Sound Equipment Rental & Audio Services in Kansas City

Sound

‘Cause nobody leaves the show hummin’ the lights.

In live performance, we utilize amplified sound to ensure that all of the audience members clearly hear what is presented from the stage, prerecorded music and sound effects.

Audio Sound System

Audio through a sound system begins and ends as a series of vibrations. Vocal cords or instruments create a vibration, and our ears perceive those vibrations and sends signals to our brain for interpretation. The vibrations take the form of multiple sinusoidal waves or sine waves, depending on the frequency of the tone. Audio can be analogous to water. Think of sound waves like ripples on a pond, spreading out from the source. Sound requires some type of medium to pass through, typically air, although it can pass through solid material, liquid, and other gases, but it cannot pass through a vacuum, so it is true that ‘In Space, No One Can Hear You Scream’. Temperature and humidity can also have an effect on how sound travels through the air.

Cupping your hands by your mouth, like using a megaphone, encourages your voice to veer in one direction so it can carry farther, a sound system is an electronic reproduction of this.

Human Hearing

The human hearing range is limited between 20 to 20,000 Hz, at best. There is quite a variation in the hearing range between individuals. The average young person can hear up to 18,000 Hz. Unfortunately, our ability to hear higher frequencies declines with age after 25. By the age of 55, some men can’t hear above 5,000 Hz and some women can’t hear above 12,000 Hz. Women tend to have better hearing than men at high frequencies. It is worth noting that the speaking voice of a man typically has a fundamental frequency between range of 85 to 180 Hz, and a woman 165 to 255 Hz.

Humans have binaural hearing, augmented by the shape of our ears, and how they are designed to capture sound, which allows us to determine the direction from which higher-pitched sound originates. This was useful for hunting, or to avoid being hunted.

The ear’s sensitivity varies significantly with frequency. The human ear is most sensitive to frequencies in the range of 2,000-5,000 Hz. Our hearing has its peak sensitivity around 3,500-5,000 Hz. This frequency is associated with the resonance of the ear canal. At frequencies above 10,000 Hz our hearing sensitivity declines.

Frequencies

Higher frequencies oscillate more rapidly (more times per second) and tend to be more directional due to the size and shape of the sound source. The higher the frequency, the shorter the wave. These higher frequencies can be easily absorbed by soft surfaces like fabrics and even humans.

Conversely, lower frequencies are longer waves, contain a lot of energy, can pass through and around most objects and are not as directional. The lowest frequencies are more felt than heard with the ear, and for that reason, humans have a difficulty determining the direction from which low frequency sound emanates.

Midrange are the frequencies which fall in between Highs and Lows. According to the Laws of Physics: energy cannot be created nor destroyed, and when sound energy hits a surface, what is not reflected is turned into a tiny, imperceptible amount of heat.

Each frequency has a unique wavelength, which is what determines its pitch. More wavelengths completed per second means a higher pitch. Throw a big rock into our pond, you get a big, long wave, which probably will make it all the way to shore. A smaller pebble makes a smaller wave which will dissipate with distance.

Sound System Basics

Signal Flow

Signal Flow is the path sound takes through your system: Input devices (including wireless mics, CD Players, Sound Effect Generators), the Console or Mixer, Processing (including effects like reverb, gates, limiters), Equalizer, Crossover, Amplifiers, and Speakers.

Mixer

The mixer has multiple channel strips which run vertically. These channel strips allow you to modify the signal and ‘mix’ it with other signals to achieve the best overall output. In the mixer, as each input is passed through the preamp, the Gain Knob, which is typically at the top of the Channel Strip, is used to adjust the level of the signal.

Pre-Amp

Through a cable, this small amount of electricity enters the mixer and goes through a preamplifier, which is used to amplify the small amount of electricity into something more robust and usable by audio equipment. The quality of the preamp is probably the most critical component in an audio mixer, because if the preamp isn’t doing a good job, there is no chance of making it better afterwards.

Microphone

The microphone utilizes a diaphragm, known as the ‘Mic Element’ or ‘Mic Capsule’, to capture the vibrations of voice or instrument and converts those vibrations into a very small amount of electrical current, in the form of a sine wave. The mic diaphragm needs to be very sensitive to function effectively, and abuse can degrade that functionality. Tapping on the head of a microphone sends a massive shockwave to the element and is not a good way to test a mic. Instead, one of the best ways to test a mic is to snap your fingers in front of it from the distance the performer will be.

Speakers

At the other end of the system are the speakers, which also contain diaphragms, albeit much larger ones. Speakers have an electrical coil, attached to a diaphragm, known as the Speaker Cone, and the coil resides within or around a magnet. By sending electricity to the coil, it also becomes a magnet, which is either attracted to, or repulsed from the magnet. By sending the electricity as a sine wave (from our console), the diaphragm pushes out and pulls back in at the same rate as the sine wave, creating a vibration of the air in front of, and behind the cone.

It is possible for a single speaker cone to create all frequencies of audible sound; however, it is not the most efficient way to do so. The smaller the diaphragm, the faster it can move back and forth, so small diaphragm speakers (tweeters, horns) are most efficient at creating high-frequency tones. The larger the diaphragm, the more air you can physically move, and these speakers, known as woofers, do better with mid and lower range sound.

Subwoofers

Some systems utilize a specialized large woofer for very low frequencies, known as subwoofers or subs. Subwoofers are designed to allow the speaker diaphragm to move a greater distance within the speaker Basket, to produce the low range tones we call bass. Humans ‘feel’ low frequencies and struggle to discern the direction from which very low frequency sounds emanate, so placement of the Subwoofer is not dictated by the audience’s ears, rather the ability to transmit the vibrations most effectively.

Crossover

The signal that comes from the console going to the speakers contains the entire range of frequencies, so a device called a Crossover is used to separate the highs from the lows before the amplifiers. In a 2-Way system, the crossover allows you to select the point where signal passes to the amplifier for the high frequency speakers, and what passes to the low frequency speakers.

Feedback

One of the biggest issues you will have to contend with is the Larsen Effect, named for Danish scientist Soren Absalon Larsen who discovered it. You probably know the Larsen Effect as the dreaded Feedback. Audio feedback is when an input hears its own output. A signal received by the microphone is amplified and sent out of the loudspeaker. The sound from the loudspeaker can then be received by the microphone, amplified further, and then sent out through the loudspeaker again, creating an ever-intensifying loop. This can manifest as a high-pitched squeal, screech, or low rumble. If feedback is not quickly mitigated, it can overload and damage the system.

EQ the Room

The room equalizer is used to try and reduce problematic frequencies, and to enhance any frequencies the room ‘absorbs’. The best way to ‘EQ’ a room is to use a Pink Noise generator which sends an equal amount of signal at every octave through the speakers. With the help of a sophisticated program using a process called a dual-channel transfer function, we can see the difference between what is leaving the console and what is coming out of the speakers.

Powering the System Up and Down

When powering up your system, start from the beginning of the signal flow: any powered input devices, then console, outboard equipment, with amplifiers being the last devices to be powered on. Powering down is the reverse of that sequence, amps or powered speakers off first, then work your way back. The reason we follow this power-up, power-down procedure is because sometimes when electronics power up and always when they power down, electronic capacitors discharge electrical current. If the amps are still on when you power down the board, you will likely get a loud pop out of the speakers, that can potentially cause significant damage.

Wireless

Wireless Microphones are becoming more challenging to use since the FCC has sold off a large portion of the available spectrum in recent years.

RF Signal

Radio Frequency or RF output of the body pack or handheld transmitter emanates primarily from a relatively small antenna in all directions in radio waves, so the farther the receiver antenna is from the transmitter, the less signal there is to receive. Water is the enemy of RF signals, and humans are essentially large bags of water, so keep receiver antenna well above the audience. The RF signal is line-of-sight, so be sure the antennas are located where they will receive maximum signal.

Diversity Signal

Most wireless systems manufactured today use what’s called diversity, which means the transmitter is sending two signals, A and B, and the receiver seamlessly switches between whichever signal is strongest. Individual receivers come with two small antennas, one for A, and one for B. If that is what you are using, make sure the back of the receivers are facing the stage and the pair of antennas are adjusted to be 45 degrees left and right.

Frequency Agile & Intermodulation

Most wireless microphones are Frequency Agile, meaning if you are experiencing another competing transmission, you can reassign the frequency to eliminate the issue. The assigned frequencies need to be properly spaced to ensure one transmitter does not interfere with another transmitter, which is known as intermodulation. The best way to avoid intermodulation is to utilize the frequency groups set up by the wireless manufacturers.

Mic Placement

Mic placement is also critical to good audio reinforcement. Most wireless systems utilize a very small element, so over the ear, or concealing at the hairline work well for theatre. Clipping a Lavaliere Microphone to clothing can be problematic due to clothing rustle or the performer turning their head away from the element.