Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Plural or compound reproducers
Patent
1997-07-10
1999-10-19
Le, Huyen
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Plural or compound reproducers
381370, 181129, H04R 2500
Patent
active
059701609
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates generally to an earmuff of the type having a cup with an elastic sealing ring arranged along the opening circumference of the cup. The sealing ring includes an annular covering and, arranged therein, elastic material, preferably foam material. More specifically, the invention relates to a method for changing the noise attenuation characteristic of such an earmuff, as well as an earmuff obtained in accordance therewith.
BACKGROUND OF THE INVENTION
In most cases, earmuffs of the type mentioned by way of introduction produce a most satisfactory noise attenuation. However, low frequency attenuation is, as a rule, substantially lower than attenuation at higher frequencies, which in certain applications may be disadvantageous. The noise attenuation characteristic is also in most cases quite uneven, which may also be a disadvantage in certain applications.
To achieve satisfactory noise attenuation, it is important that the sealing ring of the earmuff seal efficiently against the user's head. For the purpose of making it possible for the sealing ring to adapt to the user's head while providing excellent comfort properties and maintaining a good noise attenuation capability, the covering of the sealing ring is, as a rule, provided with a small hole or some small holes. The at least one small hole permits pressure compensation as the sealing ring, while being compressed to some extent, is applied to the user's head around an ear. After that, no substantial penetration of noise into the sealing ring takes place.
OBJECTS OF THE INVENTION
The main object of the present invention is to permit a change in the noise attenuation characteristic of an earmuff while using the sealing ring. It is especially an object of the present invention to change the low frequency attenuation and/or to make the noise attenuation characteristic more even.
A further object of the present invention is to indicate how such a change can occur selectively.
SUMMARY OF THE INVENTION
According to the invention, the above-mentioned objects are achieved by a method and an earmuff having the features as defined herein.
The invention is thus based on the knowledge that the noise attenuation characteristic of the earmuff can be affected by manipulation of the effect of the inner air spring of the sealing ring. Such affecting can be achieved by providing the annular covering with ventilation apertures or passages, by means of which the interior of the sealing ring, after application of the earmuff, communicates with the environment without communicating with the interior of the cup. It is a matter of ventilation apertures of a substantially larger total area than the prior-art pressure compensation holes in the sealing ring covering, which are mentioned by way of introduction.
Preferably, the annular covering of the sealing ring is provided with ventilation apertures which are preferably uniformly distributed in the circumferential direction and which can suitably be ventilation holes, although it would be possible to have a different structure of the annular covering in order to provide the desired ventilation apertures.
It has been found convenient to have ventilation apertures or holes, each having an area of at least about 1 mm.sup.2, preferably at least about 2 mm.sup.2 . A total aperture or hole area of at least about 20 mm.sup.2 is preferred, more preferably at least about 30 mm.sup.2. Especially, an area of more than 100 mm.sup.2 can be used, with excellent results. Regarding the distribution along the sealing ring, the ventilation apertures or holes should suitably have an area of at least about 1 mm.sup.2 per centimetre of length, preferably at least about 5 mm.sup.2 per centimetre of length.
It has been found to be convenient to let the ventilation apertures communicate with the environment through special ventilation ducts, which can advantageously be arranged in the cup and/or annular covering parts. These ducts yield a possibility of protection against penetration of dirt etc.
REFERENCES:
patent: 2672864 (1954-03-01), Makara
patent: 4856118 (1989-08-01), Sapiejewski
patent: 4993074 (1991-02-01), Caroll
patent: 5020163 (1991-06-01), Aileo et al.
Hiselius Per Olof
Nilsson Lars Bertil
Dabney Phylesha
Dalloz Safety AB
Le Huyen
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