NEC Acostix

This module calculates the overall SRI (TL) of an acoustic wall or barrier that may contain doors and windows. The wall can be a masonry wall, single steel plate, or double steel plate with an air gap.

The sheet enables you to select the window and door dimensions, window glass and thickness configuration, and single-plate or double-plate configuration.

You need to enter the wall, door, and window dimensions. Then, the sheet will calculate the overall SRI of the assembly. This SRI can then be used as a known SRI Value to complete the wall design for enclosures or rooms, as stated in the wall design sheet above.

The module provides two types of structures: steel plates for enclosures and a masonry wall system.

Acostix designs the acoustic louvers to achieve the required acoustical (dB) and airflow (Pa) performance. You can select either to design inlet or discharge louvers. You can select among 5 different louver shapes. Other configurations can also be added upon request.

You have to enter the noise source SPL/SWL. You need to enter the selected acoustic filling materials’ absorption coefficients and thickness. You also need to select the perforation configuration. You have to specify the noise criteria and distance. You can select whether the room is reverberant or not and accordingly enter the absorption coefficient data, which can also be calculated by NEC Acostix tools.

Then, you can choose your design parameters, such as louver blade thickness, louver depth, louver blade spacing, and free area percentage of the overall aperture.

The software will display the resultant noise dB and air pressure drop for the selected design. You can fine-tune your design parameters to optimize the results. Of course, you can select to show or hide the calculations before you print the report.

The resultant transmission losses can vary from the ones obtained through tests by 1–3 dB in the low frequency and up to 3–5 dB in the higher frequencies, but the overall weighted dB will be 0–3 dBA. For more explanations and details, please contact support@najahengineering.com.

• The main module enables you to design the acoustic enclosure for diesel generator applications to meet certain noise ratings or criteria.
• The module is fed with the engine noise data, and then the designer will select the dimensional parameters of the wall, windows, inlet/discharge attenuation, and exhaust silencing to meet the criteria.
• The module allows you to enter either SPL or SWL data. You may also select between baffle-type attenuators and acoustic louvers for inlet and discharge aperture attenuations.

These tools allow you to find the Transparency Index (TI) and the open area percent of the perforated sheet used to cover the acoustic materials used in air ducts. These two parameters affect the acoustic performance of the perforated sheet and therefore affect the overall acoustic performance of the air duct assembly.

Of course, the higher the TI, the better it will be for the noise absorption of the acoustic filling, but this may not be possible due to the perforation sheet’s mechanical characteristics and strength.

You enter the perforation geometry, and the sheet will calculate the TI and P. These two parameters are inputs to the design of the walls, attenuators, and louvers.

The results of this sheet are the TI, P, and the access factor, which will be multiplied by the absorption coefficient of the acoustic material. In other words, this access factor downgrades the acoustic materials sound absorption capability.

This tool allows the designer to estimate the engine exhaust noise SPL or SWL, engine surface noise SPL, and the inlet and discharge airflow.

You just enter the engine kW and then select from the drop-down lists the different characteristics of the engine, which must be known if the engine is physically available.

The software will display the engine exhaust and surface noise data over the 8 frequencies and the inlet and discharge airflow. These results can be used to design walls, attenuators, and louvers if the data is not available from the manufacturer.

This tool helps designers calculate the room average sound absorption coefficient over the octave band.

The sheet allows you to enter the room dimensions, and, from the drop-down lists, you may select the sidewall, end walls, roof, and floor material. The results of this sheet will be the average absorption coefficients and the reverberation times. These results are very valuable when calculating sound from inside rooms through walls, attenuators, and louvers.

The difference between SPL and SWL: SPL is the sound pressure level = 20 log P/Pref. P is sound pressure in N/m2 and Pref = 20×10-6 N/m2, while SWL is the sound power level = 10 log W/Wref, where W is sound intensity in Watts and Wref = 10-12 Watt. The sound comes out from the source as SWL, and when it travels spherically, its intensity will be distributed over the sphere’s area, which makes it pressure SPL.

You may also need to do calculations of noise inside the room if the noise source is placed at a certain distance and you need to measure noise at a certain point inside the room, taking into consideration the reverberation time of the room.

This sheet does this. You can do this as a single figure, or you can enter the noise data of the source in SPL or SWL over the octave bands and enter all other details of the room.

The resulting information will be the noise level at the point you selected. You can select to show or hide the calculations before printing the report.

This sheet obtains the pressure drop across different extended duct systems, which you may choose from the drop-down list.

It helps when, sometimes, the inlet air or the discharge air needs to be ducted at 45 degrees or 90 degrees for some distance.

This module enables you to either do the exhaust noise calculations to find the optimum exhaust silencer attenuations (dBs) at all 8 frequencies, or, if you have a silencer with known dBs, you can verify if it suites your diesel engine. Of course, you have to define the criteria, such as 90 dBA at 1 m or 75 dBA at 7 m, and so on. You have to have the engine exhaust noise SPL or SWL data from the engine manufacturer. If not known, then you can use the exhaust noise estimator, which is part of NEC Acostix, to get the engine exhaust noise.

At the end, the module will give the results and summary of all calculations. You can always hide or show this calculation for the purpose of submittal to your customers.

This is a powerful design sheet that does two things at the same time. It designs the rectangular attenuator by finding its dimensional parameters and acoustic characteristics to achieve the noise attenuation from one side, and it gives the dimensional parameters that achieve the maximum allowable pressure drop across the attenuator air ducts.

The sheet can do 4 functions: design inlet attenuator, design discharge attenuator, verify inlet attenuator, and verify discharge attenuator.

You need to enter the engine surface noise SPL data, airflow data, noise criteria, and overall aperture height and width, and then you select the number of airways and the thickness of the splitters. Of course, there are rules for how to select them, which you can learn in our noise. You can fine-tune your selection to get the best results for acoustic and pressure drop performance. You can always select to show or hide the detailed calculations. The sheet allows you to select the acoustic material filling details and enter the average room absorption coefficient, which can be calculated by NEC Acostix.

You can attend any of the following courses that will enrich your knowledge and skills in noise control and sound attenuation design. We are proud that our industrial noise control training programs are classified among the top worldwide. Attendees are from all six continents.

AC-01 Industrial Noise Control and Sound Attenuation Design

A 3-day course organized publicly or in-house. This is 18 hours of training instruction and extensive design workshops covering all the concepts of industrial noise, sound insulation materials, and design of noise control modules for power generation, residential, HVAC, and other applications, and explains the Acostix software modules.

AC-02 Architectural Acoustics: Sound in free field and inside rooms, sound reverberation, acoustic materials, masonry walls and floors acoustics, building materials, sound calculations, and sound attenuation to achieve sound criteria. This training course is only available upon request.

Sometimes, you may need to calculate the noise in the free field if the noise is known at some location.

This sheet allows for noise calculations of SPL or SWL at different distances in the free field. You can either do the calculation for a single dB figure or over the eight (8) frequencies.