Any speaker system with multiple and separate drivers is
physically incapable of providing proper phase relationships
from reflections. Quite simply, if there are two separate sources of
sound, phase distortion must occur in any sonic reflection.
cally recombine the sounds
from the multiple drivers
before it leaves the speaker
enclosure. In this way, the high
frequency and low frequency
sounds emanate from a single
opening. Thus, sonic reflections from the ceiling will still
have the same harmonic phase
relationships as the direct line.
Note that this provides phase
consistency rather than phase
accuracy. Phase accuracy is
defined as reproducing sounds
with the precise phase relationships as they were when they
were recorded. Phase consistency is defined as maintaining
the proper phase relationships
regardless of sonic reflections. The
Phase Coherent speakers mentioned
above strive for phase accuracy rather
than phase consistency. The speakers
that are presented here strive for
phase consistency rather than accuracy. (As a first step in research, it is
reasonable to choose one aspect to
determine its relative importance.
Designing a phase consistent and
phase accurate speaker system is not
a simple task.)
PHOTO 2. The tweeter sub-assembly is partially
removed to show the construction method.
The crossover network is seen on the left
mounting member. The sub-assembly is
screwed to the back of the main enclosure.
removed from the speaker enclosure.
The cross-over network ( 2 kHz,
four-pole) can be seen attached to
the left mounting piece. The black
circle to the upper right is the
terminal connector. (The hole behind
the tweeter was used when testing a
longer tweeter.)
The Buried Tweeter
Design
The basic design is shown in
Photo 1 (note that the wide-angle
lens distorts the true shape
somewhat). There are two isolated —
but identical — rectangular enclosures
that each hold a woofer. One woofer
is pointed up and can be seen. The
second is pointing down and cannot
be easily seen. These enclosures are
separated with a 9. 5 inch gap that is
open on three sides (the back is
closed). Centered in this gap is a horn
tweeter. Photo 2 shows the details of
the tweeter assembly as it is partially
The general physical dimensions
are 17. 25” wide, 15 inches deep, and
51. 5 inches tall (excluding feet) with a
weight of over 80 pounds. Continuous
RMS power at any frequency is 400
watts. However, the woofers are rated
at 350 watts each, so the low end
is robust. The frequency response
characteristics cannot be measured
because I have no facilities to do so. I
can only state that the performance is
certainly acceptable and (to my ears)
comparable to other hi-fi speakers I
have heard.
Construction details and design
rational are provided in the sidebar.
There are certainly second-order
details that are not directly addressed
(off-axis sound versus phase),
however, as a first approximation, this
design appears to provide the proper
physical characteristic that all the
PHOTO 1. The buried tweeter speaker
places the tweeter inside the enclosure
so that all of the frequencies emerge
from a single point. This maintains
the phase relationships regardless of
reflections. Note that the speaker grill
cloth is removed.
different frequencies come out of a
single opening.
Performance
The speakers were placed about
seven feet to the right and left of the
listener. The initial results were not significantly different from conventional
speakers. However, there was a subtle
difference in some instruments. The
placement of these seemed to localize inside the head, like headphones.
This effect was not conspicuous.
June 2007 61
