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.
Coordination for AVL Consultants and Project Teams
Perhaps the toughest and most critical element of designing AVL systems for auditoriums is proper coordination with all the other teams. As audio-visual and theatrical lighting designers, we find ourselves being selected to join teams all throughout the process, from design development to construction administration to commissioning, and this can create a lot of challenges for the AVL system integration. (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)
Binaural Recording with a Dummy Head
This past week, as we took acoustical measurements at the Calvin College Fine Arts Center in Grand Rapids, Michigan, a music teacher poked her head into the auditorium and asked if aliens had landed. “Well, not exactly”, I said. But I admitted that it did look and sound a lot like it. Binaural “dummy head” recording isn’t exactly something you see (or hear) everyday, so here is a brief glance at why this technique is used by acousticians. (more)
Decision 2008 – White Space Disaster for Wireless Mics
Last Tuesday, while many of us were casting our votes in the presidential election, the Federal Communications Commission (FCC) was making a landmark decision of its own. On their private ballot was a proposal to open the so-called “TV White Spaces” of the frequency spectrum for expanded use. And on November 4th, the proposal passed. Sounds all fine and good, right? Well, maybe not. If the FCC’s current plan goes through, it will lead to a crossroads for the wireless microphone industry and for AV designers. (more)
Auditorium Noise Isolation: You Gotta Keep Em’ Separated
Mixing noise pollution with an intimate auditorium setting is almost always a bad idea, and as the song says, “You gotta keep em’ separated.” There’s nothing like untimely noise pollution to ruin the flow of a good theatrical performance or vocal recital. For our purposes today, we will define “noise pollution” as any unwanted sound impeding at an unwanted time. When you’re engineering acoustical solutions for an auditorium, the importance of noise isolation is paramount, and it’s the only way to really keep the “bad sound” out. Noise pollution can hinder speech intelligibility and greatly reduce the ability for an audience to hear and understand what is being said. In auditoriums, noise pollution can come from a wide array of culprits from within or without the facility. (more)
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