About D-fend™

The patent pending D-fend technology utilized within the SA300 stand-alone unit makes use of advanced, high-efficiency power conversion techniques to provide an unprecedented level of protection for your loudspeaker system. Due to the architecture of the D-fend technology, the SA300 is the first device within the industry to provide programmable, high-voltage, high current, full range signal protection for large loudspeaker systems.

D-fend SA300In the past, protection circuits were employed only for use with high frequency devices due to the limited power handling of the protection circuits. These devices attempted to protect the high frequency driver by dissipating the undesired power into resistive elements or even light bulb components. Obviously, these power dissipative passive techniques resulted in limited power handling characteristics, no user programmability, limited response speed, no frequency selectivity, and life-cycle concerns. D-fend overcomes these deficiencies and provides you with the first-ever full-range, programmable loudspeaker protection network for use within a myriad of applications.

SA300 Retail CartonThis technology operates upon the principle of reducing the power delivered to the load, your loudspeaker, while also reducing the net electrical current required from your amplifier. In other words, the D-fend technology is a non-dissipative technique in that it does not dissipate the undesired power into heat or light output; rather it reduces the amount of power that is requested from the amplifier through the use of high-efficiency digital factoring. Obviously, we believe D-fend is groundbreaking technology that opens a door for users such as yourself to experience peace of mind concerning your loudspeaker investment. With the D-fend digital attenuator under complete microprocessor control, you have at your fingertips a world of protective configurations.

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Typical Applications of D-fend

  • Broadband protection of a loudspeaker or loudspeaker system

    By enabling the All Pass function, one can set the maximum average power level that the device will see. As with all D-fend applications, the Attack and Release times can be adjusted to facilitate natural sounding speaker protection.

  • High frequency protection

    RMS and Peak power can be limited to prevent thermal and mechanical failures of high frequency devices.

  • Low frequency protection

    Woofers and subwoofers carry the burden of the most demanding loads in audio. By properly choosing peak limits, one can maximize the performance of these devices by preventing over-excursion events and heating issues.

Watch the Installation Demonstrations

See D-fend in action on YouTubeJosh Martin, Eminence Speaker Technology Sales Manager, walks us through the process of programming the D-fend SA300 to protect the three main components of an audio system.

Main Speaker Cabinets



Watch the Technology Demonstrations

See D-fend in action on YouTubeJoel Butler, President, Butler Engineering, walks us through the concepts behind the invention of this unique technology in this introductory video,


  • 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.

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.

Click to EnlargeClick to EnlargeClick to Enlarge

Maximum Power Specifications

The D-fend SA300 has maximum peak voltage and current ratings of 300 volts and 25 amps, respectively. Therefore, maximum power specifications are impedance dependent. Below is a table listing the maximum input power D-fend is capable of safely managing.

D-fend MaximumPower Specifications
1,250W at 2ohm 2,000W at 4ohm 3,000W at 6ohm 4,000W at 8ohm 2,000W at 16ohm

Minimum Power Requirements

The D-fend SA300 requires a minimum amount of audio signal power in order for the protection circuit to function properly. The amount of power required to activate the D-fend protection circuit is dependent upon the source of the supplied power as well as the impedance load of the connected system(s) that are to be protected. The minimum power required can be greatly reduced with the use of an external power supply (sold separately) which may be advantageous for some applications. Below is a chart illustrating the minimum power requirement of the D-fend SA300 if incorporating an external power supply, or if using only the audio signal as the power source.

Minimum Continuous Audio Signal Power Required
Impedance (ohms) Using the External Power Supply (watts) Using Only the Audio Signal (watts)
2 0.500 32.0
4 0.250 16.0
6 0.167 10.7
8 0.125 8.0
16 0.063 4.0

Thermal Limits

D-fend incorporates built-in thermal protection circuitry which will temporarily disable the unit in the event that the thermal limit has been reached or exceeded. Failure to mount the device in the recommended orientation (cooling fins running vertically) will increase the likelihood of reaching this limit. Reaching the temperature threshold signifies the SA300 is being subjected to extremes beyond what it is rated for, and/or that there is an issue with the protected system or the system demands.

Weights and Dimensions

Weight Width Height Depth
SA300 Unit Only 2.4 lbs / 1.09 kg 5.94 in / 15.09 cm 2.83 in / 6.05 cm 6.75 in / 17.15 cm
SA300 in Retail Carton 3.1 lbs / 1.41 kg 8.0 in / 20.32 cm 3.0 in / 7.62 cm 7.0 in / 19.05 cm

Minimum System Requirements

Mac and PC compatible
The D-fend software is compatible with both PC and Mac operating systems.

  • Windows Vista or later
  • Mac OSX 10.4 or later
  • 500mb RAM
  • USB port
  • The SA300 uses Neutrik NL4 connectors


Please note there is a shock hazard and there are no serviceable parts inside this device. D-fend is FCC Class A certified, CE certified, and RoHs/WEEE compliant. Please read the manual before using this product.

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* The SA300 is designed for use with transistorized amplifiers with a low-impedance output. ** Auxiliary power may be required for low-power applications. External power supply sold separately. *** D-fend™ technology can be incorporated into your OEM applications in board-only configurations. Contact Eminence Speaker at (502) 845-5622 for details.