MULTI-LAYER COMPOSITE FOR ACOUSTIC MEMBRANES

Abstract

Multi-layer composites and methods of using the composites as a membrane for electroacoustic transducers. The composites and methods comprise at least one first and one second outer layer, wherein at least one of the cover layers being made from a polypropylene sulfide-plastic having a halogen content not exceeding 550 ppm.

Claims

1. A multi-layer composite adapted as a membrane for electroacoustic transducers, the multi-layer composite comprises at least one first outer layer and at least one second outer layer, wherein at least one of the at least one first and second outer layers consists of a polyphenylene sulfide plastic, wherein a halogen content of the polyphenylene sulfide plastic does not exceed 550 ppm.

2. The multi-layer composite according to claim 1, wherein the at least one first outer layer has a thickness from 1 to 50 m.

3. The multi-layer composite according to claim 1, wherein the at least one first outer layer has a thickness from 1 to 5 m.

4. The multi-layer composite according to claim 1, wherein both the at least one first and second outer layers consist of polyphenylene sulfide plastic whose halogen content does not exceed 500 ppm.

5. The multi-layer composite according to claim 4, wherein that both the at least one first and second outer layers have a thickness from 1 to 50 m.

6. The multi-layer composite according to claim 4, wherein both the at least one first and second outer layers have a thickness from 1 to 5 m.

7. The multi-layer composite according to claim 1, wherein both the at least one first and second outer layers are made of the same polyphenylene sulfide plastic material.

8. The multi-layer composite according to claim 1, further comprising a damping layer disposed between the at least one first and second outer layers.

9. The multi-layer composite according to as claim 8, wherein the damping layer is formed by, or comprises, a double-sided pressure-sensitive adhesive tape.

10. The multi-layer composite according to claim 8, wherein the damping layer is a layer of a pressure-sensitive adhesive.

11. The multi-layer composite according to claim 1, wherein the composite has a three-layer construction of first outer layer/pressure-sensitive adhesive/second outer layer.

12. A speaker membrane comprising the multi-layer composite according to claim 1.

13. A method comprising: thermoforming the multi-layer composite according to claim 1 to produce a membrane adapted for an electroacoustic transducer.

14. The method according to claim 13, wherein the thermoforming comprises at least one selected from embossing and deep drawing the multi-layer composite.

Description

EXAMPLES AND COMPARATIVE EXAMPLES

[0037] The concept of the invention will now be more particularly described with a number of examples and counterexamples without any intention to thereby limit the invention.

[0038] Initially, commercially available standard PPS films were analyzed for their halogen contents by an external laboratory. Chlorine was in each case ascertained as the halogen in question, other halogens not being detectable in significant amounts. The 10 samples measured consistently had a chlorine content of more than 1000 ppm (1000 mg/kg).

[0039] The halogen content of a low-halogen PPS film was 532 ppm.

[0040] To prepare for THD determination, three-layer composites were produced from one at a time 4 m thick PPS film, one at a time 10 m acrylate or silicone damping layer (each standard PSA; respectively identical in Example 1 and Comparative Example 1 and also in Example 2 and Comparative Example 2) and one at a time 4 m thick PPS film, while low-halogen PPS films were used for the examples of the invention and standard PPS films for comparative tests (see table 1).

[0041] These three-layer composites were thermoformed into rectangular membranes 15 mm in length and 11 mm in width, which were installed in microspeakers otherwise having the same construction. The THD curves were recorded using an R&S UPV Audio Analyzer (Rohde & Schwarz) in the same way in each case, so the values are directly comparable with each other. The absolute value determined in any one THD measurement is immaterial for a relative comparison.

[0042] The resonance frequency of the two speakers is 450 Hz. The THD curves of the speakers fitted with the multi-layer composite membranes produced from low-halogen PPS film were across the full frequency range, not only for the composites with an acrylate damping layer but also for the composites with a silicone damping layer, at between 0.1 and 10 kHz below the THD curves of the speakers fitted with membranes fabricated from commercially customary PPS film. Table 1 reports by way of example THD values at frequencies below the resonance frequency.

TABLE-US-00001 TABLE 1 Results of THD determination. PPS film used (for Damping Chlorine both outer layer content of films) each thickness PPS film THD THD THD THD 4 m thick 10 m (mg/kg) (100 Hz) (200 Hz) (300 Hz) (400 Hz) Comparative standard acrylate 1540 25% 16% 9% 5% Example 1 PPS film from Toray Example 1 low-halogen acrylate 532 14% 10% 5% 3% PPS film from Toray Comparative standard 4 m 1540 21% 15% 10% 4% Example 2 PPS film PPS/10 m from Toray silicone damping layer/4 m PPS Example 2 low-halogen 4 m 532 14% 9% 4% 2% PPS film PPS/10 m from Toray silicone damping layer/4 m PPS

[0043] The experiments demonstrate that the problem addressed by the invention is solved according to the invention by substituting PPS films of reduced halogen content (<550 ppm) for standard PPS films in an acoustic membrane. An effect due to the halogen content of the PPS films used on the sound quality of speaker membranes obtained using such films would and could not have been expected by a person skilled in the art.

[0044] It transpires that the THD values of a membrane obtained using a PPS film of reduced halogen content which are determined below the resonance frequency are consistently lower than those of a comparative membrane (same thickness and shape, same speaker) obtained using commercially available standard PPS film.