Help Question: Electronic stethoscope danger

W

WJW

Guest
Hello...a quick question looking for a good suggestion/solution/answer,

1) I have a small rural nursing school;
2) I have a $500 electronic stethoscope (micro-battery powered) that can
hear/play/record sounds using an I-Pod by using a direct wire/plug into the
I-Pod external microphone jack;
3) I-Pod sounds are very weak and you have to be within inches to hear the sound
during playback;
4) I need a room full of 10 students to hear the sounds from the stethoscope;
5) I connected it to a wall-plug store-bought powered I-Pod speaker sound system
and it worked great...everybody in room could hear the sounds fine!;
6) Was then informed it could possibly be a major shock hazard (110 power from
wall through speakers to stethoscope to person wearing (ear pieces) and to
patient's chest (diaphragm);
7) So...now I'm back to Step 1 & 2...

Any suggestions on how I could truly prevent a surge danger for under $100 bucks
so that I can safely use the stethoscope and the powered speaker system?
Would an automotive quick-jump power pack with 110 inverter work or would the
danger still be present? Is there really even a danger in the first place?

Thank you very much for your wisdom, advice and expertise!

William in Colorado
 
On Sat, 6 Sep 2008 05:59:07 -0600, "WJW" <quasho@comcast.net> wrote:

Hello...a quick question looking for a good suggestion/solution/answer,

1) I have a small rural nursing school;
2) I have a $500 electronic stethoscope (micro-battery powered) that can
hear/play/record sounds using an I-Pod by using a direct wire/plug into the
I-Pod external microphone jack;
3) I-Pod sounds are very weak and you have to be within inches to hear the sound
during playback;
4) I need a room full of 10 students to hear the sounds from the stethoscope;
5) I connected it to a wall-plug store-bought powered I-Pod speaker sound system
and it worked great...everybody in room could hear the sounds fine!;
Click to expand...
OK, that's a solution. But don't most of those systems also have a
battery option?

6) Was then informed it could possibly be a major shock hazard (110 power from
wall through speakers to stethoscope to person wearing (ear pieces) and to
patient's chest (diaphragm);
Click to expand...
Most hospitals have a staff who are trained to test and evaluate these
types of devices. I assume these use a wall-wart, right? Does the
wall-wart have a *real* UL label? (not a fake one!)

7) So...now I'm back to Step 1 & 2...

Any suggestions on how I could truly prevent a surge danger for under $100 bucks
so that I can safely use the stethoscope and the powered speaker system?
Would an automotive quick-jump power pack with 110 inverter work or would the
danger still be present?
Click to expand...
Don't do this... Trust me, don't even go there. There are so many
better ways that will work well, that this is not practical in any way
or shape.

Is there really even a danger in the first place?
Click to expand...
Possibly, especially if you are using stuff from teh likes of
WallyWorld...

Thank you very much for your wisdom, advice and expertise!
Click to expand...
Find battery powered speakers. There are thousands of examples, and
you should have no problems finding them.

William in Colorado
Click to expand...
 
On Sat, 6 Sep 2008 05:59:07 -0600, "WJW" <quasho@comcast.net> wrote:

Any suggestions on how I could truly prevent a surge danger for under $100 bucks
so that I can safely use the stethoscope and the powered speaker system?
Click to expand...
Don't use the wired speakers. You're correct that they may constitute
a shock hazard.

There are various wireless adapters for the iPod.
<http://www.griffintechnology.com/products/itripdock>
<http://www.griffintechnology.com/category/fmtransmitters>
The iPod transmits the audio to a common FM receiver. The wireless
provides the necessary isolation. Note that the various models are
specific to whichever model iPod you're using. It appears that the
transmitter covers up the microphone hole, so you may need to play
with some adapters. Worst case, you can use the iPod as a recorder
with the microphone attached, and then plug in the FM transmitter when
playing back the recording.



--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
In actuality...all the I-Pod does is play/record sound (and not very well due to
the frequency/tones of heartbeat & pulse)...so...the digital stethoscope is self
amplified and could operate without the I-Pod if I had a battery powered stand
alone speaker system I could plug into directly with the scope...or as you
suggested (great idea), a wireless transmitter that could then relay the signal
to a good powerful receiver. Any suggestions (brand/model) along either line?

Thanks again for this assistance!

William


"Jeff Liebermann" <jeffl@cruzio.com> wrote in message
news:1a55c4pmnmoidprfm5v5fekh7ckssdn0v0@4ax.com...
On Sat, 6 Sep 2008 05:59:07 -0600, "WJW" <quasho@comcast.net> wrote:

Any suggestions on how I could truly prevent a surge danger for under $100
bucks
so that I can safely use the stethoscope and the powered speaker system?

Don't use the wired speakers. You're correct that they may constitute
a shock hazard.

There are various wireless adapters for the iPod.
http://www.griffintechnology.com/products/itripdock
http://www.griffintechnology.com/category/fmtransmitters
The iPod transmits the audio to a common FM receiver. The wireless
provides the necessary isolation. Note that the various models are
specific to whichever model iPod you're using. It appears that the
transmitter covers up the microphone hole, so you may need to play
with some adapters. Worst case, you can use the iPod as a recorder
with the microphone attached, and then plug in the FM transmitter when
playing back the recording.



--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Click to expand...
 
On Sat, 6 Sep 2008 11:09:04 -0600, "WJW" <quasho@comcast.net> wrote:

In actuality...all the I-Pod does is play/record sound (and not very well due to
the frequency/tones of heartbeat & pulse)...so...the digital stethoscope is self
amplified and could operate without the I-Pod if I had a battery powered stand
alone speaker system I could plug into directly with the scope...or as you
suggested (great idea), a wireless transmitter that could then relay the signal
to a good powerful receiver. Any suggestions (brand/model) along either line?
Click to expand...
Nothing specific. Google for "battery powered speaker". Lots of
hits.

I would be tempted to suggest a battery power boom box or karaoke box.
What I'm worried about it that someone is going to run it with the
stethescope while charging the internal batteries. Too big a risk, so
we're back to wireless again.

Look at the wireless microphones available for persentations. They're
usually in the commercial sound business sites. While most have a
built in microphone, there are a few that allow external mics. They're
unfortunately kinda pricy. You might do better with wireless speakers
that are made to run off a hi-fi. You didn't supply any interface
specifications, but if the stethescope puts out home hi-fi line levels
(about 0dBm), one of these should work.

I gotta run, but I'll see if I can find something later today.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
On Sat, 6 Sep 2008 05:59:07 -0600, "WJW" <quasho@comcast.net> wrote:

:Hello...a quick question looking for a good suggestion/solution/answer,
:
:1) I have a small rural nursing school;
:2) I have a $500 electronic stethoscope (micro-battery powered) that can
:hear/play/record sounds using an I-Pod by using a direct wire/plug into the
:I-Pod external microphone jack;
:3) I-Pod sounds are very weak and you have to be within inches to hear the
sound
:during playback;
:4) I need a room full of 10 students to hear the sounds from the stethoscope;
:5) I connected it to a wall-plug store-bought powered I-Pod speaker sound
system
:and it worked great...everybody in room could hear the sounds fine!;
:6) Was then informed it could possibly be a major shock hazard (110 power from
:wall through speakers to stethoscope to person wearing (ear pieces) and to
:patient's chest (diaphragm);
:7) So...now I'm back to Step 1 & 2...
:
:Any suggestions on how I could truly prevent a surge danger for under $100
bucks
:so that I can safely use the stethoscope and the powered speaker system?
:Would an automotive quick-jump power pack with 110 inverter work or would the
:danger still be present? Is there really even a danger in the first place?
:
:Thank you very much for your wisdom, advice and expertise!
:
:William in Colorado



You could buy a medical grade 120V/120V isolation transformer to power your
speakers from but that will still be fairly expensive but you will probably have
to sort out the socket outlet for the plug-pack. You would still have the
problem that somebody could unwittingly operate the system without using the
transformer. Not a problem if you are the only one looking after and using the
equipment.

Ideally, you need equipment suitable for a teaching environment.
eg. http://www.stethoscope.com/index.cfm?event=ProductDetail&ProductID=132

If the cost seems high then you will at least be supremely confident that nobody
will have their safety threatened, and that can save a lot of worry about
lawsuits.
 
On Sun, 07 Sep 2008 02:00:19 GMT, Ross Herbert <rherber1@bigpond.net.au> wrote:
:
:You could buy a medical grade 120V/120V isolation transformer to power your
:speakers from but that will still be fairly expensive but you will probably
have to sort out the socket outlet for the plug-pack.

Some transformers come complete with enclosure - ready to go.
http://www.isobox.com/
 
WJW wrote:
Hello...a quick question looking for a good suggestion/solution/answer,

1) I have a small rural nursing school;
2) I have a $500 electronic stethoscope (micro-battery powered) that can
hear/play/record sounds using an I-Pod by using a direct wire/plug into
the I-Pod external microphone jack;
3) I-Pod sounds are very weak and you have to be within inches to hear
the sound during playback;
4) I need a room full of 10 students to hear the sounds from the
stethoscope;
5) I connected it to a wall-plug store-bought powered I-Pod speaker
sound system and it worked great...everybody in room could hear the
sounds fine!;
6) Was then informed it could possibly be a major shock hazard (110
power from wall through speakers to stethoscope to person wearing (ear
pieces) and to patient's chest (diaphragm);
7) So...now I'm back to Step 1 & 2...

Any suggestions on how I could truly prevent a surge danger for under
$100 bucks so that I can safely use the stethoscope and the powered
speaker system? Would an automotive quick-jump power pack with 110
inverter work or would the danger still be present? Is there really
even a danger in the first place?

Thank you very much for your wisdom, advice and expertise!

William in Colorado

Just isolate the patient electro-mechanically from the stethoscope by
Click to expand...
placing the probe in a Plastic Baggie. The probe is most likely Plastic
or Bakelite with a plastic or rubber hose anyway, A thin layer of
plastic sheeting will not affect the acoustics !

Yukio YANO
 
On Sun, 07 Sep 2008 04:09:24 GMT, Yukio YANO <yano@shaw.ca> wrote:

WJW wrote:
Hello...a quick question looking for a good suggestion/solution/answer,

1) I have a small rural nursing school;
2) I have a $500 electronic stethoscope (micro-battery powered) that can
hear/play/record sounds using an I-Pod by using a direct wire/plug into
the I-Pod external microphone jack;
3) I-Pod sounds are very weak and you have to be within inches to hear
the sound during playback;
4) I need a room full of 10 students to hear the sounds from the
stethoscope;
5) I connected it to a wall-plug store-bought powered I-Pod speaker
sound system and it worked great...everybody in room could hear the
sounds fine!;
6) Was then informed it could possibly be a major shock hazard (110
power from wall through speakers to stethoscope to person wearing (ear
pieces) and to patient's chest (diaphragm);
7) So...now I'm back to Step 1 & 2...

Any suggestions on how I could truly prevent a surge danger for under
$100 bucks so that I can safely use the stethoscope and the powered
speaker system? Would an automotive quick-jump power pack with 110
inverter work or would the danger still be present? Is there really
even a danger in the first place?

Thank you very much for your wisdom, advice and expertise!

William in Colorado

Just isolate the patient electro-mechanically from the stethoscope by
placing the probe in a Plastic Baggie. The probe is most likely Plastic
or Bakelite with a plastic or rubber hose anyway, A thin layer of
plastic sheeting will not affect the acoustics !

Yukio YANO
Click to expand...
Let's say you were the patient... Would you wnat your life to depend
on a plastic baggie? I don't think so.

The correct solutions (either battery operated, or proper medical
device) has been given.
 
PeterD wrote:
On Sun, 07 Sep 2008 04:09:24 GMT, Yukio YANO <yano@shaw.ca> wrote:

WJW wrote:
Hello...a quick question looking for a good suggestion/solution/answer,

1) I have a small rural nursing school;
2) I have a $500 electronic stethoscope (micro-battery powered) that can
hear/play/record sounds using an I-Pod by using a direct wire/plug into
the I-Pod external microphone jack;
3) I-Pod sounds are very weak and you have to be within inches to hear
the sound during playback;
4) I need a room full of 10 students to hear the sounds from the
stethoscope;
5) I connected it to a wall-plug store-bought powered I-Pod speaker
sound system and it worked great...everybody in room could hear the
sounds fine!;
6) Was then informed it could possibly be a major shock hazard (110
power from wall through speakers to stethoscope to person wearing (ear
pieces) and to patient's chest (diaphragm);
7) So...now I'm back to Step 1 & 2...

Any suggestions on how I could truly prevent a surge danger for under
$100 bucks so that I can safely use the stethoscope and the powered
speaker system? Would an automotive quick-jump power pack with 110
inverter work or would the danger still be present? Is there really
even a danger in the first place?

Thank you very much for your wisdom, advice and expertise!

William in Colorado

Just isolate the patient electro-mechanically from the stethoscope by
placing the probe in a Plastic Baggie. The probe is most likely Plastic
or Bakelite with a plastic or rubber hose anyway, A thin layer of
plastic sheeting will not affect the acoustics !

Yukio YANO

Let's say you were the patient... Would you wnat your life to depend
on a plastic baggie? I don't think so.

The correct solutions (either battery operated, or proper medical
device) has been given.
Click to expand...
Surgeons have been doing this for generations, only they call them
surgical gloves !

Standard, "conventional" stethoscopes were always electrically isolated
from the probe tip by rubber tubing .

If it was in the middle of a epidemic I would insist that a NEW baggie
be placed on the Probe Tip .

Where are you going to find and afford this Medical device !

Yukio YANO
 
Jeff Liebermann wrote:
On Sat, 6 Sep 2008 11:09:04 -0600, "WJW" <quasho@comcast.net> wrote:

In actuality...all the I-Pod does is play/record sound (and not very well due to
the frequency/tones of heartbeat & pulse)...so...the digital stethoscope is self
amplified and could operate without the I-Pod if I had a battery powered stand
alone speaker system I could plug into directly with the scope...or as you
suggested (great idea), a wireless transmitter that could then relay the signal
to a good powerful receiver. Any suggestions (brand/model) along either line?

Nothing specific. Google for "battery powered speaker". Lots of
hits.

I would be tempted to suggest a battery power boom box or karaoke box.
What I'm worried about it that someone is going to run it with the
stethescope while charging the internal batteries. Too big a risk, so
we're back to wireless again.

Look at the wireless microphones available for persentations. They're
usually in the commercial sound business sites. While most have a
built in microphone, there are a few that allow external mics. They're
unfortunately kinda pricy. You might do better with wireless speakers
that are made to run off a hi-fi. You didn't supply any interface
specifications, but if the stethescope puts out home hi-fi line levels
(about 0dBm), one of these should work.

I gotta run, but I'll see if I can find something later today.


This would hopefully suit you, they are available in Walmart and work
Click to expand...
quite well, I had one on my mp3 player in my car for ages due to my CD
player being bust. All you need is your radio boombox tuned to the
transmit signal.
http://catalog.belkin.com/IWCatProductPage.process?Product_Id=166903
 
Archon...Good idea but I can not tell if the Belkin requires the cigarette plug
or can it operate independently with internal batteries?

William

"Archon" <Chipbee40_SpamNo@yahoo.com> wrote in message
news:dYZwk.443024$eu.239895@fe01.news.easynews.com...
Jeff Liebermann wrote:
On Sat, 6 Sep 2008 11:09:04 -0600, "WJW" <quasho@comcast.net> wrote:

In actuality...all the I-Pod does is play/record sound (and not very well
due to the frequency/tones of heartbeat & pulse)...so...the digital
stethoscope is self amplified and could operate without the I-Pod if I had a
battery powered stand alone speaker system I could plug into directly with
the scope...or as you suggested (great idea), a wireless transmitter that
could then relay the signal to a good powerful receiver. Any suggestions
(brand/model) along either line?

Nothing specific. Google for "battery powered speaker". Lots of
hits. I would be tempted to suggest a battery power boom box or karaoke box.
What I'm worried about it that someone is going to run it with the
stethescope while charging the internal batteries. Too big a risk, so
we're back to wireless again.

Look at the wireless microphones available for persentations. They're
usually in the commercial sound business sites. While most have a
built in microphone, there are a few that allow external mics. They're
unfortunately kinda pricy. You might do better with wireless speakers
that are made to run off a hi-fi. You didn't supply any interface
specifications, but if the stethescope puts out home hi-fi line levels
(about 0dBm), one of these should work.

I gotta run, but I'll see if I can find something later today.


This would hopefully suit you, they are available in Walmart and work quite
well, I had one on my mp3 player in my car for ages due to my CD player being
bust. All you need is your radio boombox tuned to the transmit signal.
http://catalog.belkin.com/IWCatProductPage.process?Product_Id=166903
Click to expand...
 
Ross...good idea but not an option because we want the sound heard by
all...approximately 15 people at a time. We already have and use dual & triple
stethoscopes but they mean the task has to be repeated over and over whereas if
we could just broadcast for all to hear at once...presto!

William

"Ross Herbert" <rherber1@bigpond.net.au> wrote in message
news:4uc6c49p9o8qhbd7s555k7b2m5sonlc4dk@4ax.com...
On Sat, 6 Sep 2008 05:59:07 -0600, "WJW" <quasho@comcast.net> wrote:

:Hello...a quick question looking for a good suggestion/solution/answer,
:
:1) I have a small rural nursing school;
:2) I have a $500 electronic stethoscope (micro-battery powered) that can
:hear/play/record sounds using an I-Pod by using a direct wire/plug into the
:I-Pod external microphone jack;
:3) I-Pod sounds are very weak and you have to be within inches to hear the
sound
:during playback;
:4) I need a room full of 10 students to hear the sounds from the stethoscope;
:5) I connected it to a wall-plug store-bought powered I-Pod speaker sound
system
:and it worked great...everybody in room could hear the sounds fine!;
:6) Was then informed it could possibly be a major shock hazard (110 power
from
:wall through speakers to stethoscope to person wearing (ear pieces) and to
:patient's chest (diaphragm);
:7) So...now I'm back to Step 1 & 2...
:
:Any suggestions on how I could truly prevent a surge danger for under $100
bucks
:so that I can safely use the stethoscope and the powered speaker system?
:Would an automotive quick-jump power pack with 110 inverter work or would the
:danger still be present? Is there really even a danger in the first place?
:
:Thank you very much for your wisdom, advice and expertise!
:
:William in Colorado



You could buy a medical grade 120V/120V isolation transformer to power your
speakers from but that will still be fairly expensive but you will probably
have
to sort out the socket outlet for the plug-pack. You would still have the
problem that somebody could unwittingly operate the system without using the
transformer. Not a problem if you are the only one looking after and using the
equipment.

Ideally, you need equipment suitable for a teaching environment.
eg. http://www.stethoscope.com/index.cfm?event=ProductDetail&ProductID=132

If the cost seems high then you will at least be supremely confident that
nobody
will have their safety threatened, and that can save a lot of worry about
lawsuits.
Click to expand...
 
Yukio...with our electronic digital stethoscope, the microbattery & cpu unit is
actually in the diagphram head...in short, the stethoscope head is the brains.
It still uses the rubber-like tubing to the ear pieces so the danger is not the
person wearing it...but the person whom the stethoscope is placed against &
being listening to.

William

"Yukio YANO" <yano@shaw.ca> wrote in message
news:YOXwk.153910$nD.127330@pd7urf1no...
PeterD wrote:
On Sun, 07 Sep 2008 04:09:24 GMT, Yukio YANO <yano@shaw.ca> wrote:

WJW wrote:
Hello...a quick question looking for a good suggestion/solution/answer,

1) I have a small rural nursing school;
2) I have a $500 electronic stethoscope (micro-battery powered) that can
hear/play/record sounds using an I-Pod by using a direct wire/plug into the
I-Pod external microphone jack;
3) I-Pod sounds are very weak and you have to be within inches to hear the
sound during playback;
4) I need a room full of 10 students to hear the sounds from the
stethoscope;
5) I connected it to a wall-plug store-bought powered I-Pod speaker sound
system and it worked great...everybody in room could hear the sounds fine!;
6) Was then informed it could possibly be a major shock hazard (110 power
from wall through speakers to stethoscope to person wearing (ear pieces)
and to patient's chest (diaphragm);
7) So...now I'm back to Step 1 & 2...

Any suggestions on how I could truly prevent a surge danger for under $100
bucks so that I can safely use the stethoscope and the powered speaker
system? Would an automotive quick-jump power pack with 110 inverter work or
would the danger still be present? Is there really even a danger in the
first place?

Thank you very much for your wisdom, advice and expertise!

William in Colorado

Just isolate the patient electro-mechanically from the stethoscope by
placing the probe in a Plastic Baggie. The probe is most likely Plastic or
Bakelite with a plastic or rubber hose anyway, A thin layer of plastic
sheeting will not affect the acoustics !

Yukio YANO

Let's say you were the patient... Would you wnat your life to depend
on a plastic baggie? I don't think so.

The correct solutions (either battery operated, or proper medical
device) has been given.

Surgeons have been doing this for generations, only they call them surgical
gloves !

Standard, "conventional" stethoscopes were always electrically isolated from
the probe tip by rubber tubing .

If it was in the middle of a epidemic I would insist that a NEW baggie be
placed on the Probe Tip .

Where are you going to find and afford this Medical device !

Yukio YANO
Click to expand...
 
On Sun, 7 Sep 2008 22:39:55 -0600, "WJW" <quasho@comcast.net> wrote:

:Ross...good idea but not an option because we want the sound heard by
:all...approximately 15 people at a time. We already have and use dual & triple
:stethoscopes but they mean the task has to be repeated over and over whereas if
:we could just broadcast for all to hear at once...presto!
:
:William
I see. Looks to me like your best and easiest solution is the medical grade
isolation transformer then.
 
WJW wrote:
Archon...Good idea but I can not tell if the Belkin requires the
cigarette plug or can it operate independently with internal batteries?

William

"Archon" <Chipbee40_SpamNo@yahoo.com> wrote in message
news:dYZwk.443024$eu.239895@fe01.news.easynews.com...
Jeff Liebermann wrote:
On Sat, 6 Sep 2008 11:09:04 -0600, "WJW" <quasho@comcast.net> wrote:

In actuality...all the I-Pod does is play/record sound (and not very
well due to the frequency/tones of heartbeat & pulse)...so...the
digital stethoscope is self amplified and could operate without the
I-Pod if I had a battery powered stand alone speaker system I could
plug into directly with the scope...or as you suggested (great
idea), a wireless transmitter that could then relay the signal to a
good powerful receiver. Any suggestions (brand/model) along either
line?

Nothing specific. Google for "battery powered speaker". Lots of
hits. I would be tempted to suggest a battery power boom box or
karaoke box.
What I'm worried about it that someone is going to run it with the
stethescope while charging the internal batteries. Too big a risk, so
we're back to wireless again.

Look at the wireless microphones available for persentations. They're
usually in the commercial sound business sites. While most have a
built in microphone, there are a few that allow external mics. They're
unfortunately kinda pricy. You might do better with wireless speakers
that are made to run off a hi-fi. You didn't supply any interface
specifications, but if the stethescope puts out home hi-fi line levels
(about 0dBm), one of these should work.

I gotta run, but I'll see if I can find something later today.


This would hopefully suit you, they are available in Walmart and work
quite well, I had one on my mp3 player in my car for ages due to my
CD player being bust. All you need is your radio boombox tuned to the
transmit signal.
http://catalog.belkin.com/IWCatProductPage.process?Product_Id=166903

Hi, It has 2AAA batteries inside, doesn't need the 12v plug. The
Click to expand...
batteries last a reasonable time as I think it shuts down if there is no
audio signal. Mine was an earlier version that I had to switch off but
it still lasted a good time.
 
On Mon, 8 Sep 2008 11:00:15 +0000 (UTC), Mika Lindblad
<lindblad@students.cc.tut.fi> wrote:

:On 2008-09-08, Ross Herbert <rherber1@bigpond.net.au> wrote:
:>:Ross...good idea but not an option because we want the sound heard by
:>:all...approximately 15 people at a time. We already have and use dual &
triple
:>:stethoscopes but they mean the task has to be repeated over and over whereas
if
:>:we could just broadcast for all to hear at once...presto!
:> I see. Looks to me like your best and easiest solution is the medical grade
:> isolation transformer then.
:
:Why not just use active speakers which are powered by batteries?


Typical scenario:

Crowded classroom, busy instructor....

Oh bugger! flat batteries... Now where did I put those spares?

Sh.t! I didn't buy new ones after I last replaced them with the spares I had.

Now do you see?
 
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