DIY Home-Studio Acoustics 101

Home studios are great.  You can work remotely, and no one even knows you’re working in your bathrobe.  It’s super comfortable!  

If you’re like me, you’ve moved a few times, and have had to tear down and rebuild your home studio several times.  Building an acoustically-sound working environment with lots of restrictions can be really difficult and time consuming.  It can also be pretty expensive.  Through my studies in sound recording, acoustics, and lots of trial and error (and successes), I hope I can help others reinforce their not-so-acoustic-friendly spaces into working home studios.  I will offer tips and tricks on various materials I’ve had success with, as well as some instruction on creating your own, inexpensive acoustic panels.

This article isn’t intended to solve all of your acoustic problems.  Every room, building, environment, region of this planet, and varying galaxy will face different challenges and restrictions.  Every person will be able to afford different materials.  To some, this article will “sound” very basic, and will not present any new ideas.  However, any novice acoustics sleuths and do-it-yourself-ers out there: please continue on.  And for the purpose of this article I will be focusing only on rectangular rooms most often associated with home studios.

Acoustics 101

Before we get into making our space more acoustically fit, we – as I did – need to review the most common principles and issues that arise in a basic, rectangular room.  Namely: direct sound, reflective sound, flutter echo, standing waves, and acoustic interference.  I have a few illustrations, photographs, and audio examples to help out the beginners.  I used my own studio environment in the examples.  My studio measures 10′ wide, 13′ deep, with a 7.5′ ceiling.  The walls and ceiling are drywall, and the floor is wood.

Direct Sound is easy.  Its the sound that comes from a source and enters the ears or microphone without reflecting off, or traveling through or around any surfaces.

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Reflective Sound is any sound that reflects off of a surface before reaching the ears or microphone.  Reflective sound can be good or bad.  In high-end studios with beautiful, non-parallel walls and surfaces, reflections aren’t so bad.  Reflections are often dispersed and absorbed throughout the room so as not to cause problems for the person recording/mixing/mastering/etc.  Most home studios are limited to rectangular bedrooms with mostly parallel walls.  In this situation, reflective sound causes a whole host of problems including flutter echo and standing waves.

The closest surfaces are often the walls and ceiling nearest the midway point between the speakers and the listener as pictured below.

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But don’t forget about reflections off the back wall…

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And then there are double-reflections (not a technical term) from the rear ceiling and the rear wall.

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The least obvious are illustrated below. Sound from the speakers can reflect off the ceiling, returning to the usually-flat desk, back to the ceiling, etc.  And while the woofers and tweeters are most often on the front of the speaker cabinet, the entire cabinet vibrates, emanating sound in all directions, including straight up.

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Why is Reflective Sound bad?

Three main reasons: flutter echo, acoustic interference, and standing waves.

Flutter Echo occurs when sound bounces rapidly back-and-forth between two parallel reflective surfaces.  This is a nightmare in rectangular rooms such as mine.  Flutter echo is a harsh, sharp reverberation.  In the example below, I clapped my hands in the corner of my studio in one of the few places where there is no absorptive materials on the floor or ceiling.  This location is somewhere where I would neither edit or listen, nor would I record anything, so I am not too worried about it having an effect on my work.

Acoustic Interference occurs when our ears pick up both direct sound and reflective sound.  The two signals are delayed from each other and muddy the perceived sound causing intelligibility to decrease.  This is an artificial coloring of the projected sound, or simply put: your ears aren’t hearing the sound the same way the speakers are outputting that sound.  And that’s a shame.  I’m sure it was supposed to sound really really good. Sorry, I make myself laugh sometimes… Enjoy another DIY illustration.

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Standing Waves, the other elephant in the room.  This one is a little more complicated so I consulted my old textbooks for some help.  Full references below.

“Standing waves…may be set up when half the wavelength of the sound or a multiple is equal to one of the dimensions of the room (length, width or height).” – Rumsey & McCormick, p. 22

“Standing waves occur when sound is reflected off of parallel surfaces and travels back on its own path, thereby interfering with the amplitude response characteristics of the room.” – Huber & Rumstein p. 73

“The frequencies (f) at which the strongest modes will occur is given by: f = (c/2) x (n/d)

  • c is speed of sound (~340 meters per second)
  • d is dimension involved
  • n is the number of the mode (1st, 2nd, 3rd, etc)” – Rumsey & McCormick p. 22

My interpretation of all of this, including other references throughout the years, is that your room size and shape make certain frequencies resonate more strongly in different areas of the room due to acoustic interference.  When standing waves are present, certain frequencies – primarily lower frequencies – can have differing sound pressure levels, especially near the walls vs the center of the room, or even at various points in the room.

You can test your room by playing music through your speakers.  Walk around your studio space listening carefully for changes in frequency response.  If an area sounds more bass-heavy than others, you are experiencing standing waves.  Near your walls, you should experience this fluctuation.

The illustration below uses my studio as an example, super-imposed over a graph of Sound Pressure over Feet.  This is similar to multiple charts I’ve found in my research.  Using the Rumsey & McCormick algorithm, with my 13′ dimension, we see that, with no sound treatment, my space naturally produces a first mode standing wave of 13.26Hz, below the threshold of hearing.  The next modes, however, are 26.15Hz, 39.23Hz, 52.31Hz, etc.  As you see, the 2nd, 3rd, and 4th modes are very low frequencies within the threshold of hearing.

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The same algorithm can be used to calculate the standing waves of the other parallel surfaces: the room is 10′ wide, and the ceiling to floor is 7.5 feet.  All of these parallel surfaces are causing standing waves when they go untreated.  And treating them on a budget can only limit their effect, but most likely won’t completely even out the frequency response of the room.

Treating Your Room

Wow, we’re going to need to treat the heck our of our rectangular rooms. To start, here are a few illustrations to help out based on previous illustrations.

To me, the most important place to start is above the speakers, recording desk, and the listener, especially between the speakers and the listener.  This will help to reduce acoustic interfere caused by standing waves and reflected sound.  I also opted for an area rug, which extends from the edge of the desk almost to the back of the room.  Width-wise, it covers about 2/3 to 3/4 of the floor.  I also have a carpet pad under that, which helps absorption even more.  The carpet helped immensely in removing flutter echo, and general room reverberation.

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The same issues will be helped by covering the walls in a similar manner.  Remember, sound is emanating in all directions, so you have to think about all surfaces that can affect the listening position, and anywhere else in the room you might record a sound, or listen to your project.

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Next, the walls in front of and behind the listener need to be treated to knock down bad reflections.

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Now, I also have a ceiling fan.  In terms of reflections, I’m not too worried.  The base of it is mostly round, and the randomness of the blades all cause random reflections.

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I attempted to record a sample of myself clapping underneath my ceiling treatment to show the difference between that area of the studio, and where I produced the flutter echo heard above.  When I did, I noticed a metallic ringing sound.  I quickly identified the sound as coming from the metallic base of the ceiling fan.  I taped some 2″ pyramid foam to the metal base, and tried again, and the ringing sound was gone.

Clapping under the ceiling treatment at the listening position – before treating the metallic base of the ceiling fan:

Clapping under the ceiling treatment at the listening position – after treating the metallic base of the ceiling fan:

It’s not pretty, but here is the treated fan.  This and a small piece on the other side successfully dampened the ringing sound.

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Making Your Own Acoustic Treatments

Most of my studio is treated with Auralex absorption foam.  I have 2″ pyramid, 2″ DST (looks like sawtooth), 4″ metro, and some “corner” bass traps.  All of my panels were originally 2’x4′.  Some have been cut to fit specific spaces.  When I started treating the ceiling  I wanted panels that were more rigid and lightweight – I know that’s asking a lot!  The Auralex panels are anything but rigid.  They are best on walls unless you’re going to use a whole lot of adhesive to hold them in place.  Otherwise they will just droop anywhere that doesn’t have adhesive.  And adhesive can be a huge mess – especially when you need to tear down the studio.  Prepare yourself to have to replace the drywall if you go that route…

I had heard of people making their own, so I thought I would try my hand at it.  I discovered some ~2″-thick, square-ish pieces of insulating packing foam.  Next, I needed a way to present it.  They were white, and they didn’t look very stylish.  My first thought was to paint them.  While I’m sure their are spray paints out there that work just fine on foam, the first one I tried ate right through the foam.  It looked pretty rad, much like the acidic alien blood in the Alien series eating through the floors!  But, there goes my foam piece… Not good.

So I turned to textiles.  I found some old, decorative throw-pillow covers I have never, and will never use on my bed.  I cut pieces out of them and wrapped them around the front of the foam so that it could be stretched to the back.  Then I simply used a staple gun to staple the fabric to the back of the boards, stretching the material so that it wouldn’t droop off the other side when I was done.  I started with one end, then the exact opposite end, and then the two remaining sides.  Here are some photos to show the finished product:

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The final cornering was a little tricky.  I treated it a little like wrapping a gift.  Play around with it, and see what you can come up with.

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The panels were originally attached to the ceiling near the back of the room using many loops of console tape.

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This worked perfectly for about 2 weeks.  Then they started loosening.  For my next attempt I used one nail and one washer as illustrated below.  The nail has plenty of strength to hold the foam, but I worried that over time the small area of the nail head would sink into the foam.  The washer should do a good job of increasing surface area and distributing the weight over a larger area.

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With that success, I wanted more.  I really wanted a low-budget acoustic cloud.  I got the idea to build a rigid frame, and attach it to the back of one of my 4″ Auralex metro foam.  I found some long, thin boards at the local big-box hardware store, and used various connector pieces to frame them together.  To attach the frame to the foam I used a whole lot of super glue.

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Using wire intended for picture frames wrapped around the wood frame, and just two small screw-in hooks on each end, I was able to suspend the panel from the ceiling.  The picture below was my first “practicality test” near the back of the studio – in case it didn’t work, and the panel came crashing down, I didn’t want it landing on my mixing desk…

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While it works great, making and attaching that frame, and hooking it to the ceiling was kind of a pain in the butt.  I also knew one 2’x4′ panel wouldn’t give me enough coverage above my listening position, so I returned to the previous idea of making some more panels.  After a quick trip back to the big-box store, picking up some “garage insulation panels”, and decimating some old, cheap, red curtains I wasn’t ever going to use again, I made some more panels.  These were much longer, so I went ahead and attached them to the ceiling with one nail in each corner. Nail holes aren’t too difficult to fill and patch should you ever have to move your studio.  It’s much easier than filling in tears from using adhesives…

Here is the finished product:

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The walls have been treated for a while now.  I decided to simply nail the pieces to the walls.  Here are some pictures of that work:

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For the panels on the closet doors I used my trusty staple gun.  Just a few staples are needed to hold these on.  You can also see one of the bass traps in the upper corner (near top-center of picture).

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Here’s a close-up of the nails holding the panels.  You don’t really need a lot of nails, so do your walls a favor and use them sparingly.

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And finally, a quick tip on saving money on materials.  You don’t have to cover ever single surface of the room.  The best way to save on materials is to stagger some of the panels on opposing walls as illustrated below:
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To prevent/reduce flutter echo and standing waves, you can simply make sure that there aren’t any opposing walls that are both reflective.  You may end up with a few gaps here and there, but as long as those aren’t adjacent to the listening or recording positions you should be alright.

In addition to absorption I plan on adding some diffusion to the room as well.  That will have to be another post sometime down the road.

About the Author

 David Fienup is a sound engineer with a BA in Music Performance from Albion College, and a MA in Media Arts from the University of Michigan (Performing Arts Technology Department, School of Music).  Fienup’s main focuses currently revolve around sound for picture including sound design, dialogue editing, Foley, re-recording mixing, and location sound mixing.  He is the owner of Soundopolis.net where he sells his royalty-free sound effects collections.  David also has a background in music production including composition, recording, producing, editing, mixing and mastering.

If you’ve made it this far, thank you for reading!  I have included a bibliography below.  These textbooks have helped me enormously through my college and Master’s studies, as well as throughout my professional career.  They are wonderful resources for all professional sound engineers.

Bibliography:

Huber, David Miles & Robert E. Runstein: Modern Recording Techniques, 5th Edition. Burlington, MA: Elsevier Science (USA) – Focal Press, 1997.
Rumsey, Francis & Tim McCormickSound and Recording: An Introduction, 5th Edition. Burlington, MA: Elsevier Science (USA) – Focal Press, 2006.
Bartlett, Bruce & JennyPractical Recording Techniques: The Step-by-Step Approach to Professional Audio Recording, 3rd Edition. Woburn, MA: Butterworth-Heinemann – Focal Press, 2002.

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