Sound Reinforcement Technologies & System Alignment Techniques

14003172UJ908005: Live Audio ProductionLO1

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Name: Angela HillStudent ID: 14003172Groupwise Email: 14003172@uhi.ac.ukProgramme Title and Level: BSc Audio Engineering year 3Student adviser: Andrew WardellTutor: Mark LindsayModule title: Live Audio ProductionDue date: 16/01/15Assignment topic/title Sound Reinforcement Technologies & System Alignment Techniques

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Angela HillBSc Audio EngineeringUHI Perth College2014

Sound Reinforcement Technologies & System Alignment Techniques

Lecturer: Mark LindsayLive Audio Production

Introduction

The purpose of this research is to analyse sound reinforcement technologies and system alignment techniques currently used and demonstrate ways of resolving the various problems that can occur in a venue. A key contributor to live sound within the music industry is a system engineer: responsible for the complete sound experience of a live event. They choose a suitable system optimized for the performers/listeners and provide the mixing engineer with all the necessary tools to balance everything musically. [footnoteRef:1] System engineers install the PA system varying in size/design, theyre transportable and can be calibrated to suit a specific setting with regard to acoustic properties, size/layout of the venue number of individuals performing/attending. System engineers manage the monitor engineer/live sound engineer who ensure performers can hear themselves and sound is managed accordingly to give the best quality.[footnoteRef:2] [1: http://www.prosoundweb.com/article/whats_in_a_title_an_audio_system_engineer_by_any_other_name/ December 2014] [2: https://www.sokanu.com/careers/audio-engineer/ December 2014]

[footnoteRef:3] [3: https://www.google.co.uk/search?q=audio+system+engineer December 2014]

What is a PA system?PA stands for Public Address and has 3 fundamental components:1. Sound source electrical signal representing the sound. E.g. Microphone2. Amplifier strengthens electrical signals produced by sound source allowing loudspeaker to project a sufficient volume we can hear.3. Loudspeaker converts impulses generated by the amplifier to vibrations in the air our ears recognise as sound.3

[footnoteRef:4] [footnoteRef:5] [4: https://www.google.co.uk/search?q=microphone&amplifier&loudspeaker December 2014] [5: http://www.hometheaterhifi.com/volume_1_1/v1n1spk.html December 2014] 12

A PA system serves to provide audiences with a clear and pleasant sound. Placement is crucial to avoid feedback (caused by the proximity between microphones and loudspeakers, causing the signal being fed through to be looped and amplified) [footnoteRef:6] and comb-filtering (reflections colliding with original source causing summing/cancelation of certain frequencies)[footnoteRef:7]. Small venues backline serve as monitors for performers & a sound source for the crowd. [footnoteRef:8] Bigger venues backline would be miked up and put through the PA. [6: http://electronics.howstuffworks.com/gadgets/audio-music/question263.htm December 2014] [7: http://www.soundonsound.com/sos/jun13/articles/qanda-0613-3.htm December 2014] [8: http://www.livesystems.co.uk/band-tips.html December 2014]

Most speakers used in live sound are passive - an amp is required to drive them. Active require mains close by. To manage volume leaving the speaker an SPL meter is used because its more accurate than your ears. Health & Safety regulation state that there are 3 action levels the 1st is individual exposure 85dB (A). Peak is an SPL reaching a high of 200 Pascals and 2nd is individual exposure 90dB (A). An employer must make there employee aware of legislation and provide suitable hearing protection if necessary. [footnoteRef:9] [9: http://www.legislation.gov.uk/uksi/1989/1790/regulation/2/made December 2014]

Below are various types of SPL meters, they can be handheld, built into equipment and displayed on venue walls. [footnoteRef:10] [10: http://www.google.co.uk/search?q=spl+meter&espv=2&biw=1334 December 2014]

The purpose of the SPL meter is to visually represent the loudness of noise in decibels so engineers can monitor levels, recognise fluxes in SPL & make certain changes to maintain correct levels. It will also be of interest to people exposed to noise as they too can see if dangerous levels are being reached causing damage to their ears.[footnoteRef:11] [11: http://prosoundweb.com January 2015]

The range of human hearing is 20 Hz 20 kHz, if calibrating a sound system we use pink noise played through the loudspeakers because its understood by our ears as every single frequency across the 5 octave bands, low, low-mid, mid, upper-mid and high, it also has identical energy per octave. [footnoteRef:12] [12: http://www.acousticfields.com/white-noise-definition-vs-pink-noise/ January 2015]

How do you know what frequency is problematic and requires EQ? Spectrum Analysis, a significant tool enabling you to see graphical displays of how loud frequencies are produced. In a venue you would measure sound at various points to monitor if the frequency has exceeded the SPL.

Many variations in software exist to generate such graphical displays of the perceived loudness signals. The Smaart analyser Dual-channel, FFT-based software platform audio engineers use to view frequency content of signals or measure response of electrical & electro-acoustic systems. [footnoteRef:13] [13: http://www.rationalacoustics.com/smaart/about-smaart/ January 2015]

Smaart has a waterfall plot allowing you to easily spot spikes in the frequency spectrum making it easier to carry out necessary EQ. Once you assess the spectrum you modify the processor, adjust parameters and re-analyse until flat. [footnoteRef:14] [14: http://imagine.gsfc.nasa.gov/science/index.html January 2015]

[footnoteRef:15] [15: http://smaart.en.softonic.com January 2015]

A special microphone is required to measure data for the spectrum analyser which has a linear gain reaction across all frequencies. Hardware such as Field Fox handheld RF and Microwave analyser can be used. [footnoteRef:16] Typically a combination of hardware and software is required Powerful laptop, measuring microphone, pro soundcard and software. [16: http://www.keysight.com/en/pc-1742042/fieldfox-handheld-rf-and-microwave-analyzers?nid=-33903.0&cc=GB&lc=eng January 2015]

Room EQ wizard audio measurement software. [footnoteRef:17] [17: http://www.hometheatershack.com/forums/spl-meters-mics-calibration-sound-cards/10001-rew-cabling-connection-basics.html January 2015]

[footnoteRef:18] [18: https://www.hometheatershack.com January 2015]

The crossover is an intelligent processor, automatically splitting the signals into different frequency bands. Below is a simple crossover division of frequencies: DBBassMid

FHigh

If space is too big at the crossover therell be an obvious drop in volume, if its too small volume will jump. The crossovers design is advanced, if tampered with inferior sound might be produced due to speaker designs requiring specific signal feeds. Venues catering for large scale events use line array speakers which is a vertical speaker stack of drive units. [footnoteRef:19] Theyre suspended from the ceiling usually hoisted in position, stacks can be 3-15 units high and wider audience areas can be covered. Example below: [19: http://www.soundonsound.com/sos/jun12/articles/choosing-pa-systems.htm January 2015]

[footnoteRef:20] [20: http://www.prosoundweb.com/article/around_the_corner_setting_up_multiple_line_arrays_for_wide_venues/studyhall January 2015]

Phase alignment cannot be completely removed, its simply moved to a place that wont affect the listening experience of the audience. Its achieved by placing 2 point source speakers/arrays pointing exact same direction so eventually the sources travel equal distances covering identical zones and sinusoids of matching frequencies cross creating phase interference.[footnoteRef:21] [21: http://msp.ucsd.edu/techniques/v0.11/book-html/node7.html January 2015]

Systune 1.3 software [footnoteRef:22] lets you view interaction of phase and points where interference will occur. [22: http://systune.afmg.eu/index.php/st-software-en.html January 2015]

[footnoteRef:23] [23: http://afmg.eu January 2015]

Some engineers like to use lasers checkpoint because their lights sinusoids are of identical phase, meaning laser crest line up same for troughs.[footnoteRef:24] [24: http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gateway/home_energy/light_and_lasersrev4.shtml January 2015]

www.hometheatresound.com Speaker placement must spread further apart & change angles to minimise phase interference. [footnoteRef:25] [25: http://www.slideshare.net/cscottthomas/ch-17-linear-superposition-and-interference-online January 2015]

Time alignment distortion is remedied by adding delay to the crossover. Crossovers calculate this themselves providing you give them the distance they can determine the results accurately. [footnoteRef:26] [26: http://www.indiana.edu/~emusic/etext/acoustics/chapter1_speed.shtml January 2015]

Using spectrum analysis you measure distant speakers individually by placing the SPL microphone 2m in front to produce a solitary frequency in order to balance the gain. Phase must be inverted at the output and time delay is augmented till the spectrum analyser displays a reduction in gain. This is the point where phase is inverted again and time alignment of speakers is achieved. [footnoteRef:27] [27: http://sound.westhost.com/ptd.htm#s1 January 2015]

[footnoteRef:28] [footnoteRef:29] [28: http://engineeronadisk.com ] [29: http://Galaxyzooforum.org January 2015]

[footnoteRef:30] [30: http://audioholics.com January 2015]

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