RE-ENFORCEMENT — What is the Goal?

(Author’s Note: The topic for this article was originally suggested by a comment from Barry McKinnon of MC Squared Design Group, North Vancouver, BC., Canada.)

OK, ladies and gentlemen, it’s time for some serious military grade explosive driven myth busting!

MYTH #1: Sounds reinforcement is a 20th century development.

We have a tendency to think of sound re-enforcement as an exclusively 20th-century technology/capability. Well — I hate to disabuse you of your comfortable established beliefs, but for all intents and purposes, the goal was achieved slightly over 2,500 years ago!

The truth behind that statement is complex and delves deep into the history of human endeavor.

The Quest

Ever since the very first public orator (probably a politician, tribal chief or military leader) tried to reach out to more than a few folks in their immediate vicinity, humans have been searching for ways to enhance the distance over which people can hear and understand or enjoy words, music or any number of the other numerous forms of audible communication we use daily.

In the multi-thousands of years spanning the recorded historical records of the human species, this has always been a goal. However, it has rarely been achieved successfully, at least as far as the documentable chronology records would indicate.

That is until sometime around two and a half millennia ago (roughly 400 BC) in ancient Greece, where we find the first documented and verifiable records of a solution to the problem of spoken (sung) word ‘re-enforcement’ being achieved — physically anyway.

The place where that momentous achievement manifested itself is now known as The Great Theater at Epidaurus in Greece. That theater, shown in the photo below, has been accurately and reliably dated to the 4th century B.C. It was built using an arrangement of 55 semi-circular rows and remains the great masterwork of its “architect” Polykleitos the Younger.

Audiences of up to an estimated 14,000 would have been able to hear actors and musicians — unamplified — from even the back row of this unique ancient architectural masterpiece. In fact, they can still do that today as the theater is in regular use and open to visitors and tourists.

What Magic Had Polykleitos Wrought?

Without any modern science or advanced mathematics* let alone the several centuries of ‘acoustics’ research and exploration we have at our disposal, the ancient Greek builders managed to achieve the goal through the material used for and placement of the seats. (*Remember Integral Calculus had not yet been invented and wouldn’t be for nearly another 2+millena. Officially it is recognized to have been created in the 17th century by Isaac Newton and Gottfried Wilhelm Leibniz.)

The hard, scientific proof of their success came when a research team from the Georgia Institute of Technology discovered (in a 2007 study) that the limestone material of the seats provided a filtering effect, suppressing the lower frequencies of voices, thus minimizing background crowd noise (murmur). Further, the rows of limestone seats reflect higher frequencies back into the audience space, effectively amplifying the crucial intelligibility bandwidth and thus enhancing the effect. So, some 2,500 years AFTER it was built we understand what the Greek builders managed instinctively — reducing the perceived Effective Acoustic Distance (more on that topic below).

After Epidaurus’ success, a pattern developed in which such theatres usually consisted of a flat, circular dancing space known as the ensemble area (translated from the ancient Greek) at the foot of a hill, which would be associated with a small temple of Dionysus. The hill then would provide a natural seating area for the spectators (in ancient Greek and later Roman Empire Latin was known as a theatron).

It should be noted that the contemporary term architect was not in use or in the language of the era, at the time of the building of this space, but the term does apply. Throughout ancient and medieval history, most architectural design and construction was carried out by artisans, usually stonemasons and carpenters, who could ascend to the role of master builder. Until quite recently (historically speaking), there was no clear distinction between architect and engineer. In many parts of the world, especially Europe and the Arabic kingdoms of earlier times, the titles architect and engineer were primarily geographical variations that referred to the same person, often used interchangeably. Plans and drawing for buildings were not easily created with the limited physical materials available throughout the middle ages and into the Renaissance, and even as late as the 18th century, most structures continued to be designed and set out by craftsmen, except for some extremely prominent (castles/palaces for example) projects.

Two Millennia of Trying to Recreate the Magic

The Greeks must have known that they had done something very right because they made many attempts to duplicate Epidaurus’ design, but never with the same success. In fact, not only the Greeks, but the Romans and other erudite cultures kept trying for a long, long time.

Well on into the middle ages — Elizabethan England — and most certainly records show as late as the early 20th century, attempts to duplicate what Polykleitos has created continued incessantly, most with at best incomplete success.

MYTH #2: Sound systems create sound.

In one word — wrong.

Any electronic amplification system for use by actual people, properly known as a SOUND RE-Enforcement System, does not and should not create any sound of its own. It has but one singular and very specifically defined purpose.

In fact, it has precisely the same precise and exact purpose that Polykleitos defined for use so long ago — to make the sound of the spoken word and similar sources audible to the entire listening audience, over the whole area occupied by that audience.

The Concept of Equivalent Acoustic Distance

Although the ancient Greeks and all of their many studious adherents did not have a term for what they were doing, it is something modern acoustical science has accurately and quite specifically quantified and defined. It is the concept of Equivalent Acoustic Distance or from here onwards referred to by its acronym of EAD.

Defining Equivalent Acoustic Distance

As defined by John Eargle and Chris Foreman in their book “Audio Engineering for Sound Reinforcement,” Hal Leonard Corporation, 2002 — available here, Equivalent Acoustic Distance (EAD) is:

“Another way to judge the absolute level requirement (for a sound reinforcement system)* is by using the concept of EAD. Consider a string quartet playing in a quiet park for a lunchtime concert. A listener seated 10 feet from the string quartet would hear clearly and enjoy the concert. However, if the string quartet were playing to a large audience, some listeners might be seated 50 feet away. These listeners might find it difficult to clearly hear and enjoy the music.

Now add a sound system. The goal is (should be), to make it possible for the listeners seated at 50 feet to hear as well as the unaided listeners seated at 10 feet. The ten-foot distance then becomes the EAD for the system. Based on this ten-foot EAD, the absolute level goal for the listener at 50 feet becomes the level which the unaided listener hears at 10 feet.”

A secondary question must be “…is the signal to noise ratio adequate? In general, the sound level must be far enough above the ambient noise to be intelligible (for speech) or pleasing (for music).”

Although opinions vary on the specific ratio required, it is generally accepted that an absolute minimum S/N** ratio of 10dB or higher is necessary for a quality result indoors, with at least 15dB being a recommended ratio outdoors. The bigger the ratio the better.

*Italicized content added by author
**S/N is the shorthand used to represent the term Signal to Noise ratio in established symbology for audio systems.

The Goal:

Design, construct and install a system that provides enough support to the program material to create the above defined recognized standard of Equivalent Acoustic Distance (EAD).

Thus, any sound reinforcement system for a HOW space should be subtle enough to just bring everyone within the target EAD of 8-10’ from the pulpit. This is the nominal acoustical equivalent of sitting in the first row of putting you about that distance from the worship leader.

It is also equally important to remember that no re-enforcement systems can help those who are for whatever reason are not capable of speaking in front of a group. They’re intended to make worship leaders and other speakers audible to an entire congregation and not to correct for public speaking deficiencies. In fact, a good system may actually make such issues worse, because congregants will come to expect the first-row equivalent sonics and if the person speaking cannot properly deliver their message to the system to promulgate it will only be more apparent than it was without one.

In Summary

In the end, we still want to do what that stunning theater in ancient Greece accomplished- enhance the distance over which people can hear, understand and enjoy a program. Yes, we’ve added some science and a lot of complex mathematics to the process and given it a name (EAD), but the goal of sound reinforcement hasn’t changed since Polykleitos the Younger designed the Great Theater at Epidaurus.

If the people can hear the message and understand the Word, then you have achieved your goal!