Originally Posted by localhost127
Originally Posted by Phillips751
Actually it use to be very "consistent".
are you measuring rt60 (RTxx) with an omni-source (eg, dodec) and well past Dc?
Of course not.
What we have is a case of by the mere fact that the tool has a 'button' that says "RT60", that by 'pressing it' you obtain an 'answer'. And as such it must be valid - regardless of whether the required pre-requisite criteria for such a calculation are satisfied or not.
The fact that a tool is a bit easier to set up by virtue that the cables are included and pre-configured does not release the operator from the requirement that they understand what they are doing.
The use of the RTxx calculations assume the existence of a reverberant soundfield.
In a reverberant or diffuse soundfield, the time average of the mean square sound pressure is everywhere the same. The flow of energy in ALL directions is equally probable, which requires an enclosed space with boundaries featuring essentially no component of acoustical absorption. This means that at no point in the homogenous soundfield can one determine or resolve any energy measured into a path, as each path at any point in the room is equally probable with every other path. Therefore there is essentially no net energy flow..
In a semi-reverberant field, sound energy is both reflected and absorbed. Energy flows in more than one direction. Much of the energy may be from a diffuse field, but there are substantial components of the field that have a definable direction of propagation from the noise source. This semi-reverberant sound field is what is encountered in the vast MAJORITY of all architectural acoustic environments. And small acoustical spaces may be supremely challenged to establish any appreciable reverberant /diffuse element, instead being characterized by locally variable modal and specular sound fields...hence invalidating the use of any statistical calculations which necessarily assume the existence of a homogeneous reverberant soundfield.
The particular measurement platform does not determine the suitability of a particular measurement. The conditions existent in the acoustical space determine what measurements and/or calculations are appropriate. Hence it is incumbent upon the operator to learn about the factors that contribute to the proper measurement of actual conditions within an acoustical space. Just because a tool has a button labeled "RT60" does NOT render the calculation, nor a methodology for acquiring such a calculation (eg. a flawed directional stimulus signal source and a mic NOT placed past the critical distance where the gain of the direct soundfield equals that of the reverberant soundfield - which is rather difficult to do in an acoustical space that is insufficiently large to support a statistical reverberant soundfield at that frequency!)
The RTxx calculations are reserved for large acoustical spaces that support a reverberant soundfield. they are not the proper calculation for small acoustical spaces that do not satisfy the required pre-requisite acoustical behavior for the statistical models and subsequent calculations to apply.
Instead, in a small acoustical space, you are necessarily limited to evaluating the modally variant LF soundfield with the waterfall and the specularly variable soundfield with tools including the ETC by the behavior of the soundfields that actually exist - and NOT the buttons that are present on a tool.Edited by dragonfyr - 7/30/12 at 9:49am