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ramé-hart Newsletter

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December 2017

  How to Cool Your Loudspeakers

When I was in college, I bought a pair of B&W (Bowers & Wilkins) loudspeakers for $100 which was about one fifth their retail price. I got a sweet deal because one of the cabinets was damaged. (I repaired it.) This acquisition launched my interest in high fidelity. Over time I became quite the audiophile and still appreciate the masterful reproduction of music. And I still have those B&W loudspeakers lo these many years later.

A lot of engineering effort has been expended in the past century in the quest to reproduce sound and music to the highest degree of fidelity. The loudspeaker is one of the key components of any high-end audio system and its proper design is probably the most debated of any hi-fi component. My father is an audio engineer and responsible for having contributed to the ongoing debate as well as some novel speaker designs over the years.

I just recently learned that a surfactant is used in one type of loudspeaker design and thought it would be educational and entertaining to share some highlights of that design with you. Here at ramé-hart we're interested in surfactants as they lower the surface tension of liquids. It's our business to measure surface tension.

The problem to solve is heat which builds up from the voice coil moving at high frequencies around - but not touching - a magnet. Normally the space between the voice coil and magnet is a small gap of air. But this air gap can be filled with a ferrofluid as shown in the graphic below. Not only does this ferrofluid improve the sound quality by dampening unwanted resonances, but it also extends the life of the speaker by dissipating heat away from the voice coil.

A ferrofluid is a colloidal suspension made up of about 5% magnetic nanoparticles, 10% surfactant, and 85% carrier fluid. The nanoparticles have to be small, under 10 nm in order to not sink to the bottom of the fluid. Due to van der Waals force, the nanoparticles have a tendency to be attracted to one another. That's where the surfactant comes in. Once added to the fluid, an osmotic pressure between the nanoparticles causes them to become evenly dispersed. Combining the forces of gravity and surface tension and magnetism, the fluid can take on some interesting shapes - as shown in the picture below.

A ferrofluid becomes less magnetic as it is heated up. Thus when installed in a voice coil next to a powerful magnet, the magnet attracts the colder ferrofluid and moves the hot ferrofluid away from the voice coil and toward a heat sink. This cooling cycle requires no additional energy force and is very efficient.

Ferrofluids are also used as contrast agents for MRI applications, for propelling a miniature satellite called a CubeSat, for instrumentation applications such as measuring specific viscosity, for optical, heat transfer, energy harvesting, and a number of other compelling applications. If you work with ferrofluids and wish to better understand their surface tension and the effects surfactants have on them, please contact us for a quotation on one of our Goniometer / Tensiometer products.

  Happy Holidays
  From all of us here at ramé-hart instrument co. to all of our customers and users of our instruments, we'd like to thank you for another successful year. We began in 1961 and for the past 57 years we've been striving for excellence in goniometry and surface science instrumentation. We look forward to a New Year and wish you the best as well in 2018. Thank you for your continued business.

Carl Clegg
Director of Sales
Phone 973-448-0305
Contact us



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