40
Remember that we are trying to provide two types of voltage limiting:
Long-term rms limiters – to protect against over-powering drivers
(And, for advanced users, to maintain musical balance)
Clip limiters – to prevent power amplifier clipping
Long-term limiters can usually be identified by user-adjustable features like threshold voltage and
attack/decay times. These limiters are strongly recommended for all but the cosiest of domestic set-ups.
Recommended long-term limiter threshold voltages usually limit the loudspeaker drive voltage to 1dB or
more below that required to reach a loudspeaker’s maximum power rating. Threshold voltages
recommendations will depend on your power amplifier’s voltage gain or sensitivity – see the following
tables.
These recommended long-term limiter thresholds must never be exceeded. They may, however, be
reduced to maintain spectral balance (i.e. the appropriate musical level vs frequency) when the system is
being driven on the limit. This is because different loudspeaker sections in a system have different
sensitivities. A mid frequency horn, for instance, may be more efficient (i.e. produce greater spl at its
power limit) than, say, an accompanying bass enclosure. In this example, both sections would be set to
the recommended long-term limiter thresholds initially, and then the mid frequency horn threshold
reduced to maintain musical balance on a listening test with high quality tracks of the appropriate genre.
Clip limiters, such as those provided by the Funktion One XO4 or XO4A, provide additional protection
from short-term peaks and prevent amplifier clipping. Clip limiter threshold voltages are usually set a few
dB above the relevant long-term limiter threshold and help maintain audio quality at high drive level.
Limiter settings for different system impedances
As mentioned in the Section 9.4, XO series limiters control the maximum voltage applied, via the power
amplifier, across the loudspeaker terminals. This means that, as long as you have a good, stiff mains
supply, you can use the same limiter voltage thresholds irrespective of 8, 4 or 2 ohm operation.
However, if your mains supply voltage drops by more than 2 or 3% on load, you may need to reduce the
recommended long-term limiter threshold levels by a dB or so to prevent the power amplifier from
prematurely clipping with the increased mains current demand when driving a 4 or 2 ohm load.
11.1 XO series limiters with 32dB amplifiers
Fig 11.1-1
If you’re using power amplifiers such as the Funktion One E15 (PRC set to 0dB, gain set to 32dB) or the
Funktion One F40Q (pre-set to 32dB), set your loudspeaker management system output limiters as
follows:
www.funktion-one.com © Funktion One Research Limited 2011
To Next Page
Loading...