July 31, 2010

Can you simulate room modes?

There are a few different tools to simulate room modes. Are they useful? Let's find out.

Here is a measurement of a subwoofer in my room. It's a nearfield measurement, just to show you what the subwoofer is doing.

You can see the measurement is very smooth so far, and the small peak above 160 Hz is a measurement artifact.

The sub is a Rythmik servo sub:

Next I'll attempt to simulate the response of the room using the FRDC Room response calculator.

Subwoofers are placed in corners, and the "mic" in the listening position. The program assumes perfect response from the subwoofer - totally flat over that range.

Here we have two versions of the same room. One is built like a concrete bomb shelter (no damping). You can see we get narrow dips and peaks with no damping. The other has damping such as we would find in a room constructed more lightly - plasterboard walls, timber floor, etc.

Now let's look at an actual measurement:

At first glance it looks quite different, and it's tempting to dismiss the simulation. Firstly, the room gain appears to be exaggerated in the model. We can see 3 main dips in the measurement - 70, 100 and 150 Hz and these are reflected in the model to a degree.


Are the simulations accurate? As you can see, it's a bit hit and miss. You can't rely on them fully, but let's suppose I gave it some more time and fiddled until I came a bit closer to the measurements. I could use different values for how much each room surface absorbs. I could then use it as a tool to quickly show the impact of different placements quickly. That has some value, but it certainly won't replace measurements. You will need those before you can be confident in your results. If you are hoping to use this tool to design a room before construction, I would use some caution.

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