The loudness of audio is commonly measured in decibel units (dB), and it is even sometimes measured in units such as Pascals, microbars, or dynes/cm². But for this discussion, we’ll stick to decibels.

In general, a decibel is a unit for expressing the ratio of the magnitudes of two electric voltages or currents. For the purpose of measuring sound, a decibel is equal to 20 times the common logarithm of the voltage or current ratio.

How does this apply to the sounds we hear? We will look at two ways the intensity of sound can be measured.

The intensity of continuous, audible sound is measured in decibels with a Sound Pressure Level (SPL) meter, and often, the results are weighted on a scale that takes into account the typical human ear response. Above, you will see the manufacturer’s "dBA" readings, meaning that the results have been weighted on the A-scale. The A-weighted scale reduces the frequency response of an SPL meter to the 500 to 10,000 Hz range - the frequency range to which our ears are most sensitive. This gives us a better idea of the loudness of the fan when we hear it. You may have seen similar scales that show the sound of a whisper rated at 20 dB; a vacuum cleaner rated at 70 dB; and a jet engine at take-off rated at 110 dB.

For other uses, the B-weighted scale (dBB) allows the SPL meter to "hear" lower frequencies down to 32 Hz, and expands up to 10,000 Hz, while the C-weighted scale (dBC) opens the meter up to all audible frequencies from 20 to 20,000 Hz and is commonly used to measure the intensity of high-fidelity sound at car stereo competitions.

Another way sound’s intensity can be measured is in the voltage output of our audio equipment, also in decibels. But instead of measuring the SPL with a meter, we will measure volts in terms of dB, or rather, dBV.

You may have seen these levels on your cassette deck or stereo system indicated in dB, with the optimal settings at 0 dB. Oftentimes, especially for analog equipment, you will see the readings exceed 0 dB ("in the red"), meaning that the voltage level output is something greater than 1 volt. Therefore, we can say that our analog equipment has a certain degree of "headroom" that can accommodate signal levels over 1 volt. Overdriven signal levels of +1 dB or higher begin to take on a different, sometimes pleasing, sonic characteristic, and are a way of achieving natural audio compression in recordings, as the source material’s amplitude gently pushes the equipment’s limits of reproduction.

In contrast, if you are at all familiar with digital recordings or equipment, you will know that the maximum sample amplitude we can record is 0 dB, or 1 volt - and nothing more. The absence of sound has 0 voltage and is noted like this: - (negative infinity).

Unlike with analog, if you try to record input levels higher than 0 dB on digital equipment, the result is "clipping" of the audio signal where the peaks are flattened so that they will go no higher than 0 dB. Clipped digital audio tends to have a harsh, unnatural sound.

A "line-level" source signal from our stereo, CD player, or sound card, measures approximately 1 volt, or 0 dBV. Anything less than 1 volt is shown as a negative value dBV. For example, -75 dBV is equal to 0.00018 volts.

Why not express levels in terms of volts? Well, because of the great difference between 0 dBV and -75dBV and expressing it in hundred-thousandths of a volt, it’s easier to compare terms of dBV than to talk about the difference being 0.99982 volts.

Now that we have discussed two ways the intensity of sound can be measured, take a look at the manufacturer’s dBA ratings and our own dBV ratings found in the columns above. There is no "right" or "wrong" way to display the results, but we thought to show you two ways.

In general, use the dBA ratings to give you an idea how the noise level compares perhaps with a whisper (20 dB) or a person talking (in the 40-60 dB range). Use the dBV ratings for comparative purposes, for example, to see exactly how much quieter a Sunon 120x25 rates to a Sanyo Denki 80x32 - yet pushes 16 more cubic feet of air per minute!

The manufacturer’s dBA ratings were taken using SPL meter equipment, while the Sidewinder ratings were taken directly from the sound samples you hear and are measured in dBV, or the voltage your own sound card is making as you hear them! We tried our best to "put you there" as if you were standing right next to the fan as we powered it on, in order to give you a better idea of how it’s going to sound before you buy.

Our fans were recorded without the heat sinks attached, so what you’re hearing is the fan all by itself. During our tests we found that different makes of heat sinks make sounds of varying loudness based on how the air is blowing off of them. And, when you try each fan on every heat sink, you start to get hundreds of combinations for fans and heat sinks. To keep The Listening Room simple and to the point, we recorded only the fans for you in our testing lab.