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Home Theater - Science of Sound -  Components

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Speaker Sensitivity , Decibels, Speaker Systems

Determine the amplifier requirement in watts to produce the desired loudness in decibels (dB) What is the maximum output in decibels (dB) of your speakers based on their sensitivity and power rating? Determine amplifier requirements to produce desired volume with multiple speakers and variable distance
Determine amplifier requirements to produce desired volume with multiple speakers, variable distance, and placement Will the new widescreen TV fit? Check out this screenwidth calculator...  
 
Background Info
  • 1decibel (dB) is roughly the smallest change we can perceive.
  • Doubling the amplifier wattage results in ONLY a 3dB increase in volume ("slightly louder").  Switching from a 50 watt amplifier to a 100 watt amplifier or from a 100 watt amplifier to a 200 watt will only increase the volume by 3 dB as long as you use the same speakers.
  • In order to double the current volume requires roughly a 6 to 10 dB increase. A 6 dB increase requires 4 times the power! and a 10 dB increase requires a 10-fold increase in amplifier power.

Perceptions of Increases in Decibel Level

Decibel:  The decibel (abbreviated dB) is the unit used to measure the intensity of a sound.
(Key points):
1) On the decibel scale, the smallest audible sound (near total silence) is ~0-1 dB.
2) A sound 10 times more powerful is 10 dB.
3) A sound 100 times more powerful than near total silence is 20 dB.
4) A sound 1,000 times more powerful than near total silence is 30 dB.

* Near total silence - 0 dB
* A whisper - 15 dB
* Normal conversation - 60 dB
* A lawnmower - 90 dB
* A car horn - 110 dB
* A rock concert or a jet engine - 120 dB
* A gunshot or firecracker - 140 dB

Imperceptible Change -   1dB
Barely Perceptible Change -  3dB
Clearly Noticeable Change  - 5dB
About Twice as Loud - 10dB
About Four Times as Loud  - 20dB

[Any sound above 85 dB can cause hearing loss, and the loss is related both to the power of the sound as well as the length of exposure.]

dB SPL laws

Impact of the various changes on sound levels
Double amplifier wattage - increase of +3 dB
Double number of speakers - increase of +3 dB
Double distance from sound source -  Decrease of  - 6 dB
Halve distance from sound source - Increase of +6 dB
Double driver excursion - increase of +6 dB (note: Equivalent to doubling wattage and # of speakers)

-----Placement of Speakers--------------
Place speaker on the floor - increase of +3 dB -  half loading
Place speaker on floor, and against a wall - increase of +6 dB - quarter loading
Place speaker on floor, near a wall, and in the corner - increase of +9 dB eighth loading