Insertion loss

Insertion loss is the reduction in sound pressure level, when a device-under-test (DUT) is added to a system.

Measure

ACME can determine the insertion loss by comparing two measurements:

1. System without DUT (reference)
2. System with DUT

First the reference measurement must be performed. Once this is finished, it will remain valid for 12 hours and will automatically be linked to all future measurements. Next, perform the measurement with DUT.

Reference measurement

• Select Measurement type -> Insertion loss
• Tick the box Reference measurement

Measurement with DUT

The last reference measurement is shown in the box Last reference.

• Select Measurement type -> Insertion loss
• Untick the box Reference measurement

Analyze

Insertion loss builds on Power spectra. The settings of at Power spectra are applied to both measurements individually, after which the results are subtracted from eachother. The difference is plotted as the insertion loss. Any smoothing is applied before the results are subtracted.

From Power spectra, only the output types Autopower and Bode diagram can be used with insertion loss.

The following settings are available:

1. Reference measurement: if multiple reference measurements are available, select which is to be used
2. Switch sign: multiply by -1, in case the reference and DUT measurements are swapped
3. Plot with phase: plot the phase as well

Example

An example is shown below. The system is a resonant tube with a loudspeaker on one end and a microphone on the other end. The DUT is a constriction, which can be placed in front of the microphone.

First, the Power spectra settings.

The resulting bode diagrams are as follows...

...and the insertion loss is the difference between them. Note that the insertion loss is positive, even though the DUT decreased the sound pressure level at the microphone.