Audio Systems: speaker spl, nrc cnrc, reflection coefficients

Question
Hi if a speaker is 90db @1watt/1meter what would it be at 1watt/2meters?

Answer
In open space the spl drops 6db each doubling of the distance.

So at two meters it would drop to 84db.

In the home or car where there are reflections of all kinds the loss is less, depending on the reflection coefficients.  But in several acoustic tests conducted over the years it was found that in normally furnished rooms the drop we close to 3db when distance is doubled.

It is also level and program material dependent to some smaller degree.


Here is a reference:

http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc36983.pdf

Here is a reference for out-of-doors tests:

http://military.technomad.com/products/range-spl-table/

Hope you find this as interesting as I do!

C