I am glad that you are interested in my blog post series on how to build a proper control room. Our real world example will be the brand-new control room that we built here at Orthogonal Records. To keep each post at an enjoyable length, the series consists of 12 posts, one each week and deals with the following topics, organized into 12 chapters.
Table of Contents
- Prerequisites: Software- & Hardware
- Acoustic design concept
- First measurement and analysis
- Construction of bass traps
- Mounting fabric and difference measurements
- Recovery of mid and high frequency response by the use of wooden boards
- Construction of early reflection absorbers
- Construction of a cloud absorber
- Installing the studio desk
- Final tweaks using equalization, primary diffusion & installation of a sub-woofer
- Changes in the desk setup & correction using Sonarworks Reference 3
- Conclusion and discussion of final measurements
I hope that you will enjoy these articles and encourage you to ask whatever comes to your mind by commenting on the respective post. Thanks for that. Alright, let’s immediately dive into chapter one.
1. Prerequisites: Software- & Hardware
In order to objectively decide how good a given room really sounds and to judge the effectiveness of any optimization step it is absolutely necessary to take proper measurements. By doing simple “listening tests” one could easily be fooled into thinking the room sounded great already, while it actually just sounds better than before the optimization process started. All the more, if one has never heard a properly treated room. But even if you’ve worked in a lot of properly treated rooms already, simple listening can be very subjective.
Hence, the first thing to think about is how room measurements can be done. One elaborate piece of software for such measurements is called Room EQ Wizard (REW). It’s freely available for all major operating systems, i.e. Windows, Mac and Linux. In order to download the software you need to take a look at the banned e-mail list and make sure that your e-mail provider isn’t listed there.
Furthermore, one needs a measurement microphone, i.e. an omnidirectional microphone that is properly calibrated. One affordable model is the Behringer ECM8000 that is sufficiently accurate, at least when sending it to a calibration service and using the measured calibration file with REW, as we did. If you’re happy with taking comparison measurements only, you could probably even use it without specific calibration and use the calibration file available in the REW forums instead. But please keep in mind that production spread can be quiet significant with a cheap product like the ECM8000.
Moreover, one obviously needs a computer and a proper audio interface. The interface has to supply +48V phantom power to the microphone. We used a Presonus Audiobox USB together with a MacBook to be able to easily carry out measurements whenever needed during the building process.
Next in the list are studio monitor speakers to play back any measurement noises as well as proper stands to adjust the height of the speakers horizontally at ear level. We at Orthogonal Records are using a pair of EMES Black tv HR active MKIV as our main speakers. For the first few measurements we used K&M 26740 speaker stands, while afterwards a pair of custom built sand filled wooden speaker stands has been used.
In order to do the levelling an spl meter is necessary. If you own a smartphone you could also use one of those spl metering apps of course. We are using the spl meter app provided by studio six digital with an iphone 4S.
Now let’s do a quick run through of the setup procedure in REW. After successful installation and startup of the program, the following window should appear.
Clicking “Preferences” opens up a dialog to set your input and output device in the “Soundcard” tab and your calibration file in the “Mic/Meter” tab.
I suggest that you set your values accordingly for a first test run, or consult the manual for further information on these settings.
If that hasn’t been done already, now is the time to set up the speakers and the measurement microphone at the corners of an equilateral triangle. The microphone has to be set up vertically and at the same height as the speakers tweeters. As I will mention in a later post, this setup can actually be changed during the first measurements to obtain a smoother frequency response. However, it’s definitely a good idea to start out with a configuration as shown in the sketch below.
After speakers and microphone have been set up and everything has been connected correctly, one needs to set the levels by clicking on “SPL Meter” in the main window of REW, which opens up an SPL Meter window.
Please make sure to turn your speaker levels down completely and then click “Calibrate” to start the calibration process. If you now start to bring your speaker levels back up again you should hear calibration noise playing back. Position your SPL meter or smartphone with SPL app directly above the measurement microphone and then raise your speaker levels until the SPL meter reads 83dB(C), which is our reference level (cf. Fletcher-Munson curve). Then, start to raise the mic-preamp level of your measurement microphone’s channel until the “In” Meter in REW reads approximately -20dB. Click “Finished” in the small pop-up window and you are done calibrating.
Now you can start your first measurement by clicking “Measure” in REW’s main window, whereby the following dialog pops up.
Again, copy the settings from the screenshot above and make sure to use “1M” as the “Length” setting in order to get the highest possible resolution for your measurement. Then everything is set to take the first measurement by clicking “Start Measuring”. Good Luck!
We will elaborate in more detail on the first measurement and it’s analysis in the third post of this series.
That’s it as far as the prerequisites are concerned. Next week we will have a look at the acoustic design concept of our control room and compile a list of the materials that are needed to start the construction process. So please subscribe to our channels and make sure to stay tuned!
All the best,