To describe sound fields in acoustics, the sound pressure p, measured in Pascals (Pa), is widely used. As with electrical quantities in sound engineering, it is usually more convenient to use a logarithmic scale here. At the same time, the concept of sound pressure level (SPL) is introduced L = 20 log (p / p0), where p0 = 2 x 10-5 Pa is the sound pressure at the threshold of audibility. Very often, ultrasound is measured (or calculated) in separate frequency bands. The most widespread are octave or 1/3 octave bands with a relatively constant bandwidth. Geometrical average (below in the text for brevity, average) frequencies of these bands are regulated by international and domestic standards. A preferred range of mid frequencies for octave bands: … 125, 250, 500, … Hz; for 1/3 octave bands: … 125, 160,200, 250, … Hz. In addition to these narrow frequency bands, broadband correction is also applied, the form of which is indicated by the letters A, B, C, … and is also strictly regulated. Most often, curve A is used. When using it, one speaks of sound levels along curve A and introduces the designation dBA.
To assess the ability of a material or structure to absorb sound energy, in particular, the concept of sound absorption coefficient (CAP) is used. It is equal to the ratio of sound energy absorbed by a given material to all sound energy incident on the material, i.e. a = Epogl / Epad. Thus, in extreme cases, a = 1 when all sound energy is completely absorbed by the material, and a = 0 when all sound energy is completely reflected from the material. KZP is determined in octave (less often in 1/3 octave) bands, usually using the range from 125 to 4000 Hz. Sometimes in the reference literature one can find values of short-circuit breaker values greater than 1. It would seem that this is a physically incorrect result, because the absorbed energy is more incident. In fact, of course, the principle of conservation of energy cannot be violated, and values> 1 are associated only with the specifics of measuring the SCR when placing the material in a reverberation chamber.
One of the most important concepts of room acoustics is the reverberation time of T. This value refers to the time interval during which the SPL in the room falls by 60 dB after the sound source is turned off. The values of T, as well as the short-circuit breaker, are measured (or calculated) in octave or 1/3 octave bands.
When talking about classification, the wording of normative documents is usually used. It should be noted that standardization organizations usually did not pay much attention to the acoustic performance of studios. Several national and industry standards are known, including those of the former State Television and Radio Broadcasting, as well as several recommendations of the international broadcasting and television organization (OIRT). Now the Technical Committee of the OIRT has ceased to exist, but it should be noted that relatively recently most of the recommendations of the OIRT in the field of acoustics have been revised and, basically, have not lost their relevance.
Since references to these recommendations are very common in modern publications on studio acoustics, it seems justified to use them in this article. So, the following classification of studios is quite generally accepted (the numbers after the letter “C” – the studio indicate the area of the premises in sq. M.). On broadcasting: large (S-1000), medium (S-450), small (S-250) and chamber (S-150) music studios; literary and drama studio (S-100); muffled studio (S-50) and speech announcer’s studio (S-24-36). On television: large (S-450-600), medium (S-300), small (S-150) and announcer program (S-60-80) television studios.
The requirements for the background sound level in the studios are given in the table, where the maximum permissible ultrasound levels in octave bands and in dBA are indicated (the latter only for an indicative estimate). It should be noted that the ultrasonic noise measurements are carried out in an empty studio with closed doors and turned on air conditioning, special lighting and technological equipment. The latter requirements are typical for TV studios and mean that when measuring the sound background, special lighting should be switched on to the standard mode, as well as cameras and monitors placed in the studio. In addition to the specified requirements for the background sound level, the optimal values of the reverberation time are also regulated. These values will be discussed below, differentially for individual types of studios.
Studio Acoustics (Let’s talk about studio acoustics)
Acoustic Design Fundamentals
As will be clear from the rest of the discussion, the basic principles of acoustic studio design are quite simple. Nevertheless, I would like to start this section with one recommendation that applies both to radio house and television center workers and to people who decide to organize a new studio: DO NOT TRY ON YOURSELF TO DESIGN A STUDIO OR HARDWARE. IT IS ALWAYS PERFORMED TO APPLY TO PROFESSIONAL PROFESSIONALS.