7. Questions and Answers
How long does it take for the source to cool down?
If the source is used at the absolute maximum level > 122 dB, then it will typically run for 2
minutes before protection occurs. But this time could be longer or shorter depending on ambi-
ent temperature and the type of signal. The protection will typically take 12 minutes to recov-
er for a new test.
It is wise to turn the source on only for short periods during range selection and during tests;
Most of the users typically need only a measurement of 1/2 minute at maximum power, in
most cases. Then reposition microphone or source and again 1/2 minute test, reposition, 1/2
minute test, etc. In that way the temperature will not easily become critical.
How to notice the temperature protection?
When the temperature protection becomes active some lower level signal is still allowed to
go to the source. In that case the noise level is far below the normal maximum level, and
even more restricted when the power of the amp goes up. It allows the user knows that the
speaker still works when the temp protection has become active.
How do I recognize a malfunctioning temperature protection?
If the protection fails to switch, the speakers will overhead and some of the speakers will stop
working with fatal damage. They could also start rattling.
If the temperature protection acts too early, the head of the speakers still feels cold or luke-
warm, not hot. Also in this case service is at Qsources is needed.
What can I do when a longer continuous measurement duration is desired?
Do not try to cool the source with water nor with a ventilator pointed directly at the source.
These will cause damage. However, adding external cooling of the source with multiple fans is
an option. It is required to create a very even spread of the flow around the source fans. This
could extend the time up to 20%.
The effective measurement duration depends on the setting and the type of signal that is be-
ing used:
•
very slow sine sweeps (slower than doubling the frequency every 10 seconds, or +- 1
minute for the full frequency range) are not advised because it may cause damage.
•
Although uncommon to use, a slow sine sweep downwards in frequency is not advised
to use at all, because it can induce damage.
•
as white noise (H) has the shortest active time at full power, we did some more tests
on this setting. It shows that a 2 dB lower sound power level can triple the possible
measurement time. We observed here: (the absolute duration may be different for
your source and/or test conditions)
- amp level 60, output 118 dB Lw, 2.5 minutes
- amp level 54, output sound power 117 Lw, 4.5 minutes
- amp level 51, output sound power 116 dB Lw, 7.5 minutes
•
when using our own external signals, it is worthwhile to try best level-time combina-
tion before going on-site for tests
•
for isolation or facade testing applications it is allowed to use multiple Qohm sources
at the same time. (Each with independent random signal) Then a lower setting on the
amplifier can be used, and the measurement time will increase significantly.
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