GB2110502A

GB2110502A - Dynamic-type headphone

Info

Publication number: GB2110502A
Application number: GB08230446A
Authority: GB
Inventors: Yoshiyuki Kamon; Tsutomu Kakiuchi
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1981-10-26
Filing date: 1982-10-25
Publication date: 1983-06-15
Also published as: AU556442B2; JPH0235520B2; FR2515468A1; DE3239616C2; FR2515468B1; GB2110502B; JPS5871798A; CA1203014A; NL8204113A; NL191226B; KR860001103B1; NL191226C; KR840002388A; AU8947682A; DE3239616A1

Abstract

A dynamic-type headphone in which a diaphragm 5 has a bobbin 7 for a voice coil 8 located within a magnetic circuit 3, 2, 1, 4 and is formed of one sheet made of polyethylene terephthalate resinous material and in which, if the diameter of a vibrating portion of the sheet is taken as ??? and the thickness thereof is taken as t then t DIVIDED ???=4x10<-4> to 5x10<4>. <IMAGE>

Description

SPECIFICATION Dynamic-type headphone The invention relates generally to open air-type headphones and more particularly to a dynamictype headphone. It may be desirable for such a headphone to be of a compact size but still be capable of reproducing rich bass, tight middle tone and higher tone.

There is a recent trend for headphones to be made more compact i.e. smaller. When headphones are made more compact, the resonant frequency f0 thereof b raised and a lower tone or bass is rendered insufficient thereby. For example, a headphone with an aperture of 23 mm usually employs a resinous sheet of about 1 2,u to 20y in thickness as its diaphragm. However, in such a headphone, the resonant frequency f0 thereof is in a range from 200 Hz to 220 Hz and therefore an adequate bass cannot be reproduced. In this case, if the diaphragm sheet is made thinner, the resonant frequency f0 is lowered and hence the aforesaid purpose can be satisfied.With such a thinner diaphragm, however, higher tones cannot be sufficiently reproduced thereby weakening the sound on the whole whereby tightness of sound is lost. In other words, if the thickness of the diaphragm is taken as t, Young's modulus thereof is taken as E, and the stiffness thereof is taken as S, this stiffness S is given by S=k E t3 thus, if t becomes small, S becomes quite small.

Hence resolution of sound becomes poor, where k represents a proportional constant.

According to the invention, there is provided a dynamic-type headphone in which a diaphragm having a bobbin for a voice coil located within a magnetic circuit is formed of one sheet made of polyethylene terephthalate resinous material and in which, where the diameter of the vibrating portion of said sheet is taken as and the thickness thereof is taken as t, its ratio is so selected as to satisfy the equation -= 4x10-4to 5x10-4.

Such a dynamic-type headphone can have a small aperture but can nevertheless reproduce satisfactory bass and tight higher tone.

Preferably the diameter sX is less than 30 mm and the bobbin diameter is approximately one half the diameter çs, The invention is diagrammatically illustrated by way of example with reference to the accompanying drawings, in which: Figure 1 shows a cross-section through a dynamic-type headphone according to the invention; and Figures 2 and 3 are respectively characteristic curves thereof.

Referring to the drawings and firstly to Figure 1, a frame 1 of a dynamic-type headphone unit is made of magnetic material and serves as a magnetic circuit. A magnet 2 is, in this embodiment of the invention, magnetized in the thickness direction thereof. A top plate 3 is also made of magnetic material and forms, with the frame 1, a magnetic gap 4 between the outer peripheral surface of the top plate 3 and a portion of the frame 1 forming the inner peripheral surface thereof. A diaphragm 5 has its outer peripheral edge bonded to an edge ring 6, the edge ring 6 being subsequently attached to the inner periphery of an outer peripheral flange 1 a of the frame 1. The diaphragm 5 is thus located in a predetermined position with respect to the frame 1.A coil bobbin 7 of the diaphragm 5 is located within the aforementioned magnetic gap 4 and a voice coil 8 is mounted on the coil bobbin 7.

The diaphragm 5 is formed of one sheet made of polyethylene terephthalate resin (trade name: Mylar), which is one of the polyester system resins. In addition, if the diameter of the vibrating part of the diaphragm 5 (in this embodiment, equated to the inner diameter of the edge ring 6) is taken as (p and the thickness of such diaphragm 5 is taken as t, its ratio t --D is selected so as to satisfy the equation D=4x10-4to 5x10-4.

Next, data of respective exampies of the diaphragm will be indicated on the following tables.

Tables I, II and Ill show the resonant frequency f0 and the value of D when the thickness t of the diaphragm is varied, where 0=27 mm and iso=30 mm in Table l; 0=20 mm and (pro=23 mm in Table II; and 0=14.4 mm and (pro=1 6 mm in Table Ill.

Throughout Tables I to III and in Figure 1, 00 represents the aperture of the driving or headphone unit and , represents the diameter of the coil bobbin 7. In each of the Tables I, II and Ill, the ratio t (p of the unit was selected as 0.52.

Table I 0=27 mm 00=30 mm t(y) fo(Hz) D(x 10-4) 9 130 3.3 12 160 4.4 16 210 15.9 Table II 0=20 mum to=23 mum t(y) fo(Hz) D(x 10-4) 6 150 3.0 9 170 4.5 12 220 6.0 Table III 0=1 4/4 mum (p0=16mm toe#) fo(Hz) D(x 10-4) 4 150 2.8 6 190 4.2 8 230 5.6 Figures 2 and 3 are, respectively diagrams showing characteristics of Tables I and II, where the ratio D is taken as a parameter, the frequency is indicated on the abscissa and a level or response is indicated on the ordinate (x 10-4 being omitted for simplicity).

In the case of the units to which Table I relates, the unit with D=3.3 (x10-4being omitted) it was ascertained that the resonant frequency f0 was lowered sufficiently, but a so-called tightness of sound was lost in the middle and higher tone bands thereby causing an unsatisfactory sound in view of audibility. In the unit with D=5.9 it was noted that the resonant frequency f0 was made higher such as 210 Hz and therefore the so-called bass performance was unsatisfactory. Regarding the unit with D=4.4, it was noted that the resonant frequency fro was sufficiently low for bass performance to be satisfactory and the middle and higher tone bands were sufficiently smooth and tight.Thus it was discovered that the unit with D=4.4 was quite satisfactory in audibility.

In the case of the units to which Table II relates, it was found that the unit with D=4.5 has satisfactory bass performance and the middle and higher tones were very smooth. The unit with D=3.0 lost the tightness of sound and it was found that in the unit with D=6 the bass performance was unsatisfactory.

From the results of various other experiments, it was ascertained that if the diaphragm 5 was formed of one sheet made of polyethylene terephthalate resin and the ratio D, that is to say t was selected in a range from 4x 10-4 to 5x 10-4, even though the dynamic-type headphone was very compact, a headphone unit which was able to reproduce good sound with a satisfactory bass performance and tightness in view of audibility, could be obtained whatever its size.

Claims

1. A dynatmic-type headphone in which a diaphragm having a bobbin for a voice coil located within a magnetic circuit is formed of one sheet made of polyethylene terephthalate resinous material and in which, where the diameter of the vibrating portion of said sheet is taken as 0 and the thickness thereof is taken as t, its ratio (p is so selected as to satisfy the equation -= 4x10-4to 5x10-4.

2. A dynamic-type headphone according to claim 1, in which the diameter 0 is less than 30 mm.

3. A dyanamic-type headphone according to claim 1 or claim 2, in which the bobbin diameter is approximately one half the diameter s5.

4. A dynamic-type headphone substantially as hereinbefore described and illustrated with reference to the accompanying drawings.