SPL only given at 0.5m

[kipman725]

Hi I have some speakers that instead of giving the SPL/1watt/1meter they give SPL/1watt/0.5m (88dB) (Presumably to make them apear better than they actualy are). I am also running 9 of them in 3 parallel strings connected in series. I think this should give a 9.6dB boost in spl (as wiring in series only increases power handeling). Unsure of how to convert the 0.5m into the more convetional 1m though.

[kipman725]

seem to have solved my own probelm:
http://www.medc.com/catalog/pdf/NT%20TECH%20BKT.pdf

so my array should be:
88dB - 6dB (distance compensation)
+ 9.6dB (3 in parallel)
91.7 db/1watt/1meter

[Saturnus]

Slightly off. Halving distance doubles output, so it's -3dB when you convert ½m measurements to 1m measurements.

[kipman725]

this is not what the document says:

The decrease in sound pressure level compared with the SPL at a
distance of 1 metre obeys an inverse square law and can be calculated
using the following formula:
dB = 20 log Dx where Dx = distance at which the change in
o/p level is being calculated
A Guide to the Selection of Loudspeakers
for PA/VA & Background Music Systems
II
The basic rule is that each time the distance is doubled, the sound
level will decrease by 6 dB. For example, if the output level of a
loudspeaker is 90 dB at 1 metre, at 2 metres it will be 84 dB, 4 metres
78 dB etc.


are you thinking of sound power? which would decrease by 3db.