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| research:contact_mics [2017/03/19 00:52] – [Impedance] mrkva | research:contact_mics [2019/05/15 12:09] (current) – old revision restored (2018/05/27 21:36) mrkva |
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| ==== Resonance ==== | ==== 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 "metallic" or "honky" sound. The resonance can be reduced by increasing the mass of the disc. However, this can adversely affect the overall sensitivity of the element. A good strategy is to increase the mass of the metallic part, while not excessively loading the central ceramic portion. | Disc 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 "metallic" or "honky" sound. The resonance can be reduced by increasing the mass of the disc. However, this can adversely affect the overall sensitivity of the element. A good strategy is to increase the mass of the metallic part, while not excessively loading the central ceramic portion. |
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| A comparison of two different bodies is demonstrated in the following video. Notice the "tone" of the piezo without additional mass: | A comparison of two different bodies is demonstrated in the following video. Notice the "tone" of the piezo without additional mass: |
| [[http://hosatech.com/product/mit-129/|Hosa]] makes a typical adapter to convert from 50 kΩ, the typical impedance of the magnetic pickup of an electric guitar, to 200 Ohms, the typical input impedance of an audio mixer. This unit is hence not optimized for piezo disks, but might provide a partial solution. | [[http://hosatech.com/product/mit-129/|Hosa]] makes a typical adapter to convert from 50 kΩ, the typical impedance of the magnetic pickup of an electric guitar, to 200 Ohms, the typical input impedance of an audio mixer. This unit is hence not optimized for piezo disks, but might provide a partial solution. |
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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 (DC), a standard outlet (AC), or the phantom power provided by the mixer. Active impedance converters are more complicated and are often more expensive than their passive counterparts, but they can be highly optimized to their task. By using a proper active impedance converter with your piezo contact microphone, characteristics of the mixer, particularly how much clean gain is available, become less critical. | 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, but they can be highly optimized to their task. By using a proper active impedance converter with your piezo contact microphone, characteristics of the mixer, particularly how much clean gain is available, become less critical. |
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| Video exploring the effects of active impedance converter: | Video exploring the effects of active impedance converter: |
| * [[http://cafewalter.com/pzp-1/how-to-purchase/|Walter Harley]] sells the PZP-1 Piezo buffer for $49. Uses 9V battery. | * [[http://cafewalter.com/pzp-1/how-to-purchase/|Walter Harley]] sells the PZP-1 Piezo buffer for $49. Uses 9V battery. |
| * [[http://www.yannseznec.com/works/custom-contact-mic-preamps/|Yann Seznec]] builds boutique amps, based on Zach Poff's circuit. | * [[http://www.yannseznec.com/works/custom-contact-mic-preamps/|Yann Seznec]] builds boutique amps, based on Zach Poff's circuit. |
| * [[http://tritonaudio.com/bigamp-pi%C3%ABzo.html|Triton Audio BigAmp Piëzo]] is a phantom powered piezo buffer. | * [[http://tritonaudio.com/bigamp-pi%C3%ABzo.html|Triton Audio BigAmp Piëzo]] is a phantom powered piezo buffer |
| * [[http://pulplogic.com/product/ctact-box/|CTACT Box by Pulp Logic]] is a coin-cell powered impedance converter | * [[http://pulplogic.com/product/ctact-box/|CTACT Box by Pulp Logic]] is a coin-cell powered impedance converter |
| | * [[http://www.radialeng.com/stagebugsb4.php|Radial StageBug™ SB-4 Piezo DI]] is phantom powered "active DI optimized for piezo transducers" |
| | * [[http://www.stompville.co.uk/shop/26-phantom-piezo-preamp.html|Stompville Phantom Piezo Preamp]] is phantom powered piezo preamp module |
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| ==== Other resources ==== | ==== Other resources ==== |
| * [[http://www.musicofsound.co.nz/blog/the-first-rule-of-contact-mic-club|The first rule of CONTACT MIC club]] by Tim Prebble | * [[http://www.musicofsound.co.nz/blog/the-first-rule-of-contact-mic-club|The first rule of CONTACT MIC club]] by Tim Prebble |
| | * [[https://www.zachpoff.com/resources/building-contact-mics/?highlight=contact|Building Contact Mics]] by Zach Poff |
| | * [[https://www.zachpoff.com/site/wp-content/uploads/David-Dunn-Microphones_Hydrophones_Vibration-Transducers__Rolling_Your_Own__Dunn2007.pdf|Microphones, Hydrophones, Vibration Transducers: Rolling Your Own]] by David Dunn |
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| ==== Credits ==== | ==== Credits ==== |
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| Authors, editors and contributors (listed alphabetically): | Authors, editors and contributors (listed alphabetically):\\ |
| Jonas Gruska, Jerry Lee Marcel, Robin Parmar, Terry Setter | Till Bovermann, Jonas Gruska, Jerry Lee Marcel, Robin Parmar, Terry Setter\\ |
| | Videos by Jonas Gruska |