Magnetically shielded speakers means testing
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Bose 161 Review — Are These Bookshelf Speakers Worth Your Money?
In electrical engineering , electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. Shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs.
Electromagnetic shielding that blocks radio frequency RF electromagnetic radiation is also known as RF shielding. The shielding can reduce the coupling of radio waves, electromagnetic fields, and electrostatic fields.
A conductive enclosure used to block electrostatic fields is also known as a Faraday cage. The amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of holes in a shield to an incident electromagnetic field. Typical materials used for electromagnetic shielding include sheet metal , metal screen, and metal foam. Common sheet metals for shielding include copper, brass, nickel, silver, steel, and tin.
These may include conductivity, solderability, permeability, thickness, and weight. A metal's properties are an important consideration in material selection.
Another commonly used shielding method, especially with electronic goods housed in plastic enclosures, is to coat the inside of the enclosure with a metallic ink or similar material. The ink consists of a carrier material loaded with a suitable metal, typically copper or nickel , in the form of very small particulates.
It is sprayed on to the enclosure and, once dry, produces a continuous conductive layer of metal, which can be electrically connected to the chassis ground of the equipment, thus providing effective shielding. Electromagnetic shielding is the process of lowering the electromagnetic field in an area by barricading it with conductive or magnetic material. Copper is used for radio frequency RF shielding because it absorbs radio and other electromagnetic waves. One example is a shielded cable , which has electromagnetic shielding in the form of a wire mesh surrounding an inner core conductor.
The shielding impedes the escape of any signal from the core conductor, and also prevents signals from being added to the core conductor.
Some cables have two separate coaxial screens, one connected at both ends, the other at one end only, to maximize shielding of both electromagnetic and electrostatic fields. The door of a microwave oven has a screen built into the window. From the perspective of microwaves with wavelengths of 12 cm this screen finishes a Faraday cage formed by the oven's metal housing.
Visible light, with wavelengths ranging between nm and nm, passes easily through the screen holes. RF shielding is also used to prevent access to data stored on RFID chips embedded in various devices, such as biometric passports. NATO specifies electromagnetic shielding for computers and keyboards to prevent passive monitoring of keyboard emissions that would allow passwords to be captured; consumer keyboards do not offer this protection primarily because of the prohibitive cost.
Another example of the practical use of electromagnetic shielding would be defense applications. As technology improves, so does the susceptibility to various types of nefarious electromagnetic interference. The idea of encasing a cable inside a grounded conductive barrier can provide mitigation to these risks. See Shielded Cables , and Electromagnetic interference. Electromagnetic radiation consists of coupled electric and magnetic fields. The electric field produces forces on the charge carriers i.
As soon as an electric field is applied to the surface of an ideal conductor, it induces a current that causes displacement of charge inside the conductor that cancels the applied field inside, at which point the current stops. See Faraday cage for more explanation. Similarly, varying magnetic fields generate eddy currents that act to cancel the applied magnetic field.
The conductor does not respond to static magnetic fields unless the conductor is moving relative to the magnetic field. The result is that electromagnetic radiation is reflected from the surface of the conductor: internal fields stay inside, and external fields stay outside. Several factors serve to limit the shielding capability of real RF shields. One is that, due to the electrical resistance of the conductor, the excited field does not completely cancel the incident field. Also, most conductors exhibit a ferromagnetic response to low-frequency magnetic fields, so that such fields are not fully attenuated by the conductor.
Any holes in the shield force current to flow around them, so that fields passing through the holes do not excite opposing electromagnetic fields. These effects reduce the field-reflecting capability of the shield. In the case of high- frequency electromagnetic radiation, the above-mentioned adjustments take a non-negligible amount of time, yet any such radiation energy, as far as it is not reflected, is absorbed by the skin unless it is extremely thin , so in this case there is no electromagnetic field inside either.
This is one aspect of a greater phenomenon called the skin effect. A measure of the depth to which radiation can penetrate the shield is the so-called skin depth. Equipment sometimes requires isolation from external magnetic fields. For static or slowly varying magnetic fields below about kHz the Faraday shielding described above is ineffective. In these cases shields made of high magnetic permeability metal alloys can be used, such as sheets of permalloy and mu-metal [6] [7] or with nanocrystalline grain structure ferromagnetic metal coatings.
The best shape for magnetic shields is thus a closed container surrounding the shielded volume. The effectiveness of this type of shielding depends on the material's permeability, which generally drops off at both very low magnetic field strengths and at high field strengths where the material becomes saturated. So to achieve low residual fields, magnetic shields often consist of several enclosures one inside the other, each of which successively reduces the field inside it.
Because of the above limitations of passive shielding, an alternative used with static or low-frequency fields is active shielding; using a field created by electromagnets to cancel the ambient field within a volume. Additionally, superconducting materials can expel magnetic fields via the Meissner effect.
We then put this object in a constant magnetic field:. Since there are no currents in this problem except for possible bound currents on the boundaries of the diamagnetic material, then we can define a magnetic scalar potential that satisfies Laplace's equation:.
In this particular problem there is azimuthal symmetry so we can write down that the solution to Laplace's equation in spherical coordinates is:. This coefficient describes the effectiveness of this material in shielding the external magnetic field from the cavity that it surrounds. From Wikipedia, the free encyclopedia. This article is about shielding materials. For atomic effect, see Shielding effect. This article needs additional citations for verification.
Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Retrieved Retrieved 18 November Magnetic Shield Corp. Catalog MU Retrieved 26 June Archived from the original on March 15, Acorn NMR. Retrieved 27 June Classical Electrodynamics third ed.
Section 5. ISBN Categories : Magnetoencephalography Radio electronics Electromagnetic radiation Electromagnetic compatibility. Hidden categories: CS1 errors: missing periodical Articles needing additional references from March All articles needing additional references.
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Bose® Black 161™ Bookshelf Speaker-27027
This non-volatile synthetic fiber is superior to other materials because it is safe to handle and will not decay with age. Acoustic Suspension : A type of loudspeaker enclosure that uses a sealed rear chamber to contain the back wave and provide damping of the cone motion. To qualify as an acoustic suspension system, the enclosure must literally be airtight. Active Crossover : An electronic high or low-pass filter that is placed between the pre-amplifier or source and the amplifier. The benefits of an active filter include removing components from within the speaker, removing the complexities of driver impedances from the equation, and greater flexibility with regard to crossover slopes and points. Air, Airy, Airiness : A subjective term often used to describe a speaker's ability to reproduce very high frequencies with detail and low distortion. Airiness helps provide an ambient soundfield and is very important to producing a "live" sound.
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Seller: s. Startling performance. They work with your stereo receiver, but can also serve as front or surround speakers in a component home cinema setup. This means you get broader, more even sound throughout the listening area. Custom mounting brackets are included to increase placement options throughout your home. They deliver the kind of performance you'd expect from much larger speakers, making it possible to enjoy rich, low-frequency sound from smaller speakers. Magnetically shielded speakers allow for speaker placement in close proximity to your TV without interfering with the picture quality. Custom brackets included for easy installation and flexible placement possibilities. Problems with the transaction? Please contact me before you decide to leave a neutral or negative feedback.
Bose 161 white bookshelf speakers and brackets
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8 Single Speaker Studio Monitor with Magnetic Shielding M-Audio BX8 Carbon 130-watt Class A/B Power
Hi, This might have been discussed here previously, but I couldn't find anything very helpful. Anyway, how close to speakers is safe to store cassettes? I suppose it depends on the size of the speakers as well, for example I have now on my shelf a pair of System Audio Aura 1's, which are quite tiny. Now my tapes are spaced about 15cm from them. What about bigger speakers?
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It delivers the sheer power, detail and emotion of every film, music or video game soundtrack. Our HD Theater is a compact, high-definition 5. It consists of five speakers—left, center and right front channels with two rear surrounds—and one powered subwoofer. Each main and surround speaker is a sealed enclosure finished in high-gloss black with a 2. But what makes these speakers and center channel truly unique is their horn-loaded technology , an exclusive design that has made Klipsch an industry leader for over 60 years. It allows the HD Theater to deliver genuine lifelike sound and produce more output, using less energy. Over half of all new theaters in North America and several other countries choose Klipsch professional products because of the amazing benefits of horn technology.
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Your browser's Javascript functionality is turned off. Please turn it on so that you can experience the full capabilities of this site. Learn More. Stiffer cones deliver more uniform pistonic motion for deeper, tighter bass and improved midranges. This increases power handling and gives you extremely low levels of harmonic distortion.
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