# Focusing sound waves

#### ayushmorx

Can we focus parallel sound waves using convex and concave lenses since they essentially follow the same laws of refraction as light?
If not, is there any way to focus parallel beams of sound to converge at a point?

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#### dauto

Yes. Either by reflection (sound mirrors) or by refraction (sound lenses). Note that concave lenses will actually be divergent because sound speeds is higher in solid objects than in air. Convex lenses would be convergent. Also note that Parabolic mirrors will probably work better because a large fraction of the sound is reflected as oposed to being refracted.

#### Drakkith

Staff Emeritus
2018 Award
In Shreveport Louisiana they have the "Sci-Port" science center. One of the displays they have involves to large parabolic dishes about 6 feet in diameter placed about 20 feet apart. If you and a friend stand in front of each dish, you can speak in a normal voice and clearly hear the other person even across the room thanks to the dishes focusing the sound waves.

#### ayushmorx

Hey everyone thanks for your quick response!!!
I basically wanted to converge the sound waves onto a diaphragm, while keeping them in phase so as to maximize efficiency of sound energy transfer to the diaphragm(constructive interference). Will the reflection of the mirrors or reflectors cause any phase change? if so, how can I eliminate it?

#### dauto

Don't worry. The phases will be the same.

#### dauto

Don't worry. The phases will be the same.

#### sophiecentaur

Gold Member
Don't worry. The phases will be the same.
The reason for the focussing is, in fact, that the phases (path lengths) are the same for all paths. It's jet another way of looking at the process.

#### ayushmorx

THANK YOU, people!!! :D

#### sophiecentaur

Gold Member
In Shreveport Louisiana they have the "Sci-Port" science center. One of the displays they have involves to large parabolic dishes about 6 feet in diameter placed about 20 feet apart. If you and a friend stand in front of each dish, you can speak in a normal voice and clearly hear the other person even across the room thanks to the dishes focusing the sound waves.
I had two 1.2m dishes on opposite walls of my School lab for a few years. Good for sound / ultrasound and microwave experiments. Also very unnerving to walk through some random point in the room and hear some kids voice, loud and right in my ear - they don't only work on - axis.

#### Drakkith

Staff Emeritus
2018 Award
I had two 1.2m dishes on opposite walls of my School lab for a few years. Good for sound / ultrasound and microwave experiments. Also very unnerving to walk through some random point in the room and hear some kids voice, loud and right in my ear - they don't only work on - axis.
Yep.

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