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A Simple Guide To Loudspeaker Technology

The answers to the most commonly asked questions on loudspeakers.


dB Decibel - The units of how loud something is


W - Watts A measurement of power – same as for cookers, light

bulbs, heaters etc


Hz - Hertz One Hz means backwards and forwards once in one

second. Thus, a loudspeaker which is radiating 50Hz

is moving in and out 50 times a second


SPL - Sound Pressure Level Technical term for “how loud!” (Measured in dB)


Decibels (dB): General Information


The dB scale is used when referring to how loud something is. 0dB is regarded as the threshold of

hearing and 110dB is when it starts to hurt!


Double the power = 3dB increase in SPL


Power (in Watts) is related to dB in the following way: For every 3dB increase in SPL you will need to

double how much power is sent to your loudspeaker.

At low power levels, for example 5 Watts to 10 Watts, this is not a problem; however, to get the same

increase at high levels may require you to go from 1000W to 2000W for the listener to be aware of the

same increase in sound level.


To the average ear: 3dB is just a noticeable increase

10dB is twice as loud

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Typical SPL’s


140dB 30m (at the side of the runway) from a military aircraft at take off!

130dB Pneumatic drill at the operator’s position

120dB Ships engine room at full speed

Peak level in bunker at PLASA was 126dB


Very Noisy


110dB Automatic Punch Press at the operator’s position

Average Nightclub level playing mainstream dance music

100dB Platform of Underground station at rush hour with a train


90dB Heavy lorries at 6m distance

Health and Safety upper limit for noise in an average working day




80dB Kerbside of busy street

70dB Loud radio in average domestic room

60dB Restaurant/Department Store




50dB Conversational speech at 1m. General Office noise

40dB Residential area at night. Whispered conversation at 1m


Very Quiet


<30dB Background in TV and recording studios

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Loudspeakers – Some definitions

Power Handling This is probably the most commonly asked and quoted specification.

How many Watts a speaker uses is often regarded as the best way of

assessing how loud it will be. However, the keyword here is uses. A

car engine can use a lot of petrol (Watts) without moving the car very

quickly. In the same way, a speaker can use a lot of Watts without

being very loud!


Sensitivity This parameter tells how much sound you will get per Watt. To

continue the above analogy this is the “mpg” rating of the

loudspeakers. The higher, the better.

Speakers are rated in terms of how loud they will be when 1 Watt is fed

to them. This loudness is measured at a distance of 1 metre from the



Thus, if a speaker is rated as 99dB 1W/1m then you know that if you

put 1 Watt in, at 1 metre distance you will hear 99dB.


Note: This is significantly more than a speaker rated at 96dB 1W/1m,

because you will then need twice as much power to generate the

same sound level. (See Decibels: General Information)


Power Compression The Watts that are not turned into sound get transformed into heat.

This heat increases the electrical resistance of the speaker, making it

harder for the amplifier to drive. The harder you drive the speaker, the

more heat is generated.


To return to the motoring analogy: This is the “aerodynamics of the

speaker”: The faster you drive, the more wind resistance there is.

Thus, even more power is required to make up for this. The lower the

power compression figure is, the better.


Dispersion Horn loaded loudspeakers do not radiate sound in all directions. They

radiate a much greater proportion of this sound within a “dispersion

angle”. This angle is affected by the design of the horn and can vary

quite dramatically from one model to another.


They are quoted in the following manner; 90o x 50o (HxV) or

something similar. This refers to the angles, horizontal and vertical

from which you can move away from “straight out” and still hear the

sound properly. 90o is a right angle, thus the quoted speaker will cover

all areas when mounted in a corner within a 50o vertical (up & down)



Frequency Response The frequencies covered by the loudspeaker. They are measured in

Hz. The human ear can hear from 20Hz to 20000Hz to varying

degrees of sensitivity. The average “shot to pieces” DJ/Rock ‘n’ Roller

ear, probably only manages up to 15000Hz.

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Some Basic Calculations

Watts – dB increase: How many dB increase for full power input relative to 1 Watt

Watts 1 50 75 100 150 200 300 350 600 800 1200W

dB 0 +17 +19 +20 +22 +23 +25 +25.5 +28 +29 +31dB


Maximum Sound Output To calculate the maximum SPL available from a loudspeaker

Max SPL = SENSITIVITY + dB at Full Power – Power Compression at Full Power

Sensitivity and power compression are found from the specification sheet. dB at full power can be

found from the table above. If you cannot find the power compression figure then quote “excluding

power compression” and omit it from the calculation.


Example: Max SPL at 1m = 99 +25.5 = 124.5dB (excluding power compression)


Effect of Distance: To calculate the level at a distance from the speaker relative to 1m:


Distance 1 3 5 7 10 15 20 30 50m

dB 0 -9.5 -14 -17 -20 -23.5 -26 -29.5 -34dB

This can be taken off the figure at 1m to give the level at any of the above distances.


Example: Max SPL at 15m: 124.5 – 23.5 = 101dB (excluding power compression)

NOTE: This does not account for any meteorological changes such as temperature, humidity

or wind direction. However, it provides a good rule of thumb for indoor work.

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