Note: With this installment, we kick off a series of technical articles dealing with various aspects of acoustics technology, penned by experienced designer/acoustical consultant David Kennedy of David Kennedy Associates. In future installments, we will delve into topics such as creating subwoofer arrays, the mechanics of perceived loudness, the science of transducer design and more, so stay tuned! —Ed. FOH
By David Kennedy
With recent talk about democracy for listeners, this is a good time to discuss why it is important for the sound coverage in a venue installation to be as even as possible, how to evaluate sound coverage, and how speaker modeling programs can be used to design better sound coverage, along with some modeling issues to watch out for. Consistent sound coverage has actually been important for sound-reinforcement design engineers, trained by Syn-Aud-Con, for decades. For non-engineer readers, we will present some basics to help you better understand array coverage.
Since they were first introduced in the mid-1980’s, I have been using sound modeling programs for array coverage simulation (and later on, room/acoustic simulation) on almost all of my sound system designs. But my training on these modeling programs was decades ago. So, we have begun polling the loudspeaker manufacturers for updates to follow in later articles, to include: Array Modeling and Control updates along with Modeling Engineering details, with quotes from Array Modeling experts and vendors. Follow-up articles (in Part 2 and Part 3 of this article) will delve into the history and current trends in array modeling/control, with another on the modeling of cardioid subwoofer arrays. Another follow-up article will also discuss the universal programs to compare array models, and detailed acoustical analysis vs. array-specific modeling and control programs.
Music sound coverage need not be as consistent as speech, especially if the overall program has a high sound level. Getting great coverage to every seat in your venue requires a great deal of time, energy and money to get right. But in reality, there simply is no way that every seat in the venue will experience the exact same sound. That said, sound-reinforcement systems quality, and the proper design tools for coverage (dispersion) have come a long way over the past few decades.
The first step in getting great coverage is evaluating your current system. This is commonly done with listening tests that consist of pink noise followed by some music. Pink noise is very useful in this situation, because it’s easy to hear when you walk out of the coverage of your horns. If your system has Left & Right speakers, do the Pink noise test through only one output channel/array. Most rooms that suffer from poor coverage have problems with HF (high-frequency) coverage, more than lows and subs. In a venue where speech intelligibility is of paramount importance, the mid. and high-frequency coverage should be the highest priority. More on what coverage models (AKA heat maps) should look like and a few types of fill speakers will follow below.
In the November issue of 2018 of FRONT of HOUSE, author Vince Lepore, the director of event technical operations at Full Sail University, said “If you hear high-frequencies fall off at any point within the coverage area, you’ve got a problem that needs to be addressed. Before jumping to conclusions about needing a new speaker system, think critically about how your system is aimed. It’s hard to get into specifics here because every system is different, but poor speaker aiming has been the culprit in a number of projects I’ve been involved with. It’s amazing what some aiming changes can do for a system that isn’t covering correctly. A few degrees of adjustment can go a long way to improving your system’s coverage.” See fohonline.com/articles/sound-sanctuary/dispersion-great-sound-from-front-to-back/ for the entire article, including tips on employing fill speakers.
Fig. 1 on the previous/upper page, shows two views of an EASE sound model in a large, box-style proscenium venue with a balcony, showing the Broadband Total SPL in the room, which includes reflections from the surfaces in the room and does not represent the direct sound field from the loudspeakers themselves. This is typical of many sound modeling examples and proposed/free designs from loudspeaker factories and suppliers.
Fig. 2 above shows a modeling image from another array modeling program called Soundvision, from L-Acoustics (similar to EASE and others). This coverage map is a more realistic representation of how “comb-filtering” — caused by interaction between multiple loudspeakers — should be displayed (setup in the program). But both of these coverage map examples (in Fig. 1 and Fig. 2) show a 20 dB SPL (sound pressure level) variation. The problem with the marketing approach, of showing almost perfectly consistent sound (Broadband) coverage, is that it is not helpful, as the sound engineering industry standard for displaying SPL variation is 6 dB to 10 dB. Array coverage models should have the dB scale set to look more like the image in Fig. 4.
Showing two times the standard scale, over an average of a wide range of frequencies, and/or multiple arrays at the same time, is not realistic or true. And of course, someone must pay for these free, but basic services.
A recent trend is the offering by pro-loudspeaker factories to do “free” array modeling of coverage for their design/build dealers. We applaud the live-sound speaker manufacturers for taking the initiative and making the investment to create and support these and other programs, and for their willingness to provide a free service to their dealers and end-users, to help ensure that their products get implemented well, to the good of all. However, most of the modeling programs from a brand-name source, only include their own loudspeaker models in their database. We will touch more on loudspeaker array modeling trends in Part 2 of this article series.
Free array modeling has many limitations; the results can be very hard to compare, and the modeling results can sometimes be of questionable value. Limitations with “free” array modeling services from loudspeaker vendors include:
• Vendors may display multiple arrays at the same time (hiding poor coverage)
• Comb-filtering from interaction between loudspeakers may not be displayed
• Limited interaction between loudspeaker vendors & sound designer
• No universal program (various programs use different calculations)
• Lack of consideration of echoes from loudspeakers off of walls
• Lack of objective recommendations (limited to brand offerings)
• Lack of standard scale for how sound coverage is displayed
• Lack of sound system clean power & conduit plans
• Lack of venue site survey by loudspeaker vendor
An expert and independent sound consultant/engineer, should not only provide all of the above services, but should do so in an objective and integrated manner.
What is Array Coverage?
While estimating total sound coverage is fairly intuitive, the understanding of speaker array interaction and psychoacoustics does not come easy. Extensive training and years of array modeling will train a sound designer about loudspeaker interaction and sound design methods. Author Bob McCarthy has written extensive books on the subject. The graphics in the Fig. below are from his book Image from Sound Systems: Optimization and Design by Bob McCarthy. (Copyright 2014 Focal Press. Used by permission. All rights reserved.) show how coverage patterns are measured and shown.
By David Kennedy
With recent talk about democracy for listeners, this is a good time to discuss why it is important for the sound coverage in a venue installation to be as even as possible, how to evaluate sound coverage, and how speaker modeling programs can be used to design better sound coverage, along with some modeling issues to watch out for. Consistent sound coverage has actually been important for sound-reinforcement design engineers, trained by Syn-Aud-Con, for decades. For non-engineer readers, we will present some basics to help you better understand array coverage.
Since they were first introduced in the mid-1980’s, I have been using sound modeling programs for array coverage simulation (and later on, room/acoustic simulation) on almost all of my sound system designs. But my training on these modeling programs was decades ago. So, we have begun polling the loudspeaker manufacturers for updates to follow in later articles, to include: Array Modeling and Control updates along with Modeling Engineering details, with quotes from Array Modeling experts and vendors. Follow-up articles (in Part 2 and Part 3 of this article) will delve into the history and current trends in array modeling/control, with another on the modeling of cardioid subwoofer arrays. Another follow-up article will also discuss the universal programs to compare array models, and detailed acoustical analysis vs. array-specific modeling and control programs.
Music sound coverage need not be as consistent as speech, especially if the overall program has a high sound level. Getting great coverage to every seat in your venue requires a great deal of time, energy and money to get right. But in reality, there simply is no way that every seat in the venue will experience the exact same sound. That said, sound-reinforcement systems quality, and the proper design tools for coverage (dispersion) have come a long way over the past few decades.
The first step in getting great coverage is evaluating your current system. This is commonly done with listening tests that consist of pink noise followed by some music. Pink noise is very useful in this situation, because it’s easy to hear when you walk out of the coverage of your horns. If your system has Left & Right speakers, do the Pink noise test through only one output channel/array. Most rooms that suffer from poor coverage have problems with HF (high-frequency) coverage, more than lows and subs. In a venue where speech intelligibility is of paramount importance, the mid. and high-frequency coverage should be the highest priority. More on what coverage models (AKA heat maps) should look like and a few types of fill speakers will follow below.
In the November issue of 2018 of FRONT of HOUSE, author Vince Lepore, the director of event technical operations at Full Sail University, said “If you hear high-frequencies fall off at any point within the coverage area, you’ve got a problem that needs to be addressed. Before jumping to conclusions about needing a new speaker system, think critically about how your system is aimed. It’s hard to get into specifics here because every system is different, but poor speaker aiming has been the culprit in a number of projects I’ve been involved with. It’s amazing what some aiming changes can do for a system that isn’t covering correctly. A few degrees of adjustment can go a long way to improving your system’s coverage.” See fohonline.com/articles/sound-sanctuary/dispersion-great-sound-from-front-to-back/ for the entire article, including tips on employing fill speakers.
Fig. 1 on the previous/upper page, shows two views of an EASE sound model in a large, box-style proscenium venue with a balcony, showing the Broadband Total SPL in the room, which includes reflections from the surfaces in the room and does not represent the direct sound field from the loudspeakers themselves. This is typical of many sound modeling examples and proposed/free designs from loudspeaker factories and suppliers.
Fig. 2 above shows a modeling image from another array modeling program called Soundvision, from L-Acoustics (similar to EASE and others). This coverage map is a more realistic representation of how “comb-filtering” — caused by interaction between multiple loudspeakers — should be displayed (setup in the program). But both of these coverage map examples (in Fig. 1 and Fig. 2) show a 20 dB SPL (sound pressure level) variation. The problem with the marketing approach, of showing almost perfectly consistent sound (Broadband) coverage, is that it is not helpful, as the sound engineering industry standard for displaying SPL variation is 6 dB to 10 dB. Array coverage models should have the dB scale set to look more like the image in Fig. 4.
Showing two times the standard scale, over an average of a wide range of frequencies, and/or multiple arrays at the same time, is not realistic or true. And of course, someone must pay for these free, but basic services.
A recent trend is the offering by pro-loudspeaker factories to do “free” array modeling of coverage for their design/build dealers. We applaud the live-sound speaker manufacturers for taking the initiative and making the investment to create and support these and other programs, and for their willingness to provide a free service to their dealers and end-users, to help ensure that their products get implemented well, to the good of all. However, most of the modeling programs from a brand-name source, only include their own loudspeaker models in their database. We will touch more on loudspeaker array modeling trends in Part 2 of this article series.
Free array modeling has many limitations; the results can be very hard to compare, and the modeling results can sometimes be of questionable value. Limitations with “free” array modeling services from loudspeaker vendors include:
• Vendors may display multiple arrays at the same time (hiding poor coverage)
• Comb-filtering from interaction between loudspeakers may not be displayed
• Limited interaction between loudspeaker vendors & sound designer
• No universal program (various programs use different calculations)
• Lack of consideration of echoes from loudspeakers off of walls
• Lack of objective recommendations (limited to brand offerings)
• Lack of standard scale for how sound coverage is displayed
• Lack of sound system clean power & conduit plans
• Lack of venue site survey by loudspeaker vendor
An expert and independent sound consultant/engineer, should not only provide all of the above services, but should do so in an objective and integrated manner.
What is Array Coverage?
While estimating total sound coverage is fairly intuitive, the understanding of speaker array interaction and psychoacoustics does not come easy. Extensive training and years of array modeling will train a sound designer about loudspeaker interaction and sound design methods. Author Bob McCarthy has written extensive books on the subject. The graphics in the Fig. below are from his book Image from Sound Systems: Optimization and Design by Bob McCarthy. (Copyright 2014 Focal Press. Used by permission. All rights reserved.) show how coverage patterns are measured and shown.
dB SPL Basics
The decibel (dB) is a unit of measurement used to express the ratio of one level/value to another on a logarithmic scale. Suffixes like SPL (Sound Pressure Level) are commonly attached to the basic dB unit in order to indicate the reference value. One decibel, the smallest sound level change detectable to the average listener, is one-tenth of one bel, named (a century ago) in honor of Alexander Graham Bell. A quadrupling of sound power is commonly described as "6 dB" and that 6 dB figure is the pro-sound industry standard for defining the usable limit for a given speaker coverage area.
The decibel (dB) is a unit of measurement used to express the ratio of one level/value to another on a logarithmic scale. Suffixes like SPL (Sound Pressure Level) are commonly attached to the basic dB unit in order to indicate the reference value. One decibel, the smallest sound level change detectable to the average listener, is one-tenth of one bel, named (a century ago) in honor of Alexander Graham Bell. A quadrupling of sound power is commonly described as "6 dB" and that 6 dB figure is the pro-sound industry standard for defining the usable limit for a given speaker coverage area.
What Should Array Coverage Models Look Like?
Loudspeaker array coverage models should look more like the lower image in the above Fig. 4 (from d&b audiotechnik; dbaudio.com). The upper image shows a realistic representation of how “comb-filtering,” — caused by interaction between multiple loudspeakers — should be displayed (with more realistic scale not shown). But the lower image clearly shows how a single “point-source” loudspeaker — with dispersion almost wide enough to cover the venue — has much smoother sound level coverage, across the seating area.
The remaining problem below is the lack of coverage in the front corners. Small, side or front-fill speakers, digitally delayed to synch with the main speakers, will not only provide the needed supplemental sound level coverage in the front corners, but also lower the sound image, making the sound seem to come from the platform (more natural sounding). While low-level interaction between the loudspeakers will occur, it will not be very noticeable. Extremely long/tall rooms benefit from small digitally-delayed loudspeakers in the rear of venue.
Modeling of Venue Acoustics & Directional Realism
Reasonably accurate directional realism and intelligibility of the talent/worship-leaders is another related issue for me; it is quite hard to do in most venues with just Left and Right loudspeakers. Sound imaging with poor directional realism causes cognitive dissonance —essentially stress due to contradictory information. A central array is important for directional realism and optimized speech intelligibility. For more on this subject, and quotes from a few engineers on this directional realism topic; see comments online at line-arrays.com/stereo-or-mono-arrays.html
I feel the need to debunk the trend of thinking that modern loudspeaker arrays can eliminate the need for proper acoustics — that is rarely the case! The right venue-specific loudspeaker arrays, with proper aiming, can minimize the need for extensive acoustic treatment. But selection of the proper loudspeaker array, for a given venue, can rarely be separated from the acoustic space that it operates in. So, allowing vendors to recommend their loudspeakers, without the proper study of how they will cause echoes from room acoustics, is not a complete solution! Reverberation Time should be optimized and long echoes controlled in meeting, performance and worship spaces. More on the proper design of room acoustics, will be covered in the next installment in this article series.
The proper use of a 3D coverage modeling program, to design acoustics and sound, by a credible expert and ideally an objective sound engineer, can help ensure that everybody in your venue can hear the sound loud and clear.
Author David Kennedy operates David Kennedy Associates, a company specializing in the design of architectural acoustics, AV Systems and custom Loudspeaker arrays. Since 1991, DKA has worked on more than 300 projects — including churches, performing arts centers, theaters, commercial buildings and auditoriums. Visit him at line-arrays.com.
Loudspeaker array coverage models should look more like the lower image in the above Fig. 4 (from d&b audiotechnik; dbaudio.com). The upper image shows a realistic representation of how “comb-filtering,” — caused by interaction between multiple loudspeakers — should be displayed (with more realistic scale not shown). But the lower image clearly shows how a single “point-source” loudspeaker — with dispersion almost wide enough to cover the venue — has much smoother sound level coverage, across the seating area.
The remaining problem below is the lack of coverage in the front corners. Small, side or front-fill speakers, digitally delayed to synch with the main speakers, will not only provide the needed supplemental sound level coverage in the front corners, but also lower the sound image, making the sound seem to come from the platform (more natural sounding). While low-level interaction between the loudspeakers will occur, it will not be very noticeable. Extremely long/tall rooms benefit from small digitally-delayed loudspeakers in the rear of venue.
Modeling of Venue Acoustics & Directional Realism
Reasonably accurate directional realism and intelligibility of the talent/worship-leaders is another related issue for me; it is quite hard to do in most venues with just Left and Right loudspeakers. Sound imaging with poor directional realism causes cognitive dissonance —essentially stress due to contradictory information. A central array is important for directional realism and optimized speech intelligibility. For more on this subject, and quotes from a few engineers on this directional realism topic; see comments online at line-arrays.com/stereo-or-mono-arrays.html
I feel the need to debunk the trend of thinking that modern loudspeaker arrays can eliminate the need for proper acoustics — that is rarely the case! The right venue-specific loudspeaker arrays, with proper aiming, can minimize the need for extensive acoustic treatment. But selection of the proper loudspeaker array, for a given venue, can rarely be separated from the acoustic space that it operates in. So, allowing vendors to recommend their loudspeakers, without the proper study of how they will cause echoes from room acoustics, is not a complete solution! Reverberation Time should be optimized and long echoes controlled in meeting, performance and worship spaces. More on the proper design of room acoustics, will be covered in the next installment in this article series.
The proper use of a 3D coverage modeling program, to design acoustics and sound, by a credible expert and ideally an objective sound engineer, can help ensure that everybody in your venue can hear the sound loud and clear.
Author David Kennedy operates David Kennedy Associates, a company specializing in the design of architectural acoustics, AV Systems and custom Loudspeaker arrays. Since 1991, DKA has worked on more than 300 projects — including churches, performing arts centers, theaters, commercial buildings and auditoriums. Visit him at line-arrays.com.