Chances are if you’ve watched an interview with any artist or engineer in a studio, you’ve gazed off into the background and noticed a big uneven wooden panel hung on the wall. However, these aren’t put up in studios as an art piece, these are diffusers, and play a key part in the acoustic treatment of a room.
They get their name from their appearance, which bears a striking resemblance to a city skyline, but in fact, these may be the difference between an average acoustic space, and a great one. But how do they work? Do you need one? And if so, how much do they cost? Stick around because we will be answering all your questions and more in our ultimate guide to skyline diffusers.
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What is a Skyline Diffuser? What’s its Purpose?
So, what exactly is a Skyline diffuser? And why would you want one? Well, it has everything to do with room acoustics.
While most rooms are built with perfectly parallel walls (for structural integrity), this may be problematic when setting up an audio listening environment. While not an issue if you mix on headphones exclusively, when using monitors (or speakers of any kind) you are not only listening to the direct audio signal but also the signal in the context of the room you are in.
Parallel walls reflect sound directly back at the sound source, which is an issue as this creates standing waves. Two sounds traveling in opposite directions collide and depending on their phase, the result could be a significant boost or dip in different frequency bands, an audible echo, or even harmonic distortion.
Sound diffusers are installed to break up sound waves upon reflection, stopping standing waves and other unwanted sonic artifacts. Diffusers are made from dense materials in order to reflect sound instead of absorbing it and are shaped so that waves disperse evenly instead of bouncing straight back into your ears.
The purpose of the sound diffuser is not only to reduce unwanted sound artifacts but also to provide a room with a greater sense of space. This is why you would choose to use diffusers over absorbers (although absorbers do have a time and place in acoustic treatment). Diffusers ensure all distortion, filtering, and echo are negated, while still maintaining the energy and spatiality within the sound itself.
How do They Work?
So now you know the premise and function of a skyline diffuser, let’s get into how exactly they work.
Skylines are a type of two-dimensional diffuser; this means that sound waves are dispersed both vertically and horizontally in 360 degrees. Two-dimensional sound diffusion is preferable to solely vertical or horizontal one-dimensional diffusion when treating a smaller room.
This is because one-dimensional diffusion requires sound waves to fully form so they can be effectively dealt with at the point they reach the diffuser. Therefore if the room is too small, one-dimensional panels may have little or no effect. Two-dimensional have a comparatively limited use case (being to minimize reflections, and to reduce localization in doing so) so they are a safer bet in smaller environments.
Even though the blocks on the diffuser may appear random, the length of blocks, as well as the depth and width of the wells and troughs created throughout the panel are calculated based on prime numbers, and the quarter, and half wave-length rule (more on this later).
The prime number used to inform well depths has an effect on the frequency response of the diffuser. Much like how a speaker can only produce a certain frequency range, a diffuser has a limited response.
The blocks themselves are most commonly made of solid wood. Wood is a material dense enough to reflect most sound waves that come in contact with it. The material of acoustic treatment plays a large part in the panel’s function, for example, absorption typically uses sparse materials (such as foam) to capture and the kinetic energy of a sound wave, and convert it into heat.
When Would you Use a Sound Diffuser?
So, when treating a room, why would you want to reflect sounds instead of removing them completely? Absorption seems like the most obvious way to treat a room – the objective is to resolve problem frequencies, so why bounce them around some more? Well having a room that is completely absorptive may cause its own particular issues.
Take an anechoic chamber, for example, a room designed to be as quiet as physically possible. With huge foam absorbers covering every surface, these rooms are the epitome of dead space.
These would make a fantastically bad listening environment as any sound energy put out into the room is immediately captured by absorptive pads. This means that your mix would lack any energy generated by reflective surfaces, and instead would sound incredibly dull.
Along with the loss of energy, nobody has access to these kinds of spaces. When treating a room, the idea is to treat any acoustic problems, whilst retaining the acoustics of real-world listening environments.
Chances are your podcasts will be listened to in many different locations such as kitchens, bathrooms, and cars to name a few. While these spaces will have acoustic problems of their own, by mixing in a room where reflections are diffused, but not removed entirely, you will create a mix that will inevitably sound better in these different environments.
Where do you put Skyline Diffusers?
So now you know how they work, and when you would use one, now it’s on to the where. A big part of where you place your sound diffusers depends on the purpose of the room, its size, and the position of your listening setup.
Let’s say you have a perfectly symmetrical room with the desk positioned to be equal on either side, and you are looking to record and edit your podcast. This requires a fairly typical control room treatment, and what you will find is that sound diffusers are typically placed at the primary reflective points of the room in this instance.
Given your monitors are set up to form an equilateral triangle, these points of primary reflection will be on the back wall, and to the side of either monitor. These reflections are especially problematic when listening critically, as they create the most audible echo, distorting, or comb filtering of the original signal, which warps your perception of the mix.
Because the diffusers are dispersing sound waves directly from the sound source, it is important to place the panels so that the middle is in line with the monitors. Having the diffusion panels at this height also ensures that they are equal with your ears, which the monitors should be in line with anyway.
If your room is relatively dead or has high ceilings, then a sound diffuser could be effective above you. Although absorption is the most common treatment for a ceiling, if you find there are still acoustic issues after tackling the primary reflection points (and other points with absorption), then this may be what is needed to give your room that little bit extra life.
What is a Quadratic Diffuser?
Skylines are a form of two-dimensional quadratic diffuser; however, their one-dimensional counterparts are also widely popular in acoustic treatment.
As the name implies, these panels diffuse in only one dimension (either vertically or horizontally depending on the orientation). These offer 180 degrees of sound diffusion as opposed to a skyline’s 360 degrees, and they work on a similar principle of wells and troughs constructed out of hard (usually wooden) materials.
While the differences between one, and two-dimensional diffusers are subtle, one key difference is the amount of diffusion. One-dimensional quadratic diffusers are more reflective on the whole than their two-dimensional counterparts, which may sway you towards using them if you are looking for minimal energy loss in your room.
They are also more distant dependent. For maximum effect, the sound wave must be fully formed, which for lower frequencies especially means that the panels must be placed at a good distance from the sound source. If placed correctly, however, these panels create a greater sense of image, and clarity than two-dimensional diffusers.
One way to counteract the necessary distance for effective use is to use an alternating pattern of panels. By alternating between vertically, and horizontally oriented panels (sometimes referred to as a checkerboard pattern), you can create a 360-degree dispersal array, effectively mimicking the effect of a two-dimensional diffuser, albeit without the increased absorption.
Skyline Diffuser Calculator
As touched on earlier, prime numbers are the cornerstone of skyline diffuser construction. When searching diffusers, you will find them commonly referred to as a 7, 11, or 13. These prime numbers are entered into a formula as a constant, with the results informing the depths of wells (in inches).
The highest and lowest measurements in this sequence inform the frequency range of the sound diffuser. To calculate what frequency range a prime sequence will affect, we must first discuss the quarter-wavelength rule – a common principle in acoustics.
The quarter-wavelength rule stipulates that to affect a frequency, the depth of a block should be at least 25% of the target frequency’s wavelength. Knowing this, you can reverse engineer the formula to determine a diffuser’s frequency response.
To do this you simply times your depth (in inches) by 4 to account for the quarter. Then to find the frequency, you will need to first divide this value by 12 to convert the measurement to feet, then divide by the speed of sound, which is approximately 1132 feet per second.
Not only does the well depth affect the frequency response, but the width of a block also plays an important factor. All diffusor widths are calculated using the half-wavelength rule, which means to calculate the frequency response you would simply have to times by 2 instead of 4 in the first step.
In practice, these calculations are typically made prior to construction, with a clear understanding of the problem frequency range you wish to target.
Skyline Diffuser Patterns
While the blocks may seem to be placed in no particular order, the pattern formed by the different height blocks contributes to the amount of frequency reflection. This should be apparent, as the frequency response is a result of wells and troughs, which are formed by the blocks in relation to those around them.
These patterns (and block height) are determined through the use of diffusion calculators nowadays. These applications require an upper and lower range for the desired frequency response of your board, and they calculate the optimal block lengths (based on a prime number series), and pattern.
These patterns are visualized most commonly as a grid. These grids are split into sections (usually between 12 – 16 blocks on both axes, depending on block width), and each section is assigned a number ranging from 0 – 4. These numbers are linked to a specific block height, with 0 being no block.
The numbers in the boxes correspond to the height of the block, with each block being derived from a number in the prime number series best suited to your frequency range. These applications calculate the most even diffusion of sound for your specific panel, which is incredibly important in ensuring no further issues arise.
If placed randomly, the sound will be diffused haphazardly, and with unpredictable results. Having a calculator – or a formula to create your own grid system, will ensure that all frequency bands are taken into account, optimizing your diffuser for the best result.
It can’t be overstated how crucial these applications are in getting the most out of a diffuser, and it goes to show how taking the time to work out the problems in your listening environment will help create a great listening space.
SkyLine Diffuser Price
So, you know what type of sound diffuser your room requires, but you have no experience with woodwork, why not leave it to the professionals? Nowadays buying sound diffusion panels can be done online, however, there are some caveats.
Cheap, and reliable, the first place most people will check is Amazon. And unsurprisingly there are a few retailers selling panels. Some of these diffusers are made out of plastic, which while making the product cheaper overall, will have a negative effect on its reflectivity, so we will be sticking to ones with wooden construction for now.
Fortunately, Ace Punch (Amazon link) sells a wooden skyline diffuser (along with other variants). The description states that the product ‘suppresses reverberation in the mid and high frequencies’ which gives us only a vague idea of the response of the panel. However, if this is where your problems occur, it’s worth a look.
Next up is Thomann. Well known for their audio equipment, you can be sure that by buying from this site, you will be getting a product made for musicians, rather than the wall art variation of diffusers you will undoubtedly come across (which are little to no use practically).
They sell a variety of Skyline diffusers, however, the Vicoustic Multifuser Wood MKII stands out, as it is described as being constructed according to QRD sequence and variable reflection technique. This is encouraging, as the Amazon product makes no mention of calculation methods – however with this increased practicality comes an increased price.
DIY Skyline Diffusers – How to Make your Own
If you are dubious about the practicality of online sellers, you may be inclined to use a custom quote. Sites such as LA Sound Panels offer a number of custom-built panels made with your room in mind. These guys are acoustic pro’s and the requisite questionnaire ensures they craft a diffuser designed to get the most out of your space.
However, if you are on a tighter budget, there is always the DIY option. Note that this does require a base knowledge of woodworking, and to save you some time and effort, some power tools (such as a miter saw, or other wood cutting apparatus) will go a long way.
- First, you will need to gauge your problem frequencies. The easiest way to test this is by playing a frequency sweep from your speakers in their intended setup. You will need to listen to define what frequencies have an audible echo, frequency build-up, or comb filtering. This may be done with a microphone recording setup in your listening position, however, it is your ears that will be used when mixing, so analyzing from your own perspective is preferable.
- Once the problem frequencies are found, try to define a frequency range, so that you can plug it into a diffuser calculator, which will determine the optimal prime sequence, and pattern layout for your diffusers.
- Before building, you must ensure the panels will actually fit in your room. If the range has an extended low end, the diffuser will be much larger physically, and this may cause problems if you are planning to mount in a smaller room.
- Now you have the layout and block sizes, it’s time to buy and cut your wood to size. Depending on your budget, you may choose to use a denser wood such as maple or oak, however, if you are strapped for cash, plywood is entirely sufficient and much easier on your wallet.
- After you have your pieces cut to size and sanded, it is time to glue them together. As you will be hanging this on a wall, using a backboard is a safe bet, not only will this hold the pieces together, but it will also provide a sturdy surface for wall mounting.
- Now you have your panels, all that’s left to do is mount! Ensure you have your panels in the areas with the most problem frequencies, these are most commonly first reflection points (see above for positioning tips). Remember all rooms are different, so it is up to you to determine where the boards will be most effective, however, as a rule of thumb they should be in line with your monitor and ears, and far enough away to allow sound waves to fully develop. Make sure they’re securely fastened to the wall with appropriate fixings depending on the type of wall and the weight of the final panel. Incorrectly mounted panels can be a health and safety risk.
This has been our guide to everything Skyline diffusers. By now you should have a solid understanding of their mechanics, construction, and where they should be placed. That being said diffusers are only one in a multitude of different acoustic treatments available, and typically you will find a combination of varieties used to treat a room.
So where can you learn more about the other types of treatment, and how much is necessary for your listening space? Well lucky for you we have a great article on ‘How Much Acoustic Treatment is too Much?’ to help you get to grips!