After reminiscing with my fearless editor about sound theory and some “in the trenches” live sound design stories, he challenged me to share some of my better sound stories, so here we go.
Architectural Acoustics and Sound Theory
Sound system design is not completely intuitive. For example, the wavelengths of low/sub frequencies are 1,000 times longer than very-high frequencies. So, low and high frequencies behave quite differently. Low frequencies spread across a room much like water or air from an AC vent (flowing around obstacles), whereas high frequencies spread across a room much like light — very directly — and prone to shadows.
If you have no formal training in architectural acoustics, psychoacoustics and sound theory and want to be a competent, completive sound engineer, consider stepping up with more training. Since Covid-19, there’s been an explosion of online training seminars by several colleges and various sound vendors. Additionally, some of the most advanced sound system design and optimization seminars are still being offered by SynAudCon. If you’re new to the sound industry, consider seeking out an expert mentor. (Even with a formal education in audio, I sought out several expert mentors along the way).
Too Much of a Good Thing? Matching Loudspeaker Directivity to the Venue
Doing sound for bands at small outdoor festivals and in rooms with some decent acoustical absorption was relatively easy almost half a century ago. And several SynAudCon seminars made it painfully clear of the importance of sound coverage across an entire audience — especially for speech P.A. systems. But in those days, I didn’t have enough experience with rooms with a lot of reverberation to know that there was sometimes too much sound coverage for the room.
One of my first rude awakenings came after a leading industry mentor designed some proprietary loudspeakers (with premium components) for me. Multiple loudspeaker demonstrations had gone quite well. But in one case, I was attempting to do a live demonstration for a prospective client — in a small church with live acoustics — only to find that the overly wide dispersion (in both the horizontal and vertical axis) from the otherwise excellent-sounding loudspeakers proved virtually unusable in such a venue. The result was a cacophony of echoes and poor direct-to-reverberant ratio. Clearly (in retrospect), that church space needed far more directional loudspeakers — or a decent amount of acoustic absorption, especially on the rear wall.
Recently, colleagues have pointed out that some line arrays have very wide dispersion. That would seem to be a good thing. But such arrays may not be very appropriate for traditional shoebox-shaped rooms that are longer than wide, as wide-dispersion arrays can put more energy on the side walls than they do on the audience, resulting in lower sound quality due to lower direct-to-reverberant ratio and comb-filtering.
Watch Where You Point That Thing!
When working with various sound contractors, it usually turns out great, but in one case we had a bit of a speed bump. After I reviewed their line array coverage maps and I specified acoustic panels, the installed system had a significant rear wall echo. I had designed the acoustical wall panels to be installed at a critical elevation/height; thus, minimizing excessive expenditures for unnecessary panels extremely high on the walls and avoiding overly treating the architectural acoustics (avoiding making the room sound too dead). My site inspection revealed that a large amount of the array sound energy was focused on the untreated upper-rear walls. So, simply aiming the arrays downward (more on the audience), the obvious echo from the upper wall was eliminated, while still providing very uniform sound coverage of the seating area in this mega-church.
Walk the Room!
While doing a site inspection of an acoustic renovation for a performing arts theater, a local sound company owner asked me for my opinion of the sound coverage of his left/right stage-stacked line arrays. I replied that while they were a respected brand name, I had no experience with those particular arrays. Nonetheless, he pressed me into evaluating the sound coverage of his system. I asked for some pink noise through the system. I then pointed out that while the main floor had relatively good coverage, HF sound in the balcony was significantly inferior. So, after tipping up the top few boxes in each array, I advised him that the coverage was greatly improved upstairs. When I asked him what his observation of the balcony coverage had been in the past, he pointed out that while he had been providing sound there for a couple years, he had never listened to sound in the balcony! So do I need to say it? Please walk the whole venue to check for sound coverage.
While we’re talking about coverage, please choose your program material carefully. If it’s a purely live music application, listen to not only your favorite soundtracks, but also evaluate the coverage with a band actually playing, taking into account the acoustic sound coming off the stage and dynamics/headroom. For events/venues with a significant amount of speech, listening to a well-recorded dry(!) speech track or pink noise signal is important, to confirm a more-uniform reinforcement of speech than is needed for music.
As industry pioneers have explained in sound engineering textbooks, speech is information that we process in one hemisphere of our brain, while music is subjectively considered entertainment and processed in the other hemisphere. So the evaluation of speech versus music through a sound system is not the same in application.
Case Study of a Mega-Church: The Acoustics and Sound Design Process
Years ago, an architect I worked with showed me his proposed design for a 10,000-seat church. I knew enough about large acoustical projects to see that this massive cylindrical auditorium, with a central pulpit, would be very difficult (and why the church client had come to a disagreement with the previous consulting firm on how to shape the space/seating). I later showed the architect a basic 3D computer model I did, showing how and why not (focused echoes and high RT-60) to shape the massive main auditorium per his blueprints. He stated how another acoustical consultant said that “we can work it out,” but I had to agree with the previous consulting firm, that the design of the 3-million cubic foot cylindrical auditorium, with a central pulpit, would be very difficult to salvage.
Several months later, I (with the help of some pro-loudspeaker industry leaders) organized a relatively large-scale event we opened to the sound industry to evaluate current state-of-the-art speaker arrays in an existing mega-church. This allowed us to better estimate the quality of sound that could be expected in such a large space, with its very-wide coverage angle and 300-degree seating. This loudspeaker demonstration/comparison event (which took place back in 1994) proved to be the first of its kind in the U.S., and that group loudspeaker demo influenced several projects to follow.
Although I researched who were the best architectural acoustics consultants to work on the massive main auditorium project and met with a few of them, I could not find anyone who could propose any design concepts or show any confidence of coming up with a solution. To make matters worse, by that time, the architect and structural engineers had worked for months on detailing the building design, including the 10,000-seat main auditorium. I was informed that it was now too late to change the structural engineering for the cylindrical space. So in desperation, I was inspired to suggest that the rear walls of the cylindrical auditorium could be shifted at every set of columns (every 15°), almost like a Fresnel lens, leaving the structural design intact.
We later enlisted RPG Acoustical systems founder Peter D’Antonio to help validate my design concept. He did so, and recommended that the rear walls and balcony faces be covered with his then-new BAD (Binary Amplitude Diffusor) hybrid absorber/diffuser panels (see FOH, July 2021, page 17), with deep absorber chambers behind. Doing so in the computer model of the main auditorium showed a vast improvement, so the resultant room design included BAD panels on all of the articulated rear walls and balcony faces, along with a large “gondola” design by MGA, to enclose video screens and loudspeakers in the middle of the auditorium, and lower the room cubic volume (and resulting RT) by about a third.
Thankfully, during a group peer review, Craig Jansen suggested an auralization of the arrays. It indeed sounded like some time-smear (short echoes) would result from the very-large exploded loudspeaker array, that I had first designed (with coverage modeling). So, for the next several weeks, I worked to consolidate the loudspeaker arrays to improve the alignment (sound coherency).
That mega-church project was later expanded in scope to include a couple more construction phases, with hundreds of thousands of additional feet of meeting spaces, making it the largest church construction project in the nation’s history.
Fortunately, the sound coverage requirements did not extend much past 100 feet. Two rings of delayed loudspeakers were accommodated in the building design, and they were willing to build the extensive modifications and treatments to the architectural acoustics — including an electronic acoustics system. So in the end, the client reported that the quality of the acoustics and sound in the church’s newly constructed main auditorium (see photo, this page) was beyond their expectations.
Consultant David K. Kennedy, who operates David Kennedy Associates, has designed hundreds of auditorium and HOW sound systems. Visit him at www.d-k-a.com.
