What do STC ratings mean?

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Sound Transmission Class is derived from other sound metrics like NIC and NIIC. You can read more about NIC and NNIC here. 

The NIC and NNIC don’t attempt to describe how sound gets from one room to another. Does the sound go through cracks or around corners (called flanking paths) or does it go straight through walls or other partitions (called direct transmission)?  By taking care to block flanking paths, the noise reduction between two rooms can reasonably be assumed ...

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Finding STC and all his friends – NR, NNR, NIC, & NNIC

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STC tests start by setting up speakers in a room, called the source room. The speakers play pink noise, a noise that sounds like white noise TV static but contains equal energy across frequency bands.  Microphones are used to measure the sound pressure level in the source room as well as the sound pressure level in the room on the other side of a wall or similar partition. This room is called the receiving room.

By comparing the sound pressure levels ...

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Let’s Talk about STC – Sound Transmission Class

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STC stands for Sound Transmission Class. It’s a way to rank how much sound a building partition—like a wall or ceiling—blocks sound traveling through the air. STC is used in the United States while it’s cousin, the SRI (Sound Reduction Index), is used elsewhere. You can think of the STC rating as representing approximately how many decibels the partition can drop the noise. So, a higher STC number means more sound blocked. Although this is a rule of thumb, it ...

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Guide to Soundproofing & Room Acoustics

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It can be difficult to compare the acoustics of one room against another room. Not only do the size and shape of a room change its acoustic feeling, but the materials of the ceiling, walls, and floor and their construction, as well as furniture, décor, and other objects in the room can change the way sound moves throughout a space. Couple that with the subjective opinions of individuals concerning what is annoying, too echo-y, too quiet, or too noisy, and ...

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Leq: What does it mean?

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Leq (said “L E Q”) stands for Equivalent Continuous Sound Pressure Level, and is one of the most important sound level metrics. It’s nice because it boils a sound level measurement down to one decibel level number. The Leq represents the total sound energy logged over the course of a measurement.

Since the Leq corresponds with the total sound energy, it is a useful way to predict hearing damage threats as well potential noise complaints. As a result, the Leq is ...

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The ABCs of Frequency-Weighting

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Like other animals, humans hear different pitched sound differently. Some sounds, such as those in the range of speech or a baby crying, are easy to hear and emphasized by the ear. Other sounds, such as low-pitched rumbling or high-pitched buzzing might be more difficult to hear. In an effort to take these differences into account, acoustics professionals have developed patterns for emphasizing or de-emphasizing sounds at different pitches. In this article, we will discuss these patterns—called frequency weighting curves—and ...

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Are Lpeak and Lmax Different?

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Newcomers to the field of acoustics are often overwhelmed by the number of different level metrics used to characterize environmental and community noise. To make matters worse, almost all of these metrics are abbreviated with capital Ls and reported in units of decibels. The purpose of this article is to help distinguish between three of these Ls: Lpeak, Lmax, and Lmin. Of the three, Lpeak is the easiest to understand, so we’ll start there.

Lpeak

Lpeak stands for peak level. The peak ...

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Fast, Slow, and Impulse Time Weighting: What’s the difference?

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When it comes to sound level measurements, there are three types of time weighting that you see: Slow, Fast, and Impulse. In this article, we’ll talk about the difference between these ways of weighting and where they came from.

The terms slow and fast weighting go back to the days of analog sound level meters. Analog meters had a needle that would point to numbers on a scale. With differences in manufacturing and design, some of these needles reacted faster than ...

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Calculating Resonant Frequencies

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This article continues from the last article, Introduction to Resonance. If you need to review standing waves, nodes, and antinodes, you might want to check out that article first. Otherwise, let’s get right down to business.

How to Find Resonant Frequencies

Remember from the last article that standing waves happen when nodes or antinodes line up with the ends of a rope or pipe. Such standing waves create resonance. The lowest frequency that “fits” on a string or in a space ...

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Intro to Resonance

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Gallopin’ Gertie

One of the first acoustics topics most physics classes cover is resonance. Often, physics teachers will show the video clip below of the collapse of the Tacoma Narrows Bridge (also known affectionately as “Gallopin’ Gertie”) to demonstrate the potential effects of resonance.

While the rippling motion of the bridge seems unreal, the physical principle of resonance is quite real. Gaining an ...

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