Brief Explanation

Advanced Yamaha Active Servo Technology (Advanced YST) is a unique system in which the speaker and amplifier work together to cancel out impedance so as to achieve perfectly linear motion in the speaker unit. Advanced YST helps to ensure the highest levels of sound pressure and overall performance.

Technical Explanation

Audio engineers have always had to balance the characteristics of speakers and amplifiers in order to achieve desired performance. Yamaha engineers pioneered a radically different solution to this problem. Instead of settling for an imperfect balance, the new Yamaha approach was to look at speaker and amplifier as a unit.

This shift in thinking led to the development of a system that relies upon two proprietary Yamaha technologies: the Negative Impedance Converter and Yamaha Air Woofer. The two combine into one interdependent system in which speaker and amplifier are combined in a closed "Active Servo" loop.

Yamaha's Advanced YST system offers the following benefits to music lovers and audiophiles alike:

Key Benefits

Incredible bass from a smaller cabinet. Advanced YST subwoofers and speakers can easily reproduce a much lower bass response than a similarly sized alternative speaker.

Easy and convenient placement due to the smaller size of the speaker and cabinet.

Better imaging - Imagine sitting in the front row at the symphony. Close your eyes and visualize the placement of the members of the orchestra. The ability to reproduce this spacial quality of sound is known as imaging. Speaker size is one factor that can drastically contribute to imaging accuracy. Advanced YST speakers are small enough to have excellent imaging characteristics, yet still accurately reproduce tones from the very low bass of a pipe organ to the highs of a triangle and cymbals.

This document will break Advanced YST into two parts: Negative Impedance Converter and Yamaha Air Woofer (Helmholz Resonator). As we will learn, Advanced YST provides significant benefits over other speakers of equivalent size.

Ideally, the motion of the speaker cone (driver) should precisely follow the signal coming from the amplifier. However, in the world of conductor-designed amplification, the sad reality is that conductive material introduces resistance to electron flow, preventing the speaker from responding faithfully to a signal. Resistance is like an obstacle between speaker and amplifier, preventing the speaker from perfectly reproducing sound. This resistance is of greatest concern in the voice coil and the magnetic flux surrounding it.

The question then becomes: "How does this make Yamaha subwoofers and speakers output that kind of bass?" Read on…

The additional control of the speaker cone, made possible by the Negative Impedance Converter, enables the speaker to deliver incredible bass from a small enclosure.

How it works

The Negative Impedance Converter creates a condition where the loudspeaker cone becomes very stiff and rigid. In fact, the cone becomes so rigid with negative impedance control that it is as hard as the wall of the cabinet itself. It is this rigidity that allows a small Advanced YST speaker to reproduce frequencies lower than otherwise possible.

Bass reflex (vented) vs. Advanced YST

Let's compare an Advanced YST speaker with a conventional Bass Reflex or vented speaker:

In a vented enclosure, low frequencies are created when the woofer responds to a low frequency signal. The signal causes the speaker cone to move back and forth, which in turn moves air. Resonance is created in the enclosure, some of which escapes from the vent, and some from the woofer itself (most vented enclosures have a woofer that is compliant, or moves in and out rather easily).

In contrast, an Advanced YST driver is held in a rigid state by the negative impedance circuitry. Low frequency energy sent from the amp to the speaker causes the cone to resonate or excite the air inside the cabinet. Since the cone is rigid, the only way for the energy to escape is through the port in the cabinet; thus, the name Air Woofer—the air in the cabinet and port actually is the woofer. Without the additional control provided by the negative impedance converter, the woofer would behave no differently than a normal, vented speaker; however, because the negative impedance converter maintains very strong control, the low frequencies sent to the speaker cause the cone to resonate only the air inside the cabinet as it moves back and forth.