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List:       linux-sony
Subject:    Re: [Linux-sony] noisy screen with sony laptops
From:       "Raphael Langerhorst" <raphael-langerhorst () gmx ! at>
Date:       2002-12-25 12:57:38
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Hi all,


I just checked out how loud mine is:

The fan is louder than four months ago, I think because of dust. I had a
hard time to hear the sound that is generated by reducing screen
brightness but I heard it; it was a very quiet low buzz, I could hear it
up to a half metre distance. Since then I never had reduced screen
brightness. I remember that it was a very high (high in frequency) buzz
a couple of months ago, but also not very loud; you probably could hear
it for two or three metres.


>I can't hear ANYTHING on my VX88 across the room, unless the fan is
>running.  Not even when the hard drive is accessing (unless I really
>listen hard, I guess).

Yes, the Sony Laptops are EXTREMELY quiet. I was really surprised when I
turned it on the first time. In this silence you can even hear the
screen-brightness-controller buzz *g*.


more comments below...


original message:

>Great explanation Raphael.
>Is there any other means of brightness control?

I'm quite sure there is, but PWM is one of the simplest and it is really
saving energy as well. PWM is also often used for electrical motors.

>
>I ask because my GRX570 makes no noise at all when dimmed.
>Actually, this laptop is one of the quietest machines I've ever had.
>I can hardly even hear the fan (I can sometimes feel it through the
>keyboard if I rest my hand on the machine).

If there is any device that is capable of analogue voltage (or current,
I don't know) output used for brightness control then you won't hear
anything because the voltage output will be just 60% or something all
the time (and not 60% of some time period high and 40% of it low). And
if it is on a constant level all the time then you don't have any
frequency in it, so no sound.


Merry Christmas all,
Raphael



On Tuesday 24 December 2002 01:36 am, Raphael Langerhorst wrote:
> As for the noise the screen makes when not turned to full bright,
that's
> ok if it is just above level of recognizing it. If it is really loud
> then of course it is not ok.
>
> Technical reason for making noise:
> the backlight of the LCD is probably driven by a PWM module (pulse
width
> modulation). So if turned to full bright the voltage for the backlight
> over time would look like this:
>
> on    __________________________________
> off
>
> if not turned to full bright, it just turns off for a percentage of
the
>
> time in a period:
>      |oneperiod|         |         |
>
> on    _____     _____     _____     _____
> off  |     |___|     |___|     |___|
>
> this would be about 60% high and 40% low;
>
> Now that's of course some frequency and we know that such impulses
have
> a large spectrum (of sine waves) so there is likely to be some of them
> in the <20kHz area which human ears can hear -> that's the sound.
>
> Since our eyes can't follow this high frequency of changing between
high
> and low states for the screen they level it out and that makes about
60%
> of the maximum (I know the eyes have a logarithmic recognition but
that
> would only make things complicated).
>
>
> Hope that helped someone,
>
> Raphael
>
> PS: my model is the R600HFPD
>
>
>
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> Linux-Sony Documentation: http://returntonature.com/linux/phpwiki

-- 
John Andersen - NORCOM
http://www.norcomsoftware.com/

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