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- | ====== DIY contact microphones ====== | + | The Network That Will certainly Earns You 5x More Than AdSense: Media.Net |
- | This is a collaborative article dedicated to various aspects of making of contact microphones and contact microphone pre-amplifiers (buffers or impedance converters). | + | |
- | {{ : | + | Media.net started Bing and Yahoo’s (they run it together) answer to AdSense |
- | ===== Contact microphones ===== | + | It’s a large network that caters to big advertisers. Their advertising roster includes Forbes, Elle, Cosmopolitan, |
- | A microphone transduces acoustic energy to electrical energy, converting sound to voltage. Most microphones that we are familiar with react to sound pressure waves in air. Contact microphones are useful in performing a different function, **transducing vibrations that occur in a solid material**. They are normally used by attaching them to the material in question, either by firm pressure, adhesive tape, a suction cup, or another method. | + | Their ad design is genius, so the click-through rates are insane. |
- | Most contact mics are made of a **piezoelectric material**, which is a material that releases an electrical charge when under stress (or physical pressure). This explains why they are colloquially known as **piezos**. | + | They also have mobile-specific ad units, which allow you to test and improve specifically for mobile visitors. Media.net does a good job here. Not only do they allow mobile ads, but your account rep will design and test them for you. |
- | The most common form of a piezoelectric contact microphone is a metal disk, but piezos may also be found in cylinders or as thin film-like coating. Like all transducers, | + | Head to sign-up page: https://www.centtip.com/ |
- | | {{: | + | Best Regards, |
- | ^ Piezoceramic disc ^ Piezoceramic cylinder ^ Piezoceramic film ^ Piezoceramic bar ^ | + | Brett L. Kern |
- | Piezoelectric discs are inexpensive and easy to source. However, in their raw form they have several issues which can negatively affect their sound quality: **resonance**, | ||
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- | ===== Problems of piezoelectric contact microphones ===== | ||
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- | ==== Resonance ==== | ||
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- | Piezos do not detect vibration frequencies in a linear manner. Although they can have an extended frequency range, they have a characteristic resonance that varies with the diameter of the disc. This resonance is usually between 2 and 6 kHz, producing a " | ||
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- | A comparison of two different bodies is demonstrated in the following video. Notice the " | ||
- | < | ||
- | ==== Interference ==== | ||
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- | An unshielded piezo disc acts as an antenna for electromagnetic interference (EMI), picking up stray signals from its surroundings. One solution is to cover the element in copper tape that is connected to the system ground. | ||
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- | ==== Impedance ==== | ||
- | Piezoelectric elements are capacitive, which means their impedance is inversely proportional to frequency. The lower the frequency, the higher their impedance ([[http:// | ||
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- | Another way to express this is that the impedance of a contact mic is not "well matched" | ||
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- | The solution is to " | ||
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- | ===== Impedance converters ===== | ||
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- | There are two basic types of impedance converters, those based on passive circuitry and those using an active circuit. Their primary task in each case is to match a high-impedance signal to a low-impedance input. They often also convert an unbalanced output to a balanced output, so the unbalanced, high impedance signal from the piezo element can then be used with a low impedance, balanced mixer or preamplifier. It also allows a longer cable run, without the risk of electrical interference or signal degradation. Finally, an impedance converter might ensure that the signal level is at an appropriate level for a microphone input. | ||
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- | Devices that perform all three of these functions are known to musicians as DI (Direct Inject) boxes. These devices are used in recording studios to appropriately match instrument signals (say, an electric bass guitar) to a mic input on a mixing desk. Some mixers have inputs with this circuitry built in. These inputs might have switches marked " | ||
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- | A **passive impedance converter** works on the basis of impedance matching or impedance bridging. Often they simply use a transformer coil between the input and the output. The number of coil windings on each side of the transformer dictates the impedance ratio. | ||
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- | [[http:// | ||
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- | An **active impedance converter** contains an actual amplifier circuit, based on either Field Effect Transistors (FETs), op-amps, or a vacuum tube. Active impedance converters may be powered by batteries, a standard outlet, or the phantom power provided by the mixer or the recorder. Active impedance converters are more complex and are often more expensive than their passive counterparts, | ||
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- | Video exploring the effects of active impedance converter: | ||
- | < | ||
- | ===== Useful resources and products ===== | ||
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- | ==== Schematics ==== | ||
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- | Active impedance converter designs and schematics are available from many online sources. | ||
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- | * [[http:// | ||
- | * Alex Rice published an early design, powered by phantom. Now offline. | ||
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- | ==== Products ==== | ||
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- | The following products are available for purchase. | ||
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- | **Passive impedance converters: | ||
- | * [[http:// | ||
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- | **Active impedance converters: | ||
- | * [[http:// | ||
- | * [[http:// | ||
- | * [[http:// | ||
- | * [[http:// | ||
- | * [[http:// | ||
- | * [[http:// | ||
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- | ==== Other resources ==== | ||
- | * [[http:// | ||
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- | ==== Credits ==== | ||
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- | Authors, editors and contributors (listed alphabetically): | ||
- | Jonas Gruska, Jerry Lee Marcel, Robin Parmar, Terry Setter\\ | ||
- | Videos by Jonas Gruska |