Soundproofing Defined

I often hear about “soundproofing” materials that failed to deliver expected results. One of the major reasons of this is the widespread incorrect use of the term “Soundproof”. Although the term seems to be self-explanatory, there is a great deal of confusion between the terms sound quality and soundproofing.

Soundproof, Adjective:

• Impervious to sound
• Designed to prevent sound from entering or leaving
• Not penetrable by sound

Soundproof, Verb:

• to insulate so as to obstruct the passage of sound
• insulate against noise
• protect from noise by surrounding with insulating material

So whether used as an adjective or verb, a soundproof(ed) space is one that simply keeps-in (and blocks-out) unwanted sound.

It is not unusual for disappointment to result when someone installs some “soundproof foam”, “soundproof blankets”, or “soundproofing panels” (ask any search engine for examples), only to discover that while sound quality inside the space has changed, sound escaping or entering has not. It is not soundproof. What went wrong?

It turns out that many “soundproofing” products provide no sound blocking properties. Describing these products as ‘soundproof’ is a misnomer. Foam, fiberglass, and other fibrous materials by themselves are sound absorbers, not barriers. Absorbers are very useful for improving sound quality in a room that is too “loud” or “live”. They reduce reverberation, echoes, and overall noise levels by absorbing sound that would otherwise be reflected back into a room and reinforced by hard surfaces. Unfortunately, they cannot by themselves soundproof (as correctly defined above) your space.

Here are two quick-and-dirty tests for determining if a material actually has soundproofing potential:

The Chat Test: Find a relatively quiet location outdoors where there are no buildings or reflective surfaces nearby. Hold a sizeable sample of the material between you and a friend. Have a conversation. While some sound will still travel around the material, and some will travel directly through, a decent barrier material such as SilentCurtain or SilentWrap should significantly impair conversation. The larger the sample, the more ‘accurate’ this test is.

The Earblock Test: This one is a little trickier to do. Seal-off your ears with a sample of the material while listening to a constant noise source such as a fan. Alternately cover and uncover your ears. The degree to which the material does (or does not) block sound is an indicator of the results one may have with it for soundproofing a space. Many are particularly surprised when trying this with popular acoustic foam tiles.

Of course these ‘tests’ alone are not sufficient for making material decisions in your soundproofing project. Soundproofing done-right typically requires strategic use of barrier materials in conjunction with absorptive materials. Much of soundproofing is not intuitive, so please feel free to contact us anytime to discuss your project. Experienced advice can go a long way in avoiding costly mistakes.

Chennai Acoustics FAST FACTS

There are many myths and misconceptions that people have about room acoustics. Many aspects of acoustics are counterintuitive. Here’s a quick sampling of fast facts about room acoustics.

1. dB (Decibel) is a term used to describe sound pressure level
2. An increase of 3dB in sound pressure level requires twice the power. Likewise, a drop of 3dB cuts the sound power in half
3. 3dB is the smallest amount of sound pressure change normal people can discern
4. RT60 (aka “reverberation time”) is the time it takes for a stopped sound to decay 60 Decibels
5. A 60 Decibel increase is equal to increasing the power 1,000,000 times
6. To perceive a 1dB change in sound, you need to be in a recording studio or similar very quiet environment
7. To double the (perceived) loudness of sound, you need to double the power 3 times, or 9dB
8. Sound generally travels through the air at 1,127 feet per second at room temperature
9. Sound travels faster at high temperatures, and slower in a cold environment
10. Sound travels over 10 times faster through a pinewood wall stud than in air
11. Sound travels more than 4 times slower through SilentWrap and SilentImpact than in air
12. Frequency = vibrations per second. The official term for frequency is Hertz (“Hz”)
13. The frequency range of human hearing is from 20 Hz to 20,000 Hz. The high frequency range of hearing is reduced with aging. This loss is accelerated by excessive exposure to noise
14. The human voice contains both fundamental vibrations (which define “pitch”) and harmonic vibrations (which create the recognizable timbre of a given voice)
15. The fundamental frequency range of the human voice is 80 Hz to 1,200 Hz
16. However, Harmonics extend voice frequency content up to 6,000 Hz
17. Harmonics are multiples of fundamental frequencies. “Middle C” on a piano is about 262 Hz, but this sound also contains information at 524, 786, 1,048, 1,310 Hz etc
18. Harmonics are what make each voice and instrument “sound” different. Without harmonics, a clarinet, a trumpet, and a saxophone playing the same notes would all sound the same
19. “CA” sounds in speech are often caused by air moving between the spaces in a person's teeth
20. “CA” sounds range from 5,000Hz to 9,000Hz
21. The wavelength of 2,000Hz is 6.75 inches
22. The wavelength of 200 Hz is 5.64 feet
23. The wavelength of 20 Hz is over 56 feet!
24. Carpet absorbs sound primarily above the speech range, making carpet a poor controller of speech or music in a large room. Excessive absorption at high frequencies also kills the musical character of a space
25. What is not absorbed by a surface (like carpet) is reflected back into the room
26. Building acoustical control into a church, auditorium, or any other listening space when it's being constructed often doesn't cost much extra. It’s largely a matter of knowledge on how to do it
27. It always costs more to fix an acoustic problem after-the-fact