Strange results. Comparisons of measurements and simulations. When to use Global- and Quick- Estimate or Point-/multipoint- and Grid- Response.
A: When calculating Speech Transmission Index in Odeon you need to type in a total background noise level, which you type into the room setup. Below video shows how you can use sources in Odeon to find this total background noise level.
A: First consider if the reverberation time is the best parameter to use. E.g. DL2 could be a better parameter for a larger room. Simulating reverberation time in a point response calculation in Odeon, corresponds to measuring the reverberation time. Therefore refer to a measuring standard e.g. ISO 3382. Make sure that you use only one Omni-directional source for each calculation job. In large rooms it is important to have sufficient distance between source and receivers, receivers should not be placed in the near field of the source but in the reverberant far field characterizing the room. ISO 3382-2 includes an equation describing the recommended minimum distance between source and receiver:
Where: V - is the Volume in cubic meters; C - is the speed of sound in meter/second and ^T - is the expected reverberation time in seconds.
Furthermore it is a good idea to use a larger number of source receiver pairs in large rooms than the measurements standard demands, to cover the larger area.
If the room consists of many coupled or unregular areas with different properties, it will may not be possible to find one reverberation time that characterizes the room and we advise you to supplement the reverberation time with analyses of STI, SPL, EDT, DL2 and auralisations in different areas.
A: The Strength G (as defined in ISO 3382) is the same as the SPL if:
- One (and only one) omni-directional sound source is turned on, and - the overall gain in the point source editor is set to 31 dB.
In this case the bottom line in the point source editor will display a value of 0 dB for the SPL on axis at 10 m. This is exactly the reference of the Strength, G. So, all calculated SPL results are actually also G values.
However, in all tables and graphs you will only find the symbol SPL, even when the conditions for G are fulfilled.
A: First a general comment on how the reverberation time is calculated from the impulse response. ODEON follows closely the ISO 3382 standard for measurements, i.e. the T30 parameter is found from the slope of a linear regression line that follows the decay curve from -5 dB to -35 dB. In any room the decay curve is a mix of 1-, 2-, and 3-dimensional modes, and generally they have different decays, i.e. the total resulting decay curve is not a straight line, but can be more or less bent. (The 1-dimensional modes have typically the longer reverberation time, and the 3-dimensional modes have the shorter reverberation time).
When the ceiling absorption is high and the walls are reflecting this can give a strong one- and two-dimensional horizontal reverberation. When making the ceiling even more absorbing it means that the one- and two-dimensional sound field gets relatively stronger, and so the reverberation time gets longer. Normally the sound pressure level will decrease. Therefore we recommend that you use auralisation and other acoustical parameters, e.g. STI, SPL and for large rooms DL2 to analyze the acoustics.
A: Make sure source and receiver has mutual distance between them of 0.9 to 1.1 m
A: For calculation of STI with a certain Signal/noise ratio, calculate the SPL in your receiver point (read result in Energy parameters in Single Point Response). Then set the background noise to this level +/- your background noise SNR. Then when you calculate the Point response again, the STI is calculated with the desired background noise.
When making an auralisation with the same S/N – it is more complicated among things because the signals used for auralisation of voice and noise may not have the same ‘energy’ contents and because the playback level (SPL) on the headphone is not a simple matter to adjust to an absolute value. Probably the best way would be to actually measure the SPL from the headphone using a dummyhead or an ear coupler. As In the Auralisation chapter in the Manual “Adjusting levels there is an alternative suggestion.”
Below video shows how you can use sources in Odeon to find this total background noise level and ad the background noise level in an STI calculation.
A: The input you can use for simulating sound transmission in Odeon is the sound reduction Index for a certain type of wall.
Odeon does not take into account flanking transmission.
You can use Odeon for simulating sound pressure level in the receiving room from a well defined source, if the flanking transmission does not play the most important role in your construction, compared to e.g. the room acoustic complexity of the rooms. If you know the influence of the flanking transmission you can manually include it in the sound reduction Index for the wall.
It is important to check the reflection density in the receiver room. (You do that from a point response / reflection density). It should be more than 50 if you want good results. If it is less you should increase the number of rays.
To make simulations according to measurement standard, remember to use the required amount of sources and receivers.
Video describing how to simulate sound transmission.
A: The Quick Estimate should be used in connection with a rough distribution of materials. The Global Estimate ca be used for regular rooms, to estimate the reverberation time for selected source positions to give a fast average over the entire volume.
Normally you need to simulate the reverberation time for receivers in a room like in a measurement. To simulate reverberation time for a range of receiver positions you should use the job list and calculate point responses to simulate a measurement most realistically. generate the reverberation time for certain positions with Point/Multi point response. If the room is an auditorium with an audience, the grid response receivers should be used.
A: This is probably due to low diffusion of surfaces in the room, and 1-dimentional reflection paths. The decay curve will not be linear but will have a steeper curve in the beginning and a less steep curve for the later reflections. With nonlinearity in the decay curve a larger number of reflections is necessary to simulate the reverberation time. also coupled rooms with non linear decay curves should have a large number of rays in the room setup. These are good examples of a volume, where a simple Sabine calculation will not be enough to calculate reverberation time.
It can be a help in cases with nonlinear decays to look at the Global Estimate, to analyze how many rays are necessary to define the decay curve (The Global Estimate should a least go down to – 35 dB at all frequencies).
A: T20, T10 and several extra parameters will be available from version 11.
The reverberation Time T30 and EDT was selected from the beginning as these two reverberation times is enough to know the room acoustics. However, T20 and T30 are both calculated in the Global Estimate. and from version 11 it will be possible to calculate T20 and many other acoustical parameters in point responses as well.
Reverberation time, (T30) is derived from -5 to -35 dB of the backwards Integrated energy curve according to FDIS 3382-1
See below how you can analyze the decay curves from a point response in the Auditorium or Combined edition. The point response shows all curves in the 8 octave bands, to investigate decays curves in a single octave band further press A. By zooming in on the backwards integrated energy curve (E, Integrated) you can analyze different steps of the decay e.g. to see how calculations of reverberation time based on different intervals of the decay curve give different results.
A: Check 3DopenGL and ray tracing if the point-, line- or surface- sources are inside the room and transmitting most of the sound energy into the room. Make also a 3DopenGL check of the receivers. If using a grid map it is possible to exclude receivers outside of the room from being displayed in 3DGrid when the chosen parameter is over or under a selected range. This is set in the Options/Program setup/Grid colours.
A: Yes please refer to this page .