S, Study the term Schroeder Frequency. This will help. A design frequency range is the upper and lower frequencies of a range of frequencies and amplitudes that the room must handle without producing too many audible distortions.
I am an acoustic engineer with over 30 years’ experience in the business. My technology has been used in Electric Lady Land Studios, Sony Music of New York, Cello Music and Films founded by Mark Levinson, and Saltmines Studios in Mesa, Arizona, along with hundreds of others.