What are the properties of a Sound Pressure Wave going down into a Cone?

[gary350]

I do not remember the correct terms to look this information up on Google. I once read that as a pressure wave goes down into a closed cone every time cross sectional smaller by 1/2 the pressure wave doubles. My cone is 12" x 12" on the open end and 1"x1" on the closed end. Cone is 24" long the cross sectional area is half 7 times, sound should get 7 times louder with no electronic amplifier. Do I have this correct?????? What is this called?

I put a microphone in the bottom end of the cone and built a LM386 circuit to amplify 200 times. I only need the volume control on about 5% amplification it is so amazing loud. My hearing aids are being repaired that will take 3 weeks. I want to build a hearing aid I can use for 3 weeks. If I understand the science of a cone better maybe I can make this work. I think my cone needs to be much smaller.

 

[berkeman]

What is this called?

https://en.wikipedia.org/wiki/Ear_trumpet

 

[Baluncore]

Horns can be used for speakers or listeners, air pressure or EM waves.
https://en.wikipedia.org/wiki/Horn_antenna

An exponential horn has the same percentage taper per unit length, so it is more compact, better matched over a wide frequency range, and more efficient than the straight horn.
https://en.wikipedia.org/wiki/Horn_antenna#Types
https://en.wikipedia.org/wiki/Horn_loudspeaker

The exponential horn can be reentrant, folded back on itself, as is done with public address speakers. That makes the most compact form.
https://en.wikipedia.org/wiki/Horn_loudspeaker#Public_address_and_concert_use

One big advantage of a horn is that it can be directive, concentrating energy in one main beam as a speaker, or as a listener, eliminating sounds from either side of the more sensitive central beam.

 

[gary350]

I can see my cone is totally wrong. A straight tube will work best it will receive a cone shape signal, it needs to be designed to receive a range of 3' to 5' to talk to people in that range also another tube to receive 7' to 10' range. 3 different tubes for 3 different ranges with a selector switch might work great. Cones and tubes do not amplify, they concentrate same as a magnifying glass. A tube with a trumpet shape end will be better.

 

[Baluncore]

Cones and tubes do not amplify, they concentrate same as a magnifying glass.

You need more sound energy in your ear.

An exponential horn has a much greater aperture, so it captures more energy and guides it all to your ear. In that sense, it has amplification or gain.

The only advantage of a parallel tube, or speaking tube, is that you can move one end closer to the person speaking, and so suffer less inverse square attenuation, before the small amount of sound energy travels the length of the tube. A speaking tube works best with a cone or funnel at each end.
https://en.wikipedia.org/wiki/Speaking_tube

 

[gary350]

Today I built a trumpet shape but not with a continuous changing radius. I did 25° and 55° the tube is 1" square 8" long. This cardboard trumpet is surprising how well it works. I only have amp volume at about 10%, no hum, no feed back. I can hear wife talking at the other end of the house. I turned volume down to ??? maybe 4% for room use volume only needs to be about to talk to people 10 ft away. I assume trumpet shape is picking up a much better signal for mic to receive so well. Now that I have built this trumpet I am sure I can build another square trumpet with a nice radius. If I could find a graph of a real trumpet radius I could copy it very close. This is a fun and very educational project the amp does not need high implication like I thought, the trumpet needs to be able to pick up a good amount of sound for the mic. This is what you call, research and development.

 

[Baluncore]

You need an exponential curve to match the impedance of the large area aperture, to the face of the microphone. Make four flat sheets with curved edges, when you join them along the edges, you get a smooth curved exponential horn, with a square section.

Step changes in a horn cause some frequencies to be reflected. Also, a long parallel section does not do any matching, since the wave front in the tube does not change.

Take a look at your microphone, does it have a 1 mm diameter hole to communicate air pressure? Then match the horn size to that hole, not to the unused face of the microphone.

 

[gary350]

You need an exponential curve to match the impedance of the large area aperture, to the face of the microphone. Make four flat sheets with curved edges, when you join them along the edges, you get a smooth curved exponential horn, with a square section.

Step changes in a horn cause some frequencies to be reflected. Also, a long parallel section does not do any matching, since the wave front in the tube does not change.

Take a look at your microphone, does it have a 1 mm diameter hole to communicate air pressure? Then match the horn size to that hole, not to the unused face of the microphone.

I built a horn to match the curve on the graph. The mic slides into the square tube and can be pushed up the tube to any location of the 8" long tube. The LM386 amp has a gain of 200 but I only need to turn volume up to about 3% to 10% to get an excellent very sensitive loud signal. I can hear people talking 30 ft away. I can hear the neighbor across the street talking. I can hear no high frequencies because my ears have high frequency hearing lose, the amp needs tone Equalization control a volume knob for every 1k frequency range.

 

[Baluncore]

That is gradually evolving into an efficient "ear trumpet".
https://en.wikipedia.org/wiki/Ear_trumpet

The aim is to gather the energy that enters the aperture, then to guide it and concentrate it onto the microphone.

To operate efficiently, a horn only needs to open to about 45°. The front face of your model is almost flat, which makes it bigger than is necessary. Energy will be reflected from the flat face, rather than being guided into the horn by a 45° slope at the entrance.

You will find little change with the microphone position in the long neck. I would allocate much of the length of the neck to a more gentle curve from the aperture to the microphone. A long parallel neck could become an organ pipe resonator, which would upset the frequency response.

The exponential curves you show are hand drawn caricatures. Notice that the slope of e^x is 45° at x=1.
Play with the Exp() or e^x functions on your calculator.
https://en.wikipedia.org/wiki/Exponential_function

 

[gary350]

That is gradually evolving into an efficient "ear trumpet".
https://en.wikipedia.org/wiki/Ear_trumpet

The aim is to gather the energy that enters the aperture, then to guide it and concentrate it onto the microphone.

To operate efficiently, a horn only needs to open to about 45°. The front face of your model is almost flat, which makes it bigger than is necessary. Energy will be reflected from the flat face, rather than being guided into the horn by a 45° slope at the entrance.

You will find little change with the microphone position in the long neck. I would allocate much of the length of the neck to a more gentle curve from the aperture to the microphone. A long parallel neck could become an organ pipe resonator, which would upset the frequency response.

The exponential curves you show are hand drawn caricatures. Notice that the slope of e^x is 45° at x=1.
Play with the Exp() or e^x functions on your calculator.
https://en.wikipedia.org/wiki/Exponential_function

I built the new cardboard horn and tested it. Soon as I got 2 ft away from my laptop computer 60 Hz hum is gone. I adjusted the volume and had no trouble talking to my wife. Sound seem to be more clear than the other horns that I tested. Volume knob is not up very much maybe 5%. Horn is 5" square 11½" long. There is no feedback.

 

[Baluncore]

I adjusted the volume and had no trouble talking to my wife. Sound seem to be more clear than the other horns that I tested.

The design of an exponential horn is a science. You have now lost the advantage of claiming you did not hear, but it is a lucky wife, to have a husband who will go to that much effort, to listen to his wife.

 

[Averagesupernova]

...but it is a lucky wife...

Yes. Most guys don't want to hear the wife at the other end of the house. Lol

I can hear wife talking at the other end of the house.