Posts Tagged sonora
Here’s a nice example of a 3D rendering vs. real life. This 3D model was created by our acoustic analyst, Cameron Girard, for one of our church clients. We think the final results turned out fantastic!
Sonora® Acoustical Wall Panels are always a great choice where excessive reverb and diminished speech intelligibility are an issue.
For anyone new to the world of acoustics, there is a multitude of terms, coefficients and numbers that are thrown around. This flood of information can seem intimidating, especially to beginners. In this series, acoustician Cameron Girard of Acoustics First® hopes to help you distinguish between what’s useful and what’s not.
Part 1: Acoustic Terminology – Sound Absorption vs Sound Isolation
In order to make informed decisions about acoustical treatment, it is vital to know the difference between materials that are meant to absorb sound within a room and materials that are meant to block sound from leaving or entering it. In an overly reverberant auditorium, absorptive treatment is needed to reduce echoes and improve speech intelligibility. If the problem is sound passing in between spaces, like offices or apartments, then isolation treatment is required. These are two separate acoustic issues which require separate solutions.
In both scenarios, it is important to know which data is relevant and helpful. Also, given sheer volume of information available on the internet, it is perhaps unavoidable that some info will be incomplete or simply incorrect. It should not be assumed that something which sounds technical is, in fact, backed up by proper testing.
Terms for Sound Absorption
We recently encountered an acoustical ceiling tile which was said to “absorb 50% of sound”. On the surface this sounds like an extremely efficient product. However, let’s delve in closer and decipher what is actually usable information, and what is just marketing.
When sound waves meet a room surface such as a wall, ceiling or floor, some of the sound energy is reflected back into the room and the rest is considered to be “absorbed”. The absorbed sound energy has not vanished, it’s actually been converted into kinetic (vibration of a solid material) and thermal energy (heat due to friction within a porous material) or has simply passed right through the material (transmission). The more surface area a certain material has the better absorber it will likely be. “Soft” materials, like heavy blankets, fabric and fiberglass, have loads of nooks and crannies, which sound tries to “fill”. These porous materials are great for reducing reverberation within a room, but will only marginally reduce the sound that leaves it (but more on that later).
When comparing sound absorbing products, there is a particular set of terms you should look for: The Sound Absorption Coefficient (SAC) and Noise Reduction Coefficient (NRC). These are used to specify the fraction of incident sound that a material absorbs per 1’x1’ area. An NRC of 1.0 indicates perfect absorption (an open 1’x1’ window) and a value of 0.0 represents perfect reflection (polished concrete has an NRC of .02).
To measure sound absorption, a large sample of the material is placed in a reverberation room with all other surfaces being hard and reflective. The time it takes a test sound signal to decay by 60dB (rough point of inaudibility) after the source of sound is stopped is measured first with the sample in the room and again with the room empty. The difference in decay time defines the efficiency of the absorbing material and thus the absorption coefficients. Large spaces with low-NRC materials (tile, drywall, etc.) have longer reverberation times, while small rooms furnished with high-NRC materials sound much more “dead”.
Clearly, a single 2’x2’ ceiling tile is not going to reduce the reverberation in a real-world space by 50%. So is the above claim false? Not exactly… The ceiling panels do have an NRC rating of .50, so the tile does absorb 50% of incident sound. However, one might assume a much more drastic improvement based on the “50%” claim. In reality you’d need a large square footage of these ceiling tiles to cut the amount of total reflected sound in half. Always be sure to check the NRC number!
Terms for Sound Isolation
Our customers often call with issues related to neighbor noise or office-to-office privacy and are looking for “sound proofing” treatment. Unfortunately, many do not realize that simply installing acoustic foam or fiberglass panels will not appreciably reduce the level noise entering and leaving their space. These absorptive materials are great at reducing unwanted reflections within a room because they are porous and air/sound energy can flow through them. That being said, they are generally poor sound barriers for this exact reason. They will help to reduce noise buildup in a room and improve the ‘acoustics’, but will do very little to “block” sound coming in or out.
Sound is like water; it will “flow” into an adjacent space if everything isn’t sealed up. Materials that are air tight and heavy, like our BlockAid® sound barrier, provide the most relief of air-born sound transmission. Continuous coverage of floors/ceilings or walls is necessary to ensure that sound doesn’t ‘flank’ around these barriers. Multiple layers of varying materials, the use of resilient clips or channels, and additional walls will provide even more control. For a demonstration of how different materials affect sound isolation, check out our video http://acousticsfirst.com/educational-videos-the-barrier-and-the-bell.htm
Like NRC for sound absorption, there is also a laboratory tested figure that can be used to compare the sound “blocking” properties of acoustic barriers and wall constructions: Transmission Loss (TL) and Sound Transmission Class (STC). These describe how much air-born sound is attenuated through a given material.
In the lab, the material to be tested is mounted over an opening between two completely separated rooms, one with a speaker (source) and the other with a microphone (receiver). Save for the open “window”, these rooms are completely isolated with thick and massive walls, so virtually all the sound energy transmitted between rooms will be through the test specimen. The difference between sound levels in the source room and the receiving room is the transmission loss (TL). The TL is measured at multiple frequencies, which is fitted to a Sound Transmission Class (STC) “curve” at speech frequencies (125Hz-4kHz). The STC of the material is the TL value of the fitted curve at 500 Hz. For example, a material with an STC of 27 typically “blocks” 27dB of sound. Keep in mind though, the STC’s of materials do not add up linearly; in other words, adding a material with an STC of 27 to an existing wall with an STC 45 will not result in an STC of 72.
As always, Acoustics First is here answer questions and help you find the best solutions.
Ever wonder what gives us a sense of space? Obviously, our eyes visually tell us what’s going on, but there are other senses that contribute. Peak your head into a dark front hall closet, and even without seeing much, you can “feel” the close proximity of the walls and perhaps even the presence of the coats. Walk in to New York’s Grand Central Station, and you are confronted by a completely different sensation. Close your eyes, and the raucous environment tells you are in a large room with a lofty ceiling. Often times we take for granted the relationship that sound has to our spatial perception.
This sonic “sense of space” can be generally attributed to the room’s reverberation qualities. In simple terms, reverberation is the sound energy that remains in the listening environment as a result of lingering reflections. Reverberation time (RT or RT60) quantifies how quickly an impulse sound decays in a space. RT60 is how quickly the amplitude (volume) of short exciting signal decreases by 60dB in a large room. Reverberation time is dependent upon the volume and surface materials of a given room. Large spaces with hard materials (tile, drywall, etc.) like Grand Central Station have longer reverberation times, while small rooms furnished with “softer” materials, like the coat closet, sound much more “dead”.
Excessive reverberation is one of the most common acoustic issues that we encounter on a daily basis. As you may have experienced at some point, it’s difficult to understand what is being said when reflections from old information cover up what is newly spoken. In spaces where speech intelligibility is paramount, like classrooms or conference rooms, a short reverberation time (under 1 second) should be targeted.
That said, sometimes a long reverberation time is desirable. In spaces like cathedrals and orchestral halls, reverberation helps create ambience for the audience by sustaining musical notes, while allowing choirs and orchestras to blend more easily. These spaces may lack a sound system, and instead utilize the room to propagate sound. Rock venues, on the other hand, have amplified instruments, so a medium-short reverb time is needed to ensure that the music won’t become “muddy” and difficult to perform and enjoy.
There are a number of questions that an acoustician must ask when recommending appropriate treatment. These questions include, but are not limited to: Is there live music in this room? What kind of music is being performed? Is speech intelligibly important? What’s the audience size and where are they in relation to the sound source? So, the ideal amount of reverberation in a space is wholly dependent on the use of the space.
Listed below are the ranges of “ideal” reverberation times at mid-frequency (average of 500 and 1000 Hz) for a variety of rooms. The numbers are derived from David Eagan’s Architectural Acoustics (New York: McGraw-Hill, 1988), in which he breaks down rooms into Speech, Music and Speech/Music spaces. We hope you find this helpful.
Optimum Reverberation Times (T60)
Recording and Broadcasting Studio – .3 to .7 seconds
Classroom (elementary size) – .6 to .8 seconds
Conference/Lecture Room – .6 to 1.1 seconds
Intimate Drama – .9 to 1.1s
“Speech & Music” Rooms
Cinema – .8 to 1.2 seconds
Small Theaters – 1.2 to 1.4 seconds
Multi-Purpose Auditoriums – 1.5 to 1.8 seconds
Worship Spaces – 1.4 (Churches) to 2+ seconds (Cathedrals)
Dance Clubs and Rock Venues (w/ Sound System) – 1 to 1.2 seconds
Semi classical Concerts/Chorus (w/ Sound System) – 1.2 to 1.6 seconds
Symphonic Concerts (Classical) – 1.6 to 2.3 seconds
Liturgical (Organ/Chorus) – 2+ seconds
Contact Acoustics First to have our acousticians help you find the ideal reverb time for your space.
Setting the Stage for Acoustics First
by Nick Colleran
Originally Published in Productions Magazine Sept/Oct 2012 issue.
Early acoustical theaters were just that – acoustic. The good news and the bad news are usually the same news when a venue sounds incredibly good at the start. An auditorium that projects natural sound well is most often over-powered and overloaded by modern musical performances and the line array sound systems that reinforce them. That’s the bad news in the good news. This type of good room will need to be modified to handle high-powered sound from modern music performances while keeping its sound-enhancing properties. All efforts can be directed into the “how” of doing the job when everyone has heard the “why” it needs to be done.
Re-engineering reinforcement – Modifications for “loud”
The hard back wall of the stage is a significant source for monitor splash-back into the performers’ microphones, reducing gain-before-feedback and enhancing opportunities for system squeals. This is in addition to promoting timing confusion due to slap-back that is usually out of sync with the music. This disturbance and annoyance can be overcome by using materials from the province of industrial noise control. A factory finish, that is a finish for the factory, is also both “roadie-proof” and “on-the-road” compatible. Yes, you can take it with you. This allows one set of materials to follow the performances from one venue to the next.
Curtain call – Reflecting on the stage
The industrial curtains called QFM for Quilted Fiberglass Materials accomplish multiple functions:
Bass control from an internal limp mass, Absorption from quilted fiberglass, and Resistance to abuse from a tough vinyl cover.
The covering is thin enough to avoid reduced effectiveness at all but the highest frequencies and strong enough to withstand stage and road wear. Hanging mass (at one time plywood) with an absorptive cover is a long-standing studio technique to control low frequencies. The newer, non-rigid barriers allow a curtain configuration that is invisible to the audience, while providing a clean sound source for the both the performers and the listeners.
Overhead, not overheard – Many are baffled
Above the stage, there is almost always a large cavity designed for lights and to accommodate rigging. This space can act as an unintended echo chamber. Being out of harms way, the area allows for a lighter and less costly sound treatment with acoustical baffles. Besides the obvious requirement that they work acoustically, they need only to be invisible (usually black) and pass the proper fire code. Acoustically, they have about twice the exposed sound absorbing surface as a wall-mounted panel, by hanging in free space. It’s more surface, less reverberation, out-of-sight and within budget. They are light enough and small enough to travel well if strung in a way that allows easy removal for relocation, such as threaded onto aircraft cable and hung in a line from side-to-side. Adding a fabric finish to the baffles, produces a more decorative product, suitable to the audience side of the auditorium when a more permanent ceiling solution is required.
Stage One – Separating Sound
Stage one of acoustical control often is the stage. Both on-stage and in-studio sound isolation usually begin with structure borne sound traveling through the floor. It is always wise to implement isolation between instruments from the beginning, where it is a “cheap” fix rather a costly solution. This can be accomplished by floating the stage surface, and doing it in several separate sections. As noted previously with the hanging back of stage curtains, mass matters. Mass can come from many different materials whose properties are heavy and dense. They can be common materials such as gypsum or sand as well as more acoustically specific items like sheet lead or mass loaded vinyl barrier. (BlockAid® is a readily available example.) Added mass damps the damage of vibration and reduces ringing resonance.
Once the stage goes “thud” when hit due to its added mass rather than a cartoonish “boing”, it is time to handle the hollow space beneath the stage and fill it with fluffy stuff. This can be whatever attic insulation that is on sale at the local home improvement store. It need only trap the air to prevent its becoming a big bass drum when stomped upon.
Way back in the days of Disco (or Disco daze), complications arose in the studio from the required “lead-foot” kick drum getting into the acoustical piano by traveling through the studio floor as vibration and transmitted up the piano legs. Although studio floors are usually isolated from other rooms, they can still connect within a room. This problem was solved by floating the drum booth independent of the common recording studio floor. At that time this author’s studio went so far as to construct a sand-filled floor set on nine truck tires. The sand provided mass and inertia while the tires created de-coupling from the common structure. Today it is accomplished with high mass materials and off-the-shelf vibration pads, at about the same cost. Independent and transportable compact structures can be created for the individual instruments and be moved with very little heavy lifting.
After stage resonance is reduced by adding a layer of mass loaded vinyl to its surface and the cavity below is stuffed with fiberglass to prevent its ringing or singing along with the music, a second stage may be layered on top of the original and floated on ribbed neoprene pads every 12 inches along standard, 16” on-center bracing. This keeps the guitar amp’s sound out of the vocal microphone stand, bass drum out of the piano legs, and so on, to create increased clarity and improved separation in the live performance.
Islands in the stage will stop transmission transit and are relatively cheap to build into the plan. Separate sections for drums, piano, singer, bassist and guitar amplifier can be buffered with half-inch strips of flexible resilient neoprene without being seen. Much like vocals can be modulated when source through the same speaker as the bass, surfing the bass wave in the stage floor can also add an undesirable tremolo (or vibrato) effect to voice or other wind instrument. (This effect can be demonstrated by auditioning a vocal through the bass player’s amplifier while playing.)
Dome details – Round and around
One technique used in early acoustical performance theaters was the overhead dome. This feature captured wasted sound energy and focused it back to the audience to reinforce sonic energy in areas where it had diminished with distance from the source. With new systems the level is electronically reinforced, not needing further enhancement, which confuses rather than clarifies. In addition, the dome creates a sonic racetrack where the sound moves around the edge in a swirling motion. Anyone who has been in a domed facility during a thunderstorm has heard how sound travels around the perimeter. The RCA dome in Indianapolis provided a good example to CEDIA attendees a few years ago . This phenomenon of raceway runaway can be abated with acoustical “speed bumps” of Melamine foam which easily bends to conform to curves*, keeping the look while truncating the travel of the fast moving sound waves. In this case being unfocused is a desirable trait.
To reduce sound getting into the dome from the line arrays and the like, hanging baffles can be placed around the front half of the perimeter of the ellipse. These may be fabric covered to blend with the décor of the audience area and made from two-inch, seven pound per cubic foot density acoustical fiberglass to extend its absorption range. Being hanging baffles they do not permanently change the original architecture, where that is a concern.
(Don’t Look) Behind the curtain – Unseen, Unheard
When acoustical treatments must be essentially permanent, high efficiency at low cost can be achieved with utility finishes that can be field-cut to fit spaces in cavities behind auditorium side curtains. Factory fit panels require precise measurements to install within curves. Field cutting skips this step as it is, by definition being, done in real time to as-built measurements rather than made to out-of-date plans. Savings derived from the unseen, utilitarian treatments can be applied to upscale finishes for panels in plain sight.
Another common problem for an older theater in the modern world is sound returning from the balcony face. These are usually concave surfaces that not only send sound back but focus it for feedback as well. Convex curves such as polycylindrical “barrel shapes or semi-reflective half-round, hollow traps can control concave characteristics when interspersed with thicker, flat acoustical wall panels to achieve a combined “Flat” curve.
Definition by Diffusion
Sound intensity can be reduced by the decision to destroy or diffuse. Absorption is the destructive choice, eliminating the problem by eliminating the sound. Care needs to be taken to use only what is necessary and no more.
The other alternative is to spread the sound over a larger area to reduce intensity. This can be likened to spreading peanut butter on bread – it becomes easier to swallow although it is the same quantity as the original lump from the jar. With diffusion, a little goes long way. A single barrel shaped diffuser can clear up the cacophony of a board room without the deadness of absorption required for the same amount sound clarification.
Check back After Launch
With venue retrofits, some tweaks can be made after opening. Covering all walls before there is an evaluation with performers and audience, is not always a good idea. While it may be theoretically possible to model and predict acoustical performance, it can be more economical and efficient to get the room in a reasonable range and polish to the real world result. An informed conclusion, upon hearing the room in use, can produce an optimum result.
*Contrary to popular belief, acoustical foam can be painted to match décor without affecting its performance. (The author has a copy of the independent lab report comparing painted to unpainted natural. Painted measured better, but not significantly.)
Nick Colleran is past-president of SPARS (Society of Professional Audio Recording Services), past president of the VPSA (Virginia Productions Services Association), a former recording artist and audio engineer.
Starting in 1978, his company began supplying unique acoustical materials. Nick now leads a “quiet life” as a principal of Acoustics First Corporation. The company holds patents for several innovative acoustical products.
Acoustics First designs, manufactures and distributes products to control sound and eliminate noise for commercial, residential and industrial uses.
Vib-X™ vibration pads | BlockAid® mass loaded vinyl noise barrier | Stratiquilt™ quilted industrial blankets | Cloudscape® Baffles hanging acoustical baffles | Sonora® acoustical wall and ceiling panels | Select Sound™ black fiberglass board | Geometrix™ half-round broadband absorbers
Download of article available here: http://acousticsfirst.com/article-setting-the-stage-for-acoustics-first-productions-mag.htm
Acoustics First Corporation supplies acoustical panels and soundproofing materials to control sound and eliminate noise in commercial, residential, government, and institutional applications worldwide. Products include the patented Art Diffusor®, sound absorbers, noise barriers, acoustical fabrics and accessories. Acoustics First® products are sold for O.E.M applications, direct, and through dealers. For more information on acoustical materials and their application, please visit www.AcousticsFirst.com or call Toll Free 1-888-765-2900 (US & Canada).
Originally published by Home Toys.