M.Ostrowski sp.j. participated in an experimental project finance by the Ministry of Science and Higher Education – from the Warsaw F. Chopin University of Music, Tadeusz Fidecki grant. The project aimed at improving the intelligibility of audio and music at selected rooms of the Royal Castle.
The Royal Castle located in Warsaw at the Castle Square is considered a Historical and Cultural Heritage Monument. Once the seat of the dukes of Mazovia, and later till the loss of Poland’s independence in 1795, the residence of kings and meeting place of the Sejm of the Polish-Lithuanian Commonwealth. In the years 1926-39 the seat and residence of the President of the, reestablished in 1918, Polish Republic. Today, the castle is a museum open to the public as well as a place for important national ceremonies.
Destroyed per Hitler’s orders in 1939-44, it was rebuilt thanks to the Polish nation’s will in 1971-84. The individual rooms of the castle were restored based on photographs from before 1939. 
The biggest problem during reconstruction of the Royal Castle was to restore the original acoustic and building materials. This problem left its mark on the acoustics of the different rooms, in particular the Ballroom and the Concert Hall. In both of these the reverberation time exceeds 3 seconds. Both audio and music from the earlier audio system were unacceptable – the measured speech transmission index (STI) was around 0.3.
In the earlier phase of the project, M.Ostrowski’s objective was to provide the technical know-how pertaining to digital signal modeling using ICONYX active loudspeakers. This lead to further cooperation and to an order to design a suitable audio system for the Ballroom and Concert Hall. Ultimately, M.Ostrowski sp.j. designed the required system, supplied Renkus-Heinz and Yamaha equipment, and fine-tuned the audio system.
The results were remarkable, the measured STI after installation of the Renkus—Heinz system, was within 0.7 ÷ 0.8 at the entire area covered by the system, with sound coverage irregularities of ±2 dB for the Ballroom and ±1 dB for the Concert Hall.
The proposed fully digital system included:
• IC16R and IC8R Renkus-Heizn active loudspeakers operating in a digital, redundant CobraNet network,
• Yamaha LS9-16 digital audio console,
• Yamaha DME24N, DME8i C, and DME8o C multitasking digital signal processors,
• Sennheiser wireless microphone system,
• Surround sound system with Blu-ray video quality,
• audio archiving system,
• local area network (LAN).
 Rottermund, A. (2003). Zamek Królewski w Warszawie (‘Warsaw Royal Castle’). Warsaw.