[Elecraft] [K3] K3 fan noise, part XXLIV

[Tom W8JI]

The level on your recording is so low I can barely hear it 
Joe, and it also will not display on my spectrum analyzer 
software.

What I do hear sounds exactly like what I described below, 
where I am talking about something being too close to the 
blade tips. It does not sound like bearing noise to me. It 
sounds like the siren effect or tone effect caused by 
turbulent air from the blades hitting something that isn't 
moving with the blade.

If this is inside the fan, like the motor support bars, 
there is little that can be done other than slow the blade 
speed down. If this is outside the fan, like a fixed object 
too close to the blades, the fan can be moved outwards.

In really quiet fans the support bars are curved so they 
don't cause a noise pulse when the blade crosses the support 
bars, plus the blades are better shaped.

Sure doesn't sound like bearings though. From what I hear it 
sounds like a tone plus air noise.

I'm a little out of the " fan loop" because the last time I 
was heavily looking at air mover noise was in the 90's.

73 Tom





----- Original Message ----- 
From: "Joe Planisky" <jplan at jeffnet.org>
To: "Tom W8JI" <w8ji at w8ji.com>
Cc: "Elecraft List" <elecraft at mailman.qth.net>
Sent: Saturday, May 29, 2010 2:27 PM
Subject: Re: [Elecraft] [K3] K3 fan noise, part XXLIV


> That assumes that the airflow is the predominant source of 
> noise.  In  my case, the airflow noise is secondary to 
> what I believe is bearing  noise.  At low speeds, this 
> "motor noise" is what I hear mostly.  It  is the same 
> across 2 sets of UTEC fans.
>
> I've posted a recording of my K3 fans at 
> http://www.jeffnet.org/~jplan  if you're curious about 
> what it sounds like.  (note: I'm not sure the  embedding 
> works, so there's also a download link.  It's a 4.1MB WAV 
> file.)  That recording was made with an AKG C1000 mic 
> about 2 feet  directly in front of the K3, about where my 
> head would be when  operating.  Use headphones to get the 
> full effect.
>
> Of course, we can't tell anything about how loud it 
> actually sounds  from that recording since we have no idea 
> of the gain between my mic  and your ears.  I'm posting 
> that recording to give an idea of the  quality of the 
> sound, not how loud it is.
>
> I'd like to try a quality fan with sleeve bearings. 
> Sleeve bearings  don't last as long as ball bearings, but 
> they are quieter.
>
> 73
> --
> Joe KB8AP
>
>
> On May 29, 2010, at 3:31 AM, Tom W8JI wrote:
>
>> That isn't surprising. Fan mounts, although people really
>> like to mess with them, almost never have a noticeable
>> effect on noise.
>>
>> Other than the design of the fan itself, the number one
>> thing that affects noise is having an object near the 
>> blades
>> (especially out near the tips). Restricting the airflow 
>> also
>> doesn't help. The worse thing to do for a given amount of
>> restriction is place it on the fan inlet.
>>
>> I haven't played with a K3,  but cutting some thick 
>> spacers
>> to move the fans outward from the PA might be worth a 
>> try.
>> Cheap sound meters are readily available, and a good way 
>> to
>> test.
>>
>> 73 Tom
>>
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