React:IR – is a reactive-resonance load box, attenuator and impulse loader with length up to 190 ms. What do “reactive”, and “resonance” mean, and why is it important?
Let's figure it out, what means reactive, resonance and why it`s important…

Valve (tube) guitar amplifiers have relatively large output impedance due to the output transformer. The guitar cabinet represents a complex reactive load to the amplifier and drastically affects the frequency characteristic of output signal. Adding to this, the majority of guitar amplifiers have negative feedback. This means that some part of output signal returns again to the input of the power amplifier and mixes with the main signal.

Thus, when we speak about a load box, it’s important to understand principles of the device’s operation and its influence on signal. Guitar speaker manufacturers often publish the impedance curves of their respective products. Usually, guitar speaker have their largest impedance at lower frequencies around 70-90 Hz. When inside a cabinet, the peak at low frequencies resides slightly higher, for example, in 4×12 cabinet, the peak is located around 100-115 Hz due to the cabinet construction. Thus it’s important to reproduce not only speaker characteristics, but also the characteristics of the entire cabinet.

Historically, different equipment manufacturers have produced different types of load boxes. Initially, a simple passive type of load is used. Then, reactive types were introduced. However, the term, “reactive”, can refer to only high frequency component without low frequency component. Thus, the term, “reactive-resonance”, load was introduced which means correction not only of high frequencies, but also low frequencies. The graph below represents the influence of different load types on frequency characteristics of signal.

React:IR allows usage of all three regimes: passive, reactive and reactive-resonance. The respective modes can be set using switches in the Loadbox section on the front panel of the device.In addition, the device has attenuator, which allows the usage of an amplifier at maximum volume, while listening at quiet “TV” loudness.

React:IR has a number of FX-effects: -Noise Gate -Tone stack – amplifier Tone Stack emulation with several models of popular amps -PA Curve – amplifier-cabinet interaction curve -5-band paragraphic equalizer with high cut and low cut filters (LowPass and HighPass) -Tone Stack emulation can be used in when running a distortion stompbox directly into the line input, for emulation of frequency response of guitar amplifier clean channel.

Impedance Curve emulation can be used for guitar preamp connection into line input, in this case frequency response modified to emulate connection trough guitar power amp.