Microphone
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Contents |
Executive Summary
-Dan
this page needs a fricking backlink!
Engineering_Design_II_-_Conceptualization_and_Realization_Course
Stakeholders
The major shareholders of microphones and microphone stands are the consumers, retailers, manufacturers, transporters and society.
Consumer
- Ease of use - Microphone must be easy to use, stand must be easy to orient.
- Ease of assembly - Microphone should be plug and play, stand should be easy to put together.
- Effectiveness - Microphone should pick up sound without user having to be too loud, stand should hold microphone in desired place.
- Ease of storage - Microphone should not need any special storage, stand should be collapsible/occupy less space.
- Reliability - Products should perform consistently without maintenance.
- Safety - Product should not harm the user in any way.
- Cost - Microphone is priced depending on its sensitivity but should be affordable, stand should be priced reasonably depending on quality.
- Customization - Products should have replaceable or interchangeable parts for use in multitude of settings.
- Portability - Products should be lightweight but sturdy enough to be transported.
Retailers
- Appeal - Products should attract customers.
- Profit margin - Products should produce a profit so there is reason to carry product in store.
- Storage - Products should be easy to stack and store.
Manufacturer
- Material cost - The materials should be cheap and easy to obtain to maximize production and keep price down.
- Manufacturing cost - The methods of manufacture should be cheap and efficient.
- Standardization - Parts should be standardized to reduce complexity of design.
- Assembly - Products should be easy to piece together in the factory.
- Time for manufacture - Time should be minimal to produce in large quantities.
Shipping/Packaging
- Weight - Products should be light to reduce transportation costs.
- Durability - Products should be able to survive transit.
Society
- Social Media - Musical concerts, gatherings, sports games, etc., that are dependent on capturing sounds to reach masses require reliable microphones.
- Long distance communication - Reliant on microphone processing sounds so it can be transmitted to another location.
Product Function
Boom Stand
The purpose of the boom stand is simple: to be able to hold the microphone still in various orientations according to the user’s need. The boom stand which we dissected was designed to have 5 degrees of freedom, allowing the user to position the microphone in diverse settings. The stand and extension allows the user to adjust the total height of the two to a desired height between 33-61 inches. The joint connecting the boom shaft and stand has 3 degrees of freedom, allowing the shaft to pivot, rotate, and translate along its axis. The last degree of freedom is at the microphone holder, allowing the user to orientate the microphone at various angles. The microphone can be positioned at a low height downward angle for miking a drum set or high at various angles depending on the user’s height for stand up.
There are two rubber pads inside the joint connecting the stand and shaft. The friction between the surfaces of the two pads and the boom holder is strong enough to keep the entire boom stand above it still. At the same time the user can easily adjust (pivot) it. If there is too much force, whether it be too heavy of a load or a person pushing on it too hard, the force will simply overcome the frictional force and move the shaft so it won’t be directed to the pipes. One would almost have to be intentional to bend the steel pipes of the microphone stand.
The last benefit of the stand is that it is foldable and can be taken apart.
Microphone
A microphone is a type of acoustic transducer. This implies that it has the ability to covert sound energy into electrical energy. There are various types of microphones classified not only by method of converting energy but also by the directionality of use.
The microphone that we dissected was a dynamic, cardioid microphone. A dynamic microphone is one in which sound energy that enters through the head, hits a small, taut diaphragm which is placed directly above a magnet-wire coil combination. The incoming sound energy forces the diaphragm to vibrate which in turn vibrates the magnet inside the coils of wire. Due to electromagnetic induction, the movement of the magnet inside the coils of wire produces an alternating current (AC) inside the wire. It should be noted that a microphone's function is simply to relay the signals created by the changing incoming sounds to a more powerful device such as an amplifier. Therefore, the current produced inside the circuit of the microphone is not needed. All that is needed is information about changes in potential across the circuit. This is accomplished by setting the impedance within the circuit high enough such that current flowing is zero.
The "cardioid" prefix mentioned earlier indicates the directionality of the microphone. Different microphones are necessary for different purposes. For example, in a situation where many sources of sound are required to be amplified through the same microphone, an omni-directional microphone would be required. On the other hand, for a single user a uni-directional microphone would be the obvious choice. A super-cardioid microphone is a uni-directional microphone with specific characteristics that are best understood from the following figure.
User Study
Microphones and microphone stands are used a lot by professional musicians. We first considered the manner in which some famous singers have used microphones and microphone stands.For example, Bono is a prolific microphone and microphone stand user.
In this clip: Bono with only microphone - Bono uses only the microphone while walking around the platform.
However, in this clip: Bono with microphone and stand - Bono stays relatively stationary while singing into the microphone that sits atop the stand.
In our opinion, the reason for this variation is because of the setting. While in the first clip Bono had the freedom to walk amongst his fans, in the second clip he was on a stage that simply faced the audience denying him the proximity to his fans.
For other musicians, the microphone stand is more of a necessity.
In the following clip Stephen Lynch and friend, comedian-musician Stephen Lynch needs the microphone stand because he is playing the guitar and singing at the same time. Additionally, one possible area of improvement that we noticed was that Stephen Lynch had to lean awkwardly over his guitar to reach the mic. If there were some way to have the space occupied by the guitar accounted for by the stand, it might make the lives of those musicians, who play instruments and sing simultaneously, much easier.
Lastly, we observed the variations in the distance musicians held microphones from their mouths. It seems that singing from further away reduces the volume but also reduces the unwanted noise/bad notes that a singer might inadvertently hit.
Setting up the microphone stand was relatively easy. Everything was intuitive and its 5 degrees of freedom allowed for all the desired orientations. The addition of the boom arm allowed the microphone to be raised over 7 feet, accommodating most users. Attaching the microphone clip to the boom arm wasn't as straightforward. Microphone clips are not standardized, different manufacturers make different sizes, causing us to go out and buy another microphone with an appropriate size.
During the testing of the microphone system, we found that:
- Microphone was not very sensitive, we had to talk fairly loud for it to register.
- Microphone will not pick up speech-level sound from more than a foot away.
- The joint in the microphone clip is very loose, its hard to keep the microphone in position.
- Solder inside microphone was loose, microphone stopped working after a few on-off switches.
- Microphone only picked up sound that originated directly in front of it. All other sounds were muffled.
- Microphone picks up a lot of static, background noise.
- It makes me sound so bad.
Assembly
- Note: Refer numbers from the Part List Section
Mechanical Analysis
Objective: To understand the sound to electrical energy conversion that takes place in the magnetic cartridge of a dynamic microphone.
Theory: 1) A dynamic microphone works by converting incoming sound energy to electrical output. 2) This conversion is carried out in the magnetic cartridge just below the head of the microphone. 3) As sound waves enter through the head, they strike the diaphragm. 4) This causes a transfer of energy to the diaphragm which in turn begins to vibrate. 5) The vibrating diaphragm causes air molecules trapped underneath it to vibrate. These in turn push down on a magnet that is surrounded by coils of wire. 6) The movement of the magnets results in the electromagnetic effect as outlined by Faraday and Lenz. 7) This electromagnetic effect produces an alternating electric current in the wires.
Assumptions: 1) The diaphragm can be modeled as a mass-spring system (harmonic oscillator) with damping. 2) The incoming sound energy has a sound pressure level (SPL) of around 0.632 Pa. This should correspond to moderately loud singing. 3) The above sound is transferred entirely to the diaphragm of the microphone without any energy loss. 4) Air trapped beneath the diaphragm is incompressible. This assumption was made because of the low absolute velocity achieved by the magnet as well as diaphragm. 5)The spring constant of the diaphragm is as a result of the tension that is intentionally induced during manufacture and is equal to 50 N/m. This value is a conservative value for the tension of a diaphragm as described by Patent with diaphragm tension value. 6) Room temperature (300K) and pressure. 7) The diaphragm is a thin disc of mylar 8) The magnetic field strength of the neodymium magnet disc used in the setup is approx. 0.2 teslas as reported by magnet strength figure 9) Number of wire coils was around 50 10) When the magnet oscillates within the coils, any one coil goes from experiencing max. positive magnetic field strength to max. negative field strength in one half cycle.
Given: 1) Spring constant (k) = 50N/m 2) Dynamic viscosity of air at 300K (b) = 1.983*10-5N.s/m2 3) Sound Input pressure = 0.632 Pa 4) Acting diameter of diaphragm = 12*10-3m 5) Thickness of diaphragm = 0.1*10-3m 6) Density of mylar diaphragm = 1.390 kg/m3 7) Magnetic field strength(B) = 0.2 teslas
Calculations:
First mass of the diaphragm was needed:
Volume = Face Area of diaphragm * thickness
= pi * (12*10-3m)2 * (1/4) * 0.1*10-3m
We know that Density = Mass/Volume
Therefore, Mass= Density * Volume
Mass (m)= 1.390 * 1.1310*10-8 = 1.5721*10-8kg
Now, having all the constants we could use Matlab to solve for the equation of motion of the mass-spring system.
Equation of mass-spring system :
mx" + bx' + kx = Force_Input where Force_Input is an initial condition applied force called Force_Input
Force_Input = Sound_Input * Face Area of diaphragm * G
Force_Input = 0.632 Pa * 1.310 * 10-4m2 * G
Force_Input = 7.1478* 10-5 * G
where G is a modifier that makes Force_Input an impulse provided to the mass-spring system. G = 2*abs(abs(sign(t-1))-1)
Coming back to the mass-spring equation, the only unknown left is x.
We solved this equation using the Matlab function "ode23t".
First, the equation had to be rearranged → x" = -(b/m)x' - (k/m)x + Force_input
In Matlab, the main code used was as follows:
- % Solve equation of motion
- options = odeset('RelTol',1e-5,'AbsTol',[1e-5 1e-5 1e-5]);
- [t,xo]=ode23t('F',[1,8],[0,0]);
- xo(:,1)
- t
- figure(1);
- plot(t,xo(:,1));
where function f was defined as:
- function xdot=F(t,x)
- mass = 1.5721e-008 ;
- Force_input =7.1478e-005*2*abs(abs(sign(t-1))-1);
- k= 50;
- b=1.983*10^-5;
- Area= 1.1310e-004;
- xdot=zeros(size(x)); % since output must be a column vector
- xdot(1)=x(2);
- xdot(2)=-(b*x(2))-(k/mass)*x(1)+Force_input;
Using this code, we obtained the following two graphs that demonstrate the response of the system to initial conditions:
This graph takes a long time span of the system. Quite clearly, after the initial displacement due to applied sound pressure, the system settles down to steady state 0.
This graph shows a much shorter time span. Despite the system appearing to have reached steady state in the previous graph, the shorter time span shows continuing minute displacements. These are the reason for the background noise/disturbance created in microphones.
Using this code, we obtained the following O/P for time elapsed and displacement:
Additionally, we were able to calculate period of oscillation (T)= 1.0771 s.
Now, the vibration of the diaphragm causes vibration of the magnet within the coil as mentioned before. This generates emf due to electromagnetic induction.
The formula is emf = - n*dΦB/dt
Where dΦB/dt = the change in magnetic flux with respect to time
n = number of wire coils = 10
In this case, since the magnetic field is always perpendicular to the coil length, magnetic flux (ΦB) = B * Area where B = magnetic field strength and Area is face area of the coils which is the same as the acting face area of the diaphragm.
Clearly, emf would be induced by 1) changing area within the magnetic field , 2) changing magnetic field strength.
We determined that the latter was true in this case. This is because any given coil moves from a position of being influenced by positive maximum magnetic field strength to negative maximum field strength within one half period.
Since we determined the period (T) earlier and this is the same as the period of the magnet, we can determine dΦB/dt = ((Bmax - (-Bmax))*Area/(T/2)
then,
dΦB/dt = 0.4T * 1.310 * 10-4m2/0.5385 s = 9.3707 * 10-5 Weber/s
Finally, emf = 10 * 9.3707 * 10-5 = 0.93 mV.
Conclusions:
This analysis was important to get an idea of how all the different elements of the microphone's working unit are important in determining the response to a given incoming sound signal. We got an answer of 0.93 mV corresponding to an initial signal of 0.632 Pa. The sensitivity is then 1.4715 mv/Pa. This is very close to the company provided sensitivity of 1.8 mV/Pa (link
The small difference might be due to some of the assumptions that were made. For example, the air trapped underneath the diaphragm might be compressible. If this is the case, the spring constant k would also have to take into account the spring effect of enclosed air. Furthermore, the formula that was used to find emf generated was crude, a more thorough integration would have to be performed to attain the correct emf generated.
We feel that this analysis has helped us understand the energy conversion dynamic within the microphone. We feel that we might be able to exploit the conversion characteristics of a microphone and apply them for a more general sound energy capturing device.
Parts List
Microphone Stand Parts
Microphone Parts
Design for Manufacturing and Assembly (DFMA)
Design for Manufacturing
Materials: Plastic and Metal
Engineered products can be made out of a variety of materials. Depending on the application the choice of materials can allow a product to perform well or cause it to fail. Even among appropriate material choices, some materials have advantages over others for a number of different reasons. The parts that construct the boom stand and microphone are mainly constructed of either plastic or steel. In general, plastics can be good for inexpensive, complex shapes, while metals are good for it's durability and long lasting applications.
The category of plastics as a whole also has advantages and disadvantages. It is generally relatively easy to create highly complex plastic parts, with both small and large features, and with high aspect ratios. This is because plastics are easily molded in a variety of ways. Plastics also tend to be less dense than metals. From an aesthetic perspective, some plastics can be used to create unique shapes for beautiful products. However, many people tend to associate plastics with cheaper products, which can be both an advantage, or a disadvantage. For example, plastic is a good material choice for single-use forks and knives, but these utensils will never look as good as metal utensils. A major disadvantage of plastics is that they are usually made out of petroleum, which is an unsustainable resource. However, progress is being made in creating plastics from organic materials.
Another major materials category is metals. Metals tend to be very strong in both tension and compression, and tend to have a very long life span. They are less likely to deform than plastics, which makes them good for high-precision applications. From an aesthetic perspective, metals have a unique place in the human psyche. Metals also have a unique luster that people often find very appealing. The major disadvantages of metals are the potential to rust (depending on the type of metal), and the fact that they need to be mined, which can often be an inefficient process that causes a lot of environmental damage.
Microphone:
During the disassembly, one issue we encountered was removing part M6 from the body. M6, a rubber disc used to hold the pins in place, seems to have been attached to the base via a strong adhesive. Although this manufacturing method makes dis-assembly difficult, it is ideal for this product. The pins need to line up perfectly with the holes in the cable, possibly thousands of times during the product's life span. This means that the rubber disc must not be allowed to shift within the body. Even thought the disc is already press-fit inside the body, it is important that it is securely joined as well.
One possible area of improvement is in the soldering of electrical components and wires. Inconsistency in the soldering could be a sign that this was performed by hand. Automating this process would not be very difficult; both the chip and the switch electronics are rectangular. Considering the high volume of microphones being produced, it would be feasible to create a soldering rig that would quickly attach wires to the components.
Boom Stand:
The few parts that plastic (handle and end of thumbscrews) along with the rubber ends on the bottom are most likely made through injection molding. Injection molding provides a high volume mass production of identical parts with very low tolerance. The initial tooling costs are very high but the unit costs are low (meaning a high initial fixed cost but in exchange the marginal cost per unit is sufficiently low), thus when a large quantity of identical parts are produced injection molding will save money in comparison to other processes.
The counter weight on the end of the boom shaft and the tripod core are both solid pieces of metal made through the casting process. The counter weight is then either press fitted or glued onto the end of the boom shaft. The casting process (my guess is die casting) has a similar manufacturing feature as injection molding cost-wise. They are generally a high volume production with high initial tooling costs but low unit costs.
All the steel tube components have identical thicknesses and diameter, meaning that they can all be produced by the same machinery while each part is cut into the desired length. The raw steel is cast then made into a pipe by stretching the steel out into a tube. The steel tubes are seamless, which are suitable for the job as the shafts for being strong, durable, and light weight. The exterior of all steel components are sprayed on a metta-black finish for a good look to appeal to the consumers.
Design for Assembly:
The assembly of the parts can be either by man or machine. In our opinion, it would make more sense to use man power instead of having the assembly process be automated. To our surprise, the after the stand was dissected and analyzed it took less than 5 minutes for a single person to reassemble everything part together. Pliers were the only tool needed for the process, used for tightening bolts.
Failure Modes and Effects Analysis
Considering ways in which a product could potentially fail is an important part of the design process. All products should be designed so that they are safe and reliable for use. Potential dangers must be eliminated before production. FMEA reports identify potential failure modes and assign corrective measures. Risk priority numbers (RPN) are calculated (S*O*D) and then assigned to each failure mode to assure proper prioritizing. Higher RPNs are addressed first. The scale used for measuring S,O,D can be found in the Engineering Design textbook by Dieter and Schmidt. <ref>Dieter, E and Schmidt, L (2008). Engineering Design. Fourth Ed. McGraw-Hill.</ref>
S= Severity of Failure
O= Probability of Occurrence
D= Detectability of Failure
Assembly/Parts | Failure Mode | Consequence of Failure | S | Causes of Failure | O | Prevention | D | RPN | Recommendations | Responsibility |
---|---|---|---|---|---|---|---|---|---|---|
On/Off Switch | Soldering Becomes Loose | Microphone will not turn on | 5 | Bad soldering | 2 | N/A | 2 | 20 | Check soldering before assembly | Controls engineer |
Diaphragm | Torn Diaphragm | Inoperable | 5 | Misuse or Outside particles gets inside microphone | 1 | Foam Cover | 2 | 10 | N/A | N/A |
Wire Coil | Torn | Microphone inoperable | 5 | Improper use/production | 1 | Testing during production | 6 | 30 | N/A | Controls Engineer |
Wire Coil | Inadequate coating to separate each wire | Decreased electromagnetic effect | 4 | Improper use/production | 1 | N/A | 8 | 32 | N/A | Controls Engineer |
Magnet | Looses magnetism | Decreased sensitivity of microphone, inoperable | 4 | Over time or microphone is subjected to strong magnetic field | 1 | N/A | 7 | 28 | Don't go near extreme magnetic fields | N/A |
Microphone Housing | Broken | Microphone in pieces, wires exposed | 5 | Impact | 1 | N/A | 1 | 5 | Do not drop on floor after serving someone | N/A |
Microphone Clip | Loose Joint | Unable to orient to desired location | 3 | Loose Screws, wear from use | 6 | N/A | 1 | 18 | Tighten Screws constantly, add friction to joint | Controls Engineer |
Microphone Clip | Broken clip | Unable to attach to microphone | 4 | Improper use, impact | 4 | N/A | 1 | 16 | N/A | N/A |
Boom Stand Screw | Loose fastener | Unable to stay in position, falls down | 7 | Improper use, wear | 3 | Rubber pads inside boom housing | 2 | 42 | Replace rubber pads to ensure boom stays gripped in position | N/A |
Extending Stand | Grip fails | Stand does not stay extended | 7 | Wear from lots of use | 2 | Exploded end | 1 | 14 | Add rubber stoppers or grips | Design Engineer |
Rubber Pads | Worn down thickness | Boom shaft is unstable, gravity overcomes friction force | 3 | Worn pads | 1 | N/A | 1 | 3 | Do not pivot shaft aggressively or unnecessarily | N/A |
Rubber Ends | Torn or lost | Stand may slide | 2 | Worn down ends | 1 | N/A | 1 | 2 | N/A | N/A |
Cord Clip | Broken or lost | Loose Cord | 1 | Misuse | 1 | N/A | 1 | 1 | N/A | N/A |
All steel/metal parts of stand (Stand, tripod legs, boom arm , etc) | Oxidation | Aesthetic value, uncomfortable to touch | 3 | Neglect, exposure to water | 2 | N/A | 1 | 6 | Anti-rust finishing | Controls Engineer |
From the generally low RPNs, we can see that this product is extremely safe and only has one part (falling boom stand) that could potential harm the user. Most problems can be avoided with a product test before packaging.
Design for Environment
In designing a product, it is important to consider the environmental effects along with the consumer. Conducting a Life Cycle Assessment (LCA) can improve the product's environmental-friendliness and reduce costs in the long run.
Toxic Release
This table and graph show the amount of toxic release into the environment. Note that the amount released by specifically the manufacture of audio-video equipment is minuscule compared to the other sectors involved.
Energy
Since the product is heavily based on electrical power, this table shows the energy breakdown. Power generation is also the main sector here.
Greenhouse Gas Emissions
Greenhouse gases, such as carbon dioxide and chlorofluorocarbons, contribute to the prevalent problem of global warming. With a $1 million injection into the Audio-Video Manufacturing sector, the overall global warming potential (GWP) increase by 574 metric tons of CO2 equivalent.
As we can see from the graph above, the actual audio-video manufacturing process only contributes 19.7 MTCO2E, less than 4% of the total. Most of the emissions come from power supply. If a CO2 tax was passed, the manufacture of audio-video might take a hit, but not as hard as most of the other sectors.
Air Pollutants
Conventional air pollutants such as carbon monoxide largely affect weather patterns like causing smog which in turn can cause respiratory and other health problem in affected areas. Most of the problem comes from power generation and the manufacture of petroleum. Audio-video manufacturing was not even in the top 10 pollutant sources.
Conclusion and Recommendations
Team Members and Roles
Luo Xing Ni- DFE, Stakeholders, FMEA, User Study
Daniel Liptz- Parts List, Executive Summary, Conclusion, Assembly, DFMA
Justin Yi- Parts List, Assembly, DFMA, Product Function
Nakul Gupta- Mechanical Analysis, Product Function
References
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