Acoustics – Diaphragm – Critically defined material or coating
Patent
1993-06-23
1995-01-10
Weston, Caleb
Acoustics
Diaphragm
Critically defined material or coating
181169, 181170, 156242, B32B 3104
Patent
active
053809602
DESCRIPTION:
BRIEF SUMMARY
The invention concerns films or diaphragms for acoustic application that have to exhibit predetermined vibration properties, and particularly diaphragms for electromechanical transducers capable of converting an electric current received into a sound transmission (loudspeakers) or, conversely, a sound wave received into electric current transmitted (microphones), particularly for loudspeakers, and also concerns the process for the preparation of such films or diaphragms.
Present diaphragms of electro-mechanical transducers fail to meet all the increasingly severe requirements engendered by the constant improvement of the electronic portion of high-fidelity sound systems, particularly since the introduction of digital techniques.
This is because the present diaphragms do not behave at the high frequencies as perfectly rigid pistons, but exhibit natural modes and frequencies that cause reductions of the passband, irregularities in the passband, hangovers and high mechanical overpressures or stresses.
In order to broaden the passband, to reduce the irregularities, the hangovers and the overpressures or stresses, it is necessary to provide a diaphragm exhibiting increased mechanical rigidity, greater internal losses, lower density and a more appropriate sound propagation velocity.
Similar problems arise for other acoustic applications, for example for materials used in the construction of loudspeaker baffles and musical instruments.
It is a specific object of the invention to provide improved films or diaphragms for various acoustic applications.
To achieve this, the invention has firstly as an object a process for preparing a porous film or diaphragm having improved vibration properties for acoustical uses, particularly a diaphragm for loudspeaker, consisting in the succession of the following steps: containing at least 30,000 atoms in a molecule; swelling said at least one macropolymer for dosing said dispersion to have the consistency of a gel, and which has been caused in phase (b), to have the consistency of a gel, whereby obtaining said porous film or membrane.
Advantageously said macropolymer is chosen in the group consisting in the polymers of methacrylic acid, the polymers of ethyl acrylate and the mixtures of these two polymers.
More particularly, said macropolymer is the product commercially called "Appretan 9110" constitued by a mixture of about 70% of a polymer of methacrylic acid and about 30% of a polymer of ethyl acrylate.
On the other hand, the polyvinyl polymers can be constitued by the polymers of vinyl acetate and the polymers of vinyl alcohol and more generally by any polyvinylic polymers.
Another macropolymer which can be used advantageously within the scope of the invention is the cellulose or one of its derivatives.
As concerns the product added to the dispersion the following is preferably used: of a macropolymer of the polyacid type, poly(vinylalcohol type),
The invention has also for an object a porous film or membrane with improved vibration properties for acoustic applications especially a membrane for loudspeaker, obtained by the above mentioned process.
Before drying, the gel can either be impregnated on fabrics (woven or non-woven) or roves of natural, artificial or synthetic fibers, or can constitute the bonding agent of such fibers, with the possibility of adding, in each case, fillers (carbon, ceramic, glass, graphite etc.).
The material thus obtained, once dried and having become porous, can then advantageously be thermoformed due to the flexibility of the dried material upon heating, and due to the thermo-bonding of the dried gel or similar material on fabrics or fiber roves.
The invention will now be described in greater detail, with a few illustrative examples, that are in no way limitative, for implementing the invention.
A) Examples of preparation of a gel usable to make films or diaphragms, for acoustic applications, exhibiting improved vibration properties.
EXAMPLE 1
Use is made of "Appretan 9110", which is an aqueous dispersion of a mixture of macropolymers consis
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Audax Industries
Weston Caleb
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