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Tech Focus: Automatic Saturation Compensation (ASC) 

Inside a patented audio transformer technology from Electro-Voice that delivers enhanced loudspeaker performance in 70/100-volt systems.

By PSW Staff May 7, 2018

In addition to the new EVC Series, the Electro-Voice ZX1i also incorporates ASC technology.

Automatic Saturation Compensation (ASC) is a patented Electro-Voice technology that delivers outstanding audio performance from transformer-isolated loudspeakers on 70/100-volt systems.

Specifically, it preserves low-frequency performance while presenting a stable load to the amplifier, regardless of the number of loudspeakers connected in parallel. As a result, ASC-equipped loudspeakers – including subwoofers – sound virtually identical whether they’re used with a transformer or without.

The video and article presented here provide an overview of how it works.

The Problem

As a drive signal increases, every audio transformer will reach a point at which its core begins to saturate, especially at low frequencies. When this happens, the load impedance can fall low enough to cause the amplifier to shut down or fail.

When multiple loudspeaker transformers are connected in parallel, there’s an even higher risk that the impedance will drop so low that the amplifier just won’t work. When driven fully into saturation, a transformer is really no different than a dead short across the amplifier terminals.

Above, high-pass filter at 50 Hz, and below, high-pass filters at 50 Hz and 100 Hz.

A common practice in professional audio is to use a high-pass filter with a cut-off frequency – nominally around 50 Hz – that affects the entire system. This reduces the risk of core saturation by blocking some of the low-frequency energy delivered to the transformer.

Further, 50 Hz is low enough that it doesn’t affect perceived bass response for most types of music and in many applications. As more transformers are connected together, most manufacturers recommend higher cut-off frequencies to maintain amplifier stability. But a higher cut-off means less bass and less warmth in the sound.

The Solution

ASC takes a different approach by automatically inserting a high-pass filter with a variable cut-off frequency in each loudspeaker. The ASC circuit senses the low-frequency current in the drive signal and changes the filter cutoff just enough to keep the transformer from saturating. This delivers the warmth and fullness of a 50 Hz high-pass with a level of amplifier protection that would otherwise require a filter set to 100 Hz.

TK-150 being inserted via rear input panel.

ASC is a standard feature for all models in the new Electro-Voice EVC Series of fixed install loudspeakers and is optimized to pair with high-quality TK-150 audio transformers. In addition to all EVC models, ASC is a standard feature on the transformer-equipped versions of the EV ZX1i.

The combination of ASC and the TK-150 makes it almost impossible to tell whether the loudspeaker is connected through a transformer or not. And because the TK-150 is flat within ± 1 dB from 35 Hz to 20 kHz, it even provides full, rich sound through a transformer-isolated subwoofer.

It doesn’t matter how many loudspeakers are connected in parallel, ASC preserves the richness of the system’s low-end while keeping the load impedance in a safe range for the power amplifiers.

ASC is a standard feature for all models in the new Electro-Voice EVC Series.

The following video provides more information about the other unique features the ASC-equipped EVC Series offers.

Electro-Voice

 

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