Emma Mertens
Intro and Science:
Want to measure how loud your dog barks? How much noise exactly your dorm neighbors make when you’re trying to sleep? Well I’d love to tell you, “there’s an app for that,” but unfortunately the apps available for measuring decibel levels are not the most well-developed. For this experiment, I tested out apps on the iPhone that measure decibel levels. In order to do this, first I had to do some research about what a decibel actually is. A “decibel” is a measurement used to describe sound. Sound is wave, and there are two important characteristics that we can describe about a certain sound wave that make it distinct from a different sound wave. The two characteristics are intensity and pitch. Intensity is measured by the amplitude of the sound wave, or how tall the sound wave is. Intensity is what we are thinking about when we think about how loud or quiet a sound is. The larger the amplitude of the sound wave, the louder the sound appears to us. This is the aspect of sound that we measure with decibels. The other aspect of sound is pitch, which we measure by measuring the frequency of the sound waves. Frequency is how many sound waves fit into one second. The higher the frequency, the higher the pitch of the sound. We measure frequency with Herz.
For this experiment, I tested applications that measured decibels, so the frequency of each sound was not recorded. Decibels (dB) measure the intensity of sound. Because the human ear can hear such a variety of levels of sound, decibels do not increase and decrease linearly. The scale starts at zero, which represents silence. Ten decibels is ten times louder than 0 decibels, which seems to make sense. But 20 decibels is 100 times louder than zero, and 30 decibels is 1,000 times louder than 0 decibels.
Our ears can hear slight differences in decibel levels, and as always, technology is still trying to catch up with the complex human body. There are scientific tools that measure decibel levels quite accurately, but I wanted to know how accessible those tools were to us, the masses without access to a physics lab. I tested several cell phone apps that can be downloaded on the iPhone, which measure (or claim to measure) decibel levels.
Description of Project:
To do these trials and compare the apps to one-another, I used an online sound generator. I used this to make sure I had control of the fluctuation of sound that the app picked up. I turned the volume on my computer up to the maximum level, to ensure a constant level of sound throughout the trials. I set the measurement app to 0 (if the app had the available setting). Then I pressed play and waited one second before I played a tone from an online tone generator. The online generator played a constant tone for 3 seconds. I played the same tone twice with one second in between, and then played a tone that was the same level as the first, but went up 6 decibels after one second. I played that tone twice. I then played a tone that played the original sound level and then went down 6 decibels after 1 second. I played that tone twice as well. I played each of these tones with 1 second in between. I then ended the recording session and collected the data.
Results:
The first app was: Decibel 10th
This app was by far the best app that I reviewed. Some of its best features include the ability to export data by email; the ability to start, pause, and reset the data collection process; and the in-time graph of the data being taken. This app recorded the minimum, maximum, and average decibel levels collected during the data collection process. Decibel 10th collected the most data and displayed it in the most user-friendly way. Another positive aspect of Decibel 10th was its accuracy. According to the Department of Design and Environmental analysis at Cornell University, a whisper is about 34 decibels. This closely aligns with the minimum decibel level recorded by Decibel 10th, which was 38.2 decibels.
I give this app 4.5 out of 5 stars.
The second app was: DecibelMeter
The free version of this app does not have very many features. The user is able to pause the data-taking process and reset the “max value,” but these are the only major features of the app. There is a graph, but the scale of the graph is too large to be helpful tracking smaller changes in decibel levels. Additionally, this app does not appear to be very accurate. In various quiet rooms in which this app was opened, this app measured around 60 decibels of sound. This is reflected in the data set and on the graph, in which you can see that the minimum decibel level recorded during the data collection was 75 decibels.
I give this app 2.5 out of 5 stars.
The third app was: Decibel Ultra
Decibel Ultra’s main flaw is that it is not user-friendly. There are many numbers on the screen that are not labeled clearly. If you’re someone that knows a lot about sound, these labels may be helpful to you, but otherwise they’re just overwhelming and confusing. That being said, there are a lot of numbers on the screen, so if you can figure out what they all mean you’ll be in good shape. The app does have instructions, but they’re also not very clear. Some of the features of this app are helpful, however. It has pause, stop, and reset buttons which make for clear data collection. This app also has a visual, but rather than graphing the decibel level over time, like Decibel 10th does, this visual shows the decibel level at each moment independently. This app also appeared to be fairly accurate, as it would hover between 30 and 40 decibels in a quiet room.
I give this app 3.5 out of 5 stars.
The fourth app was: SoundMeter
SoundMeter is by far the app with the least number of features, of the ones that I tested. SoundMeter’s screen consists of two bars, one labeled “Average” and one labeled “Peak.” It also shows the Max level reached. This app does not even attempt to show the sound level at any given time. It does not show a minimum value or have a reset button, although it does have “start” and “stop” buttons. Clicking on the information button simply prompts the user to buy the full version. SoundMeter, like DecibelMeter tended to report higher decibel levels than expected, with the average recorded decibel level being 71.
I give this app 0.5 out of 5 stars.
Data:
| App Name | Minimum Level Recorded | Maximum Level Recorded | Average Level Recorded | Peak Recorded |
| Decibel 10th (App 1) | 38.2 | 68.5 | 62.7 | 71.3 |
| DecibelMeter
(App 2) |
75 | -* | 66 | 70 |
| Decibel Ultra
(App 3) |
33.8 | 66.3 | -* | -* |
| SoundMeter
(App 4) |
-* | 77 | 71 | 76 |
*Application did not collect this data
Conclusion:
The take-away from this experiment was pretty unfortunate. Decibel 10th is probably your best option for proving those pesky neighbors are too darn loud (unless of course you want to skew the data, then I would suggest DecibelMeter or SoundMeter, but I’m not condoning lying). Each app measured slightly different data, so in some ways it was difficult to compare the accuracy. Looking at the graph, all the apps that measured the average decibel level appeared rather similar. However, again we can see that the minimum level measured by DecibelMeter was much higher than the other two apps that measured minimums. Looking at the maximums recorded, SoundMeter’s maximum was significantly more than the other two apps that measured the maximum decibel level, which again makes me question its accuracy. Ultimately it was clear to see that Decibel 10th out-shined the rest of the apps tested, however these were just the free versions.
These results were slightly worse than I would have predicted because I was hoping more accurate technology would be available in 2017. I was especially surprised because I used a cell-phone, and intuitively one would assume that cell-phones have some of the most up-to-date sound measuring equipment since measuring sound is one of the most important aspects of a cell-phone. To capture and analyze sounds, the cell-phone uses what is called a transducer. A transducer is a device that converts variations in a physical quantity, such as pressure, into an electrical signal, or vice versa. So the microphone in an iPhone measures sound frequencies (dB) and converts it into a voltage. When you are talking to someone on the phone, the phone you speak into measures frequencies, converts them to voltage, and then sends that voltage to the other phone which converts the voltage back into physical frequencies. Because a cell-phone has this capability, I had hoped that it would be better able to measure sound frequencies (dB).
Endnotes:
In another experiment, or if I were to continue this experiment for six more weeks, someone could test the apps that must be purchased. My prediction and hope would be that these apps would have more features (like reset buttons) and would be more accurate, and therefore get more similar results. A flaw in this experiment also could have arisen from the environment it took place. I completed this experiment in my room, which has noises from neighbors and the street that do not remain constant. In order to fix this in a new experiment, I could complete the experiment in a soundproofed room.
Sources:
Information about Decibels:
http://www.human.cornell.edu/dea/outreach/upload/FPM-Notes_Vol1_Number11.pdf
http://science.howstuffworks.com/question124.htm
Online Tone Generator: http://www.audiocheck.net/blindtests_level.php?lvl=6
Information about Transducer: https://www.merriam-webster.com/dictionary/transducer
http://efxkits.com/blog/different-types-of-transducers-in-practical-applications/
Information about Sound Waves:
https://www.nde-ed.org/EducationResources/HighSchool/Sound/components.htm