I am putting up a calculator for speaker requirements on my web site, for speaker sensitivity, amplifier power and sound pressure level estimations.
Using information about room and speaker and speaker placement, the spl is estimated by summing the direct sound and the reverberant field.
Direct sound is easy, but I have not been able to find consistent information for the reverberant field calculation, valid in a small room with relatively much acoustic damping.
I have found different fomulas suggested, that will give different results.
So far, this is pretty much what I have now:
- Rx, the critical distance, is where the revb spl equals the direct.
- At least 2 formulas:
Rx=0.141*sqrt(G*A'), where A' is the room constant = f(V, T60, abs area), G=source directivity.
Rx=0.057*sqrt(G*V/T60), where G=source dir.
- Revb spl can then be calculated by using Rx.
- A correction factor for the revb spl can compensate approximately for the fact that the revb sound field is not constant in a small damped room, it will fall as a function of distance from the source.
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If someone have an idea, or even some good measurements of spl vs. distance from source in a room, that could be helpful.
If the relationship between room data (V and T60) and spl as a function of distance from the source can be established, then it will be possible to make a sufficiently accurate correction.
This does not need to be very accurate, that is also impossible with reasonable amount of data entered into the model (i.e. room dimensions and T60), but it can still be sufficient to give a good estimate.
All rooms considered as useable here will fall into the category of small and damped.
In such rooms the direct sound will be large compared to the reverberant field, in most cases larger than the revb, so that an error in estimated revb spl will not have a proportional impact on the total estimated spl.