Der ISE ist ein Baustein in einer diffizilen Kette, welche den Klangeindruck des ND in der Tradition der alten Roadster vermitteln will.
Er ist einzig und allein für den 1.5 entwickelt worden und dort teil des Klangkonzepts. In Japan gibt es keinen ND ohne. In den Exportmärkten wurde daraus dann ein Ausstattungsteil der Sportline, welcher dem Gros der G160-Fahrer (zu Recht) zuwider war.
Ich habe den ISE in meinem kleinen Schwarzen (G131) nachgerüstet und erst mit ihm klingt es für mich rund... natürlich nur in Kombination mit (m)einem serienmässigen Auspuff 
Hier mal der Blick der Entwickler... natürlich nur bezogen auf den 1.5 
Mazda Technical Review - Issue 32/2015 - About Conception of Engine Sound
It is important for sports cars to produce a “running feeling” that stimulates the driver's sensibility. Achieving a sense of running from the aspect of hearing by realizing a light feeling in the low rotation range, a beating feeling that emphasizes the strength in the middle rotation range, and an engine sound that makes you feel the sense of growth in the high rotation range.
In the low speed range, the exhaust sound was emphasized to achieve a light feeling. In order to achieve a clear sound quality in which the even-order order of the 4-cylinder engine and its overtone component are clearly emphasized, the interference of combustion pressure waves in each cylinder is equalized. 4-2-1 Exhaust manifold adopted. In addition, the resonance of the pipe length in the main silencer and the expansion chamber length emphasizes the exhaust sound pressure from 130Hz to 250Hz, which is the engine rotation 4th and 6th order components in the low rotation range. In addition, a 100 Hz Helmholtz resonator was installed in the main silencer to suppress the unpleasant noise caused by the resonance of the vehicle cabin space and exhaust sound at 100 Hz. As a result, a light feeling in the low rotation range due to exhaust noise was realized.
In order to produce a heartbeat in the middle rotation range, it is necessary to tune the vibration characteristics of the rear differential mount that transmits power plant vibration to the vehicle body. The vibration characteristics were tuned to 350 Hz in order to achieve a feeling of beating due to the effect of the beating effect of interference between the 4th and 6th engine rotations and the adjacent half order components in the middle rotation range.
The feeling of elongation in the high rotation range is adopted from the old roadster. The induction sound enhancer (ISE) is used to produce this original and inspiratory sound.
Figure 10 shows a schematic diagram of the ISE used in the new roadster. The old roadster released the sound into the cowl upper, but the new roadster adopted a layout that penetrates the dash panel and directly releases the sound into the cabin. This makes it possible to produce the intake sound more directly in the frequency range from 300 Hz to 400 Hz in response to the driver's accelerator operation.
Figure 9 shows the full-acceleration interior sound map of the new Roadster and Axela 1.5L engine realized using exhaust sound, power plant vibration transmission sound, and intake sound. Compared to the Axela sound like a passenger car, it produced a “running feeling” with a connection from low to high rotation suitable for sports cars.
In Conclusion:
In order to develop an engine suitable for the fourth-generation new roadster, almost all components such as the main motion system, cylinder head, cylinder block, intake / exhaust system, and cooling system were newly installed based on the SKYACTIV-G 1.5 for accelerators.
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Wer also den ISE als künstlich verteufelt, der muss dann wohl konsequenterweise auch an den Hauptschalldämpfer mit seinem Helmholtz-Resonator ran...
P.S.: Die Übersetzung Japanisch - Englisch verständlich zu glätten geht mir einfacher von der Hand... und lässt sich so auch einfacher von Euch ins Deutsche übersetzen wenn benötigt.
