About the optimization of guitarist Richard Kruspe’s Berlin studio using the innovative Active Bass Canceling process and the Cosinus analog filter
When we are asked to acoustically optimize a studio room that we neither planned nor built ourselves, it is a rather thankless task at first. Because as a rule – and it was no different with this project – the room acoustic installations are not documented precisely enough to really judge what they achieve acoustically – and what they don’t. This control room had already been completed and there was no space available for additional measures. The only option that actually remained was to restore the room in parts and document the changes metrologically in order to identify those fixtures that we could replace with more effective modules. Of course, this is a suggestion that is not readily made to any studio owner in the world who has just spent a considerable amount of money on the expansion and several attempts at improvement. As expected, this was not an option in this case either.
However, we have supported Richard in his studios in Berlin and New York before, and as guitarist and songwriter of Rammstein he is of course a real VIP client. Therefore we were happy to be able to lure the Swiss colleagues from Rocket Science to Berlin to test a clever and, in the studio world, completely new technology: Active Bass Canceling, or ABC for short.
Similar to noise cancelling, where noise is reduced with sound in phase opposition, in this method, sound in phase opposition at the rear of the control room is cancelled with the signal from the main monitors. Unlike all other methods known to us, the ABC algorithm includes an adaptive filter, which makes the system extremely effective and surprisingly insensitive to non-ideal set-up conditions.
In the control room of Richard Kruspe we opened a small part of the rear wall and installed a subwoofer behind a detachable fabric cover. This subwoofer reproduces the signal of the main monitors ATC SCM 50 modified in such a way that the signal is eliminated in the middle of the rear wall. This acts like a bass trap for sound propagation in the room, so that two drops in the frequency response at approx. 55 Hz and 115 Hz, which could not be eliminated by other means, have almost disappeared. It was important to Richard that the DSP for driving the compensation subwoofer with the inevitable ADDA conversion is not located in the signal path of the main monitors. The corrections in the frequency response still necessary after the calibration of the ABC system were therefore implemented with a purely analogue Cosinus filter. The control of a KH 805 subwoofer to support the ATC in the low bass range was also driven by the analog Cosinus filter.
The result is a balanced frequency response down to very low frequencies and a natural, powerful sound. In contrast to the digital correction systems also tested, it is noticeable that the popular sound of the ATC speakers is fully retained. With the help of Rocket Science’s ABC system, the low frequency characteristics of the room have been significantly optimised with minimal alterations and we have a flexible, powerful new tool in our room acoustic toolbox.
Compensation subwoofer in the open control room rear panel