The particles travel in straight lines except when, at random intervals, they bounce off the gas molecules. The Acoustic Diffusion Equationĭiffusion is often discussed as a description of the motion of particles in a gas. Sound pressure level distribution (dB) with a door added and an approximation of the direct sound included in the living room. I provided my parents with a nice printed report and gave them the thumbs up to move into the home. The total loss between the couch and the bed was now a much more acceptable 23 dB. In my second - and final - simulation, I added the direct sound hitting the couch and put up a door between the rooms. By approximating the sound sources as points and neglecting shadowing from the table, it is quite simple to add the direct sound as an analytical expression in terms of the emitted sound power and the local coordinates. With my mom sitting directly in front of the television, there is also a significant direct sound reaching her. The acoustic diffusion equation only deals with the part of the sound that has already struck the walls or the furniture and has become diffuse. It is trivial to include a door with a specified transmission loss in an acoustic diffusion simulation. If you have access to a drawing of the door and know the material that was used to make it, you can, of course, run an acoustic-structure interaction analysis to get a second opinion. This makes a difference because a significant amount of sound may sneak through the space between the door and the floor unless you install a fitting. If your door manufacturer cites a transmission loss in dB, make sure to check whether it concerns only transmission through the door itself, or if it was measured with the door in its frame. The first element is a door between the rooms. Luckily, two important elements that would increase the difference were still missing.
My first solution shows a sound pressure level decreasing by a quite modest 11 dB between the living room couch and the bedroom. The red dots indicate my mom’s viewing position and my dad’s head while he is trying to sleep. My parents understand that acoustic diffusion is not an exact science, and they appreciate my honesty.ĭistribution of the sound pressure level (dB) without a door between the rooms. If you decide on a similar time-saving measure, I suggest that you be open about it. To compensate for the lack of carpets and the relatively sparse decoration, I then nudged the wall coefficient slightly in the upward direction. I selected a constant low value for the walls (including the floor and the ceiling) and a higher one for the soft parts of the furniture. If you want to be more thorough, you can use different values in different frequency bands, or even specify them as arbitrary functions of the frequency. This was a breeze - two power sources representing the stereo speakers connected to the television, absorption coefficients assigned to the walls and the furniture, and…that was it.Īpproximate absorption coefficients for common materials are easy to find online. With the drawing complete, I set out to create my first acoustic diffusion model. This interface is very easy to use and, in most situations, it is a lot faster than the more accurate Pressure Acoustics or Ray Acoustics interfaces.įor my simulation, I created a simple drawing of the relevant rooms and included the larger pieces of furniture. The obvious start for a “quick and dirty” model of the acoustics in an apartment is the Acoustic Diffusion Equation interface. Acoustic Diffusion in COMSOL Multiphysics I just needed to establish that my dad would get his beauty sleep.
Luckily, accuracy was not a primary concern.
In short, they are bound to mess around with the input data and thereby remove digit after digit from the precision of any a priori sound level estimate. My dad is constantly moving furniture around to, as he says, “feel the space.” My mom, meanwhile, tends to pull the couch closer and closer to the television rather than admitting that she needs glasses. As they will eventually need to downsize, I decided to help them plan a home where they could stay friends.įrom past experience, I knew there was no sense in trying to optimize the location of every plant, rug, or bookcase. My mom enjoys watching late-night television talk shows, while my dad prefers a good night’s sleep whenever he gets the chance. My parents love each other to death, but their habits can sometimes clash. I will introduce the topic of acoustic diffusion by sharing my own personal experience, while highlighting the assumptions behind this modeling approach, as well as its strengths and weaknesses. In fact, this method of acoustical analysis proved particularly helpful in planning the layout of my parents’ future home. The acoustic diffusion equation is the quickest and easiest way to model high-frequency acoustics.