Spring Lab is a spring reverb with both of the propagation wave types and the reverb each modelled separately. The upper or compression wave uses loads of allpass filters (up to 5,440 poles) to achieve the frequency dependent spectral effect of the frequencies above the 'transition frequency'. The lower or shear wave also uses allpass filters (100-600) but of a slightly different, 'stretched' type. The reverb in the lower component is fairly standard but is not modulated and each delay time is a prime number of samples.
There is also a convolution module (Credit: Laurent Sevestre) with custom impulse responses used to create a very steep slope lowpass necessary in the lower, shear component. This spring reverb started out in a relatively under developed state in my previous upload called Syntrix. CPU usage varies between "very usable" to "won’t run in real-time" and depends on the number of components of various types selected.
This effect is designed to only run at 48 and 96k sample rates and the appropriate value should be chosen on the panel as well as in Reaktor itself for correct operation.
Credit to Jan Brahler for the MonsterAllpass instrument. Shoutout to Julian Parker. I hope you enjoy all the springy sproingy sounds.