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10-11-2005

Everything You Always Wanted to Know About Acoustics:
(Impress the girls when you can explain how your cochlea works)

Music is an artistic method of vibrating air. How fast, how much, and
when the air is vibrated, determines what we will ultimately hear as
sound. The science of this process is called acoustics.

When a Speaker (or anything else that has the ability to vibrate)
moves forward, the air molecules in front of the cone are compressed,
causing the molecules to run into each other moving them all forward.
This continues to happen until the speaker moves in the other
direction, which causes a rarefaction (or thinning) of the air that
was just compressed. This is the basic concept of how sound waves are
produced.

**WAVES**

A Sound wave can be described by two basic characteristics, the speed
of the vibration (Frequency), and the extent of the vibration
(Amplitude).

When a speaker moves forward, backward and back to its original
position, this is called a cycle. Frequency is determined as to the
number of cycles per second. It is labeled Hertz (Hz) after an early
scientist in the field of acoustics. Diagram 1 is a graphical
representation of a sound wave. The top half of the curve is where
pressure increases, the bottom half is the decreasing of the pressure.

Diagram 1 - The Soundwave

It has been determined that sound travels through air at sea level at
a speed of 1128 feet per second. The wavelength is the distance a
sound travels in one cycle. This distance can be determined by
dividing 1128 by frequency. With this formula we determine that a 20
Hz note is 56.4 feet long. On the other hand a 20kHz (20,000 Hz) is
.056 feet which is about 5/8 of an inch. Understanding this
relationship between distance and soundwaves will be important in
understanding how we hear, and therefore how to properly set up a
sound system.

Yet another description of the soundwave is phase. Phase refers to the
pressure change of the soundwave at a certain time and place. Once
again, refer to diagram 1, and see how the first part of the curve is
above the zero line. This is known as positive phase (increase of
pressure). When the curve is below the zero line, it is known as
negative phase (decrease of pressure). When Two or more waves combine
the combination can be referred to as being in phase or out of phase.
In phase means that the soundwaves are combining to form a wave that
is larger than either of the two. When the waves are out of phase,
meaning the phase of one wave is positive and the other is negative,
they will subtract from each other, therefore reducing the pressure
level. Soundwaves are constantly interacting with one another and
creating what is known as a complex wave. All musical instruments
create complex sound waves. The instruments combine waves to create
the sound that makes them unique.

Octaves and Harmonics

An octave is a doubling or halving of frequency. One octave up from
100 Hz is 200 Hz, where one octave down from 100 Hz is 50 Hz. A
harmonic is a doubling (2nd harmonic), tripling (3rd harmonic),
quadrupling (4th Harmonic... etc) of a fundamental frequency. Musical
instruments (with the exception of synthesizers) do not create pure
tones. The fundamental (main frequency) is combined with its harmonics
at various levels to create the sonic signature of that instrument.

**SPL**

Our ears have a tremendous ability to evaluate sounds that range from
very soft to very loud. The decibel (dB), named after Alexander Graham
Bell, is a method of describing acoustic pressure, without having to
deal with the billion-fold range of sound pressures to which our ears
are sensitive. A Bel is the difference in loudness produced by a ten
fold increase in power.

A decibel is 1/10th of a Bel. A doubling of sound pressure level (SPL)
is a 10 dB increase, where a halving of SPL is a 10dB decrease. The
human ear can detect differences as small as 1 dB, however 3dB is
commonly referred to as a level where a change is readily apparent.

A doubling of Power input into a speaker will produce a 3dB change in
output, a doubling of cone area will result in a 3dB increase over
that of a single driver.

A doubling of distance from a sound source reduces SPL by 6dB.

**Human Hearing**

A piano can produce soundwaves that range from 27.5 Hz to 4186 Hz.
This means that a piano can produce just a little over 7 octaves of
information. The audible spectrum of human hearing ranges from about
20 Hz to 20 kHz. This range varies from person to person, and
generally deteriorates with age.

Information below 20 Hz is referred to as being subsonic. Although we
can't hear subsonic information, we can feel soundwaves that fall
within this range. When a soundwave is above 20Khz, we refer to it as
being ultrasonic. In this case, we are not aware that the wave exists
(although some people can feel these frequencies). However small
animals and electronic test equipment can "hear" these
frequencies due
to their extended high frequency "hearing".

The Human Ear is made up of four basic systems; The Pinna, the
auditory canal, the middle ear and the inner ear.

Soundwaves are collected by the pinna (outer ear). The pinna
"amplifies" signals in the important speech frequencies as
well as
allowing us to better localize sounds.

The auditory canal channels soundwaves to the eardrum and increases
the loudness of the soundwaves via an acoustical resonance around 3
KHz.

The middle ear acts as a matching device, to allow airborne soundwaves
to be "heard" by the waterlike fluid of the inner ear. The
ear drum
forms one side of the middle ear. The ear drum acts as an
"acoustic
suspension" system, using the air trapped in the middle ear to
control
its movement. This trapped air is vented through the eustachian tube
to the upper throat behind the nasal cavity. This system allows the
air pressures inside the ear to equalize with the atmospheric
pressure.

The cochlea is encased in solid bone and is coiled up much like a sea
shell. The cochlea contains roughly a quarter of a million tiny hairs
that give information to our brain as to what type of vibration there
is in the fluid. Our brain then takes this information, analyzes it,
and relates it to frequency and amplitude.

**Imaging**

By comparing arrival times at both ears, our brain can determine the
direction from which a sound came from. A sound arriving at both ears
simultaneously tells our brain that the sound is centered either in
front, above, below, or behind us. The brain then looks at the
frequencies received, and compares these frequencies with sounds that
we have heard before. When the brain remembers a sound like the sound
it just heard, it looks at the late soundwaves that arrived at the
eardrum that were reflected off the outer ear. This process allows us
to perceive height. When a soundwave comes from behind, the soundwave
must pass through the pinna. This causes a filtering of high
frequencies in comparison with reflections off of walls, ceilings, and
floors. This is what allows us to localize sound sources behind us.

It becomes increasingly difficult to localize sound sources as the
frequency decreases. This is due to the wavelength being so much
larger than our heads, that it becomes difficult to differentiate
between the arrival times at our ears. This effect keeps us from
localizing pure tones below around 100 Hz. If the sound source is not
pure, however, and there are harmonics associated with the source, we
can localize these sounds and therefore localize the source.

BASSOTRONICS · 04-06-2006

What I always wanted to know is if acoustical energy has to move air to make sound or can it travel through the air without moving it. (just vibrating the molecules)

For example: When I play a 5 hz tone in a box with a large port, the air is pushing back and forth alot in the enclosure like a blow fan. So is the air that I feel actually is 5hz or is it the acoustical energy that is in that push of air. Or do both have to work together being directly proportional to each other in order to create that audiable sound?

04-13-2006

The energy is what vibrates the air. Sound forms from a depression in air, followed by a burst in the air. Sound is simply these little cycles happening over and over and over. The speed of the cycles determines the frequency. So no matter what frequency you are playing, you will always be feeling the air moving around you. The Speaker does not actually make the noise you hear, per say...but rather it manipulates the air into making the noise we hear. Does that make sense?

triple88a · 03-23-2007

Quote:

Originally Posted by speakerman

but rather it manipulates the air into making the noise we hear. Does that make sense?

Great explanation

So now lets imagine we take a speaker to jupiter lol where its helium and hydrogen.. it would a speaker still sound the same since those molecules are quite lighter than nitrogen and oxygen? Although it sounds like a jk question i'm actually interested of your gues

roxbury · 03-23-2007

If there are still molecules, but they're lighter, the sound might still be able to be heard, but would probably travel much slower.

If there's no molecules to be moved, there'll be no sound.. (sound can't travel in a vacuum) .. That's the principle i'm applying, but i dunno.

Gebrochen · 03-23-2007

The gravity on Jupiter would make the atmosphere thicker and heavier, but I think we're getting a bit off topic :-). The speaker behavior and tuning would be dramatically altered, just like elevation and temperature of the air can even make a difference in cars.

Kickerlivinloud · 04-01-2007

Awesome read!!!! A++ for you!!

Jon

jmelton86 · 07-09-2009

Wow.

Not only does this BARELY even get into the BASICS of acoustics, but you copy and pasted this article from another website...

You see, when I read 'everything you want to know about acoustics', I was under the impression that I was going to be able to actually learn everything I want to know about acoustics.

What im getting at, is that the title of this article -you didnt write to begin with- shouldve been named 'the basics of how the ear works'.

Sorry, but ive been waiting for someone else to express their disappointment in this article for some time now...

aznboi3644 · 07-09-2009

speakerman also copy and pasted "Electrical System Explained" here and took the credit as his own...I tried to call him out but no one cares people copying other peoples hard work.

http://forum.realmofexcursion.com/showthread.php?t=923

I should find a good write up and copy and paste it here so I look smart

heyitsmekyle15 · 07-09-2009

Quote:

Originally Posted by aznboi3644

speakerman also copy and pasted "Electrical System Explained" here and took the credit as his own...I tried to call him out but no one cares people copying other peoples hard work.

http://forum.realmofexcursion.com/showthread.php?t=923

I should find a good write up and copy and paste it here so I look smart

You both obviously failed to see the purpose of those posts/stickies. Its generic information, its useful, thats why its a sticky. Who cares where it came from. He's not posting it to reap praise for putting it on the forum, he put it there for our benefit. If anyone finds a good chunk of information such as he did and its applicable to car audio in any way, post it. Its encouraged to spread good, and useful info. The more good info we spread to our users on our forum, the better. He never once claimed the information as his own.

jmelton86 · 07-10-2009

You dont just copy and paste, though. Youre supposed to:
1. GET PERMISSION from the source you got it from, to actually be abe to use their work. THEY decide if its ok, not you.
2. In the case that they come from a website, like these two that he has been called out on, you post a direct link to the website at the bottom of the page.

You dont just copy and paste.

fosg8freak · 07-10-2009

Yes, you are supposed to properly cite and source or else it's plagerism. But yet the site hasn't complained yet has it? Considering its a free site and the information is out there for all to see, I dont see BCAE getting all pissed off that people are learning from their materials.

I dont get why people are pissed at speakerman for posting relavant information that does nothing but help? It's not like he posted it then posted right afterwords saying, "Will you guys worship me now?" or "Can I get rep points for this?" All he wanted to do was help and help he did.

And as for the title goes, if you have a lame title that people dont think are interesting they are not going to read it. This forum is basically like marketing/advertising. You want people to read your thread and the information whithin, whether you want them to learn or answer yoru question. But they will not read it if it's got the same ass name everyone uses like, "Question" and they will not read it if it doesnt not interest them. We all do it, trying to come up with interesting names to give the reader a hook and make them wanna read it...

Considering you read it I think it worked.

jmelton86 · 07-10-2009

No...

Quote:

Originally Posted by jmelton86

You see, when I read 'everything you want to know about acoustics', I was under the impression that I was going to be able to actually learn everything I want to know about acoustics.

Why are you defending him? What he/she did was illegal. Thats all there is to it. Period.

fosg8freak · 07-10-2009

Yeah? Im sure you probably do or have done illegal things every day. People are doing illegal things on accident every single day. He plagerized. Thats the ONE illegal thing he did. Hell, we are not even sure its illegal because if he got written consent to use the information from the owner of the site via email than it's legit.

Get the hot dog prongs out of your ass and relax.

Besides, Im defending him because all he was trying to do was help out the forum and help people learn and grow. Lets throw him in FVCKING prison for that!!

jmelton86 · 07-13-2009

Sure, people do illegal things all the time...

But, does that make it right?!

I cant believe im arguing with you. I shouldve known better -I guess I forgot that you like to argue over trivial issues... even when youre dead wrong, or just dont make sense, which so happens to be the case.

If he did get permission, which im sure he didnt, he didnt give credibility where it was due.

Oh, and I dont have hot dog prongs in my ass. I just have no respect for those that dont do the right thing. Or, those that argue when theyre wrong. Im done. Good-bye.

fosg8freak · 07-13-2009

Quote:

Originally Posted by jmelton86

Sure, people do illegal things all the time...

But, does that make it right?!

I cant believe im arguing with you. I shouldve known better -I guess I forgot that you like to argue over trivial issues... even when youre dead wrong, or just dont make sense, which so happens to be the case.

If he did get permission, which im sure he didnt, he didnt give credibility where it was due.

Oh, and I dont have hot dog prongs in my ass. I just have no respect for those that dont do the right thing. Or, those that argue when theyre wrong. Im done. Good-bye.

Yeah? And I have no respect for those that are adamant that I'm wrong when in their case they have no actual proof either. You need to read a few books on critical thinking, and a few on how the human mind works.

I may argue about trivial things, but more often than not I am not wrong and the person arguing is some hard headed adult that thinks he knows the "truth" and is too stubborn to think in any other dimension that one. Maybe if you looked at different sources, different point of view's, and critically thought about the issue you wouldn't be a stubborn jack ass.

Its not my fault that you are basing your thoughts on these ASSUMPTIONS. He could have gotten permission, me might not have gotten permission. You get some proof that he didnt get permission and you have an arguement sir, unless you do that you are just as fvcking wrong as me and that upsets you.

You're more than likely some old fart that is stubborn as fvck and doesnt have the mental capacity to think in any other point of view than the same one you've been thinking in for the past tens of years of your life.

fosg8freak · 07-13-2009

Quote:

Originally Posted by jmelton86

Sure, people do illegal things all the time...

But, does that make it right?!

With that said, I should on my way to jail right about now, I forgot my reference page to my APA format assignment for my marketing class a week ago, fvck I broke the law.. Off to jail I go!!

jmelton86 · 07-13-2009

Although I may be stubborn at times, im not 'some old fart'. Im 23.

The fact remains: speakerman did not list his source, whether or not he got permission. That is wrong.

Oh, and you dont know what education ive had on how the mind works, which, by the way, is still not fully understood -as it may never be.

Youre an idiot. Get over yourself, you little whippersnapper lol.

Fallen · 07-13-2009

Who cares...

fosg8freak · 07-13-2009

Quote:

Originally Posted by Fallen

Who cares...

Pretty much. The entire situation is a, "No biggie"

Especially considering if it WAS a biggie the owner of bcae1 would have had us take it down a long time ago.

fosg8freak · 07-13-2009

Seems like it WAS no big deal...

Flag this messageRe: Hope you still use this email addy

Monday, July 13, 2009 10:49 PM

From:
This sender is DomainKeys verified"Perry Babin" <babin_perry@yahoo.com>
Add sender to Contacts

To:
"mike manley" <durtbagg_0@yahoo.com>

I don't mind copying and pasting but it would be nice if the poster at least stated where the information came from.

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