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Ferrofluid Literature, Articles and Patents Web: http://www.pearl-hifi.com 86008, 2106 33 Ave. SW, Calgary, AB; CAN T2T 1Z6 E-mail: [email protected] Ph: +.1.403.244.4434 Fx: +.1.403.245.4456 Inc. Perkins Electro-Acoustic Research Lab, Inc. ❦ Engineering and Intuition Serving the Soul of Music Please note that the links in the PEARL logotype above are “live” and can be used to direct your web browser to our site or to open an e-mail message window addressed to ourselves. To view our item listings on eBay, click here. To see the feedback we have left for our customers, click here. This document has been prepared as a public service . Any and all trademarks and logotypes used herein are the property of their owners. It is our intent to provide this document in accordance with the stipulations with respect to “fair use” as delineated in Copyrights - Chapter 1: Subject Matter and Scope of Copyright; Sec. 107. Limitations on exclusive rights: Fair Use. Public access to copy of this document is provided on the website of Cornell Law School at http://www4.law.cornell.edu/uscode/17/107.html and is here reproduced below: Sec. 107. - Limitations on exclusive rights: Fair Use Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, includ- ing such use by reproduction in copies or phono records or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for class- room use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include: 1 - the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes; 2 - the nature of the copyrighted work; 3 - the amount and substantiality of the portion used in relation to the copy- righted work as a whole; and 4 - the effect of the use upon the potential market for or value of the copy- righted work. The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors ♦ PDF Cover Page ♦ ♦ Verso Filler Page ♦ AudioAudio GradeGrade FerrofluidsFerrofluids www.ferrotec.com Ferrotec Corporation Ferrotec is the world leader in Ferrofluidic® (magnetic liquid) technology. Ferrotec (USA), formerly known as Ferrofluidics, has been supplying ferrofluids for audio applications for over 30 years. The company offers an extensive range of fluids. With R&D and production in both the US and Japan, and 12 sales offices and distributors around the world, the company is well placed to serve your global ferrofluid needs. Ferrofluids have been extensively used in audio speakers for over 30 years. They offer significant performance advantages in tweeters, mid- ranges, woofers, compression drivers and automotive speakers. Some of the advantages in using ferrofluid include increased power handling capabilities, smoothing of frequency response curve and reduced distortion. Ferrotec Distributors In addition to audio fluids, Ferrotec also offers fluids for domain detection, quality control of magnetic media and many other applications. The company also manufactures Ferrofluidic® rotary feedthroughs for the vacuum industry, thermoelectric modules for cooling and temperature control applications, and high precision mechanical, electrical and electro- mechanical offshore contract manufacturing capabilities. 2 How is Ferrofluid used in speakers? Ferrofluid resides in the air gap of the magnet structure and completely fills the space between the coil ID/pole and coil OD/ top plate. No physical containment is needed as the fluid is held in place by the strong permanent magnetic field. The choice of ferrofluid depends on specific loudspeaker requirements in terms of the damping required and the field in the gap. Two key properties of the fluid determine the correct fluid for any application: the viscosity and the magnetization value. The higher the viscosity of a ferrofluid, the greater the viscous damping of the moving mass. A fluid with the correct magnetization value must be chosen to ensure retention of the fluid in the air gap. All ferrofluids, independent of viscosity, essentially provide the same heat transfer from the voice coil to the magnet structure. properties. This means that whatever your requirements in terms of mechanical damping and fluid retention, there is probably a suitable fluid from Every speaker design is unique. Some one of our standard ranges. If not, our team of speakers, for example super tweeters, experienced audio engineers and research chemists require only light damping but need can custom engineer a new fluid to meet the very high colloidal stability of the fluid, performance objectives of your loudspeaker. whereas tweeters often require high viscos- ity fluids. To accommodate this there is a complete range of ferrofluids with vary- ing viscosity values and magnetization 3 www.ferrofluid.de What is a Ferrofluid ? A ferrofluid is a stable colloidal suspension of sub-domain magnetic particles in a liquid carrier. The particles, which have an average size of about 10 nm, are coated with a stabilizing dispersing agent (surfactant) which prevents particle agglomeration even when a strong magnetic field gradient is applied to the ferrofluid. In the absence of a magnetic field, the magnetic moments of the particles are randomly distributed and the fluid has no net magnetization. When a magnetic field is applied to a ferrofluid, the magnetic moments of the particles orient along the field lines almost instantly. The mag- netization of the ferrofluid responds immediately to the changes in the applied magnetic field and when the applied field is removed, the moments randomize quickly. In a gradient field, the whole fluid responds as a homogeneous magnetic liquid which moves to the region of highest flux. This means that ferro- fluids can be precisely positioned and controlled by an external magnetic field. The forces holding the magnetic fluid in place are proportional to the strength of the external field and the magnetization value of the fluid. This means that the retention force of a ferrofluid in a gap can be adjusted by changing either the magnetization of the fluid or the magnetic field in the gap. Audio ferrofluids are based on two classes of carrier liquid: synthetic hydrocarbons and esters. Both oils possess very low volatility and high thermal stability. The choice of fluid is dictated by the environmental considerations of the application (e. g. humidity, adhesives, contact with water, solvent vapors and reactive gases) combined with the best balance of magnetization and viscosity values to optimize the acoustical performance. By varying the quantity of magnetic material in a ferrofluid, and by using different carrier liquids, it can be tailored to meet a variety of needs. The saturation magnetization (the maximum value of the magnetic moment per unit volume when all the domains are aligned) is determined by the nature of the suspended magnetic material and by the volumetric loading of the material. The physical and chemical properties such as density and viscosity correspond closely to those of the carrier liquid. Ferrotec’s highly refined manufacturing process, combined with a long term quality assurance program is the key to its repeatable, reproducible product quality. 4 Ferrofluid benefits: Increased thermal power handling · The presence of ferrofluid in the gap Reduced thermal power compression · enhances the performance of the · Smoothing of frequency response curve loudspeaker in many ways. · Reduced distortion · Reduced warranty returns · Increased production yields Increased Thermal Power Handling: Ferrofluid is Reduced Power Compression/Improved roughly 5 times more thermally conductive than the Dynamic Linearity: Minimizing the temperature air it displaces from the gap. The fluid provides a rise of the voice coil reduces thermal power much lower thermal resistance between the coil and compression effects. Ferrofluid in the gap not only pole/top plate, lowering the voice coil operating reduces sensitivity loss but maintains the linearity temperature under both transient and steady state of the speaker’s output. conditions. This increases thermal power handling Increased Production Yields: Due to the center- capabilities. ing and lubricating properties of the ferrofluid, Damping: Ferrofluid in the gap provides a mechanical manufacturers have reported improvements in resistance to the moving coil. The amount of damping production yields ranging from 30%…60% when is proportional to the viscosity of the ferrofluid. introducing ferrofluids into existing products. This reduction in scrap can often offset the cost of the ferrofluid itself. Voice Coil Centering: When the voice coil is dis- placed in the radial direction in the gap, a restoring Simplified Passive Network Designs: Ferrofluid’s force is obtained which is proportional to the ability to control a driver’s behavior at resonance displacement. Although this force is a fraction of that and, to some extent, break-up modes at the top end provided by the suspension, it is still enough to of the pass band, may minimize the need to address influence the centering of the moving coil. This spring these problems in the crossover network. This constant is given by: reduces the need for additional expensive resistors, t capacitors and inductors. k =M s H m h where: d Reduced Coil/Magnet Size: A 25.4 mm (1”) voice k =spring constant in N/m coil driver with ferrofluid can achieve the same power handling as equivalent sized drivers which utilize M =saturation magnetization in T s 38.1 mm (1.5”) or 50.8 mm (2”) diameter coils. The H =maximum field strength in the gap in A/m m cost savings from the smaller magnet/coil more than offset the ferrofluid cost. The weight reduction may h =height of fluid in the gap in m also be attractive in many applications.
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