Why Did I Buy This Crap? Room Acoustics Basics

Sound advice on room treatment: 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.

Very well explained John! Thank you for your time. You would have been a great teacher!

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.

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!!!!!!

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 🙂

I enjoyed this video. Nice room! New subscriber here 👈🏽

Effectively, we're trying to make room walls disappear - as much as we can, that is. Smaller the room, bigger the problems.

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!

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.

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.

Does panels like these makes would make so, it would muff tool sounds for the others living in an apartment?

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 🔈🔉🔊

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.

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.

At least you didn't pull a Bababooey and put stools in there for guests to sit uncomfortably. 👍🏻

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