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发表于 15-4-2015 12:38 PM
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If you think Mazda 3 is the noisy car, then i will say my cheapo Saga BLM probably is the noisiest car in this world.
Alot of ppl here just simply miss-intepret 'road noise'.
Like jklow123 said, road/tyre noise is dominant by low frequency, pls refer to my attached frequency analysis taken by spectrum analyzer taken in my Saga BLM.
Reduced 95%
Attached Image
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As you can see from the graph, the noise is mainly around 100-200Hz, this kind of low frequency will not be able to eliminated by foaming/dampening. So why foaming/dampening can hear 'some' improvement?
Our car chassis is hollow, when the low frequency penetrate into cabin, it will pass through the hollow seal chassis. Just imagine you shout in the hollow tunnel, what can you hear? a more louder noise and echo. Foaming just simply fill the hollow chassis pillar and reduce those echo noise, so u hear improvement.
For damping, this material is used to deadening the noise cause by panel vibration. When low frequency vibration transmitted from tyre to chassis, the panel will vibrate at the same base frequency + harmonic due to base frequency. Means let say the vibration noise transmitted from tyre is 100Hz, the harmonic will be 2X100Hz, 3X100Hz, 4X100Hz with reduce amplitude. SO dampening material (such as those STP/dynamat) is just add the mass on the panel and shift the resonant frequency to the range which our ear is not much sensitive, so you hear 'some' improvement again.
Many of you blame the car nowadays lack of soundproofing material, i will say for any Japanese car or national car or 'fake contis' in Malaysia mostly are lack of soundproofing material, but why A car is quieter than B car?
Try to knock the door panel, roof, engine hood, bootlid of Honda accord compare to cheap Proton car, you will surprise to hear that both car are equally 'hollow'.
Ok, just try to compare apple to apple, Saga BLM, Honda City and VIOS, all these 3 are B segment car with similar size and weight, so why City and VIOS is much quieter compare to Saga BLM? Becos they using higher quality steel and soundproofing material? HELL NO, all these car has almost similar minimal soundproofing material applied.
I did some 'experiment' on my car to achieve almost similar NVH compare to City/VIOS, what i did was just lowering the tyre pressure. Yes, just as simple as that.
So my conclusion is the low frequency road roar/drone is mainly due to the suspension of the car.
Try to think on it, when you lowering the tyre pressure, your tyre will become 'softer' and able to flex more, flex more mean the low frequency vibration can be absorbed by the tyre when the tyre hit the rough road, hence it reduce the low frequency road noise come into cabin drastically.
Same theory can apply on suspension, when the suspension is superior, it will absorb all kind of vibration due to tyre-road contact, else the low vibration frequency will transmitted from tyre through suspension and make the whole car to vibrate, here comes the 'road noise/roar'.
But sorry to say, if the problem is due to bad suspension design, then nothing you can do except change car. Change to silent tyre just a temporary solution that can only last you probably 10k KM before the noise come back again, becos new tyre rubber is softer during new, that's why vibration is greatly reduce. What you do based on recommendation on this thread is just to improve the situation, how many percent improvement is based on car design itself. After i read through this thread, i dun believe anyone here can turn your noisy car as quiet as those luxury car. That's why i dun agree if u just blindly follow other's recommendation without understanding the theory behind.
这一段很有道理哦 |
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