Sound Treatment - Diffusers


#1

I’ve probably said it in the forums before, but I have trouble trusting any reviewer who doesn’t have some sort of sound treatment in their listening room. Especially when it comes to small improvements like cables - I can see being able to review big improvements like jumping from a common DAC to the DirectStream, but I’m still skeptical of people without room treatment. :slight_smile:

That said, I’m wondering if anyone has tried some real diffusers, QRD, Skyline, 1D, 2D, whatever. I design and build my own, and have a few in my listening room on the back wall (and plenty of absorbers, but anyone can build a simple absorber - again, no excuse not to have some!). But I’m working on a design for a pretty serious, broadband diffuser that should work from about 275Hz to 12kHz, be about 1’ deep and roughly 3’ by 3’ each. Ultimately I hope to build 24 of these and replace all my smaller diffusers around the room and hopefully shape the sound and improve the imaging at least twofold. Just curious what anyone else has in their room?

I love the math, design, and execution of QRD diffusers. I’ve been building them on and off for about 15 years - and I have kind of a collection of images I’ve found on the web if anyone is curious.

http://lonelyraven.zenfolio.com/p968463117

A couple pictures of my past projects:

Some 4" deep QRD diffusers I built about 14 years ago. I still have them around.

Some flutter breaking diffusers I made, using some recovered and re-purposed vintage oak stair treads.

The back wall of my home theater/listening room.

I have some 2D QRD diffusers I’ve built as well, but I don’t think I have much in the way of photos of them. These are in the RPG style. Some of these are RPG I picked up from a defunct studio, some are my own. I cloned them pretty well, but I don’t care for them very much.

Oh yeah, I also have some of this 3D Wallpaper they call it. It’s made from recycled card board. I basically use it as flutter breaking “diffuser”, though it’s not a proper math designed diffuser, it helps when you get nasty flutter echos between parallel walls.

Lots of fun stuff…sometimes I think I should go back to school and get a degree in acoustics - but IT work is paying decently for me, so why change now. LOL


#2

Well done!


#3

+1. LR, in your experience what’s the right approach for getting into room treatment? What part of the range do you address first, or is there a way to make that decision based on some key room characteristics?


#4

Honestly, the correct way is to take measurements. A free program like REW, a USB measurement microphone, and a steep software learning curve (or some help from some smart guys at GearSlutz.com or AVScience.com). That’s the best way to see and document the issues in the room, then apply room treatment accordingly.

Failing that - you need to understand the general issues every room has and apply solutions by ear.

Taming early reflections, dealing with damaging echos from parallel walls, and of course bass nodes.

I was looking through the photos of peoples systems - it’s clear that looking good is more important than sounding good - I see very pretty setups, super expensive equipment, with big windows between the speakers, and zero room treatment.

Yes, I understand not everyone can make their listening room look like Blackbird Studio C, but I honestly feel you’re not serious about audio if you don’t address room as part of the system. Harsh, but true - deal with it. Once you do address the system, you get:

#1 Addressing early reflections allows your ears/brain to hear and understand the original “source sound” over the room reflections. This allows you to hear the room in the recording, the reverb, track/instrument/vocal separation, and details lost by time smearing. “But I have this already!” you say…no, you don’t. I’ve heard a 2 watt amp off a $200 CD player and two way speakers in a fully treated room that gave me sound approaching what I have with my current $15k setup with the DS. Granted, that system doesn’t have the musicality I have today, but still, you hear the recording.

#2 Addressing parallel wall reflections helps even out the frequency response. You’ll really hear the recording as it was intended.

#3 We all know bass nodes muck up the bass frequency response, so I don’t really need to get into that.

That’s just my basic overview of room treatments. Once you hear a room properly setup, you really can’t go back.

Edit to add: sorry I tapered off and ended this abruptly - it’s been a long day and I"m very tired. That said - just imagine what your system can do if you had a fully treated and dialed in room, with your fancy system, sourced by your PS Audio gear!


#5

Absolutely true and I also strongly advocate room treatments. The room is the biggest and often most influential component of your system. But we tend to scare people with talk of measuring software, custom treatments, etc.

Instead, I suggest people start simple with a couple of absorption panels to tame first-order reflections of off the side walls. This alone makes a tremendous difference, is easy, inexpensive and incredibly satisfying. Anyone can set these up in an hour or less.

Second, one can move on to a couple of bass traps - also simple. Then, if you are interested and like the improvement, you can move on to more sophisticated treatments.


#6

When my wife and I got married and we moved into a new house we had the opportunity to fix some of the room problems in a “brute force” manner. We tilted the left and right walls in by 1/2 inch at the tops and the front wall by 1 1/2 inch at the top. This fixed any slap echo / reverb problems even with no carpets and no other room treatments at all.

We took out some walls and we had to add some beams to hold up the rest of the house so we put bass traps in the kinks of the ceiling that we couldn’t get rid of. We also added fake beams to make the room symmetrical.

We also stiffened the walls with constrained layer dampening (well two different densities of thin wallboard :) ) You can hammer your fist on the walls and all you get is a thud.

We replaced all of the door hardware with quality hardware that doesn’t rattle when smacked and we replaced all of the doors with solid outdoor quality doors and weather stripping to damp their vibrations…

Anyway here are some more details:

New Room description at Audio Asylum

Pictures at Audio Asylum

I got a great buy on 10 ASC SuperTrap Tube Traps that help with the bass when strategically placed.

And I got 2 4" x 2’ x 4’ fiber filled panels that I put over the TV when I want to really lean back and listen. Tho I expected them to help with the high frequency reflections from the glass TV screen they actually make a bigger difference in the bass - I assume by nuking some bass nodes along the long axis of the room, especially at the listening position.

All of these ad hoc seat of the pants treatments worked very well.

Still if push comes to shove I want to be comfortable working and listening there 24/7, so comfortable listening is more important to me that “perfect” sound.

My daughter and her new born son in the sweet spot


#7

I love the idea of gently tilting the walls. This may be a standard trick but I was unaware of it. Sneakily clever.

Various densities of wallboard and Green Glue work magic.

I continue to find fascinating how different a well constructed/treated room feels when one walks into it. It is calmer. I have had contractors want to show my studio to their fellow workers. They get a kick out of just being in the room.


#8

Yep, when you walk just under the beams in the ceiling into the rectangle under the lights the whole room is quieter - you can really hear the difference because of the absorption of echoes and extra sound energy as you step across the threshold.

Tho many people make their rooms non-rectangular to break up room modes, I thought that tilting the walls in was much more practical and should have the desired effect.


#9

Your idea? Elegant solution.


#10

Elk, you’re right, I shouldn’t scare people away - I just tend to be a bit big sky - go big or go home kind of guy.

Ted, that’s both amazing and scary that only 1/2" tilt can make such a difference!

I have a friend that swears by the Golden Ratio for room building (Fibonacci Sequence) - and I’ve been in debates about 1" making or breaking a room…now I’m starting to wonder after what you’ve said (I’ve always felt a little fudging here and there is OK, as long as you aren’t working in perfect cubes or multiples of X). I’m partial to prime numbers myself - my subwoofer dimensions are all prime numbers, even the bracing.

Yes, those are standard sized pillows I’m using for the polyfill - it’s that big. :slight_smile:

It’s a beautiful family you have there, Ted. I’m checking out your other links now.


#11

Ted, that rack-o-jukeboxes is awesome and hilarious at the same time! A lot has changed since then, huh? You could have all that in WAV format on a single hard drive today.


#12

Nice diffusers, Raven! Impressive work and design. I was disappointed to learn that bookshelves were not a good solution for diffusion as I once thought. There is a demo video on Ethan Winer’s website that demonstrates this pretty well. Unfortunately, both side walls of my listening area are almost completely bookshelves. I thought that I had it made!


#13

I do have all of the jukebox CDs in flac now and they’re less than 0.5T :slight_smile: On the other hand I have literally thousands of SACDs and just 700 of them take up another 1.4T .

I can’t quite bring myself to get rid of the juke boxes yet - I theoretically have all of the CD cases, but sorting the CDs back into cases will be way more work than ripping them was.

@Elk, yeh it seemed like a better idea than making the room look like a coffin. For the 1/2" I just guessed in my head what slope I’d need to for 7 reflections to drive the audio into the carpet. I remember that the number was 7 but don’t remember why I chose 7 :slight_smile: Of course low frequencies aren’t affected by the slope, but no wall sloping will help there anyway.

I didn’t do the front wall at first. I demonstrated to my wife with the clap test how well side to side worked with no carpet. But when I did a quarter turn and clapped again it sounded like an arrow thwanging into a target… So we did the front wall 1 1/2". I’m glad I noticed before we painted :)

No one notices the slope unless we tell them. It turned out to be a fine idea.


#14
Lonely Raven said

Honestly, the correct way is to take measurements. A free program like REW, a USB measurement microphone

I have quite a bit of experience with REW. I've used it to measure my room and check the filter responses with the Squeezbox's plugin called Inguz, which provides a surprisingly effective DRC if you spend a little time tweaking and adjusting for things like clipping. What I have always had a hard time figuring out even with that information is just what sort of trap / diffusor / etc then gets put where. I know there is at least one large thread on Audiocircle that goes through a lot of this (with contributions by Ethan Winer), but I can't seem to "get" the translation between acoustic measurements and physical devices. It's much easier for me to understand the "virtual" changes in phase and frequency response calculated for DRC filters. But maybe that's because it's consistent with my professional background.

#15

This may be obvious or overly simplistic but sometimes just doing a little mental math with the approximation that sound travels about a foot/msec will let you translate a peaks and dips to a possible trouble spot. Then you can refine the position of a treatment by ear or remeasurement. Sometimes a mirror on the wall will help find a reflection point if the sound got to a place via a reflection. With a little experience I trust iterated seat of the pants refinements more than I trust most people’s attempts at rigor. After all if you can’t hear the difference does it really matter? Spend your money/time on things that you can hear easily. You can always revisit things later if something still bothers you.


#16

Yeah, I think it takes a lot of experience and practice with the various pieces of treatment to really get a handle on how to treat issues. The nice thing is, re-measuring doesn’t cost anything but time - and I think in the end we all agree our senses are the best final measurement.

Funny story along those lines, in the early days of REW (wow, I think it must have been 12 years ago now?!) I was in a small apartment, and using diffusers to “make the walls disappear” (diffusers not only diffuse the reflections, but due to the sound bouncing in the wells, add a slight time delay, and slight attenuation - therefor diffusers can make walls sound like they are much further away then they actually are). I could hear something wasn’t right, I kept going over it and over it. Then I did one more measurement, and sure enough there was a 5ms reflection somewhere in the room (yes, we can absolutely hear 5ms apparently). When you’re ear/brain hears the direct sound, and that 5ms reflection, it causes a “time smearing” that distorts the image. Your brain is trying to put together where that sound is coming from, but it sounds like it’s coming from two places at once. Think of how your eyes get confused when you’re in a room full of mirrors; if you’re listening room was a room full of mirrors, and you replaced your speakers with two candles in the dark…imagine how confusing that would be to your eyes/brain? Well, that’s what we’re doing to our ears - we evolved to hear in 3d outdoors, not in a box with smooth, parallel painted walls and big windows.

Anywho, back to my 5ms reflection. I’m scratching my head, I’ve got diffusers and aborbers everywhere…but…duh! I forgot to treat the damn ceiling! So I took an old fuzzy blanket and tacked it up to the ceiling - and suddenly my soundstage and image locked into place. That was the last component I needed, the last reflection that was time smearing the image. All it took was a measurement to remind me to look for a reflection 5ms away!

Today, I start my room with bass traps, and this:

More to come as I work through the logistics of building my fleet of diffusers.


#17

Yeh, my ceiling is way too low. I want the first reflection of any path to my ears to be at least 10ms longer than the no reflection path (the Haas effect) This is pretty easy for the walls, etc. but not for my ceiling. I’ve meant to add some absorption to the ceiling at the first reflection points from the speakers but I never seem to get around to it. I’m sure it would help a lot.


#18

I first learned the ceiling trick from the former head of Sony’s classical studios when he was setting up a system locally (he sold a bunch of his equipment and was helping the buyer set it up in his studio.) It’s obvious once you are told or come up with it yourself as you did. It was not obvious to me. :)

I treat the ceiling in my studio. My home main room has a 32’ ceiling. I am glad I do not feel compelled to treat it as getting up there would not be trivial.


#19

Wow, I wish I even had a 12’ ceiling, let alone 32’!

I have a friend that bought my old speaker setup from me some 10 years ago. He just tosses it up against a wall and it sound friggen amazing. The one big difference between his room and my old apartment is the vaulted ceilings. The rest was just dumb luck that the shape and size of his room helps with his near field listening style. I spent ages dialing in these speakers in my room with room treatments, and he gets them dialed in about 15 minutes after setting them up! Some rooms just work out well I guess - but that vaulted ceiling was the key.

Right now, my biggest issues is the L shaped room. My goal with the diffusers will be to stack several in the open space on the right to help trick my ears into thinking there is a wall there - and stacking some equidistant on the left to trick my ears into thinking the wall there is further away. Then I’m getting rid of all the big racks of gear so I can stack a few diffusers in front of the projection screen and make that “disappear” as well.

I just need to get back to the woodshop and work out some of these technical issues. I simply can’t afford to buy off the shelf high end diffusers that start at $500 a pop. Especially when I figure I would need at least 7 of them. That said, I truly feel the improvement to the room sound would be equal to the lift I get from something like the DirectStream, or my Decware Mystery Amp. I estimate I can build diffusers for about $100 a pop, give or take a little.


#20

Some rooms just work. Your friend has one of these.

Diffusers are silly expensive. Yours look great and I bet work well also.