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Discussion Starter · #1 ·
Hi everyone,


I've been trying to resolve a high frequency noise problem from my panny plasma. It's subtle, but enough to be heard from my listening position (8'), and within about 20 minutes, cause ringing in my ears.


I've been trying to live with it - even sound insulating the wall behind the plasma. But twice over the last 4 months I have called Panasonic and they have sent a service guy to look at it. On the first visit they opened up the back and replaced one of the boards (not the power supply board). This was a shot-gun try -- as they brought the board w/o seeing the problem and figured they'd try it. Subsequently I reopened the plasma myself and located the obviously noisiest part: one of three large transformers on the power supply board. On a second service visit (described as a second opinion to listen to the problem) I showed them a picture of the noisy part - but they didn't open up the plasma. They heard the noise, thought replacing the power supply board would be best, but that they had to call Panasonic and see what they said.


Panasonic is saying that their spec is 38db and they doubt it is that bad. So there is nothing they can do. The technician didn't have equipment to measure the noise level.


I called Panasonic to asked what I could do -- as it is causing physical discomfort. They convinced the service company to locate a sound meter and return to measure. I hope they fully understand the spec (distance, frequency, etc.) On the phone Panasonic couldn't tell me it.


The difficulty is that the buzz fluctuates with the image. And it's not simply brightness. In fact, the noisiest moments seem to be when there are either bright red or blue areas on the screen. All black is pretty quiet. All white isn't bad. Shows like MTV which have a lot of video changes and variety on the screen exhibit the problem quickly.


Does anyone know where I can find information about sound measurements? Is there a way I can figure out what 38db sounds like, so I can compare?


I have used a PC and a program called TrueRTA to try to measure the sound. But I used a cheap, $5 microphone and had no way to calibrate TrueRTA. But I'll try to ask around to see if I can do better.


Erik

Panny 42" HD


(Please excuse possibly a repeatitive question, but for some reason my searches on this forum don't work (often I get no results or horribly few). I figure I'm doing something wrong and I appologize for not having the patience to figure what it is.)
 

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It's been a while since I played with SPL measurements, but I want to say an office would be around 45-50Db. Again, I'm going on memory only, but 38Db should barely be audible at a meter, about the volume of a whisper.


Your best bet would be to run by your handy dandy Radio Shack type place and pick up an SPL (Sound Pressure Level just in case) meter. I think you can get a base model for around $35 or so, and quite frankly, they're very handy for tuning Home Theaters.


-edit-


One more thing I just thought about. I was looking at the rat shack site. As an example, I don't think their digital meter even reads below 50Db (but I'm not positive of that).
 

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As a point of reference, most computer CPU cooling fans run at about 50 to 65dB(A). I personally find most CPU cooling fans to be very annoying. FYI, +6dB equates to a doubling of sound level, while -6dB equates to halving of the sound level. I'm sure someone else here can supply better examples for refernce.


Regards,

Steve
 

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it is very difficult to measure a 38 db noise level unless you are in an anechoic chamber


also, you have to know at what distance/ weighting scale, etc


if a multi thousand dollar new plasma display is generating objectionable noise levels- you should demand that Panasonic correct it under their warranty: don't let them give you excuses


it is not your responsibility to measure noise levels :


but making some noise about your problem here on the AVS forum might help achieve some resolution to the problem!


Mark
 

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Discussion Starter · #5 ·
Thanks for all the input you guys!


I've got an idea.


I do have that Radio Shack sound meter. It wasn't at first any help, as you are right, it's not sensitive enough. So I gave up.


I also have the software audio spectrum analyzer TrueRTA ( www.trueaudio.com ) which does show a signal of my noise. But I have no idea of its calibration. I also don't understand the difference between the sound meter's dB scale (50 to 100db) and TrueRTA's dBu scale (-90 to 0 dBu). So I kind of gave up. Anyone know?


A co-worker told me the Radio Shack sound meter has an output jack. I didn't know. And I don't remember seeing this.


I realized today I could try two experiments:


(1) Situate both TrueRTA and the Radio Shack Sound Meter side by side and then at least calibrate TrueRTA where they both intersect in range. Maybe then I can get a ballpark level in the lower range I'm really interested in.


(2) Run the Radio Shack's meter ouput into my PC's input jack and see if I can use the Radio Shack as a microphone. Calibrate like above. I'd still have unknowns in the lower ranges, but I could at least look for consistency with above.


I'm going to also see if I can borrow from somewhere (maybe someone at work, maybe a sound store) a $200, more senstive sound meter. I see that these are available on the web - but I don't want to spend this money just for this measurement.


You're right -- I think this is Panasonic's job to correct -- especially as it is causing physical discomfort. But so far I haven't yet convinced them of the problem. I'm crossing my fingers that Panasonic's spec is set correctly for my hearing sensitivity and that the service tech is able to accurately measure the noise. I don't want to think of the hassles right now if these aren't true.


I'll post results of my sound measurements this weekend.


Erik
 

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Frankly, IMO it doesn't make a damn bit of difference what Panasonic's "specs" are. If one of their very expensive plasmas makes an objectionable noise you can hear from 8', it is their job to fix it, period, and not quibble about DB levels, or require you to buy and use a lot of measuring equipment to make a case.


There is no question that there are dead-silent Panasonics out there, and therefore the logic is inescapable that they can be quieted down. Let them bring a half-dozen or so sets to your house and fire 'em up; I guarantee there will be a quiet one somewhere in the batch. If they won't do this (as will probably be the case), then the same thing could be accomplished at a factory warehouse or showroom where several sets are available for comparison.


My own Panasonic is (thank God) one of the quiet ones. Panasonic claims it must make a noise; I just can't hear it. IMHO, pure BS and a corporate party line to keep them from fixing the problem once and for all.


Probably wouldn't be worth taking to a regular court, but if the limits in your location are high enough, small claims might be a reasonable alternative. Let Panasonic traipse in with their sound level meters and spec sheets and convince the judge what he hears really isn't "noise." Another possibility would be to find a few kindred souls and start a class action if you can find a lawyer who will take the case on a contingency basis.


There must be dozens of posts on the Forum about this buzzing plasma issue (and it certainly isn't limited to Panasonics). Every time I read one I thank God for sparing me, but curse the manufacturers for jacking up their "specs" to a point that lets them escape their legitimate responsibility to fix the problem..


IMHO the only "spec" that manufacturers of a luxury product like this should be allowed to cite is one that reads: "The Customer Must Be Completely Satisfied."
 

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So, first of all, I had to buy the Radio Shack digital meter for my buzzing Pioneer. It does not read below 50dB. True. No clue on the analog.


Second of all, every plasma buzzes. I know some of you doubt this, but it's a fact. That said, a properly designed one that is functioning properly and at low altitude, should not be audible from anywhere near the listening position. Which leads to...


Third of all, 38dB is very, very quiet. If the plasma was within spec, you would not be able to hear it while watching TV, even with the sound off. I have exceptionally sensitive hearing and I doubt that even with some sort of cone-shaped (or whatever), highly reflective wall it would be plausible to hear the plasma if it were below 38dB. Well, maybe plausible, but surely not easy.


Finally, my Pioneer's buzz was lower frequency noise, not higher frequency, for whatever that is worth.


Mark
 

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From Audio Engineering Handbook, K. Benson, 1988, p. 1.13:


Normal speech at 1m - 60dB - 10^-6 w/m^2

Suburban residence - 50dB

Library - 40dB

Empty auditorium - 30dB - 10^-9 w/m^2

Recording studio - 20dB

Breathing - 10dB

0dB - Inaudible - 0.0002ubar or 0.00002N/m^2. - 10^-12 w/m^2
 

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I second pretty much everything rogo wrote.


My Panny buzzes, changing level with the brightness of the screen. I *can* sometimes hear it from 7 to 9 feet away, if the sound drops out or is very, very low. But I rarely notice it, and I have very, very sensitive (easy to irritate) hearing. Perhaps the wood cabinet behind it absorbs some of the sound.


Every single Panny plasma I've put my ear to buzzes...and that's quite a few in the stores. However, none had objectionable levels of buzz...actually I couldn't hear it, from a "normal" viewing distance. I do the "buzz" or noise test with most plasmas I investigate, and I'm not sure if I've ever heard a completely silent plasma.


Although I said I can sometimes hear the Panny's buzz, it is much lower pitched than the scan-whir of CRT direct-view sets. That sound drives me NUTs, and I can hear it from a couple rooms away if a CRT is on in the house (even with the volume turned off).


FWIW.


Rich H.
 

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My Panasonic 32" tube set buzzes way more than my Panny 42HD set. My plasma makes a whirling sound when I first power up, for two seconds (it's the sound of the fans), then I never hear them again. It's definitely quieter, all around, than my previous 32 CRT.
 

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Uh oh..I feel a Plasma Song coming on...:eek:


We're caught in a trap..we can't walk out..cause we love our plasma's too much baby...don't ya know???:D


Name this Plasma Weekend tune.:D
 

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"Suspicious Minds"


Thank Ya, Thank Ya Very Much!
 

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Actually +3dB is doubling, not +6dB. In RF, 30dBm is 1 watt, 33dBm 2w, 36dBm 4w, 39dBm 8w, etc etc.
 

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Quote:
Originally posted by Glauco BruZZi
My Panasonic TH-37PW5UZ buzzes ( The same way my previous TH-42PW5UZ did ).

It's only audible around 6 inches no matter how bright the screen is.
Same here. I can only here it if I go round the back. Nothing is audible from the front, especially from 6ft away. I do live down at sea level (Mountain View is officially 97 ft above sea level.).
 

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Quote:
Originally posted by btwyx
Same here. I can only here it if I go round the back. Nothing is audible from the front, especially from 6ft away. I do live down at sea level (Mountain View is officially 97 ft above sea level.).
Ah hell, just leave your surround sound receiver at about -75 that should take care of any buzzing sound you hear (and will leave you deaf for a good portion after your done watching you movie).


Have them fix it, I have the TH-42PWD5UZ and can't hear a damn thing from >6".
 

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"Other Rich"... I know you were joking, but I find this notion of "I can't hear while I'm watching anything" to be a bad method of noise canceling. Why? Because there is nothing worse than having a quiet passage punctuated by a buzzing sound.


People in the projector forums always use the rationalization I cited when explaining why their "jet engine" projection is no problem. It scares me because I am seriously considering a projector right now.


Mark
 

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Totally agree (I have got to move the 75 gallon fish tank), just being sarcastic. I really don't notice any buzzing but my set is only a week old now.
 

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Discussion Starter · #20 ·
The attached file shows the difference in sound level between my ambient room condition and my Pannasonic plasma while it was displaying a buzz prone scene off an NTSC broadcast (Hollywood Squares). Measurements were taken with TrueRTA ( www.trueaudio.com ) calibrated at the microphone input with a multimeter (as instructed in TrueRTA). The microphone was placed 4" to the left and facing the plasma and was used in this position for both the ambient and buzz measurements. The microphone's characteristics are unknown - but it did "hear" the buzz clearly.


Graphed is the difference between the ambient and buzz measurements over frequency. TrueRTA measures the level at the PC's microphone input (which I calibrated) and is expressed in dBu. I subtracted the ambient dBu values from the buzz dBu values for each frequency to create the graph.


You'll notice the microphone generated a +13 dBu level increase over ambient at near 5khz (the largest peak). +4 through +8 dBu over the 2khz-6khz range.


I attempted to use the Radio Shack sound pressure meter to calibrate my setup in order to convert to dB sound pressure units. Unfortunately the Radio Shack sound meter only reaches down to 50 dB - which was unable to register my ambient or buzz level. I attempted to calibrate with louder sounds but became befuddled.


I just received a message from my servicer assigned by Panasonic. They are now not going to physically measure the sound level to see if it is within spec - explaining that the ambient sound in my room won't facilitate such a measurement. In consultation with Panasonic, they said they have determined, in their professional judgement, that the unit is functioning within its normal range. They said plasma TVs make noise that varies with image - including the panel itself. They say there is nothing more that can be done. (In their message they erroneously claimed that they had already attempted replacing two boards, including the power supply board. I wonder if they told this to Panasonic. Because actually, during their first visit, they changed one board, the board to the right of the power supply board - as that board was presupplied to them by Panasonic beforehand.)


I am now left with what I consider a very unpleasant task of escalating with Panasonic. I'm not used to handling these types of issues -- as I fully expect, at whatever level I reach, I'll be repeatedly told the unit is operating normally and there is nothing more to do.


Erik
 
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