Acoustic Geometry Pro Room Pack 10 Acoustic Treatment Package
Acoustic Geometry is a recently launched subdivision of Acoustical Surfaces, one of the oldest and largest suppliers of acoustic products for noise control to recording studios, band rooms, houses of worship, businesses, and industrial facilities. The Acoustic Geometry division offers a full line of individual acoustic isolation and treatment products, as well as packages designed to treat entire rooms.
AG was founded by John Calder, a musician turned recording engineer turned studio designer. John has many A-list record credits, including being mix engineer on Neil Diamond’s four-million-seller Beautiful Noise. Incidentally, Calder chose the Large Advent hi-fi speaker (1975 vintage) to mix that record rather than the standard studio monitors of the day. That fact alone says much about his audio sensibility.
As part of his more recent studio-design work, Calder developed a few core technologies and products that have become the foundation of the Acoustic Geometry line for professional and home use. The Fabric-Wrapped Panel (FWP) is a straightforward flat panel for absorbing mid and high frequencies, and for killing flutter echo. Nothing unusual there. But the other two components of the Acoustic Geometry line differ considerably from conventional acoustic treatments. One of these products is a bass trap for room corners (called the CornerSorber) that works through diaphragmatic absorption via a membrane rather than typical frictional absorption. The second core product is a cylindrical-section diffuser (called the Curve Diffusor) that also incorporates diaphragmatic bass absorption. All three products measure roughly 2′ by 4′, with varying depth (see Specs & Pricing for details). Acoustic Geometry has packaged combinations of them into a range of nine turn-key bundles, with the appropriate product mix to treat any size room. These bundles range from the Home Room Pack 1 ($453) to the Pro Room Pack 12 ($7452). Each of the items in the Room and Pro Packs is also available separately.
Acoustic Geometry has made it easy for the audiophile to choose the right acoustic treatments for his or her particular room through a series of excellent videos and white papers available on the AG website. The site’s instructional videos offer many practical demonstrations of the principles explained, and are a great resource for learning about noise control and room acoustics. The packaging of the various components into a single whole-room treatment system, along with AG’s placement suggestions for those components, takes the guesswork out of what products you need and where you should position them.
As I’ve mentioned, I’m building a new listening room, but until that is ready, I’m living in a temporary place with a less-than-ideal listening space (the new room will be finished by the time you read this). My temporary room, which measures 27′ x 20′ x 8′, has lots of windows, and needless to say, no acoustic treatment. After reading Calder’s Audio Engineering Society paper on the CornerSorbers and Curve Diffusors, and watching the many informative videos on the Acoustic Geometry website, I decided to try a Pro Room Pack 10 ($6796). I installed it about seven months ago and have experimented extensively with it over that time.
The Pro Room Pack 10 consists of two pairs of CornerSorbers, ten Medium Curve Diffusors, and eight Fabric-Wrapped Panels. Acoustic Geometry supplied a drawing showing the ideal placement in my particular room (shown on the previous page). These products can be mounted on your wall or on available wooden stands. Because I didn’t want to put holes in the rental-house walls, and valued the flexibility of moving the treatments while they were under review, I elected to use the stands. The stands are nicely finished light-colored wood, but in practice they’re a little awkward to manipulate if you have a lot of them in a room. In a normal situation I would definitely mount the treatments to the walls. The Curve Diffusors and Fabric-Wrapped panels attach to walls with short pieces of Z-channel, commonly used for hanging framed pictures. The CornerSorbers are finished in black-painted wood, and the Curve Diffusors and Fabric-Wrapped Panels are available in various fabric colors. The Curve Diffusors are also available in a range of natural wood finishes as well as automotive paint colors. The bass-absorbing diaphragm on the CornerSorbers and Curve Diffusors is a thin sheet of vinyl loosely covering the rear, which isn’t visible when the products are installed. The build-quality is high, and the fabric-wrapped products are attractive. Dozens of fabric options are available.
The CornerSorbers are part of the five Pro Room Packs, and are also sold separately for $998 per pair. The device is a six-sided wooden structure with a vinyl membrane on the back side that faces the wall. They are intended to be used in pairs positioned tightly in the room corners behind the speakers and right against the wall. Their beveled edges allow them to fit close to each other in the corner, almost forming a single unit. The tight proximity between the membrane and the wall is key to their operation. At the room boundaries, the velocity of sound is at a minimum, and pressure is at a maximum. The vinyl membrane on the wall-facing side of the CornerSorbers is 3″ from the wall, right in the zone of highest pressure. The diaphragm is moved back and forth by varying acoustic pressure, absorbing bass. As Calder explains in his AES paper, reducing the amplitude of a room-mode-induced pressure peak through this diaphragmatic absorption results in a corresponding reduction in the depth of a cancellation. The result is flatter and smoother bass response.
Measuring the performance of bass absorbers is a tricky business. It requires an inordinately large testing chamber—the larger the chamber, the lower the frequency at which the bass absorber’s effect can be measured. Even the largest acoustic chambers (about 300 cubic meters) are only accurate down to 160Hz. Consequently, a typical bass absorber’s published performance parameters below 160Hz are estimated theoretically rather than being measured directly. Unfortunately, most problems in normal-sized listening rooms occur below 200Hz, exactly in the range where measurements begin to fail. But Calder wanted definitive measurement data while developing the Acoustic Geometry products, and arranged to test the prototypes in a unique space perfectly suited to the task—a nuclear reactor containment dome that had been converted into a massive acoustic testing chamber. (Don’t worry; the reactor had never been brought on-line.) That facility is located in Elma, Washington, and features the two largest independent acoustic test chambers in the world. These chambers, one measuring 738 cubic meters, allow accurate measurements down to 40Hz. This acoustics lab is run by a former NASA scientist who has written extensively in academic journals on acoustic testing.
Calder details the design and testing procedure for CornerSorbers and Curve Diffusors in his 2017 Audio Engineering Society paper “New Research on Low-Frequency Absorption Using Membranes.” (A revised and updated version of the paper was published in Proceedings of Meetings on Acoustics, the journal of the Acoustical Society of America, called “New Research on Low-Frequency Membrane Absorbers.”)
The paper includes photos of the products being tested in the giant chamber, along with the measurement results. I’ve included here a photo of the Curve Diffusors being mounted in the test chamber, and the graph showing the amount of absorption (in Sabins) vs. frequency for three different combinations of CornerSorbers and Curve Diffusors. Calder also describes in the paper how the measured performance of the various prototypes wasn’t what he expected, leading him to refine the design in unexpected ways. From this experience, he draws the conclusion that low-frequency absorption products that were designed from theory alone, rather than as the result of empirical testing in a suitable laboratory, cannot deliver guaranteed performance.
I positioned the components of the Pro Room Pack 10 according to a diagram Calder supplied (shown on this review’s first page). Two CornerSorbers were deployed in each corner behind the loudspeakers, each with a Fabric-Wrapped Panel above it. This wall was also treated with a pair of Medium Curve Diffusors about six feet apart centered behind the speakers. Each sidewall was treated with three Curve Diffusors, one horizontally mounted on the wall next to the speaker, one at the sidewall reflection point, and one on the wall directly to the side of the listening seat. Behind the listening seat, four Fabric-Wrapped Panels were deployed in the corners, and two Curve Diffusors positioned horizontally directly behind the seat.
I had plenty of time to evaluate the Acoustic Geometry package. I started by listening in my untreated room, then added the Pro Room Pack 10 all at once. I lived with the treated room for several months, and then removed all the components of the Pro Pack 10 and listened again to the untreated room. I then incrementally added each component of the Acoustic Geometry package back into the room, but in pairs (two CornerSorbers, two Curve Diffusors, etc.) to maintain room symmetry. I listened to the effect of each product individually and then finally to the whole system, once all the treatments were back in place. A few months later I removed all the Acoustic Geometry products and listened again to the untreated room. This experience gave me a very good sense of exactly what each of the products contributed to the sound, as well as the efficacy of the entire package.
My main loudspeakers through these listening tests were Piega C711s augmented with a JL Audio Fathom f113v2 subwoofer and CR-1 crossover. This combination is capable of prodigious bass output, making it a good source for evaluating the treatment’s effect on the bass.
First considering each component’s effect, I brought one pair of CornerSorbers into the untreated room (one per corner) and listened, and then both pairs of CornerSorbers. Frankly, I was shocked by how effective the CornerSorbers were in cleaning up the entire bottom end. The CornerSorbers removed the boom and bloat in the bass, replacing a slow, muddy, and ponderous bottom end with one that had tautness, muscularity, pitch definition, and dynamic articulation. Transient detail that had been smeared was now vividly rendered, with sharper attack on the start of notes as well as faster decay. That quality engendered a greater sense of musicians playing together and driving the rhythm—a feeling of greater tightness and cohesion among the instrumentalists, a sense of agility, more propulsive and expressive rhythms, and a vividly upbeat quality. The untreated room sounded thick and slow by comparison. The music now had a solid foundation rather than a murky and ill-defined one. I could hear texture more clearly on acoustic bass, steeper attack and decay on kickdrum, and the wonderful way a great drummer and bass player work together to create the music’s dynamic underpinning. Adding the CornerSorbers was like lifting a wet heavy blanket off the sound.
By removing the smearing and bloat in the midbass, the CornerSorbers also allowed me to hear the lowest bass more clearly. It was an interesting phenomenon—I heard a lighter and leaner sound overall, but with simultaneously deeper extension. The midbass colorations had been masking the low bass. The album Jaco by bassist Brian Bromberg features some superb recordings of the virtuoso’s playing. His solo on the track “Portrait of Tracy” was a different experience with and without the CornerSorbers; each note was clearly articulated, defined, and with greater depth and power. His instrument’s timbre was also better resolved and more richly textured.
This wasn’t a subtle change. Often, adding a bass absorber in the corner behind the loudspeaker (always a good thing, by the way) results in an improvement, but one that doesn’t quite go far enough. That is, the absorber nudges the sound in the right direction, but not to the degree one wants. The CornerSorbers don’t suffer from that limitation, taking iron-fisted control over the low end rather than tinkering at the margins.
I noted all these qualities when I first heard the Pro Room Pack 10 as a complete package compared with the untreated room. But only when listening to individual components of the package did I fully realize what each was doing. All the wonderful improvements to the bass that I’ve just described increased in magnitude when I added four Curve Diffusors. Remember, the Curve Diffusors are also equipped with diaphragmatic bass absorption, although they are less effective at very low frequencies compared to the CornerSorbers. Each pair of Curve Diffusors that I added further tightened up the bass, made timbres more realistic, increased transient fidelity, and better resolved pitch. Rhiannon Giddens’ rendition of “That Lonesome Road” from her album Factory Girl features a huge-sounding “washtub” acoustic bass that comes in after her introduction with guitar and tambourine. With the CornerSorbers and Curve Diffusors the washtub bass was much more realistic in every way.
More importantly, however, the Curve Diffusors greatly opened up the soundstage, taking the sound out of the speakers and presenting a larger, more three-dimensional space populated by more clearly defined individual instruments. The Curve Diffusors also snapped the sound into focus, not just by making instruments more spatially distinct, but by generally clarifying their respective timbres. This made it easier to identify the tonal color of individual instruments rather than hearing them sounding smeared and homogenized. Going back to the Rhiannon Giddens’ track that starts with just her singing, accompanied by a guitar and tambourine, the tambourine without the Curve Diffusors sounded like a high-frequency noise, close to the front of the soundstage, dry with little air around it, and no resolution of the inner detail that conveys the mechanism by which the instrument makes sound. With the Curve Diffusors, suddenly the tambourine was surrounded by palpable air and bloom, conveying the impression of the sound expanding around it with each strike. The tambourine moved farther back in the soundstage, with the acoustic space around it better defined. I also heard much more resolution of fine detail that made the instrument’s timbre more realistic. The undifferentiated high-frequency transient noise was replaced by a richly textured rendering.
Similarly, I listened to background vocals with and without the Curve Diffusors. Without them, the vocals tended to sound fused together and attached to the speaker baffle. With the Curve Diffusors, they were detached from the speaker and seemed to wrap around the sides of the soundstage. Moreover, I could more clearly hear the contributions of the individual singers, with each one’s unique timbre intact. An audio component’s ability to resolve individual instruments from within the whole is an important quality in musical realism. I listen for this in DACs, amplifiers, loudspeakers, and every other component in the chain. But the degree to which the Acoustic Geometry products improved this aspect of the sound was far greater in magnitude than differences among electronics.
There’s another reason vocals sounded more clear and open with the Curve Diffusors; cleaning up the midbass bloat allowed the midrange to be unmasked, making it sound more transparent and “lighter,” with greater spatial and textural realism.
Adding the Fabric-Wrapped Panels further improved the sound, rendering the treble in a smoother and more relaxed way. Cymbals were more densely textured, with the gong-like lower-frequency component of their sound no longer obscured by noise-like high-frequency hash. This made for a greater sense of ease, smoothness, and musical involvement.
It would not be an exaggeration to say that the Pro Room Pack 10 completely transformed the sound of my listening room. Significantly, it rendered improvements in many ways—bass articulation and definition, transient fidelity, soundstaging, timbral resolution, treble smoothness—without any unwanted side effects. The Pro Pack attacked room problems without killing dynamics, throwing a blanket over top-octave air, overdamping, or making the room sound unnaturally dead when you walked in and heard your own voice. I attribute this to the relative balance between low-, mid-, and high-frequency absorption. There’s not too much treble absorption, which can make rooms sound overdamped, a common shortcoming of some acoustic products. Such overdamping leads you to turn up the volume in an attempt to gain clarity, which only exacerbates bass bloat. The Acoustic Geometry package had no such drawbacks, sounding open and lively, yet smooth and relaxed.
If the Pro Room Pack 10 won’t fit with your décor or budget, you can get some of Acoustic Geometry’s benefits with one CornerSorber behind each speaker, a pair of Medium Curve Diffusors, and a couple of Fabric-Wrapped Panels. In fact, just a pair of Curve Diffusors on the sidewalls positioned at the first-reflection point greatly improves soundstaging and clarity.
Acoustic Geometry has brought audiophiles professional-grade acoustic treatment in affordable, easy-to-use packages that can greatly improve the sound of a music listening room.
Specs & Pricing
Dimensions: 48½” x 24¼” x 7″
Weight: 72 lbs. per pair (shipping weight)
Price: $998 per pair
Medium Curve Diffusors
Dimensions: 21″ x 42″ x 7″
Weight: 26 lbs. (shipping weight)
Price: $399 each
Dimensions: 24″ x 48″ x 2″
Weight: 5 lbs. each
Price: $92 and up, depending on size
Pro Room Pack 10 (system reviewed)
Two pairs CornerSorbers
Ten Curve Diffusors
Eight Fabric-Wrapped Panels
By Robert Harley
My older brother Stephen introduced me to music when I was about 12 years old. Stephen was a prodigious musical talent (he went on to get a degree in Composition) who generously shared his records and passion for music with his little brother.More articles from this editor
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