This plot shows the noise level in my bedroom with the computer running as recorded with a General Radio 1551-C Sound-Level Meter. The left-hand plot is the noise level with the old computer system consisting of an 800 MHz AMD Duron with 3 cooling fans. One fan was on the processor, one in the power supply and one inside the front of the case. The right-hand plot is the new system, an AMD Athlon 1900+, with 4 cooling fans. One fan is on the processor, two are in the power supply and the 4th is the same case fan as before.
The measurements were all taken at roughly waist level. The sound meter was hand-held unless there was something of an appropriate height to set it on such as the bed or desk.
The biggest difference in the sound level between the two systems is due to the processor fans. The fan in the Duron system was possibly failing and had a rather loud rattling noise. The dual fans in the new power supply are also quieter than the single fan in the old power supply.
A few other measurements were taken which are not shown on the plot. The sound level was measured at a single point near the computer. This location was approximately 5" aft and 3" to the side of the back of the computer. Vertically the microphone was at about the midpoint of the case. At this location, a sound level of 59.5 dB was measured for the old system and 53 dB for the new one.
Finally, an attempt was made to map the sound levels in the room with the computer off. This turned out to be very difficult as the low sound levels present were easily affected by random noise such as cars out in the street, the rustling of leaves outside the apartment and my stomach growling. The average reading seen between noise events was about 30 dB.
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