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Re: fireplace Hum Solved !!!!

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  • kallio_mn
    AL Good job on isolating that Hum! Years back, the power supplies in equipment were Linear supplies. They consisted a transformer for converting the main
    Message 1 of 9 , Dec 1, 2006
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      AL

      Good job on isolating that Hum!

      Years back, the power supplies in equipment were Linear supplies. They
      consisted a transformer for converting the main supply down to a lower
      voltage and an AC to DC converter (rectifier) and a voltage regulator.
      The transformer is composed of two coils of wire wound around each other
      and as series of E shaped soft iron laminates interleaved together.
      These were then coated in shellac. If there any of the E's were loose,
      they would vibrate and cause the whole transformer to Hum. You see this
      a lotl with Fluorescent lighting ballasts.

      Now, in the interest of energy efficiency, we have Switch Mode power
      supplies. Rather than use a transformer for converting the main supply
      to a lower level, we have a more complex circuit. The input voltage is
      switched on for a brief period of time until it reaches the desired
      voltage and then switched off. This process occurs very quickly and the
      circuit stores this energy until the next switching cycle. Switch Mode
      power supplies usually operate at a high frequency, outside of the audio
      range, and thus use smaller magnetics than Linear Supplies.

      Because they switch the main power at a high frequency, Switch Mode
      power supplies tend to be more noisey electrically. You can bring an AM
      radio close to them and hear a high level of interference. And they can
      also be acoustically noisey from mechanical resonances that occur in the
      parts. The acoustic noise may arise from either the main power or the
      switching and thus do not have to be harmonically related.

      Kallio



      --- In humforum@yahoogroups.com, "dark_al1" <dark_al1@...> wrote:
      >
      > Thanks Ken, I now have the SKY+ box in my office and have a microphone
      > on a tripod next to it. I have posted a screen capture from spectrum
      > labs:
      > http://tech.ph.groups.yahoo.com/group/humforum/photos/view/b0c0?b=5
      >
      > It shows:
      > A normal mains hum @ 50hz
      > An Increased mains hum @ 50 hz when box is powered up
      > A hum @ 90 hz while box is powered up
      > A quick ramping freq hum, when the HD or cooling fan spin up @ 62hz
      > A decrease of mains hum when box powered down
      > A loss of 90hz hum when box powered down
      >
      > It seems my initial estimate of 26hz, was waaaay off. Which makes my
      > asumption of Helmholtz resonance due to the Chimney+room size
      > questionable.
      > However I still really like this theory ! LOL.
      > I will get some exact measurements of the room and chimney as there is
      > definateley some kind of resonance going on. Hopefully someone will be
      > able to use the measurements, frequency and some resonance related
      > equation to prove what is happening.
      >
      > As Winston Churchill once said 'Death to the HUM!' I'm sure that's
      what
      > he said, wasn't it? :o)
      >
      > AL
      >
      >
      > --- In humforum@yahoogroups.com, "Kenneth Smith" kensmith52@ wrote:
      > >
      > > Good work Al. That is what it takes to find something and you have
      > > worked hard at this.
      > > I have been replacing computers the last 2 days. Upgrading to new
      > > ones. Been trying to catchup on the posts.
      > >
      > > Ken Smith
      > >
      >
    • dark_al1
      I know exactly what you mean. I spent many hours as a kid pulling old transformers to pieces and seperating the E shaped plates. I have now pulled the Hard
      Message 2 of 9 , Dec 1, 2006
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        I know exactly what you mean. I spent many hours as a kid pulling old
        transformers to pieces and seperating the E shaped plates.

        I have now pulled the Hard drive out of the SKY box and powered it up
        in isolation. It is the cause of the hum and didn't sound like a
        healthy drive (no normal high pitch whine)It has a low hum like a
        transformer as described earlier.
        So I stuck an old 4 GB drive in the Sky box, put it back in the
        cabinet and powered it up. Hey presto it now works. The down side is
        that I already ordered a new one this morning!.

        With the now fixed SKY box in its original place with it's
        replacement hard drive. The hum cannot be heard either in the cabinet
        or the fireplace, just the whine of a normal Hard drive.
        Also running the old HD in isolation (in the office), spectrum labs
        shows the same 50hz and 90hz hum coming from it that I measured from
        the SKY box originally. Kind of strange as it is running on 12v and
        5v DC. So I wouldn't expect the 50hz mains hum? This could just be a
        coinsidental frequency?.

        My guess is that the platter in the drive is loose, warped, off
        balence or somesuch. which is causing the hum. When I put a finger on
        top of the drive, I can feel the vibration.
        I have checked the tech stats for the drive on maxtor website:

        Maxtor fireball 3, 40GB
        5400 rpm single platter
        Noise:
        Idle (sound power:bel) 2.7
        Seek (sound power:bel) 2.8

        I have no idea how 'bel' relates to Db? but the drive in isolation is
        much quieter than when installed in the Sky box. Also these noise
        figures are for a healthy drive.


        Now I understand the cause of the fireplace hum, I will continue with
        the fireplace itself until I understand what is happening there.
        I will do some experiments with a tone generator to see if I can
        induce some resonance. Starting with the 50hz and 90hz that the Hard
        drive is emiting.
        I have already taken accurate measurements of the fireplace
        dimensions and alcoves next to it, i will do some diagrams and post
        them. I can't get accurate measurements for the chimney flu yet as I
        don't fancy climbing on the roof in the pouring rain, but will post
        when i get them.

        AL


        --- In humforum@yahoogroups.com, "kallio_mn" <kallio_mn@...> wrote:
        >
        >
        > AL
        >
        > Good job on isolating that Hum!
        >
        > Years back, the power supplies in equipment were Linear supplies.
        They
        > consisted a transformer for converting the main supply down to a
        lower
        > voltage and an AC to DC converter (rectifier) and a voltage
        regulator.
        > The transformer is composed of two coils of wire wound around each
        other
        > and as series of E shaped soft iron laminates interleaved
        together.
        > These were then coated in shellac. If there any of the E's were
        loose,
        > they would vibrate and cause the whole transformer to Hum. You see
        this
        > a lotl with Fluorescent lighting ballasts.
        >
        > Now, in the interest of energy efficiency, we have Switch Mode power
        > supplies. Rather than use a transformer for converting the main
        supply
        > to a lower level, we have a more complex circuit. The input
        voltage is
        > switched on for a brief period of time until it reaches the desired
        > voltage and then switched off. This process occurs very quickly
        and the
        > circuit stores this energy until the next switching cycle. Switch
        Mode
        > power supplies usually operate at a high frequency, outside of the
        audio
        > range, and thus use smaller magnetics than Linear Supplies.
        >
        > Because they switch the main power at a high frequency, Switch Mode
        > power supplies tend to be more noisey electrically. You can bring
        an AM
        > radio close to them and hear a high level of interference. And they
        can
        > also be acoustically noisey from mechanical resonances that occur
        in the
        > parts. The acoustic noise may arise from either the main power or
        the
        > switching and thus do not have to be harmonically related.
        >
        > Kallio
        >
        >
        >
        > --- In humforum@yahoogroups.com, "dark_al1" <dark_al1@> wrote:
        > >
        > > Thanks Ken, I now have the SKY+ box in my office and have a
        microphone
        > > on a tripod next to it. I have posted a screen capture from
        spectrum
        > > labs:
        > > http://tech.ph.groups.yahoo.com/group/humforum/photos/view/b0c0?
        b=5
        > >
        > > It shows:
        > > A normal mains hum @ 50hz
        > > An Increased mains hum @ 50 hz when box is powered up
        > > A hum @ 90 hz while box is powered up
        > > A quick ramping freq hum, when the HD or cooling fan spin up @
        62hz
        > > A decrease of mains hum when box powered down
        > > A loss of 90hz hum when box powered down
        > >
        > > It seems my initial estimate of 26hz, was waaaay off. Which makes
        my
        > > asumption of Helmholtz resonance due to the Chimney+room size
        > > questionable.
        > > However I still really like this theory ! LOL.
        > > I will get some exact measurements of the room and chimney as
        there is
        > > definateley some kind of resonance going on. Hopefully someone
        will be
        > > able to use the measurements, frequency and some resonance related
        > > equation to prove what is happening.
        > >
        > > As Winston Churchill once said 'Death to the HUM!' I'm sure that's
        > what
        > > he said, wasn't it? :o)
        > >
        > > AL
        > >
        > >
        > > --- In humforum@yahoogroups.com, "Kenneth Smith" kensmith52@
        wrote:
        > > >
        > > > Good work Al. That is what it takes to find something and you
        have
        > > > worked hard at this.
        > > > I have been replacing computers the last 2 days. Upgrading to
        new
        > > > ones. Been trying to catchup on the posts.
        > > >
        > > > Ken Smith
        > > >
        > >
        >
      • Dave at Yaahoo
        Excellent! Thanks! :-) -dave
        Message 3 of 9 , Dec 2, 2006
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          Excellent!
          Thanks! :-)

          -dave



          --- dark_al1 <dark_al1@...> wrote:
          >
          > Sorry Dave, forgot to give US terms in my excitement. Also what the
          > upshot of this is. So for all on the other side of the pond and a
          > better explaination:
          >
          > SKY+ = digital satelite reciever box, with integrated Hard drive.
          > CT100 cable= high grade Coaxial cable for connecting to satelite dish
          > LNB Cables= The CT100 cable (above) which connect the SKY+ box to the
          > dish (the LNB is the bit in the middle of the dish which sticks out
          > on the end of the arm, this is where the cables connect)
          > There are 2 cables for sky plus as it can show one channel and record
          > another.
          > The cabinet is a TV cabinet which the TV stands on, with cubby holes
          > for Video/ DVD and satelite recorder. I stuck my head in the cubby
          > hole with the SKY+ box in.
          >
          >
          > There is no other box next to the fireplace. The sound (hum)eminates
          > from the SKY+ box in the cabinet and cannot be heard unless you put
          > your head right next to it.
          > The hum in and around the fireplace is (i believe) caused by this low
          >
          > volume sound entering the fireplace and causing resonance, which
          > amplifies the volume to an audible level. Creating a standing wave
          > like when you hum a certain note in the bathroom, which gets louder
          > and louder even when you don't hum louder. This gets to a maximum
          > level and holds there. It will continue until the source of the hum
          > (The Driver) is stopped (like running out of breath). In this case
          > the driver is the SKY+ box. When it is unplugged, it stops making the
          > hum and the resonance in the fireplace stops.
          >
          > What this really demonstrates, is that HUMs can be caused by low
          > volume sounds that are remote from the place they are heard.
          >
          > This doesn't solve the majority of hums, as I believe there is one
          > underlying hum that the majority of us are hearing (The low frequency
          >
          > Diesel engine hum), However it may solve or help solve some of the
          > higher frequency hums, which I think have mostly mechanical
          > causation.
          > The reason I chose to study the fireplace hum was because it was
          > higher frequency and as such it would have a local cause.
          >
          > Hope this helps.
          > Bill, Ken, Prof Demming, Arne and all the others on the forum with a
          > better grip on the science of this. If you want to chime in and give
          > you views or corrections I would appreciate it.
          >
          > AL
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