Loudspeaker Efficiency and Amplifier Loudness

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Guitar Amplifier Loudspeakers- Efficiency and Loudness

Transducers are the weak link in any audio chain - by transducers we mean the devices that convert one form of audio signal to another, usually that conversion is mechanical to electrical and back. So for the guitar player that means the guitar Pickup and the Loudspeaker or Drive Unit. These two units can make the difference between sounding OK and sounding Great. The Pickup is out of the control of the Amp manufacturer but not the drive unit.

What aspects of the design are we looking for, well there is the robustness of the chassis, the quality of assembly, the selection of the cone material, cone construction and fixing to chassis and finally the magnet assembly. Magnets used in loudspeakers whether solid metal or ferrite are composed of minerals that have seen rapid increases in prices in recent years. Low cost amplifiers achieve the required economies by using loudspeakers fitted with small magnets.

Sensitivity(dB)

Power Ratio

Power(W)

(GP4) 100

1.0

30

99

1.3

38

98

1.6

48

97

2.0

60

96

2.5

75

95

3.2

95

94

4.0

120

93

5.0

150

92

6.3

189

The table shows the effect of smaller magnet size on the effective loudness of a guitar amplifier. The top line is the reference of the GP4 Amplifier and its’ G12H drive unit. To get the same volume as a GP4 Amplifier, for each 1 dB drop in speaker sensitivity, the Amplifier power needs to be increased by just over 30%. 97 dB sensitivity is not unusual for many drive units and if one of these were fitted in the GP4 Amplifier, the output amplifier would need to be increased to 60 W. Many small low cost amplifiers are fitted with drivers with sensitivities nearer to 92 dB, and as can be seen from the table these would need an amplifier power of nearly to 200 W to sound as loud.