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I think I'll make one to listen to conversations in other cubes. It'll look cool towering over my cube wall, and it'll worry the hell out of my co-workers
This is true. I have taken various mathematics and physics courses that have studied the nature of parabolas, ellipses, and spheres, and their focusing qualities. When I said a "bowl" shape, I meant a sphere cut in half. I believe (correct me if I am wrong) that in this case, the focus would be halfway between the bottom of the bowl and the center of the (used-to-be) sphere.
Der Strom
A sphere doesn't have a focus in the same sense as a paraboloid has. Part of the sphere around the "axis" might approximate a paraboloid to a certain degree, and so you might get an approximate focus. It won't be the same as the focus of the original sphere though, and the focusing of the energy won't be as strong.
To blow the eardrums out!! LOL
No I was thinkingh of 7 watts so I could use a speaker instead of a headphone then more boys could hear what the BIG EAR is picking up instead of one at a time PLUS I have 5 on hand (L4950TA).
BUT have a switch that can turn the volume WAY DOWN for using a headphone ( a switch so a preset volume is used, someone can't be "funny" and turn up the volume.
have a dip switch combolock to control the volume.
remember we as adults have to be smarter than the kids.
you never know what kids will do. be perpared for anything.
I need to investigate the 2n5088 and 2n5087 transistors. maybe sub using 2n2222
2n3906?
I believe the math formula for the focus of a parabola is Y^2=4px, where Y is the radius of the dish, x is the depth, and p is the distance from the vertex of the parabola to the focal point. For example, let's say you have a dish that has a 50cm diameter and a depth of 10cm. The radius (Y) would be 25cm (1/2 diameter) and x would be 10cm. Therefore, (25)^2=4p(10). Then, solve for p to get the focus: 625=40p, so p=15.625. The focal point would be 15.625cm from the vertex.
As always, please correct me if I am wrong, as I am still learning more about parabolic reflectors.
Der Strom
I tried this once with the circuit I attached in my first post on this thread and the feedback was extremely loud and piercing. Just keep this in mind
Der Strom
I have a big ear listening device that I built using 2 LM386 ICs 32 years ago. I can hear people over a mile away talking and it sounds like they are standing right next to me. As I recall the LM386 have an amplification of 200 so 2 in series is 200 x 200 = 40,000. You need a volume control on the first stage so it will not over drive the second stage. You need to couple the output of 1st stage to the 2nd stage with a capacitor. Mine runs on a 9 volt battery but 12 volts works much better. I am using a cheap quality 6" x 9" speaker as the microphone, point it in the direction you want the listen it acts like a dish and pics up sounds like you won't beleive. This is an extremely simple device to build it only requires 11 parts to make the ICs work. If you need more power output you can add a LM3886 IC it will give you 68 watts with a 4 ohm speaker, 38 watts with a 8 ohms speaker, 135 watts peak to peak and it is so simple it only required a few parts too.
If you want the circuit drawing I still have it but it might take me a day or so to find it. If not I can probably draw a new circuit from my circuit board with all the parts soldered to it. You can probably build this in about an hours work.
To blow the eardrums out!! LOL
No I was thinkingh of 7 watts so I could use a speaker instead of a headphone then more boys could hear what the BIG EAR is picking up instead of one at a time PLUS I have 5 on hand (L4950TA).
BUT have a switch that can turn the volume WAY DOWN for using a headphone ( a switch so a preset volume is used, someone can't be "funny" and turn up the volume.
have a dip switch combolock to control the volume.
remember we as adults have to be smarter than the kids.
you never know what kids will do. be perpared for anything.
I need to investigate the 2n5088 and 2n5087 transistors. maybe sub using 2n2222
2n3906?
I have a big ear listening device that I built using 2 LM386 ICs 32 years ago. I can hear people over a mile away talking and it sounds like they are standing right next to me. As I recall the LM386 have an amplification of 200 so 2 in series is 200 x 200 = 40,000. You need a volume control on the first stage so it will not over drive the second stage. You need to couple the output of 1st stage to the 2nd stage with a capacitor. Mine runs on a 9 volt battery but 12 volts works much better. I a using a cheap quality 8" speaker as the microphone, point it in the direction you want the listen it acts like a dish and pics up sounds like you won't beleive. This is an extremely simple device to build it only requires a few parts to make the ICs work.
If you want the circuit drawing I think I still have it but it might take me a day or so to find it. If not I can probably draw a new circuit from my circuit board that I etched with all the parts soldered to it.
The speaker is connected to the circuit with a tiny little speaker transformer hooked up backwards. Perfect Impedance Matching. No one uses speaker transformers anymore so this may be the hardest part to find for this circuit all the rest of the parts are common. Remember back in the stone age when speakers used a impedance matching transformer? Maybe your not from the stone age?
The speaker is connected to the circuit with a tiny little speaker transformer hooked up backwards. Perfect Impedance Matching. No one uses speaker transformers anymore so this may be the hardest part to find for this circuit all the rest of the parts are common. Remember back in the stone age when speakers used a impedance matching transformer? Maybe your not from the stone age?
this one mile distance sounds far fetched but then maybe not?
I would be interested in this setup you have.
I think I have said transformer I purchased from Radio Shack last year but never used. just need to .
locate
If you can locate then post schematic
Look it up where? ( Show me ) I might believe if you said the dish favors higher frequencies. But it's incorrect that it won't focus mid and low frequencies. A dish, say 1/2 meter in diameter, is close to the wavelength of about 700Hz, which is certainly not high freqeuncy. And it gives good response in the mid range from 1000-4000hz. The rolloff of the gain with lower frequency is about 5db/octive, according to the chart here.
PS Sorry, I kept adding to this as I read more through the article. What's really interesting is the chart in fig. 6, which shows the gain vs angle from the source. Up to 30 degrees, there was virtually no difference at the lowest frequencies.
A 2 or 3 inch speak in place of the LNA in a DirecTV dish might work. The dish would make it much more directional that what I had. I use to pick up people talking that sounded like they were standing right next to me, we use to drive around in the car trying to find them. Sometimes we could drive in that direction a while and loose them sometimes we would drive a mile and be pretty close to them and still could not find them. After dark it is hard to see people they could be setting in the back yard in the dark.
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