It’s time for the fifth article in the control room series.
This time we’re gonna talk about how to recover mid and high frequencies without affecting the bass frequency absorption too much. I have done this by using wooden boards that are mounted onto the bass absorbers with certain slits in between them. The boards are about 19.5 cm wide while the slits are approximately 2.5 cm wide. In theory this construction should reflect all frequencies above approx. 1760 Hz while everything below that threshold is diffracted around the wooden boards and then absorbed by the bass absorbers behind the boards.
This is how the construction looks like in the finished control room (anno 2015; desk changed again already – more on that in a later article).
However, be aware that the measurements shown here have been done without the furniture, i.e., without desk, screens, racks, couch, etc. That’s very important since everything you put into the room affects the measurements. So in order to see what the effect of the wooden boards is we need to just add those and must not change anything else in the room. That’s exactly what I did.
When looking at the frequency response we can see that it changed quite a bit compared to the measurements in Building a proper control room – mounting fabric and difference measurements. You can also clearly notice the deeper dip at about 160Hz which might be some kind of resonance effect due to the panelling.
However, EDT graph, waterfall and spectrogram all clearly show that the goal of recovering mid and high frequencies has been perfectly achieved. What one sees however, is that the reflective region of the panelling already starts at significantly lower frequencies than the theory would suggest. Remember we calculated approx. 1760 Hz for the lower frequency limit while the measurement shows significant differences down to 900 Hz. This suggests that simply calculating the limiting frequency by a “diffraction model” doesn’t capture the acoustical phenomenons well enough. However, that’s no real problem here as we verify every step of the construction by measurements anyhow.
The ETC diagram is now worse than before with more and stronger early reflections. However, that is also perfectly reasonable since the panelling significantly increased the area of reflective surfaces.
Now that we have recovered the mid and high frequency response the next task is to build some early reflection absorbers and put a big couch for clients in the rear of the control room. These steps will significantly lower the mid and high frequency response again and will finally bring them into reasonable boundaries.
The main point here is the following: If one would refrain from using panelling or any other reasonable method to “rescue” mid and high frequencies and instead proceed with building early reflection absorbers the high frequencies would have been damped way to much in the finished control room. This in turn would lead to a muffled sound that no-one needs in a control room.
That’s it for now. We will see what the early reflection absorbers and the couch can do for us in the next chapter of this series. See you then.
All the best,