Eminence D-fend for Loudspeaker Protection

in Tech Preview
There's nothing more frustrating (and embarrassing) than equipment failure during a show. Bands and audiences take it for granted that loudspeakers will work perfectly every time, but sound engineers know it doesn't always happen that way.

Loudspeakers are asked to produce more SPL than they're capable of at times. Occasionally equipment ends up in the hands of eager, yet untrained, audio techs, especially systems with passive loudspeakers, which aren't always well matched to their amplification. Lay people sometimes operate rental stock or installation speaker systems. Other times even experienced operators need a safety net, especially when a system is suddenly required to go to "eleven." In short, loudspeaker transducers are vulnerable.


A New Safeguard


SLS Audio and Eminence Speaker are introducing a musical solution to this dilemma.  Evenstar, the technology division of SLS Audio, has created D-fend, the ultimate protection circuit for passive loudspeaker applications. Considering today's economy, D-fend is possibly the most relevant investment you can make. No one wants to replace equipment due to misuse, whether you are the manufacturer or the consumer.


Time-domain waveforms of D-fend holding 78 Vrms input signal (pink) to 62 Vrms (yellow)
When typical protection circuits are enabled, filaments burst or poly-switches disengage to protect the speaker. Their drawbacks are numerous, but most frustrating is that when old-school protection circuits are enabled, the show ends, or is dramatically different! Poly-switches must cool down or bulbs must be replaced before the show can continue. Evenstar provides a musical solution to an age-old problem. D-fend's patented technology doesn't use filaments, so it doesn't pose a risk of fire from heat.


"Think of the D-fend circuit as a high power, speaker-level compressor-limiter that will allow an audio designer to guarantee unmatched levels of protection for multiple components in their un-powered loudspeakers," explains Evenstar's chief engineer, Joel Butler.


Without the use of circuit breakers or resistive elements, D-fend acts as a governor rather than a kill-switch. Basically, an operator can push the speakers as hard as they want without fear of overload. D-fend only allows power to pass through up to a specific, programmable threshold. Once that threshold is reached, D-fend manages the extra juice without stopping the show. Musicians can rest assured that if they overpower a speaker cabinet, it's okay. D-fend can handle it and save the voice coils for another day.


Combining digital signal processing with on-board digital filtering, customizable microprocessor and MOSFET construction, the D-fend protection circuit enables a designer to use this technology prior to passive filtration and allows different sensitivity settings in specific frequency bands, such as woofer over-excursion bands or high frequency peak damage regions.


Employing switch mode operation, D-fend employs programmable DSP to provide precise high-speed digital load augmentation at extreme power levels, quickly raising the impedance seen by the amp at precise power levels in programmable bands. This is a revolutionary technology.


It can be used for individual drivers or before the passive crossover in multi-way passive enclosures. It's cost-effective, musical sounding, efficient and requires no auxiliary power, drawing what little it needs from the amp. The power consumed when working on 1200W into a 4Ω load is less than 17W. At the present time, D-fend can handle any amplifier on the market and its response time is fast.


Multiple Uses


D-fend can be applied to any speaker application. You can install the unit pre- or post-crossover depending on its intended use. For two- and three-way configurations, it may be necessary to install one unit for each driver, but in some applications a single unit might be optimal for an entire enclosure. High quality, low frequency protection in passive enclosures is hard to come by. D-fend is the first protection circuit of this quality for low frequency applications.


One reason Eminence has joined SLS Audio in marketing D-fend is the opportunity cost of not being involved, recognizing the improvement not only to their own products, but those of their OEM customers as well. Today you can't purchase a new car without airbags. Someday D-fend will be the "airbag" of the passive loudspeaker industry. It's too cost-effective not to pursue. For a small fraction of the cost of a driver, its performance can be guaranteed without failure.


"We're very excited about the unique opportunity to partner with Evenstar to offer our customers the ultimate in loudspeaker protection," said Eminence president Chris Rose. "By incorporating D-fend in their products, system designers, brand owners and end-users will enjoy a new level of confidence from their passive loudspeaker systems being guarded by safe, reliable protection. D-fend is economical and easy to integrate into both new and existing designs. We expect it will become an industry standard protection device for virtually all passive professional audio and musical instrument applications."


D-fend is being introduced and demonstrated at the Eminence InfoComm booth #164 in Orlando, Florida June 15-17, 2011, or inquire to This email address is being protected from spambots. You need JavaScript enabled to view it. for more information.