Published On: September 28, 2020

What You Need to Know About Acoustic Room Treatments

Published On: September 28, 2020

What You Need to Know About Acoustic Room Treatments

Brian Kahn digs deep into physical acoustic treatments vs. digital room correction and details his own experience with Vicoustic panels installed in his home theater/stereo listening room.

Why would you go through the trouble and expense of covering the walls of your listening room with unsightly acoustical treatments, especially given that just about every modern AV receiver and preamp offers some form of room correction? This was the question I was asked time and time again whenever I told someone I was planning on adding such room treatments to my own home theater space. The question is fair enough, but it does tell you something about the misconceptions surrounding room acoustics and the effectiveness of digital signal processing in dealing with the most egregious problems caused by room geometry and design.

Let's start by taking a look at what we are trying to achieve. My goal when running digital room correction software such as Audyssey, Dirac, or Anthem Room Correction is to reverse (or at least ameliorate) the effects of the room on the sound that reaches my ear. That involves proper adjustment of delays and levels for each speaker, as well as some form of filtering (or EQ) to make sure the audio reaching my ears resembles as closely as possible the sound leaving my speakers.

As senior editor Dennis Burger pointed out in his most recent article on digital room correction, though, these systems aren't equally effective at treating all acoustical problems. While many do an excellent job of taming issues caused by the size and shape of your room, few can affectively reverse the negative effects of the qualities of the surfaces within your room. In other words, most digital room correction systems struggle or fail completely to compensate for how reflective, absorptive, or diffusive your walls, windows, and furniture are.

Digital room correction systems can do a very good job with equalization, within limits. Peaks in a frequency response curve can easily be flattened, but if your room's frequency response curve has relatively large dips, these can be more problematic. If you attempt to boost certain frequencies too much, you run the risk of pushing your amplifiers into clipping. Balancing out the response by experimenting with positioning and room treatments before running your room correction system will give your system more headroom to work with. Proper physical treatment of a room can improve clarity and provide a more consistent response over a larger seating area by controlling reflected soundwaves, something that no room correction system can do -- at least not directly.

To deal with echoes, reverberation, and other such acoustical problems, it makes sense that the most effective solution is always going to be physically treating those surfaces. It's easy to say that, of course. The question remains: is it easy to do it? That's what I decided to find out recently, and that's exactly what this article aims to answer. And to make this as relevant as possible for the largest number of HomeTheaterReview readers, we decided to make a few assumptions. First, we're starting with an existing room and limiting all of our acoustical treatments to on-wall or in-room. No tearing down walls, ripping out sheetrock, or building floating rooms within rooms. This not only keeps the price down; it also reduces problems with fire codes and restoring the condition of rental property before you move out, assuming that applies to you. 

This is my room. There are many like it, but this one is mine

The room I am working with is rectangular in shape, 17.5 feet long, 12 feet wide, and 8 feet tall. As you can see in the accompanying photographs, there is a screen on the front wall, the right wall has a window in the middle, and the rear wall has no openings. The left wall has a closet with bi-fold doors on the front half, then jogs out about four inches for the back half where two inward-swinging doors are positioned. I include this information because it impacts the treatment options discussed below. 

Brian_Kahn_Listening_Room_Back.jpg

My room is asymmetrical and has some echo that impedes my ability to obtain the best performance from speakers without some sort of treatment. In the past, I've mainly relied on a pair of tunable studio traps placed at the first reflection points. This helped and had the benefit of being movable to adapt to different speaker placement.

If you're going to do nothing else in terms of acoustical treatments, treating your first reflections is probably the most important thing you can do to improve the sound of the speakers in your room. Ideally, the reflections will be attenuated and delayed from the directly propagating soundwaves to provide separation.  If you are not familiar with the term "first reflection," it refers to the primary reflections that occur between the listener and each speaker. A simple way to find the reflection points is to sit in your main listening position and have a friend run a mirror along the wall. When you see each speaker, the mirror is located at the first reflection point for that speaker. To find all your first reflection points, do this on both your right and left side walls for each speaker, then your ceiling and floor. For a two-channel stereo, this means you have eight first reflection points. And if you think that's overwhelming, imagine doing the same for five, seven, nine, or even 16 speakers. 

First_Reflections_treatments.jpg

One simple solution commonly used to address first reflections is the careful placement of bookshelves (or Blu-ray shelves), with the books (or disc cases) staggered to create an uneven surface to break up and diffuse the sound waves. A somewhat less-effective DIY treatment is the careful placement of draperies on the side walls, this may provide some absorption but typically only at higher frequencies. Neither solution is perfect, but they're both better than nothing and should be considered bare-minimum room treatments before you ever think about connecting a mic to your receiver and running room correction.


If you want to experiment with different physical room treatments yourself, there is an ever-growing number of online stores that sell panels made out of various materials. These materials provide different amounts of absorption at different frequencies, depending on the needs of your room. Many of the available panels can be had with custom-printed images, so that row of family portraits or vacation photos in your buddy's listening room may actually be doing double duty as broadband diffusers. Plants are another item that can be used for diffusion, and even provide some aesthetic. They also come in a multitude of sizes and shapes to fit just about any space.

At any rate, getting back to my own room, tunable studio traps did a good job of taming my left- and right-side first reelections. Unfortunately, they were limited in their capabilities, were often awkward to place, and wouldn't win any awards in terms of aesthetics. I decided to explore wall-mounted panels as a way of treating acoustics without having to either rebuild my room or sacrifice too much floor space.

A holistic approach to room acoustics

When you move beyond treating first reflections into the domain of whole-room acoustical treatments, there are a number of different philosophies governing the overall balance of absorption and diffusion. One of the most prevalent, at least for recording studios, is "LEDE," or "Live End, Dead End," which involves ample absorption at the speaker end of the room, making it a "dead" end, and a general lack thereof behind the listener, making it a "live" end. Assuming the walls behind the listener are farther away, no less than about 10 feet, this will enable the listener to hear the direct sound from the speakers while still getting some sense of space.

Other popular designs include the "Reflection-Free Zone" approach and something known as the "non-environment room." Read 25 articles about room acoustics, and you'll probably walk away with 30 different opinions about which of these approaches is superior.

Hiring an acoustician vs. the DIY room acoustics approach

After spending way too much time reading endless articles of that sort, I decided to consult with some professionals and leave the philosophical decisions in their hands. I reached out to a couple of companies that design and manufacture room treatment panels -- Vicoustic and GIK Acoustics -- and submitted project requests through their websites. Yes, I know there are other companies that offer similar services, but this is a time-consuming process and I had to draw a line somewhere. I submitted information about the room, including its size, construction, REW measurements, equipment, and how I use the space. Options were discussed and thoughtful proposals were provided. We decided to move forward with one of the Vicoustic proposals, which was installed by a Vicoustic dealer.

Vicoustic products are only sold through authorized dealers. The company offers a training course to its dealers to help them better understand acoustics, but the heavy lifting of acoustic design is typically handled by the engineering-and-design team at Vicoustic. The products are typically sold as part of a proposal that begins with an inquiry much like mine, either by the end user or their integrator.

Acoustical treatments for stereo vs. surround sound

The Vicoustic team typically wants room photos and dimensions, building materials, architectural drawings, anticipated use, a list of AV equipment, etc.

My room, in which the gear is always changing, is used for both movies and stereo listening. That creates something of a challenge, as cinema rooms are typically treated differently than two-channel music rooms. Gustavo Pires, Technical Director of Vicoustic, tells me that in cinema rooms he utilizes more absorption than diffusion. Music room treatment is usually the opposite. In cinema rooms, the listener should perceive what is coming from the speaker much more so than reflections, which would shift the positions of the objects being depicted onscreen. In a music room with only two speakers, some reflections are helpful in recreating a proper soundstage. The challenge is obtaining the right balance of reflection, diffusion, and absorption.

In my room, we went with a combination of Vicoustic Cinema Round Premium panels (which are broadband absorbers) and Wavewood Wenge panels (which are broadband diffusers). The size, relative positioning, and amount of sonic reflectivity of a room all affect finding the right balance.

Individual preferences will also come into play. While long reverberation times and echoes are problematic, many of the decisions related to acoustical treatment will come down to what sounds right to the listener (or designer). Many people prefer diffusers at first reflection point, as these can provide a sense of spaciousness. The downside of too much diffusion can be the loss of precision. This is a benefit of in-room panels, as they can be easily moved or swapped out. Some professionally-installed systems also allow for wall mounted panels to be switched out, though. The Vicoustic system I opted to use has an optional grid mounting system that allows for panels to be swapped out or removed. 

Brian_Kahn_ceiling_treatments.jpg

In addition to adding panels to the side walls, Vicoustic's proposal included treating the ceiling above and in front of the listening position, and treating the rear wall. Lastly, bass traps were recommended for the corners. The ceiling treatment was a mix of Cinema Round Premium absorption panels and Wavewood Wenge and Multifuser DC2 diffusion panels, all of which are roughly two-foot squares. The Cinema Round Premium panels have a slight convex curve, with your choice of several fabric covering colors. The Wavewood Wenge has a wood facing, with slots of different lengths in front of a foam backing. These panels were also used on my rear wall. The Multifuser DC2 are quadratic diffuser panels with limited absorption. The DC2s look like a miniature skyline and appear to be made of a light, rigid foam material.

VicTotem_Ultra_VMT.jpgThe last component Vicoustic used in my room is the VicTotem Ultra VMT, a free-standing product that can be used as a bass trap, absorber, and/or diffuser. It comes in a variety of finishes and can be had in two different forms: One with three panels that stands about 6 feet tall, and a four-panel model that extends floor-to-ceiling in most rooms. The Ultra VMT is oval when viewed from above, with one side covered in fabric and the other in a wood finish. It can be configured with any combination of panels, with either side facing out to adjust the amount of diffusion or absorption.

Once we decided to move forward with Vicoustic panels, the installation was arranged through Vertex AV in Huntington Beach, California. Prior to the installation, I had a few conversations with KC at Vertex, and he explained that the installation of acoustic panels is a growing segment of their business.

When installation day came, KC arrived with three installers. He reviewed the Vicoustic proposal with me, pointing out where each panel would go and recommending some slight changes to accommodate the room's architectural features. While I was not familiar with Vertex AV before I began working on this article, I was pleased by their responsiveness in getting everything set up and their professionalism while onsite. By mid-afternoon the installation was complete. When I walked into the room at the end of the installation, I could immediately tell the room sounded different, even with no movies or music playing.

First impressions of my newly treated room

The first thing I noticed was improvements in terms of reverberation time, a primary focus in room treatment. Have you ever been in a room with a lot of delayed and reflected sound? In other words, a room that sounds like a cave? This is likely a result of excessive reverberation time. Reverberation Time is often measured and reported as something called RT30 or the more common RT60. The 30 or 60 is the amount of attenuation in dB and the number that follows is the amount of time it takes for the sound waves to decay by that amount. For example, an RT30 of 0.6, means it takes 0.6 seconds for the sound to decay 30 dB. The measurements always start at -5 dB, so the RT30 time would be the time for the signal's decay to go from -5 dB to -35 dB. Most sound engineers use RT60 values, although the smaller rooms in most residences lend themselves better to an RT30 measurement. For larger venues, RT60 measurements in the range of 0.2 to 0.6 are the target for both cinema and stereo listening. Cinema is typically at the shorter end of the range due to dialogue clarity concerns and precise imaging of multiple speakers. 

RT_Before_treatment.jpg

Gustavo Pires of Vicoustic targeted an RT30 value at the lower end of the range for my room, given its modest dimensions. If you look at the attached graphs, you will see the RT30 values for my room ranged between 245 and 375 milliseconds, depending on frequency. That's not bad, but the RT curve is nowhere near smooth. Once the panels were installed, the RT30 values dropped to 165 to 265 milliseconds. More importantly, the RT curves with the panels installed are much smoother, with less reverberation in the midrange and treble. 

July_16_RT60_position_1_2.jpg

Some critical listening in my acoustically treated room

Listening to music with the professionally installed panels installed, I was able to hear several changes. The room was more balanced on the horizontal plane, and imaging became more precise. As compared with my old ASC Studio Traps, mentioned above, I found that with the newly installed panels the soundstages of a wide variety of musical selections more accurately tracked the recording. I had excellent speakers from Revel and Magico on hand, and I was able to listen to both before and after the installation of the panels. The imaging of both sets of speakers definitely improved in both precision and scope.

In addition to improving imaging, the treated room improved midrange clarity. I suspect that the reduction of echoes and smoothing of reverberation is the primary cause of this improvement. The immersive audio soundtracks of movies had previously delivered good imaging, but the room treatment clearly made a difference, especially with sound mixes that leaned heavily toward the front of the room. The biggest improvement came in the form of improved vocal clarity. This came as no surprise after hearing similar improvements while listening to two-channel music.

Potential downsides of professional room acoustics treatments

Does this mean that all is perfect and there is no downside to installing panels in your room? No. The panels still take up space, and the aesthetics of treatments not hidden behind a fabric wall may not be pleasing to some. The large VicTotem Ultra VMT towers help with the mid and upper bass notes (and also provide diffusion), but if I wanted to treat lower bass notes, I would need bass traps much larger than my room could accommodate without drastically redesigning of the space itself. I personally like the aesthetics of the panels installed in my room. In fact, I found benefits I didn't even expect, such as the black ceiling panels improving the contrast of my front-projection system. When I showed pictures of the installed panels to some of my friends, however, the reactions were mixed.

Thankfully, there are many panel designs so you can choose what best suits your taste. Just know that the more emphasis you place on aesthetics, the less-effective the acoustical treatments are likely to be. Just to give you an example of why: My room has modes that cause dips in frequency response below 100 Hz. These can be minimized and narrowed through careful subwoofer placement, as well as judicious application of room correction. What I would really love is to be able to place big, dedicated bass traps that could flatten the standing waves affecting my room, but this is not physically possible in the space provided in most installations and not aesthetically tenable for a lot of homeowners. Another option that may address some room modes is moving the listening position, but most rooms have limited options in this regard, especially if the room has multiple uses.

Bottom line: were acoustical treatments worth it in my room?

Am I glad I installed acoustic treatments in my primary listening room? Absolutely. The Vicoustic panels significantly improved how my room sounds. The improved symmetry, along with the reduced and evened-out reverberation times, combine to make the room an even better space in which to evaluate the performance of my reference gear and any new gear I review because they reduce the impact of the room on the sound and allow me to evaluate gear on its own terms.

The acoustic treatments also leave the room correction system in my preamp with less to do, which is certainly my preference. The finishes I selected for the treatments in my room both improve the contrast of the images on my front projection screen and provide a pleasant visual environment. The Multifuser DC2 and Wavewood Wenge panels in particular have a modern aesthetic that does not scream "recording studio" like the Sonex foam panels that come to mind when most people imagine acoustic treatments.


If you're serious about performance and have the space and budget for it, I highly recommend exploring the installation of acoustic treatment in your listening area. There are a multitude of technical papers and articles online that will help you learn the basics. There are even a few programs such as Guy Singleton's "The CEDIA Designer," which helps configure audio and video for a room. If you have the time, I strongly suggest you read up and learn about the basics of room treatment. If you are comfortable with what you have learned and have a relatively simple room, you may be able to configure the treatment yourself and get great results. However, for the majority of us, this is a daunting task that can go astray. Better results are likely to be achieved by enlisting the help of a full-service acoustic treatment company that will work with you to design a system that fits your acoustic needs, physical constraints, aesthetic preferences, and budget.

Additional Resources
• Room Correction Revisited 
at HomeTheaterReview.com
• Answering Reader Email: Room Correction Is Not a Panacea at HomeTheaterReview.com
• My Home Theater New Year's Resolutions at HomeTheaterReview.com

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