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How to calculate amplification of a cone?

gary350

Well-Known Member
I need some type electronic way to test sound collected by cones. When I had a photography dark room I used a light meter to test light from the enlarger to the paper to determine exposture time. I need a electronic sound meter to test cones if there is such a thing or if I can build one?

I have built several cones and I have already learned the larger the intake opening is the more sound cone picks up. The smaller the exit opening the high sound pressure amplitude is = louder. The more stream line the cone is like a rocket engine the better the cone works.

I read lots of online information about cones, horn theory, acoustics and not finding what I want. Most of what I read has to do with cones use to project sound not to receive sound. Many people over the past 100 years have tried to explain their own cone theory with lots of formulas but no one agrees on this technology. Some claim a sound increase of 150-170dB.

I learned during WWI and early part of WWII cones were use to listen for airplanes 10 miles away before the invention of electronic radar. Cones were a type of mechanical radar.

Here is a picture of 1 of my cones it is 13" square at the intake opening, 24" long, 1" square at the exit opening. I can turn living room TV down so low no one can hear it but me with this cone. I can hear pe ople across the street talking with only the cone, no electronic amplifier.

I am trying to collect my on data to learn how much sound I can collect with a cone and how much the cone shape has to do with how loud the sound is?

I know a photo cell connected to a meter can be used to determine how bright light is.

I wonder is a small speaker can be connected to a micro amp meter to test how much sound a cone receives? Is there a better way?

I can continue to build random sizes & shape cones but it might be easier to do test to see how loud sound is from each cone.

I connected my LM386 amplifier to a cone I can see and hear people 2 blocks away like they are standing right next to me. I never experimented with cones before I use to build I never realized they were so effective.

I don't have a tiny 1" speaker or 2" speaker. I know diaphragm movement produces a voltage that can be read with VOM. What about those tiny beeper speakers inside microwave ovens how do those things work do they produce a voltage? Anything that detects sound and produces voltage can be read on the VOM. ? ? ?

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Nigel Goodwin

Super Moderator
Most Helpful Member
You don't want a cone, you want a horn - an exponential horn, as in the first two B&W pictures (not sure of the third, as the outside might be different to the inside, or it's just poor one). It's a complex shape to make, but it's what's needed for maximum efficiency.

Essentially it's an acoustic transformer, matching the mechanical impedance of the air, to the mechanical impedance of the transducer.

No need to measure anything, just make them accurately, and the bigger the better.
 

audioguru

Well-Known Member
Most Helpful Member
The size of the horn determines the low frequency response.
The horn must be rigid. Cardboard will flex and vibrate which will cancel some sounds.

A little speaker used as a mic makes a boomy sound because the speaker resonates at a few hundred Hz. A piezo beeper used as a mic or speaker makes a tinny shrieking sound.
 

gary350

Well-Known Member
You don't want a cone, you want a horn - an exponential horn, as in the first two B&W pictures (not sure of the third, as the outside might be different to the inside, or it's just poor one). It's a complex shape to make, but it's what's needed for maximum efficiency.

Essentially it's an acoustic transformer, matching the mechanical impedance of the air, to the mechanical impedance of the transducer.

No need to measure anything, just make them accurately, and the bigger the better.
What is the difference between, horn & cone. I know in math cone is round. I am calling mine a cone but mine is square. I should be careful what is call it maybe horns are square. It is not possible to build round with cardboard it will not roll round.

Yes I already learned bigger is better but I don't want to carry 4 ft x 12 ft long horn around with me. LOL.

We had a thunderstorm yesterday evening WOW thunder is amazing to listen too. Even when I count to 25 and thunder is 5 miles away it is loud and rumbles very interesting. We had 1 lighting strink that was Flash BOOM 1/2 second later it almost blasted my ear off and I felt the pressure wave in the horn like hitting a drum.

Why do these pictures have so many 3 ft square horns, is it because 1 very large 6 ft square horn will pick up only low Hz?

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Nigel Goodwin

Super Moderator
Most Helpful Member
What is the difference between, horn & cone. I know in math cone is round. I am calling mine a cone but mine is square. I should be careful what is call it maybe horns are square. It is not possible to build round with cardboard it will not roll round.
Round is better, but is difficult to make - what matters more is exponential curves, flat sides are much poorer.

Just get a horn from an old PA speaker, and if it's still got a pressure unit on it you can use that as a microphone - they are commonly used that way on PA intercom systems in factories etc.
 

ronsimpson

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Most Helpful Member
Why do these pictures have so many smaller horns, is it because 1 very large horn will pick up only low Hz?
\
Not "only low Hz".
One big cone will blow over in the wind. It will be very hard to move. Hard to make.
I think 4 cones will be more directional. Radio frequencies and antennas work that way.
Every cone will add to the signal.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Aren't parabolic dishes better for this than a cone? Like this made for doing distance listening -
Similar sort of idea, but it doesn't match the impedances as a horn does.

If you've ever been to Jodrell Bank Observatory, there's a couple of big dishes set up for audio (dish to dish) as one of the displays.

Edit:

Found a picture:

 

gary350

Well-Known Member
I think cross sectional area of the horn intake is the key to more reception. I like to have cardboard corrugations running 90 degrees to the horn length it make the shape stronger. I will look to see what I can build today I might be able to build a horn 6 ft long with 3 ft sq intake. I don't want to splice cardboard pieces together. Here are better pics of my biggest best horn so far.

Maybe I can buy a small speech horn and tape to the end of cardboard cone for a mic pick up.

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alec_t

Well-Known Member
Most Helpful Member
If sound is being funnelled down from an input area A to a microphone output area a I would expect the horn/cone to have a sound-pressure gain of about A/a if there were no losses. My expectation is likely different from reality :).
 

gary350

Well-Known Member
If sound is being funnelled down from an input area A to a microphone output area a I would expect the horn/cone to have a sound-pressure gain of about A/a if there were no losses. My expectation is likely different from reality :).
I was reading online sound in a closed column is louder than an open column because of the pressure wave gain in the closed end column. I did a test if my ear is the cork that makes the closed column sound louder than if my ear is 1/4" away. I assume if an electret mic is inside the horn bottom with cardboard glued over the hole that will be louder than open end bottom on horn/cone. I was thinking about a pick up device that can be connected to a micro amp meter or VOM to test how well the horn/cone works. I don't have material to make round cone and the tapered banana peal looking horns/cones are too much work just for playing around. If it were a life or death thing need to hear German airplanes coming 2 miles sooner than better more efficient horn/cones will be required. I was hoping that I might be able to make my own data that shows cross sectional area of hone/cone intake is directly proportional to sound volume, I think it probably is.

Throw a rock into a lake waves go out in circles that get larger and large the farther waves are from rock but waves far away have less amplitude than waves near the rock. I think sound waves going into the cone/hone are like waves in the lake in reverse direction traveling toward the rock.
 
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gophert

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Throw a rock into a lake waves go out in circles that get larger and large the farther wave are from rock but waves far away have less amplitude than waves near the rock. I think sound waves going into the cone/hone are like waves in the lake in reverse direction traveling toward the rock.
Sound waves are like the water waves in a lot of ways. Including how water waves get distorted, taller, and slower and as the ocean bottom disrupts the up/down motion of the wave as it travels from its origin. The cone makes similar distortions to the sound waves. The tapered walls of your cone certainly raise the volume. And you are correct, cross-section area difference (beginning to end of cone) is proportional to the amplification (less some efficiency factor).
 

unclejed613

Well-Known Member
Most Helpful Member
Throw a rock into a lake waves go out in circles that get larger and large the farther waves are from rock but waves far away have less amplitude than waves near the rock. I think sound waves going into the cone/hone are like waves in the lake in reverse direction traveling toward the rock.
try using water waves to model the cross section of your cone (use sheets of plastic for the "walls" and not cardboard). this will allow you to determine the best shape without expensive equipment.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
try using water waves to model the cross section of your cone (use sheets of plastic for the "walls" and not cardboard). this will allow you to determine the best shape without expensive equipment.
What's to model? - the best is an exponential horn, and a round one at that. Think wind-up gramophone, or a tuba :D

However, that's difficult to make, so a square section exponential horn is sometimes used as a poorer, but easier to construct design.

But even that isn't easy to make, so a crude flat sided design, comes a poor third.
 

gary350

Well-Known Member
I don't think louder sound made by a cone/horn is true amplification. What is the real name for louder sound made by a cone/horn?
 

gophert

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Most Helpful Member
Horns with exponential growth of the cross-section are important for sound leaving the horn (I.e. speakers) based on impedance matching of air movement with that of the "voice coil" driving the air.

I think the sound traveling into a cone/horn/whatever is less dependent on the taper of the wall and more important on the beach-head it is crashing into. The magnetude of the air movement is soooo, sooo much less when trying to capture minute sounds rather than creating huge sounds that make impedence matching much less of an issue (for microphones and small amplitude signals).
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I don't think louder sound made by a cone/horn is true amplification. What is the real name for louder sound made by a cone/horn?
It's just like an aerial, it simply gives gain by limiting the reception angle, the higher the gain, the narrower the beam width. The bigger the horn the more sound it can collect, just like a satellite dish.
 

gophert

Well-Known Member
Most Helpful Member
What is the real name for louder sound made by a cone/horn?

the National Association of Broadcasters Engineering Handbook apparently calls them Acoustic Gain Devices.

 

Layla

New Member
I have read on the internet that the horn serves to improve the coupling efficiency between the speaker driver and the air. ... The main advantage of horn loudspeakers is they are more efficient; they can typically produce approximately 10 times (10 dB) more sound power than a cone speaker from a given amplifier output. Higher SPL with less power compression means a more dynamic delivery. Horn mids that work to 300Hz are HUGE. Horns can tend to have a cupped sound when improperly designed. Typically there is greater nonlinearity in the frequency response of a horn compared to a simple cone driver. Those are some of the objective differences. Subjectively, I've heard great horn speakers but I've heard better nonhorn speakers when critical listening at normal volumes is the objective. Click here for more info.

There is one other major difference between horns and cone/dome that hasn't been mentioned yet. Horns have a rising on axis (polar) response but maintain a constant power (off-axis) response. Cone/dome has a more constant on-axis response but a falling power response. Cone/dome will sound better on-axis while sitting in the "sweet spot." Horns will sound better in a large or open venue simply because of their better power response.
 
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