until the source internal protection activates. But not every type of signal allows a maximum
level setting on the amplifier.
For example, not exhaustive, the following signals could lead to damage when applied with
maximum level, before the source internal protection activates:
–
pulsed low frequency random or sine below 500 Hz, over-stroke
–
sine signals below 300 Hz, over-stroke
–
random noise or sine signals above 20000 Hz, local overheating
Over stroke; cone displacements above 8 mm peak-to-peak are audible as a sharp clicking
sound.
When using another type of amplifier, damage is possible if the peak voltage exceeds 70 V
ssph, even with normal test signals like sine, chirps, random.
The user should be careful not to exceed the short term power and prevent overstroke.
Could we use any power amplifier and signal source to drive a Qohm sound source?
In principle, any audio or public address or measurement amplifier for loads between 2 and 8
Ohm impedance can be used. And in principle any type of signal; random, music, sines, chirps
etc can be used.
Nevertheless, there are some risks or limitations when not using a Qam amplifier;
–
An amplifier with rated output power of more than 1000 W at 4 Ohm load can
potentially damage a Qohm sound source. To be more precise, if the peak voltage
level exceeds 80 Volt sspk (single sided peak) thee Qohm can damage. This has not
happened so far at customers, to our knowledge, because this is rare and very high
power level for power amplifiers. Especially for portable material. But it is possible.
–
Sine signals from external sources, applied at the maximum level of 80 Volt sspk will
quickly heat up the Qohm and trigger the internal protection.
–
Clicks or short impulsive signals at 80 Volt sspk could potentially lead to mechanical
damage of the drivers. But these are not normally used for measurements.
–
Amplifiers proposed by other measurement equipment manufacturers for
dodecahedron sound sources tend to have actual output power and voltage levels
which are significantly lower than the Qam amplifier. This means that even with a
smart choice of signals the maximum specification of the Qohm is not reached. But:
1. The sensitivity of the Qohm is as high or higher than other dodecahdron
currently on the market
2. Even with significantly lower rated electric power (like 250 Watt or 500
Watt) the output of the Qohm can still be above 120 dB LW, pink noise 50
5000 Hz.
–
Some amplifiers, proposed by other measurement equipment manufactorers for do-
decahedron sources, actually connect two or more channels to the dodecahedron. The
Qohm uses one high power channel. So, in such a case only one channel should be
connected to the input speakon socket of the Qohm, and only the output power on
this one channel will contribute. Leaving the other channels unused ( open) will not
harm a normal amplifier.
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