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Big vs. Bigger: 2′ vs 4′ Acoustic Diffusers
Posted in Diffusion, Product Applications, Products on December 16, 2025
A couple common form factors in acoustics are based on building material sizes. Ceiling grids are a common place to install acoustic devices, and you will find that many are built to either work in a 2’x2′, 2’x4′, or 4’x4′ ceiling grid installation. This makes sense, but did you know that these devices also perform differently in some cases due to their dimensions? This is especially true with acoustic diffusers.
When you’re tuning a room—whether it’s a studio, theater, rehearsal space, or even a high-end listening room—acoustic diffusers are one of those rare tools that improve clarity without taking the life out of the space. Designs like the Double Duty Diffuser, Pyramidal Diffusers, and Quadratic Diffusers all share that same mission: redistribute sound energy so your room feels open, natural, and honest.
But while they may look similar in concept, their size changes the game. A 2’x2′ panel and a 4’x4′ panel both diffuse sound, but their effect—especially in the low-frequency and low-mid ranges—can be very different.
2’x2′ Diffusers — Compact Control
2’x2′ units are the most modular diffusers in the lineup. Their smaller footprint makes them ideal for:
- Breaking up mid and high-frequency reflections
- Treating small and medium rooms
- Sitting comfortably in grid ceilings or tight wall spaces
Because of their size, 2’x2′ diffusers don’t interact as much with the low-frequency energy in a room. Bass waves—being physically large—tend to wrap around smaller objects. The result? Excellent clarity improvements in the mids and highs, with a very predictable diffusion performance. The Double Duty Diffuser and Pyramidal diffusers have been a standard in breaking up planar surfaces for decades. While their diffusion in low frequencies is limited at this size, the air cavities do help control some upper bass frequencies through absorption.
The tuned mid frequency effects of the 2’x2′ quadratic, and the smooth performance of the Double Duty or Pyramidal diffuser are perfect for control rooms, edit rooms, drum booths, and anywhere you want accuracy without sacrificing sparkle.
4’x4′ Diffusers — Where Diffusion meets Bass Control
Now we get to the big ones.
A 4’x4′ diffuser is similar in concept to its smaller relatives, but the scale moves it into a different acoustic category. At this size, diffusers begin to influence longer wavelengths, which opens the door to something smaller diffusers often struggle with…
Low-frequency interaction
Large diffusers present enough depth, volume, and surface area to affect the bass spectrum. The extra size creates cavities which are tuned to reduce bass, and they have surfaces large enough to redirect those lower frequencies.
- Break up standing waves in the low-mid range
- Reduce modes and nodes common in rectangular rooms
- Add a sense of openness to the bass field
- Prevent buildup behind listening positions
In other words: same diffuser concept, very different low-end behavior.
Wide-area coverage
A single 4’x4′ panel can modify a huge portion of a wall, creating an even, spacious character that feels less like “treatment” and more like a room that’s naturally well-behaved.
These panels shine in larger studios, live rooms, and worship spaces—anywhere you need diffusion that reaches deeper into the frequency spectrum – and can break-up large, flat, specular surface reflections, which are responsible for flutter, echoes, bass buildup, and long reverb times.
Which do you need?
There are two main factors in the decision: space and performance requirements. In certain environments, it’s impractical or impossible to install large 4’x4′ or larger diffusers; It also may not be the best solution – even if it may appear to be on paper. While a single, large barrel diffuser may appear ideal, you may not have enough physical space to allow the diffusion to develop – where several smaller diffusers would be the better solution.
In short, your physical space and acoustic conditions will dictate which size elements will give you the most benefit in your environment.
You say “Diffuser,” I say “Diffusor”
Posted in Diffusion, Q&A, Uncategorized on November 11, 2025
If you’ve spent any time around acoustic treatment—especially sound diffusion—you’ve probably noticed something odd: sometimes the product is called a “diffuser“, and other times it’s a “diffusor“. For newcomers, this can feel like a secret code or a subtle technical distinction – But the truth is much simpler.
Many trace the dual spelling back to Manfred Schroeder, the German physicist who developed the mathematically designed Quadratic Residue Diffusor (QRD).
In German, the word is spelled “Diffusor.” When Schroeder’s work entered the academic world, the spelling likely came with it.
Because his research became foundational in architectural acoustics, the German spelling spread through physics papers, textbooks, and graduate-level acoustics programs. Over time, “diffusor” became a common spelling when discussing mathematical or Schroeder-style diffusors specifically.
As manufacturers began producing these mathematically derived designs—like the ArtDiffusor® line from Acoustics First® (and many other early products)—they retained the “diffusor” spelling as a nod to the academic and scientific origins.
Before long, the industry ended up with two spellings that referred to the same thing:
- Diffuser – the standard English spelling
- Diffusor – the academically inherited, German-influenced spelling tied to Schroeder’s work
Both spellings appear throughout the professional audio world, and both are correct.
Is There Any Practical Difference?
No. None. Zero.
There is no technical difference between a “diffuser” and a “diffusor.” They both refer to devices used to redistribute sound energy and improve the acoustic quality of a space through accelerating the development of sound field diffusion. The spelling variation is purely linguistic.
Think of it like “colour” vs. “color” or “flavour” vs. “flavor.” British English keeps the “u,” American English drops it. (However, if you ask a Brit, they’ll tell you Americans are obviously spelling it wrong.)
The “diffusor/diffuser” split works the same way—just with a German twist.
So Which Should You Use?
Use whichever feels natural or matches the context you’re writing in. Many engineers and academics use “diffusor” when referring to Schroeder-type or other mathematical designs, simply out of tradition. Others stick with the standard English “diffuser.”
Tomato. Tom-ah-to.
The Spellbinding World of Owl Acoustics…
Posted in Articles, Uncategorized on October 16, 2025
Today we thought we’d take a break from the usual Acoustics First blog topics and talk about owls and the fascinating way in which they experience acoustics. Owls possess some of the sharpest hearing in the animal kingdom. But what makes their hearing so exceptional and how does it differ from our own?
The secret lies in the unique structure of their faces and ears. Owls have flat, circular faces which gives them an incredible ability. Their facial discs, a set of specialized feathers arranged in a ring around their face, act like a natural sound collector, similar to a satellite dish picking up signals. These feathers are flexible, allowing them to adjust their position for optimal sound gathering. The sound they collect is then funneled into their ear openings located on the sides of their head. Imagine if we could move our ears to “zero in” on a particular sound!
Now, you might be wondering about those “ears” that stick up from an owl’s head. These aren’t actually ears at all! Those feathers are called plumicorns, and while they help with camouflage and communication between owls, they don’t contribute to hearing. The true ear openings are located on the sides of the owl’s head, much like humans. These openings are protected by a layer of feathers, and in some species, they even have movable flaps that can cover the ears. These flaps don’t interfere with hearing; they help reduce the sound of air turbulence when the owl is in flight.
What makes an owl’s hearing even more extraordinary is the position of its ear-holes. Unlike most animals, owl ear openings are asymmetrical, meaning one ear sits higher than the other. This unique design allows them to pinpoint sounds not only left or right, but also above or below. Thanks to this setup, owls can triangulate the source of a sound with incredible precision—sometimes within millimeters! This ability allows them to swoop down and catch prey they’ve never seen. The degree of asymmetry varies among owl species—some, like the Northern Saw-Whet, have a noticeable difference in ear placement, while others have more subtle variations. Either way, it’s an impressive adaptation!
Humans, like many other animals, have symmetrical ear-holes, making it more difficult for us to pinpoint whether a sound is coming from above, below or directly in front of us. This is why central clusters of speakers installed above a lectern effectively make the sound feel like it’s coming directly from the orator, not from the ceiling speakers.
Owls also have a “sound-location memory” that further enhances their hearing. When they hear a sound, their brains create a mental map of its location relative to the owl’s position. Special cells in their brain help process sounds from different directions, allowing them to track and locate the sound later.
Finally, like dogs, owls have a broader range of hearing than humans, and they can detect finer details within sounds. According to researchers, owls can hear sounds much faster than we can. While humans process sounds in increments of about 50 milliseconds, birds can discern sounds as short as 5ms. This means that where humans might hear a single note, owls may hear up to 10 distinct notes. Their auditory skills are truly out of this world—and it makes you wonder what we might be missing in our own world of sound!
Sabins, SAC, & NRC — a practical guide.
Posted in Absorption, Articles, HOW TO on September 18, 2025
When optimizing a room’s acoustics, you’re often balancing how much sound is absorbed (loss) against how much bounces around (reverberation). Some common ways to describe absorption — sabins, SAC, and NRC — look different, but they’re closely related.
Sabins
A sabin is a direct measure of absorption: One sabin equals the sound-absorbing effect of one square foot of a perfectly absorbing surface (like an open window – sound goes out, but doesn’t come back.) In practice, manufacturers or labs will report a component’s equivalent absorption area in sabins at various frequencies. Sabins are additive: add the sabins of all items in a space to get the room’s total absorption for use in reverberation calculations.
SAC
Sound absorption coefficients (SAC) are used to simplify large square footage calculations. Each SAC itself is derived from the measured equivalent sabins of a test sample divided by the sample’s area. This allows you to multiply the square footage of a certain material by the SAC and it will tell you how many sabins it will absorb at a certain frequency. You may also see an average of all the SACs, or a subset of those values… a specific, often-used subset is the Noise Reduction Coefficient (NRC).
NRC and how it’s calculated
NRC (Noise Reduction Coefficient) is a number that represents a material’s average absorption performance at mid-to-high frequencies. It’s calculated by taking the arithmetic average of the material’s sound absorption coefficients (SACs) at 250 Hz, 500 Hz, 1000 Hz and 2000 Hz (per ASTM C423 or other standard test procedures). NRC is typically reported to the nearest 0.05 and runs from 0.00 (reflective) to 1.00 (very absorbent). Being an average, it isn’t the most accurate method, but it can give you a quick estimate which can be useful in the planning stages.
Practical Mathematic Relationship
- From measured data: SAC = measured sabins ÷ sample area.
- NRC is the average of SACs across four bands (250 Hz, 500 Hz, 1000 Hz and 2000 Hz).
- To convert NRC into a working absorption number for a planar surface:
sabins = NRC × area (ft²). - For discrete units (baffles, clouds): manufacturers often give sabins per unit, so total absorption is sabins per unit × number of units.
Why sabins for baffles and NRC for wall/ceiling panels?
Hanging devices like baffles are three-dimensional, exposed on multiple faces, and their effective absorption depends on orientation, spacing, and edge behavior. It’s more accurate and user-friendly to report their absorption as “# sabins per unit.” Flat-mounted wall or ceiling panels cover a known area and behave predictably per square foot, so SAC or an NRC (per ft²) is a convenient, normalized way to estimate absorption across a room.
Putting it into RT60 calculations
RT60 calculations depict the amount of time it takes for a sound to decay 60dB in a particular space with specific treatments. (60dB is roughly a 1000-fold reduction in sound pressure.) Reverberation-time formulas (like Sabine’s) use the room’s total absorption in sabins in the function. A basic average will use NRC × area for planar coverage and add sabins-per-unit for baffles. Sum everything up to get total sabins, then plug that into your RT calculation to estimate RT60.
If using feet your calculation is…
RT60 = 0.049 x Room Volume ÷ Total Sabins
If using metric your calculation is…
RT60 = 0.161 x Room Volume ÷ Total (Metric) Sabins
In summary:
NRC is an area-based average (for flat-coverage estimates); SAC is a sabins per square foot coefficient (for efficient absorption calculations using area); sabins per unit are direct, measured absorption values (better for discrete, hung, multi-faced items).
Similar, yet different: Angled QRD vs. Standard QRD
Posted in Diffusion, Product Applications, Products on August 19, 2025
In this installment of “Similar, yet Different,” we explore the similarities and subtle differences between a classic, standard 1D QRD and a modern, angled 1D QRD. While being based on the same mathematic function for their design, there are a couple subtle differences in the performance of these devices.
Quick review. A Quadratic Residue Diffuser is based on a mathematic equation that states that the Well Depth is decided based on the square of the position of the cell and the remainder of when it is divided by a prime number. (We know it sounds really complex… but this is how the ratios of the wells are calculated to maintain a balance of magnitude across the face of the device.)
The equation looks like this:
Well Depth = (n² modulo p)
(Note: there will not be a quiz!)
As it was stated, both of the devices use the identical calculation when coming up with their wells… but there is one important change – the well bottoms are flat on the standard QRD and angled on the angled quadratic. This change makes this diffuser perform differently in 2 key ways:
- The Diffusion Pattern is wider on the angled QRD.
- There is a more subtle transition from one frequency to the next on the angled QRD.
When you look at the two sets of polar pattern above, you will notice that the Angled QRD has a wider pattern, as shown in the first-column, horizonal polar pattern (at 2000Hz especially), where the standard QRD is a more forward-focused pattern.
What does that mean in practice?
Both of these diffusers have a 1D pattern, but the flat bottoms of the standard QRD primarily use diffraction and incidence angle to widen the diffusion… the rest of the diffusion works on the principal of phase offset from the depth of the wells and the time of travel. The Angled QRD introduces an angle which means that one side of the well is deeper than another. This changes the reflection angle, time of travel, and, in turn, degrees of phase shift depending on where the sound strikes the inside of the well. This modification smooths the transition of phase from well to well – as the wells themselves have a range of phase change. This angle also causes the sound to be redirected toward the inner walls of the wells, causing it to change direction from the angle of incidence – widening the pattern further, changing the travel time, and basically bouncing sound around more.
There are some situations where the standard QRD‘s narrow pattern and well-defined transition frequencies may be preferable. In some practice rooms or larger listening spaces, there may be a need for the diffusion to be a little more directional, maybe to hit (or avoid) a certain position in the room. In these scenarios, the standard quadratic may be the recommended choice. In other spaces where you want the reflections to spread out more rapidly – maybe in smaller rooms or spaces where you need to get more coverage from ceiling reflections – then the angled quadratic may be more appropriate.
In closing, while these two devices have a nearly identical design, a small difference can have a big effect on the performance of the diffuser – and how you use them.
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