active subwoofer
Phase
In any sound reinforcement system the correct phase is of fundamental
importance. Two speakers that are carrying the same musical program
interact with one another and this can cause destructive interference.
This means that the sound waves, emitted by two speakers, reaching
a listener's position (or a point in the auditorium) with different phase
(two different points of the sound wave) may combine in the 'wrong
way' and, instead of summing themselves and generating a sound
wave of larger amplitude (a sound pressure 'louder' than that
produced by a single speaker), will generate a lower sound pressure.
In other words, the two sound waves will subtract instead of summing.
The worst condition is when the phase of the two signal is opposite
(a phase shift of 180°: out of phase): this results in a mutual
cancellation of the sound waves. In fact, if the first wave reaches the
listener with the maximum value (positive pressure ) and the second
with the minimum (negative pressure), the resulting sound wave sum
will be of zero value (or at lest a very low value, lower than that
produced by a single speaker).
Among the possible causes of these phase shifts are the listener's
position in respect to the speakers, the type of acoustic loading used
in the speakers, the acoustics of the location, the characteristics of
the cross-over and the electronic processors.
The phase reversal button located in the control panel (6, page 13) is
meant to avoid the most extreme condition (out of phase: 180° phase
shift), and to limit, in most cases, the phase cancellations described
above. This solution is used primarily in simple systems that do not
include a separate PA speaker processor (which, in more complex and
sophisticated systems, will take care of the phase alignment by
adjusting the time delay between the speakers used in different audio
ranges). The most 'classical' application is in the relative phase
correction of a sub woofer and a satellite speaker combination.
In the cross-over region (100/120 Hz in Montarbo systems) the physical
location of subwoofer and satellites (and other factors described
above) may cause a phase shift between the sound waves generated
by the speakers, and this will result in a 'hole' in acoustic response.
In this case, the phase inversion of the subwoofer (by pushing button
8, page 14) will minimize this effect.
It is mandatory to check that the phase is set at the same value on
every subwoofer installed.
A phase inversion in one or more of them (due to the improper setting
of the control), relative to the others, will result in the quasi-complete
cancellation of the sound produced by them.
In standard installations all the subwoofer must have the same phase
setting (all set to 0° or all set to 180°).
Input sensitivity and clipping.
Every amplified speaker system is characterized by a value of input
sensitivity. The sensitivity is defined as the value of the amplifier's input
signal that will result in maximum power output.
An increase in input signal over that threshold will result, not in
increased power, but in a distortion phenomenon called 'clipping'
(output stage saturation).
In this condition, the speaker will operate improperly.
The diaphragm will exceed it's excursion limits, and the voice coil
will overheat beyond it's thermal limits, resulting in overheating
and premature failure.
The active processors will help in avoiding clipping, by reducing the
amplifier gain and thus the input sensitivity, but these protections
may be overridden in very extreme conditions.
What the active processor cannot modify is a signal that is distorted
before getting to the active speaker's input.
The effects of this type of signal are the same as described above.
How to avoid clipping
The simplest way to avoid clipping is to check each level in the
signal's chain. Start from each input channel of the mixer and adjust
the gain control and the equalizer controls so that the PFL meter will
never (or only occasionally) indicate more than 0dB.
In simpler mixers, check that the 'clip' or 'peak' indicator is always off,
or blinks only occasionally. If these levels are exceeded, reduce the mixer
channel's input gain. Once the desired mix is obtained, adjust the
output level so that it never exceeds the active speaker's or the power
amplifier's input sensitivity, as displayed on the master output VU-meter.
The input sensitivity of TANK12SA is +3dBu in stereo (L + R) mode and
+9dBu when just one input (L or R) is connected.
Important !
Attention !
The crossed out wheeled bin symbol that can be found on this product means that the product is covered by the Waste from Electrical and Electronic Equipment Directive.
The symbol is intended to indicate that waste from electrical and electronic equipment must be subject to a selective collection.
For more details on available collection facilities please contact your local government office or the retailer where you purchased this product.
The solid bar underneath indicates that the product has been put on the market after 13th August 2005.
INFORMATION ON PROPER DISPOSAL
Information on Disposal for Users (private households) -
In the European Union
Attention: If you want to dispose of this equipment, please do not use the ordinary dust bin! Used electrical and electronic equipment should not be disposed of via the normal household waste stream but must
be treated separately and in accordance with legislation that requires proper treatment, recovery and recycling of used electrical and electronic equipment.
Following the implementation by member states, private households within the EU states may return their used electrical and electronic equipment to designated collection facilities free of charge*.
In some countries* your local retailer may also take back your old product free of charge if you purchase a similar new one. * Please contact your local authority for further details.
In other Countries outside the EU:
If you wish to dispose of this product, please contact your local authorities and ask for the correct method of disposal.
In Switzerland:
Used electrical or electronic equip-
ment can be returned free of charge to the dealer, even if you don’t purchase a new product. Further collection facilities are listed on the homepage of www.swico.ch or www.sens.ch.
Information on Disposal for Professional Users
-
In the European Union
If the product is used for business purposes and you want to discard it: please contact your Montarbo dealer who will inform you about the take-back of the product. You might be charged for the costs arising
from take-back and recycling. Small products (and small amounts) might be taken back by your local collection facilities.
In Spain:
Please contact the established collection system or your local authority for
takeback of your used products.
In other Countries outside the EU:
please contact your local authorities and ask for the correct method of disposal.
