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Because your ears are sensitive to a very wide range of sound pressure, it makes sense to use a logarithmic scale to measure the loudness of a sound. Sound pressure level uses a logarithmic scale to represent the sound pressure of a sound relative to a reference pressure. The reference sound pressure is typically the threshold of human hearing: remember that it's 2 x 10-5 Pa.

Sound pressure level is measured in units of decibels (dB) and is calculated using the following equation, where p is the sound pressure of the sound wave and po is the reference sound pressure:

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STC stands for ”Sound Transmission Class.” This is a single-number rating that can be used to compare the acoustical isolation of different barrier materials or partition constructions. The method used to determine the STC of a material or partition type is complicated.

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Sound Transmission: (mildly helpful summary)

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Sound Transmission: (mildly helpful summary)

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Sound transmission. ... Sound waves are created by a disturbance that then propagates through a medium (e.g., crust, water, air). Individual particles are not transmitted with the wave, but the propagation of the wave causes particles (e.g., individual air molecules) to oscillate about an equilibrium position.

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Really informative...

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There are a large number of complex interrelated factors that determine the transfer and perceived loudness of a sound. There are many technical terms and measurements that are relevant in determining the type and intrusiveness of a sound. A very brief list of terms and definitions is provided below.

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Sound Transmission Classes (mildly helpful summary)

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Sound Transmission Classes (mildly helpful summary)

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Sound transmission class. Sound Transmission Class (or STC) is an integer rating of how well a building partition attenuates airborne sound. In the USA, it is widely used to rate interior partitions, ceilings/floors, doors, windows and exterior wall configurations (see ASTM International Classification E413 and E90). (Basically

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What Is Sound Pressure?

When it comes down to it, your ears are pretty amazing. They allow you to hear sounds as quiet as a whisper and as loud as a jet engine. How exactly do sound waves get transmitted to your ears so that you can hear?

It starts with a vibration in the air. A whisper only vibrates the air a little bit, while a jet engine vibrates it A LOT. This vibration creates a pressure wave that passes through the air, spreading out in all directions as it goes. Sound pressure is the pressure measured within the wave relative to the surrounding air pressure. Loud sounds produce sound waves with relatively large sound pressures, while quiet sounds produce sound waves with relatively small sound pressures.

Sound pressure, like other kinds of pressure, is commonly measured in units of Pascals (Pa). The quietest sound that most people can hear has a sound pressure of 2 x 10-5 Pa, so this pressure is called the threshold of human hearing.

If your ear happens to be in the path of the sound wave, the vibrating air molecules hit your eardrum and cause it to start vibrating too. When your eardrum starts vibrating, it bumps into the tiny bones in your middle ear and makes them vibrate. The vibration passes all the way into your inner ear where the vibration of tiny hair cells sends signals to your brain, thus letting you hear the sound. The pressure of the sound wave corresponds to how loudly you hear the sound. As the sound pressure increases, the pressure on your eardrum increases as well, making the sound seem louder to you.

What Is Sound Pressure Level?

Because your ears are sensitive to a very wide range of sound pressure, it makes sense to use a logarithmic scale to measure the loudness of a sound. Sound pressure level uses a logarithmic scale to represent the sound pressure of a sound relative to a reference pressure. The reference sound pressure is typically the threshold of human hearing: remember that it's 2 x 10-5 Pa.

Sound pressure level is measured in units of decibels (dB) and is calculated using the following equation, where p is the sound pressure of the sound wave and p o is the reference sound pressure:

Calculating Sound Pressure Level

Let's use this equation to calculate the sound pressure level of a jet engine if you're standing one meter away from it. At this distance, the sound pressure would be about 600 Pa.

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what is spl (sound pressure level)? - definition & examples - video & lesson transcript | study.com

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What is SPL (Sound Pressure Level)? - Definition & Examples - Video & Lesson Transcript | Study.com

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When it comes down to it, your ears are pretty amazing. They allow you to hear sounds as quiet as a whisper and as loud as a jet engine. How exactly do sound waves get transmitted to your ears so that you can hear? It starts with a vibration in the air.

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Sound Pressure is the force of sound on a surface area perpendicular to the direction of sound

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https://youtu.be/JPYt10zrclQ

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When discussing the reduction of sound vibration as it travels from one side of a wall to the other, we need to quantify and measure this loss. Do all construction techniques or soundproofing materials work equally well? Exactly how much sound is being reduced, and perhaps more importantly, what frequencies of sound are being affected? This is where understanding STC (Sound Transmission Class), and STC ratings, comes in.

STC is an integer rating of how well a building partition attenuates airborne sound. In the USA, it is widely used to rate interior partitions, ceilings and floors, doors, windows and exterior wall configurations (see ASTM International Classification E413 and E90).

In short, STC gives you a rough idea how much sound a wall, for example, might stop. STC is the most common sound reduction measurement in use. As common as this measurement is, it is quite limited and should not be totally relied upon for real world soundproofing expectations.

Let's first cover a few concepts.

Decibels: Written as dB in literature, dB is simply a measurement of how loud a noise is. 50dB is quiet while 140 dB is so loud that is can immediately injure your ears. Think of dB as the volume knob on your receiver.

Transmission Loss is a measurement of the dB (volume) difference on either side of a wall. Let's say we have a 100dB tone on one side of a wall. Pretty loud. We measure this same tone on the other side of the wall and find we have 75 dB. So we would say that at this tone or pitch, we have 25 dB Transmission Loss. 25 dB less sound energy made it through the wall to the other side.

Interestingly, a test tone with a different pitch sent through that same wall might only see a 4 dB Transmission loss. The performance of a wall will vary greatly depending upon the tone (frequency) of the sound.

Frequency: Written as Hertz or Hz., this is the measurement of the tone or musical note of the sound. Is it a really high pitch like a Flute might make (2000 Hz) or a low pitch as from a Tuba (as low as 29 Hz)? Most humans are born with the ability to hear frequencies from about 20 Hz (low) up to 20,000 Hz (high) but that range shrinks as we get older.

What are STC ratings?

Now that we have an understanding of a few basic terms we can describe what STC is. In 1961, STC was introduced as the method for comparing various wall, ceiling, floor, door, and window assemblies. STC is calculated by taking the Transmission Loss (TL) values tested at 16 standard frequencies over the range of 125 Hz to 4000 Hz and plotted on a graph. Your curve (what you actually measured) is compared to standard STC reference curves (see appendix). If your wall graph is closest to a standard STC 35 curve, your wall is said to have an STC Rating of 35.

The MAGENTA line in that graph is the standard reference STC contour. The BLUE line is the performance of the wall. To calculate TL and STC, the performance data should be obtained from a certified laboratory.

Higher STC is generally better, though not always, as we will see below.

Caution: The largest problem with relying on an STC number alone is that STC only considers frequencies down to 125 Hz. This can be very misleading due to the fact that most sound isolation complaints are from noise sources that are below 125 Hz.
Here are a few examples of noise sources that are below 125 Hz

Most of the sound energy generated by the average home theater

Traffic noise from airplanes, trucks, and heavy equipment operation

Guitar, bass, drums

Industrial Equipment, especially pump systems.

The example above demonstrates the problem with not considering data below 125 Hz. Frankly, neither of these walls stop much sound. Both are mediocre, with a low-frequency problem near 125 Hz. However one wall is STC 32, the other is STC 42!

This is because, with the blue wall, the big problem occurs at 125 Hz, and is therefore measured by STC. The black wall has essentially the same problem; however it occurs just below 125 Hz and is therefore not calculated.

Example of how relying on STC alone is a bad idea when low-frequency noise sources are present

This classification method is not appropriate for sound sources with spectra significantly different from those sources listed above. Such sources include machinery, industrial processes, bowling allies, power transformers, musical instruments, many music systems and transportation noises such as motor vehicles, aircraft, and trains. For these sources, accurate assessment of sound transmission requires a detailed analysis in frequency bands."

Caution: STC is not a measure of how many decibels of sound a wall can stop. If you have an STC 45 wall, this does not mean the wall stops 45 dB of sound.

Caution: You cannot add STC ratings. They are logarithmic values and cannot simply be added. If you have an STC 33 wall and decide to add another sheet of drywall with an STC of 20 you do not get a finished wall with an STC of 53. You might get something around STC 35.

STC Examples

Wall Assembly STC Performance

STC ratings courtesy of the NRC and Green Glue Company, reprinted with permission.

For new construction, the International Building Code (IBC) requires lab-tested STC 50 for walls, floors, and ceilings.

Appendix - calculating STC

Calculating STC involves adding something called "deficiencies" and utilizing the STC contour In the table you supply the Transmission Loss data. Then you add the STC contour adjustment to attain the adjusted transmission loss. Then you basically play with numbers in the "STC you wish to test column" until one of the two limiting conditions listed below are met. The highest number that satisfies both of those conditions is the STC.

The two STC Conditions:

1. No single frequency band may have more than 8 deficiencies

2. The total deficiencies may not exceed 32

In the case above, the highest # of deficiencies in any frequency band is 4, and the total deficiencies are 21. So both condition 1 and condition 2 are passed. The appropriate thing to do in this situation is to raise the STC you are testing to 56. In this case, the wall would pass again at STC 56, as shown in this table here:

Now the total deficiencies are 30, and it is clear that if we raised the number we wish to test to 57 that the number of deficiencies would exceed 32, and thus the wall could not pass at 57.

Therefore, the STC of this wall is 56.

Lastly, it is important to note that to accommodate the fact that the human hearing system is more sensitive to some frequencies than others, an equal-loudness contour is applied to the frequencies tested. This accommodation is known as A-weighting. In general, low-frequency and high-frequency sounds appear to be less loud than mid-frequency sounds, and the effect is more pronounced at low levels, with a flattening of response at high levels. A-weighted frequencies are measured in units called Phons.

SPC - Wall Assembly Solutions

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When discussing the reduction of sound vibration as it travels from one side of a wall to the other, we need to quantify and measure this loss. Do all construction techniques or soundproofing materials work equally well? Exactly how much sound is being reduced, and perhaps more importantly, what frequencies of sound are being affected?

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It's probably the most commonly used effect of all, but just what is reverb?

If you're a producer, home recordist or guitarist, you'll no doubt have used reverb effects at some point. If you haven't, you'll almost certainly be aware of what it sounds like.

Reverb (short for reverberation) is one of the oldest of all audio effects, and aims to recreate the natural ambience of real rooms and spaces. Adding a softer edge and a sense of 'space' to sounds, it is an essential tool when mixing a track, and commonly a bedrock of many guitarists' pedal boards.

Even if you're familiar with its sound, you still might ask, just what is reverb?

Well, here we answer that question...

A quick science lesson (no, don't run away!)

To understand what reverb is, its important to understand the acoustic phenomenon it aims to recreate. To understand this, you need to understand the science that causes it. Don't panic, though- it's very simple, and very useful to understand.

Put simply, reverb is the effect of sound being reflected back to a listener's ears from surrounding objects.

Picture this example- you're out for a walk in the country, and on the way you end up at the bottom of a wide valley surrounded by hills. You can't miss an opportunity like this, so you shout 'echo!' at the top of your lungs. A fraction of a second later, you hear it repeated back to you.

Essentially, what is happening here is that the sound is leaving your mouth at approximately 340 metres per second, travelling through the air until it reaches the valley walls, then bouncing back towards you the listener.

As this takes a certain amount of time (if the valley wall is 170m away, it will take 1 second to return), there is perceived delay between your shout and the reflection, causing the echo effect.

With me so far?

Because the valley is (aside from the walls) pretty much an open field - that is, there are no other hard objects to reflect sound back- the echo is the only reflection you hear.

Things are more complicated in enclosed spaces, however...

Rooms, chambers and enclosed spaces

If a sound is made within an enclosed space, such as room, hall, cathedral, cave, or whatever, the principles or sound reflection are much the same.

However, as you are surrounded by hard, reflective surfaces, and the surfaces are far closer, the delayed, echo effect is rarely perceptible, and the number and pattern of reflections is far more complex.

To explain how this works, image an oblong shaped room with hard walls, similar to the diagram below, with a willing subject ready to make some noise within.

When our subject makes a noise, it will travel in all directions from the source at the same speed. When it does, it reaches the walls closest to it first, and is reflected back to the listener the soonest.

These are known as early reflections. The delay time between the source sound and these early reflections is known as pre-delay, and is the main factor that dictates how 'big' a reverb is perceived to be.

The longer the delay, the further the sound has to travel, so the bigger the space must be. Going back to our valley example, the distance there is so big that it is heard as entirely separate sound. Simple, eh?

After this phase, the reflections from elsewhere in the space (of which there are far more), which have been bouncing around the other walls and hard surfaces, start to return to the listener.

The shorter the distance these have travelled, the sooner they will arrive, and the louder they will be. Conversely, the further they have travelled, the later and quieter they will be.

As these many, many reflections are arriving at fractionally different times, the effect is of a gradually decaying sound, known as reverberation.

The length and character of this decay is affected by many factors, such as room size, shape, number of hard surfaces, and the materials that these are made of. So a big Cathedral should have a long pre-delay, and a long decay, due to its size, shape and construction, whilst, say, your living room will most likely be a far shorter delay and decay.

Reverb Effects

Plate Reverbs

As previously stated, reverb effects for musical use have been around for some time. As early as the '50s, plate reverbs were used to simulate natural acoustic reverb. These worked by using a transducer (a speaker) to send the source sound through a piece of sheet metal, with another transducer (a microphone) to pickup the resulting the decayed sound.

To increase the pre-delay (and perceived space), a delay would have to be added into the reverb channel.

The effect was surprisingly, er... effective, though. However, with plates often huge and heavy. For example, the famous EMT 140 weighed a whopping 270kg.

Still, it was more practical that using a reverb chamber- a room designed specifically to created reverbs. Here, a speaker would be set up in the chamber, with microphones elsewhere in the room, such that sounds could have natural reverb added.

Spring Reverbs

A spring reverb is much like a plate reverb, except it swaps a huge and heavy plate of metal for a far more practical spring. As a result of the smaller size, spring reverbs were introduced to many guitar amps, and still feature on many today.

Digital Reverbs

When digital technology became more commonplace in music gear during the eighties, digital reverbs represented some of the most welcome uses of it.

Rather than employing physical means to generate reverb decays, these use computer chips and mathematical algorithms to calculate the audible effects of reverb. The advantages of these are huge. They can be switched to emulate different acoustic spaces, or reverb types easily (most will offer room, hall and plate settings as standard).

Many even offer the ability to get into the 'nitty gritty', and control pre-delay time, number of early reflections, decay time, decay character and more.

Though the classic studio reverbs by Lexicon and the like have become less commonplace, there are many classic guitar reverbs available. Check out the EHX Holy Grail Nano, Boss RV-5 and TC-Electronic Arena reverb.

Convolution Reverbs

Convolution reverbs are recent development of digital reverbs. These are usually software plug-ins, and harness the incredible CPU power now available to accurately model the sonic character of real acoustic spaces.

So, an engineer will head out with a measuring mic and a computer to, say, a cathedral, and 'sample' the space, creating impulse responses.

As a result, users can create their own reverb types fairly easily on many available convolution reverbs.

So there we are- 'what is reverb' explained. But, what is it used for?

In the studio, it is used to create a sense of space and depth in a mix. Sounds that have a lot of reverb seem further away, whilst dry sounds seem closer and more intimate. In addition, recorded sounds that are completely dry can sound a little bit unnatural.

Reverb is also used as an atmospheric effect- sounds that have big, spacious reverbs can suggest the 'drama' of the spaces they emulate, for example.

Here's a few audio examples...
Drum Loop Dry (No Reverb) Drum Loop Large Hall Reverb Drum Loop Drum Room Reverb
View a complete range of reverb pedals on the Dawsons Website.

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What Is Reverb? A Mini Guide To One Of The Most Common Effects

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If you're a producer, home recordist or guitarist, you'll no doubt have used reverb effects at some point. If you haven't, you'll almost certainly be aware of what it sounds like. Reverb (short for reverberation) is one of the oldest of all audio effects, and aims to recreate the natural ambience of real rooms and spaces.

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-Sound Pressure Levels - in dBa

-Sound Transmission Classes - STC

-Room Acoustics

-Reverb