Week 8

The second dock design was retrieved this morning. Unfortunately, the slot for the phone was too small and had to be cut away to fit the phone. Because of this, the horn path was disrupted, and sound did not travel as designed. For this reason, precise tests were not performed. However, subjective testing was promising. Music was played on the phone, which was then placed in the case, then the dock, while the phone volume remained constant. It was clear that the music was significantly louder when the phone was in the dock than when it was in the case alone. This test showed that the horn model is more effective than the bowl model utilized in the previous dock design. The second dock is shown below.

Dock 2

Dock 2 with case

The main accomplishment of this dock design was that it proved that a large horn can be printed with the available equipment. Building on this success, another dock was designed in CAD with features that should amplify the music according to last week's mathematical modeling. The CAD designs for the third dock design are shown below. The most important feature is the parabolic funnel shape that extends out to the mouth where sound is released. Mathematical modeling and empirical data show that this design will amplify sound. Other changes to the second dock design include a larger slot for the phone, and a more forward center of mass, since the weight of the phone tended to tip the previous dock.

CAD model of dock 3

Internal view of dock 3, demonstrating horn

Due to the fine edge at the mouth of the horn, the print has a high degree of technical difficulty and is somewhat likely to fail. To improve the chances of success, the horn will be printed in two pieces, as a semicircle is far easier to print than a circle. Supports will also be added to the inside of the dock, though it will be tedious and difficult to remove them from the neck. If this print fails, the size of the horn will be reduced to give more thickness to the mouth. Obviously this will have a negative impact on the sound amplification ability of the dock, but may be a necessary sacrifice.

The equation L=(log(A)-log(a))*4000/(f*0.4343) expresses the ideal value of one of the variables given the other 3 to maximize the amplitude of sound waves through a horn, where "L" is neck length of the horn, "A" is area of the mouth, "a" is area of the throat, and "f" is the frequency of the sound waves. The areas of the mouth and throat of the horn are 75 mm and 35 mm, respectively. The neck length is about 150 mm and will be able to be more precisely measured after the dock is printed. Using the previously mentioned equation, the ideal frequency for a horn of these dimensions is 20kHz. This value is well outside the frequencies generally found in music. In fact, 20kHz is about the highest frequency a human ear can detect. However, this does not mean the horn will be ineffective; the equation only tells which frequency will experience the greatest amplitude due to the horn. The horn will still amplify frequencies found in music. The reason the dimensions of the horn in the third design are not optimized to amplify typical music frequencies is because the main objective of this print is to confirm that a horn this intricate can be printed. If successful, the dimensions will be adjusted to optimize amplification for musical frequencies.

Week 7

The second print of the dock was completed. It was immediately apparent that the design was unsuccessful; when placed in the dock, it was clear that the speaker was not at all amplified. Preliminary tests, as performed on the case, confirmed this, so no further tests were conducted. To redesign the dock, research was conducted to develop a better model.

The research showed that exponential, parabolic, and hyperbolic shapes are best for reflecting sound waves to amplify them, and also suggested ratios for horn length and mouth and throat area. Reflecting sound waves in these shapes causes sound waves to elongate, increasing the amplitude, which is what is perceived as loudness. The ideal shape of the horn depends on the frequency of the waves. Ideal throat diameter is proportional to frequency, whereas ideal mouth diameter is inversely proportional to frequency. Ideal horn length is given by the following equation, where "A" is defined as area of horn mouth, "a" as horn throat, "f" as frequency, and"L" as horn neck length:

L=(log(A)-log(a))*4000/(f*0.4343)

The stringent parameters of the phone case make it difficult to appease this relationship, but more design liberty is available with the dock. Since music consists of a wide range of frequencies, a horn that works well for a median frequency will be utilized. The next dock will be designed with careful measurements to optimize its amplification ability. In the meantime, another dock was designed and will be available for testing in Week 8. The CAD model for the printing dock is shown below.

CAD of dock design 2

Week 6

The fifth print of the case was performed this week. For this print, the side rails that gripped the phone were removed and the top corners were cut back. This proved successful, as the phone fits perfectly in the case. It's quick and easy to put the phone in the case, yet it will not come out without the deliberate action of pushing against the lens area from the back. The lens extrusion was also chamfered to eliminate the appearance of the case in the peripheral of the camera. The shape of the case will not be redesigned, as it now functions perfectly. The images below show the fifth case print.

Case print 5 (face)

Case print 5 (rear)

Phone in case (angled)

Phone in case (angled)

 Tests were conducted to determine the amplification abilities of the case. In the first test, the phone was set to full volume, and a sound meter was placed 8.05 inches from the speaker. The phone played 11 monotones, ranging from 262-1976 Hz. The sound level was recorded for each frequency. The monotones were selected based on a normal range of normal frequencies; 262 Hz corresponds to C4, one of the lowest notes played by a typical piano, and 1976 Hz corresponds to B6, one of the highest notes typically played by a piccolo. The exact process was repeated with the phone in the case. Figure 1 below shows the results of the experiment.

A second test was performed to test the musical amplification of the case. The sound meter was again placed 8.05 inches from the speaker. An arbitrary song was chosen, and the same 30-second sample was played from it in each trial. The average sound output was measured over the 30 seconds with the phone at half and full volume, both in and out of the case. The results of this experiment are shown below in Figure 2.

The results of the first test show that, for most frequencies, the case increases the sound output of the phone speaker. This was true for 7 of the 11 tested frequencies. It is unclear why the case reduced the sound output for 3 of the frequencies, but it may be related to the relationship of sound waves and the complex path that they travel inside the case, as well as resonance with the material of the case.

The results of the second test proved the amplification ability of the case for a musical application. At half volume, the case enhanced the sound output by 6 decibels, and at full volume, 9 decibels. Sound is measured on a logarithmic scale, and a difference of 9 decibels is quite significant for this application. The data implies that, the louder the music, the greater the amplification. This test provides objective evidence that the case is effective.

The second dock print was attempted this week as well. The print succeeded this time, though the result was untestable; the slot for the phone and case was too small. The CAD model will be adjusted and a third print will be attempted. The second dock print is shown below.

Dock print 2

Week 5

The fourth print for the case and first for the dock began yesterday. The dock was retrieved immediately this morning, though its print resulted in a failure. The failure was due to a coding error in the print instruction; a support was supposed to be included in both sides of the dock, but was omitted from the side that resulted in failure. Another dock print will be attempted before next week's class. A change in printing orientation will be considered to eliminate the necessity of supports. Troubleshooting dock prints is expected to be easier than that of cases, as there are less intricate, problem-inducing details in the dock. The dock print attempt is shown below.

Dock print 1

Though the dock was a failure, the case print was a breakthrough. The fourth print attempt at the case produced a testable model that fit the phone. Only minor issues persist; the case overhang is slightly too great for the phone to be placed in the phone without breaking the case. The top overhang was snapped off so that the phone could be placed in the case for testing. The fit is good, if not slightly loose; with the top overhang removed, the phone may slide out of its case when inverted. The openings made for the camera, charger, ventilation, and buttons line up properly. However, because of the case's thickness, the case is detected by the peripheral of the camera. Chamfering this opening will likely resolve this issue.

Obviously, this case is much bulkier than most. This is necessary to include the internal horn and amplify the sound. However, the case is for an iPhone 7/8, which is much smaller than an iPhone 7/8 Plus. In the opinion of one of the group members, the phone with the case is not more difficult to hold and use than an iPhone 7/8 Plus, only different. The phone and case still easily fit in one's pocket. Photos of the fourth case print are shown below.

Case print 4 (face)

Case print 4 (rear)

Case print 4 with charger and ventilation hole

Phone in case (face, overhang removed)

Phone in case (side, overhang removed)

Photo taken from phone in case, demonstrating case perceived in peripheral

A crude, preliminary audio test was performed to observe the amplification effect of the case. A decibel meter app was downloaded on a third party phone. An arbitrary song was played from the phone outside of the case at about three-quarter phone volume, and the sound level was observed. The sound level fluctuated, as one would expect from a song, but a median value could be subjectively determined. Without the case, the volume level seemed to fluctuate near 55 dB. The experiment was repeated, all factors held constant, except the phone was placed in the case. In this trial, the sound level fluctuated near 70 dB. The range of fluctuation in both trials seemed to be around ±8 dB. It is recognized that this preliminary test is rather subjective and is not an accurate representation of the amplification abilities of the case. However, the results give some credibility to the opinions of the five people that observed the effect of the case: "the sound is louder!" Photos of the decibel meter taken during each trial of the experiment are shown below.

Decibel meter and cased phone

Decibel meter and bare phone

Another case will be printed for next week to resolve the minor issues that remain. Much more stringent tests will be performed on the case. A more precise sound meter will be acquired from the Innovation Studio for testing, and the case will be taken to a room with minimal ambient sound and fluctuation. Rather than an arbitrary song, a monotone will be played at various volumes. The readings of the sound meter will be recorded and graphed for trials with and without the case. Various monotones will be used to determine if frequency impacts the effect of the case. The sound meter will not move at all between trials, and the phone and case will be placed in the exact same position between trials (the phone must move between trials to place the phone in and out of the case). Many graphs will be produced to demonstrate the effect of the case. A fairly linear relationship between phone volume and decibel reading is expected, with a consistently higher reading for trials in the case with otherwise identical variables.

Another print attempt will be made for the dock for next week as well. The progression of case print attempts is shown below.

Case print attempts, earliest to most recent (top to bottom)