As mentioned in our tutorial on acoustic treatment, there are 3 types of products to optimize the sound quality of your room: bass traps, acoustic panels and diffusers. In this article, we will focus on acoustic sound diffusers.

What is an acoustic diffuser?

The fundamental difference between an absorbent and a diffusing concerns the management of sound energy. Absorption reduces energy, while diffusion redistributes it on the basis of a mathematical model. In some cases, in particular for Hifi or recording studios, we try to conserve sound energy. This energy is what allows you to better feel the impact, the “weight” of the sound and thus benefit from a more live effect. Sound waves are often compared to billiard balls bouncing off the walls of a room. While an absorber will seek to attenuate this rebound, the diffuser will skillfully disperse these waves in all directions. Concretely, while a treatment based on absorbent products aims to reduce reflections, diffusion will disperse the reflections which will be distributed more evenly. The sound becomes more precise and pleasant, without loss of energy. Note that there are unidirectional (quadratic) and bidirectional (poly-cylindrical) diffusers. The diffusers will therefore come in addition to absorbent acoustic panels. They will complement the effects of absorbent panels or bass trap. They aim, in fact, to disperse the waves which were not absorbed by the two previous acoustic correction systems. In other words, after having corrected the major defects of the room in terms of reverberation, the diffusers will seek to restore the sound in a natural way. That is to say, one seeks to hear the sound in an energetic way, without the absorption stifling it. Their main role is not to absorb energy, but to redistribute it intelligently to make a listening room more lively, more dynamic and more musical. It should be noted that, even if diffusers are mainly aimed at redistributing energy, there are hybrid models which also have an absorption effect.

What does an acoustic sound diffusion panel bring?

Diffusers allow many things:

• Specify details and refine the sound image
• Give a live effect
• Get a wider soundstage
• Avoid comb filtering and echo flutter
• Cut the standing waves

Specify details and refine the sound image

The broadcasters will improve the detail of the music and refine the sound image. Concretely, they will allow voices to become more intelligible, to improve clarity and reproduction. Thus, the stamps reappear and the definition regains all its meaning. This is made possible because the diffusers allow:

• An improvement in the energy returned (thanks to a homogeneity of restitution in terms of frequencies)
• Management of reflections while retaining more momentum

Diffusers are perfect for managing high frequencies.

Give a live effect

The broadcasters will also make it possible to give rhythm to the listening. They will allow immersion by giving a “live effect” to the sound. You will have the impression of being present at a concert. You will get more punch, dynamics, firmness and bass speed. After a heavy absorbent treatment, the room may sound a bit dead or dull. Acoustic diffusors will fill that.

Get a wider soundstage

You will have an impression of space in your music. Your listening point will expand. You will have a feeling of immersion in your entire room. Concretely, the diffusers will give you the impression of being closer to the sound.

Avoid comb filtering and echo flutter

Comb filtering

Comb filtering is a phenomenon of canceling or boosting the level at certain frequencies. This is a more technical way of talking about the phase shift due to primary reflections. A primary reflection, remember, is a sound that reaches our ears, no longer through the speaker but through the “bounce” of the wall. This sound, which has more distance to travel than the initial sound, will arrive with a time delay on the original sound. This delay will create collisions between sounds at the listening point. They will then cancel and amplify again. This is called comb filtering. This phase shift will create a multitude of bumps and dips on certain frequencies. Diffusers placed at the primary reflections will overcome this problem by sending the sound elsewhere than on the listener and by modifying the phase shifts.

Flutter echo

The diffusers also make it possible to combat flutter echo. Schematically, this corresponds to the effect of 2 mirrors placed face to face which send the sound wave eternally. If you clap your hands, you will repeatedly hear the same clapping sound at regular intervals. This is very bad for your acoustics.

Cut the standing waves

The standing waves are the meeting point of sounds which, with the reverberation between 2 walls, will “meet”. Concretely, when there is sound in a room, it spreads like a billiard balls in different directions at the same time. It will bounce against the walls. These different waves will then meet and collide. In this shock, the waves will amplify or cancel each other out.

When to use them?

The diffusers will be used mainly in a musical setting. Sometimes they can also be used to transmit sound in very large rooms. This is especially the case in very large auditoriums. Thus, they are ideal for:

• Concert halls
• A hi-fi auditorium
• An opera
• A home theater
• A recording studio

As explained above, they always come in addition to absorbent acoustic panels (except in very specific cases where a room would have perfect acoustics without treatment). Significantly improving the sound quality, they are used both for listening and for taking sound.

What are the types of acoustic diffusers?

There are 3 main types of diffusers:

• Quadratic diffusers
• Schroeder diffusers
• Poly-cylindrical diffusers

The qrd diffusers or quadratic diffusers

The quadratic diffusers have a varied relief, composed of cubes of different heights. Their objective is to disperse the sound in an almost chaotic way. Thus, the sounds are propagated in a more harmonious way and do not reach the ear all at the same time. The greater the differences in height of the cubes, the more the diffuser will operate at the bottom of the frequency spectrum.

Schroeder diffusers

Schroeder diffusers were invented in 1984 by Manfred Schroeder. Schroeder demonstrated the importance of the presence of broadcasters in the feeling of immersion in listening to music. His work is inspired by mathematicians like C. F. Gauss. Concretely, he has shown that it is possible to disperse the sound wave in all directions. The Schroeder diffuser looks like strips of different heights, like the quadratic, but on whole slats.

Poly-cylindrical diffusers

A poly-cylinder diffuser allows it to propagate the sound wave in different directions. Its effectiveness is due to its rounded angle of diffusion. Indeed, this rounding allows breaking the sound in several directions. Unlike the other two types of panels that return sound in the same axis, the poly-cylinder returns sound in a multitude of directions. A bit like a fogger.

The materials

Diffusers can be made from many different materials. On the market, you can find diffusers in :

• Wood
• Plaster
• Metal
• Altuglass
• Melamine foam
• Glass
• Ceramic

Wood, the better diffusing?

As explained, the diffusers can be made of different materials. In general, the more inert the materials, the more effective it will be. We try to return the sound, not to absorb it in the absolute. The sound depends on the material and its ability to return the sound. The latter plays a crucial role. In fact, the resonant frequency of the material and its inertia can significantly modify the sound of the product. Take the example of a crystal glass. There is no need to generate significant energy for it to “sing”. These same phenomena occur with metal, glass, plaster and all materials. These materials vibrate with more or less ease. The following diffusers will clearly have a more natural and softer tone:

• Solid or thick wood
• Plywood
• Designed with a certain engineering like our poly-cylinders

The engineering of our poly-cylinders results from their system of mechanical increase of inertia and suppression of concave resonances. Diffusers made of ceramic, glass or worse metal are purely “hi-fi” to use with care if you have an energetic and sensitive system.

Where to place them?

Diffusers can be placed on the wall or ceiling.

Acoustic diffuser on the wall

Their position will depend on the use of the room. For a rather hi-fi use, placing them between the speakers is a position that will make the most of their effects. In a studio configuration, rather behind the listener to increase the airy feeling of the room. They can also be placed at the primary reflection points. Absorbent panels should be positioned on either side of the diffuser to obtain a perfect compromise. In all cases, a diffuser has an operating distance. It is imperative that it is spaced 2 to 3 meters with the listener to be fully operational. When using a fogger, the water is dispersed after 50cm. It’s pretty much the same with sound.

Acoustic ceiling diffuser

This type of treatment will complement a wall treatment. However, too much diffusion is not necessarily desirable since the sound can become too fast, hard, dry and aggressive.

How many diffusers to put?

The amount will often depend on your sensitivity to the sound energy and your desire for fast, lively sound. Often there are trade-offs with absorption. Thus, it is possible to obtain very good results with few diffusers. Our diffuser packs are studied in this sense. In any case, we advise you to contact us because depending on your system and your tastes in terms of sound, the solutions can be very varied.

Installation of an acoustic sound and audio diffusers

All our hi-fi panels are fixed with Velcro, diffusers included. Other diffusers on the market are fixed with rail systems or glues. They will therefore be less respectful of your walls.

How to know if an acoustic diffuser is qualitative?

The curve

Unlike an absorbent panel, it is very difficult to assess the quality of a diffuser with a curve. In general, a good diffuser is a thick wooden diffuser which eliminates certain defects in the basic mathematical model. Likewise, it must meet your aesthetic needs.

Expert opinions

As we explained in our tutorial on choosing an acoustic panel, the opinions of specialists can be a good source to get an opinion on the quality of a product. The specialized press and the sellers of hi-fi, home studio or home cinema equipment can thus guide you in your choices.

Our solutions

At PYT Audio, we offer 2 types of broadcasters:

1. Exclusive low profile diffusers: it is a compromise between absorption and diffusion. This diffuser retains an absorption capacity on certain frequencies while seeking to “give life” to the sound. It works on the principle of the Schröder diffuser, but in an “inverted” manner. Thus, internal scattering bands return the high frequencies and are spaced according to the basic mathematical model. The absorbent will reproduce the cavities.
2. Exclusive poly-cylindrical diffusers: they work by diffusing sound in all directions with a diffusion angle of 120 °. They integrate a mechanical inertia augmentation system, which like a trampoline will return energy thanks to the inertia of a surface wooden plate and a “spring” which puts this plate under pressure. A system for suppressing concave resonances is also present. Indeed, if the panels are next to each other, at their junction we create the exact opposite of what is wanted. Concave resonance is a parabolic or magnifying glass effect applied to the sound.

This means that they remove the flaws inherent in the basic mathematical model, by strengthening the physico-acoustic principles. As a result, this allows our product to be really effective, not only from a “measurement” point of view but also from a “listening” point of view.