Nilfisk-ALTO 3.4 PC - Manual (Page 12)

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Butterworth type with 6dB, 12dB, 18dB or 24dB per octave slope
Bessel type with 12dB, 18dB or 24dB per octave slope
Linkwitz-Riley type with 12dB, 24dB or 48dB per octave slope
The different filter characteristics can be seen on the PC Editor's graphical display. For each of the filters, the
crossover point can be set between approximately 16Hz and 16kHz. The filter can be bypassed by selecting
. THRU
Using both the High-Pass and Low-Pass filters together creates what is known as a Band-Pass filter, most often
used for optimizing the signal destined for midrange and mid-bass speakers. Also for subwoofers, by using the
High-Pass as a subsonic filter typically in the range 16-30Hz.
Please note that choosing the Linkwitz-Riley 48dB/octave filter will reduce the number of EQ bands available on
that channel.
Which filter type, slope and crossover frequency you should choose will depend on the speakers you are using.
Since it is important to set-up filter points carefully to maximise speaker power handling and avoid damage, this
is usually best left to a professional car audio installer.
Phase Adjustment: When using the Low-Pass filter, it is possible to adjust the phase of the signal in the low band
in 5 degree steps. Combined with the 180 degrees polarity switch, it is possible to adjust the phase in the bass
region through a full 360 degrees.
When making fine adjustments to signal phase in the bass region, bear in mind that phase is related to frequency.
You cannot "phase-align" the entire low-frequency band, but you can align the phase of two woofers at 50Hz, for
example, or whatever frequency you choose. Where dual woofers are causing some cancellation at a frequency
"sweet spot" because of different mounting positions and/or mounting angles and/or vent characteristics, aligning
their phase can substantially improve SPL (sound pressure level) and clarity of bass.
6 CROSSOVER (XOVER)
8 DYNAMIC GAIN CONTROL (CMP/LIM)
Each output channel has its own independent COMPRESSOR/LIMITER, allowing you to determine the amount
of level gain (i.e. increase in volume) above a threshold point that you set. This helps maintain a more consistent
listening level and both protects and extends the performance of your speakers. Input and Output levels and the
amount of gain reduction are displayed on the PC screen in real-time as an aid to system set-up.
Ratio: The value selected here dictates how strongly the level is controlled when it exceeds the Threshold point
you set. The range is 1.1 to 20.0, plus an additional
setting. LIMITER
The numerical values are dB values representing the amount of level increase at the input that will result in a
1dB increase at the output of that channel. So for example, selecting a value of 6.0 will mean that for every 6dB
increase at the input, the output will rise by approximately 1dB.
LIMITER is a very hard compression setting. It prevents the channel output from increasing by more than 1dB
no matter how much the level rises at its input.
There are two things we are trying to achieve when we add compression or limit the signal. Firstly we want to
protect the speakers (and to a lesser degree the power amps) from exceeding their capabilities. They will sound
better (less distortion) and live longer.
The second thing is that we want to be able to free ourselves from having to constantly tweak the volume level.
Threshold: Allows setting of the level above which the Comp/Limiter intervenes (compressing or limiting the
signal). If the music stays below this threshold setting, the level is unchanged.
Atk/Rel: There is a choice of 3 reaction speeds combining attack and release times. You can choose whether
the Comp/Limiter reacts more rapidly or slower than the default
setting when the signal exceeds or NORMAL
drops below the threshold. Set faster for high frequencies (tweeters), slower for bass frequencies. For midrange
or full-range speakers, the
setting will generally be the optimum one. For Subwoofers, the NORMAL SLOW
setting will usually be best.
The MAXIDRIVE3.4 PC is equipped with independent High-Pass and Low-Pass filters on each of the 6 output
channels. For each filter there are 10 filter type/slope options: