Detect sound behind wall/door

[eeh]

Hi,

Is it possible to detect sound behind concrete wall or door whereas the
detector is placed outside the room?

 

[Don Lancaster]

Hi,

Is it possible to detect sound behind concrete wall or door whereas the
detector is placed outside the room?

You mean like putting a glass against the wall and your ear against the
glass?

No, not possible.

--
Many thanks,

Don Lancaster
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
voice: (928)428-4073 email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[[email protected]]

You mean like putting a glass against the wall and your ear against the
glass?

No, not possible.

The correct answer is, "That depends."

To illustrate, you're on one side of the wall with a glass against the
wall and your ear against the glass and I'm on the other side of the wall with a
sledge hammer.

Jim

 

[ray13]

It is only not possible if you can prove that it is not possible. No
proof means it is still possible.

Remember the US cosulate in Moscow, Russia. The Russians pumped in
microwaves thru the phone line. And the had a special transponder built
into the United States Seal that they gave the consulate as a gift. The
Russians heard everything that was said in the room, that the
transponder was in.

Not possible, pshaw.

 

[John Woodgate]

I read in sci.electronics.design that eeh <[email protected]>

Hi,

Is it possible to detect sound behind concrete wall or door whereas the
detector is placed outside the room?

It depends how loud the sound is, obviously. If the microphone is in
direct and intimate contact with the wall, the sensitivity will be very
much higher than if it isn't.

 

[martin griffith]

You mean like putting a glass against the wall and your ear against the
glass?

No, not possible.

rubbish, Don, see this graph
http://www.venganza.org/images/spreadword/th_pchart1.jpg


martin

 

[Richard Henry]

Hi,

Is it possible to detect sound behind concrete wall or door whereas the
detector is placed outside the room?

Yes.

 

[Michael A. Terrell]

It is only not possible if you can prove that it is not possible. No
proof means it is still possible.

Remember the US cosulate in Moscow, Russia. The Russians pumped in
microwaves thru the phone line. And the had a special transponder built
into the United States Seal that they gave the consulate as a gift. The
Russians heard everything that was said in the room, that the
transponder was in.

Not possible, pshaw.

Microwave through a phone line?

 

[John Woodgate]

I read in sci.electronics.design that Michael A. Terrell

Microwave through a phone line?

Hollow wires.(;-)

 

[kell]

Hi,

Is it possible to detect sound behind concrete wall or door whereas the
detector is placed outside the room?

Think about this:
There might be noise outside the room, which would overwhelm any sound
from inside, no matter how sensitive or powerful an amplifier you use.
Because the sound coming through the wall from inside the room will be
extremely weak, any little vibration or noise would totally obliterate
it. You need to have a very quiet room to place your detector in.

Through the door would work better, just because the signal from inside
the room is less attenuated.

Now get away from my door.

 

[keith]

It is only not possible if you can prove that it is not possible. No proof
means it is still possible.

Remember the US cosulate in Moscow, Russia. The Russians pumped in
microwaves thru the phone line. And the had a special transponder built
into the United States Seal that they gave the consulate as a gift. The
Russians heard everything that was said in the room, that the transponder
was in.

Microwaves through twisted pair. Neat!

Not possible, pshaw.

I do believe the bugs in question were the precursor to RFID. They only
responded to (massive, BTW) microwave radiation and were dormant
otherwise. They did much the same thing to the "new" US Embassy
in Moscow. You know, the one that was never occupied. Telephone lines,
pshaw!

 

[Mac]

Hi,

Is it possible to detect sound behind concrete wall or door whereas the
detector is placed outside the room?

Can you be more specific? I imagine that under some circumstances it would
be possible.

Are you trying to determine the feasibility of some kind of high-tech
eavesdropping device?

I know in the movie _Clear and Present Danger_ some kind of laser
interferometry microphone was shown being used. Don't know if that works
in real life, particularly on a concrete wall.

If it does work, then RF interferometry might work, too.

--Mac

 

[quietguy]

Or using an electronic stethoscope?

David

 

[Paul Hovnanian P.E.]

Can you be more specific? I imagine that under some circumstances it would
be possible.

Can you open the door?

 

[BobG]

I remember hearing/reading the 'bugs' were resonant cavities in all the
cast concrete beams courtesy of the local Russian contractors. So all
the walls were transmitters when a nice beefy beam was pointed at it.
The resonance was modulated by air pressure across the cavity. Similar
trick to bounce a laser off a window that is being vibrated by speech
and demodulate the return. Countermeasure is to play the radio real
loud in the room.

 

[Richard Henry]

I remember hearing/reading the 'bugs' were resonant cavities in all the
cast concrete beams courtesy of the local Russian contractors. So all
the walls were transmitters when a nice beefy beam was pointed at it.
The resonance was modulated by air pressure across the cavity. Similar
trick to bounce a laser off a window that is being vibrated by speech
and demodulate the return. Countermeasure is to play the radio real
loud in the room.

The US also imported some "cone of silence" rooms that could be installed
inside the compromised embassy buildings, complete with sound muffling and
Tempest-quality electronics interfaces.

 

[Ron G]

Hi---
If the music on the radio is identifiable, then it can be nulled out by
using the same music to null out the mish-mash (on the recording).
If it's a radio station, the same should apply.
The resultant will be the conversation that took place.

Best---
Ron

Countermeasure is to play the radio real

 

[Winfield Hill]

Ron G wrote...

If the music on the radio is identifiable, then it can be nulled out by
using the same music to null out the mish-mash (on the recording).
If it's a radio station, the same should apply.
The resultant will be the conversation that took place.

Nope, too much phase shift.

 

[[email protected]]

Ron G wrote...

Nope, too much phase shift.

Feet of clay... feet of clay...

I used to consider you my idol, but I think you're simply wrong this
time. A tracking filter with a bandwidth of a few 10's of Hz derived from the
interfering audio source should ignore phase shift. The signal may have to be
run through the filter several times, but the original conversation should
finally emerge.

The fact that conversation contains a great deal of redundant
information makes it possible.

Jim

 

[John Woodgate]

I read in sci.electronics.design that [email protected] wrote (in

Feet of clay... feet of clay...

I used to consider you my idol, but I think you're simply wrong
this
time. A tracking filter with a bandwidth of a few 10's of Hz derived
from the interfering audio source should ignore phase shift. The
signal may have to be run through the filter several times, but the
original conversation should finally emerge.

The mind boggles!