Summarizing how Quietcomfort 3 headphone functions

Conclusion

First of all, before started using the Quietcomfort 3 headphones, the user must charge the battery within approximately two hours. To charge the battery, insert the battery into the charger; swing the plug prongs out of the charger body and the plug charger into a live AC (main) outlet. As the charging completes, the charger must be unplugged and the battery removed. This is to prevent the capacity of the battery to be permanently reduced. After that, the user must install the battery into the headphones. While inserting the battery, the headphones must be in switch off mode. The user may use the headphones only for noise reduction or for listening to audio along with noise reduction. For listening to an audio source, the user must plug the headphones cords connected to the dual jack adapter into any variety of audio devices or the airline audio systems.

Describing main/major and minor parts of Quietcomfort 3 headphone

• Microphone

The microphone is a small device installed in the Quietcomfort 3 headphone. The microphone is to capture noise from the surroundings. It is placed inside the ear cup and it "listens" to the external sound that cannot be blocked passively. Inside the ear cup, noise canceling circuitry electronics also been placed. The electronics sense the output from the microphone. Then, the noise canceling circuitry electronics generated a "fingerprint" of the noise, noting the frequency and the amplitude of the upcoming wave. After that, they created a new wave that is 180 degrees out of phase with the wave associated with the sound. The new wave will be transferred to the speaker.

• Speaker

The speaker in the Quietcomfort 3 headphone is an electronic device that creates another sound with different amplitude. The "anti-sound" created by the noise canceling circuitry is fed into the speaker along with the normal audio. The "anti-sound" created by the noise canceling circuitry erases the noise by destructive interference, however, the destructive interference does not affect the desired sound waves in the normal audio. Thus, the Quietcomfort 3 headphone is able to provide an additional noise reduction of 20 decibels. In addition, the headphone is compact with on-ear design. The Quietcomfort 3 ear cushions established a critical acoustical seal between the headphones and the ears. The ear cushion outside dimensions is measured 2 7/8" H x 2 1/4" W (7.5 cm x 6 cm).

• Battery
  

Left: The rechargeable lithium-ion battery; Right: The charger

The battery is an electronic device that gives life to the Quietcomfort 3 headphone. Inside the Quietcomfort 3 headphone, a rechargeable ba ttery is inserted, that is the lithium-ion battery. The rechargeable lithium-ion battery provides approximately 25 hours of reliable run time. The rechargeable lithium-ion battery output power is 3.7 VDC, 200 mAh. The lithium-ion battery may be considered expensive; however, it is more convenient compared than using the average AAA batteries. The rechargeable battery is mainly designed for long hours of travel and thus, it is much comfortable to bring along. The lithium-ion battery charger is small and collapsible prongs for easy storage. The charger is dual rated, with input of 100-240 VAC 0r 50-60 Hz.

Noise-canceling headphones; Bose Quietcomfort 3

How Noise-canceling Headphones Work

Photo courtesy Consumer Guide Products
Bose was the first company to introduce noise-canceling headphones and produces several models, including the Quiet Comfort 2.

One man's noise is another man's music, but no matter what your taste, ambient noise is the enemy. Luckily, there's a piece of audio equipment designed especially to maximize your listening experience, keeping ambient noise out without sacrificing your music's sound quality. That piece of equipment is the headphone, and in this article, we're going to look at how headphones, especially noise-canceling headphones, work.

On a 1978 flight to Europe, Amar Bose, the founder of Bose Corporation, put on a pair of airline-supplied headphones, only to find that the roar of the jet engines prevented him from enjoying the audio.He started making calculations right there on the plane to see if it was possible to use the headphones themselves as a noise-reducing agent. Bose introduced the first noise-canceling headphones a decade later.

In order to understand headphones, you must first understand sound waves. You can check out How Speakers Work for some information, but we're also going to provide a brief introduction here.

When most people think of waves, they think of water waves, like you'd seen in an ocean or lake. A shallow water wave is an example of a transverse wave, which causes a disturbance in a medium perpendicular to the direction of the advancing wave. You can see this relationship in the illustration below. The illustration also shows how waves form crests and troughs. The distance between any two crests (or any two troughs) is the wavelength, while the height of a crest (or the depth of a trough) is the amplitude. Frequency refers to the number of crests or troughs that pass a fixed point per second.

Sound waves have many of the same characteristics as water waves, but they are longitudinal waves, created by a mechanical vibration in a medium that produces a series of compressionsrarefactions in a medium. When you pluck a guitar string, for instance, it begins to vibrate. The vibrating string first pushes against air molecules (the medium), then pulls away. This results in an area where all of the air molecules are pressed together and, right beside it, an area where air molecules are spread far apart. As these compressions and rarefactions move from one point to another, they form a longitudinal wave, with the disturbance in the medium moving parallel to the direction of the wave itself. and

Longitudinal waves have the same basic characteristics as transverse waves. A compression corresponds to a crest, and a rarefaction corresponds to a trough. The distance between two compressions, then, is the wavelength, while the amount the medium compressed is the amplitude. Frequency refers to the number of compressions that pass a fixed point per second.

For sound waves, amplitude determines the intensity, or loudness, of the sound. Frequency determines the pitch, with higher frequencies producing higher pitch notes and lower frequencies producing lower pitch notes. The brain is able to interpret these characteristics of sound, but before that can happen, the sound waves must be detected by a sense organ. That, of course, is the ear's job. To learn more about how the ear detects and interprets sound, check out How Hearing Works.

Electrostatic and Dynamic Transducers

Music versus Noise As the introduction to this article suggests, differentiating music and noise can be a subjective matter. But scientists make a clear distinction. Music is sound with a reproducible, distinct waveform. Noise refers to random and unpredictable waveforms. And white noise is the most complex type of noise because it contains many different frequencies, all possessing equal intensity.

To hear what's recorded on a record, cassette, CD, DD or MP3 player, data stored on the medium must be converted into sound waves. This requires that the stored information be turned into an electrical signal, which then must pass through a transducer to convert the transverse electrical wave into a longitudinal sound wave that the ear can interpret. Speakers play the role of transducers in audio systems. They can be located far away from the listener's ear, however.

Headphones were developed specifically to solve this problem. Headphones are essentially speakers held over the ear by a band or wire worn on the head. They are categorized by the type of transducer technology use and by their construction. Let's look first at electrostatic headphones.

Electrostatic Headphones
Electrostatic headphones take advantage of a phenomenon that most people know as static electricity. When an object becomes charged, it either gains or loses electrons. An object that gains electrons is negatively charged; an object that loses electrons is positively charged. Objects with like charge experience repulsive forces, while oppositely-charged object experience attraction. These forces are known as electrostatic forces.

To create these forces in electrostatic headphones, a thin diaphragm -- a flexible sheet made of paper, plastic or metal -- is suspended between two metal grids or electrodes. When an audio signal is applied, varying attractions are created along the grids. This pushes part of the diaphragm toward one grid and pulls part toward the opposing grid. The resulting vibrations in the diaphragm produce the sound waves that are eventually detected by the ear.

Dynamic Headphones
Electrodynamic (or dynamic, for short) headphones are made of three functional parts -- a voice coil, a permanent magnet and a cone-like diaphragm. The narrow end of the cone is attached to the voice coil and actually generates the sound waves. It does this by vibrating rapidly in response to the vibrating voice coil, much the same way the three bones of the ear vibrate in response to the movement of the eardrum.

The vibration of the voice coil is made possible by two fundamental properties of magnetism:

• Identical magnetic poles repel each other, while opposite poles attract
• Electric current flowing through a coil of wire produces a magnetic field, with the direction of current flow determining the polarity of the magnetic field

When a voice coil is placed within the unchanging magnetic field of a permanent magnet, these two properties are realized. Switching the electrical signal that is pumped into the coil causes the North and South poles to switch back and forth very rapidly. As the North and South poles of the voice coil's magnetic field switch, they are attracted and then repelled as they interact with the permanent magnet. Because the permanent magnet is fixed and the voice coil isn't, the latter vibrates and transmits these vibrations to the diaphragm.

Headphone Styles

Dynamic headphones are the most common type of headphone, so let's take a closer look at the three basic earpiece designs.

Supra-aural headphones, also known as on-ear, open-back or open-air headphones, sit lightly on or over the ear. The ear cups are generally softly padded and rotate freely to enhance fit and reduce pressure points. Because they sit on the ear, on-ear headphones leak sound into the external environment and allow ambient noise in.

Photo courtesy Amazon Supra-aural headphones

Photo courtesy Amazon Circumaural headphones

Circumaural headphones, also known as around-ear or closed-back headphones, completely enclose the listener's ears. Because they form an airtight seal, they block out external noise without leaking sound to the outside. This improves sound quality, but circumaural headphones tend to be heavier and less comfortable.

In-ear headphones come in two styles: ear buds and canal headphones. Ear buds are worn in the opening of the ear, while canal headphones are seated in the canal itself, forming an airtight seal. Sound quality tends to be excellent with in-ear headphones, although this is dependent on how well they fit in the listener's ear. For this reason, canal headphones, which fit tightly in the ear like earplugs, are often preferred by musicians or others wanting superior sound quality.

Photo courtesy Amazon In-ear, canal-style headphones are used often by musicians and others desiring superior sound quality.

We'll look at exactly how noise-canceling headphones manage to "cancel" noise next.

Headphone vs. Headset When a headphone is equipped with a small microphone, it is called a headset. Microphones are transducers just like speakers. They change sound waves into electrical signals, while speakers change electrical signals into sound waves.

Noise-canceling Headphones

Unfortunately for music lovers, many types of ambient sounds can interfere with or even block the sounds coming through their headphones. If you have ever tried to listen to a CD or MP3 player on a plane, then you know the problem well: The roar of the engines makes it difficult to hear what's being piped through the speakers -- even when those speakers are situated in or on your ear. Fortunately, noise-canceling headphones can provide a more enjoyable listening experience.

Noise-canceling headphones come in either active or passive types. Technically speaking, any type of headphone can provide some passive noise reduction. That's because the materials of the headphones themselves block out some sound waves, especially those at higher frequencies. The best passive noise-canceling headphones, however, are circum-aural types that are specially constructed to maximize noise-filtering properties. That means they are packed with layers of high-density foam or other sound-absorbing material, which makes them heavier than normal headphones. The tradeoff of all that extra weight is a reduction in noise of about 15 to 20 decibels (dB). But considering jet engines create 75 to 80 dB of noise inside the aircraft cabin, passive models have some serious limitations. That's where active noise-canceling headphones come in.

Decibel Defined A decibel (dB) is a measure of sound intensity. The dB scale is logarithmic, meaning that a change of 10 dB represents a tenfold change in loudness. So, a sound measuring 30 dB is 10 times louder than a sound measuring 20 dB.

Active noise-canceling headphones can do everything that passive ones can do -- their very structure creates a barrier that blocks high-frequency sound waves. They also add an extra level of noise reduction by actively erasing lower-frequency sound waves. How do noise-canceling headphones accomplish this? They actually create their own sound waves that mimic the incoming noise in every respect except one: the headphone's sound waves are 180 degrees out of phase with the intruding waves.

If you look at the illustration below, you can see how this works. Notice that the two waves -- the one coming from the noise-canceling headphone and the one associated with the ambient noise -- have the same amplitude and frequency, but their crests and troughs (compressions and rarefactions) are arranged so that the crests (compressions) of one wave line up with the troughs (rarefactions) of the other wave and vice versa. In essence, the two waves cancel each other out, a phenomenon known as destructive interference. The result: the listener can focus on the sounds he wants to hear.

Of course, several components are required to achieve this effect:

• Microphone - A microphone placed inside the ear cup "listens" to external sounds that cannot be blocked passively.
• Noise-canceling circuitry - Electronics, also placed in the ear cup, sense the input from the microphone and generate a "fingerprint" of the noise, noting the frequency and amplitude of the incoming wave. Then they create a new wave that is 180 degrees out of phase with the waves associated with the noise.
• Speaker - The "anti-sound" created by the noise-canceling circuitry is fed into the headphones' speakers along with the normal audio; the anti-sound erases the noise by destructive interference, but does not affect the desired sound waves in the normal audio.
• Battery - The term "active" refers to the fact that energy must be added to the system to produce the noise-canceling effect. The source of that energy is a rechargeable battery.

Using these components, noise-canceling headphones are able to provide an additional reduction in noise of 20 decibels. That means about 70 percent of ambient noise is effectively blocked, making noise-canceling headphones ideal for airline and train travel, open office environments or any other location with a high level of background noise.

While noise-canceling headphones do a good job distinguishing between the audio a wearer wants to hear and the background noise he or she wants to keep out, some people say that they compromise sound quality by muffling sounds. Users can also experience a change in air pressure, although ports built into the ear cup are meant to vent air trapped behind the speakers.

In spite of these tradeoffs, many people would never go back to normal audio headphones. That's because noise-canceling headphones do more than reduce noise. They also help alleviate fatigue when traveling, which can result from exposure to low-frequency noise for an extended period of time. You can even use noise-canceling headphones if you don't want to listen to another audio source but do want to cancel out background noise. And a little bit of quiet can be music to anyone's ears.

Article found in: http://electronics.howstuffworks.com/noise-canceling-headphone1.htm

Overview of Bose Quietcomfort 3 Acoustic Noise Canceling headphone
Ambient noise is the number one culprit to the human ears. And thus, Bose Corporation has introduced noise canceling headphones for the comfort of the ears. Quietcomfort 3 Acoustic Noise Canceling headphone is another creative invention and the latest gadget from Bose Corporation. Quietcomfort 3 or in short QC 3 is best used for travel, work and home. Wearing QC 3 headphones could definitely reduce the noise and make the distraction fade into the background. QC 3 is a smaller-sized, on-ear headphone compared to QC 2 headphone. In addition, QC 3 headphone folds flat for compact storage in a slim carrying case. With tripod acoustic headphone structure enables QC 3 to produce a rich audio performance. This headphone also includes rechargeable lithium-ion battery with approximately 25 hours of run time. Overall specifications, headphone dimensions is 7 3/8 " H x 5 1/4 " W (19 cm x 13.5 cm), ear cushion outside dimensions is 2 7/8 " H x 2 1/4 " W (7.5 cm x 6 cm), the weight with cable is 5.6 oz (156 g), battery output power is 3.7 VDC, 200 mAh with battery life approximately 25 hours.

comments on my presentation and improving my presentation skills

Before it was my turn to do my presentation, I did a few speech practices with my partner. During my practices, my practice partner had made some comments on my presentation, that are:

1. I should make eye contact with the audience
2. My voice should be loud and clear
3. I should think of a suitable attention getter

In fact I did improve some on my presentation, however, when it was time for me to present, I could not help feeling stage fright. In my power point slides, I had an audio for my attention getter but it could not be played. So, to rescue myself from that problem, I asked a question to my audience. Phew...

In the end of my presentation, I have received a few comments from madam Zarina, my English lecturer. Her comments were:

1. My slides were short and precise and therefore I should face the audience more than to my slides
2. My attention getter was a short one and I should have done better than that.

From the comments I have received, I am determined to improve on my presentation skills and be more confident when doing public speaking.