[net.audio] "Ultrasonic" hearing

wmartin@brl-tgr.ARPA (Will Martin ) (01/06/86)

In article <1260@brl-tgr.ARPA> gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) writes:
>By the way, the fellow who got headaches in the room full of burning-in
>monitor assemblies was probably being affected by the near-ultrasonic
>sound generated by the horizontal circuits (often transformer laminations
>vibrating).  Even if he didn't consciously hear them, such whistles would
>lead to irritability and headaches.

For what it's worth, the latest issue (#28, I think) of The $ensible Sound,
an "underground" audio magazine, has a report of a recent study which
found that people could *really* hear up to 40 kHz, not the
previously-believed 20 kHz limit. The older studies, according to the
item, used transducers to reproduce the high-frequency sounds which were
defective or inferior, masking the higher frequencies in distortion.

There was no reference or citation; I wonder if some of the net.med
people can locate the real study this item was based on, and post a
reference or bibliographic note? This sort of info might be used to
force terminal designers to finally eliminate all that nasty high-pitched
noise their products emit!

Will

dyer@harvard.UUCP (Steve Dyer) (01/07/86)

I don't know anything about so-called "Ultrasonic" hearing, but
I do know that the flyback transformers on most monitors emit a
buzz around 17-19 khz; the exact frequency escapes me right now.  
This is "ultrasonic" only for most people over 30 or 35 years of age.
I can hear it, and I have several friends who can hear it.  It
doesn't bother me, but this does seem to be a point of contention for
audiophiles who feel pushed headlong into a shotgun marriage of audio
and video, since they claim that the sound of the monitor is especially
disturbing during music, and makes any pretense to otherwise low
distortion and noise figures quite silly.

For example, the Pioneer CD/LaserDisc player has its programming
display on the video monitor, eschewing low-tech LEDs.
-- 
/Steve Dyer
dyer@harvard.harvard.edu
harvard!dyer

ark@alice.UucP (Andrew Koenig) (01/07/86)

> I don't know anything about so-called "Ultrasonic" hearing, but
> I do know that the flyback transformers on most monitors emit a
> buzz around 17-19 khz; the exact frequency escapes me right now.  
> This is "ultrasonic" only for most people over 30 or 35 years of age.

I think it's 15,750 Hz: 525 lines on the screen times 60 Hz refresh rate,
divided by 2 because of alternate scanning.  People's ability to hear
it seem to vary greatly by individual, even among children.

spp@ucbvax.BERKELEY.EDU (Stephen P Pope) (01/07/86)

     I've never encountered a TV receiver or monitor that
didn't emit an annoying high pitched squeal at at least a
low audible level.  I don't know (or care) whether this is
15.75, 17 or 19 KHz ( the three numbers people usually 
throw out).  I suspect it is there because the receivers
are not built real well.  A real solid frame and chassis would
almost certainly help.  
     On a related subject, I understand that some native
tribes in quiet, undeveloped third-world areas have been
found to be able to hear well up to 40 or 50 KHz.  Apparently,
the average westerner can hear only up to 12 to 20 Khz
mostly because of exposure to noise all his life.

steve

abeles@mhuxm.UUCP (J. Abeles (Bellcore, Murray Hill, NJ)) (01/08/86)

> I do know that the flyback transformers on most monitors emit a
> buzz around 17-19 khz; the exact frequency escapes me right now.  
about 15.75 kHz, actually.

alw@mit-eddie.UUCP (Alan Wu) (01/08/86)

In article <1280@brl-tgr.ARPA> wmartin@brl-tgr.ARPA (Will Martin ) writes:
>                                 ... This sort of info might be used to
>force terminal designers to finally eliminate all that nasty high-pitched
>noise their products emit!
>
Hear, hear!

If you can't hear the nasty high-pitched noise emitted by most video
terminals, think about what this says about your sense of hearing in
the region of 15,570 Hz ...

oleg@birtch.UUCP (Oleg Kiselev) (01/09/86)

In article <11370@ucbvax.BERKELEY.EDU> spp@ucbvax.BERKELEY.EDU (Stephen P Pope) writes:
>
>     I've never encountered a TV receiver or monitor that
>didn't emit an annoying high pitched squeal at at least a
>low audible level.  I don't know (or care) whether this is
>15.75, 17 or 19 KHz ( the three numbers people usually
>throw out).  I suspect it is there because the receivers
>are not built real well.  A real solid frame and chassis would
>almost certainly help.

I have heard it is usually the vibration of transformers and/or capacitors
(fly-back transformer?????). THe worst offenders I have heard were
tvi925 . Sometimes a sharp rasp on the side of the terminal would silence
it for an hour or so ( and many people got so irritated by the squeal they
did it routinely).
And what about the fan noise in large micros?

>     On a related subject, I understand that some native
>tribes in quiet, undeveloped third-world areas have been
>found to be able to hear well up to 40 or 50 KHz.  Apparently,
>the average westerner can hear only up to 12 to 20 Khz
>mostly because of exposure to noise all his life.

It was also said that their 60-70 year-olds had hearing in exess of that of the
early 30's-late 20's eurpean urban dwellers ( the researchers). The oldsters
also were very alert and had no hart illnesses....

Whoops! I have just realized MY terminal started squealing! <RASP!> jd,bc,
d||{~|
--
Disclamer: I don't work here anymore - so they are not responsible for me.
+-------------------------------+ Don't bother, I'll find the door!
|   STAY ALERT! TRUST NO ONE!   |                       Oleg Kiselev.
|     KEEP YOUR LASER HANDY!    |...!{trwrb|scgvaxd}!felix!birtch!oleg
--------------------------------+...!{ihnp4|randvax}!ucla-cs!uclapic!oac6!oleg

fish@ihlpm.UUCP (Bob Fishell) (01/10/86)

 
> For what it's worth, the latest issue (#28, I think) of The $ensible Sound,
> an "underground" audio magazine, has a report of a recent study which
> found that people could *really* hear up to 40 kHz, not the
> previously-believed 20 kHz limit. The older studies, according to the
> item, used transducers to reproduce the high-frequency sounds which were
> defective or inferior, masking the higher frequencies in distortion.
> 
> There was no reference or citation[.]

Sounds like more smoke blown up the wazoo by the anti-digital crowd to
me.
-- 
 __
/  \
\__/
				Bob Fishell
				ihnp4!ihlpg!fish

rab@well.UUCP (Bob Bickford) (01/12/86)

In article <251@birtch.UUCP>, oleg@birtch.UUCP (Oleg Kiselev) writes 
about people being annoyed by the squeal put out by monitors and tv sets.
(BTW, it is [usually] the mechanical vibration induced in the flyback
transformer at 15,750 Hertz [B/W] which is audible.)

Then the discussion turned to Ultrasonic hearing.

On this subject, I used to work installing so-called "ultrasonic"
alarm systems and several times complained to my boss that I could
hear them (and they were giving me headaches).  I finally convinced
him by doing a complete install and alignment of a system without
the usual test equipment, in a difficult location.  I still (even
after several years of rock 'n' roll) have hearing up to around 20kHz.
(the alarms were between 25 and 40 kiloHertz)  (I'm 27)

	Robert Bickford     (rab@well.uucp)
================================================
    I doubt if these are even my own opinions.
================================================

larry@kitty.UUCP (Larry Lippman) (01/12/86)

> I don't know anything about so-called "Ultrasonic" hearing, but
> I do know that the flyback transformers on most monitors emit a
> buzz around 17-19 khz; the exact frequency escapes me right now.  
> This is "ultrasonic" only for most people over 30 or 35 years of age.

	The frequency is 15,750 Hz - which is not that high, and is not
`ultrasonic'.  Whether or not you hear the flyback on a given monitor is
a poor indication of your hearing ability, since better quality flybacks
produce very little audio energy.

==>  Larry Lippman @ Recognition Research Corp., Clarence, New York        <==
==>  UUCP    {decvax|dual|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry  <==
==>  VOICE   716/741-9185                {rice|shell}!baylor!/             <==
==>  FAX     716/741-9635 {G1, G2, G3 modes}    duke!ethos!/               <==
==>                                               seismo!/                 <==
==>  "Have you hugged your cat today?"           ihnp4!/                   <==

edhall@randvax.UUCP (Ed Hall) (01/12/86)

>> For what it's worth, the latest issue (#28, I think) of The $ensible Sound,
>> an "underground" audio magazine, has a report of a recent study which
>> found that people could *really* hear up to 40 kHz, not the
>> previously-believed 20 kHz limit. The older studies, according to the
>> item, used transducers to reproduce the high-frequency sounds which were
>> defective or inferior, masking the higher frequencies in distortion.
>>
>> There was no reference or citation

The fact is plausible, but the explanation is absurd.  Nonlinearities
in reproduction may add harmonics to the acoustic signal, and for
an especially bad transducer might even excite resonances at sub-
harmonics of the test frequency.  But if an appropriate amount of
acoustic power is being generated at the test frequency, anything
masking it would have to be as least as audible.

As a personal note, at 31 I'm still bothered by TV and terminal
horizontal frequencies--but not as much.  It's one of the benifits
of getting older...

                -Ed Hall
                ihnp4!sdcrdcf!randvax!edhall

paluzzi@oddjob.UUCP (Greg Hajek) (01/15/86)

(To net.micro.mac readers:  this has been an ongoing discussion in net.audio,
 but as this posting is a bit of a digression from audio talk, I have directed
 followups to n.s.m.)

In article <251@birtch.UUCP> oleg@birtch.UUCP (Oleg Kiselev) writes:
>>     I've never encountered a TV receiver or monitor that
>>didn't emit an annoying high pitched squeal at at least a
>>low audible level.
>
>I have heard it is usually the vibration of transformers and/or capacitors
>(fly-back transformer?????). THe worst offenders I have heard were 
>tvi925 . Sometimes a sharp rasp on the side of the terminal would silence
>it for an hour or so ( and many people got so irritated by the squeal they
>did it routinely).

I have had the same problem with my Mac, and also found that the "sharp rasp"
(read: "swift kick") solution is usually effective.  Why is this?  I never
had the problem before I blew my power supply, and had to replace the analog
board.  Can anybody suggest a possible solution (or a reason why this problem
would suddenly crop up, for that matter)?

-- 
"God lives in Eternity...He doesn't have to listen to Two-for-Tuesdays."

Greg Hajek
U. of Chicago           ...ihnp4!gargoyle!oddjob!paluzzi
Laboratory for Astrophysics and Space Research

rich@aoa.UUCP (Rich Snow) (01/16/86)

In article <11370@ucbvax.BERKELEY.EDU> spp@ucbvax.BERKELEY.EDU (Stephen P Pope) writes:
>
>     I've never encountered a TV receiver or monitor that
>didn't emit an annoying high pitched squeal at at least a
>low audible level.
	
	Bothers me too. I used to work in a TV factory.  The noise 
emenates from a coil in the horizontal oscillator of the Magnavox chassis
we used.  At one time a production line solution to sqeals of painful volume
was to heatshrink the coil in question.  Kind of like a straight jacket... 

	In some sets, the flyback itself vibrates. I would not suggest
surrounding it with heatshrink, maybe RTV?  

	Does anyone out there have a "digital" tv, and assuming you are
one of us that hears this noise (some don't) does your set squeal?

		a vidiot,

	Rich Snow  AOA-----------------*
	...!{decvax,linus,ima,ihnp4}!bbncca!aoa!rich
	...!{wjh12,mit-vax}!biomed!aoa!rich

bart@reed.UUCP (Bart Massey) (01/18/86)

> (To net.micro.mac readers:  this has been an ongoing discussion in net.audio,
>  but as this posting is a bit of a digression from audio talk, I have directed
>  followups to n.s.m.)
> 
> In article <251@birtch.UUCP> oleg@birtch.UUCP (Oleg Kiselev) writes:
> >>     I've never encountered a TV receiver or monitor that
> >>didn't emit an annoying high pitched squeal at at least a
> >>low audible level.
> >
> >I have heard it is usually the vibration of transformers and/or capacitors
> >(fly-back transformer?????). THe worst offenders I have heard were 
> >tvi925 . Sometimes a sharp rasp on the side of the terminal would silence
> >it for an hour or so ( and many people got so irritated by the squeal they
> >did it routinely).
> 
> I have had the same problem with my Mac, and also found that the "sharp rasp"
> (read: "swift kick") solution is usually effective.  Why is this?  I never
> had the problem before I blew my power supply, and had to replace the analog
> board.  Can anybody suggest a possible solution (or a reason why this problem
> would suddenly crop up, for that matter)?
> 

	My old high school electronics teacher said that it is in fact the
flyback transformer vibrating (which makes sense) after it has worked a little
loose from its mounting bracket.  He claims he'd fixed many of them by shimming
them with pieces of toothpick.  WARNING:  THIS IS A HIGH VOLTAGE AREA!! DO NOT
TRY THIS UNLESS YOU KNOW EXACTLY WHAT YOU ARE DOING!!! I WILL NOT BE
RESPONSIBLE FOR YOUR ELECTROCUTION!!

					Bart Massey
					..tektronix!reed!bart