|The Basics of a Great Sounding Room and System Set-Up|
|Home Theater Feature Articles Audio Related Articles|
|Written by Jerry Del Colliano with Bob Hodas|
|Thursday, 13 December 2007|
The Basics of a Great Sounding Room and System Set-Up
When you start out as an audio/video enthusiast, the biggest improvements to your sound come from investments made in new equipment. Upgrading from your $300 bookshelf monitors to a pair of $2,000 floor-standing speakers will rock your world. Adding your first real subwoofer has a similar effect. However, we find that transcending from mid-fi to audio nirvana isn’t always as easy as flipping down the trusty old platinum card on the most swank of electronic components.
No matter how advanced your current system is, the single most important element of successful sound is your room and your acoustics. No one will argue with you on this topic. Even the world’s most respected speaker designers, who have everything to be gained by selling you new speakers, will advise you to get your room right before you install their latest and greatest products.
Beyond room design and treatment is professional set-up and EQ. In many cases, your local dealer can help you get your system tuned up pretty well, but they normally don’t have the acoustical background to be able to definitively determine whether your room is as good as it can be, physically and mathematically. When you are ready for this kind of assurance and performance, you call in a professional acoustician like Bob Hodas. Bob professionally tunes the finest recording studios, mastering facilities and home theaters on the planet, using an extraordinarily sophisticated set of measurement tools that determine the acoustical flaws of your room and your system in ways that the local stereo shop install crew simply cannot do. If your system is pushing $50,000 or more and you want to know what it really can do, you may need to look to a professional acoustician to get to the next level of performance.
I hired Bob Hodas to tune the AudioRevolution.com Reference System installed in my so-incredibly-far-from-perfect media room high above L.A. in the hills of West Hollywood. Some of my visitors jokingly argue that my "imaging" is already fantastic -- the view from the window lets you can see from the Capitol Records building all the way to Catalina Island on a clear day. However, for audio imaging, my floor to ceiling mirrors on the left wall and a full glass front wall make one shrill listening environment for my Wilson WATT Puppy v6.0 speakers, which are not exactly known for a laid-back sound, especially in the high frequencies.
Bob Hodas agreed that the room has a great view, but from an audio standpoint, we had a lot of work to do. According to Hodas, symmetry is the most important issue in setting up a room. If the left wall is all windows and the right wall is a bookshelf, then the reflections will not be even and this will pull the image to one side or the other. This is definitely the case in our room. We would need to use the level control in conjunction with Bob’s SIM measurement system to balance the imaging to exacting standards, even though the speakers were already placed symmetrically in relation to one another, thanks to the use of a Checkpoint laser placement device and diligent physical measurements.
Hodas went on to explain that speakers really need to be placed symmetrically in a well-done room. While symmetry isn’t always achievable and there are some ways around it, at some point you can’t slap any more bandages on bad speaker placement. In a perfect world, no matter what the cost of the system, speakers should be equal distances from their respective boundaries. If not, the bass response will be quite audibly different. Moreover, poor speaker placement affects overall imaging and bass impact.
Another factor to consider, which was a big deal in the AudioRevolution.com room, is the extent to whichh the listening environment is open. An open door or opening to a hallway on one side will cause one speaker to load the bass more than the other. Even equipment racks along only one wall will affect the bass, which is the case with my chest-high, double-width equipment rack. Bob advises you to keep your room as symmetrical as possible as you place your speakers, gear and furnishings. He says to think of high frequencies (above 400Hz) as behaving like light. The reflections will react to the boundaries using the simple geometry like balls do on a billiards table. The low frequencies (below 400Hz) will act more like water. Complex wave forms and interference patterns from obstructions will develop and be unpredictable.
First Order Reflections
Once you have your speaker placements down, you’ll want to deal with your second biggest issue: first order reflections. In simpler terms, first order reflections refer to the way your system reacts to the side walls in your room. You can determine the exact placements of your first order reflections by placing a mirror on the wall such that you can see your speaker’s drivers when you are sitting in your hot spot.
According to Hodas, treating first order reflections acoustically is extremely important for both the imaging and frequency response: "The first thing I do in a system is to look at its impulse response so that I can identify the room's reflections. An untreated first order reflection will cause comb filtering of the speaker response, ugly waveform convolution, and will interfere with proper imaging. The problem is that first order reflections arrive at the listening position prior to 18-20 milliseconds (20-23 feet) of the direct speaker signal and the human brain cannot distinguish these reflections as being separate from the direct speaker signal, so they are especially destructive. For most home installations, this means that these reflections come off of the ceiling, side and rear walls. I like to absorb the ceiling and side reflections, because this increases the coherence of the system. I like to diffuse the rear wall reflections, as it adds space to the room. Don't let anyone try to equalize these reflections, as they are completely dependent on your position and will change at different seating positions in the room. Equalization will not fix a high frequency reflection problem."
Most listening rooms tend to be on the live side of the acoustical spectrum, sounding bright or sibilant because of too many reflective surfaces. The AudioRevolution.com room was the poster child for this problem before Bob and I dealt with the acoustical issues and added treatments. The exact types of treatments you need are very much determined by the issues of your room. While you can try to play with different products when you are looking to go for the ultimate sound, you are better off having someone suggest the proper treatments that will fit in your room and budget, not to mention pass the wife acceptance test. A pile of ASC tube traps or RPG diffusers can be really hard to hide. The best bet, as better installers are doing in new construction homes, is to install your treatments before any of your gear is in place. In Hollywood, the importance of home theaters and home screening rooms that sound good has become so paramount that normally bitchy interior designers are now actually enthusiastic about the prospect of working around a well-treated room. It might sound harsh now, but a minor construction project could result in a spectacular sonic improvement in your room. You’d want to work with an expert and a willing interior designer to do up your room, but when you are done, you may have improved a world-class music and theater system by 30 percent without having to buy any new gear. That is NOT the law of diminishing returns, but it does require a big effort on your part.
Bob Hodas warns of a pitfall that may not seem apparent when you are first setting out to tune up your room and system. It is possible to over-treat your room. "A room that is too dead is an unpleasant listening experience," Hodas cautions, "just like a room that is too live. Another key point is that most acoustic panels sold for the home do not address bass problems, and by over-treating, you can absorb a lot of high frequencies without affecting the bass. This creates a very muddy sound. I try to treat only the surface areas that create the problem and leave the rest alone, which is more visually attractive and makes for a more real-world exciting sound when the room is done."
How Hodas Helped Tame The AudioRevolution.com Reference Room
"The AudioRevolution.com room exhibited many of the above problems and was an extreme challenge for my skills," Hodas says. "The left side wall is all mirrors and has the equipment rack midway on the wall. The right side wall is a high, deep bookcase, which offers some diffusion. While the left speaker has a corner to load into, the right speaker has an alcove on the side wall behind it that leads into a bedroom. The right speaker also has a straight shot all the way down a hall to the front door, while the left speaker has the barrier of the kitchen counter." Clearly, this was going to take some work to get some positive results.
Since the listening position in the Revolution room was pretty much fixed, due to the couch location, Hodas found a spot where the speaker's frequency response looked best by moving the left speaker around, six inches at a time. "Small movements of six inches to a foot can make a significant difference to the bass," he explains. "Even smaller physical movements will affect imaging. I set both speakers at equal distances from the front and side walls. We then treated part of the mirrored left wall with RPG Flatfussors (about $2,000 in a custom fabric color) to simulate the diffusion of the opposing bookshelf on the right side of the room."
Only one treatment was used in the room, with the goal of attempting to match the acoustic situation with the bookcase on the right. Hodas strongly advises to only treat the areas necessary in order to maintain a natural sound: "I hate rooms where all of the high frequencies have been sucked out with absorptive panels, leaving the bass to roll around uncontrolled. I might have treated the ceiling reflections with an additional absorptive panel, since the brain is sensitive to the reflections coming in from above, but Jerry nixed the idea due to cosmetics and logistics."
While the first order reflections had been dealt with to the fullest extent we could, there remained the issue of the floor-to-ceiling sliding glass doors on the front wall (behind the speakers). The glass provides no absorption whatsoever and therefore really adds to the brightness of the room. Due to video concerns as well as audio needs, we hung four-layers-thick, custom-made floor-to-ceiling blackout curtains. These curtains are very heavy and, thanks to the porous and light-absorbing material, they make for audibly significant sonic absorption on the front wall. I think the best sound was attained with the sliding glass doors all the way open, as this provides an infinitely deep soundstage, despite the road noise from Sunset Boulevard. However, open doors and loud music poses the problem of annoying the neighbors, especially in the evening. Bob and I came up with the compromise of tuning the room for listening with the curtains shut. While I don’t always adhere to this rule, it does make a big difference in coherence and musicality in the system.
How Bob Hodas and Kevin Voecks Optimized The Subwoofers
In the old days of audio, subwoofers were poo-pooed because they supposedly couldn’t be well matched to a truly high-performance pair of speakers. There is some truth to the notion that nearly every sub, even to this day, doesn’t come with EQ but instead has all sorts of other confusing adjustments like crossover point and phase which, in the hands of an amateur, can cause an audio disaster.
In a modern music or theater system, there is no reason not to use a good subwoofer or two. In a 5.1 (or 6.1 or 7.1) system, you absolutely must have a subwoofer. After all, subwoofers handle arguably the most important elements of music: the low frequencies, with their powerful emotional and physical impact. Bass (as it is pronounced, rather than spelled) is an appropriate word, considering it is indeed the base underlying the rest of frequencies.
I recently switched my subwoofers over to a pair of Revel B15s ($2,995 each – powered), which have EQ built in, as well as an innovative set-up software application called LFO. Bob Hodas and Revel chief designer Kevin Voecks took on the challenge of getting devastatingly low, tight and loud bass in my room with a 13-hour marathon set-up session, using the SIM system and over 50 years of combined audio experience.
Kevin and Bob tried and ultimately used a very out-of-the-box solution for placing my two subwoofers. During the set-up sessions, they would display evil grins from time to time when testing the results of the woofers in absolutely absurd locations. Those crazy locations lead to more modest positions that we ultimately agreed upon. The Revel subs were fed audio signal from the subwoofer out on the Proceed AVP AV preamp, utilizing the internal crossover. After moving the subs around the room quite a bit, Bob, Kevin and I settled on placing both subs on the left wall. One was in front of the left Wilson WATT Puppy and against the wall near the equipment rack. The other subwoofer was positioned behind the listener in the far rear corner of the room. Bob and Kevin wanted the subs to combine with each other as smoothly as possible and the non-symmetrical set up complemented the room geometry.
The Revel B-15 has three bands of parametric equalization, which Hodas then utilized to really tune in the response, using the SIM system. Even with this out-of-the-ordinary placement, the listener's perception is that the bass is, amazingly, coming entirely from the Wilson speakers in the front of the room. This is the effect when subwoofers are set up professionally. While the Revel subwoofer makes huge strides at overcoming the guessing game of setting up nearly every other sub with its LFO software, it doesn’t guarantee the same insane impact that comes from complete system integration, which you get with a set-up like the one done by Hodas and Voecks. Hiring a professional to tune just your subs could completely change the character of your entire system for the better.
Why EQ Is Not Evil
While Mark Levinson made quite a bit of money selling high-performance mastering EQs at Cello with the Audio Palette in the 1990s, EQ in the 1970s created a widespread negative attitude toward EQ in true audio systems. During the '70s, EQ suffered from poor designs that allowed all sorts of phase maladies in audio systems. Early Mark Levinson preamps were head and shoulders above the competition, due to their simple approach and lack of noisy EQs. Electronic audio gear is much better now, especially EQs. Should you use one? Very likely, considering what a skilled acoustician can do with your system. Should you play with it for program material? I wouldn't really recommend it, but you could if you really were into it. The Cello Audio Palette was very good for this application. Keep in mind that recording studios and mastering labs that used Cello Audio Palette also had house EQ for their monitors – not to mention EQ on each and every track via the mixing console. Should you use the new digital EQs like z-systems ($5,000 plus) and/or Perpetual Technologies ($1,200)? That depends on the decision you make with your set-up guy. While the feature sets on digital EQs are excellent and their sound is even better, they are very hard, if not impossible, to integrate into a 5.1 system.
In the AudioRevolution.com system, Bob Hodas installed a Meyer Sound Laboratories CP-10S minimum phase parametric equalizer ($3,240), which was used with information from the SIM system to fix some bass problems that the Wilson WATT Puppies exhibited due to the unfavorable room layout. Hodas likes this particular analog EQ best as neither he nor I have found anything else on the market that sounds as good from a pure audio perspective. "Parametric EQ is the only way to go for me," Hodas says, "because it allows selection of the exact problem frequency center and shapes the curve to match what is really going on in the room. Using a fixed frequency third-octave EQ is like doing brain surgery with an axe. EQ can be a good cost-effective choice for the bass when you do not have the option of doing a lot of acoustic fixes. This is especially true in a non-symmetrical room where each speaker has different bass problems. In that case, no single acoustic fix will work for both speakers."
The Meyer EQ was inserted between the preamp and amp, so it basically only affected the Wilson Puppies, which are the low frequency drivers on the WATT Puppy v6.0 system. This configuration worked well in combination with the Revel sub, which has self-contained EQ inside the sub cabinet. If you use a sub that doesn’t have EQ in it, you might need more Meyer Sound EQs. A Second EQ could be used for a sub and center speaker channel. If you are feeling really motivated and the NASDAQ is up, you could pop for a third EQ for the rear left and right speakers.
Based on my personal request, Bob ever so slightly rolled off the high frequencies of the WATT portion of the Wilson WATT Puppies in order to take some of the brightness out of my system in such a live-sounding room. This is a personal taste issue. Bob also made a slight augmentation in the upper midrange to help with the same malady. The results were successful here, as they were in my last system. We cured the biggest knock on the WATT Puppies with a simple twist of a knob and a check of the SIM system, as opposed to investing an additional $25,000 in high-end electronics.
Bob Hodas uses the Meyer SIM System II® to do his testing, measurements and analysis. It is a dual-channel FFT that displays information in an impressive 1/24th octave resolution, gathered at 1/48th octave resolution. It allows him to look at phase, frequency and coherence in real time and it is a fast, powerful tool. It also makes setting up an EQ like the Meyer Sound quite a bit easier. More information on the SIM system can be found at: http://www.bobhodas.com/process.html
For most systems, investing a minimum of $2,500 to upwards of $10,000 for system set-up, room design and fine-tuning may seem absurd, but the results are irrefutable. If you are looking at building a system that pushes the physical limits of the most cutting-edge audio playback systems, you will need to address all of the topics discussed herein and likely other issues, as well. It is recommended that, before you drop huge cash on AV gear, you look at your room, set-up and overall listening environment with a professional acoustician like Bob Hodas or one of his peers. At a minimum, consult with someone who is acoustically in the know before you redo your room.
For me, the results have been exactly what I wanted. I know my room is no mastering lab, but I have a better view from my balcony than any professional audio environment. Was the audio improvement worth two percent of the retail value of my system? Are you kidding? I now know mathematically that my system is damn near perfectly optimized to my uniquely flawed but lovable listening environment. In a world where other magazines (you know the names of the offenders) constantly imply that you should feel insecure about your system, I know my system rocks and you should know yours does, too. Will I buy more top of the line gear? Without a doubt, and when I do, I be confident that it will sound as good as it was designed to be. I would never design a large-scale audio system without the help of an expert like Bob.