two room method 34 of july 1964 in carrying out the test two 10 u00d7 14 feet suspended ceilings with communicating 30 inches deep plenum over stc 61 partition were utilized in each case the ceilings were formed of 3 4 u00d7 12 u00d7 12 inches tile the tile of the invention having a fire retardant paper backing according to example 1 and the prior art tile having an aluminum foil backing in each case the tiles were provided with a square edge kerfed and rabbeted and installed in ama standard suspension no icf the tests were carried out by measuring sound transmission to determine the normalized attenuation factor naf in decibels db at frequencies in inervals of one third octave according to the procedure designated as ama l ii 1967 in table ii column a lists the results obtained from testing tiles according to the invention as prepared in example 1 whereas the results shown in column b are of tests carried out on prior art high grade aluminum foil backed tile table ii______________________________________ naff hz a b______________________________________125 32 31160 39 40200 38 36250 32 30315 33 30400 35 33500 37 34630 38 35800 39 371000 40 391250 43 421600 47 472000 53 532500 53 543150 56 574000 59 59______________________________________ from the data above the ceiling sound transmission class stc was determined per astm designation e413 70t as follows the results of the tests as determined in the stc ratings show that both the paper backed tile of the invention a and the prior art aluminum foil.