Tip:
Highlight text to annotate it
X
(Doug Edworthy) This presentation is going to be done
by two people, myself, and my colleague, Richard McKinley, who’s going to
talk in the middle of the presentation about some of the practical problems that
can occur, and their solutions. Well let's have a look at the categories of
noise. What sort of noises do we hear in a hearing
aid? Well, I think there are three categories of noise. There's environmental
radio frequency interference, and there are more details about this in the
addendum to this presentation that you can obtain in the on-line copy. There
is also interference from the loop system itself. And once again,
there are details in the addendum. But the main part of our talk today is going
to be about environmental magnetic interference. Buzzing, static, that
sort of thing. Well, is noise really a problem? In my experience,
many loop systems have no noise problem at all. And where there
is noise, it can often be solved completely satisfactorily, and really importantly,
the possibility of noise mustn't prevent audiologists from dispensing
hearing aids with telecoils activated. I think there is
sometimes a worry that noise will be a problem for hearing aid users,
and this may stop some audiologists from dispensing hearing aids
with telecoils. Briefly, I just want to describe what radio
frequency interference sounds like. It's generally tones, warbles, static; that's
higher frequency noises, and importantly radio frequency interference
can be heard with both the "T" position, "T" program enabled, and
the microphone enabled. It can be heard when the loop system is not
switched on. If you'd like more information about this, please have a look
at the addendum in the end of this presentation. The interference that's
generated by the loop system itself can be hum, buzz, crackles and whistles. But
it's only heard when the hearing aid is set to the "T" position
or program. It will stop when the loop system is switched
off, so one way of identifying this noise, is to switch the loop system on
and off. Does the noise go away? If it does, it's generated by the loop system
itself. Once again, we don't have time today to cover that, there's more information
in the addendum. But on to the main subject of this morning's
talk, environmental magnetic interference. What does it sound like? Well,
it's hum, it's buzzing, it's crackles and importantly, it's only heard
with the hearing aid switched to the "T" position. And even more importantly,
it's heard even when the loop system is switched off. So it's not
noise that's generated by the loop system, it's noise that's present
in the environment that the loop system is installed in. How is environmental
magnetic interference caused? Well, any alternating electric current
creates an alternating magnetic field. And this is exactly the same
way that an audio induction loop, a hearing loop works. And because the interference
is caused in the same way as the induction loop works, its interference
is sound that is picked up by the hearing aid. It can come from a wide
variety of sources. Perhaps the most important is badly installed
AC power cabling, and I know Richard is going to talk more about that.
It can come from AC power transformers. It can come from electric motors, from electric
heating systems, from the cathode ray tube, the tube type of
televisions or display monitors. It can come from fluorescent--that's strip
lighting. It can come from lighting dimmers. It can even come from other
nearby loop systems, But how much noise is too much noise? Well,
this is very subjective. What might be an acceptable noise to me, would
be an unacceptable noise to you, and vica-versa. But if the loop system is
going to be used for critical listening; such as in a theater or a cinema,
then the noise level must be very low. Whatever the type of noise, whether
it's a hum, whether it's a buzz, whether it's a crackle, it must be virtually
inaudible. Otherwise it's going to spoil the enjoyment of the program. But
if the loop system is going to be used for short term communication, perhaps
at a ticket office, a teller's window, or an inquiry desk, then the noise could be
higher and still be acceptable, because in a short term communication where
it's one-to-one, you have the opportunity of asking the person to repeat
what they just said if you haven't been able to understand them. Generally,
if the noise spoils enjoyment, or it makes it difficult to understand speech,
then it's too noisy. But as I say, this is very subjective. Now
just as a short demonstration, I'm going to connect a loop receiver to the
audio system in the theater, and we're going to see just how bad, or how
good the level of noise is in this theater. (Humming Sound) Now people using
hearing aids will already be listening to any noise that's in this theater.
Let's see if anybody else (Humming Sound Off) can pick up this noise
through the audio system. What you're listening to now, is the background
magnetic noise in the theater. And I think you'll agree, it's pretty low.
Can anybody hear a distracting noise? (Audience member) I hear a high pitched beep,
about a minute or so, beep. (Doug Edworthy) Okay. Can anybody hear that
on the audio system? I'm not sure where that beep's coming from
Julia, but that seems an interesting point, and we'll see if we can track that
down. Thank you. What I wanted to demonstrate is that in many
places, interfering magnetic noise is not really a problem. And since I've been
here in Washington; I arrived here last Wednesday; I've walked around the hotels,
I've traveled on the Metro, and I've taken a hearing aid with me and listened
critically to magnetic noise, and to be honest, I haven't really heard much.
Now there is an international standard. For those of you that like numbers,
it's called "IEC 60118-4." It's an international standard for loop systems,
for the performance of loop systems, and it has technical requirements
for environmental magnetic noise. It recommends maximum noise
levels for different types of loop use. It recommends a particularly
low level for critical listening, and it allows higher noise levels for areas
or for uses where we're just using the loop for short term communication.
On a technical note, it requires a measurement of the noise, using
an "A weighted" filter. I won't go into the technical details of this
now, but there are details available in the addendum to this presentation.
But in simple terms, "A weighted" filtering mimics the way that
the human ear perceives sound, so it makes allowances for the fact that the
human ear is less sensitive to low frequency and high frequency sounds,
and most sensitive to sounds in the middle of the frequency range. If you
measure noise with a meter that has a flat frequency response, it is
quite likely the readings will be misleading. So it's very important that an
"A weighted" filter is used for measuring background magnetic noise. Now
at this stage in the presentation, I'd like to hand over to Richard McKinley,
who is going to take you through some more information about the sources of
magnetic noise, and how that magnetic noise can be overcome.
(Richard McKinley) Thank you very much, Doug. I'm going to talk about
some actual experiences with loop systems. But one of them from an installation
and engineering standpoint, is often the issue with the loop system interference
has nothing to do with the hearing aid user. Something to be aware of is that
often the hum that the facilities agent, the person who is requesting
the loop system to put in, will hear through the help of the headphones
of a loop receiver. And that becomes something that, even though we look for the
signal-to-noise ratio we want to give to the hearing aid user, it's something
that needs to be taken care of up front and handled, because somebody with
relatively normal hearing, and taking a loop receiver and turning it up,
can hear some hum; and question the value of the loop system to the
hearing aid wearer. What is the hum we actually hear? We call it "60 Hertz,"
and it's relative to the electrical system which they say in the United States,
we call it 60 hertz. It's various frequencies around the world, and there are
what we call "harmonics" of that, that we hear. We're not actually listening
to in most cases, the 60 hertz itself, but we're listening to the
third, the sixth and the ninth harmonics of those frequencies.
Doug talked a little bit about sources of magnetic interference and we'll
go into it in just a little bit in more detail; and in the end we'll kind of
summarize a little later what improvements have been made, and why,
at least in the U.S., it's much easier to install a system relative to background
interference today, than it was even 10 years ago. Doug talked about
fluorescent lighting, old tube TV's, we'll go through those.
Fluorescent ballasts. In about the 1990's, a number of the companies in
the United States ordered millions of ballasts from a country overseas,
and they all came in bad. They all had huge amounts of ground issues.
The only really good part about that is that none of them lasted very long.
Somewhere around the year 2002, almost all of them burned out.
I still do run into a few, but I've actually been into a church that just
re-ballasted the whole facility back in about 2000, and it was just a nightmare
from one end to the other. But most of those ballasts are now out of the
system, and most of the ballasts today are electronic ballasts going in,
and we do not have issues with them. Also the FCC, the Federal Communications
Commission implemented some tests since then, that have required to determine
the amount of emissions these products can give off. The third possibility with
fluorescent lights, and we'll talk about that a little more, is that poor wiring
is not uncommon with fluorescent lights. I'll often hear somebody say,
"we have bad fluorescent lights," and you check it and you go through,
and it's really the way the lights were wired by the electricians that's causing
the issue. The good part is, that that's easily taken care of.
Lighting dimmers and controllers. I often get a call that says, "I traced
the source of the problem down, and it's the lighting dimmer or the lighting
controller in the facility." It's not unusual to find a lighting dimmer
controller, when you take your loop receiver or your meter, or whatever,
you go up near it, and at a distance of two or three feet away you will hear
an interference. But in most cases, the issue will go away once you're
two or three feet away from the dimmer. What does happen, is often it's
actually poor wiring after that dimmer, and we'll talk about that and do a demo
in just a minute of what they do after that dimmer that's causing the issue.
Again, with dimmers, we have some new technologies in dimmers that have
come into effect around 2000, that have made dimmers yield much less interference
than they used to do. You can always find out if it's on a circuit
by simply turning off that circuit, and seeing if the interference goes away.
Some of us remember tube TV's. Some of us even remember tubes within TV's.
Tube TVs actually had a magnetic coil in them. Some of the manufacturers
are famous for slightly leaving that coil running over time the way they did it,
but that would cause some interference. Also the transformers within the TVs.
The good news is LCDs have almost zero emissions or interference that are
produced today. AC power distribution. We're not going to get into all
of the theory of how it's distributed, and I will say there are different
ways that AC power is distributed around the world. So I'm going to talk
mostly at this point about AC power distribution in the United States.
In ours, we have a star pattern in that the power originates, it branches out,
and then it keeps distributing and branching out. It's not circles,
some countries have circles, some countries use earth as a return
but in our case, it goes out in a star pattern, and it usually goes through
a number of wires, and depending on the distribution, the voltage,
the transformers, it can be done on either two, three, or four wires
in distribution; which should result in very little magnetic noise as long
as an equal supply of current is flowing out one of those wires
and the same amount of current is returning on one of those wires.
The supply-return next to each other usually is in the same jacket.
Even when you look up on big power poles, often you'll see maybe they're
two or three feet apart, but you should have the same amount of power
going out one, as you do. One is flowing in one direction,
one's flowing the other, and they cancel themselves out.
Power distribution system interference from power lines is directly proportional
to the separation of those power lines. I have seen it where I've gone by
a facility where there is a major high voltage line out there,
and the power lines can be separated, sometimes by 10 to 12 feet, and I drive
under them and I agree, I will find interference under those power lines.
Generally three to five times the separations of power lines you can pick up
some interference. I always recommend that I kind of have a quick story here
about an audiologist who decided to rent a facility that was very inexpensive.
I couldn't figure out why until I went, and I noticed the major high KVA lines
for the whole city ran over their building. Their computers didn't work.
Nothing worked within their facility. It was a mess. They weren't in there
very long, thank goodness. Electrical systems--and I'm going to sidestep
just one second. There's a term out there called "ground loops,"
and I want to say that term is amazingly used to cover a number of different
things. For some of you, you may even hear a slight hum in the audio system.
I don't know if that's showing up in the loop or not, sometimes it does.
That's one form of a ground loop, and that's on the signal cables,
it's on the shielded signal cables. In major electrical systems we often
use the term ground loop, when the power does return equally down
the wire next to it. What I'm going to demonstrate now, I'm going to create
a return loop for you. The power of this demonstration is, I'm going to detect
where it is, and I'll only use a loop receiver. You don't need any major--
major pieces of equipment to do it, but we're going to need to do one thing
to do this demo. We're going to need to find both sources of the magnetic
interference. If I have my two wires right next to each other in a jacket,
an electrical jacket, I may have some interference, but remember,
the width of those two wires is only a quarter inch, or a half inch apart,
and for me to find a null over the wires is almost impossible. We'll do the demo.
What we have here is a fancy, fancy, fancy electrical ground loop return.
I simply have a wire, it's a single wire, and I have another single wire
going across the table, and plugged into a power outlet. From that, my load
happens to be one of our standard very low wattage compact fluorescent lights.
What I'm going to show you is that when I turn this on, [buzzing sound],
now, one other trick is this, and hopefully--is it real loud in the loop?
(audience) Yes. (Richard McKinley) It is? Turn it down, okay.
Real loud in the loop? Can you bring in the loop? We'll do one demo.
All right, we'll try it. Here goes. [buzz] It nulls. If you hear it,
when I go right over the wire, it's gone. Same thing with detecting
the loop system. But here's the trick. There's not just one.
If I go over this side, I'm going to null, [buzz] I go over this side.
Turn this off. I'll get rid of this fancy interference system
here. The point is, is that anytime you have an
interference in a facility that's a large area, in almost all cases, that large
area has two points, or two areas where current is going out one way, and returning
another path. If you look in the picture on my slides, we're
actually using a meter, to go up, and we found one conduit and the
null is right over it. About 15 feet over in that facility, we found
the other conduit. Now here's the hard part. It's not finding
it, it's persuading the electrician to believe that there's an issue with the
wiring in the facility, because he'll come in, and he'll say "the
lights work, they all go on, that light works." But the wire, the signal
wasn't going out to the light and returning within the same cable. And that's
what will happen. Some actual examples, we have a library and
a conference room in Wisconsin. We went in, and we measured noise and got
a minus 12 db of noise. They had some breakers in a panel, and what
we found out was that we could literally shut off that electrical panel,
we still had power going through those parts of those breakers because they
were mis-wired from two separate sources. The electrician came in, moved the
breakers over to the other panel, the one they should have been in, and we ended
up with minus 48 db of noise. Not that long to do, he was quite convinced
to fighting it. We had another one, where we traced out the interference, and
discovered that the power feeding a building at a college was actually returning
down a steam pipe between two buildings. I would not want to have been
the electrician who cut that steam pipe, because I probably would not have
been here today. The other one was that we found a loose wire
connection on a chandelier, and that loose connection was touching the
conduit, and actually the conduit returning all the power from that chandelier
about 15 feet away, and it was very hot. They are find able, that's
the point. Your loop receiver, if you can find the two points where the nulls
are, you've actually found the locations where the current is going out
one way and not returning down right next to it, but down another one.
Distortion can also be found on power lines. I think Europe is way ahead
of us on this one in a lot of their efforts now to get transformers to go down
to low idle currents, and reduce that, because what distortion relative to
power lines is, that we have transformers, all our devices that we plug
into the wall, power our computers and laptops and all those.
Instead of returning all of the current back to the power company down
the neutral line, it some of it goes through the ground, and power companies
look at that as a distortion number. The good part in the United States,
is that there is a standard out there, 519, which gives a recommendation
for a maximum distortion. Nothing enforceable, sadly at this point,
but a recommendation. I want to say, I have had great success with asking
power companies to come out and take a look at it with me. Sometimes anywhere
from two in the morning to five in the morning. We've had as many as
six or eight trucks out, and often we've found out which subdivision had
the issues, and where all the distortion was coming from, and re-routed it,
so it was not going by the facility that we wished to work with.
The good news. Fluorescent lighting, new FCC rules, a lot of the old lighting
that was out there is gone. That source is being pretty well removed today.
Tube TV monitors, no new production in the United States. That's good.
The LCD monitors, no major issues. Dimmers. Dramatic improvements in the dimmers.
But even at that, they're usually not the source for the interference.
They may have a slight amount of interference, two to three feet from them,
but they aren't the reason that you're taking a whole section of a room out,
and causing major problems. Electrical wiring issues or ground loops,
whichever you want to call it, yes, it can and should be detected.
Interestingly, up at that library, where we found the problem,
the IT person called me about a month later, and said, "I have about one tenth
of the computer problems that I used to have, since we solved that electrical
wiring issue." Before we did that, every light, everything in the building
worked, it was just wired wrong. Distortion of power lines. There is some
specs out there to help. They're not specifications that are anything other
than enforceable guidelines at the moment, but it's not a common issue.
I will say, in many, many, many installs, I can only say I know of four
facilities that to date have not been looped because of power line distortion.
In most cases it was all power line distortion. Magnetic noise interference,
far less today than it was 10 years ago. When I first started doing loops
about 12 years ago, there was an issue with it, and we had to handle a lot.
Sources of electrical ground loops can be found and taken care of.
New LCD's, TV's, computer monitors; they don't cause interference,
that's great, that helps a lot, especially when you're doing counter
or loops for people, customer service loops. Most of the time, interference
below minus 32 is not an issue. So, I'm going to turn this back to Doug,
and let Doug finish the presentation. Thank you very much.
(Applause) (Doug Edworthy) Okay, thank you Richard for
that. Just looking at a few case studies that I've
been involved with in the UK, very similar to Richard's experiences.
We had problems with a ticket office that had the old fashioned tube displays.
Simply moving the display had a big effect. Simply turning it around
slightly changed the position of the magnetic field and made it very
acceptable for hearing aid users. Even better, was to replace the
tube display completely with an LCD or an LED type, and that got rid
of the noise completely. Another problem with a laser printer.
Close by the laser printer, people with hearing aids picked up a lot of noise
when they were in the "T" position, so we switched the printer off when the
loop isn't in use. Result?, no noise. Richard has covered hum and buzz
from lighting power circuits very well. In the UK, we used to have
a lot of problems, especially with fluorescent light fittings where the
line in neutral, that's the source and return conductors took separate routes.
As long as the AC power cabling is re-installed with the line and neutral
conductors in the same jacket, in the same sheath, no noise.
Buzz and crackles from an air conditioning plant. I had experience with
a synagogue in London, where we had tremendous noise running right down
the middle of the main room, and it was traced to old style thermostats
being used in the air conditioning plant and equipment, with the cabling,
the supply cabling for that running under the floor. The thermostat devices
were replaced with modern low interference types--result--no noise.
So what can we do about the noise. Richard's described using a hearing aid
or receiver to locate the source, if that's possible. You could try switching
off electrical equipment until the noise stops. Certainly, contact the venue
management, and alert them to the fact that there's a noise problem there.
Hearing aid users, perhaps more in the UK, than in the US, are a little bit
reticent, a little bit reluctant to complain--to stand up and complain.
But stand up and complain is exactly what we have to do. Alert the venue
managements to the disability legislation. The hum and the noise is preventing
you from accessing all of the facilities that you should be able to access.
Hit their wallets. Tell them about the potential loss of hearing aid users
business if hearing aid users can't use the venue. And contact the owner
of the interference generating equipment, which might be the power company.
Again, make reference, make use of the disability legislation.
Advocacy organizations like the HLAA. But what can you do if the noise
level is still too high, and you still need hearing assistance? Well, there are
alternatives to loop systems. There are infra-red or FM systems.
They use neck loops or silhouettes; those in the UK are called "ear hooks."
They still need telecoiling operation, so they can still pick up the noise,
but especially with a silhouette, which can put out quite a strong magnetic
field, it may be possible with that stronger magnetic field, to turn
volume control down on the hearing aid, and in doing so, you turn down
the volume of the noise as well. If the infra-red or FM system provides
headphones, then those headphones have got to be suitable for
hearing aid wearers. Dave Myers this morning at breakfast, gave us some
very useful information about how headphones systems can be a problem
if they're not compatible with hearing aids. Another alternative is
direct audio input. Audio shoes or boots, where the audio signal on a wire
can be connected directly to the hearing aid. And there are new technologies
becoming available. Blue Tooth or other wireless technology. But some of those
are in the future. The systems that are available at the moment for blue tooth are
a little bit battery hungry, but maybe new technology is going to improve that.
Well, I just want to take a quick review of what we've been talking about.
Donna, I hope you're going to thank us, because we're going to finish
well in time. (laughter from audience) We've looked at causes of environmental magnetic
interference, which can often be assessed and resolved quite quickly, and
we've described processes by which you can remedy magnetic interference,
and also who needs to be involved in that process. We've also mentioned compliance
with the international standard for audio frequency induction loop systems,
and that as well as describing how strong the field should be, and where it should
cover, describes how low the magnetic interference should be. But most
importantly, I hope that Richard and I have convinced you, that if
noise is a problem, then it can nearly always be overcome. So in conclusion,
I'm sure Richard will join me in saying thank you very much for listening
to us this morning. We hope that it was a good presentation for
you. We want you to think about what went well, what could have gone
better, and importantly, what else do you need to know. And if you'd like to,
please feel free to contact either myself directly, or Richard, and those are
the two Email addresses. For those of you that are interested in the
subject of magnetic noise of balanced circuits, good grounding systems,
I strongly recommend that you visit Jensen Transformers website. There's
a guy there, that has written some excellent papers on grounding systems
and how to troubleshoot hum, noise and buzz issues. His name is Bill
Whitlock, and he's a bit of a guru in the audio engineering world. So
thank you very much indeed for your time this morning, and as I say,
"Donna, do we get brownie points for finishing early?"
(Applause) (Richard McKinley) We probably do have about
five minutes, if anybody has any questions that they want to ask. Rather
than bring a mic down, we'll repeat the questions for you.
(Question asked off mic) [Inaudible] (Richard McKinley) Her question was related
to magnetic interference in an automobile. We should have Dana on this
one, because I guess you have to see her car and get that answer. I will
tell you that I have a good friend who just went shopping for a car, and went
out, and she tried about 12, until she found the three that she decided
to pick from. There's a lot of variations in how they do the wiring, the
spark control--on newer cars are better than older cars. They've done a lot
electronically to help with the new car's. There were problems with cars five,
ten years ago in time, but there are some cars that are extremely
quiet. I know when the black taxis were done, they
did some spark plug wires and other changes within the black taxis in
England to get them correct. (Doug Edworthy) There is another advantage
with the London black taxis, most of them have diesel engines, so they
don't have spark plugs, which is an advantage. One thing that might be worth
bearing in mind with in-car loop systems; the point I mentioned about
silhouette, or ear hook solenoids, because of the stronger field you get from
those, you can turn down the volume control in your hearing aid a little, just
to reduce the level of noise as well. But beware of turning up the signal from the
silhouette too much, because that can cause overloading and distortion
in the hearing aid. So you need to strike a balance between strong enough signal
to overcome the noise, but not too strong that it causes distortion.
(Question asked off mic) [Inaudible] (Richard McKinley) Restaurants--let me address--he
was saying, walking down the street in like New York City and many
cities, there are issues that you run into with interference. One of the problems
especially with an older city, and New York City is definitely old, is thousands
of people have changed thousands of wires over time. Generally, thank
goodness, we're not doing our symposiums on the streets of New York
City, so yes there are places like that that are going to have a large amount of interference.
Even in looking at facilities and restaurants--what I've found
is that when I go into a brand new restaurant, and one electrician has worked
on it, it's probably pretty good. But now they add lights and structures and
remodel over the years, and these other ones come in, not being bad, they find
the quickest way to add another light, or the quickest way to add another
dimmer, and right now we do not have a means in the inspections in the cities to
check for ground looping. One of the things you can do, is over time
in advocacy, is we love to get that test requirement into the building code. And
actually a lot of other people would like to have it, the audio guys would
like to have it. It affects their jobs, the computer people, everybody, so--one
more question. (Question asked off mic) [Inaudible]
(Doug Edworthy) The question is, In a lot of retail outlets, there are security
systems that use magnetic induction systems to detect things like clothing
tags being taken out of the store. Certainly if you're close to those systems--
they're usually located at the exits of the store, then there can be quite a high
level of noise. In addressing that point, and the point about the noise in the
environments in the streets of New York, there is an optimum setting for
the sensitivity of the telecoil in a hearing aid, and from some of the
discussions that I've heard on the loops and telecoils Email group,
it's possible, that some audiologists are setting the hearing aids too sensitive
in the telecoil position, and it's possible that this extra sensitivity is causing
people to think that there is more noise problems than there actually is.
Now there is a standard for the setting of the telecoil sensitivities,
but it may be that some audiologists either are not fully aware of the standard,
or are not sure how to adjust the telecoil to that particular sensitivity.
So, there's two sides to every coin. There's the level of noise, but there's
also the sensitivity of the hearing aid to that noise, and if a hearing aid
is set up correctly, our experience in the UK and Scandinavia is that
environmental magnetic noise is not generally much of a problem.
(APPLAUSE) �