Archive for the ‘SPL meter’ Category

Modeling a Room in 3D with Google SketchUp

Sunday, September 9th, 2007

It is now free to download and use a high quality 3D modeling software application. Just visit Google’s new 3D modeling center:

The drawing above is a scale model of the control room at Indecent Music with one monitor, sans equipment and furniture. Measuring the SPLs in a room and using a model like this helps you to interpret the data you get from your SPL. It also helps you to see how sound might be reflecting in your room. The walls and other surfaces are easy to understand in 3D.

A floor plan view or a horizontal slice lets you write in data points to make the a data model.

It’s pretty easy to see how this kind of a tool could make working in your room easy and and more scientific.

The other thing that I love about SketchUp is that it has a built in tool to get models from Google 3D Warehouse and to upload your own models to share with others. This allows for both online collaboration with colleagues and for collabs with people you don’t know. One of the things that makes 3D modeling so painful, is the need to recreate all of the models that you need to use yourself. Most people end up buying a library of components for use with their own industries. For instance, Kitchen Designers use a variety of different CAD applications to design kitchens, but who wants to model 2300 variants of a Kraftmaid cabinet? So you buy the models from the source.

With the 3D Warehouse, you can check to see if anyone has made something similar already that you can reuse or recycle. Extremely useful. As long as everyone shares, this kind of system works very, very well. Did you notice the model of the monitor? That model was downloaded and imported straight from the 3D Warehouse. I probably saved an hour or more!

Fix Acoustics Problems in Your Mixing Room

Thursday, May 31st, 2007

Now that you know all about what frequencies are out of wack in your studio (How to Test Your Mixing Room) you can start to worry about how to fix the problems.

You probably noticed that certain frequencies were louder than normal and some frequencies were quieter than normal. If you’re in a smallish room probably most of the frequencies below 500 Hz or so are pretty wonky. Low frequency sounds actually are made up of longer song waves and as the frequency increases you will see that wave length decrease. Think of a car with a sub-woofer pumping out side of your house. Most of the time, the low sounds are actually louder outside of the car, than inside of the car. It can take 20 feet or more for a low frequency sound to make a complete sound wave. You can figure out how long the sound wave is by taking 1130 ft/sec (The speed of sound in average humidity and temperature) and dividing it by the frequency you want to measure. Let’s take the example of 55 Hz which is a VERY low ‘A’ note commonly heard in songs with deep thumping bass.

1130 ft/sec
55 Hz

You get 20.5454… feet.

That’s how long that sound wave is. You need that much distance for the sound wave to finish one full cycle. Unless you have a stretch hummer, you’re not in the car at 20.5454 feet from the sub woofer. That’s why everyone OUTSIDE of the car gets to enjoy your sub so much!

So…What does this mean for listening in your room?

Let’s say when you were doing your frequency testing you noticed that 220 Hz was significantly louder than the other frequencies around it. You could get this kind of behavior if 220 Hz is a resonant frequency of something in the room. Or even the room itself! So let’s figure how long the wavelength is for that frequency:

1130 ft/sec
220 Hz

Or 5.1363… feet long. If your room is that wide or double (10.2727 feet wide) then your room is sympathetically resonating with the sound. The sound comes out of your speakers and then bounces around in the room. The harder and smoother the walls are, the more the sound bounces around before it runs out of energy. The frequencies that wavelengths are multiples of the dimensions of your room will get messed up in all likelihood.

So you either new to buy some bass traps or build some bass traps. So here’s the scoop in general about acoustic treatment products. The most cost effective products are usually not the ones that have the most advertising in stores or in magazines. The best article on building bass traps is written by Ethan Winer as is located at

Interestingly enough he is one of the founders of RealTraps, a company that builds bass traps based on his original designs and then improved over the years. So not only does his company make the best rated bass traps out there, he teaches you how to make your own! If you’re not already making a good living with music, then build your own traps. If you have some bread buy them. The pricing is EXTREMELY reasonable for what you’re getting!

Mid and High range frequencies are much easier to contend with. Soft materials like acoustic foam or even fire-rated blankets absorb mids and highs very well. They do deaden the sound very well, so you may find that your room doesn’t sound like a room anymore.

How to Test Your Mixing Room

Monday, May 21st, 2007

The way a room sounds has everything to do with how we perceive the sound in the room. A little bit of natural reverb in a tight space (like a tile shower) can inspire even the shyest singer to start belting out their favorite Fleetwood Mac hits. The best speakers in the world put into a crappy sounding room are probably going to sound pretty yucky. Let’s work on some acoustics.

How can you figure out what’s wrong with a room? How do you fix the problems?

You can do all of these tests with your naked ear, but to keep it strictly scientific it’s a really good idea to spend a few dollars ($50) and get an SPL meter. (Radio Shack) This device is designed to give you an accurate reading of how much sound pressure is happening in a single place. It measures in SPL which stands for Sound Pressure Level. Sound above 100 SPL can cause permanent damage. The ideal listening levels are between 80 and 90 SPL.

Download some test tones so that you can have an accurate idea of exactly what you’re testing. Here are some test tones that I routinely use: Test Tone Downloads

You’ll need to download the mp3’s that you want to use and then play them through the speakers that you mix through. A good first mp3 to download is the 20Hz to 20Khz Sweep. This is a ten second sweep from the lowest sound people can hear to the highest sound. When you play this file through your speakers you will probably notice that the tone will start out as inaudible and then the volume will sound like it’s going up and down slightly. You will probably notice that some of the loudest parts of the sweep are the most annoying frequencies.

So here’s the weirdness: the test tone is recorded at an equal volume across all of the frequencies. What you are hearing as volume increases and decreases are inaccuracies in your speakers, resonances in the room you’re in, and possibly that all those Metallica concerts may have actually destroyed specific frequencies in your hearing.

First Things First

Make sure that you have set your monitors up in the correct way. Here’s a good check list.

  1. CABLES. Use high quality balanced audio cables to connect your audio interface or your mixes control room outputs to your monitors (if your monitors are active) or your monitor amp (if your speakers are passive). Make sure that the cables are the same length and the same type of cable. If you are using passive monitors make sure that the speaker cables are high quality, as thick as possible and that they are the same length.
  2. PLACEMENT. Your speakers should be placed roughly at ear level. They should be the same height. You should always sit in the same place every time you mix or listen. You should sit so that each speaker and you make an equilateral triangle, meaning that all sides of the triangle are the same length. The speakers should point to where you are sitting.
  3. DE-COUPLING. If you put your monitors on a table and play music the speakers will vibrate, so the table will vibrate, and everything on the table will vibrate. There’s a resonant frequency for everything, and your table probably doesn’t sound wicked good. At a bare minimum you need to get a piece of heavy foam to put underneath the speakers, this will minimize the amount of energy that gets transferred from the speakers into the table. I have had good luck with using heavy mason’s sponges that you buy at any hardware store. You can also buy products like:

    Auralex MoPad

    Vib X

Ok. Now your speakers are hooked up right, placed right and sounding as good as they can on their own. Now you’re ready to start doing your testing. First try playing the test sweep again. You probably will notice some improvement already.

Here’s the flow of the testing. Start with your mixer set to unity or with your interface set to unity and start going through all of the test tones. The ones under 500 Hz tend to be the ones that are the most screwed up. I usually start by playing a 1Khz tone and then recording the SPL. Measure the SPL with the meter right where your head is when you’re mixing. Adjust the volume of your monitors until the SPL is close to 90. This will be your baseline. Now you know that when you play a 1 Khz tone at -12 dB it’s sounds in the room at 90.

It’s a good idea to mark down where your volume knob is set now. This is where you want to do most of your listening. Now simply repeat this procedure for as many tones as you can stand. I usually start low and work my way up. Write down which tone you’re testing and what the SPL meter says.

Now you have a pretty good idea of what’s happening at your mixing location in the “sweet spot.” Next time we’ll go through what you can do to fix the problems that you’ve found.