Leaks#
Two different leak shapes may be modelled:
- Apertures: Circular holes in a building element
- Slits: Long, narrow gaps in a building element such as a gap under a door
Two different calculation routines are available for each leak shape, the Gomperts calculation and the Mechel calculation.
Gompert's theory#
The Gomperts calculation is a relatively simple but robust routine for empty leaks. Gomperts is the default calculation routine when INSUL starts up.
The Gomperts calculation methods are described in the following papers:
- Gomperts, M. C. (1964). The “sound insulation” of circular and slit-shaped apertures. Acta Acustica united with Acustica, 14(1), 1-16.
- Gomperts, M. C., & Kihlman, T. (1967). The sound transmission loss of circular and slit-shaped apertures in walls. Acta Acustica united with Acustica, 18(3), 144-150.
Mechel's theory#
The Mechel calculation can model empty leaks as well as leaks which include some absorptive material in the cavity and/or with one or both ends of the leak sealed with a simple mass. Specifically, Mechel has extended the model for the simpler case of an empty leak, as described by Wilson & Soroka (1965), to include parameters for infill in the leak and sealed ends of the leak.
The Mechel routine is useful for understanding the effect of insulation and sealant on sound reduction performance of the leak.
The Mechel calculation methods are described in:
- Mechel, F. P. (1986). The acoustic sealing of holes and slits in walls. Journal of Sound and Vibration, 111(2), 297–336.
Accuracy#
There is a shortage of reliable measured sound reduction data for leaks. This makes verification of the leak models difficult and increases the expected margin of error in leak calculations.
Note
Leaks calculations are expected to be accurate to ±5 dB.
However, the sound reduction at resonant frequencies is generally under predicted by both calculation routines. That is, the predicted sound reduction at resonant frequencies is much lower than is measured in practice. This is likely to be due to viscous effects of air in the leak cavity and imperfections of the surfaces around a real leak during measurements.
Griffin (2018) provides a more detailed discussion of the expected prediction accuarcy for leaks.