SCHOOL SOUND


South View High School Gym and Baseball Field  Back to main menu

 


How to solve speech clarity issues in a tough acoustic environment

   
 

A case study . . . .

We have all been in gyms, multipurpose buildings, and airports where we could hear the sound system but we could not understand a single word that was said. To understand why and how to correct this problem as in Miller Gym we need to know some basics about how we hear. Think of a typical conversation.

We typically stand about 3 feet apart. There is only one source of sound - that of the talker. His or her voice is the only dominant sound that has our attention. The sound from the talkers mouth is the dominant or direct sound. Any other sound from the talker that is reflected off of walls, floor, or ceiling is the reflected sound. In a "quiet" room or even outdoors, there no reflected or "duplicate" sounds from the talker that interferes with his original speech. In other words, if she says "the house next door", there is no secondary "the house next door" right behind it to confuse your hearing. You hear the one statement with no interference.

In a highly reverberant space like a gym or cavernous airport, sound bounces all over the place creating multiple "echoes" of the same words over and over that arrive at different times and intensities at your ears. (Fig - 1) We hear the original speech or direct sound along with multiple instances or "copies" caused by reflected sound.

If the reflected sound is equal to the direct sound, speech becomes very difficult to comprehend. Saying it another way, if the reverb in the room is so bad to cause a competing noise of sound that is the same amplitude of the original sound, we will have an extremely hard time understanding the spoken or sung word. Its because of how our minds and ears work to interpret the English language.

Our brain is focused on consonant sounds in speech to comprehend what the talker is saying. We rely on consonant sounds in the English language to discern the difference between words like “bean” and “being”. For the consonant sounds to be heard clearly, the direct sound MUST be louder than the reflected sound. The assumption made by novice "sound contractors" and buyers alike, is making the sound louder is all we need to do. NOT TRUE!

A loud sound system has nothing to do with how well it delivers consonant sounds to the listener. Like the three previous failed attempts I saw evidence of at South View to install sound over the years, the common assumption is all we need to do is make sound louder - buy a PA system or what I call "a yelling machine" because thats all it is.

Making sound louder is NOT going to solve the problem. If we increase the volume of the original sound, the reflected sound will increase by the same amount! You have the same problem as before only louder.

Fig-2 shows one way to solve the problem. What we need to do is INCREASE the direct sound relative to the reflected sound. Typically acoustical treatment is placed on the offending wall, floor, or ceiling to minimize the reflected energy in the room. This by default will increase the direct to indirect ratio. This would be great in Miller Gym but its very expensive to cover such a large space with enough material to reduce the reverb to an acceptable level. Plus, any athletic facility requires the treatment to take the abuse of various sports activities at additional costs associated with the type of materials that must be used. Bottom line, acoustical treatment was simply not viable because of the expense..

Fig-3 shows another way. If a speaker system is installed 60 feet from the listener as in typical "cluster" or central speaker systems, the sound from the speaker has an opportunity to strike the walls, floor, and ceiling as it spreads out traveling to the listener. What if we moved the speaker closer to the listener? That means the sound doesnt have a chance to spread out as far before reaching the listener. The goal is to focus sound into the listeners seats before it has a chance to spread out striking reflective surfaces causing secondary images.

Now, theres a lot more to it than just this simple explanation, but you get the idea. The listener hears the direct sound BEFORE he / she hears the reflected sound.

Thats what we want and and what we did at South View High. Instead of a huge speaker system in the middle of the room or at one end, we put 2 rows of speakers down each side and put the listener within 14 feet of a speaker. We added three more over the goals and mid court for the players to hear key calls. (Fig-4,5)

Using this method, the direct to indirect sound ratio was dramatically improved. Speech clarity is excellent regardless of where you sit. You still hear the echo because we did not treat the room for sound reflections. What we did was change the direct to indirect ratio restoring lost consonant sounds over distance. THAT IS THE KEY!!!!

Many sound systems fail because they are not capable of restoring lost consonant sounds over distance. This is what the ARTICULATION COVERAGE TEST© is designed demonstrate.

Keep in mind it takes some acoustic testing and sound engineering skill to choose the right speaker for the specific job. Just using any ole speaker will not work. Every speaker has its own acoustic properties that must be known before it can be considered in any application, particularly something like this. I'm looking at another school where this IDEA was used, but the wrong speaker system. Speech clarity is terrible. The correct speaker system has been chosen and awaiting approval of the project at this point.

The control head (Below) is a removable small portable rack that houses a 4 channel mixer, a UHF digital wireless handheld microphone, and power control switch.

Simply take the case in, open it up, connect the multipin cable to the wall jack, plug in the power, turn on the switch, and you're ready to go. The system can accept any audio source, shown here with an IPHONE.

 
 
  Fig-1 The reflected sound competes with the direct sound from the source of sound - talker or speaker system.
 
  Fig-2 By reducing the reflections in the room with absorption panels the reflected sound is drastically reduced to allow the direct sound to be heard more clearly.
 

Fig-3 Move the source of sound closer to the listener

The direct to reflected sound RATIO is dramatically increased. This is the KEY to speech clarity. We want the listener in the direct sound field of the speaker system.

 

 
  Fig-6 The system is tuned and time aligned with a NEXIA SP digital processor. Power is by YAMAHA. The rack is located in a locked room. The system is powered up and down by remote control from the removable control head operated in the gym.    Fig-4,5 Six speakers spaced over each bleecher
section to cover the seating with overlapping
ARTICULATE COVERAGE ZONES©.

The speech is crystal clear at every seat.
         
   
South View Baseball Field
 

The baseball field was more straight forward.

A similar portable rack was used to house a single amplifier and mixer to power 4 high quality full range speaker systems.

Full range Community speakers were used instead of the typical "PA horns" for far better sound quality.