Archive for category Diffusion
St. Andrew by the Bay – Custom HiPer® Impact Panels to absorb and diffuse sound!
Posted by Acoustics First in Absorption, Diffusion, Product Applications, Worship Facilities on April 10, 2024
St. Andrew by the Bay is a traditional worship facility with a focus on spoken word worship and congregational singing. The large volume and hard surfaces in this space are the physical features most at fault for excessive reverberation, comb filtering and distracting “slap” echoes (discrete sound reflections usually caused by a distant, reflective back-wall).
To correct the slap-back and curb excessive reverb without “over deadening” the space, we recommend distributing approx. 550 SQFT 1” HiPer® Impact absorber/diffuser panels throughout the rear wall areas (see attached layout). HiPer® Impact panels absorb low frequencies and diffuse high-frequencies, yielding a much more even room response. In addition to controlling bass buildup, the high-frequency scattering will help retain some “life” in the room for acoustic and choral performances.
Reverb Prediction – Historically, churches relied on an abundance of hard surfaces to propagate sound to the rear of the nave, so they benefited from very long reverb times (upwards of 4-5s). Modern sound systems allow for a much more focused sound and equitable listening environment , so these extreme reverb tails are no longer necessary and can actually degrade the experience of the congregation. Churches of this size with a sound system and traditional worship services should have a reverb time somewhere in the 1.5-2.25s range. We entered the sanctuary’s dimensions and construction materials into our acoustic calculator and made a prediction of reverb times before and after treatment.
From Lee Hartman & Sons who performed the install “Here are some photos of the finished panels at St. Andrew by the Bay. It turned out great and client is very happy. Many thanks to Cameron for the detailed layout.”
Similar, Yet Different: Model C vs. Model D!
Posted by Acoustics First in Diffusion, Home Entertainment, Home Theater, Media Room, Multipurpose Rooms, Music Rehearsal Spaces, Music Tracking Room, Product Applications, Products, Recording Facilities, Recording Studio, Studio Control Room, Theater on January 5, 2024
In this installment of “Similar, Yet Different,” we take a good look at two very different looking diffusers in the 2’x2′ size… the classic ArtDiffusor® Model C and the organic, rippled ArtDiffusor® Model D – while there are some similarities, there are some key differences in how they look (obviously) and how they perform.
Quick Similarities.
The ArtDiffusor® Model C and Model D are both 2’x2′ diffusers which are made to be either wall mounted or installed in a standard drop-tile ceiling grid. They are both formed from a Class A fire-rated polymer in a single piece. Both are mathematical diffusers, which create their different physical features in a “form follows function” methodology. They also cover roughly the same frequency bands, with some minor variation in how they execute their control.
Difference in Math
The Model C is an interesting configuration. Often you will see quadratic residue diffusers with flat blocks or wells in a relatively standard quadratic cell formula configuration. The Model C runs in a much different alternating binary configuration. The basic idea is that cells are placed in a 45° array with each cell adjacency calculated as an alternating array of higher and lower cells starting in the middle and working in a pattern of alternating low/high cell clusters decreasing toward the edges of the diffuser. These diffusers also do not have flat tops on the blocks – they are angled at 10°. The orientation is then rotated in 90° steps in a pattern that maximizes the spatial redistribution of reflected sound. This was a vast design departure over the original quadratic design, and created a diffusion profile that was distinctly different.
The Model D was an even greater departure. It began with a Maximum Length Sequence (MLS) concept that first changed the varied straight channels into rings of different dimensions. These rings then broke from the MLS mold by getting varied height profiles based on the QRD sequence. As if having different size rings at different heights wasn’t enough… the randomness was further perpetuated through a Boolean process of assigning certain rings a random property that would either add or subtract height from any other ring that they crossed. Finally, the entire surface geometry was smoothed using a bicubic interpolation, creating the organic undulating surface which gracefully spans the entire profile.
What this difference in math does to the acoustic performance.
The Model C has a nice even diffusion profile through it’s primary working range. This is a product of the QRD design and binary distribution. The set size for the blocks guarantees a solid primary frequency range from about 1KHz to over 4Khz. This tunes the Model C squarely in the most sensitive bands of the human hearing range. Below this range the device becomes a bit of an absorber. Above this range and the performance becomes more effective at intervals, which can be seen in the areas of wide diffusion at 6KHz – 18 KHz. These repeating zones are common in “stepped” quadratic designs. Due to the heights of the well being at specific intervals, the intervals repeat at octaves of their effective bands.
The Model D doesn’t have the same stepping. The spline interpolation and the random Boolean shifts smooth the transition from one quadratic height to the next, and the MLS sequence causes a bit of a high-pass filter pushing the start of the primary range to around 2KHz – which is a little higher than the Model C. The main difference is that once the Model D starts it’s range it diffuses everything up to and over 20KHz without the banding that can happen in other quadratic designs.
Another difference in symmetry.
The ArtDiffusor® Model C is a fairly symmetric design, but it’s 45° angle pushes that symmetry along the diagonal (corner to corner) across the unit. The asymmetry is subtle but allows for enough variation to account for any “lobing” issues that can occur in more simple geometric devices The 10° block faces being at varied orientations is key to increasing the spatial directivity over the older “flat-faced” Quadratics. This was a very novel design when it was first introduced, and those benefits are crucial to the longevity of the Model C’s reign – It just works. It’s predictable and musical… and that’s why it’s here to stay!
The ArtDiffusor® Model D is a completely different animal from the Model C when it comes to symmetry… as a matter of fact… there isn’t really much on it that is symmetric! The Model D was designed as a departure from symmetry. Focusing on the mid to high frequencies, which are very specular, the organic geometry creates an asymmetric reflection pattern. This pattern can be used to steer the sound into a wider field.. and that profile changes with the wavelength of the sound that hits it. This steering ability and the wide frequency range has made the Model D a favorite in mixing and mastering environments, where they can get smooth performance through the entire frequency spectrum.
How these differences benefit everyone.
We have stated before that there isn’t really a one-size-fits-all solution in acoustics. Many environments will use various treatments to achieve their desired goals. You will often have different devices to address different problems, in different frequencies, in different locations, in the same space. Bass traps for controlling the lows. Absorption to reduce gross energy across the board. Large geometric surfaces to break up parallel reflections and steer the projection of sources. Mid range diffusers to create clarity to the sources and reduce artifacts. High frequency diffusers to reduce flutter and add a feeling of envelopment and airiness in the space. These devices all have their place – from the smaller listening rooms, to critical listening environments, and large multifunction spaces and venues.
It is also worth noting that these two devices have a very different aesthetic visually. The classic blocks of the Model C have become a signature look for quality sound environments, and people recognize them as they would classic geometric pyramids and barrels. The Model D aesthetic provides a visual accent that people take advantage of to set their space apart from others. The undulating, asymmetric pattern changes drastically when you rotate the individual units in the array. This allows for not only varied acoustic performance, but also a unique visual possibilities – with numerous variations.
The ArtDiffusor® Model C and Model D are two tools that are used to craft ideal listening environments around the world… and in those roles they are indeed Similar, Yet Different.
Similar, yet different: Quadratic vs. Itself?
Posted by Acoustics First in Diffusion, Product Applications, Products on July 6, 2023
For this installment of “Similar, yet different,” we will take a classic welled-quadratic sound diffuser, The Model Q, and compare its performance to itself – only installed backwards!
Taking “similar” to the extreme in this case, we are testing the difference in performance of a 1-dimensional, welled-quadratic diffuser installed in the standard welled configuration, and then installed reversed – with the sound impeding on the back side of the wells. For a bit of history, the Classic Quadratic Diffuser (or Schroeder diffuser) was designed with a grid separating the reflectors – creating wells of different depths proportional to the remainders of n2 (mod N). This design has some interesting facets.
- They are inherently symmetric if left in the original sequence.
- They are periodic (i.e. they repeat.)
- The discrete Fourier transform of the exponentiated sequence has constant magnitude.
The design principal is simple if you tear apart the math, and it’s simply wells that have a different effect on different frequencies, depending on the geometry of the wells. The Model Q is an advanced 1D-Quadratic with angled well-bottoms, which assist in smoothing out the performance and widening the 1D polar radiation. So if this design is relying on the wells to be effective, why would we reverse it?
An acoustically diffuse environment develops due to many factors, and while the frequency focus of the wells is useful, there are other scenarios where different methods may be preferred. If the geometry of the elements were flipped around, you would get the same (albeit reversed) ratio of distance, but you lose the containment and channeling that the wells provide. This imparts a diffraction on the unrestrained elements. This also allows for a different interaction between the elements, as the face of the unit is no longer planar.
Let’s look at the effect this has on the performance of the device at some different frequencies – starting low and moving up…
First, we will look at the 1150Hz performance of the devices… standard welled-install on the left, reversed on the right.
At 1150Hz, there is a little variation in the performance. Both are front focused, with a strong 1D horizontal polar response, but they are not identical. The welled-design (left) shows a broad frontal response, while the reversed design has a smoother vertical response, sharper front lobes, and stronger side performance. Overall, this difference is relatively small at this frequency.
Now, we will look at 2300Hz.
Again, we have two similar looking balloons, but there seems to be a bit more variation. The welled-design (left) shows a smoother 1D pattern in the front as the wells release sound within the same plane – at the front face of the wells. On the right you will notice sharper and more discreet lobes, but you will also notice that it has wider horizontal performance again, as it isn’t as front focused due to its free standing elements. The vertical performance is also a bit different – the welled design is broad and smoother vertically, while the reversed installation shows sharp lobes again.
Step up to 2800Hz, and we see some more drastic differences.
The performance of the standard welled-install (left) stays smooth and front-focused, while the lobes of the reversed install (right) have become even more distinct. Interestingly, the side lobes are even larger, showing an even wider polar pattern than before. These two instances show a marked difference between the smooth front-focused wells and the wide sharp scattering of the unrestrained elements. These two configurations are both very different, but are still both very effective at helping to disperse the incoming energy. Remember that the room develops diffusion through sound travelling in many different directions – these are not simple reflectors sending the specular energy in a single direction.
Now at 3650Hz we see a shift toward the reverse installation.
At around 4K the welled-installation (left) begins to move back front and center. It’s primary method of diffusion uses the wells to channel the energy, and at higher frequencies sound becomes much more directional. This directionality is used to create a temporal shift in the sound, as the reflections will occur out of phase from the source, and controlling that reflection is paramount to tuning this method of diffusion. However, as stated before, there are other mechanisms contribute to diffusion. The unrestrained elements on the right balloon, have hit their stride and still maintain a wide 1D polar pattern. The lobes are still sharp, showing the interaction of the elements with sound. This installation is showing the strength of its spatial dispersion, which will send acoustic energy in more directions and use the travel through the space to create a diffuse environment. It loses some of the frequency tuning of the wells, but makes up for it in the wide polar pattern.
Now for the super high frequencies – we jump straight to 10Khz.
This final set shows two diffusers pushed to the limits. The welled-installation (left) is a very narrow focused beam now. You will note that it has some variance due to the interactions with the walls of the wells but all of its work is done through phase shifting at this point. In contrast, the exposed elements (right) are still allowing for a bit of diffraction to occur, and the angled faces are still allowing for a bit of spatial redirection. Also note that these polar patterns were generated with a sound source directly in front of the device at 0° incidence, and the exposed elements would offer more exposure to its surface area than a welled design at wider angles of incidence.
In summary…
Diffusion develops using many different variables, including the untreated walls of the space. While both of these installations are functioning in nearly identical frequency ranges due to their geometry, the mechanisms which they work are slightly different and have different strengths. The welled-design (in classic temporal Schroeder configuration) uses the wells to channel sound and address the frequencies in a tuned and controlled fashion. By simply flipping the device around, however, you change its performance from a controlled time shift, to an unrestrained spatial redirector, which imparts time shift through dispersion, diffraction, and distance travelled – further reducing intensity by having a wide 1D diffusion polar pattern. Both have scenarios which one configuration would be preferable over the other, making the Model Q diffuser a very versatile device.
Both configurations are literally two sides of the same coin… they work in different ways, over the same frequencies, providing results – no matter how you flip them.
John Bullard Live Room – Tuning a Live Room for Classical Banjo
Posted by Acoustics First in Absorption, Customer Feedback, Diffusion, HOW TO, Music Tracking Room, Product Applications, Products, Recording Facilities on May 3, 2023
When you think of classical music; what instruments come to mind? Piano? Violin? Cello? …What about Banjo?
In the summer of 2022, classical banjoist John Bullard reached out to Acoustics First for assistance with his newly renovated home-studio. John is one of a select group of classical musicians aiming to showcase the versatility of this uniquely American instrument. The banjo, with John’s expertise, lends a very distinct, melancholy sound to contemporary and traditional compositions.
Having recorded a number of albums already, John knew he wanted his live room to be catered specifically to tracking solo, classical banjo as well as small acoustic ensembles. Acoustics First analyzed John’s live room and came up with a treatment design that would achieve an “ideal-as-possible” acoustic environment for recording classical instruments.
The largely reflective live room had walls comprised of unfinished, reclaimed wood planks over plywood, a drywall ceiling, stone fireplace and a polished concrete floor. The parallel, hard surfaces contributed to a poor tracking environment; with standing waves and “flutter” echoes adding unwanted coloration to recordings, inhibiting music definition.
Spaces used for rehearsing and recording classical music often benefit from elevated levels of reverberation, which add a sense of warmth and ambience to acoustic music. Although the reverb in John’s untreated room was only slightly excessive when measured, it was far from “diffuse”, with the majority of energy coming from early reflections.
The primary challenge in the live room was to address the early specular reflections and standing waves without taking too much “life” out of the room. To achieve this delicate balance, wide band diffusion was recommended as the primary ceiling and wall treatment with selective sound absorptive treatment with fabric-wrapped Sonora® panels.
Double Duty Diffusers™ and Aeolian® sound diffusers were recommended as they would also provide some much needed low-frequency absorption in addition to broadband diffusion.
After the treatments were installed, John got right to work on experimenting…
“…ready to start doing extensive test recordings to locate the best spot and rug configuration for solo banjo… It sounds really good to my ear – now to see how the microphones hear it!”
John Bullard
Please check out John Bullard’s music!! – https://www.johnbullard.com/
NWAA Labs goes nuclear in Stereophile
Posted by Acoustics First in Articles, Company Information, Diffusion, Mentions on July 29, 2022
Ron Sauro of NWAA Labs talks about his massive test facility, speaker measurement, sound diffusion, and more in this article in the August 2022 edition of Stereophile Magazine.
In the article, there is mention of the advances that Jim DeGrandis and Acoustics First® have made in the understanding of diffusion, the developing standards for testing in the ASTM, and their published research into modelling/simulations for refining new acoustic materials.
For more information about this edition, and other editions of Stereophile, visit them at https://www.stereophile.com/
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