Speech Intelligibility and Acoustics Comfort

Architectural acoustics is the science and engineering of achieving a good sound within a building and may be considered a branch of acoustical engineering.

According to Duncan Templeton, Acoustics in the “Built Environment: Advice for the Design Team”, architectural acoustics can be about achieving good speech intelligibility in a theatre, restaurant or railway station, enhancing the quality of music in a concert hall or recording studio, or suppressing noise to make offices and homes more productive and pleasant places to work and live in.

There are many science-based areas in architectural and engineering.  Four primary areas stand out:

  1. Building skin envelope - science analyzes noise transmission from building exterior envelope to interior and vice versa.  Materials involved are typically: walls, eaves, roofs, doors, and windows.  A primary form of measurement for the effectiveness of these materials is STC or sound transmission class.
  2. Building Services Noise Control is the science of controlling noises produced by: HAVC, Elevators, Generators, and any other infrastructure component that emits sound.
  3. Interior space noise control - science of limiting and/or controlling noise transmission from one building space to another to ensure space functionality and speech privacy.  
  4. Interior space acoustics - the science of controlling a room's surfaces based on sound absorbing and reflecting properties. Excessive reverberation time, which can be calculated, can lead to poor speech intelligibility.  Typical materials or devices used are wall coverings, ceiling materials, panels and the effectiveness of such materials is NRC or Noise Reduction Coefficient.

Now, let’s narrow our conversation to interior space acoustics.  There are several considerations when optimizing for speech and productivity in a space.  We have grouped considerations into four buckets:

The first consideration is really about understanding the space and how much square footage of acoustic solution coverage you may need to solve the acoustics of the space.  The primary solve is for reverberation.  Reverberation is the overall effect of reflected sound and the time required for reflected sound to become inaudible. Short reverberation times are good for speech intelligibility, leading to better understanding and comprehension.

There are two key questions to ask:

Do I have a problem?

How many square feet of acoustic treatment do I need?

To answer the first question, you can simply experience an existing room and determine if you have echoes and poor speech intelligibility.  Or you can measure reverberation time for an existing space or a designed space (before construction).

RT or reverberation time is measured in seconds and represents how long it takes for sound to “dissipate”.  Typically, the bigger the room and harder the surfaces...the longer the reverberation time.  Rooms with longer than 0.5 -1.5 second reverberation time (depending on type of space) is the result of sound bouncing around and making speech difficult to understand.

You can calculate the reverberation time using the Sabins Formula created by Wallace Clement Sabine. This equation is based on the volume of the space and the total amount of absorption within a space. The total amount of absorption within a space is referred to as sabins. It is important to note that the absorption and surface area must be considered for every material within a space to calculate sabins.  The equation states: RT60=.05*V/Sa, where RT60 is the reverberation time, or more specifically, the time it takes for the reverberation to dissipate below a certain level. 0.05 is a constant derived by Professor Sabin, V is the Volume of the space, and Sa is the Acoustical Absorption of the space, which is simply the Surface Area multiplied by the Acoustical Coefficient of each surface.

The second question is important to ask and understand the type of treatment and how much coverage you need.  Coverage is typically calculated as square footage of the acoustic material or product needed.  The results dramatically impact your ability to apply the solution and the investment it takes.

At Sonus, we use a simple calculation and adjust the variable based on several elements such as surface types, furniture, use of space, and how much dedicated space is occupied.  The calculation is:

Cubic feet (L x W x H) x 5% where 5% is a variable that is adjusted up or down.

Our acoustic consultants use a factor matrix to adjust this number up or down and are able to provide you with a recommended square footage.  Six percent is simply a good starting point.  With this calculation you can determine just the right amount of acoustical coverage you'll need to effectively treat your space. We typically provide ranges with minimum to recommended. Minimum coverage will provide adequate acoustical performance, while recommended coverage will provide significantly better performance than the minimum.

OK, so now we know how we are using the space, what kind of surfaces, how much cubic feet, the RT, and the recommended square footage of acoustic treatment we need.  What else must we consider?

Performance of acoustic products is really important.  Both in terms of NRC and fire ratings.  They can be very different depending on materials used.  For example, our products achieve .80-1.05 NRC and are always ASTM 84 Class A fire rated materials.  Effectiveness and safety are very important to us.

Sustainability performance may also be very important to your firm.  Does the sustainability program and materials used align with my firm’s program?  Our advice is to take the time to read the sustainability program of prospective vendors and suppliers.  Here at Sonus, we practice “Take Less, make right, and Re-use”. This program pushes us to do the right thing by each other and our products enabling you to achieve LEED certifications and support the demands of your clients.

Appearance becomes the next big consideration.  Here is where you align an acoustical treatment to the design of your space.  Knowing a supplier and having options with unique and modern solutions ease this burden.  Wood veneers are the most popular right now, but how they are built and their sound performance is not equal.  Please make sure you do your homework when choosing wood covered acoustic products.  They must have three core features or capabilities:  perforated veneer to allow sound to enter (perforations must be “clean”), a substrate that absorbs and dissipates sound, and cost of product.  

Finding unique and modern products can take some time. Sonus offers a patented multi-dimensional pattern that serves as a great acoustic treatment and has received many accolades for its aesthetic qualities in a space.  Either way, your space deserves something special and not found everywhere else.  Beautiful designs and variations of effective treatments are on the rise.

The final consideration is installation. It can be an afterthought, but don’t let this happen to you.  Installation can be very expensive if the acoustic treatment is not easy to handle and install.  Finding products that are simple in nature, have flexible hardware options that are not expensive, and a trusted installer that is trained to install acoustic treatments is important.  Do you homework upfront, specify your recommendation, and explain to the General Contractor (GC) the ‘why’ behind the chosen product.  Costs are important to a GC, especially having multiple change controls and budget overruns to address.

Open welcoming designs and beautiful hard surfaces are hallmarks of modern interior architecture.  Architectural acoustics can be a challenge, but great solutions exist if you know where to look and take the time to do your homework.  Leverage the four considerations above, prioritize that which is important to you, get samples, and challenge your vendor or supplier. The right solutions will present themselves!

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