A Series Active Monitor Speakers
E1/2 Welcome! Date printed: 29.02.00
Helmholtz resonator A cavity with an external opening is referred to as Helmoltz resonator. If a
driven diaphragm is added to this system, the well-known “bass reflex” en-
closure is obtained, having the advantage of significantly more energy gain
in the bass reflex resonance area. The transmission range can thus be ex-
panded toward the low end without overloading the speaker.
In combination with the negative output impedance, it is possible to consider
this arrangement strictly as a Helmholtz resonator again, being easily com-
pensated for the bass reflex drawbacks by electronic means. Such a combi-
nation achieves clean bass reproduction down to frequencies amazingly low
for the given enclosure size.
Group-delay-compensated filters The evaluation of a speaker cannot simply be based on one single point of
the room, but the entire radiation behavior must be considered.
The division of the frequency spectrum, unfortunately made necessary by
various reasons such as Doppler effect, partial oscillations of the dia-
phragms, etc., creates additional problems.
If the individual speaker systems are arranged vertically, the horizontal ra-
diation characteristic depends almost exclusively on the quality of the chas-
sis. In the vertical direction, however, a bundled aggregate signal is ob-
tained. If the partial signals are not in phase with each other – either due to
different acoustic propagation times or phase rotation in the crossover – the
radiation lobe changes its direction in the transition zones. If the ear is not
accurately positioned, dips or even peaks in the frequency response can
strongly influence the sound impression and the localization of the sound
source.
Delay compensation The distance from the point of origin of the sound to the speaker surface
varies because the individual speaker systems have different mounting
depth. With wide-band signals, this normally leads to dispersion (i.e. the in-
dividual frequency components arrive at the listening position at different
times).
In the Studer A series active speakers, these differences in the transit time of
the audio signals are compensated by analog delay circuits maintaining the
necessary delay up to frequencies above the audio range.
Time delay compensation, negative output impedance of the power amplifi-
ers, and a sophisticated crossover design offering steep filter characteristics
and phase linearity, all together leads to the excellent impulse behavior of
the A series and to their greatly improved reproduction of transient music
signals.
Ideally suited for surround sound A unique feature of the A-Series studio monitors is that different speaker
types can be mixed for setting up a surround system. The simple reason for
this is the group-delay compensation.
Usually, combining different speaker types with uncompensated group-delay
can cause quite unpleasant phase-domain effects, resulting in sound sources
being placed in wrong positions. Parts of a signal panned to the right side
could then be localized behind the listener or in other undesired positions.
The different A-Series studio monitors feature identical phase response over
the whole frequency spectrum and therefore give an accurate sound source
positioning.
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