In common parlance, decibels are a common way to measure the volume of sound. Decibels are a base 10 logarithmic unit: it means that an increase of 10 decibels produces a sound twice as loud as it started. In general terms, the decibel value of a sound is given by the formula 10 Log10(I / 10-12), where I = sound intensity in watts / square meters.
Steps
Method 1 of 3: Comparison Table of Noise in Decibels
In the table below, increasing decibel levels are assigned to common noise sources. In addition, information on hearing damage is given for each noise level.
| Decibels | Example Sources | Health effects |
|---|---|---|
| 0 | Silence | Nobody |
| 10 | Breath | Nobody |
| 20 | Whisper | Nobody |
| 30 | Background noise of a quiet rural setting | Nobody |
| 40 | Library noise, background noise in the urban quiet | Nobody |
| 50 | Relaxed conversation, ordinary suburban business | Nobody |
| 60 | Noise from an active office or restaurant, noisy conversation | Nobody |
| 70 | TV volume, highway traffic at 15.2 meters | Nobody; unpleasant for some |
| 80 | Factory noise, blender, car wash at 6.1 meters | Possible hearing damage after prolonged exposure |
| 90 | Lawn mower, motorcycle at 7.62 meters | Possible hearing damage after prolonged exposure |
| 100 | Motorboat engine, drilling rig | Serious damage to hearing after prolonged exposure |
| 110 | Loud rock concert, steel mill | It can be painful right away; very likely hearing damage after prolonged exposure |
| 120 | Chainsaw, thunder | Usually painful right away |
| 130-150 | Takeoff of a jet on the runway | Immediate hearing loss or possible rupture of the eardrum |
Method 2 of 3: Measure the Decibels with the Tools
Step 1. Use the computer
With the right programs and equipment, it's not difficult to measure the decibel level of a sound using your computer. Listed below are just a few ways to do this. Note that better control gear will always give you better results - in other words, while your computer's default internal microphone may be enough for some tasks, a high-quality external one will be much more accurate.
- If you have Windows 8, try downloading the free Decibel Reader app from the Microsoft App Store. The app uses your computer's microphone to read noise up to 96 decibels. Similar devices are available in the iTunes app store for Apple products.
- You can also try using a third party program to measure decibels. For example, Audacity, a free audio recording program, has a simple built-in decibel meter.
Step 2. Use a mobile app
For measuring the level of sound on the go, a mobile app can be extremely convenient. While the microphone on your mobile device may not be as good as external ones to connect to a computer, it may still be surprisingly accurate. It commonly makes a mistake within 5 decibels compared to readings made with professional equipment. Here is a short list of apps available for reading decibels:
- For Apple devices: Decibel 10, Decibel Meter Pro, dB Meter, Sound Level Meter
- For Android devices: Sound Meter, Decibel Meter, Noise Meter, deciBel
- For Windows phones: Decibel Meter Free, Cyberx Decibel Meter, Decibel Meter Pro
Step 3. Use a professional decibel meter
While not usually cheap, perhaps the most direct and accurate way to find the decibel level of a sound is to use a decibel meter. Also called a "sound level meter", this specialized instrument (also available at online retailers) uses a sensitive microphone to measure the amount of noise in the environment and give an accurate decibel value. As there isn't generally a large market for these tools, they can be a bit expensive - often at least $ 200 even for basic models.
Note that these tools can be called in different ways. For example, another type of instrument called a "noise dosimeter" basically performs the same function as a standard sound level meter
Method 3 of 3: Mathematical Derivation of Decibels
Step 1. Find the sound intensity in watts / sq m
For practical everyday purposes, decibels are usually seen as a simple measure of loudness. However, the truth is a little more complex. In physics, decibels are often thought of as a convenient way of expressing the intensity of a sound wave. The greater the amplitude of a given sound wave, the more energy it transmits; the more air particles move along the path, the more "intense" the sound. Due to this direct relationship between a sound wave intensity and its volume in decibels, it is possible to find a value given in decibels having the intensity of the sound (which is usually measured in watts / sq m)
- Note that, for ordinary sounds, the intensity value is usually very small. For example, a sound with an intensity of 5 × 10 -5 (or 0.00005) watt / square meter translates to about 80 decibels - about the volume of a blender or food processor.
- To better understand the relationship between intensity measurements and decibels, let's follow an example problem together. Suppose we are a music producer and we want to research the background noise level in our recording studio to improve the sound of our recordings. After setting up our equipment, we detect a background noise intensity of 1 × 10 -11 (0, 00000000001) watt / square meter. In a few subsequent steps we will use this information to find the decibel level of background noise in our studio.
Step 2. Divide by 10 -12.
Once we have found the intensity of our sound, we can simply insert it into the 10Log formula10(I / 10-12) (where "I" is the intensity in watts / m2) to find the value in decibels. To start, let's divide by 10-12 (0, 000000000001). 10-12 represents the intensity of a sound at 0 decibels, therefore, by comparing our intensity value with this, we will essentially find its relationship with that base value.
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In our example, we divide the given intensity value, 10-11, for 10-12, getting 10-11 / 10-12 =
Step 10..
Step 3. Find the Log10 of the answer and then multiply by 10.
To find the final solution to the problem, all we need to do is take the log to base 10 and multiply it by 10. This explains the fact that decibels are base 10 log units - in other words, an increase of 10 decibels means that the volume of the sound doubles.
Our example is easy to solve. Log 10(10) = 1. 1 × 10 = 10. Therefore, the background noise in our study has a volume of 10 decibels. It's quiet enough, but still detectable with our high-quality equipment, so we'll probably need to eliminate the source of the noise in order to make more accurate recordings.
Step 4. Try to understand the logarithmic nature of the decibel values
As noted above, decibels are base 10 log units. For any given decibel value, noise greater than 10 decibels is twice as loud, noise greater than 20 decibels is 4 times louder, and so on. This makes it easier to describe the huge range of sound intensities that can be detected by the human ear. The loudest sound the ear can hear without pain is a billion times louder than the lowest loudness it can detect. By using decibels, we avoid having to use a huge number to describe common sounds - at most, we need to use three digits.
Consider this - which notation is easier to use: 55 decibels or 3 × 10 -7 watt / square meter? The two are equivalent, but, instead of using scientific notation (or a very small decimal number), decibels allow us to use a kind of simple shorthand for easy everyday use.
Advice
- Note that the 0 level on a sound level meter does not correspond to the absolute value of 0 dB. Rather, it is the level at which the sound distortion on the device is zero.
- Watts (like watts / square meter) are a physical measure of power. There are other different units for power, such as kilowatts, milliwatts, and so on; be sure to convert them to watts before using them in the above decibel power conversion formula.
