From linux-sony Wed Dec 25 12:57:38 2002 From: "Raphael Langerhorst" Date: Wed, 25 Dec 2002 12:57:38 +0000 To: linux-sony Subject: Re: [Linux-sony] noisy screen with sony laptops X-MARC-Message: https://marc.info/?l=linux-sony&m=104261756124484 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 > > > > _______________________________________________ > Linux-sony mailing list > Linux-sony@returntonature.com > http://returntonature.com/mailman/listinfo/linux-sony > Linux-Sony Documentation: http://returntonature.com/linux/phpwiki -- John Andersen - NORCOM http://www.norcomsoftware.com/ _______________________________________________ Linux-sony mailing list Linux-sony@returntonature.com http://returntonature.com/mailman/listinfo/linux-sony Linux-Sony Documentation: http://returntonature.com/linux/phpwiki