Acoustic noise is usually perceived as being how 'loud' a machine appears to a listener. To compare the 'loudness' of products, the International Standards Authority (ISO) has produced a number of specifications (including ISO 7779 and ISO 9295) that define acoustic noise terminology and how it can be measured, and a specification (ISO 9296) defining how the measured values should be declared in a consistent way. ISO has not, however, laid down any acoustic noise limits that IT Equipment (ITE) should meet; this has been left to government and commercial authorities to set.
The specifications describe two measures of acoustic noise, Sound Power and Sound Pressure. Sound Power is effectively the total 'loudness' of a device while Sound Pressure is the measure of noise at a point in space. For Sound Power and all Sound Pressure positions, there are two measurement modes; idle, where the ITE is turned on and operational but not doing useful work; and operational, where the ITE is doing useful work (e.g. disk access). Sound Power is not affected by a change in environment whereas Sound Pressure is affected, since extraneous acoustic noise will affect the measurement.
Acoustic noise is measured by sound pressure meters (it measures all sound coming from the ITE and all other influences, whether audible or not), and is statistically adjusted, called 'A-weighting', to relate it to the audible hearing range. These values are expressed as decibels (dBA).
| Noise Levels, Macintosh Computers |
| Sound Power | Sound Pressure at 25 cm |
| Model | Operational | Idle | Operational | Idle |
| iBook | 42 dBA | 34 dBA | 37 dBA | 29 dBA |
| iMac | 44 dBA | 43 dBA | 32 dBA | 31 dBA |
| iMac (Slot loading) | 39 dBA | 35 dBA | 31 dBA | 27 dBA |
| PowerBook G3 Series (Bronze keyboard) | 49 dBA | 36 dBA | 41 dBA | 23 dBA |
Power Macintosh G3
desktop enclosure | 44 dBA | 42 dBA | 36 dBA | 34 dBA |
Power Macintosh G3
(Blue and White) | 45 dBA | 42 dBA | 30 dBA | 29 dBA |
| Power Mac G4 | 51 dBA | 48 dBA | 44 dBA | 39 dBA |
Notes
* All sound pressure values were measured 25 cm from the front of each computer.
* The hard drive noise levels vary within the same model from the same company and may result in slightly different results than that reported above. |
| LaserWriters | Standby | Printing |
| LaserWriter, LaserWriter Plus | < 45 dB | < 50 dB |
| LaserWriter II | < 50 dB | < 60 dB |
| Personal LaserWriter | < 40 dB | < 54 dB |
| Personal LaserWriter 300/320 | 36 dB | 46 dB |
| LaserWriter Select 300 | 36 dB | 43 dB |
| LaserWriter Select 360 | 36 dB | 47 dB |
| LaserWriter Pro 600/630 | 34 dB | 49 dB |
| LaserWriter 4/600 | 36 dB | 46 dB |
| LaserWriter 16/600 | 34 dB | 52 dB |
| LaserWriter Pro 810 | 40 dB | 53 dB |
| LaserWriter 12/640 PS | 31 dB | 50 dB |
| Color LaserWriter 12/600 PS | 45 dB | 55 dB |
| LaserWriter 8500 | ~35 dB | ~50.5 dB |