In any discussion about understanding sound, the unit of decibels will undoubtedly become part of the conversation. Unlike almost all other units of measurement, the decibel is not a linear scale. That is to say, 1 decibel (also written as dB) is not one-tenth the amplitude or strength of 10dB. In this article, we’ll explain how the decibel scale works and present some reference information to help you understand how the decibel scale works.
What is Sound?
Sound is a vibration of air molecules that vibrates our eardrums. The eardrum passes these vibrations through to the middle ear through tiny bones called ossicles. The inner ear has a shape similar to that of a snail shell and contains microscopic hair cells that convert these vibrations into minute electrical signals. These signals are transmitted to the hearing nerve and subsequently to our brain. Each inner ear contains roughly 18,000 hair cells, all of which are said to fit on the head of a pin. Once a hair cell is damaged, it never grows back or repairs itself.
Understanding the Decibel
The decibel unit was created in the 1920s by Bell Telephone Laboratories to describe losses in communication cables used in early telephone systems. The original unit was MSC (Miles of Standard Cable) and was the loss of signal in 1 mile of cable at a frequency of 795.8 Hz that was equivalent to the smallest perceivable attenuation detectable to the average listener.
The Decibel and Sound Level Measurement
When discussing sound levels, the proper format is to use the unit dB SPL, dB(SPL) or dBSPL. The reference for any statement is the sound pressure as compared to 0dB. 0dB is defined as the perceived sound of a mosquito at a distance of 10 feet from the listener.
Because dB SPL expresses a ratio, sounds can be quieter than 0dB. Imagine if you will, you are in the space where the sound created by that original mosquito was measured. If we take away the mosquito, the space will be quieter. How much quieter depends on other sources of noise. Electrical noise created by lighting and noise caused by heating and cooling systems all contribute. If we eliminate as many noises as possible, the room will get quieter and quieter.
According to Guinness World Records, the quietest place in the world in 2012 was an anechoic test chamber at Orfield Laboratories in Minneapolis. The sound level in this room was measured at -13dBA. In October 2015, a team of engineers at the Microsoft head office in Redmond, Washington, smashed this record with measurements taken in the anechoic chamber in Building 87. A team of independent specialists measured a noise level of -20.35 dBA. The room is not only completely isolated from all sources of noise and vibration, but the walls are lined with large acoustic foam wedges design to absorb sound.
At the opposite end of the sound spectrum we have 191 dB SPL. This is the sound level where the air is pressurized to 1 Bar or 1 atmosphere. Linear sound cannot exist above this level because the low-pressure side of the wave reaches an absolute vacuum. There are louder noises (such as nuclear explosions), but they are examined as pressure waves rather than sounds.
All Sounds Are Not Perceived Equally
The human ear is not sensitive to all sounds equally. In 1933, the results from research into how our ears perceive different frequencies was published. Researchers Fletcher and Munson released a set of human hearing sensitivity curves that are based on frequency and amplitude. The curves were created by playing a pure 1 kHz tone and a tone at a different frequency alternately. The amplitude of the 1 kHz tone was adjusted until participants felt the level of the two were equivalent. The adjustment level was recorded and they moved to another frequency.

In 1937, similar testing was done by Churcher and King, but the results differed a great deal from the Fletcher Munson charts. Researchers Robinson and Dadson repeated the testing in 1956 with newer equipment. The resulting measurements were accepted and defined the ISO 226 normal equal loudness-level contours. These remained the standard until 2003 when new testing further revised the graphs.
What the curves tell us is that our hearing is most sensitive around 2 to 3 kHz, depending on amplitude. We are less sensitive to high-frequency information around 10 kHz and 150 Hz by about 20dB. We are increasingly less sensitive to sounds below 150 Hz, but this phenomenon decreases as volume increases.
How We Perceive Sound
Many statements about sound levels get thrown around the industry. Let’s talk about and clarify a couple of the most common.
3dB is twice as loud. No. No, it isn’t. A change of 3dB represents a doubling or halving of acoustic energy. It takes an amplifier twice as much power to produce a tone at 73dB as it requires at 70dB. The reality is, most listeners can just barely perceive a change in level of 3dB at all audible frequencies.
If 3dB isn’t twice as loud, what is? Based on extensive testing, it is agreed that a change in level of 10dB is considered to be twice or half as loud.
A Listening Test
Just for fun and education, below is a series of test tones to demonstrate our ability to detect differences in amplitude. These tests are created to make the differences as easily perceivable as possible.
The tones involve a sine wave at a frequency of 1 kHz recorded at a starting level of -10dB from the full scale in a 44.1 kHz, 16-bit uncompressed .wav file format. The amplitude (volume) of the waveform is decreased at one-, two- and three-second marks by varying amounts. For most, discerning the 1dB per step decrease is easy. Many will be able to detect the 0.5dB decrease per step. The 0.25dB decrease per step is difficult to hear.
Track 1
1 kHz, decreasing in amplitude by 1.0 dB at one-second intervals
Track 2
1 kHz decreasing in amplitude by 0.5 dB at one-second intervals
Track 3
1 kHz decreasing in amplitude by 0.25 dB at one-second intervals
Now, based on your results, does this test disprove the above statements about 3dB and 10dB differences? Not at all. As mentioned, the tests are designed to make the perception of level changes very easy. If you were to listen to a song, then play the same song again five minutes later after adjusting the volume up or down by 0.5dB or 1dB, most people wouldn’t be able to detect the difference.
We’ll revisit the decibel in future articles and explain how different rating curves affect the numbers we read when looking at audio equipment noise measurements and specifications. Until then, we hope you enjoyed this article and the test tracks.
This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.
There is nothing worse than turning up your
When a mobile electronics specialist installs an amplifier in your vehicle, the
Perhaps the most dangerous control on an
If you have multiple
If your radio has an equalizer or simple bass and treble controls, turning them up will make different frequencies of your music louder relative to others. With that said, it won’t make a properly configured and tuned audio system play any louder. Just like the bass boost on an amp, equalizers and tone controls affect the signal level at specific frequencies.
All speakers and subwoofers have power ratings. In almost all cases, this rating is the amount of power that the speaker can manage from a thermal standpoint. You see, speakers are notoriously inefficient. More than 95 percent of the energy fed into a speaker is converted to heat. If you feed a woofer 100 watts of power, 95 watts go into heating the voice coil and motor assembly and less than 5 watts are converted into acoustic energy.
Another consideration about amplifiers is that most can produce 150 percent to 200 percent of their rated power as extra energy when pushed into clipping or distortion. So, a 50-watt amplifier can easily produce 75 watts of distorted power and still damage that 70-watt speaker.
Shopping for car audio upgrades is as personal as shopping for a new car or new shoes. Each of us likes something different, has a different budget and different performance and style preferences. In the case of a new car, your options range from a solid and reliable daily driver in the $14,000 range to luxury and exotic vehicles costing well over $100,000. When it comes to a new radio, speakers, an amplifier or a subwoofer upgrade for your car, the price point differs just as much, as do the features and performance levels. In this article, we will provide some tips to prepare yourself to buy new car audio upgrades and ensure they are installed and configured reliably.
A discussion about online shopping opens a monumental can of worms. One of the biggest differences between buying from an online retailer and a local independent specialist will be the level of after-sales service and support. If you buy new speakers online and you have a problem with them, you can try contacting the supplier. About all they can do is offer to let you send the speakers back (at your cost) and they will send you another set. When you deal with a local retailer, someone can go to your car and listen to the problem. The issue may not be the speakers at all. It could be the
Make no doubt, most of the installers, technicians and fabricators who work at mobile electronics retailers got their start working on their vehicles in their driveway. In some cases, this passion for working on cars and trucks grew to include their friends’ vehicles, while others sought out training from companies like
When it comes to source unit upgrades, the first thing you need to find out is whether or not you can replace the factory radio in the vehicle at all. Vehicles such as BMW, Mercedes-Benz, Mazda and many new Nissan vehicles have source units that can’t be removed.
Perhaps the most important component in an audio system is the speakers. 
When you go shopping, bring one or two pieces of music that you know well. Before you leave your house, listen to that song on as many different sources as possible: your home theatre system, a portable Bluetooth speaker, headphones with your smartphone and your existing stereo. Think about what is different between each experience so you can listen for those elements as you audition new products.
Apple CarPlay and Android Auto smartphone integration
These infotainment solutions require two components to provide you with Internet-connected voice recognition access to your music, navigation and communication functions. First and foremost, the source unit in the vehicle needs to have the software built in. Including
Up until recently, the connection between your phone and the radio for CarPlay and Android Auto has used a USB cable. With the introduction of wireless connectivity, things have changed. A Wi-Fi connection between your source unit and your smartphone replaces the wired connection for reliable, high-speed communication. Initially, a little more setup is required to get your smartphone and radio talking, but once configured, everything operates intuitively.
In November 2017, Google announced the ability for devices running Android to run Android Auto as a stand-alone app without the need for an aftermarket source unit. At CES 2018, several aftermarket manufacturers announced they would include wireless Android Auto connectivity on their new source units.
There are have been many discussions about the benefits and drawbacks of wireless connectivity. The biggest point of debate is around phone charging. In most cases, drivers take advantage of the ability to charge their phones when they get in their vehicles as they travel. For most people, this requires that the USB cable is connected to their phone. With that said, the Apple iPhone 8, 8 Plus and X include wireless charging. On the Android side, recent devices from Samsung, LG, Google, Microsoft and Blackberry include wireless charging.
Flipping back to the cons side of the debate, you need a wireless charging base in your vehicle to take advantage of the wireless charging feature. Vehicles from Audi, BMW, Chrysler, Ford, Honda, Mercedes-Benz, Toyota, Volkswagen and Volvo include Qi compatible charging solutions. Qi is the standard for wireless charging for Apple devices.
Did you know that you can get great sound in your car or truck using your
Fewer and fewer cars today have radios that only play music. They show
In the good old days, factory audio systems included a radio, a simple analog amplifier and speakers. If you had a luxury vehicle, the manufacturer may have opted to include a subwoofer for a little more (but still not enough) bass. The radio was a simple affair with a tuner, CD player, auxiliary input and maybe a USB port and satellite radio connection. The output of the radio either powered the speakers in the car directly or fed a signal to a small amplifier.
Let’s look at three common upgrades that mobile electronics retailers across the nation perform every day. Since 2009, the Ford F-150 has come equipped with an amplifier in the back of the truck that includes the master volume control for the system as well as equalization and crossovers for the speakers. Upgrading this popular vehicle required summing audio signals coming out of the amp back together and removing signal processing.
Another popular audio system upgrade interface is the iDatalink Maestro DSR1. Automotive Data Solutions partnered with the audio experts at Rockford Fosgate to develop this interface and tuning solution. ADS are experts in the field of CAN communication protocols, thanks to their experience with remote car starter integration modules.
NAV-TV has created an impressive solution that is compatible with Chevy, GMC and Cadillac vehicles with the MyLink and Cue-equipped 4-inch (IO4) and 8-inch (IO5/IO6) source units. This interface connects to the MOST (Media Oriented System Transport) digital signal that runs from the factory radio to the amplifier in these vehicles to extract six channels of full-bandwidth audio that is free from equalization or signal delay.