Diffusion: Disappointment In Recording Gear #5

Brandon Drury —  January 21, 2013 — 30 Comments

Diffusor disappointments

You can see from various articles in 2011 that I was totally NUTS about diffusion  (see the Recording Studio Construction and Acoustics category)  I built a crap load of diffusors that year . I was hoping they would be the holy grail. I became OBSESSED with ‘em. I was researching them obsessively. I was doing QRD math equations every night. I couldn’t sleep I was so excited about diffusion.  I had to know of PRD vs QRD.  I had to know about 1D vs 2D.  I have to know how important depth was.   I was mad because I had to go on a vacation when I could be building my diffusors.   Diffusion! Diffusion! Diffusion! Surely, it was going to be THAT THING I was missing.

In one of my articles where I was PUMPED UP about diffusion Danny Danzi made the following comment:

Brandon, I’m gonna go against the grain here a bit. You and everyone else will probably disagree with me. However, having worked in some pretty incredible rooms in my life recording drums, “the kit” as well as the tuning, mics used AND the player is what made the difference way more than any room I’ve recorded in. Though a room and having control over that room is important, in my experience rooms have not made a huge difference for me as much as the other stuff I’ve mentioned.

This quote is of intense value because anyone can list those things that are important, but it’s decidedly different when priority is put on those things. Just for the sake of clarity, Danny isn’t saying that he’d prefer to work in a terrible room. He’s simply stated that a great drummer with a well-setup kit can overcome much.

I have to agree with Danny…now.  My room was not my biggest problem and no subtle tweaking (like that of diffusion) was going to move any mountains.

Diffusion is a good thing at the right time. It takes a gang of 10 thugs and splits them up into single law abiding sound waves, give or take. It’s an interesting alternative to putting them in jail, which is what absorption does. The net result is bad reflections ain’t bad anymore, but it takes a huge diffusor to bust up the low end (see George Massenburg’s Room).  It’s easy to pretty up the reflections in the 1k-4k or so (depending on depth and diffusor design) and still have a mess in the low end.  There’s differing views as to how far away you have to be from a diffusor for them to work well and even more debate over the quantity of sq ft needed to be “adequate”.

So what does that mean in terms of recording quality?

Diffusion CAN do a lot if the room is good but boring.  This is a big deal in live rooms.   In the too-small home recording situation, “boring” ain’t the problem. Downright crappy is the problem. Diffusion isn’t exactly the right tool for solving “crappy”.

The Defeat….Sorta

After a room experiment I took my 2D diffusors down. They are stacked up in storage right now. I never bothered to put ‘em back up. The effects weren’t that interesting to me in my current circumstances.

What I did find was going MegaDead (Now that’s a band name!  Way heavier than Megadeth!) with room acoustics is almost always a good thing in home recording land. I have strong evidence coming in an upcoming Hyper Guide. The fear of a “too dead” room makes no sense in a room too small to have any good reflections anyway.

In the typical single-room confines of home recording land, it’s best to go neutral in the room that’ll be used for mixing. No significant obvious reverb (the kind of thing that makes you sing in the shower). That’ll cover you for everything but the bass significant instruments. We still have the problem of room modes that wreck low end response of studio monitors affecting our bass cabs, but that’s not a mega issue for tracking for non-low end instruments like vocals.

Lesson Learned: I should have just been proactive and used more EQ and overall processing. Some voices need it.

What I found was I got more aggressive with my EQ after I had diffusion. Why? Because I found out that they didn’t automatically solve my problems….any of them.  That 150-300Hz crappy stuff wasn’t the room and I was running out of things to attribute it to. It turned out most of my problems were simply the resonance in the vocal cords of the singers I was dealing with and guitars I was wrestling with. Not all singers and acoustic guitars had it and that was the real clue.  (This lesson of more proactive signal processing is an ongoing theme.)

The good room reverb is great if you’ve got it, but I doubt many of us have it.  Go dead and move on until you have the luxury (large room) to choose otherwise.

In short: Diffusion is cool, but it’s not a holy grail for everyone all the time. In the home recording world where we need to be sucking up every ounce of low end we can from bouncing around our rooms, it doesn’t make sense to waste an opportunity to suck up some more low end by tossing diffusors up instead.  (Ethan Winer’s Realtraps offer a diffusor with a bass trap built in.  I like that!)

Ultimately, I would have been just as content with a bunch of 4″ thick Roxul sheets 12″ off the wall. Of course, I went bigger than that.I replaced my wall of diffusors with a wall of 16″ thick bagged Roxul.

I don’t miss the diffusion.




Brandon Drury

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Brandon Drury quit counting at 1,200 recorded songs in his busy home recording studio. He is the creator of and is the author of the Killer Home Recording series.

30 responses to Diffusion: Disappointment In Recording Gear #5

  1. they sure look cool, though

  2. Florian Ardelean January 22, 2013 at 6:55 am

    Even Massenberg’s room has corner bass traps all around. Absorption is the way to go unless your room is over 2000 cubic feet in volume and the distance from the diffusers is at least three to five feet.

    I’m actually thinking of making some ESP diffusers to lay them in front of the bass traps – they are light enough to let the bass go through them and they diffuse the mids nicely. Win-win. Then again my mixing room is not very small.

  3. Florian Ardelean January 22, 2013 at 6:57 am

    meant to say EPS polystyrene diffusers

  4. Morten Nielsnen January 22, 2013 at 7:03 am

    I worked in many studios.. with and without diffusors..

    And IMOP at the end of the day you have to ask yourself.. what is rigtht for me/you
    does the guitar or the drums really sound better or are your ears playing tricks on you…

    i can surely be helpfull in some cases, no daubt ..but as it was said .” NOT THE HOLY GRAIL”

    Good musicians and good intruments is far more importent.

    I would rather play some music and tweak som gear.. than spending my life on how to figure out
    how to treat my studio 100 % right.. it might not be right anyway. :/

  5. Well duh.

    Diffusors only work in the right size and shape rooms. Which most of us don’t have. UNless you’re purpose-building it in a warehouse or something.

    If you are purpose-building it in a warehouse, then yeah, you’ll want diffusors. No amount of EQ or mic tweaking can get rid of crappy room sound.

  6. In order to see if there is any positive effect brought on by adding Diffusors to a room ….you need to running test signals thru SMART, SATLive, REW or the like. You need to take screen shots of the room before the diffusion and after and you cannot move the measurement microphone in between. Then you’ll be able to tell what effect the diffusion is having. Moving you ear an inch can move you from one comb filter null to another. It’s difficult to hear it moving around a room….but the Mic will hear it and your recordings will reflect the change.

  7. Diffusion is great if you are using it for the right reasons. It’s rarely the answer for the kind of rooms most of us are working in though.

  8. I should start my reply with an admission: I have a conflict of interest. I do have a financial incentive. I do make diffusers as part of my income. I have spent hours and hours evaluating room treatments (especially diffusers) and I have a number of observations that are NOT consistent with the common wisdom and academic research/opinions out there. Diffusers can affect frequency below the quarter-wavelength frequency by careful placement of the diffusers NOT at the room boundaries. Andy Hong from TapeOp’s review of my diffusers describes the effect of properly located diffusers behind the mix position best.

    First I should say that I completely agree that the most important part of a good recording is a good performer. This is particularly true with drummers because how the stick (or hand) strikes the instrument can be varied a zillion different ways. This is more important that nylon/wood tips, stick species, stick weight, drum head, drum shells, yada yada. One of the first great drummers that I ever worked with had a story about Tony Williams sitting down to play on my friend’s crappy sounding drum set and making is sound like Tony Williams. It IS the player.

    The room is super important. It doesn’t need to be big to sound good. Speaking mainly about drums, a dead room really doesn’t work for a realistic drum sound. The drums might still sound good, but they won’t sound acoustic. In standard untreated rooms, especially small rooms, what we hear mostly is the early reflections. There are many, many more reflected transients than the original direct transient. The loudness of the drum increases perceptually with more reflections because the sound is loud for longer amounts of time. The room is amplifying the sound. The room gives the drum sound balls. If the room is treated only with absorption, lots of the sound gets absorbed and not reflected. The perception is that the drums are less loud. What’s worse is that absorption is a function of frequency so more high frequencies are absorbed. It’s VERY hard to absorb low frequencies (16″ of ROXUL anyone?) You will often find that you will need to boost high frequencies and upper mids on a kit that is recorded in a room that’s too dead.

    The control room is where I find diffusion to be the most useful. You want the control room to sound like a “normal” but controlled sounding room. Think of it as trying to emulate a living room where people listen to the HIFI. (What’s a HIFI?) If the room is too bright, you will mix dark. If it’s too dead, you will add too much artificial reverb. Etc.

    Diffusion is a way of controlling bad sounding (specular) reflections without deadening the sound. In my opinion, phase cancellations and comb filtering are the biggest source of problems because they alter timbre. Targeted low frequency absorption is almost always necessary below 300 Hz or so to control uneven bass response. But if your control room doesn’t sound like a real room, it’s not very helpful for mixing in.

    If you have a small room that doesn’t have all parallel walls/ceiling/floor and doesn’t have large flat reflective surfaces, you probably have a pretty good sounding room without adding bunch of treatment. Not all rooms need diffusers, not all rooms need a ton of broadband absorption either. You need to listen to the room, identify the problems and fix the problems with targeted and thoughtful treatments.

  9. @Jeff Scott Hi Jeff-> I have done some extremely extensive testing of control rooms and diffusion. What I have found is that I am able to hear things with my two ears that are not always reflected by a single testing microphone. When we listen our brain is constantly integrating the audio information from both of our ears and we get both the sum of both ears and the differences between both ears. We also move our heads around constantly which changes the early reflection delay times and comb filtering. If you move the mic around for each test and make and average several tests you can often discover the weirdness that isn’t being shown in a mono test. One super fun thing to do is to plug one of your ears and try to listen to room in “mono.” I have found that this is much more similar to single mic sweep testing.

  10. That is the one thing many people seem to rely on, in the teaching industry, is the use of “diffusion” to help reflective waves from creating a poor quality recording.
    Being in the music business and taking engineering classes [and being certified] it’s kind of like having to get 2nd and 3rd opinions from doctors! It really depends on the room situation you have to deal with along with the recording equipment you have!
    I use Cubase 6.5, which I am certified in, and have little to no problems recording with out all the professional “whistles and bells”.
    From my experience, which started in the late 80′s to late 90′s in recording studios, I’ve learned that it takes a certain type of ear rather than the total padding and diffusers used today. My home studio is cut up into different angles and heights which works perfect for me to overcome recording problems. Nowing how to EQ the recorded sound can clear up a lot of the battles! So I agree with Brandon, try using less and training your ears what to listen for. I took a course on it and I feel every artist should because you can hear frequencies that you couldn’t hear before! It really works!

  11. Couldn’t agree more Brandon. Nothing wrong with diffusion at all and it certainly can be helpful. It’s just not some overwhelming delight.

    I’ve gone to a totally dead room. I mean totally dead. You can add reverb that way at any stage of the game. Seems silly to be stuck with what you record. Close micing really makes the differences fairly small to begin with.

    In a monitoring environment…maybe it’s useful. The meaningful evidence would say ‘not really’ but ‘maybe’. According to the evidence, we tend to learn the room characteristics above 300Hz and hear the source. Diffusion isn’t happening in small rooms below 300Hz.


  12. brandon your cold truth is appreciated. a lot of people, after spending time and money, are reluctant to admit it wasn’t quite worth it. but then that’s why i, and others, like your take on things. your misstep could be our shortcut. i remember reading about your diffuser build.

    yeah i agree. i haven’t built the diffusers but i had my suspicions. i think the conventional wisdom on small rooms is actually true. low end is the issue. i would change that a bit to say that low end is the hardest thing to solve but not the only problem. you can have serious problems from mid range and high end bouncing around. the difference is you can treat this with a lot less time and expense.

  13. your misstep could be our shortcut. i remember reading about your diffuser build.

    I always look at this gig as the mad scientists experimenting on myself. I like to report my findings without all the convoluted kool aid mustache advice that pervades. I know my tastes aren’t going to be universal, but a person can decide if I’m out of my mind or not. (Don’t answer that!)

    On one hand, I do feel a little odd about a 6-part article series warning people what NOT to do (or at least not overhyping something relative subtle). Then again, I can’t imagine it ever being a bad thing knowing some bad weather may be on the road.

    I can’t wait until I start covering the optimistic side of this thing because I’ve got a feeling that’s going to be even more controversial.

  14. I’ve gone to a totally dead room. I mean totally dead.

    The rumors fly about how this sucks the “life” out of an instrument. I can’t comment on that because I think a bad room sounds like death. I do know that a totally dead room DEFINITELY sucks the death out. I’ve done this with my tiny little live room. I have 4″ of Roxul spaced 12″ from the wall on all 5 walls. I have 16″ of Roxul in the ceiling. By far, this has WAYYYY less death in it. (I mean the bad death.)

    I’ve recorded in situation where the room did something awesome that a reverb would have a hard time with. I’ve also been stuck with ambiance I wasn’t digging. This is debated in high end recording studio design books like It’s VERY tricky designing a huge ultra mega room. Most robo studios end up going with something that they think will work for Slipknot and a large orchestra the best they can. Rarely is it ideal for everyone.

    When the drums are 100% dry, for example, it does put pressure on the processing a hair. I sampled the Superior Drummer 2.0 room mics (okay, I rendered the samples) and tossed those into Trigger and that’s been my bread and butter. A person could use regular ol’ reverb, too, if they were so inclined. It’s rarely been an issue thus far.

  15. I have found this to be largely the case. Large commercial studios have spent millions to get a space and equipment specifically for recording. That makes the subtle differences audible. That is why they have to have the best electronics. My room is so filled with compromises that some of that sublety is overpowered by the space itself. Buy the best you can afford and learn to use it to the best of your ability. If you need better go to the best and let them do it.

  16. Thank god for convolution reverb. You can record in any room you like.

  17. …or use just about any digital reverb you want.

  18. And a lot of other stuff. I’ve made impulses of all sorts of madness. What a cool tech. Thank you Fourier!

  19. mind=blown ….. how bad of a noob am I when nearly all of that was greek to me?

  20. This couldn’t of came at a better time I’m currently in the process of tuning my room.. My room is 15x17x8 .. And I’m actually covering all the walls with stacked cubicles..( I got 32 4x5ft walls for free!!) these cubicles are made of 2- 2″ rigid fiberglass with a thin aluminum sheet in between the 2- 2″fiberglass, and it’s all covered with fabric of course.. Anyways. I’m planning on goin completely dead.. The cubicles will be spaced about 2″ from the walls with rubber stoppers and they are also gonna br standing on rubber stoppers.. I figured the dense cubicles will help yield some bass.. I’m also goin to put a combination of batting and some
    Of my auralex foam on top of that and cover everything with burlap.. Anyways I know it’s kinda out of context… Any one care to comment on this setup?? Feel free to email me..

    Btw great article.. I’m still learning about acoustics ..
    All these kids coming out of recording schools
    Always underestimate good room treatment .. And rather buy an Avalon or a 103 first.. I was one of them kids not too long ago :/

  21. So Brandon, I take it from this that you aren’t using the homemade 2D QRD Diffusors anymore?

  22. The diffusors are currently in storage. I will use them in my super studio (probably in the live room). They do their thing….it’s just their thing ain’t nearly what I got all excited about. The running theme with these articles isn’t necessarily that any of these tools are “bad”. It’s just getting my hopes up and shelling out big time/cash has not resulted in substantially better mixes. Interesting stuff.

  23. I thought they looked awesome but seemed to have quite a large footprint in the control room. Good news that they worked anyway. Check out this room>>>

  24. Oh yeah. I’ve been to George Massenburg’s room. We hung out for a bit when I was at the Michael Wagener Worshop in 2006.

  25. Woww, that is insane!!! What’s it like being in a room like that soundwise? I would otherwise hate to fall over into one of those walls lol

  26. It’s ok dude, I just copped your experience with the Dark Side of the Moon album. Again WOWWW!!! So did is basically the way to go?

  27. I think there’s a video somewhere on youtube of him actually recording a band in that same room. I’ll see if I can find it.

  28. I agree with the comments about how small rooms can sound very bad without some agreesive treatment.

    Regarding this comment: “That 150-300Hz crappy stuff wasn’t the room and I was running out of things to attribute it to. It turned out most of my problems were simply the resonance in the vocal cords of the singers I was dealing with and guitars I was wrestling with.”

    Isn’t this a matter of matching source to mic better?

  29. That’s a great question. Conventional engineering wisdom is that we should run out and grab a new mic every time we run into a snag. I haven’t found this nearly as effective as is implied. The workflow from switching mics this often is a major hassle to the point of killing the vibe of the session. Very few people are going to run to the mic locker for those 4 words where a singer gets very soft and the big low end comes in.

    Mic selection (at least when dealing with opinionated mics) is always a factor with vocals. However, it never really compares to improving the source when that is an option. I suspect my challenges with vocal mud have a lot more to do with working with a handful of specific singers who all that that Southeast Missouri nasal thing going on. It’s not been a problem at all with other singers.

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