al@gtx.com (0732) (08/20/87)
One often hears about people blowing whistles or air horns into a telephone to thwart obscene callers. Is a telephone capable of transmitting enough sound amplitude to cause pain or damage to the ears? If so, this seems to be a dangerous capability in the hands of some crank. -------------------------------------------------------------- | Alan Filipski, GTX Corporation, Phoenix, Arizona 85021, USA | | {ihnp4,cbosgd,decvax,hplabs,seismo}!sun!sunburn!gtx!al | --------------------------------------------------------------
ken@nsc.nsc.com (Ken Trant) (08/21/87)
in article <414@gtx.com>, al@gtx.com (0732) says: > One often hears about people blowing whistles or air horns into a > telephone to thwart obscene callers. Is a telephone capable of > transmitting enough sound amplitude to cause pain or damage to the ears? > If so, this seems to be a dangerous capability in the hands of > some crank. Yes it can, I once worked for PacBel and there were several people (operators, 411) who received permanent hearing loss while working. The headsets (and phone system) could and did transmit a db noise level that would cause this to happen. -- Ken Trant, Real Estate Professionals 415-651-3131 408-721-8158
ark@alice.UUCP (08/21/87)
In article <414@gtx.com>, al@gtx.UUCP writes: > One often hears about people blowing whistles or air horns into a > telephone to thwart obscene callers. Is a telephone capable of > transmitting enough sound amplitude to cause pain or damage to the ears? I highly doubt it. Telephone transmission lines must be sharply amplitude-limited to keep crosstalk in check.
larry@kitty.UUCP (Larry Lippman) (08/22/87)
In article <414@gtx.com>, al@gtx.com (0732) writes: > One often hears about people blowing whistles or air horns into a > telephone to thwart obscene callers. Is a telephone capable of > transmitting enough sound amplitude to cause pain or damage to the ears? > If so, this seems to be a dangerous capability in the hands of some crank. The general answer to your question is that acoustic injury via telephone is improbable, but not impossible, depending upon specific circumstances which I will outline below. Bear in mind that there is a substantial difference in sound energy required to make a listener "uncomfortable" versus the energy level required to say, damage the tympanic membrane. First of all, consider the receiver element in a telephone handset. Almost all receiver elements in use today are electrodynamic transducers, not unlike that of a radio speaker. In a typical receiver element, the changing voltage as applied to an electromagnet coil creates a variable magnetic field which causes a magnetized, thin metal diaphragm to flex, thereby compressing and rarefying the air, thereby creating sound waves. Now the point is that this diaphragm can only move SO much, regardless of the magnitude of applied voltage, thereby _limiting_ the maximum sound level it can produce. A typical electrodynamic receiver element, such as the "U1", will "top out" at well under 120 dB SPL, even at its peak reproduction frequency (say, around 1 kHz). For what might be referred to as "casual" exposure, 120 db SPL is not going to cause any physiological injury. As a point of comparison, the threshhold of pain is generally considered to be 140 dB SPL. Second, there are limits to the amount of electrical energy which can be transmitted over a dialed telephone connection. Audio frequency energy transmitted over a telephone line will not be propagated beyond a certain level; the reason is that certain telephone network components such as transformers and inductors will magnetically saturate and thereby limit transmission level. Furthermore, active functional components of the telephone network such as amplifiers, repeaters, PCM codecs, etc. will also saturate and not pass audio energy beyond a certain level. In general terms, if one were to electrically connect an audio frequency generator to a dialed telephone connection, regardless of the magntiude of input energy, it is improbable that more than 20 dBm (100 mW) of energy could be delivered to the receiving telephone IF the call were switched through an electromechanical central office, and IF both the calling and called party were in the SAME central office. If the telephone central office were ESS and/or if the called party was served by a different central office, it is highly improbable that more than 10 dBm (10 mW) of energy could be delivered to the receiving telephone. Even using the worse-case figure of 100 mW as applied to say, a U1 receiver, it is improbable that even 110 dB SPL could be achieved - still a far cry below even the threshhold of pain. Furthermore, at this kind of energy level, the "click-suppression" varistor across the U1 handset would begin some serious conduction, thereby shunting energy away from the receiver. Third, a telephone transmitter - either traditional carbon or the newer reluctance variety - will saturate if a sound level (like a boat horn) is applied to it, thereby limiting the amount of any electrical signal it may generate. So, for any or all of the above reasons, it is improbable that sufficient acoustic energy (sound pressure level in dB) could be created such that physiological injury would occur. There is one factor that could contribute to possible physiological injury - but it is not commonly found. I will relate a little firsthand story... As a combination EE/biochemist with a multidisciplinary background, I have done some forensic science consulting for a number of years. About ten years ago, I was retained as a consultant in a workmen's compensation case. It seems that a middle-aged woman who had worked as a switchboard operator for 20-some years had applied for compensation resulting from partial hearing loss in one ear. Her allegation was that then presence of clicks and loud noises in her "headset ear" over many years caused her hearing loss. My function was to work with an otolaryngologist to disprove her claim. My first reaction was that there was insufficient sound pressure level to cause such injury. However, I learned that for the past five years the woman used a Plantronics miniature headset (the kind with a flexible plastic ear tube). Now with such a headset, there was an almost perfect sound conduction between the receiver element and the ear. So, we contacted Plantronics and got some engineering information. We got a sample headset and conducted our own sound pressure measurements using a Bruel & Kjaer "artificial ear". The conclusion was that the maximum sound pressure level which could be experienced through this headset in a switchboard environment was still insufficent (by generally accepted medical criteria) to cause hearing impairment. But the use of a receiver with a plastic ear tube did make me seriously consider the possibility of injury. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
tjhorton@utai.UUCP (08/22/87)
Properly designed systems 'should not' be able to injure
(but that's 'should not', not 'cannot').
With digital systems, you can easily design in limits on the maximum
sound level, since there is always filtering of SOME sort anyways.
(this may be 'implicit' in the design, but nevertheless there)
The trouble is, with digital systems, things don't always behave.
"PCM hits" are a class of problem that have plagued some transmission
systems, and can come in in any number of ways, on the switch side.
On the phone side, there's always static discharge, lightning, etc.
But in any case, none of these are ways that a caller can use to
hurt your ears. Since most phone calls in North America get digitized
somewhere along the line (I don't have figures) this should be the rule.
In analog systems, it's easy enough to use current or voltage limiting
on the drivers, but I'm not sure that this is as suitable or flexible.
The human ear can tolerate enormous sound levels in general, but it
all depends on the phones and switching equipment involved. You have
to take into account evan what the handsets can pick up and deliver.
Speaking of lightning... I had the pleasure of doing some work to
design protection systems for phones... to put it simply, it's
damned well impossible to lightning-proof a phone.
You can get lightning hit one or both of tip and ring, thousands
or millions of volts get through to the phone, and any nature of
impedance between the actual strike and the phone.
I know someone personally who had a 12 inch arc go from the phone's
mouthpiece (in her hand) to a nearby windowframe. Surprise!
--
Timothy J Horton (416) 979-3109 tjhorton@ai.toronto.edu (CSnet,UUCP,Bitnet)
Dept of Computer Science tjhorton@ai.toronto.cdn (EAN X.400)
University of Toronto, {seismo,watmath}!ai.toronto.edu!tjhorton
Toronto, Canada M5S 1A4robert@uop.UUCP (Glen Fiddich) (08/23/87)
there is a class action suit against a few corporations who will remain nameless for the wireless phones they built that had the ringers in the earpiece... if you did not take it off hook before you put it to your ear... well, bye bye eardrum!! this almost happened to me once with a webcor phone, but i do believe that some changes have been made in the portable phone areas regarding this sort of thing. btw-just what can be transmitted over a phone?? what is the bandwidth, and amplitude cielings?? always curious about something....
commgrp@silver.bacs.indiana.edu (08/24/87)
In article <414@gtx.com>, al@gtx.com (0732) writes: > One often hears about people blowing whistles or air horns into a > telephone to thwart obscene callers. Is a telephone capable of > transmitting enough sound amplitude to cause pain or damage to the ears? > If so, this seems to be a dangerous capability in the hands of some crank. Larry Lippmann responds: > ...it is improbable that sufficient acoustic energy (sound >pressure level in dB) could be created such that physiological injury >would occur. > > ...As a combination EE/biochemist with a multidisciplinary >background, I have done some forensic science consulting for a number >of years. About ten years ago, I was retained as a consultant in a >workmen's compensation case. It seems that a middle-aged woman who >had worked as a switchboard operator for 20-some years had applied for >compensation resulting from partial hearing loss in one ear. Her >allegation was that then presence of clicks and loud noises in her >"headset ear" over many years caused her hearing loss. My function >was to work with an otolaryngologist to disprove her claim. > > My first reaction was that there was insufficient sound pressure >level to cause such injury. However, I learned that for the past five >years the woman used a Plantronics miniature headset (the kind with a >flexible plastic ear tube). Now with such a headset, there was an >almost perfect sound conduction between the receiver element and the >ear. So, we contacted Plantronics and got some engineering >information. We got a sample headset and conducted our own sound >pressure measurements using a Bruel & Kjaer "artificial ear". The >conclusion was that the maximum sound pressure level which could be >experienced through this headset in a switchboard environment was >still insufficent (by generally accepted medical criteria) to cause >hearing impairment. > > But the use of a receiver with a plastic ear tube did make me >seriously consider the possibility of injury. The big danger of plastic ear tubes, as in Plantronics headsets, is transmission of ear infection if headsets are shared. Wearing such a device, even if clean, for long periods might help incubate ear infections. Plantronics' latest models use a lightweight conventional external earphone instead of the ear tube. I like Plantronics headsets, especially the old model MS-50 with the headband (as worn upside-down by Clint Eastwood in the airplane hijacking scene in "Dirty Harry"). Plantronics headsets configured for telephone service are available for $10 to $20 at hamfests (regional gatherings of ham radio operators). They are easily modified for radio service; I use them while flying, and with my mobile and handheld ham rigs. I also have a custom-made hard plastic earmold with an external bar for mounting the MS-50, and a flexible tube to connect to the earphone output. It's very comfortable, and ideal for emergency service and high-noise environments. (Kits are available for making your own ear impression, which is mailed back to the company which makes the finished product.) reference: ---------- Reid, F. "Using Simulated Carbon Microphones with Amateur Trans- mitters" _Ham Radio_ magazine, Oct. 1981 p. 18. -- Frank Reid PO Box 5283 Bloomington, IN 47402 reid@gold.bacs.indiana.edu
jeff@aiva.ed.ac.uk (Jeff Dalton) (08/25/87)
In article <1952@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: >It seems that a middle-aged woman who had worked as a switchboard >operator for 20-some years had applied for compensation resulting from >partial hearing loss in one ear. Her allegation was that then presence >of clicks and loud noises in her "headset ear" over many years caused Could the "many years" have been significant? My understanding was that prolonged exposure to noise levels well below the threshold of pain (say at 90 db) could cause hearing loss through damage to the inner ear. The maximum level of transmitted sound would not be the only factor. -- Jeff
larry@kitty.UUCP (Larry Lippman) (08/25/87)
In article <154@aiva.ed.ac.uk>, jeff@aiva.ed.ac.uk (Jeff Dalton) writes: > >It seems that a middle-aged woman who had worked as a switchboard > >operator for 20-some years had applied for compensation resulting from > >partial hearing loss in one ear. Her allegation was that then presence > >of clicks and loud noises in her "headset ear" over many years caused > > Could the "many years" have been significant? My understanding was that > prolonged exposure to noise levels well below the threshold of pain (say > at 90 db) could cause hearing loss through damage to the inner ear. The > maximum level of transmitted sound would not be the only factor. You could very well be correct. My involvement in this matter happened in 1975. Since that time, however, a number of occupational health studies of hearing loss have occurred (spurred by OSHA, of course). I should have posted a bit more information about the case. The woman had a hearing loss in _both_ ears, although she only wore a headset in one ear. The headset ear had a greater hearing loss than the non-headset ear. Two otolaryngologists diagnosed the woman as having a hearing disorder known as otosclerosis; this condition is an organic disease, and is not the result of any excessive sound level exposure. However, the woman wanted to get workmen's compensation benefits (I suppose you can't blame her for trying :-) ), so she claimed that the greater hearing loss in her headset ear was NOT otosclerosis, but was an occupational injury. All I did was to examine the electronics and acoustics of the headset and telephone switchboard environment, and give the acoustic measurement data (sound pressure level, etc.) to an otolaryngologist for use in his medical evaluation. The woman was denied workmen's compensation benefits because: (1) she had a clearly diagnosed organic ear disease which was not related to occupational exposure; and (2) based upon the measurements of acoustic exposure and the generally accepted standards of the time, the sound pressure exposure was insufficient to cause hearing loss. The truth (with some hindsight): Who knows? <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
larry@kitty.UUCP (Larry Lippman) (08/25/87)
In article <24300015@silver>, commgrp@silver.bacs.indiana.edu writes: > The big danger of plastic ear tubes, as in Plantronics headsets, is > transmission of ear infection if headsets are shared. Wearing such a > device, even if clean, for long periods might help incubate ear > infections. Plantronics' latest models use a lightweight conventional > external earphone instead of the ear tube. Yucch! If you have even seen the earwax that accumulates in the plastic tubes, that is a truly disgusting thought... :-) Any place where I have seen shared headsets, the operators had their own plastic ear tubes. Personally, I dislike the Plantronics headsets with the ear tube. Some switchboard operators just refuse to wear them, and would rather use the somewhat ancient 52-type headset or a conventional telephone handset. > I like Plantronics headsets, especially the old model MS-50 with the > headband (as worn upside-down by Clint Eastwood in the airplane > hijacking scene in "Dirty Harry"). Plantronics headsets configured > for telephone service are available for $10 to $20 at hamfests > (regional gatherings of ham radio operators). They are easily > modified for radio service. If you "shop around", you can find these headsets in a version that has a push-to-talk switch on the amplifier housing. Actually, there are two versions with a switch; one version uses the switch to open and close the microphone circuit, while the other version leaves the microphone on all the time but uses the switch to close the circuit on an auxiliary wire pair (this version uses a double plug with tip, ring, and sleeve on each plug). If you have the kind which uses a switch to open and close the microphone circuit, you can still use this for transmitter keying if you sense the DC current flow in the microphone circuit when the switch is closed. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
jeffw@midas.UUCP (Not the Plantronics Enforcement Department) (08/26/87)
In article <1952@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: [lots of evidence that you can't usually suffer ear injury from sounds over the phone] [Continues with story of one case he consulted on...] > My first reaction was that there was insufficient sound pressure >level to cause such injury. However, I learned that for the past five >years the woman used a Plantronics miniature headset (the kind with a >flexible plastic ear tube). Now with such a headset, there was an almost >perfect sound conduction between the receiver element and the ear. So, >we contacted Plantronics and got some engineering i Here transmission ends. So remember, kiddies, say only nice things about Plantronics. Or else. Plantronics. A division of Pepperidge farms. And Pepperidge farms REMEMBERS!
adam@gec-mi-at.co.uk (Adam Quantrill) (09/07/87)
In article <414@gtx.com> al@gtx.UUCP (Al Filipski) writes: >Is a telephone capable of transmitting enough sound amplitude to cause pain >or damage to the ears? > I don't know about the transmission capabilities, but the Post Office in the UK was sued when an engineer accidentally dropped 250V ac onto a connected line and blew someone's ear away with the noise. I have a feeling that the exchange could limit the amplitude of incoming signals. -Adam. /* If at first it don't compile, kludge, kludge again.*/