JBL efficiency at 1meter - as opposed to 15' per the spec sheet

[aaronz28]

I have a set of JBL Sovereigns and the spec sheet says efficiency is 82db at 15'

i'm trying to compare them to a restored pair of Quad ESL57 which have a db rating of 87 @1m/1w

so the issue that i'm trying to determine is this...
i believe my quads to be needing rebuild, as they are significantly quieter than the JBLs- i just really have no way of knowing.... they are from 1979 and completely original - so i trust that new power supply boards and reconditioned panels would increase output some - just not sure how much and if its worth the reconditioning price.

any help on the loss of db per foot - would be helpful.

thanks

[Don C]

Doubling the distance would reduce the SPL by 6db. 15 ft is about 4.6 meters, and would reduce the sound pressure level by about 13db compared to the level at 1 meter. So your JBLs should have had about 95 db output at 1w and 1 meter. Roughly. When they were new. If my math is right.