ESA vs independence of triangles
The times we live in are not the times of a speaker revolution. The foundations of most of the solutions
currently in use were invented many years ago and today are being improved, at the most. In the
1960s and 70s, so fruitful both for the music and music playing technology, there were tens of fresh
ideas, including on original speaker sets - unique not for their visual but structural design. Today, the
proportions are reversed - the main emphasis is placed on design as this is what the customers,
supposedly increasingly often bullied by women they live with, whatever it should mean, expect. Also
the quality of sound, however, with small steps forward that have been made for so many years has
undoubtedly reached a higher level and became available for an affordable price. Even so, for
professionals it is obvious that presenting an increasingly long list of "proprietary solutions" as
inimitable, unique for a specific company and guaranteeing quality improvement impossible in any
other equipment, is dictated solely by marketing objectives - and possible owing to the nonprofessional customers' ignorance of the matter. Even such obvious characteristics of a good
loudspeaker as properly aligned crossover network and a robust cabinet are sometimes being pointed
out to customers as warranting greatest admiration.
ESA does not contend with specialists in devising marketing baits. For the fifteen years of our
company's existence we have been dealing nearly exclusively with designing speaker sets. We have
been using conventional, proven and effective formulas. They require, however, not only using the
best transducers but also their correct matching, mating organization, coordination with all structural
features, with proportional consideration of primary and secondary issues. Nor should we accept the
familiar schemes as absolutely binding. Any innovation, being a component of technological progress,
is a successful attempt of breaking prior conventions. With time these innovations become standard
solutions which, however, only await further changes?
The cabinet - its type, size, shape, all inner and outer measurements, enforcements, alignment
method, attenuation; the electrical system - type of filters, grade of components, assembly method,
cabling; finally, the transducers themselves? this is a very complex system of communicating vessels,
closely related phenomena, a conglomerate of mechanical, magnetic, electrical, acoustic components.
The secret of the ability to construct speaker sets consists in becoming acquainted with parameters of
individual system components and relationships between them, as well as in reading their actual
meaning. Every product, even declared to be "uncompromising", is made within a specific budget and
reasonable limits. In practice, then, compromise is necessary and the whole trick is to render it
accurately. Day-dreaming leads to uncompromising solutions, existing only in the imagination and
promises of the catalogues. Understanding the facts and costs leads to optimum solutions, feasible in
the real world.
The latest ESA constructions feature not only excellent Danish transducers and crossover network
components, more than averagely robust and perfectly finished cabinets, but first and foremost they
make maximum use of the components for final acoustic and visual effect. Following the track of
relationships between individual features and components of a speaker system, we have obtained a
really new, proprietary solution we have abbreviated to PPW - move, tilt, align (from Polish: Przesuń,
Pochyl, Wyrównaj). We move the speakers, tilt the front wall and align the characteristics.
Linearity of processing characteristics is not the aim as such and is not the only parameter that the
design engineer must bear in mind. If, however, natural sound, that is neutral processing, is desired
then - undisputedly - good linearity of characteristics may be nothing but helpful. The characteristics
usually presented - measured on the selected principal axis or possibly on a few other directions show only a fragment of the problem of the general tonal equilibrium. Speaker sets radiate acoustic
waves not only directly towards the listener but in all directions, however this radiation is far from
regular - the acoustic pressure changes both with the distance of the listener from the principal axis of
radiation as well as with the frequency. What reaches the listener is not only the wave directly from the
speakers (though it has the greatest share) but also waves directed by the speaker in other directions
and then reflected from various surfaces in the listening room. These surfaces are in various distances
from the speaker and have various absorption characteristics, which means they attenuate various
frequencies in various ways. The arrangement deciding about the tonal characteristics of the sound
reaching the listener becomes even more complex, and simultaneously unique - each room has a
different acoustics; moreover, in various sites within one room the same acoustics will yield different
effects. Even if we were able to deliver each processing characteristics by free determination of the
acoustic pressure value on any axis and at any frequency, it is impossible to clearly define
theoretically what these characteristics should be like?
Hence the dramatic variety of concepts - speakers and speaker sets radiating in a very specific
direction (horn loudspeaker) or in all directions (roughly, of course), or bidirectionally (bipolars and
dipolars); narrow front walls allow greater dispersion (however at the cost of effectiveness measured
on the principal axis, as a large proportion of the energy "runs away" to the sides and to the back),
wider act just the opposite? In spite of all these conceptual divergences, or maybe due to them, most
design engineers does not question the fact that the only relatively universal test of a speaker set?s
tonal equilibrium is to measure the processing characteristics on the principal axis. This is the image of
sound running directly from the speaker to the listener. If we are unable to determine the invariable
principles of interaction between the speaker set and the room, we must completely disregard those
phenomena and completely eliminate their effect, i.e. any reflection, to standardize the measurement
method. During measurement these are eliminated by a dead room or an impulse system, which
closes the measurement time before reflected waves make their way to the microphone. Obviously,
these conditions are only a convention (and not a perfect one ? sound in a dead room, though
distinguished by a unique precision of localizing apparent sound sources, does not seem natural at all
because a complete lack of reflections is not characteristic of natural acoustic environment in which
music is created), but they are the only reasonable conditions for comparisons between different
speaker sets, allowing to establish whether at least on the principal axis the loudspeaker is operating
correctly.
In each room there is, however, one common factor strongly affecting the sound as it affects the
pressure course in the listening site. This is an effect which can be predicted and taken into account in
designing a speaker set. This is never done because measurements disregarding any reflections as
presupposedly random (taking into account completely different rooms) also reject the effect of such
reflections which occur in an easily predictable way. The effect of waves reflected by the floor!
Freestanding loudspeakers, also called floorstanding loudspeakers, stand on the floor as their name
indicates. Other surfaces - the ceiling, walls, windows, furniture - can be located at a greater or smaller
distance but the floor is always exactly where the loudspeaker set is standing. And where the listener
is sitting. In the case of stand mounted speaker sets, this issue is only slightly uncertain - the stands
are usually 60 cm high and thus set the speaker?s distance from the floor. Unfortunately, our concept
of correcting the errors caused by reflections from the floor is only practicable in floorstanding devices.
Why do we call them ?errors?, anyway? Reflections are after all supposed to have a positive effect on
the naturalness of sound? That is correct, but does not apply to reflections from surfaces located so
close to the source. Waves reflected from the floor will be delayed in the listening site compared to the
direct waves to a too little degree to be able to make the sound ?spatialized?, but enough to be able to
distort the location of apparent sound sources, and reaching their target in a phase offset against the
direct wave phase (they have a longer way to cover) they will interfere with it in the listening site,
causing amplification of the acoustic pressure at some frequencies and damping at other.
We cannot find what frequencies these will be without establishing the distance between the speaker
and the listening site. The speaker and the listening site define the location of the point on the floor in
which reflection reaching the listener will occur (reflections will obviously occur on the entire floor but
most of the reflected waves will by-pass the listening site), and then these three points make up a
triangle in which the direct and reflected waves compete. When the listening site is moved, the triangle
changes its shape, the ratio of its side lengths, and thus also phase relations. Even so, at a specific
height - let us assume 80 cm - of the speaker (midwoofer, as this frequency range will be mostly
reflected from the floor and distorted) and the height of the listener's ears (let us assume 80 cm as
well) it can be found that moving of the listening site from 2 to 5 meter distance changes the difference
in the distance to cover for the reflected and direct waves from 56 cm to 26 cm approximately. This
results in damping of the wave, half of which is of such length exactly. With approx. 2-meter distance
between the speaker and the listener, damping occurs at approx. 300Hz, and with 5-meter distance at
approx. 650Hz. There is no hope that any speaker will radiate waves of such length directionally, i.e.
only towards the listening site (it is anyway easy to check how small is the angle to the principal axis of
the direction leading to reflection from the floor, running further to the listening site - on the distance of
5 meters between the speaker and the listener it will be as small as 30°). Neither are there any
chances for attenuating such waves even with a very thick carpet... We have made attempts, as this is
one of procedures necessary for impulse system measurements with time frame extended at least as
much as to be able to measure the 200-300Hz band; to markedly attenuate reflections from the floor,
the floor needs to be covered with an attenuating structure several dozen centimeters thick.
fala bezpośrednia - direct wave
fala odbita - reflected wave
How can it be helped In fact, with one midwoofer, i.e. in two-way structures - floorstanding or stand
mounted - it cannot be helped. Purely theoretically, if we brought the midwoofer closer to the floor, the
difference in distances for the direct and the reflected wave would be very small and would shift the
phase problems to higher frequencies (which would also be easier to attenuate). Such a solution is not
considered, though, as the midwoofer must be located directly by the tweeter, and the medium and
high frequencies should be radiated from the height of approx. 1 meter (equivalent to the height of the
listener's ears - to obtain the impression of a natural location of the sound sources). Only the bass due to its radiation all around and a very large proportion of reflected waves making source location
impossible - may be radiated by any part of the speaker set (we make use of this phenomenon in the
subwoofers). Certainly, many reservations and conditions required for correct operation of a woofer
moved away from the midrange&tweeters can be presented here, but we only note the possibility of
moving the woofer away from the other speakers. This way in three-way systems a very elegant
solution is theoretically possible, a solution which would largely reduce the above-described problem
of waves reflected from the floor (those reaching the listener).
If we take into account the conditions of the previous example ? with listening point at the height of 80
cm, in the distance from the speaker set varying from 2 to 5 meters, but with the speaker at the height
of 20 cm, then we can calculate that the waves running directly and those reflected from the floor will
be in the opposite phase in the frequency range from 1kHz to 3kHz approximately. This is a range
clearly above the frequencies usually processed by woofers (and also radiated in a much more
directional way). If, then, in a structure with a midrange speaker at the height of 80 cm, and thus
potentially capable of causing problems in the range of 300-650Hz, a crossover frequency would be
set between 650Hz and 1kHz we would prevent the distortions resulting from reflections from the floor.
Such a high crossover frequency, however, especially with such a marked shift, is not good for other
reasons so this plan is rather out of the question. It is always worth to take these phenomena into
account and both move the woofer closer to the floor and not enforce too low crossover frequency.
Even if it is not in the range ideal for the purpose of solving the reflection problem, even a close
neighbourhood will bring benefits. After all a woofer affects the characteristics also slightly above the
crossover frequency and may, at least partly, compensate for the adverse phenomena caused by the
midrange speaker.
This is why in the three-way Credo 4 the woofer section is moved away from the midrange speaker,
and the crossover frequency is set not as low as the large resistance of the latter would allow (the
maximum amplitude of which is more resembling of a midwoofer and not a midrange speaker). Also,
always the smaller the power supplied to the midrange speaker, the smaller the resulting compression
(created because of the coil temperature increase). Woofers are much better prepared to operate not
only with high amplitudes but also with greater heat doses (which do not decrease so fast as the
amplitude with the frequency increase). Woofer coils are not only longer (allowing a greater amplitude)
but also larger in diameter, so have a much larger area resulting in much smaller temperature increase
as a result of a specific heat power dose. To culminate this issue we should add that the woofers used
have coils with titanium carcasses (hence with a very large heat capacity) being excellent radiators for
the coil winding itself.
The main area of our study on reflection effect reduction, however, was the two-and-half-way systems.
This is obviously also because this type of systems is much more popular nowadays than the threeway ones, and not without a reason. Moreover, the two-and-half-way system has proved very
susceptible to our concept and against all appearances not at all less appropriate than the three-way
system. We have shown above that it is difficult to completely evade the adverse reflections caused by
the midrange unit - they are located to high to set the crossover frequency at an even higher level. Let
us assume that the adverse effect occurs at approx. 500Hz (the speaker at the height of 80 cm, the
listener - 100 cm, distance - 4 meters). If the midrange tones processing unit is trapped anyhow, then
it can be considered a midwoofer from the point of view of reflections from the floor. This will not result
in further adverse phenomena below 500Hz. However the addition of a woofer allows reduction of the
damping at 500Hz which would be evident in operation of a two-way system - unless this speaker is
located directly below the midwoofer as it is in most of the two-and-half way systems! In such a typical
configuration, the adverse reflections occur for similar frequencies and are cumulated on the entire
set's processing characteristics. If the woofer at all reaches this range in processing. One way or
another, the problem is unresolved even though an additional speaker allows it. What must be done is
"only" to lower its position, not necessarily to 20 cm as we do not want its potential problems to be
shifted much above 1kHz. Enough if they occur clearly somewhere else on the frequency scale than
those caused by the midwoofer. A woofer must also process (not necessarily with full effectiveness)
the range up to 500Hz to compensate for the damping caused by the midwoofer. Many measuring and
listening experiments with settings and filters, with various distances between speaker sets and the
listener (within 2-5 meters) led to definition of a similar configuration for all two-and-half-way systems:
a midwoofer is typically set at the height of 80 cm, with tweeter directly above it and the woofer at 30
cm.
Reflections from the floor with a two-and-half-way PPW system
fala bezpośrednia - direct wave
fala odbita - reflected wave
The filtering method for such a system is by no means trivial. Against appearances, development of a
good crossover network for all two-and-half-way systems does not consist only in adding the woofer to
amplify and better spread the low frequencies. One must take into account that the low-pass filter of
the woofer, aligned to a lower boundary frequency than the filter for a midwoofer, will not only result in
different processing characteristics but also different phase characteristics. And too large differences
between the phases of these two speakers can lead to wave damping and further non-uniformity of
characteristics. What must be done, then, is to synchronize phase characteristics of woofer and
midwoofer sections. The simplest solution is to use a lower class filter in the woofer (which causes
smaller phase shift in the stopband and directly before it) than in the midwoofer. Such a solution is
also at stake in our concept. If, however, with mild filtering of the woofer we spread its characteristics
to as much as approx. 700Hz (6dB drop) to make it compensate for the distorted characteristics of the
midwoofer, then with effective mating of both speakers up to this frequency and simultaneous moving
the woofer away we must take into account another adverse phenomenon - and, obviously, find a
smart solution to it yet again"
At the vertical front wall, the speaker location defined above makes it seem to the listener at the height
of 1 meter being not far away from the speaker set (let us say 2 meters away) that the woofer is 12 cm
farther away than the midwoofer. This is nearly - of the 1300Hz frequency wavelength, which means a
phase shift of approx. 90° and in itself is not yet disastrous (two equivalent vectors set at an angle of
90° give a resultant vector still stronger than each one of them). We must bear in mind, however, that
at this frequency, even with mild filtering of the woofer, we obtain phase shift caused by this filter
larger than that coming from the midwoofer filter. Both phase shifts ? from the previously attenuating
filter and mechanic distance ? regrettably go in the same direction and thus the resultant acoustic
phase shift at approximately 1300Hz may approach 180° and hence cause wave damping. Therefore,
this shift needs to be reduced by tilting the front wall, which should equalize the distances from both
speakers to the listening site to a sufficient degree (depending on the distance and height the listener
is located at, this difference may amount to up to 3 cm, which already is an insignificant phase shift of
a 700Hz wave).
We have asked ourselves whether moving the woofer participating in 700Hz processing, 50 cm away
would not result in blurring the soundstage due to the spreading of apparent sources of midrange and
high frequencies. But even if both speakers sounded with the same frequency range producing
identical sound intensity, the apparent sound source of midrange frequencies would be shifted by 25
cm ? between both speakers. In our system, meanwhile, at 700Hz the lower speaker is damped by
6dB, thus the apparent sound source for this frequency is located much closer to the midwoofer.
Going down the frequency range, the sound level produced by the woofer gradually approaches the
level produced by the midwoofer (at 500Hz the difference is 3dB); the apparent source may shift but
below 300Hz what we have is a delocation effect for apparent sound sources due to their alldirectional radiation and reflections. It is also worth checking that the typical relation of distance
between the midwoofer and the tweeter (15 cm) to the wavelength of the crossover frequency
between them (let us assume 3kHz) is by no means smaller than our relation of distance between the
woofer and the midwoofer (50cm) to the 700kHz wave. This means that neither will the directional
characteristics in vertical plane be impaired due to this configuration. Thus, first the problem with
phase interferences will arise between the midwoofer and the tweeter. This happens not only in
theory, but also in practice ? i.e. in intense listening tests in which such systems, upon final alignment,
sounded with balance, cohesion and plasticity. The recommended distance of the listener from the
speakers is within 3-6 meters.
Tilting of the front wall in our devices is therefore somewhat related to operation of 1st order filters
(woofer filtering), equalization of the distance from the speakers and compensation of phase shifts, but
has not arisen from the concept of a speaker set to feature a ?linear phase? but from the abovedescribed idea of mating the woofers and midwoofers in order to equalize processing characteristics in
the mid bass range. As for organization of mating of the midwoofer with the tweeter, we are not
convinced about the 1st order filters which make it very difficult to obtain equalized processing
characteristics, deteriorate directional characteristics, burden the tweeter and increase distortions, and
rarely achieve their aim ? a phase characteristics giving perfect impulse response. Certainly, when the
front wall is already tilted and the location of the tweeter in relation to the midwoofer has been
adjusted, this will affect the crossover network shape, although it does not need to lead to using 1st
order filters but can be used otherwise. Owing to this partial compensation of the phase shift between
the midwoofer and the tweeter we can increase filter slope, keeping at the same time compatible
polarization of all sections favoured by us.
Our new designs not only have the front walls but also the back walls tilted. This is yet another
example of the interdependence of various characteristics of a complex system typical for our designs.
We have made use of the necessity to tilt the front wall (for coordination of the woofer and midwoofer
phases) to construct a cabinet of a shape best also in quite other respect ? in reducing standing
waves in the cabinet. Many myths have been said on this subject. A slightly tilted upper wall or
rounded sides are enough to boast that the problem has been solved. The standing waves,
meanwhile, are still raging as they will not subject to design and marketing solutions only. They are
subject to different rules than many design engineers would wish them to. We have ourselves become
humble upon our experience with many earlier models in which in the cabinet bottom we had installed
a partition at an angle of 45° thinking this was a nearly perfect way of removing standing waves
generated between the top and bottom wall. In spite of this, the bass-reflex radiation manner (which,
apart from the basic system resonance and tunnel parasitic resonance, to some extent also transmits
the standing waves from the cabinet) signalized that the problem still existed? It is commonly accepted
that the standing waves are a result of parallel cabinet walls. Therefore, to remove these parallelism
should be to remove the standing waves. Unfortunately, this is not so simple. Tunnel resonances (pipe
resonances) arise in systems in which one dimension is much longer than the others - e.g. in a
speaker with a height much greater than the width and depth. Then it is not enough to set the bottom
or top wall even at an angle of 45°. It will not eliminate the marked privilege of one, vertical dimension
of the device. If, however, the high cabinet with tilted front and back walls should be divided inside with
a partition set at an angle of 45°, the situation would be much different. In the lateral vertical section
not only there will be no parallel walls, but also the distances between them will clearly change. The
only potential generator of standing waves is still the system of parallel side walls with the smallest
distance compared to the distances between the other walls, which reduces the resonance risk and
also complies with the wavelengths which can be handled using appropriate attenuation of the wall
surfaces only.
Our devices have for many years been equipped only with excellent Danish transducers. The PPW
generation is based on Scan-Speak's reference products - the Revelators and the Illuminators in
Credo models, the latest Wavecor’s in Neo 2 & Neo 3 and the latest Vifa’s from NE series in Neo 3SE
& Neo 4. The new Wavecor’s have nomex cones, and traditionally for the Danish products are based
on cellulose, this time enriched with new admixtures setting optimum parameters of rigidity and
internal attenuation. The tweeter in Neo 3 is a ring-dome Scan-Speak DX tweeter, and in the Neo 4 &
Neo 3SE it is the best neodymium-magnet ring-dome Scan-Speak DX. The Illuminator midwoofer
maintains the very low level of distortions throughout the band as well as at high amplitudes and
powers, which allows effective and accurate processing of low frequencies while keeping the top
resolution of the midrange frequencies. These possibilities are a result of a combination of
sophisticated design features unprecedented in any other speaker: powerful neodymium motors with
under-hung voice coil and a basket moulded into a perfectly aerodynamic shape. The advantage of
cellulose cones is that they are good in dispersing resonances, which is the effect of their structure
(different length fibres arranged in various directions); usually cellulose cones are sufficiently rigid and
guarantee good results even without any special efforts. In the Illuminator, the cone is made up of two
layers in which the wavy overpresses are „phase-shifted” in relation to one another, which gives the
whole cone special stiffness with moderate weight and particularly effective damping of the standing
waves.
A pair of 18-centimeter Illuminators has a very high potential in the low tone range, however to obtain
top characteristics it requires appropriate alignment of the bass reflex cabinet. As research has shown,
no conventional system with a bass reflex will work here, as it forces us to use either a very long
tunnel, which is troublesome and enhances parasitic resonances, or to reduce the opening area,
which in turn causes compression and turbulence noise. In this situation, the best solution - already
used previously by ESA - is to install passive radiators. At the back wall in the Credo 3 Illuminator we
have placed as many as four 18-cm passive radiators with very large excursion. Each speaker drives
two passive radiators, creating a resonance system aligned perfectly in every respect - in the best
volume, to the optimum frequency - and ensuring very good low bass reproduction and excellent
impulse response. Freedom of operation of this system is not limited by the opening size; the system
is also less susceptible to transmitting standing waves from the cabinet. In the three-way Credo 4, the
achievement of the reference level of low tone definition was helped by using a pair of 22cm alucone
Revelators. Midrange is reproduced by a papercone 15cm Revelator and high frequencies - by R29,
top ring radiator tweeter from Scan-Speak.
In terms of basic electrical parameters, our new speakers are typical, by no means problematic burden
for each "robust" amplifier. Although most manufacturers declares an 8-ohm nominal impedance with
impedance characteristics showing drops to as little as below 3 ohms in the range of low frequencies,
in our devices we never go down below 3.5 ohms. At the same time, in compliance with the traditional
and reasonable method of determining nominal impedance, we declare our speakers to have a 4-ohm
impedance. Likewise with the effectiveness - we specify a reliable value determined by way of
measurement in an open space. As with any high class device, also our loudspeakers play better
connected to a better amplifier and player. However, both because of the nature of the transducers
alone as of the sound profiling of the whole speakers, they are not very demanding. It will not be
necessary to find the one and only equipment configuration or to buy particularly expensive devices.
Clearly, however, they like good and well recorded music - bad music will sound badly.