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7 Nov 2020

How to stop guessing and trust your room - small room acoustics - part 4

producer How to stop guessing and trust your room - small room acoustics - part 4

This article is a collaboration with GIK Acoustics that is part of a series of 7 blogs. Read the other blogs below.

Enjoy reading part 4!

Testing Testing Testing

More than ever now, when it comes to discussing acoustics on forums, applying acoustics, or for example looking where to place speakers in a tricky shaped room you will hear people ask for your ‘test results’.  It has almost become a caveat to all recommendations. If you are considering two or three set ups in a room for example, almost all acousticians now will give an opinion and it will be followed up by I would test this first. So why testing, what is it and how do we do this for ourselves?

So why testing? 

One of the largest issues within the Pro Audio community is that it appears that everybody seems to have a different opinion of how to fix an issue, how to build traps, which traps to use and where to place them. In fact, on almost every acoustics theory or solution, someone, somewhere will have written the opposite view and in both cases, it almost certainly will be written with authority that they are right. 

So why is this? Two reasons instantly spring to mind, and both relate to physics. The first is that due to physics, and how sound interreacts with everything that is in a room, although certain acoustic models can be used it is extremely difficult to accurately predicts how sound is going to react in a room so acoustic testing actually shows us exactly what is happening in that room in a given moment in time. The second reason is that physics is an extremely difficult topic to master and it yet again another case of a little knowledge can be dangerous.

What is acoustic testing?

Acoustic testing in our small room scenario is a way to measure what is happening to sound that is introduced into your room once it has left the speakers. By the use of multi directional microphones and acoustical testing software which both provides frequency and impulse responses and measures that response we are able to measure aspects such as distortion, phases, decay, frequency loudness (level) and reflections amongst other measurements (data). 

Basically, we are able to build up a picture of how sound is reacting to the room, the objects you have inside that room at a given point in the room and at a given point in time. Once this information has been gathered, we can start to see exactly where your problems are in the room and start to consider our strategy to deal with it. What is even better, is this process is so simple and quick that we can continue to use the software to measure, makes adjustments, test hypothesis’ and even EQ individual frequencies if needed. Basically, this simple process takes the guesswork out of acoustic consultation.

How to Test?

In the rest of this article I am going to talk you through how we test. From which microphone and software to use, to setting up and running the program. Feel free to contact me via Inside Audio if you have any particular questions about this process and we can perhaps run a FAQ section on our next article.

The Software 

We recommend the use of Room EQ wizard for your acoustical room testing. Why?

  • This excellent piece of software is free to use (they ask only for donations if you wish).
  • It is pretty much glitch free, really easy to run and can be used for both the room testing and EQing your room later if you wish
  • They have an excellent online forum and community who are more than happy to answer any questions or queries about the software that you might have.

Download it for free (or make a donation) at https://www.roomeqwizard.com

The Microphone

There are two approaches with regards to microphones and that is either to connect a mic via your audio interface or what is most commonly used these days due to simplicity (and the method that I am going to use in these notes) are measurement microphones with a USB connection.

Firstly, what type of Mic is that it you need? You need an omni directional small diaphragmen condenser mic. It is unlikely that you will already have one of these in your arsenal unless it came with room adjustment software. Basically, it is a measurement microphone.

We recommend the Mini DSP UMIK 1 / 2 as the best and most usable USB Measurement Mic in the market currently. It is accurate, easy to use and each mic comes with its own calibration file. Currently retail approximately 100 Euro.

GIK Acoustics Simple Step by Step Guide to Testing Your Room. 

What you need.

  • A measurement Mic (We are using the Mini DSP UMIK 1)
  • Measurement Software. We recommend the Free Room EQ Wizard Software. Download at https://www.roomeqwizard.com
  • A Computer
  • A connection to your monitors

1. Download the Free Software for your computer operating system and install (I am using a Macbook Pro in this guide)

2. Connect your Microphone to your computer. Once connected the small blue light will display.

3. Open the Room Eq Wizard Software. If you have a calibrated mic like the Mini DSP UMIK 1 it should recognize it and ask if you have a calibration file.

4. If you have the calibration file, it will ask you to select it.

5. If you do not have the calibration file, then go to MiniDSP.com and on the Microphone page it will ask you to enter your serial number. It will then allow you to download two calibration files specific to your microphone. For the purpose of this exercise we want the one named after the serial number. Do not use the 90 degree Axis one here.

6. Next click the measure icon in the top left-hand corner of the screen.

7. You should now be on the Make A Measurement page, which looks like the below.

8. Check the settings. Type should be SPL and method Sweep. You also have your first opportunity to name the file here.

9. Check the Start and End Frequency. Set the Start Frequency to 0 and the end Frequency to 20,000hz

10. Setting Length should read 256K

11. Sample rate should be 48khz and set the delay to 0. The delay setting is in seconds and can be used if you wish to move from the mac to a different position for the start of the test. It is a delay from when you press test until the test begins

12. Input – This should be your microphone

13. Positioning of the microphone. For this first test we are ideally going to place the microphone in the listening position. So, remove your chair (ideally well out of the way, I have seen many confusing reflections show on results from high backed reflective chairs) . The Microphone needs to be ideally at ear height and pointing towards the ceiling in your normal sweet spot.

14. We are now ready to check levels. Press the Check Levels button

15. You should hear some white noise. It will now tell you the result

16. My level is set to OK which means I can begin. Note that it is about 82db’s which is normal listening levels

17. Before we actually being the testing make sure that you have the room as silent as possible. Do not talk or make a sound, if there is noise from outside wait for it to stop before you commence. Also check that such items as air conditioners have been turned off before you begin

18. Now we can begin. Press the start button. Please note, it is always wise to cover and protect your ears whilst the sweep is taking place.

19. If the settings are still not right, you will get a warning like the below. As you can see, I left no headroom so clipping occurred. Turn down the volume and recheck your levels before pressing. Start again.

20. In this example I am using testing the stereo position, but we recommend you repeat these steps for the left monitor and the right monitor separately as well.

21. In a few simple seconds you should see the following screen

22. If you do, you have now successfully captured a sweep of your room

In our next article we are going to talk about what these results mean and how to interpret what that means for your room

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