Posts Tagged noise control
Glass is a universal building material that is attractive to architects and clients, while posing a variety of challenges to acousticians.
Due to its transparent nature, glass creates an open and pleasing atmosphere. Curtain walls, skylights and windows allow for a view both outward and inward; connecting occupants to the building’s natural or urban setting. The use of natural light can lower electricity bills, brighten the rooms of a building, boosting the mood of the occupants. Glass is also a renewable building material, with 30% of new glass comprised of recycled materials. For all these reasons and more, glass will continue to play a major role in architecture in the future.
However, glass has a number of acoustical properties that can contribute to a poor occupant experience. To illustrate this, let’s take a closer look at what happens when sound interacts with glass.
When sound encounters a window, the glass converts some energy into thermal and kinetic energy (resonate vibrations), allows some sound to pass through, and reflects the rest back.
Glass only “absorbs” sound near its resonant frequency (and subsequent harmonics). The resonant frequency of glass is dependent on many factors, including density, thickness and panel size. As is the case with many “hard” building materials, the absorbed sound accounts for only a small fraction of sound energy’s interaction; most sound is either reflected or transmitted through the glass. Sound reflection and sound transmission are two separate acoustic issues with separate solutions.
Sound Reflection – Reflected acoustic energy from an internal sound source can cause a number of issues for occupants. Large, uninterrupted spans of hard materials like glass and gypsum cause specular reflections (echoes) and contribute to excessive reverberation and noise levels. These conditions can contribute to a poor acoustic environment in which speech is difficult to understand and music clarity suffers.
Specular reflections are compounded when there are other hard surfaces in the room. Flutter echo, heard as “ringing”, happens when sound bounces back-and-forth between parallel reflective surfaces (between walls or floor-to-ceiling). Flutter echoes greatly degrade speech intelligibility and music definition. This is a big problem in studios, offices, conference rooms and theater/media rooms. If there is an abundance of reflective surfaces, background “noise” from latent energy will cover up or distort the direct sound.
Typically, these issues are corrected with sound absorbing materials. However, we cannot simply “resurface” the glass with sound absorption, like we would with concrete or gypsum, without impacting transparency. Until someone invents invisible acoustic foam or fiberglass, sound reflections off glass will continue to be a challenge that needs accounted for.
Sound absorptive materials like thick curtains or acoustic shades provide adequate sound absorption and coverage flexibility. Other creative solutions include “stand alone” furnishings like tall, leafy plants or translucent perforated plastic sheets mounted over top the window. Essentially, any irregular surface you can introduce in front of the glass will help diffuse sound and break up harmful wall-to-wall reflections.
Sound Transmission – More than 90% of all exterior noise comes in through doors and windows. This can be partially attributed to poor weather stripping. “Leaky” windows will not only cause uncomfortable drafts, but allow sound to more easily work its way into our homes and businesses. Sound is a little like water; it will “pour out” through any gaps in the building assembly. Improving sound-loss across glass often starts with replacing the weather stripping and properly sealing any joints with non-hardening acoustic caulk.
Air-tight, limp, massive materials are the best at blocking sound. Glass is rigid, and its heft is limited by transparency requirements that keep it thin. Glass transmits a lot of sound energy, particularly at low frequencies. Laminated glass and insulated glazing assemblies both reduce sound transmission through glass by reducing resonance and adding air-space.
Including an acoustic consultant early in the design process will allow architects and owners to make well-informed decisions. An acoustical consultant will best identify potential pitfalls of using glass and recommend glazing systems and construction techniques to minimize future headaches. This measured approach will result in more beautiful looking (and sounding) spaces!
Sometimes you just don’t have the wall space for acoustic treatment. When this is the case, you will often see treatments move to the ceiling… but what do you do if you have lower ceilings, or many ceiling fans and fixtures?
This ceiling was sloped toward the massive windows on the outside wall, and it had lights and fans running right up the center. Complicating things further, the opposite wall had sconce lighting, doorways, HVAC, and even more windows. Finally, the floor was not carpeted to facilitate cleaning – as is the norm in many dining spaces.
Direct-mount acoustic panels are a great solution in these scenarios. Here we see an array of 4’x4’x2″ Sonora® panels attached to the ceiling in rows running down the length of the space. While our Tone Tiles® are often selected for their ability to blend in aesthetically, this particular installation proves that Sonora® panels wrapped in fabric are also a solid choice.
There is a saying in our industry: When it comes to designing a space, acoustic consultants are blind and architects are deaf. In reality, it is in both parties best interest to consider the other side when designing a space, so visual form meets acoustic functionality.
Let’s be real, standard acoustic treatment is far from sexy. Typical 2’x4’ panels, while fully functional, don’t present the architects with much in terms of visual interest. This is where Acoustics First can supplement the design goals of the architect/interior designer with our technical expertise to find a custom solution that sounds and looks great.
Recently, Acoustics First® was asked to provide the custom panels for the cafeteria at Kramer Middle School in Washington DC. It was settled that hexagonal ToneTiles™ would be suspended as clouds in a geometric pattern around the ceiling. The resulting “honeycomb” effect is not only visually appealing, but the treatments effectively cut down the overall reverberation; increasing speech intelligibility and making the space more comfortable for a variety of activities.
Acoustics First® enjoys the inherent challenge in making these custom panels a success. We have plenty of experience in fulfilling the design goals of architects and interior designers. Interested in seeing more of these custom projects?
Visit http://acousticsfirst.com/installations-education-school-museum.htm to see some more examples.
Feel free to give Acoustics First® a call to discuss your custom treatment needs!
Since it’s been a while, I have received approval to write about phones and scones – yummy! Oh, I misread that… I can talk about phons and sones? Oh boy. I mean… hmm… uh…
Every so often, you get exposed to a term that you’ve never heard; it seems like someone just made it up – and the more you learn about it, the more made up it seems.
(Disclaimer: I swear I didn’t make these up.)
Today, I will introduce you to two of these amazingly real terms, and do my best to explain why these terms exist… prepare to be amazed!
OK. Phons and Sones are two related terms in Psycho-acoustics that refer to how humans perceive the “LOUDNESS” of sounds. These are actual real concepts. (Stop laughing.)
Don’t we all perceive sound differently? YES!
So how can you have an actual measurement based on something that everyone perceives differently? EASY!
Take a bunch of people.
Play a 1Khz sine wave.
Play another frequency.
Ask them if it sounds just as loud.
Repeat. (No kidding.)
OK, this is over simplified… Let’s start by setting some rules that make this a little easier.
For reference – whatever dB level that 1KHz wave is will be the reference for the whole group… compare a bunch of frequencies at different levels to 1Khz at 40 dB – and we’ll call all the ones that sound just as loud the “40 PHON Equal Loudness contour.”
Why? Because they sound just as loud as the 1kHz wave at 40 dB. (I’m not joking!)
Then compare a bunch to a 1KHz wave at 50dB and call all of those that sound as loud, (wait for it)
the “50 PHON Equal Loudness contour.”
Then 60dB, 70dB, 80dB… etc (see a pattern?)
Now, plot all of these from a bunch of people who hear pretty well… take an average and WHAMMO!!!
The PHON Equal Loudness contours!
(To be fair this is the data from a bunch of 18-25 year olds who still have reasonably good hearing…)
Remember this is PERCEIVED LOUDNESS. The average of what the test subjects said “yeah, uh, that’s just as loud, Dude.”
It seems strange doesn’t it – that these aren’t nice straight lines? That’s because the human ear is constructed in such a way to be more sensitive to certain frequencies than others.
So according to this chart – a 1KHz wave at 40 dB sounds just as loud as 125 Hz at ~60dB and 3150 Hz at ~35 dB. (All on the 40 Phon contour.)
That’s Psycho-acoustics for you. (Wow.)
So if you’re an average person with average hearing, your bass perception is terrible and over 16KHz you’re basically – well… deaf.
But you hear really well from 2kHz – 5kHz!
Anyway… what’s the point?
Phons measure how loud the human ear perceives sounds at different frequencies. (TADA!)
FINE! – then what are Sones ? To make this simple – Sones are relabeled Phons.
You start with 40 Phon being 1 Sone then double it every 10 Phon.
40 Phon = 1 Sone.
50 Phon = 2 Sones.
60 Phon = 4 Sones.
70 Phon = 8 Sones.
80 Phon = 16 Sones
90 Phon = 32 Sones
100 Phon = 64 Sones
(Hmm, thought that would be more complicated? It is – but that’s basically it in a nutshell.)
You will almost never see a phon or a sone. Bathroom exhaust fans and blowers are sometimes rated in Sones – to let you know how quiet they are… The problem is that no one actually knew how quiet that was until now!
I guess it sounds better to say –
“This bathroom fan operates at only 2.5 Sones!”
…Than it would be to say…
“This bathroom fan resonates at over 80dB,
but it’s in a frequency range that humans don’t hear very well,
so it sounds quieter than it actually is… no… really!”
Human perception of sound is very important to the development of acoustic products – Psycho-acoustics are not a joke.
(Why are you still laughing?)
Airflow is good. Circulating stagnant air has many health benefits, but what do you do when that ceiling fan is just making too much noise?
To start, check all the normal suspects; is it balanced, cleaned, level, blah blah blah… You’ve probably already checked these anyway. It’s an older fan, the motor hums, because older fans hum. If it’s vibrating through the structure, there may be something you can do to isolate that extra vibration – and at least keep the other occupants happy.
When most people think of Vib-X pads, they think of a musical function; Isolate your speakers, isolate an amplifier, isolate a (insert name of miscellaneous musical gear here)… but there are some really useful everyday functions for this wonderful material. Like keeping that fan from vibrating the entire house!
The simple install may involve a contractor, or at least some one who knows electricity, so you don’t electrocute yourself… but after shutting off the power to the fan, it’s pretty quick. Take down the fan and find the box. Disconnect the box. Cut some Vib-X to separate the box from the wood. Cut some Vib-X squares to use as washers. Remount the box using the diagram, a couple fender washers, maybe a couple optional grommets if you desire – then re-install the fan.
Ceiling fans are usually mounted to an electrical junction box in the ceiling, which is usually just screwed to a ceiling joist or some simple wooden frame. By using the Vib-X to isolate the electrical box from the wood, the vibrations do not directly transfer from the fan into the structure of the house, turning that old, vibrating ceiling fan – into a breath of fresh air.
Simple. Thought so. Don’t forget to balance, level, and clean that ceiling fan while you’re doing all this. Turn that power back on and enjoy the breeze.