Observations of an ANC Industry Insider 1 of 3

Active Noise Cancellation vs. Passive Noise Cancellation

Any time I am questioned what I do in a social setting I have to brace my self for a lot of blank looks. In the beginning I would answer with a very forthright; “We produce active noise cancellation systems for heavy industry.” This was always followed by a lengthy silence until some courageous soul would say, “So you make insulation?” or something to that effect. To the lay individual, when confronted with the words active noise cancellation, all they really hear is noise cancellation, and they fall back on their previous experience to help them categorize what I do, that generally means insulation.

In the last few years, active noise cancellation has become more common place and understood because of the remarkable efforts of BOSE and others in producing active noise cancellation headphones. There is still a significant amount of confusion though about what exactly active noise cancellation (ANC) is and how it is different from passive noise cancellation products such as insulation. The purpose of this document is to try and describe those differences in a manner that is both accessible and understandable to all.

The Basics

Simply place, passive noise cancellation treatments are all about deflection and absorption. They are in essence a barrier between the observer and the noise source. Passive treatments take the form of foam plugs in the ear, foam lining between the engine of a car and the interior and even the 20 foot concrete barrier walls that line busy streets. Their sole purpose is to either absorb the sound, and turn it into something else (commonly heat), or reflect it in another direction.

Active noise cancellation on the other hand relies on the principle of destructive interference; the thought of using one wave to cancel out another wave. The simplest way to visualize this principle is to use waves in water. If I drop a pebble in a pond, it makes ripples (waves). By dropping a second pebble in the pond shortly after the first, as the ripples from each rock intermingle, small areas are made where there are no waves visible. In fact at those points the surface is perfectly smooth. This phenomenon is a product of destructive interference.

Another way of visualizing it is by imagining a wave.  Every wave has two core properties: how quick it goes up and down (frequency) and how far it goes up and down (amplitude). Also, remember that a complete wave has peaks and valleys. Now, imagine adding a second wave to the first. This second wave is identical in frequency and amplitude, but the second wave is out of synch with the first. So much so, that the peaks and valleys of the second wave line up exactly with the valleys and peaks respectively of the original sound wave.  When identical sound waves are combined, they add their energy. Let’s say the first wave at its peak has an energy of 1, and the second wave at its valley has an energy of -1. Adding the two together causes the combined energy to equal zero!

Why use Active Instead of Passive

If that explanation sounded very complicated, don’t worry, it is. Implementing active noise cancellation is even more complicated than describing it. So why bother with it all? Because there are certain waves that passive treatments are not able to stop. A co-worker of mine is fond of saying “With enough concrete and re-bar, anything can be made silent.” Unfortunately there are lots of applications where concrete and re-bar are not an option.

Take your home for example. Usually, with the doors and windows shut, you don’t hear birds chirping, or the typical car drive by. But even with everything closed tight, you can still hear that car with the bass thumping as it drives by. The reason for this is that low frequency noises are able to penetrate physical barriers more effectively than high frequency noises. It’s the same principle that allows you to get an AM station while driving in the hills when you can’t get an FM station at all. AM waves are much lower in frequency and not affected as much by physical barriers.

That being said, passive treatments have a practical lower threshold at which point they offer limited or no reduction. The lower limit is debatable, but for the most part, passive treatments start suffering reduced effectiveness at about 1000 Hz, and their performance degrades as the frequencies get lower.  Active noise cancellation works best on noise below 300 Hz. It is possible to use ANC on noise up to 500 Hz but the reductions are limited and have to be considered on a case by case basis. (For more information on why ANC is only useful up to 500 Hz, please read part 2 of this series.)  As you can imagine, with such distinct areas of effectiveness, the two methods for reducing noise are really complimentary to one another. Active noise cancellation should not be considered as a replacement for passive treatment. In fact, we often recommend to our customers that they first do everything they can with passive noise cancellation, and if the noise levels are still too much of an issue, then consider active noise cancellation.

Conclusion

While active noise cancellation is a high tech solution to unwanted noise. It’s not a substitute for a excellent piece of high density foam. Because of the costs associated with each system, we recommend doing everything possible with passive forms of treatment and then re-evaluate your environment before deciding to implement active noise cancellation.

For anyone wanting to delight in their portable DVD player outside of the privacy and solitude of their own room, headphones are a critical accessory. They allow the viewer to listen to movies and music without disturbing those nearby and often act to reduce environmental noise which can intrude on the audio experience. Both comfort and audio quality are vital considerations when selecting earphones.

• For those who will be using their portable DVD player to entertain two viewers at a time it is vital to assure that the device has 2 headphone ports on it; otherwise a splitter (Y-plug) will be needed.

• Various styles of headphones offer different advantages.

For anyone wanting small, inconspicuous devices any style of in-the-ear headphones can be a excellent choice. They are often the headphone of choice during activity, but in the case of use with a portable DVD player this is generally not a concern unless it is used for listening to music. Ear bud style headphones are often less comfortable and offer lower quality sound than in-the-canal type headphones. On the other hand, in-the-canal headphones generally require more frequent cleaning. Both require a excellent fit to offer the best quality sound.

Around-the-ear headphones with earcups can be quite secure and reduce the intrusion of outside sound without consuming additional battery power although they tend to be a bit more noticeable to the wearer than in-the-ear models.

Over the ear headphones help reduce the risk of hearing loss as the signal from in- the-ear devices is amplified by several dB. For comfort, padding over the earpieces and an adjustable headband is recommended. Some users feel that sound quality with over the ear headphones is superior and helps to reduce noise escaping which can disturb others. Some models even offer behind the neck or headband-less styles for added comfort which allows users to don a hat and avoid disturbing their hair. These types of headphones tend to be lighter but also more fragile.

Wireless headphones free the user from wires but have the drawback of using a fantastic deal of battery power in conjunction with a portable DVD player which already consumes a fantastic deal of energy. With wireless headphones, users are also given freedom to go about when listening to music via their player.

Noise canceling headphones are effective at eliminating environmental noise by making an out-of-phase signal to cancel unwanted outside noise. As this is not a passive process, additional battery power is consumed to achieve this effect.

• A final, but vital consideration in selecting headphones for a portable DVD player is to assure that it is compatible with the device. The cord on the earphones must obviously be capable of connecting to the player or an adapter will be needed, adding more weight and bulk where it is not wanted.

The history of bass guitars dates back to 1930s when it was first developed by Paul Tutmarc of Seattle, Washington. A bass guitar looks similar to an electric guitar except it is larger in terms of body and neck length. The guitar is tuned to pitches that are one octave lower than those of the four lower strings of a guitar (E, A, D and G). Like electric guitars, bass guitars are attached to an amplifier or speaker for live performance. What are bass guitars made of? The bass guitars usually have bodies made of wood. The body may also be made of other materials like graphite as in some of the Steinberger guitars. Different types of woods are used for the making of the neck, body and the fretboard of the bass guitars. Usually the body is made of alder; the fretboard is made of rosewood and the neck of maple. Other types of woods used are ash, mahogany and maple for bodies, maple and ebony for the fretboard and mahogany for necks. The bass guitars have various flat and curved designs and oil, wax, or lacquer finishes. What makes the bass effect? Most of the bass guitars have bodies with hollow chambers to enhance the resonance and tone of the instruments. This design also reduces the weight of the guitars. Acoustic bass guitars usually have piezoelectric or magnetic pick ups and amplifiers. Bass Guitars may also be classified on the basis of the frets. The Fender basses have about 20 frets whereas modern basses have about 24 or more frets. The Fretless basses produce distinct sound due to lack of frets. Usually the bass guitars have four, five or six strings. You can take formal bass guitars training in a wide range of styles like jazz, rock, Latin, funk and R&B. You may even learn informally from records or CDs. There is a wide variety of brands and styles of bass guitars. You can buy them along with many different accessories according to your individual needs. Some of the accessories that are often required are amplifiers, cables, straps, tuners, headphones, Instructional DVDs and gig bags. You can even shop online. The different websites will offer you the opportunity to make a well informed buy. They can also make personalized packages that contain the accessories that you want to suit your individual tastes and preferences

Grand cinemas, theaters, home entertainment environments, gaming, arcade and other public areas, and the internal movement of today use surround sound systems to improve the entertainment. Surround sound is basically when the maximum reach their own voice (or sound waves), a sort of The Twilight Zone. In other words, you can make a regular three-dimensional sound production, known as mono / left-right, and turn it into multiple dimensions, two or three.
Audio Systems
To make a surround sound, you can go to any of a number of different directions. Probably the oldest and simplest way would be to establish a series of speakers from all public, so that the sound comes from all over the audience, but in different directions.
Different way to connect is to use the headphones with the volume of local production of psycho-acoustics. The simulated result is a three-dimensional effect.
And another way to make surround sound with a rebuild ambisonics sound is a key issue. But, as the quality decreases gradually moving outward.
Another way is to use the field of wave synthesis (WFS), a series of speakers, and computer support.
People today are everyday devices such as stereo, PC sound card, some camcorders and AV receivers. These features of the digital signal or audio processors that make surround sound from stereo sources, or additional elements, such as video camera, in some cases.
Forms
Just as nothing stays the same, ditto the sound format. Above them is included in the
Several of 5 1 surround sound format is DVD-Audio, which is also known as DVD and SACD, which means Super Audio CD. Ambisonics you go, then a four-channel Dolby Surround 5 1 of. And later are: DTS, DVD-Video or DVD-V, and the latest MP3 Surround.
Surround Sound More
3. 0 Surround (Matrix):
3 audio channels: 2 front speakers – left, right, 1 back
4. 0 Surround (four-channel matrix):
4 audio channels: 2 front speakers – left, right, 2 rear
4. 1 envelope (matrix Prologic):
4 audio channels: 3 front speakers – left, center, right, 1 back (. 1 = subwoofer)
5. 1 envelope (matrix Prologic II):
5 channel audio: 3 front speakers – left, center, right, 2 rear or side (. 1 = subwoofer)
5. 1 Surround (discrete Dolby Digital, DTS)
5 channels of digital audio: 3 front speakers – left, center, right, 2 rear or side (. 1 = subwoofer)
6. 1 Surround (discrete Dolby Digital EX, DTS-ES):
6 channels of digital audio: 3 front speakers – left, center, right, 3 back side (. 1 = subwoofer)
7. 1 envelope (SDDS separately):
7 channels of digital audio: left, right, center, surround left, surround right, left rear, right rear positions (. 1 = subwoofer)