XI. Other Design Considerations

SPEAKER TRANSFORMER SATURATION

Speaker transformers tend to be fairly small, and some vary widely in quality. They tend, therefore, to be prone to core saturation at low frequencies. Saturation occurs when the magnetic field induced in the transformer’s iron core by the audio signal waveform has built up as high as the core can handle. Even if the signal voltage increases, the magnetic flux cannot increase any further, so it “clips,” in a way. High frequencies are less likely to cause saturation because the signal waveforms, rapidly alternating in polarity, reverse the direction of the magnetic flux before saturation can occur.

Saturation causes audible distortion. In extreme cases it can damage the power amplifier driving the line, because as the transformers go out of saturation, their magnetic fields collapse and induce a voltage spike across the line. That voltage spike travels along the line back to the amplifier, which has to absorb it. Interestingly, this phenomenon is much more likely to happen on a lightly loaded line than on a heavily loaded one.

An effective way to eliminate the saturation problem is to filter out the frequencies most likely to cause it, without adversely affecting the audio quality. The CX6T and CX12T both have built-in 45 Hz high-pass filters with an 18 dB per octave bass roll-off, while the CX4T has a 50 Hz high-pass filter with a 12 dB per octave roll-off. This is adequate prevention for virtually all good-quality speaker transformers. However, if any speaker transformers on the line do not have low-frequency responses that extend down to 45 Hz, you must insert corresponding high- pass filtering in the audio signal path before the amplifier.

CONNECTING BOTH A DISTRIBUTED LINE AND A DIRECT LOUDSPEAKER ON ONE

CHANNEL

The T versions of the CX amplifiers have simultaneous direct outputs (for loudspeak- ers) and 25-, 70-, and 100-volt isolated outputs (for distributed lines). This adds a measure of versatility that few other amplifiers can match: being able to drive both a loudspeaker and a distributed line on a single channel at the same time.

Setting up such an arrangement is simple, but it requires some precautions:

• Use an 8-ohm speaker for the direct connection. Make sure it has an adequate power rating (150 watts for use with the CX4T, 200 watts for use with the CX6T; 400 watts for the CX12T). Connect it across the low impedance outputs.

• The distributed line must not be loaded any higher (sum of transformer taps plus allowance for insertion loss plus allowance for headroom) than 40 watts for the CX4T, 60 watts for the CX6T, or 125 watts for the CX12T. Connect it across the appropriate transformer terminals.

The directly connected speaker will constitute most of the load on the amplifier channel, so it will receive considerably more power than the distributed line. If you adjust the amplifier gain controls to vary the sound level from the directly connected

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QSC Audio CX Series user manual XI. Other Design Considerations, Speaker Transformer Saturation
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CX Series specifications

QSC Audio, a recognized leader in professional audio solutions, presents the CX Series of amplifiers, a fusion of power, efficiency, and cutting-edge technology designed to meet the demands of various sound reinforcement applications. Known for their reliability and outstanding performance, the CX Series amplifiers are perfect for installations in venues, theaters, and houses of worship, delivering high-quality audio reproduction regardless of the setting.

At the core of the CX Series is its robust Class D amplification. This technology not only ensures excellent audio fidelity but also enhances energy efficiency, resulting in lower operational costs and cooler running temperatures. The amplifiers utilize a linear power supply, which contributes to exceptional audio quality by providing stable and clean power to the components. With varying power ratings, including options ranging from 200 to 1200 watts per channel, the CX Series caters to different venue sizes and specific audio requirements.

The CX Series is engineered with a range of features that enhance usability and performance. Integrated DSP (Digital Signal Processing) allows users to access advanced sound processing algorithms, enabling fine-tuning of audio settings for optimal performance. The amplifiers include comprehensive protection circuitry to safeguard the equipment from thermal overload, short circuits, and signal clipping, ensuring longevity and reliability in demanding environments.

Connectivity is also a significant aspect of the CX Series. The amplifiers are equipped with a variety of input and output options, including XLR, 1/4" TRS, and barrier strip connectors, facilitating seamless integration with a wide range of audio sources and speakers. Moreover, the user-friendly interface includes LCD displays for easy monitoring, making setup and adjustments straightforward for audio engineers and technicians.

Another defining feature of the CX Series is its lightweight design. This portability makes installation and transport easy without compromising on performance. Additionally, QSC’s commitment to sustainability is evident in the design, as the amplifiers are constructed with environmentally friendly materials and have a reduced carbon footprint, aligning with modern practices in eco-conscious audio engineering.

In summary, the QSC Audio CX Series amplifiers blend professionalism with versatility, delivering exceptional performance that satisfies both audio quality and operational reliability. Their innovative technologies and thoughtful design make them a powerful ally for professionals in any sound reinforcement scenario.
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