Not All Acoustical Surfaces Are Created Equal
The orchestra that I play in used to perform at local public schools. The high school auditoria that we regularly used were so-so for acoustics, but we learned to appreciate them when a scheduling conflict bumped us to a junior high school for one concert. This auditorium ceiling was treated with a spray-on absorbing material that made it feel like we were playing into a sonic black hole. After we finished, it sounded like twenty people were clapping, which I hope there were more…maybe not if they couldn’t hear us. (more)
Reflections at Little Beaver Lake
On a beautiful autumn day a long time ago, I was on a glorious backpacking trip to Pictured Rocks National Lakeshore in Michigan’s Upper Peninsula. One still morning while rinsing off in Little Beaver Lake, I was alarmed to hear voices that sounded very near, as I was sporting my birthday suit. After quickly sinking into the water up to my neck, I searched for the people and to my relief found them on the opposite shore of the small lake, out of “detailed sight” range. That was a memorable lesson in how well water reflects sound. (more)
Several weeks ago, a client invited me to a rehearsal in their highly reverberant space that ABD was hired to test and correct. I declined, as I already had plans to attend a play that evening at a different facility, and joked that during the performance I’d also be listening to sirens from the main street outside the theater. Nearly every time we attend a performance in this space, we hear sirens going by the building. Sure enough, on cue in Act II, “errrrrreeeeeerrrrrhhh” slices into the hall. My husband and I shake our heads. This is why sound isolation of performance spaces from outside noise intrusion is so important. (more)
Mechanical Background Sound in Exam Rooms
January 2010 held a highly anticipated milestone for acoustical consultants. The definitive guide called 2010 FGI/ASHE Guidelines for Design and Construction of Health Care Facilities has a greatly expanded acoustics section in this year’s edition. How will you deal with the new noise, privacy, and acoustical requirements for healthcare facilities? Join us at SoundHealthcare 2010, a Health Care Acoustics Training Seminar, and find out what you must know about the new FGI Guidelines for HIPAA Compliance and LEED HC. This is a brand new chapter in the 2010 FGI Guidelines, which went from a solitary partition transmission loss table in prior issues to an eighty page guideline that comprehensively covers exterior noise, acoustical finishes, background noise, sound isolation, vibration, sound masking systems, audio systems and alarms. As a result, acoustical consultants are hoping that architects and engineers will appreciate the breadth and importance of acoustics and consequently incorporate acoustical design early in a project when it is most cost effective. (more)
Psychoacoustics: Annoyance from Tonal vs. Broadband Sounds
For today’s topic, let’s think of driving our car with the wind rushing by, when all of a sudden our attention is drawn by that annoying squeak coming from the dashboard. The changing of the squeak with time was the topic of a recent blog, but this time we’ll examine its tonal nature. (more)
Your Conversation with your Doctor may not be as Private as you Think
While I was at the doctor’s office the other day, I was allowed to listen to a conversation between a doctor and another patient. Was I in the room with them? I didn’t have to be. The sound isolation between exam rooms was so poor that I could hear virtually everything that was said. (more)
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Psychoacoustics: Transient Noise Grabs Attention
Have you ever noticed how some sounds catch your attention and others do not? For example, you are driving down the road thinking of your plans for the day and all of a sudden you hear a squeak in the dashboard. It draws your attention immediately, while the air conditioning fan likely does not. The squeak is intermittent (and likely tonal, but that’s a topic for another blog) and therefore stands out over the more constant sound of the fan. This reaction is similar to vision, where our attention is drawn by moving objects much more so than stationary ones. (more)
When One Size Does Not Fit All | Diffuser Sound Levels
On a recent trip to India, I discovered a cute clothing sizing term called “free size” which is equivalent to “one size fits all”. Free size clothing must be a manufacturer’s delight since production and distribution are greatly simplified. Adjustments to the size of the garment are typically made through waist ties of various designs and if needed, permanent alterations.
In the A/E/C industry, diffuser, grille and register (air device) manufacturers have chosen the free size philosophy when it comes to providing sound data. (more)
The Leaky Bucket | How Sound Escapes
Blocking sound is often analogized to plugging the holes in a leaky bucket. If you plug up all the bucket holes except one, the bucket is still going to drain. In acoustics, an outstanding partition design will not adequately block sound if holes and weak spots exist where sound can find its way through. (more)
Elbows vs. Sound Attenuators: Interchangeable?
It is common belief that a series of elbows near an air handling unit (AHU) can accomplish the same insertion loss as a manufactured duct sound attenuator. It’s true that elbows are less expensive than sound attenuators, but what acoustical performance is really achieved with this “low cost” substitution?
Let’s compare the two designs. Using the tables presented in the 2007 ASHRAE Handbook – HVAC Applications, for any type of elbow (round, rectangular, acoustically lined or not), the width of an elbow (in the plane that it turns) must equal or exceed 30 inches to get ANY insertion loss at 63 Hz. A 30 inch wide elbow provides only 1 dB of insertion loss (IL) at 125 Hz . These two frequencies are typically of concern when reducing sound from AHUs.
Rooftop Roulette | Noise and Vibration Isolation for Air Handlers and Mechanical Units
Over the years as an acoustical consultant I’ve seen a lot of architectural firms locate rooftop air handling units over or near acoustically sensitive spaces; then they put up resistance to doing the necessary extensive noise controls that are needed for such a situation. The protest usually includes “but we’ve never had to do that in the past…” I call this rooftop roulette, because while not incorporating noise control design may have worked in the past, it does not guarantee future success. (more)
It’s time for another semester, and I tell my architecture students that if there’s one thing they learn in my acoustics class, it’s that porous absorbers do not block sound. A porous sound absorber, by definition, has many tiny interconnected voids that sound travels through. Fiberglass and open cell foam are examples. The sound wave loses its energy through friction between the air particles and the fibers/void walls of the material it is passing through. (more)
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