SOUNDS

Expansion chamber excited by a runup signal

The inlet duct of the expansion chamber shown in Figure 1 is connected to an engine intake. The engine is runup through a speed range in 30 seconds. The mean flow varies with the engine speed.

An acoustic block diagram model of the expansion chamber is also shown in Figure 1. The sound pressure radiated from the tailpipe is calculated by ADEM at the external microphone position, when the acoustic pressure at the wall mounted microphone position is as Signal 1.

**Figure 1** **Expansion chamber and its acoustic model**. **Color is used to indicate the parts of the system represented by the blocks.. Element 6 models the open intake end with mean flow.**

Play Signal 1 to hear the sound created in the inlet duct at the section of the wall mounted microphone.

Signal 1 Measured by the wall Microphone. Amplitude scale factor of the time domain data is 2841.2:1

Play Signal 2 to hear the sound computed by ADEM at the external microphone position in an anechoic chamber.

Signal 2 Computed by ADEM at the External Microphone position when Signal 1 is applied at the Wall Microphone section. Amplitude scale factor of the time domain data is 35.22:1.

Play Signal 3 to hear the sound measured by the external microphone.

Signal 3 Measured by the Ext Microphone. Amplitude scale factor of the time domain data is 19.39:1.

A production air duct excited by a runup signal

**Figure 2 An air duct of the intake system of a passenger car and its block diagram mode**l. **Block 44 represents the measured acoustic model of the resonator. Block 3 represents an inhomogeneous non-uniform duct.**

Figure 2 shows a schematic of the intake system duct of a passenger car. The resonator has an irregular geometry and its wave transfer matrix is measured by using the four microphone method and the microphone signals are processed in the measurement module of ADEM. The elements of the measured wave transfer matrix are shown in Figure 3.

Play Signal 1 above to hear the sound at the wall mounted microphone.

Play Signal 4 to hear the sound computed by ADEM at the external microphone position in an anechoic chamber.

Signal 4 Computed by ADEM at the External Microphone position. Amplitude scale factor of the time domain data is 33.38:1..

**Figure 3 The measured wave transfer matrix of the resonator (element 44 in Figure 2).** **‘Im’ and ‘Re’ denote the real and imaginary parts. Note that the elements of a wave transfer matrix are non-dimensional.**

Aftermarket tripass exhaust mufflers

Several tripass after market exhaust mufflers are mounted on a car with a 4 cylinder 85 kW gasoline engine at the same position on the exhaust line and the sound radiated from the exhaust tailpipe is measured, at 500mm and 45 degrees from the tailpipe outlet center, as throttle opened momentarily to 4000 rpm (Source: AutoSpeed).

Measured unmuffled sound