Neil Diamond wrote and sang a song entitled “Beautiful Noise”. To many sound or noise is beautiful, peaceful, calming and enjoyable. To others it is annoying, disruptive, bothersome, and intrusive and something to be eliminated or controlled. Whether it is one or the other depends on the location & circumstances but in the business of Operable Partitions it is always the latter: something to be contained and controlled, beautiful or not. Next to visual separation the most specified and requested feature of an Operable Partition is “sound” and how to minimize it’s transference through or around a partition The purpose of this and subsequent papers is to examine “sound”, what it is and how can an operable partition and the surrounding construction participate in it’s successful containment within a defined space.
Let me say at the outset, there is no operable partition that is “soundproof”. When I say “soundproof” I mean that the partition will stop all sound from being transferred from one side to the other. It is difficult to make a permanent wall “soundproof; it is impossible to make a “wall that moves” soundproof. Hopefully the following will help to explain.
What is sound?
Sound, in our case, is the movement of generated energy (the sound) through the air (the medium) and then received by a source (an ear). Take away any of these conditions and there is no sound. For example there is no sound in space because there is no air.
An operable partition is designed and installed to prevent as much as possible the transmission of sound from one side of the wall to the other. In order to accomplish this, the partition manufacturer has to be concerned about and address three sound components.
Frequency (measured in Hertz [Hz] or “cycles per second”) which is the rate of vibration that determines the PITCH of the sound: high pitch sounds (a whistle) have high frequencies, short wave lengths, and low pitch sounds (a drum) have low frequencies with long wave lengths. The human ear is most sensitive in the range of 100 Hz to 5000 Hz which is where the majority of music, speech and other important sounds are found.
Amplitude (measured in decibels [dB) is the magnitude (size) of the vibration or change in air pressure which determines how loud the sound is. Amplitude or LOUDNESS ranges from the threshold of hearing (0 dB) to the threshold of pain (140 dB).
Duration is the TIME the sound lasts as measured in seconds. The duration may be an indication of how long the source is vibrating or how long the sound is echoing within the defined space or both.
With partitions we are most concerned about what it is like on the “opposite side”: the side of the partition opposite of the sound source. Essentially you do not want to hear anything that is occurring on the “source side” on the “opposite side”.
The partition cannot address the problem of sound frequency but it can control, to a limited extent, amplitude and duration. Remember that sound is a mumble jumble of different frequencies (think of an orchestra). When this cacophony of noise is directed towards a partition three circumstances will occur:
- Some of the noise is stopped & reflected: a barrier.
- Some is absorbed by the partition: an absorber.
- Some goes through (typically low frequency sound) or around the partition (a flanking path) and is transmitted to the other side.
Panel Design
The design of a partition panel in order to minimize through transference involves several considerations including weight, cost & ease of movement. The most common design principles are:
Mass: Up to a certain point the more mass the better the partition will function as a barrier. Mass impedes the transmission of sound simply because it is harder for the sound waves to shake (vibrate) a heavier object than one that is lighter. The problem is that once you get to a certain weight additional massive changes result in only small changes in performance. And since we are dealing with an “operable” partition, too much weight is not acceptable.
Isolation of the panel components: Where the panel components touch each other (skin to frame for example) a sound transmission path is created and component vibration results. Isolating panel components from one another as much as possible as well as providing air cavities within the panel impedes the transmission of sound.
Absorption: Install insulation in the panel cavity. The insulation will bounce any intrusive sound energy around, converting the energy to heat and thus destroying a good part of it. However insulation is poor at very low frequencies (drums, tubas etc) as these wave lengths are very long and pass through easily.
Resonance: resonance is vibration. An object that is very rigid or tight (think about a snare drum) will vibrate. Manufacturing a partition that is “acoustically limp” (damp the resonance) reduces the resonance through the partition (loosen the skin on the snare drum) and less sound is transmitted by means of panel vibration.
In summary for a “panel” to function as a “sound isolator” it must be a “barrier” and an “insulator” and utilize all 4 of the design principles noted above. Moderco uses all of these principles in the design and manufacture of its panels.
Perimeter Seal Design and Options
But so far all we have is a panel. What are we going to do with the edges? The panel perimeter? A basic rule of sound isolation is paying attention to perimeter “seal quality” If the panels are not properly & adequately “sealed” into the opening then all is lost and a high level of performance cannot be attained. So let’s look at panel perimeter seal options.
Vertical seals or Astragals; The astragal serves two purposes: to align the panels ensuring that they fit together properly and snug and to prevent as much as possible the transmission of sound between the panels. Terms such as “deep nesting” and “dove tail design” are often used to describe the shape. Astragals are designed to provide a circuitous route of travel for sound as the energy is rapidly dissipated in every bend & curve. In addition manufacturers will put in small finger sweeps, usually 4, in each astragal to block sound.
Top seals: Fixed (sweeps) or retractable (mechanical or automatic) are the two options. Fixed usually consist of two “finger” sweeps and a “bulb” seal on each side of the panel. The sweeps are there to aid in sound control but also to hide the internal bulb seal. The bulb seal is flexible and compresses itself to the track along its entire length providing a tight acoustical seal. In addition the finger sweeps often overlap at the top of each panel blocking sound transference between panels. The other option is a retractable seal that when disengaged is enclosed within the panel itself. They typically have a maximum 1” movement.
Base seals: as for top seals except fixed are rarely used due to difficulty in moving panels because of constant friction. The base seals must also be designed to accommodate and positive or negative building deflections.
In general the most common combination is a fixed top sweep with a mechanical base seal, maximum 2” movement.
In the next few blogs we will address building construction, flanking paths, testing and procedures, installation etc. Stay tuned.
