Building, Design for Sound and Acoustics, Part 2: Understanding Decibels

By John J. Lupo
Division Manager, North Florida, Dynamark Systems

decibels-0516This is part 2 of a multi-part series of articles that will provide a solid understanding of the principles of sound and acoustics as it relates to design and construction of both public and private spaces. Part 1 covers the basics of sound. Parts 3-5 will cover STC Ratings, Soundproofing and Room Acoustics.

Quick Point # 1 Decibel (dB) = standard measure of the loudness of a sound.

A basic understanding of the measurement of sound levels or loudness is an integral ingredient in the proper planning and design of any room or public space. To fully understand decibels we need to understand that loudness without a standardized measure is subjective. Anyone living with a teenager understands what I’m saying. What is loud to one may not be to another. As we age and experience life our ears will be affected by both normal and outside influences. These changes may affect how we hear and may also have an effect on our sensitivity to sound levels at certain frequencies. The point is that no two people hear things the same way.

The most common measurement in the audio industry is called the Decibel (dB). A (dB) is a measurement of the Sound Pressure Level (SPL) or sound intensity, loudness or volume level of a sound. The dB is the standard measure used in audio equipment specifications. It is also the standard used with construction industry professionals regarding soundproofing materials and other applications involving the treatment or containment of sound energy. The decibel scale was developed to place a universally accepted measure on sound pressure levels. The scale is alogarithmic measure of the effective sound pressure of a sound relative to a reference value. Shown below is a quick reference to give you an idea of sound levels in the real world.

40dB – Quiet Library

50dB – Average Home

60dB – Conversational Speech

80dB – Busy Road

90dB – Electric Drill or iPod/head phones

100dB – Snowmobile, Motorcycle

It is important to understand that when using the decibel to measure sound 1 does not equal 1. A change of 1 dB is equal to a (+ or -) 10% change in volume level. A change of (+) 10dB is equal to a 100% increase in the reference volume level. A change of (-) 10dB is equal to a decrease of 50% of the reference volume level. Logic tells us that 100 dB should be twice as loud as 50 dB. In actuality it is 32 times as loud. Let’s take a look at one of the common specifications utilizing the dB as a reference. The specification shown below is a standard Loudspeaker. It shows a frequency response of 38hZ (bass) to 22kHz (treble). If you read Part 1, Understanding Sound you should have an understanding of the frequency range. In this writing I am concerned with the (+/-) 3dB. What that tells us is that this speaker can vary from this specification by as much as +30% or -30%. When you think of it in those terms that 3dB difference can be fairly significant in the performance of those speakers..

“Speaker Frequency response 38Hz – 22kHz ±3dB”

The measurement scale can be a bit confusing at first but once understood becomes a vital tool in the planning, design and construction of a facility. It will give you an accurate way of determining the effectiveness of any equipment or material used in the construction process. If you’re concerned about sound transmission from room to room or sound reverberation (echo) within a room an understanding of the decibel measurement scale is imperative. In order to properly specify the correct solution for your project you will need to understand the decibel scale.

Just remember that 10 dB is more than just 10 dB it is = to ½ or 2x of a sound level.

Hopefully this writing gives you a better understanding of how the decibel scale works. If you have any questions or comments please contact me at

John J. Lupo
Commercial Audio Video Manager
Electronics World
Gainesville, FL

This article was reprinted with permission from John J. Lupo and originally appeared here.