Loudspeaker

Details Loudspeaker Loudspeaker

2000-02-17

2001-11-20

Le, Huyen (Department: 2643)

Electrical audio signal processing systems and devices

Electro-acoustic audio transducer

Electromagnetic

C381S423000, C381S337000, C381S343000

Reexamination Certificate

active

06320972

ABSTRACT:

The present invention relates to a loudspeaker of the special type which is disclosed in the publically accessible Danish Patent Application No. 1162/85, and which is illustrated in
FIG. 1
of the present drawing. The speaker has a conventional magnet system with an annular air gap
2
for a voice coil
4
connected to a loudspeaker diaphragm generally designated
6
. The construction is comparable to a so-called dome speaker, having an annular edge suspension
8
of half circular cross section connecting the voice coil
4
with a surrounding chassis portion
10
, and normally having the voice coil connected with a forwardly projecting, central dome; the difference is that in this particular speaker the dome is replaced by a “ring dome”
12
having a retracted central, flat portion
14
which is rigidly secured to a central portion
16
of the fixed structure.
It was found that in several respects such a-loudspeaker is highly suited for highquality sound reproduction, in particular due to a good suppression of higher harmonic of distortion products and almost total avoidance of resonances in the audible frequency range. The functional main difference from a conventional dome speaker is that the central ring dome
12
will act as a rolling membrane rather than as a piston element, while also the relatively large suspension portion
8
, acting in a similar manner, will contribute pronouncedly to the sound reproduction.
It was also found, however, that the speaker had one weak point, viz. a clearly measurable efficiency reduction in the highermost frequency range, typically in the 18-20 KHz range. Many listeners would not notice this, but in connection with Hi-Fi equipment the purely technical measurements of the transfer function are highly decisive.
Further experiments in the applicant's laboratories resulted in various improvements, some of which will be disclosed in the present case, but the said weak point still existed. It was a major breakthrough, therefore, when it was realized and demonstrated that the associated problem could be solved in a manner not even affecting the design of the diaphragm, viz. by adding a generally conical, rigid wave guide member to the loudspeaker structure just in front of the said retracted and fixed central portion of the ring dome portion.
This solution was based on an assumption of the problem being due to interferences of the sound waves in the innermost area in front of the said central area, where the “rolling membrane” movements of the interfacing surfaces of the ring dome portion
12
will give rise to vividly intersecting radiations of sound waves in that area, and if this could be avoided or minimized by positively guiding the inwardly directed waves less inwardly and more forwardly, then this could perhaps reduce the problem. In view of all of the previous experiments it was surprisingly found that this measure was indeed a key to a solution of the problem. Even highly sensitive measurements confirmed that the said critical efficiency drop in the higher frequency range disappeared completely and that no additional drawbacks were introduced.
It was then also realized that the problem could be solved in a modified manner, viz. by providing a regular shield in front of the critical area, which is the area inside the annular top of the ring dome
12
. The tweeters in question will typically be quite small, e.g. with a total diaphragm diameter of less than 10 cm and even less than 5 cm, and the central area thus shielded off will not contribute significantly to the effect of the loudspeaker.


REFERENCES:
patent: 5537481 (1996-07-01), Voishvillo et al.
patent: 5875252 (1999-02-01), Lesage

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