Nidecs, Seasonic, and 125 Hz

halfpower · Post by **halfpower** » Sat Apr 08, 2006 7:29 am

My computer includes two Samsung Nidecs, a Seasonic 350W Super Tornado Rev. 2, and an Antec 3000B. The Nidecs are hard mounted.

Today I stopped my case and CPU fans and made a few recordings from the front and side of my case. The recordings were made with an MXL 990 and done so in a relatively casual fashion.

In general the spectral energy was spread out. Most of the energy occurred below 5000Hz and showed a slight rise below 1000Hz. A couple of frequency components stood out, most notably 125Hz and to a lesser degree 14Hz, 5800Hz, 7200Hz (7167Hz), and 8700Hz. The 125Hz wave was much more apparent in spectrograms when recordings were made from the door side of the case, then when they were made from the front of the case. Indeed, analysis of the waveforms from the recordings made of the front of the case appeared to be much less orderly where as the ones made from the side showed a 125Hz wave with good clarity. The 14Hz did not show up at all in some of the recordings. When seek noises were edited out of the recordings, only minor changes were observed in the spectrogram.

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Does anyone know what the 125Hz wave is? Is it mechanical resonance? Is it my hard drives, my PSU, etc?

qviri · Post by **qviri** » Sat Apr 08, 2006 7:37 am

Perhaps 120 Hz is close enough?

120 Hz is 120 times/second. This is also 7200 times/minute, which bears striking resemblance to your hard drives' rotational speed.

cmthomson · Post by **cmthomson** » Sat Apr 08, 2006 7:44 am

It's almost certainly the drive motors. My Samsung SpinPoints are soft-mounted, and when I put a finger on one I can feel it vibrating, but can't hear them. I'm betting if you soft-mount your disks, the hum will go away.

Devonavar · Post by **Devonavar** » Sat Apr 08, 2006 1:08 pm

As others have said, it's almost certainly your hard drives.

How far away from the case was the microphone when you made the recording? The reason I ask is that the 120 Hz spike that you're seeing will probably be much more pronounced in a near-field recording than one from your operating position. Low frequencies drop off quite a lot outside of a foot or so.

halfpower · Post by **halfpower** » Sat Apr 08, 2006 10:08 pm

qviri wrote:Perhaps 120 Hz is close enough?

120 Hz is 120 times/second. This is also 7200 times/minute, which bears striking resemblance to your hard drives' rotational speed.

120 Hz is probably with in error range.

halfpower · Post by **halfpower** » Sat Apr 08, 2006 10:10 pm

Devonavar wrote:As others have said, it's almost certainly your hard drives.

How far away from the case was the microphone when you made the recording? The reason I ask is that the 120 Hz spike that you're seeing will probably be much more pronounced in a near-field recording than one from your operating position. Low frequencies drop off quite a lot outside of a foot or so.

The microphone was about 6cm from the case

halfpower · Post by **halfpower** » Sat Apr 08, 2006 10:12 pm

cmthomson wrote:It's almost certainly the drive motors. My Samsung SpinPoints are soft-mounted, and when I put a finger on one I can feel it vibrating, but can't hear them. I'm betting if you soft-mount your disks, the hum will go away.

That will help, but I'm trying to solve the whoosh noise too. I might enclose them in a vented foam air tank.