[SoundStage!]Home Audio
Equipment Review

December 1998

Michael Green Designs
Pressure Zone Controller Tunable Room Devices

by Doug Blackburn


Review at a Glance
Sound Easily discernible improvements when compared to an untreated room, an LEDE setup, and even the liberal use of original Room Tunes. Only the Argent Room Lens competes -- but not in the same ways.
Features Large variety for corner, wall, ceiling and floorstanding use; adjustable tuning board; available in a number of finish options.
Use Best to let Michael Green Designs assess your requirements; PZCs that sit on walls or in corners require mounting with drywall screws.
Value Not as cheap as doing nothing, but effective at squeezing the most from your listening space -- and thus your audio system.

In the late 1980s, Michael Green revved up the high end by searching for better sound in listening rooms. Up until that time there had been crude attempts such as the supposedly ideal "live-end dead-end" room setup. Green introduced low-cost Room Tune products that revolutionized tuning the sound of the listening room. Dealers and show exhibitors everywhere were using Room Tunes in ever more elaborate setups as the array of Room Tune products grew over the years. Today, some of the cost-effective Room Tune products remain in production, but last year a slightly higher-cost line of acoustic room treatment devices was added. Dubbed Pressure Zone Controllers, these new designs expand on what was possible with Room Tune products. The name comes from Michael Green’s research, which lead him to focus his room-tuning products on the "pressure zone" that occurs within the first four to six inches of air space along walls, ceilings and floors. Green’s experiments showed him that by controlling the "pressure zone," his Pressure Zone Controller products can control the sound in the room.

In fact, Pressure Zone Controllers (PZCs) are a byproduct of Michael Green’s work in several areas. First, he has been pursuing for many years the concept of the "tunable room" which permits altering the sound of a room to make it be whatever the listener wishes it to be. Full-blown tunable rooms contain special tuning brackets mounted under floors, behind walls and above ceilings. Each has an adjustable "nut" that controls how tightly the wall is coupled to the structure. By adjusting these tuning nuts, the acoustics of the room can be changed to a startling degree. In addition, for new construction, Green found out that varnishing the wood used for wall studs and for ceiling and floor joists would enhance the effect of the tuning to a significant degree. Tunable-room products remain available today, but they really require a full remodeling or new construction in order to be properly implemented.

While working on tunable rooms, Green was also busy working with symphony orchestras, including the San Francisco Symphony, to develop platforms for pianos, cellos, tympani and other instruments which would alleviate setup problems when the orchestra rearranged its configuration or when it traveled to other venues to perform. The goal of these tunable platforms was to give the instruments the same sound regardless of where the instrument was being used.

As work progressed on tunable rooms and instrument platforms, Green realized he could apply what he learned on those projects to a new room acoustic-treatment product. PZCs have a front-facing tuning board which has a brass tuning nut in the center. Behind the board is an open wooden frame. Inside the frame is a very small amount of damping material and a coupling device that connects the tuning nut to the open wooden frame. There are a number of different sizes of PZCs, some designed to be hung on the wall, something like a picture. There are also floorstanding PZCs for people who can’t or won’t make holes in their walls. Green and Lance Binns, the Michael Green Designs national sales manager, sent quite an array of PZCs for me to try. These include six 36" units for on-wall use, one in each corner of the room mounted on corner mounts, plus one in the center of the left and right walls hanging like pictures; four Mini-Corner PZCs, one for each corner around the ceiling, mounted on corner brackets; four Mini-Echo PZCs, one for the center of each wall, mounted up near the ceiling and hanging on the wall like a picture; two floorstanding PZCs, about 40" high, to be experimented with. The floorstanding PZCs include four brass MTD cones for feet to couple the PCZ to the floor.


To do this review, I had to first remove the Argent Room Lenses (see review in SoundStage! archives) room acoustic treatment devices and carefully measure for and mount the PZCs. My home has 2"x6" stud walls with 5/8" drywall. For this kind of construction, the recommended mounting method for the PZCs is drywall screws. If the PZCs are intended to be corner-mountable, there are corner brackets included. The wooden corner brackets are mounted with drywall screws and the PZCs hang on the corner brackets like a picture hangs on the wall -- although the PZCs are "captured" at top and bottom. If the PZCs will be mounted flush on the wall, you simply drive drywall screws directly into the wall and use them as the hangers.

Sound enters the PZCs through the open sides, top and bottom. Some sound resonates against the tuning board -- and direct room sound also hits the tuning board. A controlled amount of sound entering the PZC is absorbed, but this is intentionally kept small because Michael Green is convinced that the best room sound is achieved with a minimum of sound damping. His approach is to control the sound in the room, not to damp it to death as is done by a number of other room treatments. Some people may be familiar with tuning boards in professional studios. These boards are actually tuned by increasing and decreasing tension on the middle of the board. It is important to understand that the tuning nut on PZCs does not put the board under tension. It simply controls how tightly the tuning board is coupled to the proprietary energy-transfer device behind the tuning board.

The open wooden frame of the PZCs is covered with cloth. There are several colors of cloth to choose from. Standard tuning boards are painted MDF in white, black or primer. If you get them in primer, you can paint the tuning boards the same color as your walls. I suppose you could even apply wallpaper to match the wall if necessary. Cherry hardwood tuning boards are optional for a moderate extra cost. For the review, the PZCs were all supplied with gray cloth and cherry hardwood tuning boards. The natural finish on the cherry hardwood is quite remarkable, definitely fine-furniture quality. The cherry hardwood is solid cherry, not veneer.

The tuning nut is in the center of the front-facing tuning board. There is about 1/3 of a turn adjustment of the tuning nut from fully loose to fully tight. It is best to start the setup process with all the tuning nuts set to a similar mid-point position so that there aren’t a lot of mismatched PZCs fighting each other. As you tune the tightness of the tuning nuts, you will usually be working with a pair of PZCs, one on the left side of the room and its compliment on the right side of the room. The effect of the tuning nut is quite significant and easy to hear. When the nuts are fully loose, the room takes on an uncontrolled and "blowsy" sound. Fully tight on the tuning nut and the soundstage is tightly focused on the center image and the width of the soundstage closes up. Somewhere between these extremes you’ll find just what you are looking for. In my case, I ended up with all the tuning nuts just slightly tighter than fully loose.


So how do PZCs affect the sound of the room? Well, at first it wasn’t very obvious. I went from Argent Room Lenses to PZCs with no stop to listen to a bare room. When I realized the PZCs weren’t going to allow me to evaluate them until I had heard the room bare again, I got out the ladder one more time (ceiling height is 10.5') and removed all of the PZCs. I then spent a depressing three days listening to the untuned room. This room was specially constructed to be my listening room when the house was built. Dimensions were selected to minimize the stack-up of room modes (23.5' deep, 19.5' wide, 10.5' high; all vertical corners and all ceiling corners have 1'-wide 45-degree angle surfaces to minimize bass buildup in the corners). Even when the room was bare people would walk into it and comment on the amazing acoustics. Yet here I was listening to music in this special room and depressed because it didn’t sound particularly good compared to what I was used to with the Argent Room Lenses or with the not-yet-properly-set-up PZCs.

After three days I couldn’t take it any longer. I had to have a room treatment back. So out came the ladder again and up went all the PZCs one more time. Ahhh, good sound again. But it wasn’t the best yet. The tuning nuts were still not adjusted. Concentrating on a single pair of PZCs at a time I experimented with a full range of adjustments from fully loose to fully tight. This is where I realized that just a little tighter than fully loose gave me what I wanted in my room -- big, wide soundstage with no real sense of walls influencing the sound. It wasn’t so much that the walls seemed to disappear, it was more a matter of the walls becoming unimportant. Slap echo (clap your hands, the echo you hear after the clap is the "slap echo" of the room) was reduced overall and eliminated completely around the listening position, which is just a little to the rear of the center of the room. As I moved on to adjusting other pairs of PZCs, I started at the same position for the tuning nut -- just a little tighter than fully loose. I would experiment with some tighter adjustments in each position just to be sure my nearly loose setting was correct. In each case, I preferred the nearly loose adjustment point. When I was done tuning all of the PZCs, the soundfield was gloriously large and seamless. There was no sense of speaker position/location, just sound emanating from anywhere and everywhere it was sourced in the recording.

The wall-mount PZCs were a rousing success in my room. Time to play with the floorstanding Deluxe Pressure Zone Controllers. My only problem with these is that I could not find one preferred location for them. They sounded a little different in different locations, but in each location they were an improvement. This made it difficult to pick any one place for them and leave them there. The floorstanding PZCs do have one negative, however. Michael Green supplies four threaded brass cones for feet on each Deluxe PZC. The Deluxe PZCs only weigh 10 or 15 pounds total. This means there is only 3 or 4 pounds of weight on each cone, and this is nowhere near enough weight to cause these cones to pierce through wall-to-wall carpeting and padding. I added 10 pounds of sand and a 17 pound iron dumbbell to the base of each Deluxe model, and still the brass MTD cones would not pierce the carpet. I never did get the full measure of how these could/would sound if I could get them coupled to the floor. Nevertheless, they were still useful and saw duty in a variety of locations. Occasionally I found it worthwhile to use alternate settings for the tuning nut to make small adjustments to the sound.

The questions you’re dying to know the answers to

But how do the PZCs compare to other room acoustic treatment devices? Quite well. I had a number of treatments available for comparison, including 6'x 2' compressed fiberglass ceiling panels mounted in wooden frames; three quilts of similar quality and materials hung on the front wall and the fronts of the side walls to give a live-end dead-end effect to the room (dead at the speaker end, live at the listener end); ten original Echo Tunes (mounted in corners) and five Deluxe Room Tunes (floorstanding); and the Argent Room Lens.

To keep things in perspective, I think a numerical rating system is needed. "0" (zero) will represent the sound of the bare listening room. A negative number would mean the treatment sounds worse than the bare room. A positive number would mean the treatment sounds better than the bare room. There is no maximum number that can be assigned (i.e. this will not be a 1-10 rating scale).

I used the home-brew flat panels at the first-reflection points. I also used a pair behind the speakers to reduce reflections off the wall behind the speakers. I’d give the flat panels a +2 or +3 rating depending on how well placed they were. They were better than the bare room, but not by a lot.

The live-end dead-end experiment resulted in a -3 rating -- sounded even worse than the bare room. The sound was congested and flat compared to the bare room. There was absolutely no question the room sounds different this way. However, I’m not sure how anyone could ever mistake this flavor of different for better.

The original Room Tunes produced about a +5 improvement, definitely better than the other configurations described so far. These could very well be the "bang for the buck" champs.

The Argent Room Len was easy; let’s call it a +10, a definite big improvement over the bare room. Definitely and obviously better than the original Room Tunes.

Finally, the moment of truth. Michael Green’s Pressure Zone Controllers were also clearly and obviously better than the bare room. Clearly more effective than the original Room Tunes. The magnitude of improvement? I hate to do this to you -- audiophiles love it when there are answers that are black and white, true or false, yes or no. When the answers come out like that, it tacitly removes audiophiles from any responsibility for having to research something themselves. I say this only partially in jest. It is too true too often! I have to give the Pressure Zone Controllers a +10 rating also.

Associated Equipment

Loudspeakers – Vandersteen 3A, Vandersteen 2Wq subwoofers, NSM 600-SE.

Amplifiers – Warner Imaging "endangered species" 200Wpc solid-state stereo amp, Melos MAT-1000 triode monoblocks, Belles 150A.

Preamplifier – Audible Illusions Modulus 3A w/gold phono boards.

Analog – Roksan Xerxes turntable, SME V tonearm damped and rewired with Nordost Moonglo, low-output Cardas Heart moving-coil cartridge.

Digital – Heavily moded Adcom CD player, lightly moded Panasonic DVD A-310 CD/DVD player, California Audio Labs CL-25 HDCD CD/DVD player.

Interconnects – Nirvana SL-1, Magnan Signature, Magnan Vi, Nordost SPM, Nordost Quattro Fil, JPS Labs Superconductor.

Speaker cables – Magnan Signature, Nirvana SL-1, Nordost SPM, JPS Labs NC Series.

Power cords – Audio Power, JPS Labs, VansEvers, Magnan.

Accessories – Michael Green Deluxe Justaracks; Bright Star Air Mass, Big Rock and Little Rock isolation and damping devices; VansEvers PLCs; AudioPrism PLCs; Statmat; CD Blacklight.

OK, that must mean that the Argent Room Lens and Pressure Zone Controllers sound alike. All I need to do, then, is tell you which one is cheaper and you have your answer, right? Wrong. PZCs and Room Lenses both score a +10 improvement. However, they don’t sound the same. What they do to achieve their +10 ratings is a little different. The Argent Room Lens affects the space a few feet in from the walls the most. In other words, imagine the volume of air most affected by the Room Lenses to be the central portion of the room. They give clarity, remove smear, unmask harmonics, and open the sound without affecting the size or shape of the sound too much.

The wall-mount PZCs do things that seem to make the room boundaries (walls, ceiling and floor) less influential on the sound. The walls don’t disappear, but they become much less important, and the walls no longer impart much of a sound to what is heard at the listening position. The PZCs seem to do more to remove the influence of the perimeter of the room. The wall-mount PZCs, when adjusted to give this expansive size to the soundstage, don’t do anything to enhance the center image. This is where the floorstanding Deluxe PZCs come into play. Properly placed, they can anchor the central portion of the soundstage to a significant degree. When the PZCs are dialed in, there is an overall wholeness to the sound that just plain isn’t there with other treatments, not even the Argent Room Lenses. The PZCs remove sterility from the sound. I was tempted to say that they make the sound warmer, but that’s not it. It isn’t the same kind of warmth added by an old-school tube amp or an over-ripe phono cartridge. It isn’t a distracting thing in any way. In fact, it is a very natural sound and makes it easier to relax while listening, more like real sounds in natural space. What the PZCs don’t do is clarify and even out the sound like the Argent Room Lenses do.

Another question begging for an answer

Well now, if one room treatment sounds good, two at the same time must sound better, right? Not in this case. There was only one combination of two treatments that sounded better than the best single treatments.

The PZCs and Room Lenses together produced about a +15 improvement. You don’t get the +20 improvement you might hope for, but +15 is isn’t bad. The central oriented, airy, detailed, unmasking Room Lenses and the spatial, anti-sterile, boundary-beating PZCs work in concert to give you something pretty darn special.

There is no possible way I could pick one of these over the other -- they are both great, but for slightly different reasons. What about other room treatment devices? I am convinced a lot of absorption is the wrong approach. Trying to brute-force the room into submission with absorbing types of room treatment devices won’t give the same level of improvement you get with well designed minimal-absorbent room treatment products. Not over-doing the absorption keeps the room sounding more "right," less obvious, and less manipulated than the room will sound with absorbent treatment devices. Knocking down first reflections and others from walls and ceilings fundamentally changes the sound of the room. It changes the sound so much, you get a psycho-acoustic effect caused by your ears and eyes not agreeing on what this space should sound like. When that happens, you tend to be edgy while in the room instead of relaxed. There has been a fair amount of research into this effect, so it is fairly well documented.


Michael Green has a most interesting product line with the Pressure Zone Controllers. In my experience, you’ll get the most pay back for your investment if you are willing to mount an appropriate array of PZCs on your walls. If this is not possible, the floorstanding Deluxe PZCs can do almost as much if your placement options allow for putting them where they need to be. The success of the original Room Tunes is expanded significantly by the PZCs. Michael Green’s unique approach to controlling sound that travels along walls and into corners is capable of producing an expansive soundstage while removing obvious room influences.

PZCs are being used successfully in performance halls, church sanctuaries, and in band and orchestra practice rooms. Their dramatic improvement to the acoustics in these non-audiophile facilities is readily apparent and is being increasingly sought after as word-of-mouth information spreads about the significant improvements possible for far less cost than with other types of sound-control measures. If non-audiophiles find the improvements so obvious and desirable, what are you waiting for?

One word of caution: Don’t try to figure out on your own how many and which types of PZCs you might need. Call the Room Tune hotline and have Michael Greens Designs assess your needs and make recommendations. This can save you aggravation and money.

...Doug Blackburn

Michael Green Designs Pressure Zone Controller Tunable Room Devices
Mini Corner Controller, $74.95 each (+$15 for cherry tuning board); Mini Echo Controller, $99.95 each (+$15 for cherry); 36" wall-mount Controller, $179.95 each (+$90 for cherry); 48" wall-mount Controller, $289.95 each (+$90 for cherry); ceiling-mount Controller, $179.95 each (+$60 for cherry); floorstanding Deluxe Controller, $224.95 each (+$90 for cherry).

Michael Green Designs
221 West High Ave.
New Philadelphia, OH 44663
Phone: (888) 766-6886 (888-ROOMTUNE)
Fax: (330) 308-5600

E-mail: tune66@hotmail.com

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