U.S. patent application number 13/818374 was filed with the patent office on 2016-01-21 for loudspeaker system with improved sound.
This patent application is currently assigned to Knowles IPC (M) Sdn. Bhd.. The applicant listed for this patent is Johannes Kobler, Maria Papakyriacou, Jurgen Sauer. Invention is credited to Johannes Kobler, Maria Papakyriacou, Jurgen Sauer.
Application Number | 20160021439 13/818374 |
Document ID | / |
Family ID | 43243733 |
Filed Date | 2016-01-21 |
United States Patent
Application |
20160021439 |
Kind Code |
A2 |
Papakyriacou; Maria ; et
al. |
January 21, 2016 |
LOUDSPEAKER SYSTEM WITH IMPROVED SOUND
Abstract
A loudspeaker device (200) is presented which includes a zeolite
material (100) comprising zeolite particles (102) having a silicon
to aluminum mass ratio of at least 200. For an increased pore
fraction of pores with a diameter in a range between 0.7 micrometer
and 30 micrometer shows an increased shift of the resonance
frequency down to lower frequencies has been observed.
Inventors: |
Papakyriacou; Maria;
(Vienna, AT) ; Kobler; Johannes; (Munich, DE)
; Sauer; Jurgen; (Munich, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Papakyriacou; Maria
Kobler; Johannes
Sauer; Jurgen |
Vienna
Munich
Munich |
|
AT
DE
DE |
|
|
Assignee: |
Knowles IPC (M) Sdn. Bhd.
Penang
MY
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20130170687 A1 |
July 4, 2013 |
|
|
Family ID: |
43243733 |
Appl. No.: |
13/818374 |
Filed: |
August 23, 2011 |
PCT Filed: |
August 23, 2011 |
PCT NO: |
PCT/IB2011/053685 PCKC 00 |
371 Date: |
February 22, 2013 |
Current U.S.
Class: |
381/338 |
Current CPC
Class: |
B01J 2220/66 20130101;
B01J 20/28092 20130101; B01J 20/183 20130101; Y10T 428/2982
20150115; C01B 39/38 20130101; C01B 39/44 20130101; B01J 20/261
20130101; B01J 20/28083 20130101; B01J 20/2808 20130101; H04R 1/00
20130101; B01J 20/186 20130101; B01J 20/28004 20130101; B01J 20/165
20130101; B01J 20/18 20130101; B01J 20/28078 20130101; B01J
20/28016 20130101; B01J 20/264 20130101; B01J 20/28088 20130101;
H04R 1/2803 20130101; H04R 1/2811 20130101; H04R 1/288 20130101;
B01J 20/2803 20130101; C01B 39/46 20130101; H04R 1/02 20130101;
B01J 20/28085 20130101; H04R 1/28 20130101 |
International
Class: |
H04R 1/00 20060101
H04R001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2010 |
EP |
10173765.8 |
Claims
1. A loudspeaker device comprising: a loudspeaker; a loudspeaker
receptacle for receiving the loudspeaker, the loudspeaker
receptacle having a resonance space; and a zeolite material
disposed within the resonance space, wherein the zeolite material
comprises zeolite particles having a silicon to aluminum mass ratio
of at least 200.
2. A loudspeaker device according to claim 1, wherein at least part
of the zeolite particles have the structure FER.
3. A loudspeaker device according to claim 1, wherein at least part
of the zeolite particles have the structure MFI.
4. A loudspeaker device according to claim 1, wherein the zeolite
material further comprises a binder adhering the individual zeolite
particles together.
5. A loudspeaker device according to claim 4, wherein the zeolite
particles comprise first pores having a diameter in a first
diameter range; and wherein the zeolite material comprises second
pores between different zeolite particles.
6. A loudspeaker device according to claim 5, wherein the second
pores have a diameter in a second diameter range; and the second
diameter range is spaced from the first diameter range by at least
one order of magnitude.
7. A loudspeaker device according to claim 5, wherein the second
pores have a pore diameter larger than 50 nanometer.
8. A loudspeaker device according to claim 5, wherein the second
pores have a pore diameter distribution with a local peak in a
diameter range between 0.7 micrometer and 30 micrometer.
9. A loudspeaker device according to claim 4, wherein the zeolite
material further comprises grains having a plurality of the zeolite
particles adhered together with the binder the grains having an
average grain size in a range between 0.2 millimeter and 0.9
millimeter.
10. A loudspeaker device according to claim 4, wherein in relation
to the whole mass of the zeolite material the mass fraction of the
binder is in the range from 1% to 20%.
11. A loudspeaker device according to claim 1, wherein the zeolite
particles have a mean diameter below 10 micrometer.
12. A loudspeaker device according to claim 1, wherein the zeolite
particles have a mean diameter above 0.1 micrometer.
13. A zeolite material obtainable by: preparing a zeolite
suspension from zeolite particles having a silicon to aluminum mass
ratio of at least 200 and a solvent that includes an organic
solvent; mixing the zeolite suspension with a binder suspension to
obtain a zeolite-binder mixture; drying the zeolite-binder
mixture.
14. A method of producing a zeolite material for use as a sorber
material in a loudspeaker device, the method comprising: preparing
a zeolite suspension from zeolite particles having a silicon to
aluminum mass ratio of at least 200 and an nonpolar solvent; mixing
the zeolite suspension with a binder suspension to obtain a
zeolite-binder mixture; drying the zeolite-binder mixture.
15. (canceled)
Description
FIELD OF INVENTION
[0001] The present invention relates to the field of loudspeaker
devices.
ART BACKGROUND
[0002] In loudspeaker devices, including a loudspeaker, a housing
and a resonance space, gas adsorbing materials--in the following
referred to as sorber--like e.g. activated carbon or zeolite may be
placed therein to improve sound generation of the loudspeaker
device. A sorber in the resonance space of the loudspeaker leads to
an apparent virtual enlargement of the resonance space by gas
adsorption and desorption. The resonance frequency of the
loudspeaker device is thereby lowered to a value that can be
achieved without sorber only with an essentially larger resonance
space.
[0003] However, it turned out that the use of sorbers bears several
problems. One problem is the aging of the sorber in particular by
irreversible adsorption of substances with high vapour
pressure.
[0004] EP 2 003 924 A1 relates to a loudspeaker system in which a
gas adsorber, obtained by adding a binder to a porous material
including a plurality of grains so as to perform moulding, is used
to physically adsorb a gas in a closed space of the speaker system.
The porous material may be made of one selected from the group
consisting of an activated carbon, zeolite, silica (SiO.sub.2),
alumina (Al.sub.2O.sub.3), zirconia (ZrO.sub.3), magnesia (MgO),
iron oxide black (Fe.sub.3O.sub.4) molecular sieve, fullerene and a
carbon nanotube. The binder may be one of a powdery resin material
and a fibrous resin material.
[0005] In view of the above-described situation, there exists a
need for an improved technique that enables to increase the virtual
acoustic volume of a resonance space of a loudspeaker device while
substantially avoiding or at least reducing one or more of the
above-identified problems.
SUMMARY OF THE INVENTION
[0006] This need may be met by the subject matter according to the
independent claims. Advantageous embodiments of the herein
disclosed subject matter are described by the dependent claims.
[0007] According to a first aspect of the invention there is
provided loudspeaker device comprising a loudspeaker receptacle for
receiving a loudspeaker, and a zeolite material comprising zeolite
particles having a silicon to aluminum mass ratio of at least 200.
According to embodiments, the zeolite material comprises zeolite
particles in pure SiO.sub.2 modification. It should be noted that
herein the term "silicon to aluminum mass ratio of at least 200"
includes higher silicon to aluminum mass ratios, e.g. 250 or 300,
as well as aluminum-free zeolite particles. In the latter case, the
whole zeolite particles of the zeolite material are in pure
SiO.sub.2 modification.
[0008] The experiments performed by the inventors showed that such
zeolite particles may provide a good sorption capacity per volume
unit and a slow aging behaviour. Zeolites are microporous minerals,
usually aluminosilicate minerals, and are known to a person skilled
in the art. Basic information about zeolites is available from the
International Zeolite Association and the corresponding web site
(http://www.iza-online.org/).
[0009] Generally herein a loudspeaker refers to any type of
electro-acoustic transducer.
[0010] According to an embodiment of the first aspect, the at least
part of the zeolite particles have the structure FER. According to
a further embodiment, at least part of the zeolite particles have
the structure MFI. According to an embodiment, the all zeolite
particles are of the same structure, e.g. the structure FER.
According to other embodiments, the zeolite material includes
zeolite particles of at least two different structures. For
example, in an embodiment, the zeolite material includes zeolite
particles of the structure FER and zeolite particles of the
structure MFI. Herein the three letter code relates to the
classification of zeolites according to the International Zeolite
Association and can be obtained inter alia from
http://www.iza-online.org/.
[0011] According to a further embodiment, the zeolite material
further comprises a binder adhering the individual zeolite
particles together. This allows grains of zeolite material to be
formed which are larger than a single zeolite particle. Further a
certain spacing between zeolite particles can be established by the
binder and appropriate processing of the ingredients of the zeolite
material.
[0012] According to a further embodiment, the zeolite particles
comprise first pores having a diameter in a first diameter range
and the zeolite material comprises second pores between different
zeolite particles. The size of first pores in the zeolite particles
usually have a sharp pore diameter distribution. The diameter of
the second pores can be influenced by the manufacturing process of
the zeolite material.
[0013] According to an embodiment, the second pores have a diameter
in a second diameter range and the second diameter range is spaced
from the first diameter range by at least one order of magnitude.
For example, if the first diameter range extends up to about 4
nanometers, according to an embodiment the second diameter range of
the second pores extends from about 40 nanometers to higher
diameters.
[0014] According to a further embodiment, the second pores have a
pore diameter larger than 50 nanometer.
[0015] According to a still further embodiment, the zeolite
material has second pores in the range between 0.7 micrometer and
30 micrometer. According to a further embodiment, the zeolite
material has second pores in the range between 1 micrometer and 10
micrometer.
[0016] According to an embodiment of the first aspect, the second
pores have a pore diameter distribution with a local peak in a
diameter range between 0.7 micrometer and 30 micrometer. According
to an further embodiment, the second pores have a pore diameter
distribution with a local peak in a diameter range between 1
micrometer and 10 micrometer.
[0017] According to a further embodiment, the zeolite material
comprises grains having a plurality of the zeolite particles
adhered together with the binder and the grains have an average
grain size in a range between 0.2 millimeter and 0.9
millimeter.
[0018] According to a further embodiment, in relation to the whole
mass of the zeolite material the mass fraction of the binder is in
the range from 1% to 20%. According to a further embodiment, in
relation to the whole mass of the zeolite material the mass
fraction of the binder is in the range from 2% to 10%. According to
a further embodiment, in relation to the whole mass of the zeolite
material the mass fraction of the binder is in the range from 4% to
6%.
[0019] According to an embodiment, the zeolite particles have a
mean diameter below 10 micrometer. According to a further
embodiment, the zeolite particles have a mean diameter below 5
micrometer. According to a further embodiment, the zeolite
particles have a mean diameter below 2 micrometer.
[0020] According to an embodiment, the zeolite particles have a
mean diameter above 0.1 micrometer. According to a further
embodiment, the zeolite particles have a mean diameter above 0.3
micrometer, or, according to still other embodiments, above 0.5
micrometer.
[0021] According to a second aspect, a zeolite material is
provided, the zeolite material being obtainable by: (i) preparing a
zeolite suspension from zeolite particles having a silicon to
aluminum mass ratio of at least 200 and an nonpolar solvent; (ii)
mixing the zeolite suspension with a binder suspension to obtain a
zeolite-binder mixture; and (iii) drying the zeolite-binder
mixture. According to embodiments of the second aspect, the zeolite
material is configured or processed as described with regard to the
first aspect or embodiments and examples thereof.
[0022] According to embodiments of the herein disclosed subject
matter, a zeolite material is obtained by (a) preparing a zeolite
suspension with an organic solvent, e.g. alcohol, wherein the
zeolite particles have a mean particle diameter smaller than 10
micrometer or, according to another embodiment, smaller than 2
micrometer. (b) The zeolite suspension is homogenized, e.g. by
stirring. (c) Then homogenized zeolite suspension is mixed with a
binder suspension, e.g. a latex suspension. Embodiments of Latex
suspensions include at least one of a Polyacrylate suspension,
Polystyrolacetat suspension, Polyvinylacetat suspension,
Polyethylvinylacetat suspension, Polybutadienrubber suspension,
etc. According to an embodiment, the mass concentration of the
binder, e.g. the polymer, is between 1 weight % and 10 weight %,
or, according other embodiments, between 4 weight % and 6 weight %.
The resultant suspension is then dried. Drying can be performed in
different ways, e.g. by means of a fluidized bed, a spray method or
by pouring the resultant suspension onto a hot plate (according to
embodiments the temperature of the plate range is in a range
between 120 degrees Celsius and 200 degrees Celsius or between 150
degrees Celsius and 170 degrees Celsius). If the grains of the
resultant solid are larger than desired, the resultant solid may be
cut or broken into smaller pieces e.g. by means of a mortar mill, a
hammer rotor mill, a cutting mill or a oscillating plate mill. (d)
Subsequently, the resultant solid (optionally cut or broken) is
screened with sieves to obtain grains in a desired diameter
range.
[0023] According to a third aspect, a method of producing a zeolite
material for use as a sorber material in loudspeaker device is
provided, the method comprising (i) preparing a zeolite suspension
from zeolite particles having a silicon to aluminum mass ratio of
at least 200 and a solvent that includes an organic solvent; (ii)
mixing the zeolite suspension with a binder suspension to obtain a
zeolite-binder mixture; and (iii) drying the zeolite-binder
mixture. According to embodiments of the third aspect, the zeolite
material is configured or processed as described with regard to the
first aspect or embodiments and examples thereof.
[0024] According to an embodiment, the solvent consists of at least
one organic solvent. According to a further embodiment, the solvent
comprises at least one organic solvent and at least one inorganic
solvent.
[0025] According to a fourth aspect, there is provided a use of a
zeolite material having zeolite particles with a silicon to
aluminum mass ratio of at least 200 in a loudspeaker device region
that is exposed to sound generated by a loudspeaker of the
loudspeaker device. According to embodiments of the fourth aspect,
the zeolite material is configured or processed as described with
regard to the first aspect or embodiments and examples thereof.
[0026] In the above there have been described and in the following
there will be described exemplary embodiments of the subject matter
disclosed herein with reference to loudspeaker device, a zeolite
material, a method of producing a zeolite material and a use of a
zeolite material. It has to be pointed out that of course any
combination of features relating to different aspects of the herein
disclosed subject matter is also possible. For example, some
embodiments have been described with reference to apparatus type
claims whereas other embodiments have been described with reference
to method type claims. However, a person skilled in the art will
gather from the above and the following description that, unless
other notified, in addition to any combination of features
belonging to one aspect also any combination between features
relating to different aspects or embodiments, for example even
between features of the apparatus type claims and features of the
method type claims is considered to be disclosed with this
application.
[0027] The aspects and embodiments defined above and further
aspects and embodiments of the present invention are apparent from
the examples to be described hereinafter and are explained with
reference to the drawings, but to which the invention is not
limited.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 schematically shows a measurement circuit for
impedance measurements.
[0029] FIG. 2 schematically shows a measurement circuit for
measuring the impedance response of a loudspeaker device.
[0030] FIG. 3 schematically shows a measurement circuit for sound
pressure level measurements.
[0031] FIG. 4 schematically shows a grain of a zeolite material in
accordance with embodiments of the herein disclosed subject
matter.
[0032] FIG. 5 schematically shows a zeolite material in accordance
with embodiments of the herein disclosed subject matter.
[0033] FIG. 6 shows nitrogen adsorption isotherms for zeolites in
accordance with embodiments of the herein disclosed subject
matter.
[0034] FIG. 7 shows nitrogen adsorption isotherms for BEA zeolites
before and after aging.
[0035] FIG. 8 shows nitrogen adsorption isotherms for MFI zeolites
before and after aging.
[0036] FIG. 9 shows nitrogen adsorption isotherms for FER zeolites
before and after aging.
[0037] FIG. 10 shows electrical impedance curves for zeolites in
accordance with embodiments of the herein disclosed subject
matter.
[0038] FIG. 11 shows cumulative pore volume curves for zeolites in
accordance with embodiments of the herein disclosed subject
matter.
[0039] FIG. 12 shows electrical impedance curves for zeolite
materials of FIG. 11 and for an empty resonance space.
[0040] FIG. 13 shows sound pressure level measurements for a
loudspeaker device in accordance with embodiments of the herein
disclosed subject matter, for a loudspeaker device with empty
resonance space and for a loudspeaker device having activated
carbon fibers in its resonance space.
[0041] FIG. 14 shows electrical impedance curves for different
grain sizes of zeolite material in accordance with embodiments of
the herein disclosed subject matter.
[0042] FIG. 15 shows electrical impedance curves for zeolite
materials with different polymer content in accordance with
embodiments of the herein disclosed subject matter.
[0043] FIG. 16 shows a loudspeaker device in accordance with
embodiments of the herein disclosed subject matter.
DETAILED DESCRIPTION
[0044] The illustration in the drawings is schematic. It is noted
that in different figures, similar or identical elements are
provided with the same reference signs or with reference signs,
which are different from the corresponding reference signs only
within the first digit.
[0045] In the following, the measurement methods employed to
determine the experimental results which are presented herein are
described.
Room Temperature Nitrogen Sorption Measurements
[0046] Nitrogen adsorption isotherms have been determined at 25
degrees Celsius (.degree. C.) between 25 millibar (mbar) and 1100
mbar with a sorption measurement device "Nova 1000e" of the firm
"Quantachrome". Further technical information is available from the
technical datasheets of the firm "Quantachrome", e.g. in the
section "A Method for the Determination of Ambient Temperature
Adsorption of Gases on Porous Materials" in Powder Tech Note
19.
Measurement of the Electrical Impedance
[0047] The measurement of the loudspeaker impedance is based on the
circuit 30 shown in FIG. 1. A reference resistance R2 is connected
between an exciting signal source 2 and a loudspeaker 3. R1 denotes
the ohmic resistance of the supply lines 1.
[0048] The electrical impedance is frequency dependent. After
measurement of the voltages U1 and U2 as a function of frequency f,
i.e. U1(f) and U2(f), the impedance Z of is calculated according to
the following equation:
Z ( f ) = U 2 ( f ) U 2 ( f ) - U 1 ( f ) R 2 ##EQU00001##
[0049] The measurement circuit 40 for determining the impedance
response shown in FIG. 2 comprises a loudspeaker of the type NXP
RA11x15x3.5, serial No. 0001A5 9205E 11141345, indicated at 3 in
FIG. 2, which has been mounted hermetically sealed with a sealing 4
over a closed volume 5 (ca. 500 mm.sup.3, 12.5 mm.times.9.5
mm.times.4.2 mm). The closed volume 5 forms a resonance space for
the loudspeaker. The resonance frequency with the resonance space
being empty is 1000 Hz. In an exemplary embodiment, the exciting
signal was generated by a computer soundcard 7 wherein the exciting
signal is provided to the loudspeaker via an audio output port 6 of
the computer soundcard 7. The left line output port 6 serves to
output the test signal, the left line input port 8 serves for
acquisition of a device under test (DUT) signal and the right line
input port 9 serves as a reference input port. The resistance 10
serves for damping the test signal.
[0050] By a resonance effect there is generated an amplification of
the test signal, wherein the amplification depends on the volume of
the resonance space. If the volume of the resonance space is empty,
there is a certain amplification of the test signal at a certain
frequency. By reducing the volume, the amplification shifts towards
higher frequencies. By enlargement of the volume or by placing a
suitable zeolite material in the resonance space the maximum of the
amplification can be shifted to lower frequencies.
Sound Pressure Level Measurements
[0051] FIG. 3 schematically shows the experimental setup 50 for the
sound pressure level measurements. The left output port 11 of the
soundcard 12 is used as a signal source for the loudspeaker 3. The
left input 14 of the soundcard is used for recording the output
voltage of a microphone 15.
[0052] For evaluation of the measurement data the programs "Arta"
and "Limp" have been used. Further details on the evaluation and
the experimental setup can be taken from the users guide of the
programs "Arta" and "Limp". The users guides are available under
http://www.fesb.hr/.about.mateljan/arta/.
Results and Description of Embodiments
[0053] According to the findings of the inventors, the prior art
does not provide a loudspeaker system with an aging resistant, well
functioning adsorber with a low acoustic resistance. For example,
activated carbon can be used as gas adsorbing material, however
there are a plurality of problems. Activated carbon is electrically
conducting and can interfere with the electromagnetic transducers
of the loudspeaker or other electronic parts within or external to
the loudspeakers. Interaction with the surrounding equipment
generated by induction of currents in the electrically conducting
material are usually undesirable. For example, if an antenna is
placed close to the electrically conducting material, the transmit
power of the antenna is reduced.
[0054] Further, the use of carbon-based materials can lead to
further problems. For example, it has been observed by the
inventors that the chemically reactive activated carbon can react
with metal parts of the loudspeaker housing leading to corrosion.
Another severe problem with the use of activated carbon is the
occurrence of short circuits by aberration of the activated
carbon.
[0055] No electrically non-conducting sorption material is known
which results in a virtual acoustic enlargement of the volume of
the resonance space by at least a factor of 2 for resonance
frequencies of larger 500 Hz. By an enlargement of the virtual
acoustic volume by the factor of 2, resonance shifts to lower
frequencies of over 150 Hz can be achieved with known miniature
loudspeaker systems. For achieving a high virtual enlargement of
the resonance space a high sorption capacity for nitrogen as a main
portion of air and a high sorption coefficient (dn/dp) at 10.sup.5
Pa is important in order to allow a large volume of gas to adsorb
on or desorb from the sorption material when pressure variations
occur. Herein "n" denotes the adsorbed amount of gas and "p"
denotes the pressure of the gas.
[0056] For a good sorption capacity the surface of the sorber
should be as large as possible since the gas molecules adsorb
primarily on the surface. However, other parameters such as
morphology, chemical structure, curvature of the surface, etc. is
important for the sorption capacity of the material. However, an
exact correlation between the above properties of a substance and
its sorption properties is unknown, at least for gases at
temperatures above their critical temperature Tc. This is the case
for Oxygen and Nitrogen at ambient temperature, since
Tc(N.sub.2)=126 K and Tc(O.sub.2)=155 K. Since the volume that is
available for the sorber is limited, a criterion for suitability of
the sorber for virtual acoustic volume enlargement is the sorption
capacity per volume unit. Hence, the sorption capacity per mass
unit are only of limited interest.
[0057] According to the findings of the inventors, a sorber with
intrinsically non-porous material and low particle size is
unsuitable for achieving a virtual acoustic enlargement of a
resonance space. Such a material is dried colloidal SiO.sub.2 with
a particle size of about 9 nm. For such a particle size, the binder
particles should be of the same size because otherwise the amount
of sorber particles per volume unit and hence the adsorbing surface
per volume unit would decrease to a large extent. However, a
distance between sorber particles in nanometer range results in an
undesired high acoustic resistance for the sorber.
[0058] For materials with a large internal surface, i.e. for
intrinsically porous materials such as zeolites, larger particles
can be used for building the sorber.
[0059] Zeolites are typically synthesized in particle sizes up to
10 .mu.m. If these particles are glued to each other in a simple
manner, the resulting acoustic resistance is too high due to low
distances between the particles.
[0060] One problem with zeolite particles with a diameter over 10
.mu.m is the accessibility of the inner regions of these particles.
Since the time span for the respective adsorption and desorption
process is within a few milliseconds, the path to the absorption
location should be as short as possible which is not realized for
particles greater 10 .mu.m. Hence, in comparison to smaller
particles there is only a limited increase of the virtual acoustic
volume of the resonance space filled with such particles.
[0061] FIG. 4 shows a zeolite material 100 in accordance with
embodiments of the herein disclosed subject matter. The zeolite
material 100 comprises zeolite particles, some of which are denoted
by 102 in FIG. 4. The zeolite particles have internal, first pores
104, indicated by the structure shown within the individual zeolite
particles shown in FIG. 4.
[0062] The zeolite particles are adhered together with a binder
(not shown in FIG. 4). In accordance with an embodiment of the
herein disclosed subject matter, second pores 106 are formed
between the zeolite particles 102. In an exemplary embodiment the
second pores 106 have a diameter of about 1 to 10 micrometer, as
indicated in FIG. 4. Due to the binder, the individual particles
102 in FIG. 4 are adhered together to form a grain 108.
[0063] It should further be mentioned that although the zeolite
particles 102 are drawn with a rectangular shape in FIG. 4, the
real zeolite particles may have a different form which depends on
the actual structure of the zeolite particles.
[0064] FIG. 5 shows a plurality of grains 108 of the type shown in
FIG. 4. As indicated in FIG. 5, the diameter of the grains 108 is
about 0.5 mm to 0.6 mm in an embodiment.
[0065] By extensive experiments the inventors found that good
sorbing characteristics can be obtained with a zeolite of the
structure type FER or MFI. In the experiments it turned out that
zeolites with a high silicon to aluminium mass ratio are
advantageous regarding the adsorption/desorption requirements. This
may be due to an increased hydrophobicity of these zeolites such
that generally possible concurrent water adsorption processes take
place only to a limited extent.
[0066] Zeolite structures which can be synthesized in the form of
pure SiO.sub.2 or almost pure SiO.sub.2 are for example the types
DDR, FER, MFI or BEA. The three letter code relates to the
classification of zeolites according to the International Zeolite
Association and can be obtained inter alia from
http://www.iza-online.org/. The code orders the zeolite according
to their atomic structure. A zeolite in the form of at least pure
SiO.sub.2 is characterized by a very low aluminium content, i.e. by
a silicon to aluminium mass ratio over 200.
[0067] By extensive measurements it was found that the zeolite type
FER has the highest sorption capacity for nitrogen at room
temperature among the investigated zeolites. Details of the
experimental results are shown in FIG. 6 where the amount of
adsorbed gas (nitrogen) A in millimol per milliliter (mmol/ml) is
shown over the pressure p in millibar (mbar) for the zeolite types
BEA, MFI, FER and DDR. For measurement of the adsorption capacity,
the pure silicon zeolites in powder form have been activated for 1
h at 500 degrees Celsius. Activation was performed to remove any
possible residuals from the zeolite. The volume of zeolite was
determined by measuring the mass of the zeolite and dividing the
mass by the cristallographically determined density of the zeolite
which is also known to the skilled person.
[0068] To determine the aging behaviour of the investigated
zeolites, nitrogen adsorption isotherms have (amount of adsorbed
gas A in mmol/ml over pressure p in mbar) been determined after
activation (curve 1) and after aging for one week at ambient air
under normal conditions (curve 2).
[0069] The results are shown in FIG. 7 for the zeolite type BEA, in
FIG. 8 for the zeolite type MFI and in FIG. 9 for the zeolite type
FER.
[0070] To summarize the above findings, among the zeolites under
consideration in pure SiO.sub.2 modification the structure type
ferrierit (FER) as the highest sorption capacity for nitrogen per
volume unit at normal pressure and, in contrast to the zeolite type
BEA in its almost pure SiO.sub.2 modification does not age. Up to
now there is no explanation for this surprising experimental
result. Although it is known to the skilled person that zeolites
can adsorb different substances and that adsorption of substances
of high vapour pressure can lead to an obstruction of the pores and
hence to a reduction of the sorption capacity of small molecules,
it is not clear why the substances which are adsorbed by zeolite
BEA apparently lead to an irreversible reduction of the sorption
capacity and why this effect does not occur with the zeolite FER.
With the zeolite type MFI only negligible aging processes occur due
to environmental influences which lead to a likewise negligible
reduction of the sorption capacity in the loudspeaker device.
Hence, the zeolite MFI in its aging behaviour is comparable to the
zeolite type FER.
[0071] Hence, zeolite type FER is a promising candidate for the
application as a sorber material in a loudspeaker device in
accordance with the herein disclosed subject-matter. However, it
should be understood that also other types of zeolites can be used
for providing a zeolite material according to the herein disclosed
subject matter.
[0072] In a comparison of the pore diameters of the intrinsic pores
of the zeolites under investigation, it was found that the
diameters of the intrinsic pores of the zeolites BEA, MFI, FER, DDR
fall continuously in this order from 0.7 nm to 0.4 nm. From the
experiments it appears advantageous to use zeolites with a small
intrinsic pore diameter, wherein the lower boundary for the
intrinsic pore diameter is given by the size of the nitrogen
molecule which is about 0.4 nm. However, up to now there is no
explanation for the bad performance of the DDR zeolite with the
pore diameter of 0.44 nm.times.0.36 nm which should provide a good
accessibility for nitrogen.
[0073] Generally it is possible that other zeolite types which can
be produced in a hydrophobic form are as well suitable for
providing a zeolite material according to the herein disclosed
subject matter. For example, the zeolite types CHA, IHW, IWV, ITE,
UTL, VET, MTW can also be produced as pure or doped SiO.sub.2
modifications and have hydrophobic properties. Doping can be
performed with, for example, elements of the fourth group of the
periodic table, e.g. with germanium.
[0074] From the experiments it was found that the particle size of
the primary particles of the zeolite is advantageous below 10
.mu.m. According to an embodiment of the herein disclosed
subject-matter, the diameter of the primary particles is below 5
.mu.m. According to a further embodiment, the diameter of the
primary particles is below 2 .mu.m. According to a further
embodiment, the diameter of the primary particles is larger than
300 nm.
[0075] It was shown by comparison measurements that a diameter of
the primary particles larger than 10 .mu.m is detrimental for the
enlargement of the virtual acoustic volume of the resonance space
of the loudspeaker device. FIG. 10 exemplarily shows measurements
of the electric impedance I in Ohm (.OMEGA.) over frequency f in
Hertz (Hz) of a loudspeaker device with FER zeolite in powder
application with different diameters of the primary particles. To
this end, the electric impedance curves of a loudspeaker device
with an empty resonance space and with the resonance space filled
with FER zeolite in pure SiO.sub.2 modification was measured for
two different particles sizes. The applied mass of zeolite was 60
mg in each case. The results are shown in FIG. 10. Curve (1) shows
the impedance of the loudspeaker device with FER zeolite with a
diameter of 5 .mu.m. Curve (2) of FIG. 10 corresponds to the empty
resonance space and curve (3) corresponds the resonance space
filled with FER zeolites with a diameter of the primary particles
of about 100 .mu.m. Since the zeolite was applied in powder form no
more zeolite could be applied in the resonance space of the
loudspeaker without considerable damping. From FIG. 10 it can be
taken that for the primary particle diameter of 100 .mu.m the
obtained shift of the resonance maximum compared to the empty
resonance space is lower than the shift of the resonance maximum
for a diameter of the primary particles of 10 .mu.m. Further, the
full width at half maximum of the resonance peak is much larger for
the larger primary particle size.
[0076] From the experiments performed by the inventors it was found
that for in presence of macropores with a pore diameter of larger
than the intrinsic micropores of the zeolite the shift of the
resonance peak is further increased and the damping is reduced
compared to the same material without macropores. One experimental
example (referred to hereinafter as first method) how a large
amount of these macropores can be obtained is to use 44 g
calcinated zeolite MFI in pure SiO.sub.2 modification and with a
primary particle size of 1 .mu.m (diameter) and disperse this
zeolite in 96% ethanol. Then, a polyacrylate suspension is provided
in an amount such that the concentration of the polyacrylate in the
solid product is 5%. To this end, an initial, aqueous polyacrylate
suspension was provided with a concentration of 11 weight %
polyacrylate. The polyacrylate suspension at first has been doubled
in its volume with 96% ethanol and has been then added to the
zeolite suspension under extensive stirring. The resultant mixture
was pured onto a plate of size 50.times.50 cm.sup.2 and a
temperature of 160 degrees Celsius within 3-4 seconds. The
resultant solid was then broken up with a cutting mill and
fractionated with analysis sieves. Of the thus obtained solid a
cumulative pore distribution was determined by mercury porosimetry.
The result is shown in FIG. 11, curve (1), where the cumulative
pore volume Vp in cubic millimeter per gram (mm.sup.3/g) is plotted
over the pore diameter d in micrometer (.mu.m). It should be noted
that the cumulative pore volume means that the volume level is
constant if no pore volume is present at a specific pore diameter.
Hence a pore diameter distribution can be obtained from the first
derivative of the cumulative pore volume (d(Vp)/d(d)).
[0077] Further, results of a comparison material according to
embodiments of the herein disclosed subject matter are also shown
in FIG. 11. The comparison material has been obtained from
dispensing 44 g calcinated zeolite MFI in pure SiO.sub.2
modification and a primary particle size of 1 .mu.m in water.
Subsequently, an aqueous polyacrylate suspension (11 weight %
polyacrylate) was added such that a polymer portion related to the
whole solid content was 5%. The mixture was homogenized with a
stirring device and was dried under stirring with hot air. The
resultant solid was broken with a cutting mill and fractionated
with analysis sieves. The cumulative pore volume over pore diameter
of this material which was also obtained by mercury porosimetry is
shown as curve (2) in FIG. 11. From FIG. 11 it is apparent that the
first method for preparation of the zeolite material leads to a
considerable increase of the fraction of macropores with a diameter
in the range of 1 .mu.m-10 .mu.m.
[0078] FIG. 12 shows the electric impedance (I) measurements of
both materials over frequency f, wherein curve (1) corresponds to
the material with increased macropore fraction, curve (2)
corresponds to the comparison material and curve (3) corresponds to
the empty resonance space. The material with the increased
macropore fraction leads to a higher resonance shift, a higher
increase of the virtual acoustic volume, and, at the same time, to
reduced damping.
[0079] In FIG. 13 sound pressure level (SPL) over frequency f
measurements are shown for a commercially available
micro-loudspeaker device type NXP RA11x15x3.5, the back volume
(resonance space) of which amounts to 1 cm.sup.2. Line 1 shows the
frequency response of the loudspeaker device with empty resonance
space, line 2 shows the frequency response of this loudspeaker
device with activated carbon fibre web in the resonance space and
line 3 shows the frequency response of the same loudspeaker device
with the zeolite material with increased macropore fraction in the
resonance space. The resonance frequency shifts to the same extent
by both materials, the activated carbon fibre web and the zeolite
material with the increased macropore fraction, from 800 Hz down to
630 Hz. Also the damping of the two materials is comparable. Both
materials are damping the loudspeaker to such a weak extent that
the original sound pressure level of about 90 dB is maintained.
However, the zeolite material with the increased macropore fraction
is an electrically non-conducting material and is not subjected to
aging.
[0080] According to an embodiment, the individual constituents of
the zeolite material, referred to as grains herein, have a diameter
between 0.1 mm and 0.9 mm and include a plurality of zeolite
particles (see FIG. 4 and FIG. 5 above). According to a further
embodiment, the grains have a diameter in the range of 0.4 mm and
0.7 mm. For example, the above referenced zeolite material with
increased macropore fraction has a grain size of 0.3 mm. For
investigating the influence of the grain size, different grain size
fractions have been taken with respective sieves and electrical
impedance spectra of these materials have been taken. FIG. 14 shows
the measured spectra (impedance I in Ohm over frequency f in
Hertz). The respective grain diameters for the individual curves in
FIG. 14 are given in mm. As is apparent from FIG. 14, for a grain
diameter of 0.6 mm as well as below a grain diameter of 0.3 mm, the
frequency shift of the resonance maximum is smaller and the damping
is higher as for grain diameters in a range of 0.3 mm to 0.6
mm.
[0081] A grain size below 0.1 mm results in an undesirable movement
of the grains in the loudspeaker which may result in non-linear
distortions of the sound. For grain diameters larger than 0.9 mm
the acoustic resistance undesirably increases.
[0082] According to a further embodiment of the herein disclosed
subject-matter, the sorber material contains less than 20% binder
(polymer material). According to a further embodiment, the sorber
material contains less than 10% binder. According to a further
embodiment, the sorber material contains at least 1% binder. The
binder glues the zeolite primary particles together. It has turned
out in the experiments that for polymer fractions larger than 10%
(in the solid-state), the virtual acoustic volume enlargement, that
is achieved by introducing the material in the resonance space of
the loudspeaker device, is below 1.5. For polymer concentrations
below 4% (again related to the whole mass in the solid-state (mass
of polymer/whole mass)), the resulting material is instable and
shows heavy abrasion. FIG. 15 shows electrical impedance (I) curves
of materials with different polymer concentrations over frequency
f. The materials used for the spectra in FIG. 15 include zeolite
particles of the zeolite with the increased macropore fraction
obtained as described above (curve 1 in FIG. 11). Curve 1 of FIG.
15 is obtained for the zeolite material with 6% polymer and curve 2
of FIG. 15 is obtained for the zeolite material with 12% polymer.
As is apparent from FIG. 15, the higher polymer content leads to a
smaller shift of the resonance frequency towards lower
frequencies.
[0083] FIG. 16 shows a loudspeaker device 200 in accordance with
embodiments of the herein disclosed subject matter. The loudspeaker
device 200 comprises a loudspeaker receptacle 202 for receiving a
loudspeaker 3. Further, the loudspeaker device 200 comprises a
zeolite material 100 according to aspects and embodiments of the
herein disclosed subject matter in a region 204, e.g. a resonance
space, that is exposed to sound generated by the loudspeaker 3 of
the loudspeaker device 200.
[0084] It should be noted that the term "comprising" does not
exclude other elements or steps and the "a" or "an" does not
exclude a plurality. Also elements described in association with
different embodiments may be combined. It should also be noted that
reference signs in the claims should not be construed as limiting
the scope of the claims.
[0085] In order to recapitulate the above described embodiments of
the present invention one can state:
[0086] A loudspeaker device is presented which includes a zeolite
material comprising zeolite particles having a silicon to aluminum
mass ratio of at least 200. For an increased pore fraction of pores
with a diameter in a range between 0.7 micrometer and 30 micrometer
shows an increased shift of the resonance frequency down to lower
frequencies has been observed.
LIST OF REFERENCE SIGNS
[0087] 2 signal source [0088] 4 sealing [0089] 3 loudspeaker [0090]
5 closed volume [0091] 6 audio output port [0092] 7 soundcard
[0093] 8 left line input port [0094] 9 right line input port [0095]
10 resistance [0096] 11 left output port [0097] 12 soundcard [0098]
14 left input [0099] 15 microphone [0100] 30 impedance measuring
circuit [0101] 40 impedance response measuring circuit [0102] 50
setup for sound pressure level measurement [0103] 100 zeolite
material [0104] 102 zeolite particle [0105] 104 first pore withing
zeolite particle [0106] 106 second pore between zeolite particles
[0107] 108 grain [0108] 200 loudspeaker device [0109] 202
loudspeaker receptacle
* * * * *
References