Diffusion

November 14, 2021
 by Paul McGowan

We’d all like our speakers to disappear and in their place enjoy the illusion of a deep and wide soundstage. Once heard, it can become addictive.

One of the easiest ways of achieving this vanishing act is by the addition of diffusers on the front wall (the wall behind the loudspeakers).

Regardless of the type of loudspeaker you’re listening to, this simple technique almost always works. In fact, over the many years I have been setting up systems, a set of diffusers against the front wall has never failed to offer exactly what I suggest.

The type of diffuser is important. Here’s the kind I have found works best.

There’s plenty of online shops that make or sell this kind of wooden diffuser. And, the more filled the front wall is with these acoustic diffusers, the more palpable the soundstage that forms behind the speaker pair.

Sometimes the simplest methods are the best.

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55 comments on “Diffusion”

  1. While Paul’s away, the Rat will play 😀

    Check out this girl’s vocal abilities when she ‘turns the power on’
    Be patient; watch the whole thing.

    https://www.youtube.com/watch?v=dRIS77mu5xM

    All of the egg cartons, & oh God there a lot of them, that I so
    labouriously glued to my ‘front wall’ over a period of a week,
    all fell down after 2 months.
    I think that the glue was well over it’s expiry date…so depressing 🙁

  2. I don’t doubt Paul’s words but it’s not going to work too well in my room, blocking out the light from the window. Out of interest though, for when I eventually do brick up the window in search of better sound, 😉 a sense of scale would be helpful.

      1. In my current situation there is 13 feet to the front wall so I’m thinking it may not matter. Now I’m too close to the wall behind and i think all the “experts “recommend absorbing rear reflection because I’m too close . diffusing can cause odd noise?

  3. You learn something new every day, today I learned that a yoctosecond is 0.000000000000000000000001 of a second. Forget speeding bullets and blinking eyes, we’re talking the timescale of the love-hate relationship between Hydrogen-7 and its protons. They just don’t get on. Birthday cards don’t feature in Hydrogen isotope lifespans. However, they aren’t even in the same ballpark when it comes to my wife and diffusers. Talk about nuclear reactions. I’ll settle for the soundstage just as it is.

        1. So a country who are rubbish at short format cricket meet another who can’t get over the line in major tournaments. Who’d have thought?

    1. Steven, I realize physics and chemistry are not your strong suits. Hydrogen 7 is one proton and 6 neutrons. It is a love hate thing between the 6 neutrons.

      1. When it comes to all matters relating to the physical world, I’m happy to represent the ignorant majority that is impervious to Paul’s tales of inductance and … all the other stuff that goes over my head.

  4. Okay, as a follow-up to my 6:11 comment :
    Meanwhile I asked my German interior designer (over the phone) and his answer was : Nein, Nein, Nein !
    (English : No, No, No).
    Then I decided to give it another shot by telling him the idea was from no one less than Paul McGowan.
    He disconnected.

  5. Question:
    While most speakers have some dipole properties, what’s the thought on diffusers behind speakers specifically designed as dipoles?

    The PSA FR30 came to mind.

    1. As a long time Magnepan lover, I can tell you diffusers on the front wall work well. I have read that the diffusers act as a comb filter as well as helping imaging and this effect is seen as positive by some folks. Or maybe the comb filter effect is what helps the imaging…

      1. Hi Bob, i thought comb filtering is bad thing…like standing waves with the bass frequencies. Some places in the room they add together and other spots they can cancel each other out?

        1. you are probably correct – I have read that the Magnepan users like the effect of diffusers on the front wall and I thought I read that it provided a comb filter effect. I’m not well versed enough to know….

  6. Well, I’ll probably get shot down but here goes…
    … my front wall defusers have always been… curtains.

    Not just any curtains, but thickish that create large pleats from ceiling to almost the floor, a few feet away from full range’ish stereo towers. OK, there’s two windows behind them but as my music listening is in the evenings, which starts around 15:00 at the moment, this is fine. When it’s sunny I’m probably outside anyway… 🙂

    Now I’ll wait to hear why thick pleated curtains don’t work as well as many hundreds, probably thousands, of pounds of wood defusers that look like squared edge curtains…

    Oh, Paul, did I see your nice white FR30’s standing proudly in the corner of an empty wood floored room close to the walls, under the tag ‘Impressions of the FR30’? Really…

    1. I don’t see anything wrong with curtains. In fact couldn’t they be the perfect solution providing the dual function of a curtain and diffuser, and oh so domestically acceptable.

      I have a similar set up. Floor to ceiling coving curtains across the entire front wall, which is mostly window. Whether they are as effective as the diffuser described by Paul I shall likely never know.

      A local dealer had a pair of curtains across the solid brick front wall of his multi speaker demonstration room. Presumably and to some extent, it enabled him to tune the sound of the speakers if required.

      If we’re talking squared edge curtains perhaps we ought to try box pleats.
      In fact there’s a wife pleasing opportunity for an entrepreneur, sound optimised hi-fi curtains.

      1. Longplayer is correct in that curtains absorb and do not diffuse.

        One suggestion was made that I like and that is covering the wooden diffusers in fabric. That way you’re looking not at the diffuser mess but nicely covered blocks.

    2. Alan, you ideally want a somewhat hard, broken surface to scatter the sound on your front wall. Curtains tend to absorb more than scatter. I’ve achieved acceptable results with large plants and accordion pleated, honeycomb blinds, which I can raise and lower depending upon whether I want better sound or solar heating. There is a woman in Canada, I believe, that has turned wooden diffusers into an art form with different shapes of wood painted different colors…but that’s not much help to you in the UK, except maybe to plant a seed of creativity.

  7. There is no negotiating with the laws of physics and you can’t joke your way out of it. IMO, if you have no diffusion of sound between your speakers, your soundstage and imaging is worthless.

  8. Paul, After looking at several offerings of commercial products. seeing the prices and recovering from my first myocardial infarction, I noticed that many of them are designed for a frequency range. Some do better in high frequencies, some are best for low frequencies. Do you have any suggestions here? Especially if I’m going to make them. It’s getting chilly in my workshop, aka barn, this time of year. I don’t want to get the design wrong.

      1. To be clear, it was the cost of the diffusers that shocked me. My. health is fine. I have no plans on checking out, although I was within feet of a road rage incident on Tuesday that had me more than concerned. Civilization scares me.

    1. Invalid,

      In the case of my Apogees I found (so far) that that leaving a 2- 3 foot wide flat wall gap behind the long thin ribbon helped with the highs – diffusion either side of that helped with sound stage width. I have a separate audio room so my freedom to ‘play’ is pretty wide open. I don’t know if wood is any better than foam or if wood blocks of varying projection depth into the room are best. Not sure I want to take the time to find out…. But then again it wouldn’t be a huge expense… – in the case of foam I would guess there are many choices… closed cell hard (more reflective?) or softer open cell…

  9. My front wall is very non-uniform and complicated in geometry and texture. There is only one portion of the wall that is glass. I could try getting vertical blinds for that portion and play around with the angle of opening of the blinds and see what that does to the sound stage. Right now that is not very high on my to do list.

    1. That’s what I do with my vertical blinds Tony. It works just fine for me. Made of plastic backing with a faux fabric facing which is possibly absorbing some of the sound and reflecting is accomplished by adjusting the opening of the verticals little by little. Right in front of my double front double glass sliding door wall.

    2. Tony, we had a product from Luxaflex called Silhouette. Very nice product. After 20 years we’ve gone for a Luxaflex vertical blind this time. Being installed this week I hope. They can all be motorised.

  10. With my stand rear ported direct radiating monitors 24″ from wall boundaries, my 9ft listening wall is non-treated sheetrock that is the live front of my dedicated music room. It supports a very wide and deep soundstage that has much air around the musicians, with pinpoint center images and huge venue ambiances that far exceed room boundaries!

    A couple of years ago I experimented with 2″ thick, 23″ square diffuser panels to solidify the presentation even more. After 4 weeks of many trials/setups along the front wall, side reflection walls and the listening wall, them seemed to only take away from the “live 3D presentation” of my balanced room’s natural acoustics (all compliments of built-in room decor)!

    Possibly I was using the wrong product, but did much research and asked several manufactures before delving into this activity before trying these: https://www.gikacoustics.com/product/2a-alpha-panel-diffusor-absorber/

    To date, the listening love seat, carpeted flooring, side double french door-windows/double raised panel closet doors and high ceiling seem to provide just the right amount of ambient reflections that properly reinforce the listening positions playback realism and holographic presentation! 🙂

  11. As I have a dedicated listening room my wife doesnt worry what I put on the wall I have a mixture of absorbing and diffusing panels. I got very good advice from GIKs David in UK and I have diffuser and Bass traps on front wall , absorber/diffuser at side reflections and a mixture on back wall as suggested by David. Was lucky to get practically at good prices for B quality. The room sounds good from a music point of view so am very happy with my outlay. Do recommend you at least loaning and trying if you can

  12. Back in the 70’s I saw “cork tiles.” They were not peg board smooth. It was grainy and a bit crude. I covered a good part of some side walls. The only thing family complained about was how they put off an odor when new. Apparently, they were doing something excellent. For my KEF 104 AB’s made the walls disappear with this arrangement. I was shocked how good they sounded. Its only now that I am realizing what their ability to diffuse was doing…

    If I remember them correctly they looked like this:
    (right click and open in new tab)
    https://i5.walmartimages.com/asr/9c1715bf-8d5e-4029-b97f-8d4d45aeefcf_1.699ef8358e92b46002b2c50a66ce9264.jpeg?odnHeight=612&odnWidth=612&odnBg=FFFFFF

  13. Ive been longing for this moment to share the hundred hours of internet knowledge on room treatment. But this popped in my noggin, both local restaurants on the lake here remodeled,have less decor,no (nasty) carpet,lots of glass etc…and it can be painful acoustically and i have trouble focusing on conversations . Well,you guys can figure it out from here.

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