Home Theater - Science of Sound -  Components

home theatre

Impact of Multiple Speakers , Distance, and Placement

Enter your Speaker Sensitivity (SPL)   (dB 1W/1M)
1 watt/1meter SPL (sound pressure level) - Usually printed on the back of your speaker cabinet.
Highly sensitive speakers (sensitivity >95 SPL or even > 100), can produce extreme sound levels with minimal power. 
Speaker placement within room:
Amplifier power (watts) (watts)
Number of speakers:
(Note: Program assumes each speaker has the same sensitivity)
Listening position (number of feet from speakers) feet

Important Background Information

  • 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.

Sound Levels

barely audible 0 dB - Threshold of hearing
10 dB - Rustling leaf
20 dB - very quiet  - Quiet room
30 dB - Soft whisper
40 dB Quiet library
50 dB Average home
60 dB - moderately loud. Ordinary conversation, Light traffic.
70 dB - Vacuum cleaner, Heavy traffic
80 dB - Very loud.  Garbage disposal.
90 dB - Diesel truck
100 dB -  Snowmobile, Motorcycle, Train, garbage truck, 15th row of rock concert, chainsaw,
          Level - 5 to 10 using earbuds and a standard IPOD or walkman.  Uncomfortably loud. 
110 dB - Jackhammer, power saw, symphony orchestra, front row of rock concert, Car horn.  Extremely loud
120 dB - Rock concert, Jet engine.  Painful.  Threshold of pain.

Perceptions of Increases in Decibel Level

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

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

Permanent Hearing Loss

Decibel Exposure Time Guidelines Accepted standards for recommended permissible exposure time for continuous time weighted average noise, according to NIOSH and CDC, 2002. Each 3 decibel (dB) increase above 85 decibels cuts the permissible exposure time in half.   Exceeding these times will likely result in permanent hearing loss.   
Continuous dB Permissible Exposure Time
85 db 8 hours
88 dB 4 hours
91 db 2 hours
94 db 1 hour
97 db 30 minutes
100 db 15 minutes
103 db 7.5 minutes
106 dB 3.75 min (< 4min)
109 dB 1.875 min (< 2min)
112 dB .9375 min (~1 min)
115 dB .46875 min (~30 sec)