amroc pro

THE room mode calculator for non-rectangular rooms


Before you start using amroc or amroc pro, you should first understand a bit about standing waves in rooms, how they depend on the rooms' size and how they affect acoustics. Read my article about room modes first to get an introduction into those topics.

What's amroc pro?

In general amroc and amroc pro are both "online room mode calculators". So they try to help you understand, visualize, learn or teach, standing waves in rooms (= room modes).

  • amroc is doing this for free and very fast in your browser but only for rectangular rooms
  • amroc pro does the same but it uses a process called „Finite Element Method“ that can calculate modes for arbitrary shaped room models. Those calculations are more complex and need powerful computers, so they are not done in your browser but on my server with the help of openCFS.

Main acoustic use cases

You use a room mode calculator to understand or tackle problems in the low frequency range of rooms or other closed volumes. The most important factor influencing these phenomena called room modes, is the size and the shape of the volume.

With amroc and amroc pro you can play around with those two factors and see how they affect the appearance of modes. You can for example

  • enter the size and shape of an existing room you have troubles in. Try to dive deep into the problematic frequency range. Search for clusters of modes that can lead to amplification of certain frequencies. Or maybe there is a "hole" in your frequency diagram and some frequency band is not 'supported' by any mode.
  • visualize which modes are to blame when there are low frequencies that can't be heard. See how you can move your listening or speaker positions out of a "null" to let certain mode-affected frequencies become audible again.
  • play around with arbitrary room sizes to find the best dimensions for a room that is not built yet and that should meet the highest acoustical demands also in the low frequency range.
  • use the calculators to find modes in other volumes than rooms. For example in speaker enclosures.


amroc pro screenshot - blank office 3D model
An office
The blank 3D model as seen in amroc pro
amroc pro screenshot - office room mode visualized
The model with one of the modes visualized. You see pressure zones of a standing wave colored.
amroc pro screenshot - blank hall 3D model
Hall with orchestra pit
The blank 3D model as seen in amroc pro
amroc pro screenshot - hall room mode visualized
The pressure zones of one mode again.

How to use amroc pro

There are three phases. You start by modeling your room. Then you check the 3D model. And finally you let the room modes be calculated for this model.

The Modelling Phase

In short:

  1. Shape the floor
  2. Set a room height
  3. Click the 3D Button

amroc pro screenshot - select a box to drag it around
To change the shape of the floor just click the boxes and drag them around.
amroc pro screenshot - setting a room height
Use this input field to enter the height
amroc pro screenshot - invalid floor shape
If the shape turns red you tried something that does not produce a valid result. No wall may cross another wall.
To add new boxes just move the mouse to the position you want to add the box at. Once the box is created just move it around like all the others.
amroc pro screenshot - add new corners to the floor shape
If you move your mouse close to some wall you see a new box that you can click to create it.

To delete a box, select it with a mouse click and press delete on your keyboard. If just 3 boxes are left you can not delete anymore as with just two boxes you can‘t build a valid room.

Modelling Angled Ceilings or Floors

This process of modelling works great, but it does not allow for arbitrary shapes.

Note, that it makes no difference which cross section of your room you shape in the 2D view. It does not have to be the floor. Shape a side wall and use the height input field to enter the width to do something like this

amroc pro screenshot - blank hall 3D model
A 3D model with angled ceiling and floor. In this case the side walls need to be straight and parallel.

Additional modeling possibilities will be added over time until hopefully any shape can be done.

You finish the modeling phase with a click on the 3D button.

The Visualization Phase

After clicking the 3D Button you see the 3D view of your model. You can turn it by clicking and dragging on the screen. Move it by clicking with the right mouse button or pressing ctrl.

amroc pro button - change floor shape or size
Click this button to go back into the modeling phase.
amroc pro button - Calculate 5 modes for free
Or this button to catch a glimpse on how the first 5 modes will look like.
amroc pro screenshot - mode frequency diagram
After calculating room modes you see the resulting mode frequencies in the diagram above the model. Each vertical line is one mode frequency.
amroc pro screenshot - mode frequency diagram

Click the line to see the pressure zones of this mode in the 3D model.

See my room modes article for tipps on how to interpret the red and blue visualization.

Buy a mode calculation

Most of the time it will not be sufficient to analyze just the first 5 modes as problems reach much higher in frequency.

amroc pro screenshot - mode frequency diagram

Modes are getting denser the higher you go in the frequency diagram. At some point they are so dense, that you have multiple modes per musical note. The negativ effects of a single mode are averaged out as you have nulls and pressure zones basically everywhere.

The frequency where modes are dense enough is not always the same. It depends on room size and reverberation time so you can‘t just always calculate modes up to for example 200Hz every time.

When you buy the calculation you get all modes up to around the Schroederfrequency. Unfortunately I can't guarantee it at the moment as the FEM on the server calculates a specific number of modes and not all modes up to a specific frequency but I am working on a solution for that to ensure a specific upper frequency in the future.

How I determine the number of modes that will be calculated

First I calculate the volume of the room and estimate a reverberation time for this volume.

With those parameters I can calculate the Schroederfrequency.

Formular for the Schroeder Frequency

I calculate the Schroederfrequency

Source: S.332, Gl.11.3, Müller/Möser - Taschenbuch d.techn.Akustik 3.Aufl., Springer 2004
Formular for calculating the number of modes under a specific frequency

This formular calculates the number of modes up to a specific frequency.

I calculate the modes up to one third above the Schroederfrquency (f = fS * 21/3)

Source: S.332, Gl.11.1, Müller/Möser - Taschenbuch d.techn.Akustik 3.Aufl., Springer 2004

To estimate a reverberation time, I took two reference rooms. A small studio and the Wiener Musikverein and interpolate your reverberation time depending on the volume.

Please note: I want paying users to be able to set those input variables themselfs. But as you could easily set parameters that would lead to hours of calculation time, I need to work on some sane protections in the background before.

The payment process

It is super easy. You can choose between different payment providers like Credit Card, PayPal and Google Pay.

Please note that I DON'T get access to your credit card data or paypal or google passwords during this process!

Formular for calculating the number of modes under a specific frequency
If you are a business, you can add the relevant business information to pay no VAT. Click "Add VAT" to do so.

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