Sound Analysis of an amphitheater project was given to me during my Internship period by BIM Studio Department at United Design Group (UDG), Shanghai.This project was jointly governed by UDG shanghai and BDP groups.During this task I was asked to analyse the acoustical interior features (mainly False Ceiling ) by using  Autodesk Ecotect.My objective of the Analysis was to ensure the Noise Reduction Coefficient(NRC value) of the ceiling for a good quality of the sound

Importing the Model to Ecotect

Importing the model that is an amphitheater in my case from a whole building was quite a difficult task.I tried to import in .3ds file format than to other model formats like .dxf and .dwg but all of this meant for no use to Ecotect.Thereafter I thought to cull the model by discarding the layers etc but the geometry imported here on the Ecotect canvas was far way too difficult.It actually divides the cylindrical object into a triangular planes which eventually made the model a bit heavy and was very difficult to analyse, I mean it took hell lot of time to go for 1% of its any analysis.

Lastly I tried to model it on Revit Architecture,a BIM product developed by Autodesk, which was in a bit more useful model making techniques than modeling itself in an Ecotect software because if transferred the file in a .gbxml format it collects the energy related information along with the file.In order to transfer any model to these energy file scripting you need to “tag the rooms”  option in Revit.But the problem was still not resolved due to its cylindrical form.The sub division of triangular plane still continued to show on the ecotect canvas which was imported by using Revit Architecture.But this modeling method has atleast started my analysis part and was quite smooth as compared to directly imported model in other formats.

Modeling Adjustments:

Inside the hall of the theater I managed to simplify my model as far as possible.Latter after going through the slides you might come to know that it affects not much to the analysis.Because I reflected my acoustical rays directly to the ceilings as I was only concerned about that.

I would prefer to avoid complex modeling while working with any kind of Analysis software because at this stage they do not poses any specialized tools for complex modeling.

Meanwhile I further simplified my model into a cylindrical box in Ecotect for that I deleted the part which previously comprises of the building covering.

It may seem quite doubtful that why I went for .gbxml file formatting in Revit? Well I was modeling precisely about the false ceiling’s orientation and angles,since they can drastically affect by analysis part.

Now dont forget to save you file by simply pressing cntrl+s during each and ever step while modeling.

Acoustical Analysis:

Before starting the analysis make sure about the visualization of  the model.Try to make it more understandable to the viewers.This software encourages people who can’t spend time to study the graphs and tabular format through its ‘visually sound’ features.

Step 1:Start assigning the sound source.This is very simple. Click on the speaker on the 3-d editor pallet.Position it at the level of 1.7-1.9 m above the stage.That height is taken as work-plane of the average human speaker’s height.Central allocation of the speaker is preferable but it doesn’t affect much.

Step 2:Select the ceiling material and tag the object as reflector.This option comes after selecting  just right click and assign it as reflectors or by selecting rays and particles option on the right side .To understand why we do such tagging is very important.Reflectors are those objects which we are concerned about.Our objective is to calculate the parameters that governs the quality of sound.

Step 3:Our goal for this step is to shoot the sound rays to the reflectors from the source so we will do that just by managing the option on the Ray and Particles –sub heading: Generate Rays –To Tagged reflectors.If it seems like model is bit heavy to handle than prefer to start to shoot less ray just for trial.This means that the more the No. of rays generated , more good results will be achieved.

Step 4:This step is flexible to the user to do whatever you wish to change for rest of the sub headings of the Rays and Particles.I mean try to explore the other options.

From this four important steps try to see and analyse the results from the animation generated.For a client it is more easier to make him understand what type of material is required.I shown in the slides that NRC values are the most governing factor after the building form is already decided by the team.

Some Technical Terms Dealt:

In general we must know that for higher NRC values like 0.8-0.9 the sound striking on that surfaces never reflects back,for striking incident sound source only few are reflected back.Hence this is useful where we have to seal the sound completely. But amazingly for an amphitheater were musical instruments are to be played we need to have a Reverberation of the sound.In simple terms this computes the ‘dryness’ of the musical note played.It is suggested that reverb sound to a limited amount is allowable.So as we can now judge that NRC should be of controlled amount.Not too high for loosing the Musical pleasure and not too low for echoing and annoying noises.

Assigning NRC values:

This is a bit tricky here on Ecotect software.For understanding this part Noise Reduction is a frequency dependent parameter that is for different variable frequency from the source ,the acoustical responses of a material is different.

Go to the help dialogue by pressing F1 than search for materials (shown in my slides) you will find the different materials assigned for ceilings with different parameters like frequency,NRC values etc. Just hit and try if you are not sure about the product which would be helpful for the interior.Or you can work other way round too.If you know the product and the company of the ceiling than there must be the catalog stating its various properties.Feed the values on the material editor for the feasibility of the product with respect to Acoustics.There are other features like fire resistant moisture tolerance light reflectivity  etc which is in your hand to decide which is the dominant factor.