[Dave O'Heare[_3_]]

One of my regular clients has asked me for help with their inductive loop
hearing assist system. I have zero experience with this stuff, but since
I've fixed a lot of random stuff for them, and since the pros that came in
claimed to fix the system and it still apparently doesn't work, they want
me to look at it.

I have a basic understanding of the theory (feed fairly narrow bandwidth
audio into a copper loop from a fairly standard audio amp, the magnetic
field generated around the wire excites the coil in the hearing aid). So
far, so good. What I am missing is real-world info. My Google-fu seems to
be lacking; I can find lots of folks claiming to be able to come and fix
your system or sell you a new one, but little in the theoretical or
practical on *how* to fix.

For instance, the loop shows an infinite resistance between the two ends of
the loop at the amplifier end (a Logia system, if that makes a difference).
So, a broken wire, that explains it. But I haven't got a TDR. and I wonder
if my toner and wand will help determine the location of the break.
Thoughts? (I will be testing that tomorrow, mind)

As well, the loop seems to be a length of 16-ish gauge lamp cord strung
around the balcony. That in itself isn't a problem, I don't think; what I
find odd is that the amplifier is connected + and - at one end of the
length of cable, while the other end (after going around the church on the
balcony rail) is twisted together and Marretted. This seems that the signal
goes out around the church and back along exactly the same path, instead of
running from the amp, and in a loop around the church ending at the amp.

Are there any repositories of info on how this stuff works in the real
world? Or anyone who might have insights off the top of their head?

Thanks.

[Phil Allison[_4_]]

Dave O'Heare wrote:



As well, the loop seems to be a length of 16-ish gauge lamp cord strung
around the balcony. That in itself isn't a problem, I don't think; what I
find odd is that the amplifier is connected + and - at one end of the
length of cable, while the other end (after going around the church on the
balcony rail) is twisted together and Marretted. This seems that the signal
goes out around the church and back along exactly the same path, instead of
running from the amp, and in a loop around the church ending at the amp.


** Such an arrangement cannot possibly work.

You are either trolling or having your leg pulled by someone if they claim it once did.

Just install a new loop and be done.


..... Phil

[Dave O'Heare[_3_]]

Phil Allison wrote in
:

Dave O'Heare wrote:



As well, the loop seems to be a length of 16-ish gauge lamp cord
strung around the balcony. That in itself isn't a problem, I don't
think; what I find odd is that the amplifier is connected + and - at
one end of the length of cable, while the other end (after going
around the church on the balcony rail) is twisted together and
Marretted. This seems that the signal goes out around the church and
back along exactly the same path, instead of running from the amp,
and in a loop around the church ending at the amp.


** Such an arrangement cannot possibly work.

You are either trolling or having your leg pulled by someone if they
claim it once did.

Just install a new loop and be done.


.... Phil


I don't troll. I figured it couldn't work; but I know that I don't know
everything, which is why I asked.

[geoff]

On 5/12/2016 2:47 p.m., Phil Allison wrote:
Dave O'Heare wrote:
This seems that the signal
goes out around the church and back along exactly the same path,
** Such an arrangement cannot possibly work.

You are either trolling or having your leg pulled by someone if they claim it once did.

Just install a new loop and be done.


.... Phil

Could have been a miracle.....

geoff

[jason]

On Sun, 04 Dec 2016 19:07:14 -0600 "Dave O'Heare"
wrote in article
what I
find odd is that the amplifier is connected + and - at one end of the
length of cable, while the other end (after going around the church on the
balcony rail) is twisted together and Marretted.


It sure is odd. Our local library is in the process of installing a
hearing loop. A pair of loops of inch-wide copper tape winds around half
the perimeter and up the middle of the room under the flooring, so two
loops, but they really are loops. They are in parallel at the amp output.
I have questions about loads and impedances - but a dead short seems like
a really bad idea.

[Phil Allison[_4_]]

Dave O'Heare wrote:


As well, the loop seems to be a length of 16-ish gauge lamp cord
strung around the balcony. That in itself isn't a problem, I don't
think; what I find odd is that the amplifier is connected + and - at
one end of the length of cable, while the other end (after going
around the church on the balcony rail) is twisted together and
Marretted. This seems that the signal goes out around the church and
back along exactly the same path, instead of running from the amp,
and in a loop around the church ending at the amp.


** Such an arrangement cannot possibly work.

You are either trolling or having your leg pulled by someone if they
claim it once did.

Just install a new loop and be done.


I don't troll. I figured it couldn't work; but I know that I don't know
everything, which is why I asked.


** Might be the original loop used two turns or copper around the premises - in which case there has to be a single wire join near the amplifier.

Sound like the join has gone missing or the wire cut.

When you get it right, the loop ought to measure *at least* 4 ohms resistance.


.... Phil

[geoff]

On 5/12/2016 5:04 PM, Jason wrote:
On Sun, 04 Dec 2016 19:07:14 -0600 "Dave O'Heare"
wrote in article
what I
find odd is that the amplifier is connected + and - at one end of the
length of cable, while the other end (after going around the church on the
balcony rail) is twisted together and Marretted.


It sure is odd. Our local library is in the process of installing a
hearing loop. A pair of loops of inch-wide copper tape winds around half
the perimeter and up the middle of the room under the flooring, so two
loops, but they really are loops. They are in parallel at the amp output.
I have questions about loads and impedances - but a dead short seems like
a really bad idea.


A couple of ohm or less - no problem. They are current-driven.

geoff

[Scott Dorsey]

Dave O'Heare wrote:

For instance, the loop shows an infinite resistance between the two ends of
the loop at the amplifier end (a Logia system, if that makes a difference).
So, a broken wire, that explains it. But I haven't got a TDR. and I wonder
if my toner and wand will help determine the location of the break.
Thoughts? (I will be testing that tomorrow, mind)

It will. Fox and hound will find it. And you will also find that it is
likely failed at a splice.

As well, the loop seems to be a length of 16-ish gauge lamp cord strung
around the balcony. That in itself isn't a problem, I don't think; what I
find odd is that the amplifier is connected + and - at one end of the
length of cable, while the other end (after going around the church on the
balcony rail) is twisted together and Marretted. This seems that the signal
goes out around the church and back along exactly the same path, instead of
running from the amp, and in a loop around the church ending at the amp.

Yes, this is a good way to get a loop that doesn't work, all right, since
the two loops produce opposite fields that cancel one another out. So
the first question is what happens is you measure one end to the other?
If one of the two leads is good, try using just it (along with a series
resistance to make the amp happy).

Are there any repositories of info on how this stuff works in the real
world? Or anyone who might have insights off the top of their head?

I think the Yamaha Sound Reinforcement Handbook actually has a nice
description of how the thing works. It's not always obvious where the
coverage of the signal is unless you're thinking about fields in your
head, especially when you have multiple interacting loops.

But I think you're headed in the right direction.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

geoff wrote:
On 5/12/2016 2:47 p.m., Phil Allison wrote:
Dave O'Heare wrote:
This seems that the signal
goes out around the church and back along exactly the same path,
** Such an arrangement cannot possibly work.

You are either trolling or having your leg pulled by someone if they claim it once did.

Just install a new loop and be done.

Could have been a miracle.....

Likely the two leads aren't exactly the same and the tolerance difference
between the two means there's a little field leakage... and consequently
the loop works a tiny little bit... and the people running the place have
no idea that it's supposed to work a lot better in part because they have
never actually used it and aren't deaf.

Incidentally the fox used for finding a cable break is also very useful for
demonstrating the loop and showing where the fields are.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Jason wrote:
On Sun, 04 Dec 2016 19:07:14 -0600 "Dave O'Heare"
wrote in article
what I
find odd is that the amplifier is connected + and - at one end of the
length of cable, while the other end (after going around the church on the
balcony rail) is twisted together and Marretted.

It sure is odd. Our local library is in the process of installing a
hearing loop. A pair of loops of inch-wide copper tape winds around half
the perimeter and up the middle of the room under the flooring, so two
loops, but they really are loops. They are in parallel at the amp output.
I have questions about loads and impedances - but a dead short seems like
a really bad idea.

Some people will arrange things so that the resistance of the cable or foil
is enough to keep the amplifier happy. Some will add a series resistor.
The loop reactance at audio frequencies is very low, the real part dominates.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Fred McKenzie]

In article ,
(Scott Dorsey) wrote:

I think the Yamaha Sound Reinforcement Handbook actually has a nice
description of how the thing works.

Scott-

Thanks for mentioning that. I did a search and found a 1989 edition,
which I downloaded. I found a brief reference to an inductive loop on
page 171, but they mentioned using infra-red systems for hearing
impaired.

https://soundsfxedit.files.wordpress...nforcement-han
dbook.pdf

I'm thinking Dave's client's original system may never have worked. I
think of such a loop as being a complete circle, each end connected to
opposites sides of the amplifier output. With an ordinary amplifier,
such a connection may have shorted the output, killing its use with PA
speakers. Therefore, using a series resistor would seem appropriate.

The value of such a resistor depends on whether the amplifier is
intended for use with a low impedance speaker, or uses a constant
voltage distribution system. Either way, a voltage-to-speaker
transformer may be sufficient with the loop connected to one of the
speaker terminals.

Fred

[geoff]

On 6/12/2016 12:24 p.m., Fred McKenzie wrote:
In article ,
(Scott Dorsey) wrote:

I think the Yamaha Sound Reinforcement Handbook actually has a nice
description of how the thing works.
Scott-

Thanks for mentioning that. I did a search and found a 1989 edition,
which I downloaded. I found a brief reference to an inductive loop on
page 171, but they mentioned using infra-red systems for hearing
impaired.

https://soundsfxedit.files.wordpress...nforcement-han
dbook.pdf

I'm thinking Dave's client's original system may never have worked. I
think of such a loop as being a complete circle, each end connected to
opposites sides of the amplifier output. With an ordinary amplifier,
such a connection may have shorted the output, killing its use with PA
speakers. Therefore, using a series resistor would seem appropriate.

The value of such a resistor depends on whether the amplifier is
intended for use with a low impedance speaker, or uses a constant
voltage distribution system. Either way, a voltage-to-speaker
transformer may be sufficient with the loop connected to one of the
speaker terminals.

Fred

Using a 'standard' amplifier is hardly ideal as there certainly would
need to be a dropping resistor to make up the amp's minimum load
impedance. It would need to be a high-wattage resistor so that the amp
could drive sufficient current for the loop to be effective.

Best use the right tool for the job, or which there are many because
induction loops were the original (and often mandatory) standard. They
with have a 'Loop Current'; control, and some a control for 'Metal
Correction Factor'. Brands I have worked with include Ampetronics,
I-Amp, Univox , and Williams Sound. For basic setup you will need a
'Listener' device, and for proper a field strength meter.

And then the loop does need to be correctly routed !

geoff

[Dave O'Heare[_3_]]

"Dave O'Heare" wrote in
.131:

One of my regular clients has asked me for help with their inductive
loop hearing assist system.

The loop shows an infinite resistance between the two
ends of the loop at the amplifier end (a Logia system, if that makes a
difference).

As well, the loop seems to be a length of 16-ish gauge lamp cord
strung around the balcony. That in itself isn't a problem, I don't
think; what I find odd is that the amplifier is connected + and - at
one end of the length of cable, while the other end (after going
around the church on the balcony rail) is twisted together and
Marretted.

Problem(s) solved.

First off, the reason that there was an infinite resistance was that the
wiring was somewhat wonky. The pair from the amplifier was split inside a
box, with one side going to both conductors in a chunk of identical lamp
cord that formed the loop around the church, and the other going to a
piece of insulated 14ga copper wire that went to the other side of the
church. The end that was twisted together and Maretted, after some
digging, was covering up a hole in the wall where the other end of that
14ga had fallen out of the Marette and sort of fallen into the wall.
Careful excavating brought the end back out, I got it back into
connection with the lamp cord (fresh Marette of appropriate size, of
course), and we have a nice solid 7.8Ohm resistance at the amplifier end.

Then checking the signal into the Logia. Things are complicated because
there are two mixers feeding the DBX that feeds the power amps and Logia;
one is an automated mixer used for Sunday services, the other a Mackie
used for occasional musical events (they are not located near each other,
and I do not know why). Turns out that the master output for the Aux
feed from the Mackie had been turned down to 0 (no idea why, but anyone
could've done it). Turned that up, still nothing. Further investigation
showed that the output to the Logia was configured on the DBX so that
only the automated mixer was feeding the Logia. The Aux out on the Mackie
didn't run through the DBX, but into a second input on the Logia, only it
didn't; the connection from the Mackie got buried in the cruft in the
rack. Hauling it out and plugging it it made *that* work.

And another thing -- it all has to be turned on for it to work. There is
a nice rackmount power distribution at the amp rack, and the hearing
assist is not plugged into it, so it has to be turned on separately. That
distro is full, so some reconfiguration is needed there.

So -- Is it plugged in? No. Is it turned on? No. Is it getting signal?
No. Sigh...

Now what's needed is a mapping of the whole system, a repair/replacement
of the Mackie board, a rationalizing of the wiring, tune the Casavant,
bolt down the grate around the wiring to the Mackie, etc., etc., etc..

[Phil Allison[_4_]]

Dave O'Heare wrote:



First off, the reason that there was an infinite resistance was that the
wiring was somewhat wonky. The pair from the amplifier was split inside a
box, with one side going to both conductors in a chunk of identical lamp
cord that formed the loop around the church, and the other going to a
piece of insulated 14ga copper wire that went to the other side of the
church. The end that was twisted together and Maretted, after some
digging, was covering up a hole in the wall where the other end of that
14ga had fallen out of the Marette and sort of fallen into the wall.
Careful excavating brought the end back out, I got it back into
connection with the lamp cord (fresh Marette of appropriate size, of
course), and we have a nice solid 7.8Ohm resistance at the amplifier end.

Then checking the signal into the Logia. Things are complicated because
there are two mixers feeding the DBX that feeds the power amps and Logia;
one is an automated mixer used for Sunday services, the other a Mackie
used for occasional musical events (they are not located near each other,
and I do not know why). Turns out that the master output for the Aux
feed from the Mackie had been turned down to 0 (no idea why, but anyone
could've done it). Turned that up, still nothing. Further investigation
showed that the output to the Logia was configured on the DBX so that
only the automated mixer was feeding the Logia. The Aux out on the Mackie
didn't run through the DBX, but into a second input on the Logia, only it
didn't; the connection from the Mackie got buried in the cruft in the
rack. Hauling it out and plugging it it made *that* work.

And another thing -- it all has to be turned on for it to work. There is
a nice rackmount power distribution at the amp rack, and the hearing
assist is not plugged into it, so it has to be turned on separately. That
distro is full, so some reconfiguration is needed there.

So -- Is it plugged in? No. Is it turned on? No. Is it getting signal?
No. Sigh...

Now what's needed is a mapping of the whole system, a repair/replacement
of the Mackie board, a rationalizing of the wiring, tune the Casavant,
bolt down the grate around the wiring to the Mackie, etc., etc., etc..


** Your story is very hard to follow.

Care to explain just what the heck is a "Logia" and also what the "DBX" unit is too.

I already had to look up "Marette" and TDR.



.... Phil

[Dave O'Heare[_3_]]

Phil Allison wrote in
:


** Your story is very hard to follow.

Care to explain just what the heck is a "Logia" and also what the
"DBX" unit is too.

I already had to look up "Marette" and TDR.

Sorry.

Marrette is a brand name of wire nut.

TDR is a TLA (three letter acronym) for a time domain reflectometer,
standard piece of equipment for tracing cable breaks in network gear.

Logia is the brand name of the hearing assist loop amplifier, which I'd
never seen before.

The DBX unit was a DriveRack 260, which reconfigures the system to take
audio from the automatic mixer or the Mackie regular analog mixer, and feed
it as needed to the as-yet unmapped depths of the amp rack and assorted
other stuff.

And yes, the story was hard to follow; I apologize. The debugging process
was a little hard to follow too. :-)

[Phil Allison[_4_]]

Dave O'Heare wrote:



** Your story is very hard to follow.

Care to explain just what the heck is a "Logia" and also what the
"DBX" unit is too.

I already had to look up "Marette" and TDR.

Sorry.

Marrette is a brand name of wire nut.

TDR is a TLA (three letter acronym) for a time domain reflectometer,
standard piece of equipment for tracing cable breaks in network gear.

Logia is the brand name of the hearing assist loop amplifier, which I'd
never seen before.

The DBX unit was a DriveRack 260, which reconfigures the system to take
audio from the automatic mixer or the Mackie regular analog mixer, and feed
it as needed to the as-yet unmapped depths of the amp rack and assorted
other stuff.

And yes, the story was hard to follow; I apologize. The debugging process
was a little hard to follow too. :-)



** Logia must be the most obscure brand name on earth - you did well to sort that pile of audio tech out as quickly as you have.

Reminds me of a similar job once on a line voltage PA system - all sound had stopped and the cause was some handyman type decided to tidy and secure the figure-8 speaker cables to the skirting using a staple gun.




..... Phil

[John Williamson]

On 06/12/2016 03:13, Dave O'Heare wrote:
"Dave O'Heare" wrote in
Snip, snip
So -- Is it plugged in? No. Is it turned on? No. Is it getting signal?
No. Sigh...

Now what's needed is a mapping of the whole system, a repair/replacement
of the Mackie board, a rationalizing of the wiring, tune the Casavant,
bolt down the grate around the wiring to the Mackie, etc., etc., etc..

For your sake, I hope this is a paid gig.

--
Tciao for Now!

John.

[Scott Dorsey]

Fred McKenzie wrote:
In article ,
(Scott Dorsey) wrote:

I think the Yamaha Sound Reinforcement Handbook actually has a nice
description of how the thing works.

Thanks for mentioning that. I did a search and found a 1989 edition,
which I downloaded. I found a brief reference to an inductive loop on
page 171, but they mentioned using infra-red systems for hearing
impaired.

Spend the money, get a newer edition! It's a good book! It's worth supporting
the authors!

I'm thinking Dave's client's original system may never have worked. I
think of such a loop as being a complete circle, each end connected to
opposites sides of the amplifier output. With an ordinary amplifier,
such a connection may have shorted the output, killing its use with PA
speakers. Therefore, using a series resistor would seem appropriate.

You want an amplifier just for the loop, because you want to feed the loop
a different mix than the straight PA mix for one thing.

The value of such a resistor depends on whether the amplifier is
intended for use with a low impedance speaker, or uses a constant
voltage distribution system. Either way, a voltage-to-speaker
transformer may be sufficient with the loop connected to one of the
speaker terminals.

You do NOT want an amplifier designed for a high-Z constant voltage system
for a loop. The loop is exactly the opposite, a very low impedance load.
The normal procedure is to use a series resistor or to employ the series
resistance of the wire to make sure the amp sees a reasonable load. Doing
this, the vast majority of power is lost in the resistance but that's fine
because we live in the solid state world and we can afford to do that.

There are some amplifiers specifically sold for loop use, but there's
really nothing special about them other than some fancy output protection
and usually an internal load.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Dave O'Heare wrote:
Problem(s) solved.

Excellent!

Now what's needed is a mapping of the whole system, a repair/replacement
of the Mackie board, a rationalizing of the wiring, tune the Casavant,
bolt down the grate around the wiring to the Mackie, etc., etc., etc..

As long as it's billable!
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Phil Allison wrote:

Care to explain just what the heck is a "Logia" and also what the "DBX" unit is too.

Sheesh, Phil. Logia are direct communications from God.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[[email protected]]

On Tuesday, December 6, 2016 at 9:13:42 AM UTC-5, Scott Dorsey wrote:
Dave O'Heare wrote:
Problem(s) solved.

Excellent!

Now what's needed is a mapping of the whole system, a repair/replacement
of the Mackie board, a rationalizing of the wiring, tune the Casavant,
bolt down the grate around the wiring to the Mackie, etc., etc., etc..

As long as it's billable!
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

make a good diagram of the works and stick it on the wall and keep yourself a copy.

m

[Ty Ford]

Great story and I learned a few new terms.

Good Work!

Regards,

Ty Ford

[Phil Allison[_4_]]

Scott Dorsey wrote:



Care to explain just what the heck is a "Logia" and also what the "DBX" unit is too.

Sheesh, Phil. Logia are direct communications from God.


** Yes, I read that during my searching on the word.


...... Phil