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Pro-Audio
General FAQs & FYI
Amplifier RMS
RMS
stands for “Root Mean Square,” which is a fancy mathematical formula
for finding the average amount of power an amplifier can continuously
produce. There is no legal standard for calculating RMS watts for an
amplifier, but our amplifiers are tested by the Underwriter’s
Laboratories (UL) to obtain a true RMS power rating.
“Phantom Power,” “Headroom?” — What are they talking about?
Though Phantom Power might
sound like a superhero’s catch phrase, it isn’t. Phantom power simply
powers the pre-amp of a condenser microphone. Many powered mixers
feature phantom power (MX-300-8) so users won’t need to rely on
additional batteries or power sources. While phantom power functions
ideally on condenser mics, an unbalanced dynamic mic can be damaged.
So, do not turn phantom power on unless a mic that needs it is
connected to the mixer.
Headroom is
a concept that refers to a system’s (amp, mixer, etc.) dynamic range,
or normal working volume. Headroom refers to an average (in decibels)
between the normal volume of a system and the volume at which it starts
to distort. Basically that means if you have a system that sounds good
at +6db and distorts at 18db, that system has headroom of +12db.
Knowing how much headroom your system has will allow you to use it to
its full capacity without damage the system.
Impedance Defined …
In
very simple terms, impedance is the ability to resist electrical power.
Impedance is measured in Ohms. The lower the impedance, the more power
the system will accept *because the resistance is low). Speaker
cabinets are generally rated at 8 Ohms. If you plug them in to each
other the Ohms are cut in half, and become 4 Ohms. This is because two
speakers resist power half as much as one speaker. Power amps are
sometimes rated at 4 Ohms, because it is expected that you will use two
8-Ohm speaker cabinets. A 100-watt (@ 4oms) amp will give each speaker
about 50 watts. But, what if you only plug in only one (8 ohm)
speaker, will it get all 100 watts? No, because the impedance and watts
are related. If the impedance is doubled then the watts are cut in
half, the single speaker will only get 0 watts. Never go below the
minimum impedance of an amplifier. It can cause serious damage to the
amplifier. So, don’t try to plug 8 speakers into one 100-watt amp to
get more power, because it is a trick you can only try once.
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