The AM Forum

this could have more than a few uses for ham radio..
https://www.fastcompany.com/90316833/scientists-have-discovered-a-shape-that-blocks-all-sound-even-your-co-workers

you'll notice they didn't block music...

Something to passively prevent home invasion by the pulsating bass of the disco and/or rap would be a real boon to mankind. It takes the police a whole hour to put a stop to it.

I was once asked to install a burglar alarm at a small company I was working for. Along with the usual external alarm horns on the front and rear of the building, I installed a very loud alarm horn in the ceiling of the small front office. The idea was that an offender can't steal anything with his hands covering his ears!

Upon completing the installation, I needed to test it. At that time, the only person in the office was the company receptionist/secretary/malcontent, Gail. Directly above her seat was mounted the piercingly loud alarm horn that I had chosen for the job. As I prepared the test, I could have warned her of the impending din. For the sake of realism though, I did not.

Needless to say, the test returned to me a very satisfying result. Although Gail, who happened to be on the phone at the time, was not so favorably impressed.

Pretty funny.
Well if the alarm was so piercing and if the phone was a POT, then the audio induced voltage probably overrode the carbon mike bias and her yammering into the phone.  - so all that was heard on the other end might have been silence..    They probably thanked their muses.


It's a wonder she didn't report you to the OSHA dB police.  ;D

I have a pain transducer in the ceiling of my house tied in with the horn.

Works surprisingly well.  So well in fact the time my alarm was tripped and I wasn't home the neighbor forced the police to show up.

I'm Bakersfield the police won't respond.  Fill out a report online is their mantra.

--Shane
KD6VXI

Here it is folks. A remote controlled sonic nausea inducing device! Great for use at restaurants, county fairs, and hamfests. Fun for the whole family! :D

https://www.amazing1.com/products/sonic-nausea-device-with-radio-control.html

I'm very puzzled by this: I didn't know that carbon microphones could be overloaded so as to produce silence. Please tell me where I can find an explanation of the phenomenon online, and thanks in advance.

Bill, W4EWH

Bill, I was kidding.   ;D
But I did think it sounded negatively possible.
The actual piercing alarm sound might at least breakup the secretary’s voice into incoherent syllables, cross modulate it, and at best would stop her from talking, heh heh.

Meant to add earlier a quote:
“Paul Harvey said in one of the ‘Rest of the Story’ episodes that it was the carbon
Microphone that started ‘crooning’ “

-resistance run-on in a delta current device?  ;D

The invention is very limited.

It is essentially an acoustic lowpass elliptical filter.
Not a good one either. Only about 12dB of attenuation.

The notch is high Q. Good for one frequency essentially.

Thus, the demo...

Although larger, a helmholtz trap would likely do a better job.
For cars these are called "mufflers"... :D

But still it is clever, since I can't read the entire journal article, I'm not quite
sure what the mechanism is. They reference "Fano" effects, but again, it's unclear
if what they have here merely has a similar curve or works on a principle
other than re-inserting energy at one frequency 180deg out of phase.

Note that they get ~12dB of attenuation.  Not more.

If the spiral mechanism was coincident with the walls of the pipe, I suspect it would
have little effect. It looks like it depends on "harvesting" a percentage of the pressure
wave, which if it were coincident would pass by and nothing would happen.

Most of the comments online indicated that people had very little idea what the
invention did or how it works.

                    _-_-

Using 20 Log (V1/V2) I get 14 dB differential.  I'm assuming a linear reacting microphone over that SPL differential.  

I also notice a slight, momentary drop in noise when the hand is removing the multi spiral trap. Really slightly muffled with a momentary increase in back pressure from the hand.  

And also notice column exponential drop ringing after the trap is removed for the first few
pressure release cycles ringing at the natural frequency of the organ pipe.  

If the trap is highly frequency dependent,*  then a wall of them could be built using a grid of different lengths of tubes, a dot matrix so to speak.   The wall could be tailored to type of noise expected, say a different set of lengths for an outdoor plaza next to a road.

 An application there might actually enhance the conversations and pleasure of the customers by diminishing primarily low freq. motor noise with another band of tubes to diminish the more pinkish tire swishing noise.  14dB from a non-electrical dependent
device might be just the ticket, almost like being inside instead of out next to the traffic.
This of course is probably most do-able for new construction.

*I suspect the trap's radial spiral annulae lengths are freq. dependent like all partially stopped organ pipes, over a range of harmonic related fifths, etc., thus not as many needed for a range or band of frequencies.

Looks like this device may make a good silencer for a gun. Better living through science.

It would be rather huge at low freqs...

seems like it's a novelty, at least at this point in time.

I was researching noise reduction methods for a low back pressure muffler for marine diesel engines when I ran across this device...
Sound suppressor for a gun might be a possibility as well...

This almost sounds like an early release of something that was supposed to be announced on April 1. I'm surprised that this was not paired up with DED's (a.k.a. LAD's) otherwise known as Dark Emitting Diodes  / Light Absorbing Diodes ...

No, because this works on a single frequency.
Gun output is a pulse, not defined as a single frequency at all.

Further, this invention has to be put in the end of the bore, not annularly off to the side of the bore like a traditional silencer, hence will be shot at sunrise.
 
Gunfire is a shock/ pressure wave already supersonic before muzzle release in all but rimrire and lesser cartridges. Might be more fun and sun for our Sonic SWR reflector to deal with. Upon release from muzzle constraint,  a gunshot noise rapidly encounters expansion, pressured front air cooling and deacceleration to speed of sound limit.  The escaping bullet being relatively solid maintains its supersonic velocity and trails a continuous and expanding sonic boom with angular dispersal waves, the escape angle of which are a function of velocity.

Also There is however a predominant frequency to a gun shot plus the white noise component. Thunder doesn’t sing high notes nearly as well as bass.  Shock Displaced Air movement is a fickle mistress, more a basso profundo.

Well, whatever, Hiram would have been proud.


klc

By "prevent home invasion by the pulsating bass of the disco and/or rap " I mean that I don't want to hear that bass booming through the walls of my home, invading it with that noise. There are possible countermeasures, but bass carries far and as far as I know the only legal thing to do is call the police. What a waste of their valuable time, unless there's a higher offense going on at the source.