Nandino Boulevard Lexington, Kentucky 40511 USA
Telephone: 859-254-9427 Fax: 859-254-0075 E-mail: mail@thielaudio.com
Web: www.thielaudio.com
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Technical Information
THIEL CS.5
Coherent Source
®
Loudspeaker
This paper describes some of the technical performance aspects, design
considerations and features of the THIEL model CS.5 loudspeaker system. It is
intended to supply information for those who are interested in such matters. It is not
intended to imply that good measured technical performance is sufficient to
guarantee good sonic performance. THIEL DESIGN PHILOSOPHY
All THIEL speakers are intended to be precision instruments that very accurately translate electronic information into musical sound. All
our efforts have been directed toward achieving extremely faithful translation of all tonal, spatial, transient and dynamic information
supplied by the amplifier. THIEL speakers are not intended to mask or mitigate shortcomings of the recording or other components in the
music playback system. We believe this approach is the only way to provide the potential of experiencing all the subtle aspects that help
make reproduced music a most enjoyable human experience.
Performance goals
Since quality of musical performance is a very complex issue it is helpful to objectively identify the aspects involved. We believe
musical performance can be described, with not much oversimplification, as performance in four areas.
Tonal fidelity
includes overall octave-to-octave balance, the fidelity of timbres, absence of vowel-like colorations, and bass extension.
Spatial fidelity
includes how wide and deep the performing space seems, how convincingly instruments are placed from the center to
beyond the speakers laterally, how realistic the depth perspective is, how little the speakers positions seem to be the source of the sound,
and how large the listening area is.
Transient fidelity
includes how clearly and cleanly musically subtle lowlevel information is reproduced and how convincingly
realistic is the reproduction of the initial or attack portions of sounds.
Dynamic fidelity
includes how well the speaker maintains the contrasts between loud and soft and how unstrained and effortless is the
reproduction of loud passages.
Fundamental design considerations
In our opinion, natural spatial reproduction requires creating a realistic sound field within the listening room by mimicking the properties
of natural sound sources. These properties include wide area radiation and the absence of out-of-phase energy. To meet these requirements
all THIEL speakers employ dynamic drivers. Dynamic drivers have the advantages of providing a point source radiation pattern with good
dispersion of sound over a wide area, great dynamic capability, good bass capability and a lack of rearward out-of-phase energy. Another
advantage of dynamic drivers is that their small size allows the multiple drivers to be arranged in one vertical line. This alignment avoids the
problem of line source designs which must place their different drivers side-by-side, causing the distance from each driver to the listener to
change with different listener positions.
The major potential disadvantages of dynamic speakers are diaphragm resonances (cone breakup), cabinet resonances and cabinet
diffraction. Also, they share with other types of speakers the potential problems of time and phase errors introduced by multiple drivers and
their crossovers. None of these problems is a fundamental limit and all can be minimized or eliminated by thorough and innovative
engineering, allowing the possibility of a speaker system without significant fundamental limitations.
Technical requirements
The task of engineering a speaker system requires the translation of the musical performance goals into technical goals. Although there
are also many minor design considerations, the following are what we believe to be the major technical requirements that contribute to each
of the musical goals.
Tonal fidelity
Accurate frequency response so as not to over or under emphasize any portion of the sound spectrum
Absence of resonances in the drivers or cabinet so as not to introduce tonal colorations
Spatial fidelity
Point-source, unipolar radiation
Time response accuracy to preserve natural spatial cues
Lack of cabinet diffraction
Even dispersion of energy of all frequencies over a wide area
Transient fidelity
Phase coherence to provide realistic reproduction of attack transients
Very low energy storage to provide clarity of musical detail
Dynamic fidelity
High output capability
Low distortion
Design goals
The technical requirements result in the following major technical design goals:
1. Very uniform frequency response
2. Time response accuracy
3. Phase response accuracy
4. Low energy storage
5. Low distortion
1 THIEL CS.5 SPECIFICATIONS
Bandwidth (-3dB)
Amplitude response
Phase response
Sensitivity
Impedance
Recommended Power
Size (W x D x H)
Weight
Driver Complement:
Woofer
6
1
/
2
" (5" radiating area) with treated paper cone, cast frame,
1" diameter voice coil. Underhung coil (short coil/long gap) motor
system. Linear travel
1
/
4
" pk-pk. Two magnets with total weight of
1.4 lb. Copper pole sleeve.
Tweeter
1" aluminum dome with short coil, ferrofluid, vented pole to rear
chamber, reinforced chamber cup.
55Hz - 20KHz
55Hz - 20KHz
±
3dB
minimum
±
10
°
87dB @ 2.8v-1m
4 , 3.2 minimum
30-150 watts
8 x 11 x 31 inches
35 pounds 2
DESIGN AND ENGINEERING FEATURES
FREQUENCY RESPONSE
Since frequency response errors are a measure of tonal imbalances which alter music's tonal characteristics, we believe that accurate
frequency response is an absolute requirement for a truly good speaker. In our opinion the human ear is sensitive enough to the balance
between component harmonics of musical sounds to detect frequency balance errors of as little as 0.2dB if they are over a range of an
octave or more. Therefore, even more important than the maximum amount of response error at any frequency is the octave averaged,
octave-to-octave balance which has a very high correlation with perceived tonal balance. Our design goal for the CS.5 was to achieve
octave-averaged response within
±
1dB from 100Hz up to 10KHz with even tighter tolerance within the midrange from 200Hz to 3KHz.
Therefore, any deviation more than these limits is confined to only a narrow frequency range and therefore will have less effect on the
perceived balance.
Achieving these goals requires the use of drivers with very uniform responses, drivers with high consistency (so that few units need be
rejected), reduction of usual cabinet diffraction which causes response errors, and an unusual degree of compensation of driver response
anomalies in the electrical network.
Driver response
The major cause of nonuniform driver response is diaphragm resonances. These resonances are also the major energy storage
mechanism. All THIEL tweeter diaphragms are constructed of aluminum which provides much higher stiffness and compressive strength
than conventional diaphragm materials. The primary benefit is that the lowest internal resonance is much higher than with other materials.
Below this lowest resonance there are no resonances to store energy and cause ringing. An additional benefit is that the aluminums much
higher compressive strength results in almost all the energy of a transient attack being transferred to sonic output rather than being
absorbed in compression of the diaphragm material. In the tweeters the lowest diaphragm resonance occurs above the range of hearing at
26KHz. Therefore, there are no resonances in the audible range to cause energy storage or response irregularities.
Diffraction
Diffraction causes frequency response and time response errors and therefore a reduction in
tonal, spatial, and transient fidelity. Diffraction occurs when some of the energy radiated by the
drivers is reradiated at a later time from cabinet edges or other sudden change of environment. For
musical signals that remain constant for a few milliseconds, diffraction causes, by constructive and
destructive interference, an excess of energy to the listener at some frequencies and a deficient
amount of energy to the listener at other frequencies. Diffraction also causes all transient signals to
be radiated to the listener a second (and possibly a third) time, smearing transient impact and
distorting spatial cues.
To reduce diffraction the CS.5 employs a grille board that fits around (rather than on) the baffle
and one that is curved at the edges so energy radiated along the baffle can continue into the room
without encountering abrupt cabinet edges.
Off-axis response
In addition to on-axis response accuracy, it is also important that the off-axis response be even,
without major dips, for two reasons. First, listeners may be located far from the optimum position
and therefore will be hearing the speaker as it performs off-axis. Secondly, off-axis response is an
indication of the uniformity of the speakers total energy response. Since the total energy (in all
directions) radiated from the loudspeaker determines the amount of reverberant energy in the room,
it is important that the off-axis response be uniform to
avoid changes in perceived character and spatiality at
different frequencies.
Most speakers with high-slope crossover systems cannot maintain uniform off-axis
response because the dispersion of a driver narrows as frequency increases toward the
crossover frequency. Above the crossover frequency the radiation of the next driver is again
wide since it is operating at the low end of its range. First-order crossover systems hav