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Positive Feedback ISSUE 28
november/december 2006


Room Tuning Redux: Further Refinements
by Marshall Nack


How quickly one forgets. Everything in the room contributes to the sound. Remember that. I should make up a poster and hang it on the wall of my tweak closet. The old adage surfaced the other day while listening to my friends' studio / showroom system. Lots of quality gear was in line, and a lot of it was familiar. mid-line mbl digital front-end, which I have in house right now. Kharma CRM 3.2 FE speakers were stationed roughly a third of the way into the room: the listener another third back. Amplification was new to me: it was the highly regarded ASR Emitter integrated amp. I settled into the sweet spot.

I have to say the sound was fabulous. So good, in fact, that I was caught off guard. About all I could criticize was a slight over-damping. Now, I owned the CRM 3.2 FEs for two years and I could never get them to sound this good. How the heck did he manage that?

The room dimensions approximated my own, with both speaker and listener positioning roughly the same, too. My friend has quite a record collection, and… Wait a minute: of course, that's it! All four sidewalls were crammed nearly floor to ceiling with LPs in bookcases! Riddle solved. The major difference between this rig and my place was the room furnishings. Most of the gear was the same, even the layout was similar, but my place didn't sound as good, so it must be the diffusion / absorption provided by the LPs.

This realization re-kindled the initiative to do something about my room, and I knew two areas that needed immediate work.

Acoustics First Corporation

My listening room has a built-in climate control convector on the front wall. This 5 x 2 foot unit projects about 9 inches into the room from the baseboard. It's hollow behind the thin aluminum front panel, except for the heating / cooling fins of the unit. This is a large, uncontrolled sound source, an especially troublesome one, because it's located behind and between the two speakers. I had tried to null it with freestanding Echo Buster absorption panels and liked the result, but those things moved around too much and blocked the airflow into the base of the unit. Plus their 2½" thickness reduced the crawl space behind the audio racks. For all these reasons, a thick, freestanding panel was not a good solution. Unsure about what to do next, I left it with three Harmonix RFA-78i Room Tuning Discs on it, hoping the dots would help a little. They did, but not anywhere near as much as the Echo Buster panel.

Browsing through the latest issue of TAS magazine, my eye alighted on an ad for something called the Vinyl Sound Barrier. The copy read: "Vinyl Sound Barrier is used to block unwanted noise. Prevents unwanted sound transmission through walls, ceilings, and floors. Increases Wall Mass without increasing its Depth—only 1/8" thick!" That last caught my eye: sound damping with only an eighth of an inch thickness. The next day, a pleasant saleswoman at Acoustics First Corporation listened to my needs and made suggestions. I wound up getting three linear feet, which set me back a whopping $19.80, plus $7.20 shipping (it's sold in units of feet, at $6.60 per). I also got a catalog of their extensive offerings, most of whose prices are similarly billfold-friendly.

The Vinyl Sound Barrier worked—it silenced the treble artifacts emanating off the convector. Tonal balance smoothed out and lowered. The center of the soundstage anchored, resulting in imaging improvements. This was as good as the Echo Buster panel. Unhappily, the next day this successful solution began to detach from the front plate of the convector. I went back to the hardware store for a supply of stronger double-faced tape and applied a massive dose (this wound up costing $20), and is holding. Scratch item number one off the list.

Marigo VTS Superdots

Item number two is an imported Italian breakfront or étagère of cherry wood and glass. It's beautiful, expensive, and a devil—chock full of vibration and resonance contaminants. On heavy bass tracks, its off-axis, low frequency buzzing to the beat was clearly audible. On all other material, you didn't hear the unit per se, but its insidious presence made itself known, as you'll see.

Through trial and error, I had come to decorate it with seven Harmonix RFA-78i discs, quite an expense ($800 16 disc set). However these discs are not really intended for this purpose, but for use on walls, ceilings, and especially ceiling corners.

The solution I discovered for this bugger worked so well, I felt it worthy of a capsule review.

Let's start with the latest from Wm. Christie and his period instrument ensemble, Les Arts Florissants (Judicium Salomonis, Virgin 3 59294 2). The last of les grands motets of Marc Antoine Charpentier, composed when he was in his fifties, it sounds much like many of his other compositions. I like track two for Marc Mauillon's robust, forward and very focused bass-baritone, although he tends to become too big and dwarfs the continuo group. I didn't care for the massed, less than mellifluous vocal choir, however, when it arrives on track three—best to pass this track by.

Track five is notable for a recitativ by Paul Agnew, my favorite Baroque tenor. On view are his distinctively nasal and uncommonly expressive vocals, for which I admire him. He's less there than Marc was on track two, but there are no real issues, except maybe it's a tad too restrained. (My ever-present inner voice tells me to tweak something for more treble extension.) Track six brings back the full chorus, and this time they sound great—decently spread across the stage, all ranges represented, a balanced sound.

Now let's return the breakfront to its virgin, untreated form to see what that's like. After removing all RFA-78i, the sound is moving freely and the sense of constraint or over-damping went away. There's a lot more treble: tonal balance has elevated noticeably. The baritone on track two is much less focused; the messy chorus of track three is less objectionable (this is what usually happens when you back off on resolution). Let's go to track six. Now the chorus is peaky on crescendos. I'm missing the added bloom and plumped up bass through lower midrange of the Harmonix RFA-78i. The untreated sound could be described with one adjective: the dreaded bright.

The next step was to see what an equivalent number of 40mm Marigo VTS Superdots do ($159 set of 8). Placing them in roughly the same locations as the RFA-78i, the treble peakiness vanished. Tonality moved back down almost to the level it was with the RFA-78i. But there's no sense of constraint now, no awareness of damping as Paul Agnew traverses track five. By Jove, there's more life in his voice! Marc, the baritone on track two, is less dominating at first, but as you listen, he gradually crescendos while the orchestra maintains a steady volume. In due course, he clearly dominates, but now it seems like a natural relationship.

I couldn't resist the prospect of more discs. The recommended treatment calls for one dot in each corner of a glass pane. So far, I've only been playing with one for the entire pane. I upped it with an additional four discs. Immediately, there was more depth of tone and depth of image. Paul was in about the same place behind the plane of the speakers, but he acquired front-to-back dimension. Buckets of atmosphere surrounded his image and it had an openness that let the music breathe. More of the micro-info of the venue was evident as murkiness departed and the presentation became more vivid.

Marc on track two was about as focused and tangible as he had been with the RFA-78i. Some scary stuff was going on. The effects were so noticeable and beneficial; I was scratching my head with the addition of each additional disc. It began to remind me of the old days, when I was known as the tweakaholic. At the best of those times, my sound had a stage that some compared to watching a film on 35mm stock (rather than video), with image precision and depth layering of uncommon exactitude. (There were plenty of other issues, but in these few regards it was certainly exceptional.) The section with the chorus on track three suddenly displays full frequency range. Where did that punchy double bass come from? I'm hearing tight low notes that I didn't even know were there before.

I knew that breakfront was a problem area, but I had no idea it was as destructive as this. How can localized treatment of one piece of furniture make such a big improvement?

VTS Theory

Marigo Audio makes various species of VTS dots. All are multi-layered composites of constraining and rigid, metal and non-metal layers. I interviewed Ron Hedrich, the aerospace physicist designer behind the company, about his innovative theory.

Here's how he explained it: Most dots, footers, and other surface tweaks attempt to shift the materials primary resonant mode. The VTS dots leave that alone. Instead, they target tension and compression waves on the materials surface, secondary by-products thrown off by the primary excitement. In his language, they are "high amplitude, frequency specific oscillations."

Think of an acoustic suspension bookshelf speaker. When the driver cones make a compression excursion and retract into the box, they pressure the air, which in turn causes the rear of the cabinet to flex outward—the rear of the cabinet moves backward in the horizontal plane. That's where the primary resonance mode lives. At the same time, the flexing rear wall causes tension waves to propagate all over the surface of the rear panel. This pressure, or energy, spreads over the surface as it travels to all four corners of the rear panel. This is happening in the vertical plane. It is these vertical stresses that are targeted by the VTS dots. They target sound energy that operates in a plane perpendicular to the primary resonance. Got that?

Or, here's an analogy that might help. Ron believes vibration /sound artifacts behave in a manner similar to RF energy. Current thinking views RF riding along the surface of conductors wherever electricity is present, the so-called "skin effect." Ron believes these high amplitude, frequency specific oscillations behave similarly, except that one is physical, and the other is electrical.

After placing a dot, you have about 24 hours (the adhesive's fixing time) to change the location. The longer it sits in place, the more difficult it is to remove and the chances of damaging it increase. The time to try out different locations is shortly after affixing it. (Marigo will honor refund requests if you don't like what the dots do and want to return them. They won't replace those that you damage.)


I like what the VTS SuperDots do very much, but my wife isn't as happy with them. The 40mm dots are the circumference of a small doorknob. The pockmarked breakfront does not look the same. "We didn't spend two years looking for the perfect display piece so you could put paste-its all over it," she rightfully complained. I inquired with Ron about smaller dots, and got a set of 30mm ones in black: they cost less ($99/8) and they're less powerful. While WAF was somewhat appeased, tread carefully if you go this route.

Also, my preliminary experiments indicate caution on several fronts. First, don't mix different size dots, i.e. 40 and 30mm, on the same surface. Second, well before I implemented even half of the manufacturer's recommended number of dots, everything I liked about them started to fade away, replaced by an increasingly thin, tight and analytic sound (much like other brands of room tuning dots I've tried). Go slowly: start with one dot per panel. Third, a combination of Marigo and Harmonix dots worked well together (maybe that's because one works on vertical stresses and the other on the primary resonance?) This is the combination I'm sticking with.

I'm tempted to conclude that any large glass surface in the listening room must be reckoned with.

VTS 40mm SuperDots: $159 - 8 pcs

VTS 30mm SuperDots: $99 - 8 pcs

Marigo Audio
Portland, OR 97206
TEL: 503. 284. 1163
web address: