Introduction

The MA25 array complements the Zircon V2 hardware. It holds 5 microphones (which can be re-used from the MA24 array) and is connected directly to the CI24 control unit. This immediately results in a five times reduction of the total measurement time. The new TH24 tilt head for the LS24 loudspeaker allows the source to be pointed to the top of the barrier. In addition to the MA25 array and TH24 tilt head, the complete Zircon V2 system now includes extender tubes that allow the LS24 and MA25 to be positioned at heights up to 4 m.

New functions in Dirac 7.3 enable the calculation of the Diffraction Index DI, from 20 impulse responses (4 LS24 positions and 2 MA25 positions). Two sets of measurements, with and without the added device, can be used by Dirac to calculate the Single-number rating of sound diffraction index difference DL_ΔDI.

In situ diffraction measurements using the MA25

The EN 1793-4 and EN 16272-4 standards define 4 source positions (S1..S4) and 10 receiver positions (R1..R10). Dirac can capture 20 source-receiver combinations (S1-R1..R5, S2-R1..R5, S3-R6..R10 and S4-R6..R10) in 4 measurements using the MA25 array. These measurements have to be performed in 3 setups: a reference measurement without NRD, a measurement with the NRD but without the added device on top of the NRD, and a measurement with the added device on top of the NRD. A complete measurement therefore results in 3 x 20 impulse responses.

Zircon/diffraction processing in Dirac

In Dirac, the impulse responses are collected in 3 groups, reference measurements without NRD, diffraction measurement without added device, and diffraction measurements with added device on top of the NRD.

Using the Zircon dialog (Process - Zircon), 2 new groups are created - with and without the added device. You can choose between the 1793-4 and 16272-4 standards, which changes the traffic noise spectrum used in the calculation of DL_ΔDI. When an NRD height lower than the default 4 m is entered, DIRAC will adjust the Adrienne window length accordingly, and display the minimum valid third-octave band for the results.

For both groups, Dirac can calculate the Diffraction Index (DI).

Finally, Dirac can calculated the single number rating of sound diffraction index difference DL_ΔDI on the project level from the (first two) selected groups. Note that DL_ΔDI is a parameter that can only be calculated on the project level (as opposed to the group or file level), and that the project level node needs to be checked to make the value visible.

Expanded options for transmission measurements and DL_SI,G

For transmission measurements following EN 1793-6 or EN 16272-6, DIRAC 7.3 can now calculate the global single number rating of the sound insulation index DL_SI,G based on measurements in front of a barrier element and measurements in front of a barrier post.

The Zircon dialog for transmission measurements can now be used to specify whether a measurement was performed in front of an element or a post. The element width can also be specified, and this will be used in the weighted averaging of the DL_SI of the element and post.

Note that the DL_SI,G is a project level parameter, just like the DL_ΔDI. Also, the groups containing the element and post measurements need to be checked, as DIRAC will use the first two checked groups for the calculation of the DL_SI,G.

Changes in reflection measurements DL_RI

In DIRAC 7.3, the DL_RI is no longer calculated from the average RI over all groups in the project, but from the average RI over all checked groups in the project.