D-fend™ SA300


D-fend SA300
With D-fend there are no more worries about blown speakers, HF drivers or crossovers. Or even worse: fire caused by excessive heat. Not only does D-fend keep your system safe, but your venue and audience as well. The user simply sets the thresholds and D-fend monitors and limits the amount of input power it passes through to the loudspeaker. It’s USB compatible, and can be programmed to your specifications from a desktop or laptop. Just set it and forget it. Protect your products, venue, customers, and your reputation with the first passive speaker protection system that is virtually indestructible.

Learn more at D-fend.com Find an authorized dealer

D-fend loudspeaker protection is ideal for:


Word of mouth can be an installer’s best friend or worst enemy. D-fend will not only protect your carefully installed equipment, but also gives you peace of mind knowing your reputation is protected as well.

Equipment Rental CompaniesRental Companies

By using D-fend you can rent out your speakers and know that you’ll get them back in the same condition they left. So what comes in on Monday can go back out the door again without a visit to your repair shop.

OEM ManufacturersOEM Manufacturers*

What can be better than offering a bullet-proof loudspeaker system? With D-fend you can offer your customers something they’ve never seen before: a passive speaker that can’t be destroyed, no matter how hard you punish it.

End UsersEnd Users

Own some passive speakers? Chances are you’ve come closer than you think to blowing a driver. There’s nothing worse than stopping a show in progress because you just lost your subwoofer. Why take the chance?

*D-fend technology can be incorporated into your OEM applications in board-only configurations. To license this technology for Professional Audio and Musical Instrument applications worldwide, please contact Josh Martin, Technology Sales Manager, at 502.845.5622 ext. 245, or via e-mail at josh.martin@eminence.com

Watch the Technology Demonstrations

See D-fend in action on YouTubeJoel Butler, Director of Engineering and Electronics at Evenstar, walks us through the concepts behind the invention of this unique technology in this introductory video, and offers five key demonstrations:

  • Demo #1: Pink Noise – This video demonstrates the slewing capabilities of D-fend™ technology in excessive voltage conditions.
  • Demo #2: Reverse Sweep – The uncommon low-frequency protection abilities of D-fend™ technology are demonstrated.
  • Demo #3: Speed – Using a real-world snare drum pulse, D-fend’s speed, attack, and release times are demonstrated here.
  • Demo #4: Fidelity – D-fend’s ability to protect without changing the overall sound of the loudspeaker is demonstrated.
  • Demo #5: Excessive Power – You might need safety equipment just to watch this video! Do NOT try this at home.


Digital Signal Processing

With on-board digital filtering, D-fend provides multiple frequency dependent thresholds and independent attack/release timing parameters. This enables the user to employ D-fend technology prior to passive filtration, and allows increased sensitivity in specific frequency bands such as woofer over-excursion bands or high frequency peak damage regions.

Digital Attenuation

Significantly reduced heat, no bulbs, no light output.

Fully Programmable

On-board microprocessor allows user customizable attack, release, and threshold settings to maximize loudspeaker performance.

High Power

Capable of protecting high power woofers and sub-woofers from over-power conditions as well as mechanical damage thresholds; an achievement unseen within the audio industry.


Allows damage-free operation of woofers, tweeters, and/or midrange devices. Any combination of parallel, series, or parallel-series connected speaker systems can be used on the output of the SA300. The SA300 is designed for use with transistorized amplifiers with a low-impedance output.

No Auxiliary Power

Operates from a standard speaker-level signal, does not require auxiliary power except for low-power applications. External power supply sold separately.


Attenuation slewing algorithms provide lamp-like musicality without the nuisance of light and flammability concerns. Think of it as a high-power, speaker-level limiter allowing the user to guarantee unmatched levels of protection for their unpowered loudspeaker solutions.

The following plots illustrate how D-fend™ can be programmed to match a loudspeaker’s power handling characteristics, including both response time and required attenuation levels.

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