Loudspeaker
US 20020154785A1
(19) United States
(12) Patent Application Publication (10) Pub. No.: US 2002/0154785 A1
(43) Pub. Date:
Pedersen
(54) ADJUSTING A LOUDSPEAKER TO ITS
ACOUSTIC ENVIRONMENT: THE ABC
SYSTEM
(75) Inventor: Jan A. Pedersen, Holstebro (DK)
Int. Cl.7 .
(52)
US. Cl. ............................... .. 381/59; 381/96; 381/58
(57)
H04R 29/00; H04R 3/00
ABSTRACT
of, in a ?rst acoustic environment, Which may be regarded
as a reference, determining the acceleration, velocity or
580 White Plains Road
displacement of the loudspeaker diaphragm and the sound
pressure in front of the diaphragm, and, based on these
quantities, determining the radiation resistance, radiated
(73) Assignee: BANG & OLUFSEN A/S
acoustic poWer or real part of the acoustic Wave impedance.
Thereafter, the above step is repeated in a second acoustic
10/062,086
environment, Which Will normally be the actual listening
Jan. 29, 2002
room in Which the loudspeaker is to be used. Based on the
Related US. Application Data
tances, radiated poWer or real part of the acoustic Wave
(22) Filed:
above measurements, the ratio betWeen the radiation resis
impedances is determined, and the ratio, optionally after
Continuation of application No. 08/743,593, ?led on
Nov. 4, 1996, noW abandoned.
(30)
(51)
performance of a loudspeaker in a room includes the steps
Tarrytown, NY 10591 (US)
(63)
Publication Classi?cation
A method and corresponding apparatus for controlling the
Correspondence Address:
Corporate Patent Counsel
U.S. Philips Corporation
(21) Appl. No.:
Oct. 24, 2002
correction ?lter inserted in the signal path of the loud
speaker, Whereby the performance of the loudspeaker in the
Foreign Application Priority Data
Nov. 2, 1995
suitable further processing, is used to control a controllable
(DK) ............................................ .. 1224/95
second acoustic environment can be brought substantially to
match the performance of the loudspeaker in the ?rst acous
tic environment.
Loudspeaker
Diaphragm
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Accelerometer
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Microphone
Patent Application Publication
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Oct. 24, 2002
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US 2002/0154785 A1
C
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Loudspeaker
Diaphragm
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Drive unit
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Microphone
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Accelerometer
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Source ———> Correction ?lter ———> Power ampli?er
ego CD player
Loudspeaker
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Lrstenm room
Power output or radiation resistance or wave resistance
FIG. 3
Oct. 24, 2002
US 2002/0154785 A1
ADJUSTING A LOUDSPEAKER TO ITS ACOUSTIC
ENVIRONMENT: THE ABC SYSTEM
[0001] The invention relates to a method and apparatus for
controlling the performance of a loudspeaker in a room.
[0002]
The actual performance of a loudspeaker is knoWn
to be highly dependent on the acoustics of the actual
listening room and the actual loudspeaker position Within
this room. In particular the performance of a loudspeaker
Will change very noticeably When it is in proximity to the
boundaries of the room. This is caused by the loading of the
room on the loudspeaker as a radiator, or in other Words due
to the changing radiation resistance. A change of listener
position changes the perceived performance of the loud
speaker, in particular due to early re?ections and standing
[0006] It is the purpose of the invention to provide a
method and apparatus for controlling the performance of a
loudspeaker in a room in order that it becomes independent
of the placement of the loudspeaker. This is obtained in a
method according to the invention Which is particular in that
in a ?rst acoustic environment the movement, e.g. velocity,
of the diaphragm of the loudspeaker driver and the force,
arising from the sound ?eld, acting on it are determined by
measuring suitable parameters, de?ning thereby a ?rst com
plex transfer function, that in a second acoustic environment
a second complex transfer function is determined by mea
suring the same or different parameters of the loudspeaker
driver, relating to the room, that the ratio betWeen the real
parts of the ?rst and second transfer functions is used to
de?ne the performance of a correcting ?lter, that the ?lter is
Waves. HoWever some boundary effects are universal in the
applied in the signal chain to the loudspeaker driver.
room, in particular in the bass frequency range, and hence
the perception of this range is less in?uenced by the listener
[0007] The invention is based on the realiZation that there
is a strong link betWeen the Way the loudspeaker sounds, in
particular in the bass range, and its radiation resistance as a
position.
[0003] Loudspeaker designers experience this fact by hav
ing to make a compromise When optimiZing the timbre of the
loudspeaker so that the perceived sound Will be acceptable
under a number of different conditions, i.e. different room
acoustics, loudspeaker positions, and listening positions.
function of frequency, being the real part of the radiation
impedance. Implementing the invention for a loudspeaker
has proved to signi?cantly increase the certainty that the
customer Will alWays experience the quality intended by the
loudspeaker designer. This is achieved by measuring the
Even though making this compromise, the designer cannot
radiated poWer output, radiation resistance or any similar
ensure that the customer Will alWays experience the intended
physical parameter, e.g. real part of the acoustic Wave
impedance near the diaphragm, When the loudspeaker is
placed in the actual position and comparing this to a refer
quality. Thus, the listener Will experience a performance of
the loudspeaker that depends on the acoustic properties of
the actual listening room and the position chose n for both
loudspeaker and listener. There is a risk that an expensive
loudspeaker Which performs very Well in the shop, Will turn
out performing badly or at least disappointingly When placed
in a different environment and/or in a different position.
[0004]
In order to compensate for this problem it is knoWn
to ?t a sWitch in the cross-over ?lter unit in the loudspeaker
in order that the bass response may be modi?ed to suit a
ence measurement. More precisely this is obtained in that
the loudspeaker in a ?rst step is put in a reference room
environment Where it performs to a standard to be deter
mined, and during Which a reference radiated poWer output
(real, i.e. active) or reference radiation resistance of a driver
as a function of frequency is measured, and in that in a
second step the loudspeaker is put in its room of usage Where
its attendant radiated poWer output or radiation resistance is
considered a poor compromise, and if at all possible, the
precise adjustment Will be dependent on a measurement of
measured, the ratio betWeen the said real (active) poWer
outputs or radiation resistances respectively being used to
de?ne the transfer function of a correcting ?lter in order to
obtain said standard of performance determined in said
the room characteristics. Some automatic systems are based
reference room environment, and that in a third step said
particular placement of the loudspeaker. At best, this must be
on measuring the transfer function from the input of the
loudspeaker to an omnidirectional microphone, placed at the
preferred listening position or a number of representative
positions. An equalizing ?lter is then inserted so that the
resulting transfer function approximates a target function,
Which e.g. can be ?at in the frequency range of interest. A
major problem of such systems is the sensitivity to changes
in the position of the sound source as Well as the receiver. If
the position of the loudspeaker or the listener is changed
after calculating the equaliZing ?lter, the effects can be
severe colouration, pre-echoes, etc. Another problem of such
systems is the choice of a suitable target function, Where a
?at function may not be found to be optimal.
[0005]
It has in the present invention been realiZed that
since all the involved acoustic phenomena’s are considered
to be linear, What is actually compensated through the
apparently sensible procedures discussed above is the super
position of several phenomena, such as standing Waves/
natural frequencies of the room, early re?ections, reverbera
correcting ?lter is introduced in the electrical signal path to
the driver. In principle a multi-driver loudspeaker should
have each driver subjected to such a measurement, hoWever
one or several may be selected as representative. At the time
of measurement of one particular driver or a group of
drivers, the other drivers may either be short-circuited,
disconnected or connected to the signal.
[0008] When the loudspeaker is placed in a position Which
is not identical to the reference position/room, the bass
performance changes. HoWever, the method according to the
invention is able to detect a major part of this change in the
acoustic environment of the loudspeaker and to correct
accordingly. sWitching on and off an apparatus Working
according to the principles of the invention can lead to
dramatic changes of the bass performance of the loud
speaker depending on hoW different the actual position and
room are from the reference conditions. If a loudspeaker is
designed to operate aWay from the Walls of a room, then
When placing such a loudspeaker close to a corner of the
listening room, the bass performance becomes boomy,
tion and the reduction of angular space angle due to the
boundary effect, and it is considered that this is the reason
Why the knoWn procedures Will only function for one
coloured, and the sound pressure level increases. In such a
listening position.
invention corrects the timbre in such a Way that the per
situation the apparatus according to the principles of the
Oct. 24, 2002
US 2002/0154785 A1
ceived timbre is almost the same as in the reference position.
The effect of the apparatus in this situation has been
exponential, multiplication, addition etc. and combinations
of these. For instance, de?ning the amplitude response of the
described by listeners as quite startling. The bass perfor
correction ?lter as the square root of the ratio seems to be a
mance then Was not plagued by the rumble Which is tradi
tionally a characteristic of a corner position, and the bass
performance becomes more even and neutral Without
becoming “thin”. In a corner position this is perceived as a
reasonable choice.
dramatic improvement of the bass performance.
[0015] FIG. 1 shoWs the electrical, mechanical and acous
tical signal paths associated With a loudspeaker placed in a
[0009] An advantageous embodiment is particular in that
the loudspeaker is permanently ?tted With measurement
[0014] The invention Will be further described in the
folloWing With reference to the draWing, in Which
room,
means, the ratio betWeen reference and use measurements
[0016]
being used to de?ne the parameters of the correcting ?lter.
measuring transducers, and
This enables a measurement to be initiated by a user or in the
event that some prede?ned conditions are met, e.g. poWer up
of the apparatus. This measurement cycle could be per
formed using a dedicated measuring signal, e.g. obtained
from a particular Compact Disc.
[0010] A further advantageous embodiment of the inven
tion is particular in that the loudspeaker is permanently ?tted
With measurement means, and the complex transfer func
tion, Which corresponds to the situation during usage, is
continuously measured during operation of the apparatus.
The ratio betWeen reference and usage measurements being
used to de?ne the parameters of the correcting ?lter. This
means that the loudspeaker Will be automatically and con
tinuously adaptable to any neW listening room environment,
eg using the played music as the stimuli When measuring
the complex transfer functions. In this case the transfer
function in the usage situation is continuously measured,
and eg a digital signal processor in the signal chain
calculates and performs the ?ltering Which provides a sound
from the loudspeaker Which is very similar to the sound in
the reference position/room and Which presumably Was
judged positively during the design of the loudspeaker.
[0011] Afurther advantageous embodiment is particular in
that the listening room is divided into Zones of eg 30 cm by
30 cm, each having a correction ?lter transfer function
assigned to it, and that information on the particular Zone is
fed to the correcting ?lter in the electrical signal path to the
loudspeaker. By this means it is possible to accomodate a
number of typical placements of a loudspeaker and to obtain
a large degree of the improvement according to the inven
tion, Without having to perform a measurement.
[0012] A simpler arrangement is obtained by instructing
the user to activate sWitches according to a schematic
shoWing various typical placements of a loudspeaker in a
room. This functions in practice, provided the loudspeaker is
FIG. 2 shoWs a loudspeaker With a driver and
[0017] FIG. 3 shoWs a schematic of hoW the correction
?lter can be inserted in the signal chain according to one
embodiment of the invention.
[0018] By Way of example FIG. 1 shoWs the signal path
and transfer functions relating to a loudspeaker in a room.
The electrical signal from the source is fed to a poWer
ampli?er A Which drives the loudspeaker Which is desig
nated B and comprises the electrical and mechanical parts of
the loudspeaker driver unit and the acoustic in?uence of the
cabinet enclosure. The output from the loudspeaker is trans
formed by the transfer function C from the acceleration of
the diaphragm to the sound pressure in front of the dia
phragm Which may be measured by a microphone D as one
example of hoW to obtain the force, arising from the sound
?eld, acting on the diaphragm. An accelerometer E for
example may measure the diaphragm acceleration directly.
At point 1 the source signal is provided, at point 2 the
electrical input signal to the loudspeaker driver is available,
point 3 refers to the acceleration of the diaphragm of the
loudspeaker, and at point 4 the sound pressure at some
predetermined and ?xed point in front of the driver is
available. After being converted by the microphone D an
electrical signal representing the sound pressure is available
at point 5, and correspondingly, an electrical signal repre
senting the membrane acceleration is available at point 6.
[0019] FIG. 2 shoWs one embodiment of the invention
Where the loudspeaker B With one of a multitude of possible
placements of a microphone D and an accelerometer E.
[0020]
FIG. 3 shoWs hoW a measurement of the radiation
resistance of the loudspeaker is used When calculating the
?lter F, Which is sWitched into the signal path. The signal
processing may occur through any means available to the
skilled person, the result Will be a linear pre-distortion of the
signal to the poWer ampli?er in order that the loudspeaker
provides an excitation of the listening room so that the
of the same type as the loudspeaker used in the reference
environent.
perceived sound is a good approximation to the quality
[0013] An apparatus according to the invention is particu
making the measurement continuous is that the system Will
determined during the design phase. The advantage of
lar in that it comprises a ?lter, the transfer function of Which
automatically compensate eg for an in?ux of listeners or a
is controllable by electronic/numerical signals, said signals
changed placement of furniture or the loudspeaker place
being obtained from a unit Which determines the ratio
ment itself, Which disturbs the sound distribution in the
betWeen a stored reference radiation resistance or active
poWer output (real) as a function of frequency and a mea
perceived sound is essentially unchanged.
room. Such a disturbance is noW compensated so that the
sured radiation resistance or active poWer output (real) in the
usage situation. This ratio basically de?nes the amplitude
response of the correction ?lter, and various ?lter imple
speaker in a room, characteriZed i n that in a ?rst acoustic
mentations, e.g. minimum phase can be obtained from this.
environment the resultant movement of the loudspeaker
HoWever various operation might be performed to modify
the ratio before implementation, e.g. smoothing, convolu
sound ?eld in the room, acting on it are determined by
tion, frequency limiting, correction limiting, logarithm,
measuring suitable parameters de?ning a ?rst complex
1. A method for controlling the performance of a loud
driver diaphragm and the associated force, arising from the
Oct. 24, 2002
US 2002/0154785 A1
transfer function, that in a second acoustic environment a
5. Amethod according to claim 3, characteriZed in that the
second complex transfer function is determined by measur
ing the same or different parameters of the loudspeaker
driver relating to the room, that the ratio betWeen the real
parts of the ?rst and second transfer functions is used to
de?ne the performance of a correcting ?lter, that the ?lter is
measurement means are activated by a user or in the event
applied in the signal chain to the loudspeaker driver.
30 cm, each having a correcting ?lter transfer function
assigned to it, and that information on the particular Zone is
fed to the correcting ?lter in the electrical signal path to the
2. A method for controlling the performance of a loud
speaker in a room, in particular in the loW frequency range,
according to claim 1, characteriZed i n that the loudspeaker
that some prede?ned conditions are met, e. g. poWer up of the
apparatus.
6. Amethod according to claims 1 and 2, characteriZed in
that the listening room is divided into Zones of eg 30 cm by
loudspeaker.
in a ?rst step is put in a reference room environment Where
7. An apparatus for performing the method according to
it performs to a standard to be determined, and during Which
a reference radiated poWer output (real, i.e. active), refer
ence radiation resistance (acoustic or mechanical) of a driver
or any similar physical parameter, e.g. real part of the
acoustic Wave impedance near the diaphragm of the driver,
claims 1 and 2, characteriZed i n that it comprises a ?lter, the
transfer function of Which is controllable by electronic/
Which determines the ratio betWeen a stored reference
radiation resistance or active poWer output (real) or Wave
as a function of frequency is measured, and in that in a
second step the loudspeaker is put in its room of use Where
measured radiation resistance or active poWer output (real)
numerical signals, said signals being obtained from a unit
resistance near the driver as a function of frequency and a
a usage radiated poWer output (real, i.e. active), usage
or Wave resistance near the driver in the usage situation. This
radiation resistance of the same driver or any similar physi
ratio basically de?nes the amplitude response of the correc
tion ?lter, and various ?lter implementations, e.g. minimum
phase can be obtained from this. HoWever various opera
cal parameter, e.g. real part of the acoustic Wave impedance
near the diaphragm of the same driver, is measured, the ratio
betWeen the real part of said poWer outputs (active), radia
tion resistances or any similar physical parameters, eg real
parts of the acoustic Wave impedances near the diaphragm of
the driver, respectively being used to de?ne the transfer
function of a correcting ?lter in order to obtain said standard
of performance determined in said reference room environ
ment, and that in a third step said correcting ?lter is
tions might be performed to modify the ratio before imple
mentation, e.g. smoothing, convolution, frequency limiting,
correction limiting, logarithm, exponential, multiplication,
addition etc. and combinations of these. For instance, de?n
ing the amplitude response of the correction ?lter as the
square root of the ratio seems to be a reasonable choice.
8. A method according to claim 3 or 4 or 5 or 6,
introduced in the electrical signal path to the driver.
3. Amethod according to claims 1 and 2, characteriZed in
that the loudspeaker is permanently ?tted With measurement
measurement according to claims 1 and 2. HoWever one or
means, the ratio betWeen reference and usage measurements
several may be selected as representative. At the time of
being used to de?ne the parameters of the correcting ?lter.
4. Amethod according to claims 1 and 2, characteriZed in
that the loudspeaker is permanently ?tted With measurement
means and is continously measuring the second compleX
transfer function, the ratio betWeen reference and usage
measurements being used to de?ne the parameters of the
correcting ?lter.
characteriZed in that a multi-driver system, eg 2 Woofers
and 1 tWeeter, should have each driver subjected to a
measurement of one particular or a group of drivers, the
other drivers may either be short-circuited, disconnected or
connected to the signal. Each driver may have individual
?lters implemented or some groups may have a common
?lter implemented.
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