There is no fatality involved in how bad a space is sounding. Be it an airport, a dance club or a concert hall, or anything else for that matter, If you can’t hear a PA system, a singer or your neighbour friend in a restaurant, or if you feel uncomfortable in a place without being able to name your feelings, there is always, ever, for sure, someone to blame for the bad acoustical or sound reinforcement, or both, options taken. So regain your trust about your feelings, if it sound bad it isn’t an issue with how mysterious or strange unseen elements at work can behave, simply there are ways to do it right.
I mean, you paid for you show, your meal, you travel, your home, and there are no sensible reasons at all to have an uncomfortable time in any of these places, just for the sake of making sure the very building you are in looked pretty good in magazines. You are the one who have to spend time in this so get on top.
Here we have just seen one law, the law of diffusion, but the very same logic applies, albeit with a different set of rules, to absorption. No magic here too, despite what many astrologist & gurus would like you to believe. Absorption can be envisioned very simply by a very simple thought experiment: if waters gets in it absorbs sound, if water stays out it reflects sound. But, hey this is a thought experiment, don’t go all out with splashing walls of your preferred venue, loft or restaurant, it is a thing you just have to do in your mind.
If conceptually in your head water drips from a surface, chances are great that this surface will pretty much reflect all your sound.
Just a tiny extra precision needs to be added at this stage. Sound waves, unlike water, differ in size depending on frequency. So the lower the sound the longer the wave. Ranging in the audible spectrum between say 10 meters to a 10th of a millimetre. So for low notes to be absorbed you may feel that some very thick material would be required but for these to be reflected a fairly flat surface will do, even a rough one. While for the much smaller sound waves of high frequencies, even tiny holes in an otherwise sleek looking structure will absorb sound. Now in a mirror or tiled room with near 100% of reflective surfaces, a sound played will last for an awfully long time, all the while, a room full of 1 meter thick pyramid shaped foam blocks will sound pretty much as 0% reflective, pretty much like what would happen in a desert, and nothing will come back at you once played, minus the ambiant sound of shifting sands, winds and passing coyotes. With just that knowledge, you have the tools to envision how “live” or how “dead” your room, hall or space can be.
I would add that long waves are only stopped by large thick walls while short waves will, logically, be stopped by even thin walls, this will help you imagine how much of your sound will go across the walls of a said space, knowing that if it goes across then it is somehow absorbed, just like in an open space or a room with very large chucks of heavy foam. Finally, having furniture, non linear walls, plants and stuff in a room, will almost in no way absorb any substantial amount of sound, but these no flat surfaces will diffract your sound waves and thus help with the overall quality of the room by breaking the sound into lots of waves going back and forth at different angles. That it is pretty much it.
So, I would really like to understand, how a knowledge gathered in say 30 minutes on the web and well understood a mere 50 years ago, can remain, or become so obscure as to allow any sort of mystery and magic to slide in. Could it be because sound cannot be seen?
Let me state it again here, just like there is no magic to be found in pieces of wood or pieces of copper, room acoustics is pretty much based on common sense and knowledge widely available throughout modern human race, despite what sound gurus and/or glass and concrete lovers will want you to believe.
– Understanding further
But now I have to clear some small misunderstanding about acoustics that keeps on popping up in conversations around me, even so often from people “in the known”:
Absorption is the technique, in room acoustics, the deals with preventing the sound from reflecting all over the surfaces and coming back at you later, interfering with the original signal and degrading the overall sound quality and intelligibility on the way. This problem, reflections, and its solution, absorption is the very issue that makes you speak louder in the vain hope that you will be understood by your loved one in a restaurant, or the very same problem that make the sound engineer of your average show or sport game turn up the level of the system to a point where it hurts, in the hope that it will sound better. It will not. Period. When you you turn up the main sound you incidentally and quite logically turn up the reflexions too, so same mess, only louder. Ironically, absorption techniques, in the most offending frequencies, are easy to be dealt with. Even after a building is finalised and in operations. For the bass frequencies it is another story altogether, but you usually can live happily with low frequency late reflexions, if only because your ears take basses as a confort bonus but only really refer to mid frequencies (hint: the frequency of the human voice) to localise, identify and on a general base feel happy about a sound. But more on both topics later…
A bit of curtain here and there, some thick soft stuff on the walls and ceiling it is that easy. So it still is beyond my understanding as to why clubs or restaurants or venues don’t take the appropriate measures at rather reasonable costs. Or almost worst, because of a well intentioned friend, take cosmetics only under dimensioned measures that are almost totally useless. As a quick simple rule of thumb, for your room to be pleasant sounding, 30 to 50% of its surface (not volume, just surface) needs to be highly absorbant (read real thick and soft material, like rock wool, theatre curtains, thick cloth etc.). It takes a day off or two to install, it can be hidden behind fire safety approved ceiling cloth, it can be hidden in artwork, how easy is that? But still, offices, venues, bars, clubs and restaurant owners somehow prefer to infer with the success of their endeavour to the point of commercial no return instead. Could it be because of the essentially non visible, magical, nature of sound? (See astrology chapter)
Isolation is an altogether different sort of beast. Hence me insisting that the difference to be well expressed and understood. Sound isolation (not to be confused with thermal isolation, which uses resembling but entirely different sort of material, btw.) is more often than not mixed and confused by professionals, be they architect, facilities owners and confused by musician and sound engineers too. Isolation is the opposite of absorption, it is incredibly tricky to envision what can happen with sound travelling across walls in existing problematic buildings and there is not much that can be done as a retrofitted measure. Isolation has to be planned for and designed before any sort of construction job is undertaken, be it refurbishment of an existing place or the creation of a new building. Once the thing is up and in use, you can pretty much forget about any real improvement and pray. Which leads us back to the very mythical nature of sound, but I am afraid prayers here won’t do much about your neighbours complaining.
When well planned in advance, isolation is a fairly easy task, on paper. But because isolation can’t simply content with soft material, you usually mostly will be working with large heavy concrete walls or floors, with a bit of soft thing in between to allow for air and prevent shocks to be conveyed across rooms, so try to retrofit that in an existing building. Ironically, because of the confusion between the two acoustical domain or possibly because people pretty rapidly envision the very costly nature of the isolation work, they tend to forget about it during the whole construction process, hoping to somehow escape the consequences, but they usually do not and consequences there are. Then this is exactly when a professional is called in and this incidentally is exactly when there is not much to do about it. This is why there are now rules and construction guidelines for modern building and this has helped the situation quite a bit I must say.
This post is also available in: French