How do speakers displace air?

I just really want to know what goes on inside a speaker. because i dont understand how my subwoofer can pump so much air out of it without using a fan
anyone know?

the speaker cone with a flexable rim moves in and out acting like a piston pushing air out the front and out the port after it is reflected inside the enclosure.

[B]The Physics of Sound [/B]

Sound travels through the air (and different media) in waves, called Sound Waves
These waves cause the air to oscillate (vibrate) back and forth

[B]Not Just Any Wave [/B]

The waves (ripples) created by throwing a rock into the pond are Transverse Waves
Sound waves are NOT transverse waves
Sound waves ARE Longitudinal Waves

[B]Transverse Waves[/B]

Pretend like you are at a football game.
Everyone do the wave starting from the left to the right!
What direction is the wave traveling?
The wave travels to the right
What direction is the displacement caused by the wave?
Displacement is vertical; Perpendicular to the travel direction.
Transverse Waves,NOT SOUND WAVES !!!

[B]Longitudinal Waves [/B]

Do the wave again, but this time, instead of moving your arms up and down, move them side to side.
What direction is the wave traveling?
The wave travels to the right
What direction is the displacement caused by the wave?
Displacement is horizontal; Parallel to the travel direction

[B]Sound Wave Basics[/B]

Two main components of a sound wave that affects what we hear are amplitude and frequency.
Amplitude determines how loud it is.
Frequency determines the “pitch”.

[B]Amplitude [/B]

The Amplitude measures the displacement of the air molecules.

[B]Frequency [/B]

Frequency is the number of times the wave oscillates back and forth in 1 second. It has units called Hertz.

[B]Sound Production [/B]

How does one make sound?
Vocal cords, speakers, headphones etc.
What do these all have in common?
They all vibrate the air!

[B]Sound Reproduction [/B]

Speakers take an electronic signal, and reproduce sound.
By far most common type of speaker is the Dynamic Speaker.
Other types of speakers include piezoelectric speakers, plasma arc speakers and electrostatic speakers.

[B]Dynamic Speakers[/B]

[B]Voice Coil[/B]

The voice coil is solenoid (loop of wires) that is attached to the diaphragm
When a current passes through the wires, a magnetic field is produced. The direction of the magnetic field depends on the direction of the current.

[B]Apply an Electronic Signal [/B]

What happens when an electronic signal is applied to the sound coil?
The magnetic field created in the sound coil will either be opposed or attracted by the field from the permanent magnet.
This causes the sound coil to oscillate.
The diaphragm oscillates as well and thus produces a sound wave.

Thus movement of air.

:cool::cool:

The bass driver, though maybe only a 4" diameter unit, tends to be quite long throw, using a roll surround to allow larger movennts than would be possible with a basic corrugated surround.

A 1/4" displacement of a 4" diameter cone is equal to a 1" displacement at a 2" diameter port

What about the length of the port too!

Air volume = Sd * Xmax

Sd = piston area
Xmax = maximum linear cone movement

sd * (xmax * 2)

We can start to get really technical with the formulas based on a bunch of different variables. But I believe the original post will probably not want to go there.

:cool::cool:

[QUOTE=tony.willson;1943501]I just really want to know what goes on inside a speaker. because i dont understand how my subwoofer can pump so much air out of it without using a fan
anyone know?[/QUOTE]

A speaker pumps in as much air as it pumps out. It does not operate like a fan. If you put a flame in front of a port it will move both ways depending on the direction the speaker cone is traveling.

[QUOTE=platinumsword;1943782]
[B]Apply an Electronic Signal [/B]

What happens when an electronic signal is applied to the sound coil?
The magnetic field created in the sound coil will either be opposed or attracted by the field from the permanent magnet.
This causes the sound coil to oscillate.
The diaphragm oscillates as well and thus produces a sound wave.

Thus movement of air.

:cool::cool:[/QUOTE]

the speaker vibrates, the inward movement causes air to flow out of the box through the port. the outward movement causes air to flow into box through the port. think of your lungs, your lungs collapse, you breathe out. your lungs expand you, breathe in.

troy

[QUOTE=troy512;1944358]the speaker vibrates, the inward movement causes air to flow out of the box through the port. the outward movement causes air to flow into box through the port. think of your lungs, your lungs collapse, you breathe out. your lungs expand you, breathe in.

troy[/QUOTE]

And what’s your point?

Because in a nutshell that is what is being said.

:cool::cool:

[QUOTE=platinumsword;1944362]And what’s your point?

Because in a nutshell that is what is being said.

:cool::cool:[/QUOTE]

my point is…is…well i guess i dont have one.:rolleyes:

Great explanation. It also shows why a long thro woofer sounds so crappy, not enough time in that long stroke to produce very good bass waves.