| 摘要 |
The filter comprises two high pass units (8,9) and one low pass (10), coupled in series. The one high pass filter (8) has a damping which decreases at the rate of 24 dB/octave to a break point of 300 Mz. The damping in t-e other such filter (9) reduces at the rate of 6 dB/octave to a break point of 1600 Hz. The low pass filter (10) damping increases at the rate of 12 dB/octave from a break point of 3400 Hz. Interference noise in a vehicle comprises, inter alia, engine noise, bodywork noise, tyre noise, and to a certain extent that from fans or from wind drag. Such noise is dominated by a low frequency level, the strength of which decreases at frequencies up to some thousand Hz, after which it is constant, or re-increases somewhat. Damping in the frequency band 300-3400 Hz decreases in the same way as the expected strength of interference noise occurring in the vehicle decreases pro rata to the increase in frequency. |
