6) Measuring – Sound

Hey! Hi. This page is was duplicated at the Training Courses site, with new edits, at: Measuring Sound

Please use this new site, since it will be the most up to date and it will come with new features. Thanks!

Since there are many goals and purposes for this project, there are many things that need to be done. Training is high on the list. Practice should be high on the list…but who has the time!?!?
Perhaps you don’t have the a friendly tech or projectionist to

  • download DCPs onto a USB drive and
  • load them into the Media Player/Projector system and
  • make a nice playlist,

You can still download some audio and light measuring tools, and experiment and practice with them until you can use them easily in a dark room. 

Audio Tools for the iPhone – There are many…too many, in fact. Some are extremely significant professional tools at great cost – not knocking them, since they are reasonable if you are a pro who needs the complexity.

Some are too simple or have pop-ups that will annoy you in the dark room.

Some need several taps on the screen to set it up the way you need it for the auditorium measurement.

We recommend one that is not only free, but it is quick and simple to get good data from.

What we need is something that quickly tells us 2 numbers. The first number is called Peak, which measures the sharp blast of energy that a clap of lightning or a single hand clap might have.

The other number – the one we actually need most often – takes an average of all the sounds for a particular segment of time…a moving window of time, in fact. The name goes by the abbreviation of “RMS”, which stands for a technical term that sounds like a rapper’s name on a science cartoon: Root Mean Square. If you are thinking it sounds like math and Must. Be. Ignored., you are right!

Many of the tools will have a Peak and RMS number displayed quickly and at the same time. This is what you want. You can skip the Peak level, but it is good to be familiar with it. Usually, we will just report the RMS level.

But there is another layer of complexity. There are choices in how we measure RMS levels. The first choice is Fast or Slow. The second choice is A or B or C or Z weighting.

Let’s cut to the answer and ignore the reasons:

Slow and C weighting.

We can study why in another lesson. Engineers talk for hours about these things.

We will also skip to the recommended iPhone tool. The app that we keep coming back to is from dspmobile.com, named

dB Volume.

A very simple and clean interface gives all the details you need. And, most important, you can change the weighting and response speed from the front panel.

great shot of the dB Volume tool
dB volume is a nice tool, with easiest access to the variables that you need to change.

People may tell you that the iPhone isn’t exact, or argue that you need something more precise. But both of those statements are not true.

We need something consistent. We measure today, we measure tomorrow. If the sound level is the same, the measurement should be the same. Which is the situation – unless your iPhone gets thrown into a pizza, which makes the microphone read differently than the day before – you will get a consistent reading. Which means that we can measure the speakers consistently, and tell if there is something different from day to day. When the sounds come from speakers, we can see their levels, mark them down and compare the results from last week and last month…all the way back to the time when the room was set up by a technician. Oh…and sometimes we will measure silence.

This is our only goal. Finding differences. It does no good to tell a tech, “Hey, it’s only 80 dB in the room.” They will have no reference~! But it does good to say, “The left surround was 85 dB last week and is only 80 dB this week.”

A quick story about the term ‘dB’. And a quick hint.

The person who is honored for his research in sound, and sound transmission across a distance (he was the first to get a telephone to work), is Alexander Graham Bell. That is why the ‘B’ is always capitalized. The ‘d’ is short for ‘deci’ meaning one tenth. Rarely do we use the term ‘Bel’ by itself. The typical measuring unit is the ‘decibel’.

And finally. When you have finished measuring your auditoriums, turn off the dB Volume tool. It may stay running in the background. If so, it will cut your battery time.

Go and do well. Practice a lot! …and mark up up those Manager’s WalkThrough Report forms.