Are LED backlights quieter?

They make noise, too.

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DragonMaster
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Are LED backlights quieter?

Post by DragonMaster » Sun Jan 25, 2009 4:20 pm

Noise coming from LCD monitors is often caused by the backlight inverter being PWM-controlled.

Has anyone noticed if LED-backlit monitors are quieter? Yeah, I know, there's no 500V inverter, but LEDs are also PWM-controlled.

green
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Post by green » Sun Jan 25, 2009 5:07 pm

i may be wrong but i always thought all fluorescent lighting produced a buzing noise which can vary on power provided or environment temperature

with that in mind led backlighting would be quieter

lm
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Post by lm » Sun Jan 25, 2009 5:13 pm

Green: It also depends on the frequency of the electricity. If the electronics increase the frequency over 20kHz then it can't be heard, but if they are too cheap they don't do that.

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Post by NeilBlanchard » Sun Jan 25, 2009 5:27 pm

Welcome to SPCR!

I would guess that LED's would be quieter: fluorescent lights have to flash in order to work, and then to dim them the PWM can interfere with the basic flashing frequency. LED's are steady state light sources, so this would reduce the chances of there being an audible noise; since it is only the PWM working at a frequency.
Sincerely, Neil
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DragonMaster
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Post by DragonMaster » Sun Jan 25, 2009 6:11 pm

Welcome to SPCR!
Thanks!

Well, a CCFL inverter's frequency is 25kHz or more, and the bulb itself doesn't really whine from what I've seen.

I replaced the CCFL in my laptop, and the inverter board makes LOADS of ~450Hz whine when bulb brightness isn't set to 100%, which points to the dimming PWM.

What I don't know is if the low-voltage PWM circuit itself whines due to current (could be the case with a LED controller), or if it's the HV circuit part (which would be absent in a LED panel).

I also have to think that the SMPS could be noisy in a monitor. But, if there are less noisy components, getting a LED-backlit monitor would be a better bet than a CCFL one.

I guess the best thing to do would be to test some panels in a silent environment (not that easy to do).

Anyways, the reason I started the thread is that I'm getting a little tired of hearing my CRT monitor buzzing at a 100Hz refresh rate constantly (and introducing a little bit of hum in my phono cartridge and tape heads at the same time), and I haven't found a single totally-silent LCD monitor in a silent environment.

I don't think that buying a screen from one person's opinion on it's sound levels is a good idea since noise levels are probably quite different between units of the same model, as even a slight change with the tension of each screws holding the monitor case, PSU and inverter board together can make a drastic change in whine/noise levels if the mfg. doesn't take care about it.

lm
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Post by lm » Mon Jan 26, 2009 2:09 am

I just wish some hardcore modder here tries and succeeds in silencing a whining LCD monitor by attacking the problem at the source rather than just settings brightness to 100%.

That would be a great subject for an article.

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Post by jessekopelman » Mon Jan 26, 2009 5:51 am

lm wrote:I just wish some hardcore modder here tries and succeeds in silencing a whining LCD monitor by attacking the problem at the source rather than just settings brightness to 100%.

That would be a great subject for an article.
Did you search? I believe it has been done. Sometimes a bit of glue on the coils is all it takes.

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Post by NeilBlanchard » Mon Jan 26, 2009 9:13 am

Hi,
DragonMaster wrote:Well, a CCFL inverter's frequency is 25kHz or more, and the bulb itself doesn't really whine from what I've seen.

I replaced the CCFL in my laptop, and the inverter board makes LOADS of ~450Hz whine when bulb brightness isn't set to 100%, which points to the dimming PWM.
Right, that is my point: it's the interference between the electronics that generate the bulb's operating frequency, and the electronics the generate the PWM frequency -- that causes the noise, most likely.
Sincerely, Neil
http://neilblanchard.blogspot.com/

lm
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Post by lm » Mon Jan 26, 2009 2:04 pm

jessekopelman wrote:
lm wrote:I just wish some hardcore modder here tries and succeeds in silencing a whining LCD monitor by attacking the problem at the source rather than just settings brightness to 100%.

That would be a great subject for an article.
Did you search? I believe it has been done. Sometimes a bit of glue on the coils is all it takes.
Yes, I did search. I found lots of frustration and lots of speculation. Maybe somebody did it, but they are just forgotten rare forum posts. Like I said, it would be a nice topic for an article. Taking a system where just about every component has a whine, and fixing it, and taking a lot of pictures and writing a lot of text about it.

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Post by nutball » Mon Jan 26, 2009 2:19 pm

lm wrote:Like I said, it would be a nice topic for an article. Taking a system where just about every component has a whine, and fixing it, and taking a lot of pictures and writing a lot of text about it.
Sounds like you just volunteered to crack open your 30"-er, fill it full of gunk, take pics and let us know how it went :)

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Post by CyberDog » Mon Jan 26, 2009 11:28 pm

Hi all!

I tried to fix coil whine from my old motherboard. I first tried with hot glue. Didn't work. Then I tried super glue. It worked a few days. But then the whine came back. I was going to try with coil lacquer or something like that but I sold the comp before I got the chance.

Now my new comp don't whine. It does sounds from sound out put subjected to bright parts from monitor etc. And has some weird things on jacks. If I put the male jack whole way to bottom it doesn't work.

But no more off topic. My monitor has whine under 75% brightness. I'm going to crack it open and try to put that lacquer on coils. But right now I don't have time to do that. But I'm going to take pictures and hit them to forum when I do that. Any advises are welcome.

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Post by thejamppa » Tue Jan 27, 2009 4:12 am

Led themselves will be quiet. Matter is completely different how the electronics controlling them will be done.
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lm
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Post by lm » Tue Jan 27, 2009 8:12 am

nutball wrote:
lm wrote:Like I said, it would be a nice topic for an article. Taking a system where just about every component has a whine, and fixing it, and taking a lot of pictures and writing a lot of text about it.
Sounds like you just volunteered to crack open your 30"-er, fill it full of gunk, take pics and let us know how it went :)
Well, I am very tempted to do it, but I have very limited time until beginning of june, and this monitor is totally mission critical to me, so don't want to have it laying in pieces when I need to do stuff on it. Also it's too expensive to accidentally break, and I paid for warranty extension from 3 to 5 years.

What would be more doable is to try to get an old used small LCD for cheap/free somewhere, the worse quality the better, and experiment with that. With the experience gained, try to attack the large monitor next.

However most of these are useless until I can get my air cond silenced. That drowns every other noise out before 22:00 every day. I can't just shut it down because it's shared between others in this block of flats.

lm
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Post by lm » Tue Jan 27, 2009 8:16 am

CyberDog wrote:But no more off topic. My monitor has whine under 75% brightness. I'm going to crack it open and try to put that lacquer on coils. But right now I don't have time to do that. But I'm going to take pictures and hit them to forum when I do that. Any advises are welcome.
I don't have any real advice, but I wish you luck on this. Does your monitor have backlight bleed btw? It seems that can also be reduced by taping some parts of the monitor, but the validity for this as a long-term solution is questionable, because of the qualities of tape.

DragonMaster
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Post by DragonMaster » Tue Jan 27, 2009 10:03 am

I tried to fix coil whine from my old motherboard. I first tried with hot glue. Didn't work. Then I tried super glue. It worked a few days. But then the whine came back.
Epoxy is what you should use normally. Super glue breaks easily on materials it doesn't stick well to (lacquered cooper for instance), that's the problem.

Inverters aren't exactly like mainboards though, they don't necessarily have filtering ferrite beads, but have an HV transformer that can potentially whine (like the yellow-taped one in your PSU, but smaller.)
Does your monitor have backlight bleed btw? It seems that can also be reduced by taping some parts of the monitor, but the validity for this as a long-term solution is questionable, because of the qualities of tape.
When the reflective layer isn't properly touching to the diffusing layer, that's what happens. That layer is just a piece of cardboard, and is just held by the LCD frame, with nothing behind as it's the last layer. Adding tape behind the panel only works if there's a flat surface right behind it that can apply pressure on the tape.

CyberDog
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Post by CyberDog » Wed Jan 28, 2009 7:52 am

I have some light bleed. I try to fix that also. Thanks for the tip. I'll try that lacquer from the electronic part shop. But now that the DragonMaster said that inverters are different I do not know if I have much of a succeed. I don't know much of an electronics...

lm
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Post by lm » Wed Jan 28, 2009 8:19 am

CyberDog:

I found this guide with pictures about fixing/reducing backlight bleed:

http://www.tftcentral.co.uk/articles/de ... ht_fix.htm

Those pictures are originally from this thread:

http://www.hardforum.com/showthread.php?t=1032268

It does not mention anything about coil whine however, only backlight bleeding fix.

Take note that it's very important what kind of tape you use, because if the tape starts disintegrating it will be a major PITA. I guess it should be something designed for high temperatures.

Remember to take before/after pictures of the screen on at 100% brightness but showing a completely black screen with the camera and the display in same positions for both pictures and preferably during the night with closed curtains and no lights so you can make a fair comparison of how well you eliminated it.

Also if you can, put a mic next to the monitor before and after and make some recordings (during the night to eliminate background noise if possible).

Easy way to find the source of whine is to fold a sheet of paper into a long but narrow pipe, put the other end to your ear and move the other end around near the suspected circuits when the device is running (beware of giving yourself any electric shocks, it's dangerous). The pipe will only let the noise from a small area in to your ear so you should easily be able to identify the point source of noise.

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Post by CyberDog » Thu Jan 29, 2009 12:06 am

Thanks for the tips :) I'll check that out.

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Post by DragonMaster » Thu Jan 29, 2009 9:54 am

Take note that it's very important what kind of tape you use, because if the tape starts disintegrating it will be a major PITA. I guess it should be something designed for high temperatures.
Panels run cool, so high temp tape isn't absolutely necessary. I'd worry about HV though. If the frame is taped, it's not grounded properly anymore, and the frame is electrically left floating.

When I changed my laptop's CCFL, I tested it without having the panel installed in the top cover, with the bulb connected to the inverter. Well, guess what, I was getting shocks when touching the LCD and the plastic case at the same time. (Just from the electrical fields coming from the bulb and HV wiring.)

You can touch the panel even when the case is closed. You don't want to leave HV on that part. (A simple ground wire is enough to fix the problem though)

lm
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Post by lm » Thu Jan 29, 2009 10:34 am

DragonMaster wrote: Panels run cool, so high temp tape isn't absolutely necessary.
I read elsewhere that somebody ruined his monitor because the glue in the tape started running after some months and was clearly visible in the lcd screen. I guess there are at least tapes that are designed for high longevity?

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Re: Are LED backlights quieter?

Post by Barnard » Thu Feb 10, 2011 11:15 pm

I think that you might be able to replace your backlight so that it will take a good condition for it. Then, try to check and clean the other parts. It is necessary to make some replacement for the best option.
My TV shows flashlight

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