In music, dB is a unit of measurements which is known in full as decibels. Decibels can be a bit of a harder concept to wrap your head around in terms of Music theory but can become quite simple when explained properly.
A decibel is a unit that measures the ratio of change in sound level, whether that be an electrical signal level or an acoustic sound pressure level. The decibel scale is a logarithmic system rather than a linear scale.
Below, we’ll tell you all about decibels, from how they’re used in audio, to how loud is too loud when it comes to speakers and human ears. But first, let’s rule out what decibels are not.
Decibels often have some different uses and purposes within the world of music. In this article we are going to cover what a Decibel is and where and when they are used.
Keep reading to learn about decibels and even more about music theory.
What Is A Decibel?
A decibel (dB) is a measurement of the intensity of a sound. The human ear is super sensitive, if you even brush your finger as gently as possible over almost any surface in an ear shot, the likelihood is that you will hear it.
With this in mind, the decibel scale is used to actually compare sounds relative to one another.
If we know that 0 dB is near total silence, and we know that anything above 100 dB is essentially dangerous to our ears if we are exposed for too long, we can figure out the intensity of a noise.
There are many things that can affect how we hear the noise in question such as distance, obstacles and more.
For instance, if we stood right next to a jet engine, the decibels would likely exceed 100 with ease. Yet, if we stood 50 meters away from that engine, what would the decibels be then?
In another sense, decibels can help you figure out the proficiency and efficacy of physical technology.
For example, if you had one speaker you put to volume 10, and then listened to another speaker which you put on volume 10, they would not necessarily be producing the same volume.
Even their full volume levels will be different, and with the aid of decibels you can measure this.
With the aid of decibels, you can use the logarithmic measurement to figure out which speaker is essentially louder, a comparison of arbitrarily decided volume measurements is hard to tell or measure how loud something is.
This is basically in the film Spinal Tap when the guitarist boasts his guitar amp goes ‘up to 11’. The joke being that 11 is exactly the same as what 10 would be, they would be the same decibel, the numbers are arbitrary.
Making these comparative and relative measurements can help us figure out the intensity of a sound.
Finding out the intensity of a noise can be really helpful for things like soundproofing your house, ear safety for humans or animals, as well as just basic volume measurements.
How Are Decibels Measured?
A decibel is measured with a piece of equipment called a sound meter or audio meter. This is a handheld device that usually has a large microphone on one end.
This can immediately read out decibels as opposed to doing the manual equations necessary to work out decibels.
When using a sound meter, there are two ways to determine decibels. One way is to take an average of all the decibels recorded at once.
Another way is to take a single reading and then multiply it by ten, as the decibel scale is logarithmic, this is possible to do.
The first method is much easier to do, but does not give you a true indication of the actual decibel level. It is easy to get a false number because the sound meter may pick up other noises besides the decibel you want to measure.
For example, if you were recording the decibel level of a speaker the audio meter may pick up the sounds of the road, etc. So for these reasons people sometimes choose the second method as it can potentially provide more accuracy.
You can buy an audio meter pretty easily, they are available on Amazon here.
How Are Decibels Applied?
Decibels are used in everyday life for many purposes. They are used to compare the loudness of different speakers, headphones, music players, etc.
You can also use them to measure the intensity of a fire alarm, or even the intensity of wind blowing through trees, etc. But perhaps most often they are used to measure the safety of a noise.
Decibels are a good way to measure how dangerous a noise can be, and they are regularly used in hearing safety applications. The general measurement of when a sound is too dangerous to hear is around 85 dB. Anything above this is considered unsafe.
If you have ever been near a construction site, you know how loud it can be. Someone will know the exact decibels of each drill and machine in order to know they are safe hearing levels.
If they are not then you will see construction workers wearing ear defenders which is a common sight.
What Decibels Are Not
Decibels are commonly mistaken for a few things, but they are not a measurement of audio signal amplitude or audio signal voltage, a measurement of acoustic or electrical power, a measurement of loudness that is perceived, or a measurement of sound pressure.
Basically, decibels are not absolute measurements. They don’t automatically tell us a lot about perceived loudness, power, sound pressure level, or volume.
Instead, decibels inform us how much of a given quantity of sound there is in relation to another amount of sound that has the same quantity.
There are several reference points that scientists are in universal agreement that allow us to effectively use decibels to measure audio and sound quantities.
How Decibels Are Used In Audio
This refers to a loudspeaker’s output. Many speakers are directional to some degree (particularly at mid and upper frequencies) because of their relatively large enclosures and drivers.
Decibels that are relative to the on-axis response are helpful for determining a set cutoff threshold that defines the directionality of the speaker.
Decibels define the boosting and cutting that happens with audio equalization that depends on frequency.
Filters such as those used in speaker crossovers also use decibels. In particular, filters are mainly defined by the roll-off (decibels/octave) which decreases the audio level.
Noise cancellation is a specification for headphones that lets you know how much the headphones will suppress external noise.
This is usually measured in decibels in relation to the noise we would hear without the headphones. This is the case with both active and passive noise cancellation.
Passive noise cancellation is the basic mechanical blockage of sound waves that prevents sounds from reaching your ear canal.
Meanwhile, active noise cancellation describes complex circuits that are used in feed-forward and feedback circuitry, microphones, phase and volume adjustments, and speakers that put the anti-noise sound waves in the headphone output.
How Loud Is Too Loud? How The Human Ear Perceives Loudness
Ears are complex parts of the human body, and how sensitive they are depends on the frequency of the noise they are hearing. Some sounds can also be felt as well as heard.
So the threshold for hearing changes according to frequency. For example, a considerable amount of acoustic output is required for us to be able to hear a 20Hz tone.
If you look at an equal loudness curve you will notice how the ear registers sound increases in SPL.
At 1kHz, a 10dB gain is parallel with a perceived increase in volume in some ranges of frequency. As the frequency decreases however, you may notice that the lines in the curve get closer and closer together.
Rather than requiring a 10dB gain to multiply the perceived volume by two, you will need about 4-5dB in the deep frequencies of the bass.
Fun fact: Jill Drake broke the record for the loudest human scream that was measured at 129dB. A human with typically healthy vocal cords and lungs can scream as loud as 110 – 120 dB.
Why Can Speakers Only Handle A Certain Volume Level?
Magnetic/Compression: This occurs when the power input is so strong that the magnetic structure of the speaker saturates and is unable to turn the input signal into an additional mechanical energy A speaker.
This is a transducer, which is a device that turns one electrical form of energy into an acoustic/mechanical form of energy.
But when compression happens it can no longer perform this function. At these severely powerful levels, the speaker emits a softer signal.
This is called compression, because the output of the speaker is compressed as it responds to a larger input signal.
Mechanical: Too much power input will force the speaker’s drivers to attempt to travel long distances, probably further than they were meant to.
This causes the driver’s voice coil to go so far that the voice foil emits from the gap, is aligned incorrectly, and can’t go back to its previous position.
Thermal: Too much power is hot! Too much power can heat the voice coils so much that they widen and bind in the voice coil gap.
Heat can also distort VC formers, melt adhesives, burn crossover resistors, and cause all kinds of other damage.
Speakers can of course withstand some thermal abuse for short amounts of time, but if an excessive amount of heat builds up over a long period of time, the speaker will succumb to thermal failure, or burn out.
We hope this article has provided you with a better understanding of what dB stands for, and its role in audio, as well as what loudness actually means in audio terms.
If you’re new to audio it can be pretty confusing trying to wrap your head around all these abbreviations and numbers, especially if you didn’t have much of an understanding of decibels or were thinking about them in a linear scale.
We hope you can use this information to make more informed purchases with your audio equipment, help you set up your systems, and what kind of damage excessive sound and power can do to your speakers.