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Topic: Mobile Phone usage inside the house
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 05-26-2005 02:06 PM
If you can shield every wall, ceiling, and floor of your auditorium with grounded metallic shielding, you create a "Faraday Cage" that will prevent any RF signal from getting in. But any opening in the shield (e.g., the entrance doors) could provide enough "leakage" to still allow a cell phone to operate if the signal strength is sufficient.
http://en.wikipedia.org/wiki/Faraday_cage
quote:
The Faraday cage is an electrical apparatus designed to prevent the passage of electromagnetic waves, either containing them in or excluding them from its interior space. It is named for physicist Michael Faraday, who built the first one in 1836.
Faraday stated that the charge on a charged conductor resided only on its exterior, and had no influence on anything enclosed within it. To demonstrate this fact he built a room coated with metal foil, and allowed high-voltage discharges from an electrostatic generator to strike the outside of the room. He used an electroscope to show that there was no excess electric charge on the inside of the room's walls.
This shielding effect is used to eliminate electric fields within a volume, for example to protect electronic equipment from lightning strikes and other electrostatic discharges (ESDs).
The same effect was predicted earlier by Francesco Beccaria (1716–1781) at the University of Turin, a student of Benjamin Franklin's work, who stated that "all electricity goes up to the free surface of the bodies without diffusing in their interior substance". Later, the Belgian physicist Louis Melsens (1814–1886) applied the principle to lightning conductors.
The Faraday cage is sometimes known as a Faraday shield. The latter term is also used more generally for any kind of electrostatic shielding.
http://www.rabc.ottawa.on.ca/e/Files/01pub3.PDF
quote:
Use of Jammer and Disabler Devices for Blocking PCS,
Cellular & Related Services
http://www.rabc.ottawa.on.ca/e/Files/tp201rl1.PDF
quote:
2.1.5 Type “E” Device (EMI Shield - Passive Jamming)
This technique is using EMI suppression techniques to make a room into what is called
a Faraday cage. Although labour-intensive to construct, the Faraday cage essentially
blocks, or greatly attenuates, virtually all electromagnetic radiation from entering or
leaving the cage – or in this case a target room.
With current advances in EMI shielding techniques and commercially available products
one could conceivably implement this into the architecture of newly designed buildings
for so-called “quiet-conference” rooms.
Emergency calls would be blocked unless there was a way to receive and decode the 9-
1-1 transmissions, pass by coax outside the room and re-transmitted. It is unclear whether or not such techniques may still contravene the
Radiocommunication Act section 9.(1)(b), which states:
No person shall without lawful excuse, interfere with or obstruct any
radiocommunication.
In addition, municipal or provincial building code by-laws may or may not allow this type
of construction.
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Steven C Y Chan
Film Handler
Posts: 16
From: Hong Kong, HKSAR
Registered: Jan 2005
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posted 05-26-2005 07:19 PM
Thanks John, you had give me a great information on it. very interesting, thanks.
Thomas, we had try your way, result is - people here will 'strike back' will a louder voice, and someone others will sent a complain to our head office, not the one using mobile (how can complain them, or we will do it 1st), but the staff speaking loud.
Lyle, my boss had found a germany company working with a very small output jammer, they say they will only jam inside the theater, no outside even the lobby, some tips I only know is their output is very low (some tens mW) so not far and not strong enough to pass most wall, direct antenna and reflector is used (hope I remember it right), some people in our company had seen the result and say it is ok, lawyer work on it to related government department. Don't know the result, but time used a lot, so not a good sight.
They had also make a point is by today technical, using 3G mobiles, it is possible to sent the movie out illegal(?), with these they only need a capture device (CCD?) and some 3G mobile, capture and bluetooth to the phone and out, I haven't see the demo, but people had seen a demo by the jammer company, using a modificated sony IP-55 camrecorder, 5 pcs 3G mobile, and say can work.
If so, hope something can be happen later.
I still remember when ONJ in concept here, when she told people turn off mobile and paging, seen all people do it (sure, she charge over 2-3 times more than normal singers here), its so great. And pre-show of the SW EP-3, phone collected and stored. If possible, I want it in every show. (sure my ground level manager will kill me) ![[beer]](graemlins/beer.gif)
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 05-29-2005 08:03 AM
A Federal Act does not equal Rights (the highest form of protection in the US). Like everything, it is up to interpretation.
A jammer has the issue that you, the theatre owner, must be broadcasting something in order to jam the signal...the problem will be with the authorization to broadcast.
The RF shielded theatre, on the other hand, is a passive system and can happen naturally through building construction. A subway is often not a good cell phone are, as are tunnels and many buildings with a lot of steel about.
In Colonial Williamsburg, they have a pair of theatres that were constructed in the 1950s in their Visitor's center...the ceiling and walls are all made from perforated metal panels. To top it off, the screen is a silver type with aluminumized particals to maintain the color of the room more so than for projection quality since it creates a bit of a hot spot. Don't count on your cell phone working in there. In fact, it posed a problem for us to come up with a wireless system to broadcast up to 6 foreign languages. We had to run the antennas down to the screen and hang them from the center speaker platform. The screen was the weak link in the cage. You couldn't broadcast from the booth to the theatre...the signal just died. Even putting the antennas so close didn't yield 100% coverage from a system that can normally reach very far (a block or two). On the upside, there is no inter-theatre interference (they are back to back theatres).
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Dave Williams
Wet nipple scene
Posts: 1836
From: Salt Lake City, UT, USA
Registered: Jan 2000
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posted 05-29-2005 12:58 PM
quote: Steve Guttag
The RF shielded theatre, on the other hand, is a passive system and can happen naturally through building construction
Today many businesses are saving money on construction by having buildings prefabed from steel, then adding concrete, wood, more steel, more concrete, whatever, after the initial installation.
So they end up with every bit of wall, cieling and floor made from steel. Quite often you may be in one of these prefab buildings without even knowning it. However you may also find that your cell phone seems to not be able to get a good signal.
Ciao
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Martin Brooks
Jedi Master Film Handler
Posts: 900
From: Forest Hills, NY, USA
Registered: May 2002
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posted 05-31-2005 07:24 PM
One thing I’ve noticed lately: while earlier “shut off your cell phone” trailers didn’t seem to work, there’s one that AMC has been using lately which features the sound of a baby crying and then a cell phone ringing. The sound effects are recorded so well (and they playback only out of one channel) that the first time I saw this trailer, even I thought it was a real baby crying.
During the presentation of SW3, this trailer received audience applause at the screening I attended. And no cell phones rang during the screening.
So while I still see people checking their phones 10 times during a screening (and the glow of the their screen is annoying enough), I think audiences are finally getting the message and turning the ringers off.
On the other hand, Billy Crystal tells a story about how in spite of his requests to shut phones off, five different cell phones rang during a performance of his Broadway show. Some people are so arrogant, rude and obnoxious, it boggles the mind.
IMHO, a cell phone ringing during a movie or stage performance is grounds for ejection.
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Randy Stankey
Film God
Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99
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posted 05-31-2005 09:39 PM
We do a PowerPoint slide show before our movies with sound and video. (I HATE PowerPoint but I have to use it.)
We had a rash of interruptions from phones during the movies until I put a special slide into the slide show.
Picture = A cellular Phone with text superimposed: "Don't forget to turn off your cell phone!"
Sound = Sound of a phone ringing. (Using stereo effect to make it move around the room.
Since I put that slide into the preshow there has been, maybe one or two interruptions for the rest of the year! I'm pretty sure the interruptions came from latecomers.
Besides the sound as an attention getter I think the key to its effectiveness is the use of the line "Don't Forget..."
Everybody knows (or ought to know) that they should turn their ringers off during the show. This serves as a gentle, yet direct reminder to do something they know they should.
I've gotten a lot of laughs from people who hear the ring, not knowing its a sound effect, and start looking for the source of the sound. When they see slide on the screen, almost universally, they check their phones right then and there. I've actually witnessed people do it.
Trailers that use cute animation, sayings or sound like they are putting people down will, I believe, be less effective than a polite and to-the-point reminder to turn off the phone.
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we even get complain as we walk around to found the ringing phone. Any suggestion? We had try to use a jammer but government say it is illegal. Sometime we refund them.
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