Time coherent topology
An important design goal for the PowerPoint which is not
shared with our floor-standing products is placement flexibility.
The requirement that the speaker provide time coherence while
placed in any orientation and at any height necessitates that the
speaker’s drivers be placed symmetrically both horizontally and
vertically and, therefore, that it use either coincident or
D’Appolito driver configuration. The PowerPoint uses
coincident/coaxial mounting of a very high output 1" tweeter and
a high output 61/2" woofer.
Two-way speaker positioned on its side
causes the sound from the drivers to reach
the off-axis listener at different times.
Coincident driver mounting results in
all listeners hearing the sound from
the drivers at the same time.
Wall Reflection Problems
Speakers mounted on a wall with their woofer parallel to the
wall exhibit serious cancellation problems due to wall
reflections. The upper graph below shows this effect. There is a
depression in the response of about 5 dB at 350 Hz followed by
an exaggeration of about 5 dB around 800 Hz. This rather severe
coloration cannot be compensated in the network and results in a
very characteristic “sound” of such speakers.
The PowerPoint uses an unusual cabinet configuration to
eliminate this effect. The woofer is mounted on an angled
surface that is adjacent to the wall which allows the woofer to be
closer than 1/2 wavelength to the wall at frequencies that the
woofer disperses widely and, therefore, to essentially eliminate
the wall reflection as an alteration on the speaker’s output. This
is illustrated in the lower graph above which shows the cabinet
producing only very minor effects. The PowerPoint’s unique
cabinet therefore allows its reproduction to be as uncolored by
the wall surface as any high performance floor standing speaker.
Coverage benefits
Since the PowerPoint’s performance axis is 45°from the
wall rather than the 90°of other on-wall and in-wall speakers,
significant advantages in room coverage and placement
flexibility are provided.
In ceiling applications the advantages are great. Whereas
most speakers direct their energy straight downward and
therefore provide reasonable sound only for listeners near the
10K
Frequency
1K
25
20
15
10
5
0
-5
-10
10020 20K
Amplitude — dB
On-wall cabinet response
Conventional in-wall speakers used in ceiling applications allow coverage for only those
listeners near the speakers.
THIEL PowerPoint speakers provide coverage for listeners in a large area.
speakers, the PowerPoints project their energy at an angle of 45°
and therefore allow coverage anywhere from directly under the
speaker to the other end of the room. Furthermore, whereas most
ceiling-mount speakers can only provide an “above your head”
source of sound, the PowerPoints provide a more pleasing “in
front” or “behind” source for most listeners. Since there is no
wall reflection effect and the speaker provides very even and
wide dispersion due to the coaxial driver mounting, the sound
image projected by the speakers is not from the ceiling but much
more in front of (or behind) listeners who are at least 5 feet
behind the speakers. For these reasons the PowerPoints can
provide extremely good performance as ceiling speakers for left/
center/right applications as well as rear channel applications.
The PowerPoints can also be used in many ways for wall
mount applications. If the room is not extremely wide, they
perform extremely well as left/right speakers when mounted on
the side walls pointing forward toward the listening location. As
rear speakers they can be mounted on the side walls behind the
listeners pointing toward the front of the room. If the listening
location is at the rear of the room, rear channel speakers can be
mounted on the rear wall near the ceiling pointing down.
If an indirect type of sound presentation is desired for the rear
channels, the PowerPoints can be mounted pointing away from
the listening positions. For example, they can be mounted on the
rear or side walls somewhat near the ceiling pointing upward.
THIEL PowerPoint speakers can be mounted on the side walls for left/right usage.
