Zalman CNPS 9900 MAX review

Posted by Hilbert Hagedoorn on: 12/16/2010 02:00 PM [ 0 comment(s) ]

Noise levels - Sound pressure readings

Noise Levels

With a certified dBA meter we measure how many dBAs originate from the PC. It's slightly subjective as there is always noise in the background, from the streets, from the HD, PSU fan, etc so this is by a mile or two not a precise measurement. You could only achieve objective measurement in a sound test chamber. Take this measurement as an indication, not a precise measurement please.

The human hearing system has different sensitivities at different frequencies. This means that the perception of noise is not at all equal at every frequency. Noise with significant measured levels (in dB) at high or low frequencies will not be as annoying as it would be when its energy is concentrated in the middle frequencies. In other words, the measured noise levels in dB will not reflect the actual human perception of the loudness of the noise. That's why we measure the dBA level. A specific circuit is added to the sound level meter to correct its reading in regard to this concept. This reading is the noise level in dBA. The letter A is added to indicate the correction that was made in the measurement. Frequencies below 1kHz and above 6kHz are attenuated, whereas frequencies between 1kHz and 6kHz are amplified by the A weighting.

TYPICAL SOUND LEVELS
Jet takeoff (200 feet)	120 dBA
Construction Site	110 dBA	Intolerable
Shout (5 feet)	100 dBA
Heavy truck (50 feet)	90 dBA	Very noisy
Urban street	80 dBA
Automobile interior	70 dBA	Noisy
Normal conversation (3 feet)	60 dBA
Office, classroom	50 dBA	Moderate
Living room	40 dBA
Bedroom at night	30 dBA	Quiet
Broadcast studio	20 dBA
Rustling leaves	10 dBA	Barely audible

But let's have a peek at noise levels. We take a dBA gun and point it at the working PC and take a distance of 75 CM. The PC again is stressed at 3300 MHz on the CPU with 80% RPM set in the BIOS. These, as such, are noise levels measured under heavy CPU load.

On average and with a PWM regulated motherboard controller the cooler will run at roughly 65% RPM. In performance mode with 80% RPM we find the cooler too noisy at 43 DBa.

In silent mode the cooler definitely is not silent at 41 DBA / =<1500 RPM, but it remains an acceptable noise level to work in though.

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