DE202013012087U1 - Sound transducer (loudspeaker) with electromagnetic drive, in which a freely oscillating mounted diaphragm in the center of a permanent magnet is fixed, is excited centrally between two electromagnets by driving with an alternating current to vibrate - Google Patents

Abstract

Main claim sound transducer (speaker) with electromagnetic drive, in which a freely oscillating mounted diaphragm, in the center of a permanent magnet is fixed, is excited centrally between two electromagnets by driving with an alternating current to vibrate.

Description

Sound transducer (loudspeaker) with electromagnetic drive, in which a freely oscillating diaphragm, in the center of which a permanent magnet is fixed, is excited centrally between two electromagnets by driving with an alternating current to oscillate.

State of the art and its disadvantages

The current standard in the loudspeaker area is the electrodynamic sound transducer, which moves a voice coil, which is mechanically firmly coupled to the membrane through the NF signal, in an air gap of a permanent magnet and thus generates sound pressure by piston-shaped diaphragm movement.

There are also other systems, such. As electrostatics and magnetostats, which, however, are rarely represented.

My following statement of the disadvantages therefore concentrates on the most common systems, ie on the electrodynamic sound transducers, as they are used today predominantly for sound reproduction in the audible frequency range.

The disadvantages of conventional drives:

• - High power consumption, especially in the low frequencies.
• - Low, system-related efficiency through the air gap.
• - Mechanical tilting of the voice coil as the most frequent failure cause.
• - Mechanically oscillating electrical components (voice coil, lead wires).
• - Poor heat dissipation of the power loss in the air gap.
• - Only limited possibilities for external cooling of the voice coil.
• - High weight, especially in so-called woofers and subwoofers.

For a pulse-faithful reproduction parameter determining spring constant or restoring force of the membrane in its oscillation zero point of this electrodynamic transducer is defined solely by the mechanical suspension of the membrane and the mechanical properties of the voice coil centering spider. This inevitably leads to technical and physical limits, which affects the lower limit frequency at high levels.

For a low resonance frequency, a soft suspension is required, which has on the signal reproduction tends to uncontrolled behavior of the membrane in the de-energized state and a possible reproduction of low frequencies only in very large volumes.

If the spring constant, that is to say the restoring force in favor of the pulse reproduction, is increased mechanically, a stronger drive is required as a result, which is achieved by means of large magnet systems and higher power requirements of this conventional construction.

At a current efficiency of about 3 percent between input power and sound converted power, today recording power z. B. in the bass range of up to several thousand watts required and common.

When operating in a horizontal membrane layer in so-called downfire systems, the sound radiation low frequencies is not delivered as usual on the vertical baffle, but by the installation of the transducer in the bottom of the housing leads to these systemic partly heavy membranes, the horizontal mounting method inevitably an offset from the center diaphragm zero point in the idle state and additionally by different acceleration conversions of the applied voltage to an asymmetrical vibration behavior around the mechanical zero point of the membrane.

The disadvantages of the mechanically defined spring constant / membrane restoring force

• - Beading parameters influencing bead and Zentrierspinnenmechanik.
• - Only mechanically definable, one-time adjustable restoring force.
• - Partly high mechanical losses.
• - Partly high required electrical drive power to overcome this mechanical spring constant.
• - Change in speaker parameters due to aging of the mechanical diaphragm and voice coil suspension.
• - Possible long-term fatigue of the mechanical suspension during operation of these transducers in a horizontal position.
• - Possible asymmetries of the mechanical zero point during the reproduction of sounds in horizontal position of the loudspeaker.

The electrodynamic transducer is due to its construction for the reproduction of audible sound only for a limited frequency range considered to be ideal. An uncompromising full-range speaker, which has the audible frequency range of 20 Hz to 20 kHz with only one driver / Loudspeaker chassis does not exist. Deep tones require large membranes, medium tones medium and high frequencies require very small, small membrane areas.

Today's broadband speakers according to the electrodynamic principle cover a maximum of the range from 200 Hz to 10 kHz linearly and must be supported for the playback of the entire audio frequency range by a separate woofer and an additional tweeter. This leads to the construction of so-called multi-way boxes, which have on their baffle 2, 3 or more specialized in the respective frequency range individual driver / transducer. From a distance of about 1 meter, it is assumed that the sound reproduction of these individual sound sources adds up to a homogeneous field for the listener. However, in practice, differences in transit-time due to the mechanical different positions of the drivers on the baffle lead to a loss of spatiality, which is strongly influenced by the position of the drivers on the baffle. Ideal would be a sound transducer, which radiates the entire audible frequency response from a single acoustic center.

So-called coaxial loudspeakers, which mechanically interlock two electrodynamic loudspeakers, are already going in this direction, but remain compromising. In addition, these transducers build mechanically partly strong inside the housing.

The invention and its advantages over the prior art

The invention underlying this application relates to the field of sound reproduction audible frequencies in the form of sound transducers (speakers) and claims the patents of technical innovations in the areas of membrane drive (main claim), the electromagnetically adjustable spring rate for membrane return in the membrane oscillation zero point (additional claim) and the innovation of the realization of a point sound source with segmented membrane and drive unit within a common sound transducer (additional claim).

The invention specified in the protection claim 1 uses the use of a coil pair ( 8th ), which is achieved by the use of two structurally identical, opposing electromagnets ( 8th ) is realized.

Ideally, when defining the distance between the two coils ( 8th ) (Electromagnets) applied the principle of the Helmholtz coil. Thus, a very homogeneous magnetic field is formed between the two electromagnets which face each other at a distance of their radius, with identical current flow strength through both coils.

In the center of this magnetic field is a on a membrane ( 1 ), which is freely swinging and airtight at its outer edge, fixed permanent magnet ( 7 ) whose magnetic field is aligned in the direction of its axis so that it is an electromagnet ( 8th ) a north pole and the other electromagnet ( 8th ) has a south pole.

The center in which the magnet ( 7 ) is in the de-energized rest state, defines the oscillation zero point.

If this two-part coil is now fed with an alternating current, which flows through both coils in opposite phase, according to a Maxwell coil, results in consideration of signal snapshots, in each point of the alternating current, an attraction of the poles of coil and permanent magnet in the direction of a partial coil and at the same time an identical in amplitude repulsion of the permanent magnet from the second coil.

As a result, the membrane ( 1 ) according to amplitude and frequency of the flowing alternating current between the two electromagnets ( 8th ) (Partial coils) around their oscillation zero point.

If the alternating current component is fed in the form of a low-frequency audio signal (NF), this transducer converts the membrane vibrations into audible tones.

The advantages of this drive

• - Low power consumption.
• - High efficiency due to missing air gap.
• - Negligible mechanical losses.
• - No mechanical tilting of a voice coil possible.
• - No mechanical oscillating electrical components.
• - Very good heat dissipation and possibility for external cooling of the power loss
• - Strong weight reduction of woofers and subwoofers.

The specified as a dependent claim 1 invention describes an innovation to the electromagnetic adjustment of the spring constant for membrane recovery reference to the transducer below 1, the main claim.

If the two sub-coils of this coil arrangement are now traversed by a DC current in the same direction, a static homogenous bias is produced in their center which acts on the magnet floating in the center from both partial coils with the same force in the direction of the membrane.

This force is depending on the common direction of current through the coil sections, an identical in both directions attractive or in both directions identical repulsive force, which always centers the permanent magnet in its zero oscillation. I refer to this process as bias and the associated current as bias current. The magnetic force, which acts on the permanent magnet and thus on the membrane from both sides, changes linearly in proportion to the magnitude of the bias current.

Thus, a return of the diaphragm to the mechanical zero point between two phase-rotated LF signal deflections takes place exclusively electromagnetically.

I refer to this force, which presses the permanent magnet from both sides with identical force, as membrane restoring force or electromagnetic spring constant.

By this principle, the desired spring constant of the system can be freely selected.

Contrary to conventional electrodynamic acoustic transducers, this spring constant does not have to be overcome by high additional electrical power when applying / superposing the audio AF signal.

The superimposed electrical NF signal increases the magnetic field of a coil and simultaneously reduces the magnetic field of the opposite coil with theoretically constant power consumption of the entire system.

As a result, the membrane is set in motion, ie the point in which the identical static forces of the coil sections (electromagnets) meet and cancel with respect to the diaphragm movement, with the LF signal frequency and amplitude shifted.

In summary, there is an AC-induced shift of the bias to the DC magnetic field caused vibration zero point of the membrane.

The advantages of the electrically adjustable restoring force

• - Only electrically defined and freely configurable spring constant
• - Stepless, freely adjustable spring constant
• - Theoretically load-free vibration control of the DC premagnetized system.
• - Adjustment of an unbalanced spring constant around the zero point for horizontal use, especially as a bass speaker
• - Absolute freedom of influence of the loudspeaker restoring force during material fatigue of the diaphragm suspension.

Specified as a dependent claim 2 invention describes a point sound source with segmented membrane and drive unit within a common sound transducer based on the main claim.

The drive described and the freely adjustable spring constant of the membrane allow the construction of multi-way point sound sources with common acoustic and mechanical center and independently of the respective transmission range optimized vibrating sub-segments of the driven sound-generating membrane.

A mechanical embodiment of the invention will be described with reference to FIG 1 and 2 explained.

Show it:

1 The top view of a possible mechanical implementation.

2 The side view in section of a possible mechanical implementation.

In the 1 and 2 is the transducer with membrane 1 , Beading 2 , Membrane surround 3 , Electromagnet holder 4 , Fittings 5 , Cable entry 6 , in the center of the membrane fixed permanent magnet 7 and the two electromagnets (coils with or without core) 8th shown.

The membrane 1 , the bead 2 and the membrane enclosure 3 document the freely swinging membrane.

The cable entry 6 serves to carry out the connection lines of the two electromagnets away from this, to the sound transducer exterior.

Claims (3)

main claim Sound transducer (loudspeaker) with electromagnetic drive, in which a freely oscillating diaphragm, in the center of which a permanent magnet is fixed, is excited centrally between two electromagnets by driving with an alternating current to oscillate. Next claim: Electromagnetic resetting (spring constant) of the diaphragm in its oscillation zero point by an adjustable electromagnetic DC biasing of the two opposing electromagnets. Next claim: Point sound source with segmented diaphragm and drive unit within a common sound transducer.

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