Running up against a wall?

The Gangrel · Post by **The Gangrel** » Mon Jul 13, 2009 6:26 am

These days it's easy to create a very quiet PC, what with the proliferation of large heatsinks and smooth sounding fans.

Yet with the moving of the power supply into the back of LCD monitors (purely to save money?), we now have a new menace to deal with...monitor squeal.

For instance, my last monitor (Acer 193w) howled like a banshee at anything below 100% brightness. This kind of noise is far more irritating than the rushing sound of even a medium quality fan. Add to that the variance from monitor to monitor (some will say x model whines, others claim it's silent) and I wonder where we stand as a group, given that this seems to be the biggest backwards step with regards to quietness for some time.

As I'm now shot of the Acer and in the market for a new 19-22" monitor, how, other than hope alone, does one acquire a silent monitor, go around PC shops listening for squeal from the back of monitors?.

fyleow · Post by **fyleow** » Mon Jul 13, 2009 11:14 am

Supposedly an LED backlit LCD does not have squealing. There are some "green" Dell LCDs that use an LED backlight.

SebRad · Post by **SebRad** » Mon Jul 13, 2009 1:30 pm

Hi, there was a SPCR article on this very issue.
The recomendation is to turn the monitor up to 100% brightness (or lowest value the noise dissapears) and then turn the brightness down again in the graphics driver so the monitor isn't eye wateringly bright.
Hope this helps, Seb

Matija · Post by **Matija** » Mon Jul 13, 2009 2:15 pm

Don't do that, it destroys colour accuracy.

Xobim · Post by **Xobim** » Tue Jul 14, 2009 6:37 am

It's the CCFL that creates the whine in the LCD displays, allmost never the coils. The only way to prevent this problem, is by buying a led-screen, I'm afraid.

jhhoffma · Post by **jhhoffma** » Tue Jul 14, 2009 1:08 pm

Xobim wrote:It's the CCFL that creates the whine in the LCD displays, allmost never the coils. The only way to prevent this problem, is by buying a led-screen, I'm afraid.

Actually, it's the (DC>AC) inverter that powers the CCFL that makes the noise. LED units work directly off DC and do not require inverters, so will not suffer from the squealing noise.

DAve_M · Post by **DAve_M** » Tue Jul 14, 2009 3:13 pm

jhhoffma wrote:Actually, it's the (DC>AC) inverter that powers the CCFL that makes the noise. LED units work directly off DC and do not require inverters, so will not suffer from the squealing noise.

If that is true then just buy a monitor that runs off mains AC voltage instead of off a DC power brick. Unless the monitor is badly designed, they won't need to put an inverter in there at all.

My LCD monitor is not LED backlit and it is silent. It does also run off the mains not a DC supply so my theory stands.

BTW my monitor is a Hyundai N91WP or N91W.

The Gangrel · Post by **The Gangrel** » Wed Jul 15, 2009 2:11 am

If that is true then just buy a monitor that runs off mains AC voltage instead of off a DC power brick. Unless the monitor is badly designed, they won't need to put an inverter in there at all.

Are you sure there isn't a DC power supply inside the monitor?.

I was of the understanding that all LCD monitors need a DC power supply of some sort...

DAve_M · Post by **DAve_M** » Wed Jul 15, 2009 2:43 am

An inverter turns DC into AC to drive the backlight. Mains is already AC you just need a transformer to step the voltage up or down to the voltage you need.

Otherwise it will be going AC input >> DC PSU (built into monitor) >> inverter >> AC output to backlight.

Better would be AC input >> Transformer >> AC output to backlight. If they don't do it this way then an inverter must be cheaper than a tranformer.

Another LCD we have in the house does make a whine. That monitor runs off a DC supply so I can guarantee that it DOES have an inverter inside. I'm guessing the inverter is causing the trouble. Again, my monitor is completly silent.

DAve_M · Post by **DAve_M** » Wed Jul 15, 2009 2:48 am

The Gangrel wrote:Are you sure there isn't a DC power supply inside the monitor?.

I was of the understanding that all LCD monitors need a DC power supply of some sort...

Yes I'm sure my monitor DOES have a DC PSU inside it. I never said there wasn't. Just that my monitor runs off mains voltage instead of a DC power brick.

I believe the CCFL is not being powered by an inverter, but instead by using the mains AC with a transformer.

lobuni · Post by **lobuni** » Fri Jul 17, 2009 5:46 am

DAve_M wrote: Yes I'm sure my monitor DOES have a DC PSU inside it. I never said there wasn't. Just that my monitor runs off mains voltage instead of a DC power brick.

I believe the CCFL is not being powered by an inverter, but instead by using the mains AC with a transformer.

Why do you believe so?

A computer monitor CCFL needs a frequency which is different than that available at your wall socket. A simple transformer can not change the frequency.

From Xbitals we can conclude that on some monitors the brightness is controlled through pulse-width modulation of the power of the backlight lamps at a frequency within human hearing range. Maybe this is the cause.

BTW i have the same monitor as in the article (Samsung 940B). It has no external power brick and it whines at lower brightness settings.