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When RPN magazine needed an article to teach readers how to improve their room acoustics, they turned to Acoustics First® to get the scoop.
YOUR ROOM’S ACOUSTIC SYSTEM – and How to Improve It
Ever wonder why some rooms sound better than others? What components contribute to
perception of sound in a space? What knowledge do you need to solve the sound problems that
When people read the heading “The System,” there will be a great number who assume I am
talking about the “sound system” in a room – the speakers, amplifiers, signal processors, and
other electronic components that generally produce sound in a space. This is only part of the
acoustic system that creates the soundscape we hear when we are exposed to sound in a space.
Yes, sound comes out of speakers, and they are important, but the source of sound isn’t what
gives us a perception of the space we are in – it’s the space itself!
The walls, ceiling, floors, seats, sculptures, drapes, artwork, construction, and even people in the
space are all contributing to how we perceive that sound source in any given acoustic
environment. I’m not saying that the speakers aren’t important – but they are just the source of
If you have a room with a 5-second reverb time, it doesn’t matter what type of speakers you
have, any sound they make is going to continue to be heard for five seconds – as is every sound
What does this mean? Even if you have the best speakers in the world in that room, it will sound
terrible (unless you are listening to Gregorian Chants…then it will sound awesome.)
However, if someone is speaking at a normal rate of speed, it will be unintelligible after the first 2
or 3 words – as those words will continue to bounce around with the sound of the next 15
words…like listening to 15 people all saying different things at the same time.
Your room is an acoustic system – from the sound source, to the ears of the listeners – as well as
everything in, around, and even outside of that room.
Have you ever watched an acoustical consultant begin the analysis of a new space? It’s
fascinating. You will undoubtedly see them walking around the room while making noises –
clapping their hands, snapping their fingers, whistling, even talking loudly, shouting, and singing.
It’s as if they are bats using different sounds to figure out the characteristics of the room they are
in. They are, in fact, analyzing the room’s acoustic system. Where does sound reflect? Are there
echoes or flutter? What is the character of the reverb? They look at the structure, materials,
corners, architectural elements, floors, carpets, walls, windows, doors, ceilings and more.
Note: They begin this analysis WITHOUT using the speakers.
Why? If the room is bad, your speakers will not fix it.
What are they doing? They are listening. That’s it. Nothing fancy here – just listening.
I will say that many acousticians have done this so many times, in so many different spaces, that
they have an idea of what the room is going to sound like, without even making a peep – just by
looking at it. What are they looking for? What are they listening to? What can you learn from this?
Time to Listen
Everyone has a room where they dislike the acoustics. Go in there. Clap your hands. What
happened? Clap again. Snap your fingers. Make some noise – but make sure to listen. Where is
the sound coming from? Turn around, clap again. Walk to another area…clap.
As you walk around, you will hear the sound change. Turn your head. Is the sound coming from
the corner, the ceiling, both? Angle your ears in between two corners. Maybe that’s where it’s
coming from. Is there a large open balcony or a curved wall? Ask yourself these questions as you
walk around and listen.
Are any of the surfaces hard? What about the floor? Is the sound lingering over your head up in
the ceiling? Is there a defined slap off the back wall when you clap your hands? Is there a ringing
noise? Does the echo wash over you and linger?
Sharpen your listening skills. Map the room with your ears.
What Are You Doing in the Room?
This is an important question. For most uses involving speaking and understanding speech, there
are some good general targets. For example, for most rooms over 100m3 (15’ cube), a 0.8 to 1.7
second reverb time is ideal for many different functions.
However, keep in mind, some spaces may have special reverb requirements. If you’re doing
Gregorian Chants, a three to five second reverb time is still great!
Now, How Do You Fix It?
Most rooms are going to benefit from reducing the acoustic energy in the space. Absorption is
the most direct and easy to understand method – add soft stuff.
This sounds overly simple, but the initial experiments on calculating absorption were done by
moving around seat cushions – simple, but effective.
Fabric-wrapped absorber panels are today’s high-tech equivalent to the seat cushions. Curtains,
blankets, carpets, and other soft materials will also help to reduce the acoustic energy of a space.
Treatments like diffusers help to reduce focused acoustic reflections by spreading the energy
around. When sound hits a surface that is not flat, it will cover the entire surface, bending
around the corners and curves, and then bounces off in different directions.
This reduces what we refer to as ‘specular’ reflections – or direct, mirror reflections – which are
responsible for slap echoes, ringing, and flutter.
However, some hard, reflective surfaces in the front of the room can be beneficial to help
reinforce acoustic sound sources, like speaking, singing, or acoustic instruments.
Treating corners with bass traps can help to reduce bass buildup, as well as corner reflections,
which can cause other clarity issues within the listening environment.
Don’t forget…look to the ceiling for rafters and other elements that cause sound to bounce
around and put some absorption up there.
Thanks to everyone who flooded our booth at the 2017 AES/NAB show last week at the Javits Convention Center in NY! We enjoyed all the enthusiasm of the attendees, and all of the conversations about projects, products, and acoustics!
If you kept your AES Dailies, you may have seen Jim and the Art Diffusor® Model D on Page 4 of the 2nd edition.
Enjoy the spinners!
(Note: Fidget Spinners are not an acoustic device… technically)
*spin* *spin* *spin* *spin* *spin*
Here at Acoustics First, we often receive inquiries from business owners who have moved into a commercial building shared with other tenants. Unsurprisingly, the most common acoustic issue is excessive sound transmission between neighboring businesses.
In commercial buildings with multiple tenants; such as outlet malls, office buildings and shopping centers, it is important to understand the nature of the neighboring businesses, especially ones directly next to, above or below an occupant. The following are categories of adjacent tenants with distinct acoustic environments which can disrupt or be disrupted by neighboring businesses.
Standard Adjacencies: These neighbors tend to be have soft to moderate ambient noise levels that range from about 40-75 dBA, which generally remain constant throughout their operating hours. This often includes low-moderate levels of background music or chatter that has no significant amounts of low bass frequencies. Some examples of these spaces would be standard retail, electronics, clothing, or shoe stores, coffee shops, grocery stores, department stores, call centers, or an office with an open layout. The requirements for sound isolation associated with these types of adjacencies are less stringent, so standard construction practices are generally acceptable.
Dynamic Adjacencies: These neighbors come in two categories “loud” and “soft”. The neighbor that would be categorized as “loud” would have an average of ambient noise levels above 75 dBA for long periods of time throughout operating hours. This level of noise sustained over long time periods will conceivably disrupt other neighbors that share adjoining walls. Some examples of these spaces are pre-schools or daycares, kennels (doggy day cares), high-sound-intensity fitness studios (cycling, aerobics, Zumba, CrossFit, etc.), bars/restaurants with loud or live music, recording studios and live music venues.
The dynamic neighbor that would be categorized as “soft” would have average ambient noise levels below 40dBA during operating hours. With this type of noise level, there is less tolerance for excessive noise coming from adjacent spaces/tenants. It’s important to minimize the overspill of noise to these spaces to avoid disturbing them. Some examples of these types of spaces would be doctor or law offices, spas/massage therapy, yoga studios, upscale retail, fine dining restaurants, libraries and book stores.
Dynamic adjacencies will usually need specialized acoustic treatment and/or construction in order to control excess noise transmission. If you are surrounded by dynamic neighbors (both loud and soft) or would classify your business as dynamic, you may have to apply fundamental construction and extensive acoustic treatment to control noise transmission. That said, even after taking these precautions, the noise transmission may not be reduced to tolerable levels. Some examples of these situations would be a high intensity fitness studio next to a yoga studio, a live music venue sharing a wall with an upscale restaurant, a Law Office above a Daycare or a recording studio under a book store. Avoid the hassle and expense of extensive construction by choosing your neighbors wisely!
So remember: when you are considering commercial locations for your business it is quite possible that you may encounter a number of these issues. It’s always best to design your space with the acoustic requirements of your neighbors in mind.
For anyone new to the world of acoustics, there is a multitude of terms, coefficients and numbers that are thrown around. This flood of information can seem intimidating, especially to beginners. In this series, acoustician Cameron Girard of Acoustics First® hopes to help you distinguish between what’s useful and what’s not.
Part 1: Acoustic Terminology – Sound Absorption vs Sound Isolation
In order to make informed decisions about acoustical treatment, it is vital to know the difference between materials that are meant to absorb sound within a room and materials that are meant to block sound from leaving or entering it. In an overly reverberant auditorium, absorptive treatment is needed to reduce echoes and improve speech intelligibility. If the problem is sound passing in between spaces, like offices or apartments, then isolation treatment is required. These are two separate acoustic issues which require separate solutions.
In both scenarios, it is important to know which data is relevant and helpful. Also, given sheer volume of information available on the internet, it is perhaps unavoidable that some info will be incomplete or simply incorrect. It should not be assumed that something which sounds technical is, in fact, backed up by proper testing.
Terms for Sound Absorption
We recently encountered an acoustical ceiling tile which was said to “absorb 50% of sound”. On the surface this sounds like an extremely efficient product. However, let’s delve in closer and decipher what is actually usable information, and what is just marketing.
When sound waves meet a room surface such as a wall, ceiling or floor, some of the sound energy is reflected back into the room and the rest is considered to be “absorbed”. The absorbed sound energy has not vanished, it’s actually been converted into kinetic (vibration of a solid material) and thermal energy (heat due to friction within a porous material) or has simply passed right through the material (transmission). The more surface area a certain material has the better absorber it will likely be. “Soft” materials, like heavy blankets, fabric and fiberglass, have loads of nooks and crannies, which sound tries to “fill”. These porous materials are great for reducing reverberation within a room, but will only marginally reduce the sound that leaves it (but more on that later).
When comparing sound absorbing products, there is a particular set of terms you should look for: The Sound Absorption Coefficient (SAC) and Noise Reduction Coefficient (NRC). These are used to specify the fraction of incident sound that a material absorbs per 1’x1’ area. An NRC of 1.0 indicates perfect absorption (an open 1’x1’ window) and a value of 0.0 represents perfect reflection (polished concrete has an NRC of .02).
To measure sound absorption, a large sample of the material is placed in a reverberation room with all other surfaces being hard and reflective. The time it takes a test sound signal to decay by 60dB (rough point of inaudibility) after the source of sound is stopped is measured first with the sample in the room and again with the room empty. The difference in decay time defines the efficiency of the absorbing material and thus the absorption coefficients. Large spaces with low-NRC materials (tile, drywall, etc.) have longer reverberation times, while small rooms furnished with high-NRC materials sound much more “dead”.
Clearly, a single 2’x2’ ceiling tile is not going to reduce the reverberation in a real-world space by 50%. So is the above claim false? Not exactly… The ceiling panels do have an NRC rating of .50, so the tile does absorb 50% of incident sound. However, one might assume a much more drastic improvement based on the “50%” claim. In reality you’d need a large square footage of these ceiling tiles to cut the amount of total reflected sound in half. Always be sure to check the NRC number!
Terms for Sound Isolation
Our customers often call with issues related to neighbor noise or office-to-office privacy and are looking for “sound proofing” treatment. Unfortunately, many do not realize that simply installing acoustic foam or fiberglass panels will not appreciably reduce the level noise entering and leaving their space. These absorptive materials are great at reducing unwanted reflections within a room because they are porous and air/sound energy can flow through them. That being said, they are generally poor sound barriers for this exact reason. They will help to reduce noise buildup in a room and improve the ‘acoustics’, but will do very little to “block” sound coming in or out.
Sound is like water; it will “flow” into an adjacent space if everything isn’t sealed up. Materials that are air tight and heavy, like our BlockAid® sound barrier, provide the most relief of air-born sound transmission. Continuous coverage of floors/ceilings or walls is necessary to ensure that sound doesn’t ‘flank’ around these barriers. Multiple layers of varying materials, the use of resilient clips or channels, and additional walls will provide even more control. For a demonstration of how different materials affect sound isolation, check out our video http://acousticsfirst.com/educational-videos-the-barrier-and-the-bell.htm
Like NRC for sound absorption, there is also a laboratory tested figure that can be used to compare the sound “blocking” properties of acoustic barriers and wall constructions: Transmission Loss (TL) and Sound Transmission Class (STC). These describe how much air-born sound is attenuated through a given material.
In the lab, the material to be tested is mounted over an opening between two completely separated rooms, one with a speaker (source) and the other with a microphone (receiver). Save for the open “window”, these rooms are completely isolated with thick and massive walls, so virtually all the sound energy transmitted between rooms will be through the test specimen. The difference between sound levels in the source room and the receiving room is the transmission loss (TL). The TL is measured at multiple frequencies, which is fitted to a Sound Transmission Class (STC) “curve” at speech frequencies (125Hz-4kHz). The STC of the material is the TL value of the fitted curve at 500 Hz. For example, a material with an STC of 27 typically “blocks” 27dB of sound. Keep in mind though, the STC’s of materials do not add up linearly; in other words, adding a material with an STC of 27 to an existing wall with an STC 45 will not result in an STC of 72.
As always, Acoustics First is here answer questions and help you find the best solutions.
Posted by Acoustics First in Absorption, Articles, Broadcast Facilities, Customer Feedback, Diffusion, DIY, Home Entertainment, Home Theater, HOW TO, Media Room, Music Rehearsal Spaces, Music Tracking Room, Product Applications, Recording Facilities, Recording Studio, Studio Control Room, Teleconferencing, Theater, Vocal Booth, Voice Over on July 14, 2016
This month we thought we’d share a few Real-Life pictures of an idea we first introduced back in summer of 2013: The “Back Wall Diffuser Array/Bass Trap”.
This is the DIY project which incorporates our Art Diffusors®, Cutting Wedge® foam and a couple of isolation hangers into one large free-floating unit, which is acoustically decoupled from the wall.
This particular array was put together by a music producer/bass player for his home. As you can tell from the pics, the construction of this unit was executed beautifully and it’s very close to the original concept drawings.
It’s never too late to get started on your own DIY project.