report.pdf
(Should be noted that the paper above details a highly complex Digital Hybrid ANC project also done in one semester)

http://www4.ncsu.edu/~rsmith/MA574_S15/silence.pdf

https://www.ee.iitb.ac.in/uma/~wel/wel45/public_html/edl11s/G05_2011.pdf

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