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The animation above shows how our Direct Servo Technology works. The following steps are illustrated:
The plate amplifier receives a signal which is filtered on the pre-amp board to achieve correct integration. The power amplifier sends a signal to the driver.
As the amplified signal passes through the voice coil, the cone moves.
A very thin sensing coil is attached to the voice coil. As the cone moves, a signal is generated. This signal is used to accurately track the movement of the cone. Effectively the sensing coil is a specialized microphone which measures the precise output of the driver.
The correction signal is fed back into the summing points of the amplifier. It is compared to the original signal and corrections are made without the use of any active circuits.
The driver now reproduces a signal that is corrected. The sources of distortion which plague other subwoofers are dramatically reduced. |
1. Amplified signal
top | Direct Servo technology: why do we need it? |
Conventional subwoofers have extremely high distortion. Well regarded conventional subwoofers typically have measured distortion levels exceeding 15% at 20 Hz at 100 dB. This includes many subwoofers costing more than US $3000. We think this is far too high. A well designed servo subwoofer will achieve distortion levels under 3% under the same conditions. |
Why you need a servo |
A servo is essential in a subwoofer that aims to be true to the original. The benefits are clear:
These benefits are all unique to a servo controlled subwoofer, and can't be achieved in a practical and affordable way without a servo. Without servo technology, a massive sub bass horn is required. |
What are memory effects? |
A subwoofer driver contains parts which have a memory effect. This means the driver will not respond perfectly to the signal. The spider and surround both contribute to memory effect in a driver. The voice coil which carries the signal that drives the cone also exhibits a memory effect. This is because the temperature of the voice coil changes with operation, and this changes the resistance. The result is a loss of dynamics. As the driver excursion and power input level increases, both effects get worse in conventional subwoofers. Detail and resolution is lost. |
Direct Servo corrects both mechanical and thermal memory effects. The result is much lower distortion, and bass that is true to the original, preserving the subtle details, capturing dynamics and revealing a level of detail well beyond the reach of most conventional subwoofers. |
How is Direct Servo different? |
Our philosophy is to make audio products as simple as they can be. Less is more. Our subwoofers put as little into the signal path as possible. This approach applies to our amplifiers, Direct Servo technology and drivers. Most servo subwoofers use an accelerometer, which is another mechanical system with its own limitations. Also extensive protection circuits are required, and these further degrade the signal. As a result, accelerometer based servos are not as accurate as Direct Servo. The superiority of Direct Servo is derived from its simplicity. |
How it works |
Direct Servo uses a very thin sensing coil which is wound adjacent to the voice coil. This coil induces a signal which is fed back into the summing points of the amplifier. This signal is used to correct sources of distortion, and this is achieved without placing any active devices such as transistors or operational amplifiers in the signal path. This simplicity eliminates any secondary or mechanical effects which plagues other technologies. |
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