Docstoc

BASIC SOUND REINFORCEMENT

Document Sample
BASIC SOUND REINFORCEMENT Powered By Docstoc
					According to Dale Shelton
Portions of this material were gleaned from the following sources and used with their permission: Peavey Advanced Sound Reinforcement Seminar, Peavey Corporation, (Thanks to Marty McCann) Rane Technical Notes, Rane Corp, (Thanks to Dennis Bohn) Sound and Light Team (SALT) Training Manual, Advent Lutheran Church, Boca Raton, FL (Thanks to Ken Ellis)

COURSE OBJECTIVES
• • • • • • • • • Create a Team of Transparent Sound Techs Basic Math and Electronics Nature of Sound Electronic Domain Propagation Components of a System Interconnection Soldering & Cable Fab Other Communications Systems

Transparent Sound Techs
• Pray about it!
– Pray before each event that you glorify God

• Have a servant’s heart
– NEVER upset the Pastor or any performer before the service or program

• Get the training you need

Pray without ceasing. - 1 Thessalonians 5:17

Transparent Sound Techs
• Work as a Team
– Support, help, and encourage each other – Give and accept criticism gracefully

• Help the performer be comfortable
– Not be distracted by the sound system – OR Sound Technician

• SMILE (it really does make a difference)
A cheerful look brings joy to the heart, and good news gives health to the bones. - Proverbs 15:30

Transparent Sound Techs
• Never become the focus of the audience • The system should realistically reproduce sounds as they occur
– – – – Sounds should be natural Sounds should be clear Quiet sounds should be audible throughout Loud sounds should not be too loud
If it is possible, as far as it depends on you, live at peace with everyone. - Romans 12:3

Transparent Sound Techs
• Give out a complement or word of encouragement now and then • Be prepared well before the program starts
– Check-out the sound system before performance – Check mics, instrument, monitor levels, and queue tapes – Obtain a sequence of events or script
A hot-tempered man stirs up dissension, but a patient man calms a quarrel. Proverbs 15:18

Transparent Sound Techs
• NEVER antagonize the performers! • Pay attention during the entire service
– Don’t allow yourself to be distracted – Take your service seriously – If someone picks up the wrong mike, make sure you are there to turn it on. – Listen to the program & make needed adjustments
A fool gives full vent to his anger, but a wise man keeps himself under control. - Proverbs 29:11

Transparent Sound Techs
• Pay attention during the entire service cont...
– Be prepared for unexpected changes. If the performer moves to an area that is not lit, make sure you are there to adjust the lighting (if applicable)

• Strike the system
– Neatly stow the equipment after the event – Take good care of God’s equipment
Everything devoted is holy to the highest degree; it's God's inalienable property. – Lev 27:28

Basic Math and Electronics
• Terms:
– – – – – – – Voltage (E) Current (I) Resistance (R) Power (P) Impedance Inductance Capacitance

Basic Math and Electronics
• Voltage is the unit of measurement for electricity and it is analogous to electrical pressure or the potential to perform work. • Voltage is sometimes referred to as emf or electromotive force.

Basic Math and Electronics
• Current is the rate or number of electrons that flow past a given point in an electrical circuit and is measured in amperes.
– Direct current flow (DC) occurs when the electrons flowing in an electrical circuit path move in one direction only – Alternating current flow (AC) occurs when the electrons flowing in an electrical circuit path continuously change directions.

Basic Math and Electronics
• Resistance is the opposition to DC electron flow and is measured in ohms. • Impedance is the opposition to AC electron flow and is measured in ohms.
– Varies with frequency and the capacitance or inductance of the electrical circuit.

Basic Math and Electronics
• Ohm’s Law: An electromotive pressure of one volt in a electrical circuit with one ohm of resistance will result in one ampere of current flow and one watt of power.

Basic Math and Electronics
• Inductance is that property in a circuit that offers high opposition to current flow at high frequencies.
– An inductor is a coil of wire that offers high opposition to current flow at high frequencies and low opposition to current flow at low frequencies.

Basic Math and Electronics
• Capacitance is that property in an electrical circuit that offers high opposition to current flow at low frequencies.
– A capacitor consists of two electrical plates or conductors separated by a dielectric or something that will support an electrical charge. – A capacitor offers high opposition to low frequency current flow and low opposition to high frequency current flow.

Basic Math and Electronics
• Power in watts is equal to the voltage squared divided by the resistance of the load.
402 = 40 x 40 / 4 = 1600 / 4 = 400 watts
4

• Power equals current times voltage.
40v x 40Amps = 1600 watts

Basic Math and Electronics
40 v

Amplifier Amplifier “rail” voltage Resistor (Speaker in our application)

Ground

Basic Math and Electronics
40 v 8 ohm

? Watts
40 V x 40 V / 8 ohm = 1600 / 8 = 200 W

Basic Math and Electronics
40 v 4 ohm

? Watts
40 V x 40 V / 4 ohm = 1600 / 4 = 400 W

Basic Math and Electronics
40 V 4 ohm

______ W _____ A

40 v

8 ohm _____ W _____ A

Basic Math and Electronics
8 ohm 40 V 8 ohm ______ W ______ A

Basic Math and Electronics
8 ohm 8 ohm

40 V
8 ohm 8 ohm

______ W

______ A

Basic Math and Electronics
8 ohm 8 ohm

40 V
8 ohm 8 ohm

_______ W

______ A

Basic Math and Electronics
• Logarithmic Scale
– Easy way to represent huge and complex numbers 1000000 100000 10000 1000 100 10 1

106 105 104 103 102 101 100 Log(100) = 2 Log(1000000) = 6 Log(100000) = 5 Log(10) = 1 Log(10000) = 4 Log(1) = 0 Log(1000) = 3

Basic Math and Electronics
• Logarithmic Scale
– – – – 10 100000 871291812 11298

Basic deciBels
• The Decibel Scale involves changes in the electrical gain (volume), or the amplification of the audio signal, that results in changes in the intensity of the Sound Pressure Level (SPL), perceived by the listener. • Gain changes in dB and the resultant changes in system power and voltage to the loudspeaker:

Decibels dB
Changes in: Audible Decibel Perception + dB Just Noticeable

Power Times Times Times

Voltage % % %

+ +

dB dB

Moderate Twice as Loud

Decibels dB
Changes in: Audible Decibel Perception +3 dB Just Noticeable

Power 2 Times 4 Times 10 Times

Voltage 40% 100% 300%

+6 dB +10 dB

Moderate Twice as Loud

dB Examples in Specifications
Loudspeaker Frequency Response: 50 Hz - 17.5 kHz +/- 3 dB Power Amplifier Frequency Response: 10 Hz - 20 kHz +/- 0.5 dB Common Mode Rejection Ratio: -100dB Equivalent Input Noise: -129 dB Equalization or Tone Control Range of Boost & Cut: +/- 15 dB Signal to Noise: -105 dB Crossover Slope: -24 dB/Octave Amplifier Gain: 30 dB Power Amp Sensitivity: 1.4 dB Loudspeaker 1 Watt 1 Meter Sensitivity: 101 dB Dynamic Range: 120 dB 0 dBv = 1 volt 0 dBm = 0.77456 volts

The Decibels’ most Important use in System Design
• The Inverse Square Law • High Frequency CD Horn -6 dB Patterns of Coverage

Inverse Square Law:
• The sound eminating directly from a source will change in sound pressure level (SPL), directly proportional to the inverse of the square of the distance away from the source.
– Sound drops 6 db in level (SPL) each time you double the distance away from the source.

Inverse Square Law:
AREA OF A CIRCLE: = Radius Squared x Pi AREA OF 1/2 CIRCLE: = 1/2 Radius Squared x Pi

Circle
Radius 4 ft = 8 ft = 16 ft = 32 ft Area 25.13 ft2 100.53 ft2 402.12 ft2

= 1,608.49 ft2

Sphere
Volume Of A Sphere: = 4R2p Volume Of 1/2 A Sphere: = 2R2p

Area Of 1/2 Sphere
Radius 4 ft 8 ft 16 ft 32 ft = = = = Area 100.53 402.12 1,608.49 6,433.98 ft3 ft3 ft3 ft3

Nature of Sound
• Introduction to Sound Reinforcement
– – – – – Sound as Vibrations of Air Molecules (VPS) Musical Sound + Speech Sound = Audio Electronic Audio Signals Frequency and Hertz (CPS & Hz)

Nature of Sound
• Introduction to Basic Decibels
– Human Auditory Perception and the Decibel Scale – Rules of Thumb for the Decibel – 30 Volt 100 Hz sound wave verses an unknown sound wave – Dr. Flecther & Dr. Munson - Perception in decibels

Nature of Sound
• Velocity
– Common value is 1132 Feet Per Second

Frequency

Wave Length

• Wavelength

l=

Velocity Frequency

160 320 640 1280 2560 5120 10240 20480 40960 81920

Hz Hz Hz Hz Hz Hz Hz Hz Hz Hz

7.1 3.5 1.8 0.9 0.4 0.2 0.1 0.1 0.0 0.0

Ft Ft Ft Ft Ft Ft Ft Ft Ft Ft

Nature of Sound
• Sound Pressure
– Force exerted by a sound wave – Sound pressure is measured in N/m2. – The logarithmic response of the ear makes it useful to map decibel value

20log10(

p p0

)dB

Nature of Sound
• 0dBA The threshold of audibility
– A reference value must be used
• p0 • Lowest sound level which can be heard by the human ear is 2x10-5 N/m2, the Internationally agreed level for p0. This is the value which represents 0dBA (deciBels Acoustic).

Nature of Sound
Description Threshold of Feeling Large jet aircraft (40m) Large orchestra (5m) Tube Train passing Inside Tube Train Noisy Office Conversational speech Reading From a Book (1m) Average Office Quiet Office Public Library Whisper (2m) Quiet Whisper (1m) Threshold of audibility Sound Pressure N/m2 63.2 20 6.3 2.0 0.63 0.2 0.063 0.02 6.3x10-3 2x10-3 6.3x10-4 2x10-4 6.3x10-5 2x10-5 dBA 130 120 110 100 90 80 70 60 50 40 30 20 10 0

Nature of Sound
• Acoustical Properties of Sound
Velocity Wavelength Sound Fields Free Field Direct Field In-Direct Field Reverberant Field Critical Distance

Nature of Sound
• Time Delay Calculations
– Delay is required if the sound paths to a point differ by a period of more than 40 ms (40 ft at 14°C). – To maintain the directionality of the implied source the "direct" sound should arrive first (Hass Effect).

Nature of Sound
• Acoustical Properties of Sound
– Propagation of Sound Waves
• Omni-Directional • Hemi-Spherical • Conical

Nature of Sound
• Acoustical Properties of Rooms
Finding Critical Distance Reflections Standing Waves Room Modes Boundary Cancellation Absorption Diaphragmatic Absorption Diffraction Diffusion Room Treatment

Nature of Sound
• Acoustical Properties of Rooms
– Reverberation Time
• Formula developed by W.C.Sabin, 19th century • Unit is a measures absorption from 0 to 1
– Adsorption coefficient of 0 indicates a material that reflects sound totally
– Coefficient of 1, a material that adsorbs sound totally

Nature of Sound
• Acoustical Properties of Rooms
– Sabin’s Formula
• Rt • VR = Reverberation time = Volume of the room in m3

• S1...Sn = The Sabin coefficient for a particular material • A1...An = Surface area of the material in the room in m2 • Sa
Rt

= The Sabin coefficient of air
= 0.16VR  (S1A1) … (SnA) + (SaVR)

Nature of Sound
• Acoustical Properties of Rooms
– Sabin’s Formula cont...
Typical Absorption Coefficients 250 Hz Brickwork 0.04 Concrete 0.02 Plaster - Solid backing 0.03 Carpet - Thick pile 0.25 Air - per m3 0 Audience in Upholstered Seat 0.04 Wooden Seat - Empty 0 Rostrum 0.1 500 Hz 0.02 0.02 0.02 0.05 0 0.46 0.15 0 1000 Hz 0.04 0.04 0.03 0.05 0.003 0.46 0 0

Nature of Sound
• Sound Insulation
4" (100 mm) brick, plastered both sides 9" (230 mm) brick plastered both sides 4" brick walls with 2" (50 mm) cavity, plastered both sides 6" (150 mm) concrete block wall, solid and plastered 3/8" gypsum wall board 1/2" gypsum wall board 5/8" gypsum wall board Partition of 3/8" plastered gypsum wall board with 4" cavity 40 dB 52 dB 56 dB 50 dB 26 dB 28 dB 31 dB 43 dB

Nature of Sound
• Loudspeaker Q
– A measure of a loudspeakers "throw” – Calculated from the horizontal and vertical beam angles measured at 6 dB down point – Loudspeakers with a very wide beam will have a low Q and those with a narrow beam will have a high Q

Nature of Sound
Q=
sin
–1

(

180 sin(AH)sin(AV) 4

)

– AH = Horizontal beam angle in degrees – AV = Vertical beam angle in degrees
SPEAKER TYPE Mid/Low Frequency Unit Line Source Column HF Horn HORIZ 180 180 40 VERT 180 40 40 Q 2 9 26

Nature of Sound
• Articulation Loss
– Most vocal clarity is contained in consonants. – Early research with telephone systems indicated that if 15% or more of the consonants were lost the speech intelligibility would be poor – The main cause of this mussying of the sound is the interaction of the direct sound (from the loudspeaker) and the reverberated sound.
• Monitors set too loud are reverberant when heard in front of house

Nature of Sound
• Articulation Loss
200d2Rt2(n+1) %Acons = VRMQ
%Alcons = The percentage of lost consonants d
Rt n

= The distance from the loudspeaker to the furthest member of the audience
= Reverberation time = The number of loudspeaker groups

VR Q M

= Volume of the room in m3 = The Q of the loudspeaker groups = Usually 1, more accurate M=(1 - average absorption coefficient of the room) x (1 - average absorption coefficient of the area covered by the loudspeaker)

Nature of Sound
• Constant Directivity Horns’ angle of coverage are determined by the -6 dB down points of the horn in the Horizontal and Vertical planes. • The angles of coverage are the points that measure -6 dB less than the onaxis measurement.

Nature of Sound
• Place speaker(s) to achieve a barely perceptible change in volume (±3dB)
100 dB on axis at 1 meter 6.5 Ft

52.9 Ft
96 dB

7 Degrees

13 Ft

11.5 Ft
81.9 dB 11.5 - 52.5 Feet = +/- 3dB

52.5 Ft
75.8 dB

65.9 Ft

Nature of Sound

Electronic Domain
• The Electronic Audio Signal Domain
– – – – – – – – Voltage Current Resistance AC Impedance Power Ohm's Law Calculating Power Output D D T / Compression

Electronic Domain
• Amplification in General
– – – – – Electrical Gain Power Supply DC Voltage Rails Clipping Headroom General Gain Stages

Electronic Domain
• Amplification is the increase in electrical level (Gain) of a signal. • The microphone’s signal level is increased by the subsequent gain stages of the audio system. • Amplification occurs because within any gain stage is a Power Supply that allows the signal to pass through a Positive and Negative voltage window. • The audio signal is said to swing between the two (+/-) voltage rails of the amplifier stage.

Electronic Domain
• The maximum positive and negative voltage swing available are refered to as the “voltage rails” or limits. • When the signal reaches either voltage rail it is said to Clip. • Amplifier clipping is the most common cause of distortion. • Headroom is defined as the difference between the average signal voltage level and the maximum level at clipping.

Electronic Domain
CLIPPING

} HEADROOM

Electronic Domain
• Signal Flow
– General Identification and Sequential Placement of Components:
• • • • • Microphones / Sources Pre Amp / Noise-Gate / Limiter / Feed-Back / Mixer Signal Processors Power Amplifiers Loudspeakers

Electronic Domain
• Signal Flow cont...
– – – – Operating Levels Component Hookup Unbalanced & Balanced Cable Loudspeaker Cable

Electronic Domain
• Microphones
– Types:
• • • • • • • Pressure Gradient Velocity Dynamic Neo-Dynamic Condenser and Electret Condenser Ribbon Boundary

Electronic Domain
• Microphones cont...
– – – – Pick-up Patterns Proximity Effect Microphone Placement Applications Polarity

Microphones Application Hands-On Workshop

Electronic Domain
• Mixers
Balanced Inputs Line Inputs Pre Amp \ Input Gain Channel Patch \ Insert Monitor Sends Types of Equalization: Active EQ Passive EQ Shelving EQ Peaking / Dipping, Boost / Cut Paramid Parametric EQ Effects Sends Aux Sends

Electronic Domain
• Balanced Lines
– – – – – – EMI - Electro-Magnetic Interference CMRR - Common Mode Rejection Ratio Electronic Balanced Inputs Transformer Balanced Inputs Balanced Outputs Ground Loops and Pin 1 Lift

Electronic Domain
• 70 Volt Distributed-Line Systems
– – – – – – High Current Signal Loss Step-up Transformers 70 Volt via Bridge Mode Line Matching Transformers Selecting Input & Output Taps Calculating SPL

Electronic Domain
• Electrical Power Distribution
– – – – – – Electrical Safety NEC - National Electrical Code 120VAC 60 Hz Single Phase U.S. Commercial Electrical Distribution Large System and Ground Loops A Studio Performance Solution to Ground Loops

Electronic Domain
• Power Amplifiers
– – – – – – Specification Definitions: Sensitivity Output Power Minimum Load Impedance Current Limiting Headroom

Electronic Domain
• Power Amplifiers
– – – – – Dynamic Headroom “DDT” Signal to Noise Ratios Frequency Response Total Harmonic Distortion

Electronic Domain
• Power Amplifiers
– – – – – Damping Factor Slew Rate Amplifier Classes Power Consumption Power Amplifier AB Comparison

Electronic Domain
• Is is possible to get 400 watts from a 280 watt amplifier?
– RMS volts = .707 X Pk to Pk – Sine wave is at right – Root Mean Squared is the power under the curve
40 volts

0 volts

Electronic Domain
• Is is possible to get 400 watts from a 280 watt amplifier?
– The power, shown in blue is what drives the voltage up – Assuming 40VDC power supply rails, we have 40 * .707 = 28.28 VAC(or RMS)

Electronic Domain
• Is is possible to get 400 watts from a 280 watt amplifier?
– Assuming our power supply is 10 amps, pwr = Volts * amps so:
282.2 watts = 28.28VAC * 10A

Electronic Domain
• Is is possible to get 400 watts from a 280 watt amplifier?
– HOWEVER: If we drive the signal to clipping, the area under the curve gets a LOT larger.

Electronic Domain
• Is is possible to get 400 watts from a 280 watt amplifier?
– Computing the area under a square wave is easier, no need for trigonometric conversion, it’s equal to the rail voltage

Electronic Domain
• Is is possible to get 400 watts from a 280 watt amplifier? YES!
– VAC = 40 SO 400pwr = 40VAC * 10A

• CLIPPING IS BAD
– Especially for speakers

Electronic Domain
• Loudspeaker Transducer Technology
– Basic Construction – Loudspeaker Enclosure Types
• • • • • • Direct Radiators Infinite Baffled Vented Boxes Horn Loaded Straight Horn Folded Horn & Vented Horn Resonant Bass Systems

Electronic Domain
• High Frequency Horns & Compression Drivers
– – – – – – – Why We Need Them How They Work Motor Structure Phasing Plug Cut-Off Frequency Exponential Radial Horns Constant Directivity Horns

Electronic Domain
• Constant Directivity Horn Equalization
– – – – – Driver Mid-Band Sensitivity High Frequency Roll-Off High Frequency Compensation Passive Crossovers Active Crossovers

Propagation
• Decibels and Sound Engineering
– – – – – The Inverse Square Law Loudspeaker Sensitivity Logarithm Decibel Calculations Power = 10 x Log Distance, SPL, Voltage, & Current = 20 x Log

Propagation
• Loudspeaker Placement
– – – – – – Room Considerations Importance of Aiming the High Frequency Horns Don’t Overlap Constant Directivity Horns Trapezoidal Box Considerations Mutual Coupling Woofer Arrays

Propagation
• Loudspeaker Placement
– – – – – – Horizontal Coverage Near and Far Field Coverage Cost Effective Bridged Array Delayed Loudspeaker Systems 0.9 Feet per millisecond The Haas Effect

Propagation
• Bi-amping & Triamping Sound Systems
– Dr.’s Fletcher and Munson Revisited – Composite Waveform of Low & High Frequency (100 Hz/1000 Hz) – Demonstration of a Bi-amped versus a Full Range Speaker System

Components of a System

Interconnection

Soldering & Cable Fab

Other Communications Systems
• Typical Components
– – – – – – – RJ-11 RJ-45 66 Block 110 Block Cat V Hub Tools

Summary
• • • • • • • • Create a Team of Transparent Sound Techs Nature of Sound Electronic Domain Propagation Components of a System Interconnection Soldering & Cable Fab Other Communications Systems


				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:118
posted:11/15/2009
language:English
pages:92