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Integrating a telescope [light bulb moment] - advice

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Many people on SNA like to keep abreast of the latest research and discoveries and one of the more interesting recent announcements comes from an Israeli University. Their researches have literally delivered me with a light bulb moment. As a result I am seriously reconsidering my system design.


Because this is at the cutting edge of audio I am having some trouble working from first principles to integrate the telescope into the signal path and thought the SNA brains trust would be onto this and able to provide some guidance.


I better explain. Here is the advice. It explains things better than I could. Please excuse the length of the quote from Wired via Ars Technica.



The list of sophisticated eavesdropping techniques has grown steadily over years: wiretaps, hacked phones, bugs in the wall—even bouncing lasers off of a building's glass to pick up conversations inside. Now add another tool for audio spies: Any light bulb in a room that might be visible from a window.


Researchers from Israeli's Ben-Gurion University of the Negev and the Weizmann Institute of Science today revealed a new technique for long-distance eavesdropping they call "lamphone." They say it allows anyone with a laptop and less than a thousand dollars of equipment—just a telescope and a $400 electro-optical sensor—to listen in on any sounds in a room that's hundreds of feet away in real-time, simply by observing the minuscule vibrations those sounds create on the glass surface of a light bulb inside. By measuring the tiny changes in light output from the bulb that those vibrations cause, the researchers show that a spy can pick up sound clearly enough to discern the contents of conversations or even recognize a piece of music.


"Any sound in the room can be recovered from the room with no requirement to hack anything and no device in the room," says Ben Nassi, a security researcher at Ben-Gurion who developed the technique with fellow researchers Yaron Pirutin and Boris Zadov, and who plans to present their findings at the Black Hat security conference in August [2020]. "You just need line of sight to a hanging bulb, and this is it."


In their experiments, the researchers placed a series of telescopes around 80 feet away from a target office's light bulb, and put each telescope's eyepiece in front of a Thorlabs PDA100A2 electro-optical sensor. They then used an analog-to-digital converter to convert the electrical signals from that sensor to digital information. While they played music and speech recordings in the faraway room, they fed the information picked up by their set-up to a laptop, which analyzed the readings.


The researchers found that the tiny vibrations of the light bulb in response to sound—movements that they measured at as little as a few hundred microns—registered as measurable changes in the light their sensor picked up through each telescope. After processing the signal through software to filter out noise, they were able to reconstruct recordings of the sounds inside the room with remarkable fidelity: They showed, for instance, that they could reproduce an audible snippet of a speech from President Donald Trump well enough for it to be transcribed by Google's Cloud Speech API. They also generated a recording of the Beatles' "Let It Be" clear enough that the name-that-tune app Shazam could instantly recognize it.


The technique nonetheless has some limitations. In their tests, the researchers used a hanging bulb, and it's not clear if a bulb mounted in a fixed lamp or a ceiling fixture would vibrate enough to derive the same sort of audio signal. The voice and music recordings they used in their demonstrations were also louder than the average human conversation, with speakers turned to their maximum volume. But the team points out that they also used a relatively cheap electro-optical sensor and analog-to-digital converter, and could have upgraded to a more expensive one to pick up quieter conversations. LED bulbs also offer a signal-to-noise ratio that's about 6.3 times that of an incandescent bulb and 70 times a fluorescent one.


An immediate first step of course is in relation to wattage. From now on when someone talks to me about wattage, I'm going to have to ask if they are referring to amplifier wattage or light bulb wattage. For example hereabouts we are looking at a 2 x 375 watt combo, this is serious hi-fi, except it's infra-red and being installed in the bathroom ceiling as part of the renos, which means that the best listening position is not where the seat is.


Then there's the telescope question. Does that mean monaural? Are binoculars a better option to provide depth of field and soundstage?


How does one ensure good imaging? Should the telescope be fastened to the floor or completely decoupled by way of anti-vibration mounts etc. I think I'm going to have some real-life results for you, as in order to get the light bulb/ telescope signal path working properly I have no option but to put the telescope in the middle of the laundry floor. WAF has suddenly become a critical factor, and a dim view is being taken about limiting the times when the washing machine operates to periods when the stereo is off.


This research looks to be a positive contribution to civilization and in particular to audio technology. Given the nature of the research I can only assume that the research was sponsored by Mossad, and if so, this is a very good thing! Secret services get a bad rap, last news I heard about Mossad was they used New Zealand passports for an assassination in the Gulf, which really raised the question of "if that's how you treat your friends..." So sharing this cutting-edge audio news is certainly a step in the right direction.


Currently I'm looking at a pair of these, because non-spherical light bulbs might have a profound effect on the algorithms, such as loss of bass. Obviously I've taken the clear option for transparency.







Edited by ThirdDrawerDown
fixed the quote
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Everything is pretty much OK with some one listening in, so long as you don't turn on the light!

So work in the dark, most of us here do that normally don't we?


The listening in to another persons system whilst interesting however difficult it may be, say with a 7.1 HT system, how do you manage to get them to provide the music you prefer?

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18 hours ago, ThirdDrawerDown said:

An immediate first step of course is in relation to wattage. From now on when someone talks to me about wattage, I'm going to have to ask if they are referring to amplifier wattage or light bulb wattage.


Yes, and distance of the listener to the light bulb is to be measured as whattage.


FYI, LED's don't sound as warm.

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