Very special question - bit of physics | John Sayers’ Recording Studio Design Forum archive

It is well known, that calculating the axial mode frequencies for rooms with parallel walls involves simple mathematics (calculating the standing waves frequencies and the corresponding harmonics for a given distance between 2 parallel walls). Sure, from a rigorous point of view many considerations are taken into account (for example: not taking into account the tangential and oblique modes, …) when doing these “simple” calculations, the results are still very acceptable. BUT How do you calculate the “axial” mode frequencies for rooms with splayed walls? I know splayed walls will help in reducing flutter echo, and they will help to “break up” coincident frequencies (degeneracies), too, but to what values are the modal frequencies shifted? Stefan.

I've seen a recent paper by the good folks at RPG concerning room modes in non-rectagular rooms and I think there is some research floating about regarding the extreme complexity in calculating room modes when using angled boundary walls and such. Some people have opined that using measurements in such rooms is more likely to lead to proper treatment than just estimating anyways. when you think about room design though I think you have to take into account whether the room might be rectagular in nature with angled wall treatments to optimize it, or the room may be constructed so the room boundaries are constructed on angles to achieve more optimal use of floor space (for example) and to reduce flutter, reflection zone positioning, etc.... I think in the case of a "treated room" within a rectangular room, the rectangular room modes should still be viewed as the baseline for the design (understanding the treatments will alter the modes substantially). whereas the purely angled walls design approach means investing in some software (slide rule? :? ) capable of making the calculations correctly; estimating it by selecting some "average" value and using the rectagular room calculations; or designing the room using best practices (for a given set of requirements...) to alleviate a given set of common problems (like flutter, reflection zone, reverberation time, etc.) and then measuring and treating as needed. I guess it also really depends on how far you want to go in the design phase versus available budget, time, and resources. when I'm looking at a design I try to take into account various room mode aspects of the dimensions, materials, isolation requirements, and then use (a series of averaged value rectangular) room mode calculations as a means (trying) to identify which modes may be most troublesome. this way I can think about what frequencies may need more control and how broad a range of control may be needed. In general, I think final treatment should really be done by measuring and treating rather than purely as a design exercise (assuming the design allows for some post-construction treatments/adjustments...)