WO2006130101A2

WO2006130101A2 - Acoustic form resistance

Info

Publication number: WO2006130101A2
Application number: PCT/SE2006/050152
Authority: WO
Inventors: Tommy Skogsberg
Original assignee: Tommy Skogsberg
Priority date: 2005-06-03
Filing date: 2006-05-23
Publication date: 2006-12-07
Also published as: SE527940C2; SE0501267L; WO2006130101A3; EP1891832A2

Abstract

The invention before us concerns arrangements for loudspeakers built on the principle off a membrane or other kind of medium (fig. 1 arrow 9) connected to a cabinet (fig. 1 arrow 10). The invention intend to substantially reduce the disturbing effect on the sound occurred by the wave transmission directed into the cabinet (fig. 1 arrow 2). The invention shows how this can be done by forming the details inside of the cabinet so they form a level acoustical resistance for the membrane over the frequency range covered by the loudspeaker. The result will be a higher quality of the sound than with an ordinary design and a more natural sound reproduction.

Description

Name on the invention

Acoustic Form Resistance

Background to the invention

Wave transmitters like for instance loudspeakers will have supplementary forces on the membrane and the transmission system caused by the waves directed into the cabinet.

Inside of the cabinet those supplementary forces is caused by the forms on the details included in the design, by reflections and resonances.

This supplementary forces conveys unlinearities in the acoustical resistance of the membrane, unlinearities that can occur anywhere in the loudspeakers frequency range.

This supplementary forces will bring about alterations on the movement of the membrane that will alter the original sound that was meant to be reproduced.

The invention intend to eliminate or substantially reduce this feedback and unlinearities in the acoustical resistance on the membrane and the additional movements that unsuitable design on details inside of the cabinet will bring about.

Description of the figures.

Fig. 1 Drawing example on a loudspeaker. The numbers in the text refers to the numbers in the drawing.

Fig. 2 Diagram showing how a cylinder will rise the acoustical resistance.

Fig. 3 Diagram showing how a conical cylinder will rise the acoustical resistance.

Description of the invention.

This invention can be applied on most sound reproducing systems like loudspeakers built on the principle off one or more membranes (fig. 1 arrow 9) (Figure 1 will further on be referred to only with the numeral of the arrow in question, accordingly: (9)) or other kind of medium connected to a cabinet, capsule, box or similar (10).

Repercussions from the waves directed into the cabinet (2) will distort the sound that the loudspeaker is intended to reproduce. When this invention is applied the disturbances will be reduced. This is done by forming the interior and the details inside of the cabinet so that their disturbing influence on the acoustical resistance of the membrane will be minimised and the acoustical design in the interior will interact in the best way or in an intended way with the whole sound system in it' s function to reproduce sound.

Usage field of the invention The invention is used in the designing of sound transmitters like loudspeakers and loudspeaker systems to rise the quality of the sound.

The technique the invention is based on.

The invention is based on the technique loudspeakers are built on, described in the technical literature and periodicals like Journal Of Audio Engineering Society, by L. L. Bernie, H. F. Olson, E. M. Villchur, A. N. Thiele, R. H. Small and others.

What the invention brings about.

Conventionally built loudspeakers with a membrane fitted in a cabinet will by their build up add its own contributions to the original sound that they was meant to reproduce. A great deal of this contributions is caused by repercussions from the sound waves that goes into the box. This is the great problem with loudspeaker reproduction that every designer of loudspeakers try to handle in one way or another. To make a loudspeaker design that produces a sound that will be experienced very similar to the sound of a concert hall, jazz club, the nature etc. is very complex and demands knowledge in many fields and aspects. What will be reached when this invention is applied is that the form of internal details can be designed so they will interact on the acoustical resistance on the membrane in a way that the designer can chose.

The invention before us shows how different shapes effects the acoustical resistance. By using the principles of the invention an engineer can design for instance loudspeaker elements so they will show up a level acoustical resistance in the frequency regions that their build up parts will influence. Furthermore, the engineer can use extra details that alters the shape on the details that will be hard to manufacture in an ideal shape, like loudspeaker magnets etc. Details which sole purpose is to by their shape fill hollows in the acoustical resistance can also be used. When applying this patent and its technique the designer now can give the loudspeaker system a very even acoustical resistance over the whole frequency range, witch will result in an even transient response over the frequency range and this will be experienced as a very balanced and enjoyable sound. Our ears are very sensitive for unlevel transients in sounds and will experience unlevel transients as softness and harshness in different frequency areas witch is very disturbing for the listening experience. This will be cleared out when applying this invention in an appropriate way and the sound result will be closer to the origin, a clearer, cleaner and more enjoyable sound.

Means of the Invention

The means of the invention is the inner design of the cabinet (10). The design and shape of inner details in the cabinet (for instance the frame of loudspeaker elements). Elements that are altering the shape of unsuitable formed details in the cabinet (like loudspeaker magnets) and elements (11) which have the purpose of damping the sound waves. The invention that lies before us describes how different shapes interacts with the acoustical resistance on the loudspeaker membrane. All the means can be used to minimise the repercussion on the membrane so that the disturbance from the sound waves that goes into the cabinet can be kept to a minimum and the original sound will be transmitted as unaltered as possible. All means can be used together, alone or in any combinations.

Explanation of the invention

In conventional loudspeakers the inner shape of the cabinet and the shape of details inside of the box will give rise to unlevel acoustical resistance over the loudspeakers frequency range. To avoid or compensate this unlevel acoustical resistance this invention are using forms that are shaped to function as controlled acoustical resistance, adapted in size and shape so that the loudspeaker system receive a level acoustical resistance on the membrane over its frequency range. This forms can consist of the loudspeaker elements which have been shaped not to interfere on but to maintain a desired acoustical resistance off the loudspeaker system over its frequency range. (With the term loudspeaker system is meant the whole design with cabinet, elements etc. With loudspeaker element is meant the electromechanical element that are producing the sound)

This forms can also consist of form elements (7, 8) with the purpose of changing the shape of unsuitable formed details to more appropriate shapes and of elements with the only purpose to shape the acoustical resistance. (11)

When designing this shapes, the discovery protekted by this invention before us is used: Every shape with a fixed position in the interior of a defined loudspeaker will interact on the acoustical resistance of the membrane with forces in frequency sections that corresponds to the shapes and their dimensions, (fig. 2, fig. 3.) The figures show how a form with an even dimension will constitute a strong acoustic damping in a narrow frequency band (fig. 2) while a form with varying dimension will constitute a weaker damping in a broader frequency band than the first form. (Fig. 3) This is the basic principle in this discovery and it can be used by a skilled designer with good understanding of sound in a very refined, advanced and powerful way. This form elements can be made in many different materials, forms and arrangements so that the designers purpose can be fulfilled in various applications.

The invention can also be used to design the acoustical resistance to be larger or smaller in different frequency regions to meet special requirements. This is done by using bigger forms to influence the acoustic resistance in lower frequencies and smaller forms to influence the acoustical resistance in higher frequencies.

The acoustical resistance or reactance can be very exactly formed by the discovery protected by this patent: The forms and the dimensions on the forms that are on the rear side of the membrane will interact with acoustical forces on the membrane (9) in frequency regions that directly corresponds to the shape, size and location of the forms. In the case there is a closed box behind the membrane, the influence from the walls on the forms and the forms location and direction inside the box will also effect the acoustical resistance that the forms represents. This resistance can be looked upon as a part of the Q value. This patent specifies this Q- value or acoustical resistance as a variation in acoustical resistance over the frequency region of the transmitter. In the same way as loudspeakers in common tests will have a frequency curve for the sound level. The inventor have named this Q- value: Qafr according to the name of this patent. This resistance that now can be given a specific form have earlier on to a substantial part been given an arbitrary form because many details like loudspeaker frames and magnets to a great extent has been formed from the aspect of beeing designed and manufactured.

The resistance that are caused by the form of the details are relatively small compared to the electrical forces from the bobbin of the loudspeaker element. But they are substantial enough to make a loudspeaker which is well designed in other aspects either to sound mediocre or to sound superior.

Addressed performance

Figure 1 shows an example on how this invention can be applied on a state of the art loudspeaker. Naturally, many different applications, variations and forms of this invention can be done.

The movement of the membrane is generating sounds that goes out into the room (1) to be listened to. Also, sound is going in the other direction, in this case into a closed box but the invention can also be applied on open designs. The sound that goes into the cabinet (2) is loaded acoustically by the forms inside and of the details inside of the cabinet, like loudspeaker magnets,

(3) loudspeaker frame (4) and other parts.

When the invention is applied, the forms of the details on the rear side of the membrane are given shapes that will interact as a level or desired acoustical resistance on the membrane.

Normally there is not mutch details in front of the loudspeaker element, ahead of the membrane, but the invention is applied in the same way in this area as behind the membrane. Forms with level dimensions (3) will be avoided, or altered with reshaping elements, instead the dimension will be varied along their length. (5) When a number of similar forms is used, they will be given different dimensions (6) to spread out the acoustical resistance over broader frequency band than a number of identical details will represent.

When details that are difficult or expensive to give an appropriate form are used, like magnets. (3)

They will be given the wanted forms by form elements that are added to give the desired forms

(7, 8 and 12)

When the acoustical resistance of the membrane in a loudspeaker shows a depression, a reduction of the acoustical resistance in a certain frequency area. Then form elements (11) that compensate for this reduction is mounted so that an level resistance will be the result.

If a higher acoustical resistance of the membrane in a special frequency region or a special profile of the load is wanted then one or more details is formed to correspond to this profile of the acoustical resistance .

The invention have been addressed on a common base/middle frequency loudspeaker to explain the invention. The invention can be used in various applications in most loudspeaker elements and loudspeaker systems. The invention can also be applied on earphones and other sound transmitters.

Claims

Name on the inventionAcoustic Form ResistanceWhat is claimed is:

1. For loudspeakers of the principle one or more membranes (9) in a cabinet (10) and other types of sound transmitters. DISTINGUISHED BY THAT THE FORMS ON THE REAR SIDE OF THE MEMBRANE/MEMBRANES/MEDIUM WILL INFLUENCE THE ACOUSTICAL RESISTANCE OF THE LOUDSPEAKER MEMBRANE in a way so that for instance a cylinder with an even diameter (fig. 2) will influence the membrane in a narrow fixed frequency band with a high acoustical resistance that will be higher the longer the cylinder is whereas a conical shaped cylinder (fig. 3) will influence the membrane over a broader frequency band and with a lower acoustical resistance than the cylinder with an even diameter, and the part of the cone with bigger diameter will interact with an acoustical resistance on lover sound frequencies and the narrow part of the cone will interact on the membrane with an acoustical resistance in higher sound frequencies, other shapes is to be formed according to this principle so that the designer can rise the acoustical resistance in a lower frequency regions by increasing the dimensions of a form and rise the acoustical resistance in a higher frequency by giving a part of the form smaller dimensions, a cleft from an orange can be used as an example of a form that have the biggest dimension on the middle and diminishing dimensions towards the ends, the details behind the membrane in the cabinet, if the design has a cabinet, and in front of the membrane, is to be formed according to this patent and the principles described, in shapes that gives an acoustical resistance on the membrane that will result in a sound character that the designer with the help of this patent can choose.

2. For loudspeakers of the principle one or more membranes (9) in a cabinet (10) and other types of sound transmitters according to claim l. D I S T I N G U I S E D BY THAT THE FORMS BEHIND THE MEMBRANE IS SHAPED by the principle that this patent is claiming, that any given form in a given loudspeaker interior influences the acoustical resistance on the movements of the membrane with a force and in a frequency area that directly corresponds to the form, its dimensions, its location and direction in the cabinet, when the invention is applied it is used to shape or reshape details rear of the membrane, inside of the cabinet, if the design has a cabinet, so that the resulting acoustical resistance will effect the produced sound in a desired way chosen by the designer.

3. For loudspeakers of the principle one or more membranes (9) in a cabinet (10) and other types of sound transmitters according to claim 1 and 2. D I S T I N G U I S E D BY THAT THE ELEMENTS INCLUDED IN THE CONSTRUCTION like loudspeaker elements, crossovers, braces etc (5, 6) is shaped so they will constitute an acoustical resistance that adds up with the whole loudspeakers working condition in a way that results in a delivered sound chosen by the designer and desired by the users. The metods to reach superior sound quality with this patent is the common ones when constructing loudspeakers, like listening tests and measurements and those are used when shaping and reshaping the forms of the details.

4. For loudspeakers of the principle one or more membranes (9) in a cabinet (10) and other types of sound transmitters according to claim 1,2, 3.DISTINGUISEDBY DAMPENING ELEMENTS that have been added for the purpose of altering the acoustical resistance of the transmitting system. (11)

5. For loudspeakers of the principle one or more membranes (9) in a cabinet (10) and other types of sound transmitters according to claim 1,2, 3 and 4. DISTINGUISEDBY ELEMENTS (7, 8 and 12) that rebuild and reshape details like loudspeaker magnets so they will constitute a desired acoustical resistance in the system.