Total absorption

November 18, 2022
 by Paul McGowan

One of my YouTube viewers writes:

"Paul, love almost all your videos. but. I think TOTAL ABSORTION behind the speakers is crucial. Reflection behind the speakers is just noise. PERIOD. WORST CASE. A glass window in the imaging space. PERIOD. Sorry."

This is part of the old live-end vs. dead-end debate in rooms (the actual debate more centers on which end of the room to place absorptive materials). And from the way he is phrasing the question, it makes logical sense. Who wants noise?

The problems with the statement are many but chief among them is this notion that reflections are nothing but noise. In my experience, it is those reflections that are essential to achieving a live sound in the room. Properly managed with a bit of diffusion, reflections can help bring a bit of magic to the soundstage.

That said, as with any rule of thumb, it isn't a universal truth.

There are cases where the dead-end absorption method (or a variation of it) just might be the ticket to better sound. Imagine a smaller room where the main loudspeakers have no room behind them and cannot be pulled out from the front wall. An argument might easily be made that a bit of absorption on the front wall might sound preferable.

My preferred method of diffusion on the front wall (behind the speakers) is really only effective if there's enough space between the rear of the speaker and the wall.

A bit of experimentation with both methods won't take long and the end result is likely worth the effort.

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37 comments on “Total absorption”

    1. Thank you, Martin! : )

      You defused beautifully my automatic annoyance at the dogmatic boomer intermittently shouting at Paul oblivious that he doesn’t know what he doesn’t know.

    2. I read that reply after watching Paul‘s video yesterday and I don’t think he intermixed anything. It was a rant from a ‘know it all’ who, more than likely does not know what he’s talking about. He used the word sorry like a finishing touch to end his rant and prove his point which had no factual information. That word ‘sorry’ was really demeaning IMO.

  1. There is reverberation and echo. There are early and late reflections. Just talking about "reflection" and "noise" seems a bit vague. Having replaced my windows 2 years ago there are also very different types of glass with different acoustic properties. Then there are speakers designed to sit flat against the front wall (Tannoy, Audio Note etc.), some fairly close (within 12 inches, Harbeth, Spender etc.) and others further away (Wilson, Quad and lots of others).

    I was completely ignorant about these things, having done a rebuild I'm slightly less ignorant and, given the end result, I also think I'm rather lucky. I also last night got a fantastic result from a single subwoofer, placed in the left rear corner of the room, behind the listening position, within inches of brick walls and firing exactly across the diagonal towards the external brick walls. I very rarely see the subwoofers at the back of the room, it is a technique that seems limited to AV.

    I think there is some pretty good advice out there, but no firm rules and quite a bit of "suck it and see".

  2. And here again: why not better address the most fundamental question: do you prefer to listen to your listening room or to the loudspeakers? Just make a comparison with a pair of good headphones. If you now want better spatial imaging add crossfeed to the headphone - some even add an active subwoofer. Concerning the loudspeakers: go for near-field listening and have the loudspeakers placed as far as possible from the wall and minimize reflections from floor and ceiling. And as the cherry on the cake: add crosstalk-cancellation. For those who have to listen in far-field conditions: you will always create your own sound and will rarely come close to the sound intended by the sound engineer.

  3. I’ve played around with both diffusion and absorption and currently have a mixture of both. It was kind of surprising to me how much you can change the room sound if you have free rein to do so. I like the dipole presentation from a big ribbon panel. Personally I’m not so interested in some sound engineers intent. Two channel audio is as individual as the person listening

    Enjoy your preferences and ta

    1. I have a pretty large double glass sliding door in the center of my front wall so when I moved into this place I immediately purchased vertical blinds that had a fabric finish and before a listening session, I pull the blinds closed which seems like it adds both absorption and diffusion. I can change these qualities to some small extent by adjusting the verticals just a bit with the wand that rotates the slats to change the total room acoustics in very small increments. For the most part, they stay fully closed yet they solve the problem of all of that glass on the front wall. Not sure whether to call this a Tweak or a Kluge.

  4. My respect for (probably more or less daily) reading most or many Paul’s post, forum and YouTube contributions and I don’t know what else. I’m not sure if this would keep me mentally healthy or make me go nuts, but you’re a (positive) miracle anyway 😉

  5. Why do so many people want to create the exact sound intended by the recording engineer? First of all, it may not even be the sound intended by the artist. Second, the sound engineer’s taste in how the music should sound may be very different than your taste.

    I say put together a sound system that makes music magical for you and be happy if you achieve that.

    1. I could not agree with you more Mr Boucher.
      Some listeners are just so uber-anal-retentive about hearing with
      absolute accuracy what the studio guys (the recording) have created,
      instead of just finding a sound that it pleasing to their ears & brain.

  6. A lot of times the musicians don't even get a say in how the recording sounds, Rudy Van Gelder comes to mind changing the tone of the musicians instrument's sound. That's why I say don't go for accuracy, just what sounds good to you.

      1. Fat Rat what i hope for when listening is:
        Neck hair raising
        Total emotional involvement
        Feeling like the musicians are communicating directly with me.
        Not even knowing there is a world beyond what i am experiencing at that very moment.
        I do not care for accuracy

  7. I have my Magnepan 1.7i's 6 feet from the front wall and I had all absorption placed there. I decided to try a little diffusion and the room came ALIVE!!!! Won't go back...

  8. My new room is small and has bass traps occupying every corner and soffit. I was debating what to do with the front behind the speakers. The most I can have the speakers from the sides is about 20 inches, and 2 feet from the front wall. The soundstage is wide enough, I think, but I really get strong center-image, maybe too strong. So I chose to put 2 ft. x 4 ft. panels on the front wall that are hybrids - 2 in. of absorbing panel insulation, but diffusive BAD plates on the front. So far it seems to give me depth, but not deadness. More experimentation will happen.

  9. Dipoles, bipoles and most panel speakers need some reflection behind them to give their best. And how do we know that the engineer didn't make the mix a bit dry with the intention that the playback system will have its own ambience?
    If reflection behind the speaker is a no-no PERIOD how about reflection from the side walls or rear walls? Do the reflections suddenly become good after a few milliseconds or coming from a different angle? So many questions...

  10. We bought the house we now live in twenty years ago. We bought it for is modern Bauhaus ( the school of architecture and design, not the band ) design. The main room of the house where the stereo system is has exposed beams and columns. It was a given that I would do nothing to mask the simplistic features of the room. Thus the only room correction that I have done is a large rug in front of the speakers and no coffee table on it.

    Fortunately, it is a large room, my speaker are sealed so the sound they produce is less sensitive to room placement and they are reasonably far from the walls.

  11. This guy would go nuts if he saw my VERY live room (currently without even a carpet on the tile floor) and a large grand piano's soundboard affecting the sound.
    Yet it all works. The only change will be an area rug in the near future.

    1. My sister's sound room doubles as her husband's small engine repair shop. She often finds that what she thought was a guitar solo in an Iron Maiden track was her husband testing a chainsaw.

      OK, not really - I don't even have a sister. I just wanted to see if I could do you one better.

  12. Some speakers are designed to work with the room. Not everyone wants an anechoic chamber or wants to place absorbent materials all over their walls, ceilings, and floors. Unless the speakers are made to sound best that way in a dedicated room.

    Acoustic suspension speakers don’t have ports, passive radiators, or transmission lines so they rely on the room loading the very low end and be placed closer to the front wall. My speakers are for real world placement. Not all rooms are big enough to bring out speakers 4-6 feet from the front wall and not all speakers sound best when doing that unless you’re using subwoofers.

  13. Magnepan owners: Before setting up my Magneplanars I called the factory. THE MAN answered. In a 5-10 minute conversation Wendell repeated 3-4 times 1. No absorption on front wall. Reflection only. He never heard Maggies sound right with absorption behind them. 2. As long as you have 100 watts AND sufficient current Maggies will be happy. The way to know is if the power amp approximately doubles output at 4 ohms compared to 8 ohms. If so, the amp should at least mate very well. That is why they never answer the frequently asked question, "which amps are best?" Wendell says Maggies are not fussy about power amps if that condition is met.

  14. A timely topic for me since I just reconfigured my listening room, a 15x23x8’ space. (Not quite as great as it sounds because a closet takes up one corner of the back wall. But better than a 10x10!) I remembered that Paul’s a proponent of diffusion behind speakers, but as I recall so is Jim Smith, author of Get Better Sound (and a recent guest on The Absolute Sound website). Plus, I have Maggies. So I’m sold on moving those panels out 4 feet into the room with bookcases behind them. My big surprise came when I accidentally put the tweeters on the inside of each panel. Wow, kind of a “sonic beam aimed right at your ears”kind of sound compared to tweeters on the outside. I’ve also got to some temporary absorption on the back wall. Not nearly as influential as diffusion on the front wall, but I’ll play with it. Cheers.

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