I've lurked on the gearslutz forum for years and always knew Ethan was a man that knew his stuff, but the man can also get on video and explain everything eloquently in easy to understand terms, with visual representations. One thing is for sure, room treatment is vastly over looked and underrated. When I was younger I tried everything I could to get around having to CORRECTLY treat my recording spaced etc, but once I took the time to soak up the knowledge online and put in some time building some DIY absorbers etc, my mind was made up real quick. Top notch video, even 6 years after the fact.
I don't know what i enjoyed more about this video. The huge amount of good information, the dad jokes, or the dudes disgust for poly diffusers. Well done Ethan, you made a masterpiece
Glad to know Flutter Echo is the name for why a house sounds different inside when you move all your stuff out that was acting as diffusers and informal absorption surfaces
It really helps to close my eyes while listening to these demos on my headphones.. I'm surprised the differences are so easily noticeable. I noticed the QRD sounded the "harshest" on both my tablet and my headphones.
Fantastic demo!! The QRD device clearly sounds the best... I'm strictly a voice over guy so I much prefer a DEAD room as apposed to a LIVE one.... And no doubt for musicians diffusion makes a LOT of sense!
Best explanation and demo on diffusion! I ve been searching for something like this for ages! Do have 1 question, placing them directly behind speakers on a wall, which are 45 cm from the wall (bassport in rear). Is that going to help? It's a normal livingroom, no studio. Some folks keep pushing that idea....
I always question people who say "how do people not know this video". This is the first time I agree . I am weirded out by the sub count. Wish you many more in the future
Remember Ethan, things like flutter are heavily dependent on the placement of the source. Generally when the source is near a wall, flutter is greatly reduced as the reflection is not even remotely equal from the near wal to a far wall. But when the source is more centered, or worst of all, dead center in a room with self divisible or square dimensions(i.e. 10’x20’, 9’x27’, 15’x45’, etc) where the flutter can be quite unnerving. But the source placement is crucial. The worst I’ve ever heard was in a theater just about dead center and clap. The reverberant sound was like a spring, meets a slinky, meets a flanger, meets and wiffle ball bouncing within a foot wide gap really fast. Big room. Very quick flutter. In fact this example was the most textbook example of “flutter” I’ve ever heard because it truly sounded like something was “fluttering”, waving back and forth, but more like a hummingbird’s wings than a butterfly. But, for the gig, it was nonexistent, because the sou4ce wasn’t anywhere around that center area. No biggie. And as you very well know, the placement of the source of the sound of concern is crucial. Want a huge drum sound? Try placing it dead center. But depending on dimensions and volume, the whole thing could cancel itself out. If the walls and/or ceilings are irregular, you’ve struck gold! Throw your PCM91s in the trash cases the room has your canned verb in visceral form! But verb doesn’t have to be outrageous when the source is closer to the reflective surface. Of course that usually makes it farther from another maybe reflective surface. So……. Refraction is key, even for bass. If you are lucky enough to be able to absorb bass, more power to you. My solution for bass resonance is to prevent that level and eq of bass from even making enough volume in that direction as to reduce said ill resonance. Even that has side effects, cause as we all know, there are no free lunches. Or are there? No. There are not. Good ole pro tips I learned from veterans who can still school me: The smallest drivers you can get away with. If you can use a 10” instead of a 15”, do it, all day long. If you can make the bass you need with 12” instead of 18” drivers, do it man. And cross over as low as you can, whether from hi or mid, as low as the driver and phase will allow. You’ll notice that nowadays these guys are letting their line arrays go down to 60 and 50 hz before the subs pick up the rest. Wow. But there you go again. A shit load of 6” drivers will blow your mind for low end coherence and reduced phase issues because the note may be the same, but the distance between the sources of the notes can be so much less with smaller drivers giving you better control of things like the impossible to control interference between the outer edge of one 18” driver with the same edge at just the wrong distance apart, where the larger circumference simply aggravates the issue by spreading the tones across a larger surface, with less choice of placement. An SVT makes tons of low end, yes. But it’s an uncontrolled line array, and the inherent phase alignment is as problematic as it is beautiful. For each step you take away from an SVT or even off-axis, the resonant and loudest tone will change, so that low E was nice a full step away,but disappeared into feel-only zone when you step back to it, and then the F chews you up in one particular place, but is gone if you move around too much. A gradient array can help that, but even that has layered compromises and dimensionally difficult to comprehend, as height plays a big factor too. Sitting down can sound totally different that standing u in the same spot. Of course one the other pro tips they used to tell me was point source, point source, point source, where you can. Delay fills are fine, but keep the volumes lower than higher, and psychoacousticly the delay times will be less a liability by position, but a more realistic and forgiving plug in the acoustic hole. Nowadays, after 27 years of live mixing, where I thought I had a pretty solid grasp of acoustics, have discovered a whole new way to look at sound reproduction and sound reinforcement. I don’t look at two drivers trying to do the same thing the same way anymore. Never again. No matter what, there is a compromise. The purity of source versus reception(your ears) can never be as high with more than one driver, especially low frequency drivers. Notice co-axial speakers. Still though, a compromise, by construction restraints. The idea is golden. But the horn never has sounded right to me, as the LF driver seems to reverberate the “lense” of the HF “throat” gets harmonic “fluttering” (see what I did there?) that does affect the tones above crossover point. Now the 400-600 hz has to go “around” the HF lense before joining the rest of the LF content, just as a loose example, and becomes literally “behind” the 90-400hz material. This can used by tuning the shape and placement to get things back in phase that may be out by inherent wave lengths anyways, but regardless, there is going to be a compromise somewhere. This may be intuitively obvious to some. But point source is always best, smallest drivers crossed over as low as possible. So a nice 1.5” horn with a 3” diaphragm might just work with a 12” LF driver with cabinetry designed to cancel its own reflections and sum where the driver might be weakest. West Lake monitors use 15” LF drivers, two of them per cab, and if you are dead center or way off to the side there are holes down low, depending on how far away you are. But otherwise sound KILLER. But, they are willing to accept the compromise for the exceptional results. Bass traps? I try to use various diameters of soft, heavy, cylinders, either right in the corners or just out of them along the wall. What is soft, heavy, cylindrical, and dense? Punching bags. Various weights, sizes, not expansive, irregular as you want, and incredibly effective bass diffusers. I wouldn’t call them traps, but hey can break up a ton of would-be summation built up in corners or opposite walls from the subs. Traps? Good luck. It’s incredibly difficult to really “trap” bass. A sub gradient is the best way I know to truly “trap” sub-bass. With that you can tune and control direction, less in a room, but still very doable and effective, yet confoundingly difficult if you let the theory get away from you. Bass. Ahhhh. Bass. Nose twitching, eyes rippling. Nearby rolling thunder. Bass.
One well deserved like from me. I can see you know, what you are talking about, and the way you explain the inner workings of an acoustic science is both information dense and easy to understand. Well done.
Bass-Absorption + Diffusion: A way which produced interestingly nice results was to use polystyrol diffusors in front of classical bass traps. The styro diffusers are very light weighted and had been additionally covered with epoxy and clay to create a rigid surface. Anyway the whole object still mostly transmits wavelength beyond 200Hz allmost up to 100% as expect. These run into the bass trap.
There used to be a gigantic bookshelf in my mixing room. In fact it covered all of my back wall except for like a foot near the ceiling.Filled with all kinds of books (small large and inbetween) The day It was taken away from my room OH BOY did it sound nasty.
There are some cases of well known sound engineers using bookshelf in their studio as part of their absorption/diffuser components and seems to work well for them.
Thanks for the video. Would there a a better audio result if you put some kind of fabric on it? What about the material of the diffusor, how much does it affect the sound? Thanks
If you have technical questions about this video that require a reply, please do not post them here as comments. TH-cam is not a good venue for a technical exchange. Instead, please post your questions in the Acoustics section of my Audio Expert forum: the-audio-expert.freeforums.net/
Thank you for the actual demo of the subject. Theory & fact are great but then adding actual application and demonstration is the way to teach. Subscribed !
I received the mobile bass trap "vocal booth" from you years ago that is absolutely indispensable. I do voice overs and narration and no matter what else acoustically I add to my humble home studio, those foldable panels are still great to put up in a free standing position or making use of elsewhere for additional coverage.
To me the QRD enhanced the guitar sound the most followed by the poly with the microphone near the outside. The poly with the mic near the inside sounded harsh and muffled. Absorption sounded even more muffled and dead. The bookcase sounded the same as the plain wall.
We're having issues with 70 hz on the vertical axis. The room is for singing, spoken word, and mid to high frequency instruments. No percussion. What should we do? Where should we buy our products?
70 Hz is pretty low for voice and mid/high frequency instruments. But if you really do need to trap that, my company RealTraps can help you: realtraps.com/
Thank you for such a helpful video. I recently purchased 3 modern Skyline wooden diffuser panels. Each panel is 33 inches x 17 inches & 3 inches deep. This is enough to cover over 1/3rd of my total back wall starting from the top of the sofa in the listening position. I want to add some absorption panels in this location along with the diffusers to increase treatment effectiveness. How should I lay them out on my back wall? Should I stagger 1 diffuser panel with 1 absorption panel? I am wondering what my options are. By the way, I am using these panels to increase my enjoyment of listening to my 2 channel stereo system. My stereo is in a multu-purpose room. Thanks, David
I wish you had asked before you bought those diffusers. The RealTraps Diffusers my company sells are made of bass trap material. So they diffuse from about 700 Hz and up, then transition to absorption below that. In your case, I'd center the diffusers vertically at ear height, as a single group adjacent, then add serious (thick) absorption above and below.
@@EthanWiner Thank You for this information 👍. Can I have a 2 inches of seperation between each diffuser panel for esthetic purposes? My ceiling is 8 feet high. What should the approximate total height of the diffusers & absorbers be? For esthetic purposes, I don't want my back wall to be completely covered by accoustic panels. Thanks!
You're asking a lot of questions and a truly complete answer would take half an hour to write. About the 2-inch spacing, ask the people who sold you the diffusers. For the absorbers, thicker is always better, and the more surface you cover the better.
I'm changing the acoustic of my studio and wasn't sure about what kind of diffusers to get...Had polystyrene ones, less than half-inch depth.... With your demonstrations am gonna get the QRD's straight away! Thanks a lot Ethan for sharing your knowledge with us!!!! think the best video on youtube found so far :)
So, Mr Winer, should I calculate QRD diffuser to a certain problem frequency? I'm building control room 6x4 meters, with 3m ceiling, and I notice, that on the couch is a lot of low end, and on a "sweet spot" less. I get some low end cancellations?
Yes. If you need much more guidance, post in my Audio Expert forum, that's easier than trying to explain here in TH-cam comments: the-audio-expert.freeforums.net/
one can hear the phasing on the last strum with the QRD. Poly with mic on the outside sounds way better (after loudness match)...but yea, probably only in this distance and that specific spot
I'm listening on a Bluetooth box that is also my grotbox, the bookcase isn't nearly as good as the qrd, but better than the inside of the poly and way better than wall and absorber at scattering usable highs towards the mic. There was some dose of myth busting here, but I'm glad that I'm stuck with our giant Billy full of crap behind my listening position.
Thank you @ethan winer for your video. That was pretty refreshing :). Im currently trying to 3d print some acoustic piramide diffusers. But I have no idea if they will work, if they are too small... I am currently printing either 3 by 3 cm and 2,1cm heigh. They have a wall thickness of 2 (around 1mm, yet its pretty strong), and the piramides are hollow. The idea is to print sheets of 7 by 7 piramides, so 49, and then I can just tile them. My other option is piramides of 6 by 6 cm, and 4,1cm heigh... My question is, will this work, even when the piramides are hollow... And how much surface should I cover to effectively test it. Thanks in adance!
It depends where the slope is in the room. Please see the note above about asking technical questions in my Audio Expert forum. TH-cam is not a good place for this sort of tech advice.
Thanks very much for the informative video! It's given me a better understanding of the role diffusion plays in control rooms, and in recording situation. I particularly appreciate the simple, very useful A/B comparisons.
Brilliant video, so well explained, and on top of this, the phenomenon being described (flutter echo, comb resonance etc.) is actually shown (or more importantly heard!) Very useful information!
Ethan, 1) what are the frequency bands you consider as low/mid/high? 2) What is your opinion of diaphragm/pressure based bass traps vs your ploywool/velocity based bass traps? Thank you.
It would take six paragraphs to answer all of that completely. So briefly, the bass range is up to around 200-300 Hz, mids go up to maybe 2 KHz, with highs above that. RealTraps are velocity based but we use no plywood. Our bass traps have a thin plastic membrane behind the front fabric. This is much better than tuned pressure-based traps.
Really informative video. To me the only surfaces that sounded bad were the book shelf and absorber, although I could hear the differences between all of them. I thought the bare wall sounded ok.
It's difficult if not impossible to measure the sound quality of a diffuser, because moving the microphone even an inch or two changes the sound captured by quite a lot. So if the goal is to compare different types of diffusers, where would you even mic two different devices to fairly compare them? I do think you could assess the sound in person. And my comparison here with a measuring microphone was the best I was able to do.
Skyline diffusers are also QRD, but they're 2-dimensional instead of 1-dimensional. They work better on the ceiling of a recording live room than the rear wall of a listening room.
Ethan Winer I’ve seen these skyline diffusers mounted on the front wall behind or between speakers by audiophiles or even by well know audio companies in their demo room. What’s up with that?
@@Ab20222 Please see the link to my forum in the video description above. I can't reasonably carry on a technical discussion in TH-cam comments. Or Friend me on Facebook if you're there, and post in one of the audio groups and tag me.
I'm late to this video, and new to acoustics. But I have a question that I'm hoping someone can help me with. If you place a hand held mic inside one and only one of the wells, is the depth of the well cancelled by the fact that the mic is not at the exact distance? Also if you are recording only the one well, is the back of that well not a flat surface? This would lead me to believe the difference in sound would be due to the width making it just small room versus large room. Am I wrong, and if so, how?
@@EthanWiner sorry, I wasn't very specific. I loved the guitar examples of the difference in acoustic treatments. I could tell exactly what you were trying to demonstrate. I'm just recently trying to wrap my head around sound improvement with out " gear upgrades". I think I understand how friction absorbers work. " Traps" using a membrane, that's not as clear. When it comes to refraction, I am getting the basics... I think. My understanding (and I could be wrong) , is that the difference in " well" depths would be to stagger the reflected sound, reducing the intensity (volume) of the delayed sound. So my question was, in the example shown, you placed a hand held microphone in the opening of one of the wells. Would that not be mostly, if not completely picking up the reflected sound from that one well. If they we're different depths, from each other, was the recorded sound I heard not from one well. If so that well appeared to be a constant depth from top to bottom, and therefore a flat surface. However I did hear a little different sound from two of those wells. Finally the real question. If the sound was bouncing back from one distance per recording, was the difference I heard as much a result of the difference in width as depth? You know, like small room vs large room reverb. Or am I missing a fundamental? Sorry if my questions are confusing. And thank you for trying to explain it to me.
Staggering the reflections with different well depths is more to come back at different times than at different volumes. That also has the effect of scattering the reflections left and right, not just straight back toward the source. With the microphone deep inside a well you are hearing mainly that one well's resonance. With diffusers, generally, the deepest well depth dictates the lowest frequency diffused, and the well width determines the highest frequency affected. Narrower wells diffuse to higher frequencies. But we don't want or need diffusion to very low or very high frequencies. So the dimensions in the RealTraps diffuser are pretty much ideal.
@@EthanWiner thank you so much for replying. The string section that was on the magazine you mentioned, with the difusors behind the players. I wonder what it sounds like, but it seems like a good ideia for me from the beginning
oh wow. the qrd diffuser was definitely way better than the poly and light years better than everything else. i might have to watch the video again but does it make sense to use acoustic sound panels to absorb room reflection while still using a qrd diffuser as close as you did for the acoustic guitar recording? in lets say an average sized bed room?
Diffusers aren't usually placed very close to a source or a microphone, though the photo example of the string quartet in this video shows diffusers behind the players to increase a sense of "close" ambience.
When recording with a mic, the front wall becomes the wall you’re facing, correct? I was wondering, if you were about 7 feet from that wall would you use a diffuser at mic height there? (With bass traps in the corners)? Or would only panels be better? Would you use a mixture of both on the side walls?
It depends entirely on the shape and size of the room, where you are in the room, and what else is in the room. As explained in the video description above, this is better discussed in my Audio Expert forum. So sign up and post there.
Great video, thanks for making and posting! Your test of the bookcase was interesting for "no effect" which has given me an idea for hiding/disguising bass traps. Do you think a bookshelf unit with a false back and with 100mm Knauf Earthwall behind and space for CDs and DVDs at the front would work well for a bass trap? I'm not an audiophile, just want to get rid of a terrible low frequency null at our listening points which will obtain wife approval. Could use the same concept for corner traps.
As explained in the description for this video, I can't reasonably give technical advice in TH-cam comments. Please post in my Audio Expert forum linked in the video description. Thanks.
Ethan, this is a great idea for a video. However, I noticed that the volume between each surface differed, and the QRD sounded the loudest. I understand that it may be that the QRD was the loudest surface of the three, but when it comes to recording, doesn't it make sense to compare these surfaces at equal volume (which I understand could be a challenge with the different harmonics presented by different surfaces)? Also, in the past you used a speaker for a similar test, rather than a live instrument. I thought that was a clever way to avoid the inherent differences between different performances- was that a consideration for this demo? At any rate, thank you for sharing your insight!
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+Steven Morris Yeah I would also like to see a non dynamic variable method ( guy playing guitar) of the test. Your point is very important IMO. Even a mono speaker but highest quality recording ( tape or 24 bit for those extended frequencies) would work.
+Steven Morris The volume differences are what they are, but you and goat are correct that having a person play live adds an undesirable variability. An acoustic guitar radiates sound differently from a loudspeaker, so I'm not sure how I'd position a speaker for these comparisons. More important, to my ears the differences between these surfaces are very distinct. It's not like some types of audio testing, where the differences are so subtle you're not totally sure the differences are even real!
Ethan Winer Thanks for taking the time to reply. I understand your point and agree with the fact that the audible differences between the surfaces aren't exactly subtle, which was made apparent when you were testing them with your voice.
Hi Ethan, Firstly thank you for making these videos, they have been very helpful in my learning of room acoustics. I've seen many types of diffusion: 1.) Space Couplers 2.) Curve Diffuser 3.) Skyline Diffusion However, many acousticians swear by QRD Diffusion. Is there a reason why?
I think this video explains very well why QRD diffusers are better than curve surfaces. And space couplers are not diffusers. So the direct answer is that QRD diffusers work better and sound better. Skylines are good, and are also QRD, used mostly on a ceiling where you want the sound to scatter in two planes. On a rear wall, scattering left and right only makes more sense.
Got a tip for ya - Anderson International Trading in Anaheim carries plywoods in ALL KINDS of curved dimensions. You could simply order 1/2 circles, 1/4 circles etc in all different thicknesses, prime them as you like and save yourself a LOT of time. Still, I thought the QRD diffusers and the bookcase sounded better. Where can I buy your bookcase full of acoustic books?
I have spent hours online doing research on acoustic absorbers and defusers and it is amazing how people give such opposite information, it's hard to find two that agree with everything, but so far, I like the advice by this guy the best. The thing is, acoustics of a room is super important to how it sounds and any little adjustment can have huge changes in the sound and each room is different so one sizes fits all is out and that is important to remember, something that works great in one space will have horrible effects in another space. Experimenting is a must, no matter how well you measure, only real listening can get you where you need to be. These panels can cost a lot, so experimenting may not be possible and you need to just jump in and start moving things around. I think anyone can make a room sound great unless they are in a square or a round room, round is very rare but square is not and I feel bad for anyone attempting to make a square room sound great, you may want to buy more headphones because it is that bad for sound.
I actually quite liked the sound of the bookshelf, had an element of absorbtion to it as well, it has to be said that scattering the books front to back will make a massive difference. Of course is sounds way less "airy" then the QRD diffusers.
It sounds to me like all the surfaces apart from the real trap are absorbing the higher frequencies whilst amplifying or reflecting the lows making them sound incorrect? To my ears the absorption sounds ‘dead’ The real tap is the only only one that seems to maintain the natural balance throughout the frequency range. Interesting that it works so well that close to the microphone. It would be nice to do a similar test with pink noise and measure the frequency responses near each one.
Good comments, Paul! Yes, the absorber is more "dead" sounding than the diffuser because it kills the mids and highs from being reflected and adding to the sound getting into the microphone. But that's also an artifact of having the microphone and guitar so close. If the mic and guitar were two feet away, the absorption would sound more natural, though the audible effect would be reduced and not as obvious. I also agree that seeing the response for each surface would be useful.
That’s interesting, So it’s really the wall behind that’s important, especially if you have a room that is small and your head is close to the wall behind you. Not the wall behind the sound source (speakers) because the further away you are the less it will be noticeable? Which is why you recommend using a diffuser behind the listening position which all make total sense. Thank you for an excellent explanation backed up by an understandable practicable demonstration, if only there were more people out there doing this kind of insightful education. 👍
Thanks again for your good comments. And yes, diffusion or thin absorption behind "box" type speakers makes little sense because the sound from the speakers goes the other way. Reflections from behind the listener are often the most damaging.
The best books are very expensive. One is Recording Studio Design by Philip Newell. Another is the classic Master Handbook of Acoustics by Everest, but some of the info is obsolete, and the newer edition that someone else took over is riddled with errors. My Audio Expert book isn't cheap either, but it contains everything I know about acoustics, plus literally 20 times more useful info about audio generally: ethanwiner.com/book.htm
i love these old skool guys, they are so honest, knowledgeable and thorough!
Absolutely! No show, no bullshit, just information and a few jokes.
i truly love how hard he's rocking those two chords
Those 2 chords sound the same as from a song that had a rather famous copyright lawsuit.
There I thought you were referring to the eyebrows, but yes chords too.
@@VEC7ORlt damn ya beat me to it
@@jcisme Those two chords are Em and A Major. They form the basis of thousands of songs.
@@VEC7ORlt definately ...!
You rarely see such a professional person visibly passionate about his subject these days. I enjoyed this video a lot.
Thanks Alex.
Ethan, you ROCK!
I've studied acoustics since 1978 and testify your videos are BAR FAR the most concise presentation of acoustic science.
he absolutely rocks!!!!!
He's the best man. He makes himself accessible to all of us because he truly loves the science!
WOW the diffuser brought the guitar to life. Much more definition and energy.
I've lurked on the gearslutz forum for years and always knew Ethan was a man that knew his stuff, but the man can also get on video and explain everything eloquently in easy to understand terms, with visual representations. One thing is for sure, room treatment is vastly over looked and underrated. When I was younger I tried everything I could to get around having to CORRECTLY treat my recording spaced etc, but once I took the time to soak up the knowledge online and put in some time building some DIY absorbers etc, my mind was made up real quick. Top notch video, even 6 years after the fact.
Thanks!
It's sad to see that now its GEARPAGE. Fragile world.
Once in a while you find educative videos that are more focused on actually learning something than just entertainment....
This explanation reinforced by the guitar comparison demonstrations at the end was superb!!! Really terrific!
Thanks!
I laughed at the Acoustic Books joke.
Same :)
he seemed slightly pleased to make the gag
i know right XD, really helpful otherwise
I was a lot more excited than I thought I should be...
acoustic book. hahaha
This is a true masterpiece of a learning video. Great job
7:07 acoustics books joke was hilarious
By far the most in depth informative video I've seen on diffusion yet.
At last - a chap who knows what he's talking about. ESPECIALLY at the end with the A/B demo... THANK THANK YOU!
Thanks, glad you liked it.
The man is straight to the point with no embellishing , dramatics like some of the other clowns . Thanks Ethan
I don't know what i enjoyed more about this video. The huge amount of good information, the dad jokes, or the dudes disgust for poly diffusers. Well done Ethan, you made a masterpiece
Why is this guy not an awesome meme yet?
people who have listened to him are busy treating their rooms
@@Dm3qXY Ohhhh shit! lmfao
cuz 12 year olds don't hang around here
@@ByGraceThroughFaith777 Yes they do, it's TH-cam.
@@QoraxAudio No, they don't watch these types of videos...
Thats exactly the style of explanation in a nutshell i was looking for all over the internet. Thank you very much!
Thanks, and you're welcome!
Glad to know Flutter Echo is the name for why a house sounds different inside when you move all your stuff out that was acting as diffusers and informal absorption surfaces
THEE single best video I've ever watched to explain diffusion. Thanks man, great work.
It really helps to close my eyes while listening to these demos on my headphones.. I'm surprised the differences are so easily noticeable. I noticed the QRD sounded the "harshest" on both my tablet and my headphones.
this is my new favorite person
Excellent video. Where do I get one of these "bookcases"
Fantastic demo!! The QRD device clearly sounds the best... I'm strictly a voice over guy so I much prefer a DEAD room as apposed to a LIVE one.... And no doubt for musicians diffusion makes a LOT of sense!
The most concise explanation of diffusion I have seen on YT. Thanks for this.
I really learned from this. I like that you put different kinds of acoustic treatment to the test like this in an A/B listening - thanks :-)
Best explanation and demo on diffusion! I ve been searching for something like this for ages!
Do have 1 question, placing them directly behind speakers on a wall, which are 45 cm from the wall (bassport in rear). Is that going to help? It's a normal livingroom, no studio. Some folks keep pushing that idea....
With normal "box" speakers that send most of the sound forward, diffusion on the front wall behind the speakers is a waste.
I always question people who say "how do people not know this video". This is the first time I agree . I am weirded out by the sub count. Wish you many more in the future
Thanks Guido.
Remember Ethan, things like flutter are heavily dependent on the placement of the source. Generally when the source is near a wall, flutter is greatly reduced as the reflection is not even remotely equal from the near wal to a far wall. But when the source is more centered, or worst of all, dead center in a room with self divisible or square dimensions(i.e. 10’x20’, 9’x27’, 15’x45’, etc) where the flutter can be quite unnerving. But the source placement is crucial. The worst I’ve ever heard was in a theater just about dead center and clap. The reverberant sound was like a spring, meets a slinky, meets a flanger, meets and wiffle ball bouncing within a foot wide gap really fast. Big room. Very quick flutter. In fact this example was the most textbook example of “flutter” I’ve ever heard because it truly sounded like something was “fluttering”, waving back and forth, but more like a hummingbird’s wings than a butterfly. But, for the gig, it was nonexistent, because the sou4ce wasn’t anywhere around that center area. No biggie. And as you very well know, the placement of the source of the sound of concern is crucial. Want a huge drum sound? Try placing it dead center. But depending on dimensions and volume, the whole thing could cancel itself out. If the walls and/or ceilings are irregular, you’ve struck gold! Throw your PCM91s in the trash cases the room has your canned verb in visceral form! But verb doesn’t have to be outrageous when the source is closer to the reflective surface. Of course that usually makes it farther from another maybe reflective surface. So……. Refraction is key, even for bass. If you are lucky enough to be able to absorb bass, more power to you. My solution for bass resonance is to prevent that level and eq of bass from even making enough volume in that direction as to reduce said ill resonance. Even that has side effects, cause as we all know, there are no free lunches. Or are there? No. There are not.
Good ole pro tips I learned from veterans who can still school me: The smallest drivers you can get away with. If you can use a 10” instead of a 15”, do it, all day long. If you can make the bass you need with 12” instead of 18” drivers, do it man. And cross over as low as you can, whether from hi or mid, as low as the driver and phase will allow. You’ll notice that nowadays these guys are letting their line arrays go down to 60 and 50 hz before the subs pick up the rest. Wow. But there you go again. A shit load of 6” drivers will blow your mind for low end coherence and reduced phase issues because the note may be the same, but the distance between the sources of the notes can be so much less with smaller drivers giving you better control of things like the impossible to control interference between the outer edge of one 18” driver with the same edge at just the wrong distance apart, where the larger circumference simply aggravates the issue by spreading the tones across a larger surface, with less choice of placement. An SVT makes tons of low end, yes. But it’s an uncontrolled line array, and the inherent phase alignment is as problematic as it is beautiful. For each step you take away from an SVT or even off-axis, the resonant and loudest tone will change, so that low E was nice a full step away,but disappeared into feel-only zone when you step back to it, and then the F chews you up in one particular place, but is gone if you move around too much. A gradient array can help that, but even that has layered compromises and dimensionally difficult to comprehend, as height plays a big factor too. Sitting down can sound totally different that standing u in the same spot. Of course one the other pro tips they used to tell me was point source, point source, point source, where you can. Delay fills are fine, but keep the volumes lower than higher, and psychoacousticly the delay times will be less a liability by position, but a more realistic and forgiving plug in the acoustic hole. Nowadays, after 27 years of live mixing, where I thought I had a pretty solid grasp of acoustics, have discovered a whole new way to look at sound reproduction and sound reinforcement. I don’t look at two drivers trying to do the same thing the same way anymore. Never again. No matter what, there is a compromise. The purity of source versus reception(your ears) can never be as high with more than one driver, especially low frequency drivers. Notice co-axial speakers. Still though, a compromise, by construction restraints. The idea is golden. But the horn never has sounded right to me, as the LF driver seems to reverberate the “lense” of the HF “throat” gets harmonic “fluttering” (see what I did there?) that does affect the tones above crossover point. Now the 400-600 hz has to go “around” the HF lense before joining the rest of the LF content, just as a loose example, and becomes literally “behind” the 90-400hz material. This can used by tuning the shape and placement to get things back in phase that may be out by inherent wave lengths anyways, but regardless, there is going to be a compromise somewhere. This may be intuitively obvious to some. But point source is always best, smallest drivers crossed over as low as possible. So a nice 1.5” horn with a 3” diaphragm might just work with a 12” LF driver with cabinetry designed to cancel its own reflections and sum where the driver might be weakest. West Lake monitors use 15” LF drivers, two of them per cab, and if you are dead center or way off to the side there are holes down low, depending on how far away you are. But otherwise sound KILLER. But, they are willing to accept the compromise for the exceptional results. Bass traps? I try to use various diameters of soft, heavy, cylinders, either right in the corners or just out of them along the wall. What is soft, heavy, cylindrical, and dense? Punching bags. Various weights, sizes, not expansive, irregular as you want, and incredibly effective bass diffusers. I wouldn’t call them traps, but hey can break up a ton of would-be summation built up in corners or opposite walls from the subs. Traps? Good luck. It’s incredibly difficult to really “trap” bass. A sub gradient is the best way I know to truly “trap” sub-bass. With that you can tune and control direction, less in a room, but still very doable and effective, yet confoundingly difficult if you let the theory get away from you. Bass. Ahhhh. Bass. Nose twitching, eyes rippling. Nearby rolling thunder. Bass.
One well deserved like from me. I can see you know, what you are talking about, and the way you explain the inner workings of an acoustic science is both information dense and easy to understand. Well done.
Thanks Juraj.
I respect what you’re trying to do. It’s hard to get people to understand how much it matters. Which is why it’s so easy to go broke trying to do it.
The final back-to-back-to-back demonstration was VERY helpful.
Bass-Absorption + Diffusion: A way which produced interestingly nice results was to use polystyrol diffusors in front of classical bass traps. The styro diffusers are very light weighted and had been additionally covered with epoxy and clay to create a rigid surface. Anyway the whole object still mostly transmits wavelength beyond 200Hz allmost up to 100% as expect. These run into the bass trap.
Book cases are actually great to have at the rear of your control room, not to be underestimated! Especially in a small home studio.
if I can do 15 mn of Ethan's videos everyday, I can defend my PhD thesis in acoustic / math by next xmas. I am in IT.
I appreciate your honesty about diffusion for small rooms. Thank you
There used to be a gigantic bookshelf in my mixing room. In fact it covered all of my back wall except for like a foot near the ceiling.Filled with all kinds of books (small large and inbetween) The day It was taken away from my room OH BOY did it sound nasty.
Who's stealing your books? Who hurt you?
had fantastic results with mine
There are some cases of well known sound engineers using bookshelf in their studio as part of their absorption/diffuser components and seems to work well for them.
I'm only about 4.5 minutes in, you haven't started a demo yet, but this video is GREAT! Lots of good info.
Thanks for the video. Would there a a better audio result if you put some kind of fabric on it? What about the material of the diffusor, how much does it affect the sound? Thanks
If you have technical questions about this video that require a reply, please do not post them here as comments. TH-cam is not a good venue for a technical exchange. Instead, please post your questions in the Acoustics section of my Audio Expert forum:
the-audio-expert.freeforums.net/
thank you for the knowledge
Thank you for the actual demo of the subject. Theory & fact are great but then adding actual application and demonstration is the way to teach. Subscribed !
bookshelves ARE excellent i have to say - they worked a treat for me - especially when they have built in traps
The best video on this topic. Thank you!
Great audible comparison, Thank you Ethan.
Glad it was helpful!
Ethan Winer is truly THE BEST!! Thank you so much for this. It helps that so many acoustics books have been written, to help treat the finest studios!
Hi sir my room length is 166 inches, I'm unable to find the right place and position for Acaustic could panels. Please help
I think this is what you want:
realtraps.com/art_room-setup.htm
There are many more educational articles on the same site:
realtraps.com/articles.htm
I received the mobile bass trap "vocal booth" from you years ago that is absolutely indispensable. I do voice overs and narration and no matter what else acoustically I add to my humble home studio, those foldable panels are still great to put up in a free standing position or making use of elsewhere for additional coverage.
Great, thanks for the nice note.
This guys great! Where has he been?
LOL, thanks, I've been around for a long time:
ethanwiner.com/music.html
To me the QRD enhanced the guitar sound the most followed by the poly with the microphone near the outside. The poly with the mic near the inside sounded harsh and muffled. Absorption sounded even more muffled and dead. The bookcase sounded the same as the plain wall.
I saw "diffusion" and thought I was getting a video about semiconductors... but the quality of the presentation held my interest.
We're having issues with 70 hz on the vertical axis. The room is for singing, spoken word, and mid to high frequency instruments. No percussion. What should we do? Where should we buy our products?
70 Hz is pretty low for voice and mid/high frequency instruments. But if you really do need to trap that, my company RealTraps can help you:
realtraps.com/
Thank you for such a helpful video.
I recently purchased 3 modern Skyline wooden diffuser panels.
Each panel is 33 inches x 17 inches & 3 inches deep.
This is enough to cover over 1/3rd of my total back wall starting from the top of the sofa in the listening position.
I want to add some absorption panels in this location along with the diffusers to increase treatment effectiveness.
How should I lay them out on my back wall?
Should I stagger 1 diffuser panel with 1 absorption panel?
I am wondering what my options are.
By the way, I am using these panels to increase my enjoyment of listening to my 2 channel stereo system.
My stereo is in a multu-purpose room.
Thanks,
David
I wish you had asked before you bought those diffusers. The RealTraps Diffusers my company sells are made of bass trap material. So they diffuse from about 700 Hz and up, then transition to absorption below that. In your case, I'd center the diffusers vertically at ear height, as a single group adjacent, then add serious (thick) absorption above and below.
@@EthanWiner Thank You for this information 👍.
Can I have a 2 inches of seperation between each diffuser panel for esthetic purposes?
My ceiling is 8 feet high.
What should the approximate total height of the diffusers & absorbers be?
For esthetic purposes, I don't want my back wall to be completely covered by accoustic panels.
Thanks!
By the way, my condo walls are made of concrete....if that helps.
Finally Mr. Winer,
Will 2 inch thick panels do the job or must they be 4 inches?
Thanks So Much
You're asking a lot of questions and a truly complete answer would take half an hour to write. About the 2-inch spacing, ask the people who sold you the diffusers. For the absorbers, thicker is always better, and the more surface you cover the better.
I'm changing the acoustic of my studio and wasn't sure about what kind of diffusers to get...Had polystyrene ones, less than half-inch depth.... With your demonstrations am gonna get the QRD's straight away! Thanks a lot Ethan for sharing your knowledge with us!!!! think the best video on youtube found so far :)
Glad to, thanks.
So, Mr Winer, should I calculate QRD diffuser to a certain problem frequency? I'm building control room 6x4 meters, with 3m ceiling, and I notice, that on the couch is a lot of low end, and on a "sweet spot" less. I get some low end cancellations?
Diffusers are meant to operate over a range of frequencies. A reasonable range is 700 Hz to 3 or 4 KHz.
@@EthanWiner so, below 700 Hz I should build some absorbing panels?
Yes.
If you need much more guidance, post in my Audio Expert forum, that's easier than trying to explain here in TH-cam comments:
the-audio-expert.freeforums.net/
@@EthanWiner , Thank you!
one can hear the phasing on the last strum with the QRD. Poly with mic on the outside sounds way better (after loudness match)...but yea, probably only in this distance and that specific spot
10:11 holy shit, that sounded beautiful
It"s the acoustics books fam
I'm listening on a Bluetooth box that is also my grotbox, the bookcase isn't nearly as good as the qrd, but better than the inside of the poly and way better than wall and absorber at scattering usable highs towards the mic. There was some dose of myth busting here, but I'm glad that I'm stuck with our giant Billy full of crap behind my listening position.
I loved the ventriloquist dummies in the corner watching along with the demo. Bravo, you truly are informed and unique.
Thanks for your comments, Edward. The puppets were made by my friend Robert Rogers, who does that for a living:
www.robertrogerspuppets.com/
Great video!! The traps and the wall sound nice…
Thanks! Glad you liked it.
WRT polys, for the exact reason you stated, you should not have designed them to butt up against each other to avoid detrimental acoustic effects.
Finally, someone who truly knows what he’s talking about.
Thanks.
Thank you @ethan winer for your video. That was pretty refreshing :). Im currently trying to 3d print some acoustic piramide diffusers. But I have no idea if they will work, if they are too small... I am currently printing either 3 by 3 cm and 2,1cm heigh. They have a wall thickness of 2 (around 1mm, yet its pretty strong), and the piramides are hollow. The idea is to print sheets of 7 by 7 piramides, so 49, and then I can just tile them. My other option is piramides of 6 by 6 cm, and 4,1cm heigh... My question is, will this work, even when the piramides are hollow... And how much surface should I cover to effectively test it. Thanks in adance!
That sounds pretty small. You should ask this in my Audio Expert forum. See the note and link above in the description for this video.
The most useful information I’ve found in 12 and a half minutes on TH-cam. Thanks a million!!
hello. How do you treat a sloping roof? thank you for your advices
It depends where the slope is in the room. Please see the note above about asking technical questions in my Audio Expert forum. TH-cam is not a good place for this sort of tech advice.
@@EthanWiner thank you Ethan. No prob...
Finally an YT video that clearly illustrates acoustic treatment. I finally have a better idea on what to do with my home studio.
Wow, very educational and easy to understand. Exceptional presentation!
Thanks!
best YT video i've seen in a while, i'd highly recommend this course instructor to future students. :)
Thanks very much for the informative video! It's given me a better understanding of the role diffusion plays in control rooms, and in recording situation. I particularly appreciate the simple, very useful A/B comparisons.
Brilliant video, so well explained, and on top of this, the phenomenon being described (flutter echo, comb resonance etc.) is actually shown (or more importantly heard!) Very useful information!
Glad it was helpful!
Ethan,
1) what are the frequency bands you consider as low/mid/high?
2) What is your opinion of diaphragm/pressure based bass traps vs your ploywool/velocity based bass traps?
Thank you.
It would take six paragraphs to answer all of that completely. So briefly, the bass range is up to around 200-300 Hz, mids go up to maybe 2 KHz, with highs above that. RealTraps are velocity based but we use no plywood. Our bass traps have a thin plastic membrane behind the front fabric. This is much better than tuned pressure-based traps.
Ethan Winer is a Legend. Most of you youngsters may not know this.
Really informative video. To me the only surfaces that sounded bad were the book shelf and absorber, although I could hear the differences between all of them. I thought the bare wall sounded ok.
in this small sample size the bare wall sounds alright, but walk into any fully bare walled empty room and the sound is rarely pleasant or desirable
i liked the way the bookcase sounded. has anyone put that on a spectrum analyzer against along side the real traps?
It's difficult if not impossible to measure the sound quality of a diffuser, because moving the microphone even an inch or two changes the sound captured by quite a lot. So if the goal is to compare different types of diffusers, where would you even mic two different devices to fairly compare them? I do think you could assess the sound in person. And my comparison here with a measuring microphone was the best I was able to do.
thanks for the video Ethan
What about the modular “skyline” diffuser? What’s your opinion about it and how does it compare with the quadratic diffuser used in your video?
Skyline diffusers are also QRD, but they're 2-dimensional instead of 1-dimensional. They work better on the ceiling of a recording live room than the rear wall of a listening room.
Ethan Winer I appreciate your fast reply. Thanks
Ethan Winer I’ve seen these skyline diffusers mounted on the front wall behind or between speakers by audiophiles or even by well know audio companies in their demo room. What’s up with that?
@@Ab20222 Please see the link to my forum in the video description above. I can't reasonably carry on a technical discussion in TH-cam comments. Or Friend me on Facebook if you're there, and post in one of the audio groups and tag me.
I'm late to this video, and new to acoustics. But I have a question that I'm hoping someone can help me with.
If you place a hand held mic inside one and only one of the wells, is the depth of the well cancelled by the fact that the mic is not at the exact distance?
Also if you are recording only the one well, is the back of that well not a flat surface?
This would lead me to believe the difference in sound would be due to the width making it just small room versus large room.
Am I wrong, and if so, how?
I honestly don't know what you are asking.
@@EthanWiner sorry, I wasn't very specific.
I loved the guitar examples of the difference in acoustic treatments. I could tell exactly what you were trying to demonstrate.
I'm just recently trying to wrap my head around sound improvement with out " gear upgrades". I think I understand how friction absorbers work. " Traps" using a membrane, that's not as clear.
When it comes to refraction, I am getting the basics... I think. My understanding (and I could be wrong) , is that the difference in " well" depths would be to stagger the reflected sound, reducing the intensity (volume) of the delayed sound.
So my question was, in the example shown, you placed a hand held microphone in the opening of one of the wells. Would that not be mostly, if not completely picking up the reflected sound from that one well. If they we're different depths, from each other, was the recorded sound I heard not from one well. If so that well appeared to be a constant depth from top to bottom, and therefore a flat surface. However I did hear a little different sound from two of those wells.
Finally the real question. If the sound was bouncing back from one distance per recording, was the difference I heard as much a result of the difference in width as depth? You know, like small room vs large room reverb.
Or am I missing a fundamental?
Sorry if my questions are confusing. And thank you for trying to explain it to me.
Staggering the reflections with different well depths is more to come back at different times than at different volumes. That also has the effect of scattering the reflections left and right, not just straight back toward the source.
With the microphone deep inside a well you are hearing mainly that one well's resonance.
With diffusers, generally, the deepest well depth dictates the lowest frequency diffused, and the well width determines the highest frequency affected. Narrower wells diffuse to higher frequencies. But we don't want or need diffusion to very low or very high frequencies. So the dimensions in the RealTraps diffuser are pretty much ideal.
@@EthanWiner thank you. It all makes sense now 🙂
Would anyone know what song that string section is in? I’d love to hear what it sounds like
What string section, where?
@@EthanWiner thank you so much for replying. The string section that was on the magazine you mentioned, with the difusors behind the players. I wonder what it sounds like, but it seems like a good ideia for me from the beginning
That photo is from a cover of Mix Magazine showing a recording session at Skywalker Sound. I believe the group is the Kronos String Quartet.
@@EthanWiner thank you so much! I really appreciate your time too
Excellent demonstration. Thanks.
This is the best and the most informative video I’ve ever watched on acoustic diffusers..thank you for sharing such valuable information..❤
Wow, thanks!
oh wow. the qrd diffuser was definitely way better than the poly and light years better than everything else. i might have to watch the video again but does it make sense to use acoustic sound panels to absorb room reflection while still using a qrd diffuser as close as you did for the acoustic guitar recording? in lets say an average sized bed room?
Diffusers aren't usually placed very close to a source or a microphone, though the photo example of the string quartet in this video shows diffusers behind the players to increase a sense of "close" ambience.
When recording with a mic, the front wall becomes the wall you’re facing, correct? I was wondering, if you were about 7 feet from that wall would you use a diffuser at mic height there? (With bass traps in the corners)? Or would only panels be better? Would you use a mixture of both on the side walls?
It depends entirely on the shape and size of the room, where you are in the room, and what else is in the room. As explained in the video description above, this is better discussed in my Audio Expert forum. So sign up and post there.
@@EthanWiner will do!
Great video, thanks for making and posting! Your test of the bookcase was interesting for "no effect" which has given me an idea for hiding/disguising bass traps. Do you think a bookshelf unit with a false back and with 100mm Knauf Earthwall behind and space for CDs and DVDs at the front would work well for a bass trap? I'm not an audiophile, just want to get rid of a terrible low frequency null at our listening points which will obtain wife approval. Could use the same concept for corner traps.
As explained in the description for this video, I can't reasonably give technical advice in TH-cam comments. Please post in my Audio Expert forum linked in the video description. Thanks.
Sorry, didn't see that as the description shows up in "less" mode and I didn't expand it.
Ethan, this is a great idea for a video. However, I noticed that the volume between each surface differed, and the QRD sounded the loudest. I understand that it may be that the QRD was the loudest surface of the three, but when it comes to recording, doesn't it make sense to compare these surfaces at equal volume (which I understand could be a challenge with the different harmonics presented by different surfaces)? Also, in the past you used a speaker for a similar test, rather than a live instrument. I thought that was a clever way to avoid the inherent differences between different performances- was that a consideration for this demo? At any rate, thank you for sharing your insight!
+Steven Morris Yeah I would also like to see a non dynamic variable method ( guy playing guitar) of the test. Your point is very important IMO. Even a mono speaker but highest quality recording ( tape or 24 bit for those extended frequencies) would work.
+Steven Morris The volume differences are what they are, but you and goat are correct that having a person play live adds an undesirable variability. An acoustic guitar radiates sound differently from a loudspeaker, so I'm not sure how I'd position a speaker for these comparisons. More important, to my ears the differences between these surfaces are very distinct. It's not like some types of audio testing, where the differences are so subtle you're not totally sure the differences are even real!
Ethan Winer Thanks for taking the time to reply. I understand your point and agree with the fact that the audible differences between the surfaces aren't exactly subtle, which was made apparent when you were testing them with your voice.
Hi Ethan,
Firstly thank you for making these videos, they have been very helpful in my learning of room acoustics.
I've seen many types of diffusion:
1.) Space Couplers
2.) Curve Diffuser
3.) Skyline Diffusion
However, many acousticians swear by QRD Diffusion. Is there a reason why?
I think this video explains very well why QRD diffusers are better than curve surfaces. And space couplers are not diffusers. So the direct answer is that QRD diffusers work better and sound better. Skylines are good, and are also QRD, used mostly on a ceiling where you want the sound to scatter in two planes. On a rear wall, scattering left and right only makes more sense.
wow, so much info and demos, thank you.
A lot of information packed in your presentation. Thankyou.
Glad it was helpful!
Book shelf sounded the most natural.
Sound Elevation It would have sounded better if he would have changed the size and orientation of the books. Alas, he isn’t selling bookcases.
So in a 220 cm wide, 396 cm long room... Absorbtion is better?
Greetings from Switzerland
Diffusion is good in the back of the room, but it costs more than absorption.
That book case sounds amazing!
On the concrete tube thing, suppose you put a styrofoam tube, such as those used to insulate copper tubing in the valley area?
Got a tip for ya - Anderson International Trading in Anaheim carries plywoods in ALL KINDS of curved dimensions. You could simply order 1/2 circles, 1/4 circles etc in all different thicknesses, prime them as you like and save yourself a LOT of time. Still, I thought the QRD diffusers and the bookcase sounded better. Where can I buy your bookcase full of acoustic books?
Fantastic guitar head movement, A+
Awesome education accoustic class with lots of precise information for sound enthusiast
Great and eye opening video . Thank you for your knowledge.
I have spent hours online doing research on acoustic absorbers and defusers and it is amazing how people give such opposite information, it's hard to find two that agree with everything, but so far, I like the advice by this guy the best. The thing is, acoustics of a room is super important to how it sounds and any little adjustment can have huge changes in the sound and each room is different so one sizes fits all is out and that is important to remember, something that works great in one space will have horrible effects in another space. Experimenting is a must, no matter how well you measure, only real listening can get you where you need to be. These panels can cost a lot, so experimenting may not be possible and you need to just jump in and start moving things around. I think anyone can make a room sound great unless they are in a square or a round room, round is very rare but square is not and I feel bad for anyone attempting to make a square room sound great, you may want to buy more headphones because it is that bad for sound.
why aren't more youtube tutorial vids this informative and organized?
The best part was seeing Microsoft Office 97 on his bookshelf. You never know when you might need to refer to that one. :-)
Don't laugh! I still use Excel and Word from that package and they still work perfectly.
I actually quite liked the sound of the bookshelf, had an element of absorbtion to it as well, it has to be said that scattering the books front to back will make a massive difference. Of course is sounds way less "airy" then the QRD diffusers.
What are the LxWXH of these diffusers?
2 feet wide, 4 feet high, 6 inches thick:
realtraps.com/diffusor.htm
First video, that actually shows the effect of diffusing... and super helpful
The bookcase was an improvement over the bare wall :-) Thanks for reminding me of the Alton Everest book, of which I had forgotten
It sounds to me like all the surfaces apart from the real trap are absorbing the higher frequencies whilst amplifying or reflecting the lows making them sound incorrect? To my ears the absorption sounds ‘dead’
The real tap is the only only one that seems to maintain the natural balance throughout the frequency range. Interesting that it works so well that close to the microphone. It would be nice to do a similar test with pink noise and measure the frequency responses near each one.
Good comments, Paul! Yes, the absorber is more "dead" sounding than the diffuser because it kills the mids and highs from being reflected and adding to the sound getting into the microphone. But that's also an artifact of having the microphone and guitar so close. If the mic and guitar were two feet away, the absorption would sound more natural, though the audible effect would be reduced and not as obvious. I also agree that seeing the response for each surface would be useful.
That’s interesting, So it’s really the wall behind that’s important, especially if you have a room that is small and your head is close to the wall behind you. Not the wall behind the sound source (speakers) because the further away you are the less it will be noticeable? Which is why you recommend using a diffuser behind the listening position which all make total sense. Thank you for an excellent explanation backed up by an understandable practicable demonstration, if only there were more people out there doing this kind of insightful education. 👍
Thanks again for your good comments. And yes, diffusion or thin absorption behind "box" type speakers makes little sense because the sound from the speakers goes the other way. Reflections from behind the listener are often the most damaging.
What are the best Acoustic Books for Acoustics? ;)
The best books are very expensive. One is Recording Studio Design by Philip Newell. Another is the classic Master Handbook of Acoustics by Everest, but some of the info is obsolete, and the newer edition that someone else took over is riddled with errors. My Audio Expert book isn't cheap either, but it contains everything I know about acoustics, plus literally 20 times more useful info about audio generally:
ethanwiner.com/book.htm