Lincoln once said, "All sound systems are created equal." (Well, okay, so it was Wilbur Lincoln, the chairman of the school board at the small school in Lake Wobegon). Wilbur's wife, Hilda, who was the choir director and organist for the local church, disagreed. "All sound systems certainly are not created equal," she stated. Hilda was right. There are many different types of sound systems.
Voice systems and music systems are the two basic types that are found in schools. If you are involved in the use of a sound system, it is important for you to understand the primary characteristics of each of these types of sound systems.
VOICE SYSTEMS
The primary function of a voice system is to reinforce speech. Podium, lavalier, and handheld microphones are frequently used to achieve this purpose. Two characteristics of a voice system are very important: intelligibility and natural tonal quality.
Intelligibility
A sound system that does a reasonable job of reproducing the human voice so that the speaker can be understood has performed as intended. Simply stated, for a sound system to have adequate intelligibility, the audience must be able to understand what is spoken.
Natural Tonal Quality
In order for a voice to sound natural, a sound system's frequency response must be low enough to reproduce the deep male voice but also high enough to replicate a soprano's highest fundamental tone.
Additional tones, called harmonics, are created by the human voice. These harmonics give the voice an open and airy sound. Harmonics are a primary benefit to the blending of several voices. Without these upper harmonics, voices would tend to sound harsh or strident.
A sound system requires a low-frequency response of approximately 80 Hz for those deep male voices. A soprano's highest fundamental tone is approximately 1100 Hz. The upper harmonics are multiples of the fundamental tones, and a sound system needs a frequency response of at least 6,000 to 8,000 Hz for these tones. A system with 10,000 Hz or higher is preferable.
MUSIC SYSTEMS
Dynamic range and frequency response are two important characteristics of a music system. Let's discuss each of these characteristics separately.
Dynamic Range
Figure 1 is a scale of Sound Pressure Levels (SPL). The louder a particular sound, the farther right it will be on the horizontal scale.
Figure 1
Notice that music has a much greater dynamic range than speech. Dynamic range is the span between the softest and loudest sounds. Music not only has softer levels for some instruments, but it can also produce levels in excess of 20 to 30 dB louder than the human voice. Remember, each increase of 10 dB makes a tone twice as loud. Human speech is generally reproduced somewhere in the 55 to 70 dB range; however, the upper SPL of music will typically range from 65 to 100 dB or higher.
Notice that human speech is different from the singing voice. A singing voice has a much greater dynamic range than the spoken word. Therefore, it is necessary to use a music system to reproduce vocal performance.
Frequency Response
The ability to reproduce the lowest and highest frequencies (i.e. the frequency response range) produced by musical instruments is an important characteristic that differentiates a music system from a voice system. Figure 2 illustrates how certain musical instruments produce much lower frequencies than the human voice. Instruments that produce the lowest frequencies include piano, electric bass guitar, most electronic keyboards, and bass or kick drum. Many background accompaniment music tracks also have very low frequencies. Generally speaking, a bass music sound system should have a low frequency response limit of at least 40 Hz.
Figure 2
Looking again at Figure 2, you will note that most woodwind and string instruments fall within the same frequency response range as human voices. If the sound system has at least an 80 Hz low frequency response, it can faithfully reproduce vocals and many acoustic instruments.
Check Figure 2 again. Notice that many musical instruments have fundamental frequencies higher than that of soprano vocals. This means the upper harmonics of instruments are higher in frequency than their vocal counterparts.
A very good music system needs to reproduce the highest and lowest frequencies produced by musical instruments; therefore, that system will require an upper frequency response of at least 15,000 Hz to reproduce the harmonics of the instrument. A good voice system requires only 8,000 to 10,000 Hz.
Figure 3
Figure 3 shows the bandwidths necessary for different types of systems. The bandwidth tells you the lowest and highest frequencies the sound system needs to reproduce.
WHAT KIND OF SOUND SYSTEM DO I NEED?
Voice and music systems have different requirements for loudspeaker components and electronics. Typically, a music system needs several woofers (large low-frequency loudspeakers) to reproduce the lowest frequencies. It will also need quality high frequency components to generate the upper harmonics. To produce higher Sound Pressure Levels, the music system will require at least 4 to 10 times the amount of amplifier power of a voice system. Of course, this also means the loudspeaker components will need to handle higher power levels.
Typically, a music system will cost more than a voice system for the same facility. Communicate your voice and music reinforcement needs to a knowledgeable sound system design contractor.
