Crown Audio 133472-1A manual Glossary of Terms, Amplifier Application Guide, ILoad/ILimit Indicator

30 Chapter 3: Glossary of Terms

ILoad/ILimit Indicator

An indicator of some Crown amplifi ers that shows current fl ow to the loudspeakers (“current load”) and the maximum cur- rent available from the amplifi er (“current limit”). Typically, the indicator will glow one color to indicate that current is fl owing to the loads connected to the amplifi er output channel, and change to another color to show that the amplifi er channel is delivering its maximum output current.

Impedance

Impedance refers to the resistance of a circuit or device to AC (alternating current). Most modern electronic audio devices have extremely high input impedances so they can be driven by very low power outputs. Impedance is measured in ohms. The symbol Ω (omega) is often used to represent resistance.

Input

The connection going into an audio device. In a mixer or mixing-console, a connector for a microphone, line-level device, or other signal source.

Intermodulation Distortion (IMD)

Nonlinear distortion that occurs when different frequencies pass through an amplifi er at the same time and interact to create combinations of tones unrelated to the original sounds. IMD specifi cations are usually expressed as a percentage of the amplifi er’s output, and the lower the percentage the better.

IOC®

The IOC (Input Output Comparator) circuit compares the output signal of the amplifi er with the input signal. If there is any difference other than gain, then it is considered distor- tion and the indicator comes on. The LED indicator will come on whenever there is distortion of 0.05% or more. This is a dynamic Proof of Performance of the amplifi ers functionality. Anytime you experience distortion in your system you can view the IOC indicators. If they are not lit then you know that the amplifi er is not at fault. If the IOC indicators are on, then the amplifi er is in distortion.

To learn more about IOC, download and read the IOC white paper at www.crownaudio.com.

Limiter

A limiter is a dynamics processor very similar to a compres- sor. In fact, many compressors are capable of acting as limit- ers when set up properly. The primary difference is the ratio used in reducing gain. In a limiter, this ratio is set up to be as close to infi nity:1 as possible (no matter how much the input signal changes, the output level should remain pretty much constant). The idea is that a limiter establishes a maximum gain setting, and prevents signals from getting any louder than that setting.

Line Level

Generally defi ned in the audio industry as +4 dBu (1.23 volts) for balanced “pro” gear, and .316 volts (–10 dBV) for unbal- anced “semi-pro” gear. “ It is best to match the levels of the gear you are using so that –10 dBV equipment isn’t directly feeding +4 dBu equipment, and vice versa. If you use gear of both levels, there are various level matching devices on the market to properly interface the items.

Linear Power Supply

A power supply that converts AC mains power for use by the amplifi er by means of a conventional transformer operating at the same frequency as that of the AC mains supply (usually

50 to 60 Hz).

Loudspeaker

A transducer that converts electrical energy (the signal) into acoustical energy (sound waves).

Loudspeaker Offset Integration

A feature on some Crown amplifi ers that helps reduce output clipping and off-center woofer cone movement caused by the presence of large infrasonic (subaudible) frequencies. The circuit adds a third order high-pass Butterworth fi lter with a –3 dB frequency of 35 Hz.

Low-Pass Filter

A fi lter that passes frequencies below a certain frequency and attenuates frequencies above that same frequency. It can also be called a high-cut fi lter.

Mic Level

The level (or voltage) of signal generated by a microphone. Typically around 2 millivolts.

Negative Feedback

If some of the output of an amplifi er is made to be out of phase, and mixed back with the amp’s input signal, it will partially cancel the input, reducing the gain of the amplifi er; this is called negative feedback. But, because it contains and therefore cancels any distortion introduced by the amplifi er, negative feedback also has the effect of improving the linear- ity of the amplifi er. Negative feedback can also lower output impedance, increasing damping factor, and can sometimes be made to fl atten frequency response. The key to negative feedback amplifi ers is careful design. Too much phase shift and the amp will be unstable, and too much feedback will cause Transient Intermodulation Distortion.

Noise

Unwanted sound, such as hiss from electronics or tape. An audio signal with an irregular, non-periodic waveform.

Noise Floor

The noise fl oor of a device or system is the amount of noise generated by the device itself with no signal present, it is measured in decibels. All electronic devices will generate a certain amount of noise, even a piece of wire! Minimizing the noise fl oor leads to expanded dynamic range, and cleaner recordings or sound production.

ODEP®

ODEP (Output Device Emulator Protection) is an analog computer simulation of the output device thermal imped- ance. In layman’s terms ODEP stores how much power the amplifi er delivers to its load and its heatsink temperature. If the protection circuit determines that the output stage is being overstressed or cannot dissipate any further heat, then output stage drive is limited.

To learn more about ODEP, download and read the ODEP white paper at www.crownaudio.com.

Output

A connector in an audio device from which the signal comes and then feeds successive devices.

Overload

The distortion that occurs when an applied signal exceeds a system’s maximum input level.

Parallel-Mono

As implemented in Crown amplifi ers, an operating mode of

Amplifier Application Guide