Archive for the ‘acoustic treatment’ Category

Introducing the Acoustic Ramp™ Diffuser

Monday, August 1st, 2011

As some of you already know, I invented a new type of number-theoretical diffuser a while ago and I have been working on developing it into a product and filing the necessary patent applications.  It’s called the Acoustic Ramp™ because it is wedge shaped.  The diffuser became my master’s thesis for my degree work at the University of Massachusetts in Lowell in Sound Recording Technology.  The degree that I will earn is called a Master’s of Music in Sound Recording Technology (M.M. S.R.T.) and will hopefully make it easier to get a job that pays the bills!

This past Saturday 7/30/2011 I spent the day running a series of tests on the diffuser and comparing its performance to that of a flat reflector.  Essentially what I am trying to show is how much better the back wall of a control room would be if it had an array of my Acoustic Ramp™ diffusers and wasn’t a flat wall.  When sound hits a flat wall it bounces back, a lot like a rubber ball might bounce.  The problem is that the sound bouncing off the wall interferes with the sound going towards the wall and causes problems like comb filtering, flutter echo and bass buildup. One option for handling the problem is to absorb all of the sound hitting the wall and preventing it from reflecting.  This works, but really changes the sound of the room, deadening the frequency response and creating an unnatural ambiance. The other option is to use diffusion to reflect the sound in many directions and to prevent the sound bouncing back in only one direction.

Testing the Acoustic Ramp

Testing the Acoustic Ramp at U. Mass Lowell's Concert Hall

Testing a diffuser is actually pretty complicated and involved, but in a nutshell the process is as follows:

Shoot an impulse burst of sound at the diffuser and then record what bounces back every 5 degrees in the semi-circle around the diffuser.

The white tape in the picture shows the test points where I placed the microphone. The first test point is at 0 degrees directly underneath the speaker.  This test point simulates what a listener might hear if they were sitting directly in front of the speaker and the sound went past them and hit the back wall of the control room and then bounced back.  A flat wall would reflect a sound very similar to what was coming out of the speaker, essentially an echo that hasn’t been greatly changed. A diffuser should have multiple smaller echoes spread out over time with seriously reduced sound pressure. This is what the 0 Degrees test results look like:

Flat Reflector vs. Acoustic Ramp

Diagram showing the difference between sound reflecting of a flat reflector and sound being diffused by the Acoustic Ramp

As you can see from the diagram, the large reflection in the top response is changed into a series of three smaller reflections  and greatly attenuated (reduced) amplitude when diffused by the Acoustic Ramp.  The reflection is spread across time and diminished greatly in amplitude.

Hurray! It Works!

Audio Quality: How to Build a Listening Room (Part 2)

Saturday, October 31st, 2009

Just a quick update about our listening room project.  It turns out the New England Institute of Art will not be interested in treating room 112 because the room is being given to the admissions department.  There is currently no information about where the new room will be located.  I have been told that NEIA has recently built a new critical listening space in a different building, but I have not seen the space yet.

So we are on the search for another room to work in!  Please send a note or leave a comment if you think you might know of a good room for us to work in.


Audio Quality: How to Build a Listening Room (Part 1)

Saturday, October 24th, 2009

At this year’s AES meeting in New York City, the AES Educators took up the topic of how to teach our students to recognize and strive for the highest quality audio possible.  In order for us to teach  techniques to attain the highest audio quality,  students must have access to good listening environments. The traditional concept behind building a great listening room is to build a room which is essentially a studio control room.  Unfortunately this is extremely expensive, usually requires an acoustician and often an architect and is way out of the price range of most learning institutions.   What is needed is a clear set of guidelines to convert existing horrible sounding rooms into adequate critical listening spaces as cheaply as possible.

Gone are the days of the listening party, where people would come together and listen quietly to music together.  But the listening party teaches us a lot about what a listening room should be like.  Here are some ideals that we should strive for in the listening room:

  1. As Quiet as Possible
  2. As Symmetrical as Possible
  3. Use DIY Acoustic Treatment to Control Problems
  4. The Best Loudspeakers that Can Be Afforded in Good Positions
  5. Use the Creation of a Listening Room to Educate the Students

I teach Audio Technology 2 at the New England Institute of Art in a concrete box, which arguably the worst possible environment to do critical listening in.  If memory serves the dimensions are about 17 x 19 feet with 10 foot ceilings with a drop ceiling at about 8 feet.  I will try to use this room as the guinea pig room to talk about these issues. With any luck, I will get permission and a small budget to improve the room’s acoustics so that it becomes a better environment both for listening and for teaching.

– Hendrik

In the spirit of using my blog as a great way of complaining about the general state of the world I offer the following whine:

Today we have a great many adversaries to high quality audio, some of which I have outlined below:

  1. The dominant listening device is an iPod with Apple-made earbuds. (eew!)
  2. Most modern music productions are over-compressed so that they sound as loud as the other over-compressed recordings. (grody!) This is usually referred to as The Loudness Wars. (Also check out: The Death of High Fidelity)
  3. The second most dominant listening device is the car. (very noisy!)
  4. The third most dominant listening device is the craptop computer. (Noooooo!!!!)

DIY: A Jecklin Disk for Stereo Recording with Omni’s

Tuesday, May 20th, 2008

What’s a Jecklin Disk?
A Jecklin Disk is a device that helps to record the most natural sounding stereo image that I have been able to achieve. It is a 12 inch circular disk with acoustically absorptive foam on both sides. Omni-directional microphones are mounted on both sides of the disk. The foam acts much the way your head works to block high frequency sounds from being picked up by both microphones equally. The sound is delayed as it tries to get around the disk and high frequency sounds are absorbed.

For instance, if there’s a sound coming from your left side, sound travels first to your left ear and then to your right ear. The delay that occurs between the left and the right helps us to determine directionality of the sound source. Additionally the sound gets partially absorbed by your head. So you get more high end sound on the side of your head that is closest to the sound source. The Jecklin Disk emulates this. Our friends at Mercenary Audio have a great version of the original article by Jürg Jecklin. ( If you aren’t interested in making a disk yourself, you can easily order a really nice commercial model at Mercenary!

This is what a Jecklin Disk looks like in use with a pair of Earthworks TC25 omni’s:

Now that you know that you want one, but you don’t have $260 here’s how to put one together:

First step is to get out your trusty compass and set it for a 6″ diameter, which will create a 12″ circle. Compasses are really great for working with measurements and drawing circles in specific distances from the edge of a flat surface.

Stick the point of the compass as close as possible to the corner of a piece of 3/8″ nice-on-both-sides plywood and mark out 6″ on both the edges of the plywood. You can just draw an arc across the whole board if you want. I put the lines on the plywood already so you can see what I’m doing.

Next, you stick the point of the compass at the edge of the board where you drew the arc. This point is 6″ away from the corner. Draw an arc on the board where the center of your disk will be. Now move the point of the compass to the other point where your first arc intersected with the edge of the board and draw another arc where the center of the disc will be. Where these two arcs intersects is the center of your disk.

Now you can draw out your 12″ circle by pointing the compass in the center and making a complete circle.

Now it’s time for POWER TOOLS! Be sure to use hearing protection and eye protection. You never get you hearing back when it’s damaged. I prefer to use a saber saw (also called a Jig Saw) for cutting arcs and circles. You want to use a smallish blade with small teeth designed to cut wood, not metal.

Carefully cut the circle out of the plywood. Don’t worry about small imperfections in the cut because you will be sanding the edges smooth.

Now that you’ve cut the circle out of the plywood, take the rest of the plywood over to the table saw. We’re going to cut out 5 of squares of plywood to make the base of the Jecklin disk. These will all get sandwiched together to make the base that the mic stand threaded flange will attach to. Rip the first rectangle from the edge of the cut circle so that the disc will nestle perfectly in the base.

After cutting out all the little rectangles, you can see the odd one with the arc cut into it. This will be the middle piece of the sandwich.

Get your clamps, wood glue and blocks ready to glue together and clamp.

Glue is art. The glue is a abstract representation of the emptiness of the skulls of our nations leaders. After you get all the pieces together, clamp them after making sure all the pieces line up as smoothly as possible.

Go ahead and put the base aside to dry (give it at least an hour or so). Now go to the drill press to putting the mounting holes through the disc. This will be where you’ll mount two microphone stand flanges on either side of the disc. My drill press has lasers! Jealous?

After you get the disk drilled out and the base is dry. Go ahead and glue the disk into the slot in the base that you left with the arc cut out. Notice the two mic flanges on the table saw to the right of the disk. After the glue dries, you’re going to need to thoroughly sand the entire surface of the disc and the edges of the base as smooth as possible.

Fit self-sticking foam to the disc in preparation to attach it permanently.

After you have your foam cut correctly, you can go ahead and seal the disk with a few coats of Polycrylic, a latex version of polyurethane. Polycrylic is great for furniture that isn’t going to be walked on, but it really sucks for floors because its just not hard enough.

Notice that the wood grain is coming out more with the layers of clear finish.

After the Polycrylic dries, go ahead and attach the self-sticking foam to the disc and trim all the excess off with an hobby knife.

The last step is to bolt on the mic flanges through the disk. You will mount your mic clips onto the flanges.

Here’s a close-up of the base of the Jecklin Disk.

Now add a couple of omni’s and you’re good to go. Two omni’s on a Jecklin Disk, a few feet in front of a drum set, make for a wonderfully natural drum sound. A great inexpensive omni mic is the Audix TR-40, which sounds wonderful and almost as good as mics costing 5 times as much!

DIY: Building Acoustic Treatment for a Piano Room

Wednesday, April 9th, 2008

The following is a step-by-step explanation about how to build acoustic treatments that are easy, economical and quite beautiful.

Why We Needed the Treatment in the First Place
At our wedding, my wife and I were given by our friends and family contributions toward buying a Yamaha U-3 upright acoustic piano. We fell in love with one at East Cambridge Piano (which is actually in Somerville now!). A couple of months after the wedding when the dust had settled we paid for the piano and had it delivered to our home. We were both so excited about it coming, but when it got to its new home the instrument sounded really different. The tone was still very good, but the rooms reverberations made the piano really loud and at times unpleasant sounding. An acoustic guitar could never play with the piano because the piano would take over the sound in the room.

Laura, my wife, plays piano and performs in a Latin American fusion group called Son del Sur (Song of the South). The group has a minimum of 4 women singers, 1 male singer, 2 percussionists, 2 guitars and assorted other musical snacks. To be frank, they sounded absolutely awful in the room. The sounds were all competing with each other: the voices covered the guitars, the percussion had no where to go but louder and louder. The musicians couldn’t hear themselves or the people they were playing with. Something needed to be done:

This is what the room looked like when we started:

As you can see from the photos, the room is bare except for the piano and the table. The bay window breaks up the parallel walls from front to back and the closet door and the bed room door create a nice diffusion to break up the side walls. The natural reverb is really quite lovely and for a solo instrument (like a violin, vocal or acoustic guitar) the room sounds great. Unfortunately, anything louder than that and the ambiance turns in a noisy, brassy screech.

Based on the shape of the room I calculated that the most important walls to treat were largest flat wall (opposite bottom photo) and the wall above the piano. The goal would be to start with a minimal acoustic treatment and add more later if necessary. The plan was to build 4 panels, 4 inches thick in frames 2 feet by 4 feet. The acoustic absorptive material is Owens & Corning 703 Rigid Fiberglass Insulation. We would then stretch fabric over the frame and the fiberglass to keep the fiberglass from getting in the air and then getting into people.

Here’s how we did it:

The following 2 photos show the wood stock and 703 Fiberglass that we used to build the acoustic panels. The wood is 3/4″ furniture grade plywood from Home Depot which was $26 for a 4′ x 8′ sheet. We ripped in into 4″ strips with my trusty Makita portable table saw. (very dangerous…don’t try this at home kids…we’re professionals…) The 703 stock is 2″ thick 2′ x 4 panels. I bought them at Kamco in Woburn, MA for $80 for 12 sheets or 83 cents per square foot. This is about HALF the price that you pay when you buy it on the web. Do yourself a favor and find a good insulation supply house! (Eat you heart out Auralex! ($3.75/sq. ft)

Here we are setting up our first 45 degree cut for where the corners of the frame are joined together.

Ty Smith cutting the 45’s with earplugs in but without a dust mask:

Ty with earplugs AND a dust mask…Sawdust makes a bad lunch.

Squirting glue on the joint:

Spreading glue with the glue spreader that mother earth gave us:

Using 90 degree corner clamps to hold the corner while we nail the frame together and wait for the glue to dry:

More clamping:

Popping in a couple of 8 Penny finishing nails for over kill at the joint:

Waiting for the glue to dry:

This is what a frame looks like after it has been assembled:

Ty stacking the frames so they can dry completely:

A Jecklin Disk was used to record the ambiance of the room before the treatment went up. Look for the actual before and after sound files in a later post…

Recording the bare room:

Assembling the acoustic panels on the table. The 703 fiberglass was pressure fit into the frames and the material was held in place with friction:

These are some panels that have been assembled but the material hasn’t yet been glued down:

The first panel has been hung, one glued panel is drying against the wall and another panel is being glued closed:

Three panels mounted on the wall in their final locations:

An additional panel mounted above the piano to absorb reflections from the top of the piano:

I hope that this post has helps some people control the acoustic in their music spaces. Please feel free to post links to your own DIY acoustic treatment projects.


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.