Testing the speakers
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Important: Always test the speaker before plastering over it and again once plaster is dry.
The following procedure is required as a minimum.
CAUTION:
Without plaster on the surface of the speaker it is highly efficient and will generate very high
sound pressure levels with minimal power input. Take care to protect your ears when testing
at this stage.
Using a multimeter and without the APU protection device connected, check the nominal
impedance (DC resistance) of the speaker at the amplifier end of the speaker cable. Allow
for approx. +10% for cable resistance. The impedance should coincide with the values on
the respective loudspeaker datasheets. If it measures significantly different, check for
breaks or shorts in the cable.
Amina recommends a tone sweep be used at a moderate volume level (0.5 Vrms). Such
a test will quickly highlight any buzzes or rattles that could be caused by loose screws,
cables touching the speaker or loose elements/studs within the wall itself.
If the plasterboard is not securely fastened to the joists this could also create a buzz or a
rattle. Apply more screws if necessary - particularly around the speaker location.
Ensure that the speaker cable is not touching any part of the speaker (or backbox) as
this can lead to buzzes and rattles. To avoid this it is advised to lay the cable behind the
mineral wool or other wadding.
If metal studs are used, ensure the crossover point of the studs are secured together. This
can be achieved by applying drywall screws through the wall surface and through the
metal joists. If they are not secure this may well lead to audible vibrations and rattles.
Play music to check for buzzes and rattles during transient peaks: if these are apparent,
check the above points again. Do not judge the speaker’s tonal balance at this stage. The
overall speaker performance must be clean and distortion free, although at this stage it
will appear biased toward mid and high frequencies. Once plastered over the speaker will
have a fuller, richer sound.
Always connect the APU when testing, except when measuring impedance.
Perform these tests again after the plaster is dry.
If the correct 2mm thick plaster coat has been applied, the speaker face, when tapped with
fingers, will sound slightly more hollow than the surrounding areas of plasterboard. If there
is little or no difference between these two sounds it is almost certain the plaster coat is
too thick. This will compromise the speaker performance.
Full frequency response tests are recommended before and after plastering
Amina have a lot more information available from its technical help desk for those wishing to
measure frequency response curves at different stages of the installation.
Please c44 (0) 1480 354390 for assistance.
Continue on to Section D (page 18 - plastering & decorating)
C
Testing
18
