Why Did I Buy This Crap? Room Acoustics Basics
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- เผยแพร่เมื่อ 16 ต.ค. 2023
- Sound advice on room treatment: / @acousticsinsider
The basics of room acoustics are simple - use lots of thick absorbers to reduce the reverb time in the room.
Of course you don't have to start off with a lot, but keep adding as you can afford it until you've reached a point where they are working effectively. But don't fall into thinking that you can get away with using more thinner panels - they need to be a minimum of 6" (150mm) thick, otherwise you are wasting space and money. And you are also killing too much of the high frequencies that you need to preserve to make a room that sounds good.
The key with thick absorbers is that they start working right away in the right way. They help to fix the problems that every small room has, and that's room modes and excess energy in the room. They are the easiest, the least complex and generally the most effective way to treat a room.
While there are other effective methods, like Helmholtz and diaphragmatic, they are harder to design, build and put in a place where they'll work best.
There are also electronic bass traps, but they are quite expensive and may not be more effective than standard absorbers.
So on to the idea of cancelling room modes by timing a signal to do that.
I used the ringing bell as an example, but stopping that from continuing to ring would be trivially easy compared to doing that with an enclosed volume of air inside a room. And assuming you could do it and have it work as it needs to, you'd be unable to change anything in the room or it would stop working. That includes adding more people to the room or leaving the door open - it would throw off that delicate balance.
And like I said in the video, to stop the ringing you need to make a sound that's not part of the original signal to do that, and that's distortion. Any change to the original signal is, by definition, distortion.
The best, proven method is with the brute force absorption I talked about. Room acoustics have been studied for hundreds of years and in the last 100 every possible method has been looked at in detail and tried.
That doesn't rule out further discoveries in the future, but they would have to be much more sophisticated than the method described above.
Worth mentioning that I didn't mention diffusers. Those are only used after you've put in as much bass absorption as you possibly can. Diffusers only work on higher frequencies and have no impact of the bass frequencies.
Also my absorber charts show the flow resistivity as 10,000 for both the foam and the fiberglass / rockwool. This isn't accurate, but is "close enough" to show the glaring differences between the thicknesses. That was the point - making the panel thicker so they will be effective down low. The flow resistivity has an effect, but not as much as making the absorber thicker.
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Sound advice on room treatment: www.youtube.com/@AcousticsInsider
The basics of room acoustics are simple - use lots of thick absorbers to reduce the reverb time in the room.
Of course you don't have to start off with a lot, but keep adding as you can afford it until you've reached a point where they are working effectively. But don't fall into thinking that you can get away with using more thinner panels - they need to be a minimum of 6" (150mm) thick, otherwise you are wasting space and money. And you are also killing too much of the high frequencies that you need to preserve to make a room that sounds good.
The key with thick absorbers is that they start working right away in the right way. They help to fix the problems that every small room has, and that's room modes and excess energy in the room. They are the easiest, the least complex and generally the most effective way to treat a room.
While there are other effective methods, like Helmholtz and diaphragmatic, they are harder to design, build and put in a place where they'll work best.
There are also electronic bass traps, but they are quite expensive and may not be more effective than standard absorbers.
So on to the idea of cancelling room modes by timing a signal to do that.
I used the ringing bell as an example, but stopping that from continuing to ring would be trivially easy compared to doing that with an enclosed volume of air inside a room. And assuming you could do it and have it work as it needs to, you'd be unable to change anything in the room or it would stop working. That includes adding more people to the room or leaving the door open - it would throw off that delicate balance.
And like I said in the video, to stop the ringing you need to make a sound that's not part of the original signal to do that, and that's distortion. Any change to the original signal is, by definition, distortion.
The best, proven method is with the brute force absorption I talked about. Room acoustics have been studied for hundreds of years and in the last 100 every possible method has been looked at in detail and tried.
That doesn't rule out further discoveries in the future, but they would have to be much more sophisticated than the method described above.
Worth mentioning that I didn't mention diffusers. Those are only used after you've put in as much bass absorption as you possibly can. Diffusers only work on higher frequencies and have no impact of the bass frequencies.
Also my absorber charts show the flow resistivity as 10,000 for both the foam and the fiberglass / rockwool. This isn't accurate, but is "close enough" to show the glaring differences between the thicknesses. That was the point - making the panel thicker so they will be effective down low. The flow resistivity has an effect, but not as much as making the absorber thicker.
Thank you for your time. There was some useful explanations there. One thing I would say though, is that if you're starting on a project like this, do absolutely everything you can to avoid using a perfectly square room. I know some times there's no choice, but this is absolutely the worst room you could have.
Very well explained John! Thank you for your time. You would have been a great teacher!
For some of us he is now :)
except there's an error :)
while he's correct, those absorbers are not 2" and can't absorb any kind of bass, they're not 1.25" either.
profiled panels perform better than flat panels w/ half the thickness and also act as diffusers. because of the "cuts" more surface area/more foam pores are in contact w/ air.
a 2" wedge acoustic panel offers an absorption coefficient of about 0.70 at 500Hz compared to the calculated value at 3:41 of less than 0.5 (that would correspond to a pyramid shaped 2" foam profile).
---------------
see if you can find a few explanations from manufacturers about the difference between flat and profiled acoustic panels.
(this is just one example, search for "Does The Profile Of The Foam Make A Difference"
Thank you for this John. I like my music to be on the "bright" side and I have struggled with my room treatment. You mention the carpet and ....... yup, I forgot all about it. Without the carpet the room ( 10 x 11 x 7" 6" ) reverbs like crazy but with the carpet the highs are missing. I will roll the carpet up to half its size and see if that helps. I will also take out the thin insulation and use it to build up my bass traps. I did not know about pulling the panels away from the wall. I need to thicken my panels to 6", transfer the thin insulation to the bass traps and use the carpet as a control for the high end reverb. I think that this will help me go in the right direction.
Update:
10 minutes of work and I have my bright sound again. All I did was to roll the carpet to 1/2 its size and remove the 3" insulation that I had behind the diffusers that were on the front wall between the speakers. There is still lots of work to do on the low and a little on the high end but at least I am at a point where I can make the necessary adjustments. Off to the big box store to grab more safe n sound to build the first reflection panels to 6" from 3" and to increase the height of the bass traps. I will head to "Acoustics Insider" to get info on how to use REW.
Thanks again John!!!!!!
Even though I've got a ton of absorption in my room, it's still mostly reflective. The floor, walls and ceiling are mostly covered with wood, so it retains that "live" feel that you want, while reducing the low frequency reverb that you don't want.
Good luck with it Paul, and thanks :)
Love all your videos in general and this one in particular. I am building speaker by myself and I know that that the next improvement lay in the room treatment. Much more important than cables and even amplifier (I use strong enough amplifiers). The room treatment is a field I never really explored. This video provide good enough information to start to understand the directions I should follow or at least understand the problem domain.
So thank you very much for this wonderful short, clear and explanatory video!!
Joel Israel.
this was a great way to explain some absorption and acoustic properties. i have also found acousticsinsider channel to be educational over the years.
and i found some use for those cheap acoustic foams: when you only rent and want something on the ceiling they can work ok if you stack them two layers and have that thickness as air gap. i have covered my ceiling that way after i diy some 8" think absorbers.
thank you for sharing
Thanks for sharing.
When you use the example of carpet/drapes only you point out that only the higher frequencies are reduced making the room sound dull.
That's true, but, if you have good low end treatment also then both the high and low end will be more in balance and the room will not sound dull.
Carpet only leaves the low frequencies with lots of reflections causing it to be muddy sounding and it is more apparent when you only reduce the high reflections
Acoustic Insider talks about that.
Thanks for all your efforts to teach people how to get good audio 🙂
The balance is what you are after, but high frequencies are much easier to absorb than lower ones, so you need to be careful to not over-absorb in the high end. That's what carpet can do, if it's covering too much of the total square area of the room, including walls and ceiling in that total.
@@IBuildIt , I agree but that's why I point out that if you combine that with lots of low end absorbtion it is no longer a problem.
If you are over-absorbing the highs, the room will sound too dead, regardless of how much low end absorption you have.
@@Fograys What? i am confused by your "logic" - You seem to be saying that it is ok to absorb TOO MUCH high end as long as you absorb TOO MUCH low end as well.
Shouldn't the goal be to only absorb the proper amount in the first place so you do not have to bring the other down to sub optimal ?
I.E. Not screw the second one up just because you are screwing the first one up ? Screwing both up IS a problem.
I enjoyed this video. Nice room! New subscriber here 👈🏽
Interesting discussion on macro vs big picture views. I have suffered from the macro view “trap”, however, the better you can remove flaws at the macro level, the better the end product, even if you can’t see it in the big picture view. 😅😅 See - it’s a trap that we all suffer from. On the other hand, production construction contractors often ignore flaws at the macro level that are visible in the big picture, all in the name of efficiency and costs control, missing the lesson in the statement, “it is cheaper to do it right the first time, then to fix it the second time”. As always, John, great content!
The better you remove SIGNIFICANT flaws, the better the outcome. In all things there is an order of importance that sums up to the end result, and if you are spending 50% of your time on something that has a 1% impact overall, that would be a wasted effort.
Even worse is spending 80% of your time doing something that won't work at all, or if it does will have a negative outcome.
Do you mean small by saying macro? Asking because macro means big.
@@IBuildIt You very honest in your presentations, speaking your understanding of things and clarifying your level of expertise. I have liked that about your videos, even if I didn’t agree or have an opinion of my own. But I have to ask because you have been working on you room for some time now and I know that “doing it right the first time” isn’t always possible and experimenting is part of the process, but how many times have you scrapped ideas in your quest for the “perfect” 🥴 listening room? Not trying to be critical, just that I understand the difference between research and production. Metaphor - the engineering department will research and perfect forever, but the production department has a schedule and a budget. Believe me when I say that I will spend countless hours on a project only to scrap it. But I also learned a lot in the process, so not a complete waste of time. 😊😊
@@ekketiivas7603 hmm… yes, I did mean small, micro! Now I’m thinking I miss heard the word John used in his discussion, but I did understand what he was thinking. I went back and listen to the video again and sure enough he said “micro”. My bad. Thanks for pointing this out.
I made several videos talking about the room as I built it, including measurements and my reasoning. Basically, my goal was NOT perfection, but something that is good enough. In the acoustic sense, good enough is as close to perfection as you can get.
I made no changes to what I did at all, other than cosmetic ones (paint, hardwood floor) and I'd do nothing differently if I had it to do over. The method just works, so there's no reason to tinker.
John I found that this channel "Acoustic Fields" has some of the best information and myth debunking on Acoustic for home theaters, listening room etc. I think you will find this gentleman interesting and informative.
That is a channel that I was watching early on, but it became clear that his understanding of the science isn't what it should be. I can't recommend his channel because he's actually perpetuating myths instead of debunking them.
I did save that channel that you recommend, I'm always looking for more and better information that I can find. Great video as always, keep them coming. I followed you over here from your woodworking channel that I've been following for many years.@@IBuildIt
Its easy to spend a lot on thick absorber for no benefit at all (I've done it!). The most important thing I learned about selecting the right porous absorber is the effect of 'flow resistance'.
If an absorber has a higher flow resistance (i.e. density) the sound will at some point 'give up' trying to go though it and turn around back to the room. This means the thicker your absorber, the lower the material density you want. e.g. RWA45 rockwool is good for about 4" no more.
Flow resistivity has little impact on how well an absorber works. Thickness totally eclipses any differences in GFR.
I have a room with proven (with detailed measurements) results that show that. See my videos on that.
BTW, your idea of the sound "giving up and turning back" is fairly ridiculous. Sound dissipates, diffracts and / or reflects, it doesn't "give up" like it has a mind of its own.
Here's a couple........................
1. BEAN BAG CHAIRS; Now filled with memory foam chunks & a microfiber bag, they are attractive, easy to move around, cost effective and dual use. Stack them in the rear corners as a bass sink.
2. VERTICAL BLINDS; Install floor to ceiling vertical blinds with PVC slats and fabric inserts at the first reflection point. Align the slats to the incoming sound wave & you'll get a perpendicular sink on the rebound. Just like "Riffles in a Sluice Box".
Reggae, Funk & Brass 🔈🔉🔊
PS,
Variable crossovers are available for sale at a reasonable price.
Does panels like these makes would make so, it would muff tool sounds for the others living in an apartment?
Not really. You'd want sound proofing, which is a different thing.
@@IBuildIt thank you kind sir.
Effectively, we're trying to make room walls disappear - as much as we can, that is. Smaller the room, bigger the problems.
Would a definition between the 2 types of acoustic panel treatments are, the panels you built are for listening to sound in the room while the foam sections are creating sound someone else will listen somewhere else?
It's a balance between mass and volume, sound waves need to be able to enter the material but not leave. I think of sound panels as capacitors in parallel, like a low pass filter. I've wrapped mine in 8 micron kitchen foil with 80mm rockwool inside and 3.6mm plywood backing . Keeps the dust and smell inside and very high frequencies bounce off of it while it is transparent to lower frequencies. On top of that I've wrapped it in canvas for looks and a bit of diffusion. When you stand close you get that silence you feel similar to an anachoic chamber. I've used the panels to divide the room in two with a 3m airgap. I'm considering treating the drywall ceiling but I'm not sure if it would be an improvememt. Maybe a smaller panel and see how it performs. I have wool carpet with insulation panels under it, all in all 20mm I think.
do you know ethan winer?
Not personally, but I've seen his work. He's another very reliable source for info on room treatment.
@@IBuildIt - I thought so, so I figured you might be aware, or might be interested, in him...I've had a couple of interesting discussions with him about things like very expensive support systems for your speaker cables, you know, to keep the coloration of your floor coverings from getting into your music...that kind of thing (I'm an electronics development guy, and love to learn about the intricacies of solid copper, gold-plated multi-conductor, balanced, USB cables... and...)
All the best, sir.
Something I discovered by accident was to add Microspheres (for epoxy filling) to ceiling paint. It made the appearance of the paint much flatter, and the surprise was acoustic damping.
As I didn't expect this, I didn't make before / after measurements, but people who were in the room before and after the ceiling paint noticed the difference in reverberations.
I added about 2 coffee cups of microspheres per gallon keep stirring frequently. I put on 2 coats, at 90 degrees, for a uniform look.
I'll suggest it for living rooms, etc. I don't believe it would fix a listening room.
One device that exists now is server subwoofers. They are not widely adopted but have existed for some time. Same concept.
I haven't' heard of this trying to be done in the whole room. Cool idea but it a very tough timing issue
Recently I read about a membrane (that covers a whole wall with same gap) with a heavy weight in a middle. People say that it absorbs low frequencies extremely good. Of course, a tension and the weight mater. If it really works like is promised, that would be the cheapest and fastest way to prepare a room acoustically.
Those are limp mass absorbers, similar to the diaphragmatic absorber I mentioned in the video (my walls). They work the same way, by reacting to the specific frequency they are tuned to. So one tuned to 40Hz will absorb very effectively at 40Hz, but do very little at other frequencies.
@@IBuildIt Hm.. We have to take into a consideration that heavy weight. The close to a center, the higher resonance frequency is. I guess such membranes demonstrate wider range of an absorption. I'm full of an enthusiasm to try
You should, since it's the best way to learn if you are open to that.
Materials resonate at one frequency, generally, and that frequency is determined by a number of factors, like size, mass and stiffness. A limp mass may be differentially loaded to resonate at more than one frequency - that heavy weigh you mention. Still, it can't be as broadband as a thick porous absorber, which covers several octaves.
At least you didn't pull a Bababooey and put stools in there for guests to sit uncomfortably. 👍🏻
The corrugation adds damping, by making an acoustic impedance matching from air to the foam, so the sound in the air passes into the foam, where the speed of sound is slower, and there is damping, so the sound can be damped in a shorter distance.
Sincerely, acoustic physicist.
If it adds anything, it will be minuscule and of no significance overall. I doubt it would even show on measurements.
Sincerely, a guy that does stuff :)
@@IBuildIt denies the effect of acoustic impedance matching, without any evidence or math.
I have built acoustic horns which use this effect, and which amplified my iPhone to loud levels, with bass. I have done the math, and so have others. It is documented and not that hard to find on the net. The Webster horn equation is a start.
If anything, the corrugation is supposed to act as diffusion, but the material is not hard enough to reflect. You can do the math and even invent some, but nothing will make this foam suitable for room treatment.
As for acoustic horns, that's impedance matching, yes (I've made videos about that, in fact my last one...), but the effect it would have on this foam is negligible! It's too thin!
There is a good reason million dollar anechoic Chambers use wedges, not flat panels. It's not to save money on material costs 😅 On such a thin panel as 2" and low density it probably does very little though, that's true.
Anechoic chambers use wedges that are LARGE and reflective. They are designed for the sound to enter and bounce back and forth to dissipate the energy. And there's more going on behind those wedges.
The foam I show in this video is for people who have no idea what's required to properly treat a room to waste their time and money on.
And the Aliexpress stuff is even worse
Here’s what I’ve learned a year or so ago about room modes/frequencies from legit (I think) engineers…
For reducing low/mid freq echoes via panels… it is said that it is most effective away from wall as its’ thickness, like you’ve stated. Any further, it doesn’t improve.
However… regarding room modes/frequencies (like how a glass bottle has its own freq when blown into it)… the greater distance of panel away from wall actually reduces room mode freqs better (unlike reducing echoes)…
eg: a panel 6-10’ away from wall is more effective at reducing modes (unlike reducing echoes).
Have you heard of this??
I guess reason it isn’t done/known much, because it looks silly to have a panel 6’ away from a wall, lol.
Great video. Yes many of us have bought those worthless waffle panels. I know I did....
I think you are a bit off on the labcoat discussion though. By your logic, all noise canceling headphones are also garbage and do nothing but cause distortion because noise cancelation works the same way they are looking at canceling room nodes. If you play the pronlematic tone 180 degrees out of phase it will cancel out the issue.
Noise cancelling headphones take a sample of the noise and use that to cancel the noise. The noise is not part of the original signal, while the tones excited by room modes are a part of the original signal.
And headphones are not rooms, so you are not dealing with a problem of closing the gate after the cows have escaped.
ahhh yes. Thanks@@IBuildIt
The Best room is no room. Essentially outdoors.
And tats what a anechoic room trys to emulate.
So i digress that high frequency reflections in your listening room are a good thing. They have reflections in the Recording room, this enough form me. i don't want to add the "color" of my room to the recording.
Have you ever listend to speakers outside or in an anechoic chamber? It sounds just wrong.
@@luxxer12 Have you ever used Headphones?
@lambda7652 yes and it is instantly apparent that headphones have no soundstage like speakers have, because there are no reflections. Thats why they can not reproduce recordings accurately unless made with a binaural recording head.
@@luxxer12 All the reflections from the room it was recorded in are already on the record.
There is no need to alter it further.
If you want to add additional reflections/reverb and effects just do it in software.
@@lambda7652 Thats just not correct. Almost no music is just recorded in a room with a stereo microphone setup. But i dont want to lecture somebody. Do your thing. Maybe look up some research from the 80s till now to broaden your horizon.
Let’s be clear, that foam crap ain’t good for ANYTHING, vocals included.
You’re an audiophile which literally means someone who likes sound.
You don’t subscribe to certain beliefs but you’ve created a TH-cam channel dedicated to good sound where you talk about what works and doesn’t for you. And as you sit in front of your QRD’s.
Don’t for a second think that you are significantly more rational than “the average audiophile”. You simply subscribe to different beliefs.
Why? Because with every claim comes an often intangible unquantifiable translation to the subjective realm.
Case in point: we understand the technical shortcomings of tubes. They do have the capability of sounding “better” subjectively. My opinion/belief is that the second order harmonic distortion emphasizes spacial cues when they occur. Also, the increased distortion during transient peaks creates an illusion of increased dynamics.
We really don’t need another speaker quasi DIY manufacturer . Audio shows are overrun by new “me too” products.
Respectfully, If I wanted an open baffle speaker made by a science driven designer I would buy a pair of lX521. That would be much more “rational” than buying something slightly similar made by one of SL’s fans.
You said it John, you are not an expert. Me = serious money making songs, you + a lame you tube video nobody. Go make some music, measure your room less.