The 25 minute, $25 acoustic panel (or $42.00 bass trap)

[studio_drums]

nixx- you're welcome! (I kept things simple because at this point I was very tired after building the studio!)

benirose- using two 2" sheets of "unfaced" 703 is the same as one 4" sheet. That's what I did.

(diggin' the graphic)

[Chris-P]

studio_drums: Thank you so much for this 703 tutorial.

I built a few of these last night using your approach and it couldn't have been simpler.

I'll post pics soon.

Thanks again!

[Teflon]

Okay so it's old but I too want to say thank you so much for posting this tutorial. Very helpful.

+1 for xSpace's french cleat suggestion. I've used that in cabinetry too. I also used the french cleat method in conjunction with a marine adhesive when I reworked a sailboat's galley. It gives a nice professional look and is easy to make sure it's level.

[studio_drums]

You're welcome, everyone- I'm glad this thread has helped so many.

[Vasily K]

Nice plans. I have build 24 panels for about $200. Acoustics in my room are even better now.

[studio_drums]

Sweet

[phlange]

this might reveal my ignorance but I learned:

You don't want any part of those panels flat against the wall, you want them Spaced from the wall.
Using the "picture hanging" method of mounting those absorbers flush against your wall,
you're trapping a negligible width of frequency (probably something like 100Hz-150Hz),
making those gorgeous traps a lot less effective than they should be.

What you want is this:

| |
| |----------------------- || your ||
|W |--5cm (2 inches)----|| absorber||
|A |-------of------------- || here ||
|L |-------space-------- || ||
|L |
| |
| |

Remember: it's the empty space that traps the bass
The fiberglass only slows the bass waves down so they can be trapped in the empty space behind it.

PART TWO: if the sides of the wool ARE exposed, you're absorbing about 200Hz-400Hz,
which is HighBass, which is the kind of absorbers you've built, albeit that you have them too close to the wall to be trapping much.
But unless your wool is inside an AIR TIGHT FRAME (with front and back covered
with 1/4" thick wood), everything below 150Hz is bouncing right back out
of the absorbers in these photos.
you should take two or three of your absorbers and seal their fronts and backs, and you should mount ALL of your absorbers at least 2 inches from your walls.
ESPECIALLY if you're treating a drum kit area.

[Soundman2020]

Remember: it's the empty space that traps the bass
The fiberglass only slows the bass waves down so they can be trapped in the empty space behind it.

Actually, that isn't true at all! The bass is not "trapped" by anything: the fibers in the absorptive material simply convert air particle motion to heat, thus taking acoustic energy out of the wave as it passes. The reason you space the material away from the wall is to put it in the zone of the wave where velocity is higher and pressure lower. At the wall/air boundary itself, the velocity component is zero and the pressure component is maximum, which is why panels and membranes work at the wall boundaries but absorption does not. Of course, this assumes normal incidence of the wave: if it isn't coming in normal to the wall (and most waves do not) then it might indeed have some non-zero velocity component very close to the wall. But you will still get greater efficiency and coverage down to longer wavelengths by placing the absorption away from the wall. It has nothing at all do with "trapping" the wave in the space behind the absorption.

But in any case, it is a myth that the space behind the absorption somehow "traps" the wave. It does not. It only places the absorption in a more effective location in the room.

It is also a myth that the absorption "slows down" the wave: it does not. The speed of sound does not change appreciably in the fiberglass, and even if it DID change it would go UP, not down, since the glass fibers are more dense than air. The passage of the wave merely causes the fibers to vibrate, thus extracting energy from the wave and converting it to heat.

But unless your wool is inside an AIR TIGHT FRAME (with front and back covered
with 1/4" thick wood), everything below 150Hz is bouncing right back out
of the absorbers in these photos.

That isn't true either. If you seal the back of a bass trap that is spaced away from the wall, you will REDUCE its ability to absorb bass frequencies, not increase it, because you will have defeated the entire purpose of spacing it away from the wall!

you should take two or three of your absorbers and seal their fronts and backs,

No you should not! (Unless you want to destroy their bass-trapping capabilities).

if the sides of the wool ARE exposed, you're absorbing about 200Hz-400Hz,
which is HighBass,

I reckon most sound engineers would consider that more "low mids" than "high bass"! In any event, exposing or not exposing the sides of your absorption has absolutely no effect on the frequencies that it will absorb. Exposing the sides might increase the coefficient of absorption for certain frequencies, but that's an entirely different thing.

But unless your wool is inside an AIR TIGHT FRAME (with front and back covered
with 1/4" thick wood), everything below 150Hz is bouncing right back out
of the absorber

Which, of course, is exactly what you want to happen, if you want the bass trap to actually work!



By the way, "bass trap" is a misnomer: Bass traps do not actually trap any bass at all! Maybe if they had been given a more technically correct name to start with, we would not see so much of this type of wrong guesses floating around the internet.

- Stuart -

[phlange]

I am still learning, but I did get this info from
this site.
One of the room-analyzing softwares I saw mentioned
at the forums you're in right now was actually developed
by this man.

http://www.ethanwiner.com/acoustics.html

"...There are a few reasons for sealing panel traps. If there's a place for air to escape - let's say at the seam between the front panel and the side of the box - then pressure from the diaphragm as it pushes into the box will send the waves out the leak rather than push them into the fiberglass. Another, more relevant, reason is that a leak will let the internal pressure escape, reflecting the waves back into the room instead of absorbing them."

[Soundman2020]

"...There are a few reasons for sealing panel traps.

Maybe you didn't notice that you were first talking about absorbent bass traps, made with fiberglass, and now you suddenly switched to talking about panel traps! Two entirely different concepts. Two entirely different principles of operation. A panel trap works on the principle of sympathetic resonance, MUST be sealed and should NOT be spaced away from the wall. An absorbent bass trap works on the principle of gas flow resistance must NOT be sealed and SHOULD be spaced away from the wall.

If you are interested in learning about acoustics, then I'd suggest that you buy "Master Handbook of Acoustics" by F. Alton Everest. He explains all of these concepts, and the math behind them, in great detail, but his explanations are clear and easy to understand.

One of the room-analyzing softwares I saw mentioned at the forums you're in right now was actually developed by this man.

Ethan is actually a regular poster here, and will most likely read this. Maybe he can explain to you the difference between panel traps and absorbent bass traps, how to use them, and where to place them in the room.


- Stuart -

[phlange]

Good. I am glad Ethan posts here.

Maybe he could also tell you that
a fiberglass panel covered with fabric
is absorbing MIDS and HIGHS.

I actually just walked in from visiting someone
who Definitely has experience in the same field
as Mr. Winer here in New York. His company has built
some floating rooms etc...

It is confirmed: you want to TRAP bass? ->
put your fiberglass inside a Sealed frame with a
"membrane" of 1/4" thick plywood.
You want the plywood to vibrate in sympathy with
the lows and inside the sealed frame, the pressure
is converted to heat.
Exposed fiberglass isnt trapping bass.

To people who have been mixing in an untreated room,
the deadening effect of hanging the burlap-covered
mid/high absorbers will sound like it's all you need.
But an experienced studio builder will tell you that 1/3rd
of your absorption treatment must consist of sealed
membranes of some kind. Ideally, a floating room.
Your room's deep bass are not being absorbed
using only those exposed 703's.

[Soundman2020]

Exposed fiberglass isnt trapping bass.

Hooooo Boy! Do you have some learning to do!

Maybe he could also tell you that a fiberglass panel covered with fabric is absorbing MIDS and HIGHS.

... and lows.

Please let us all know when you get past the first few chapters of MHoA. Pay special attention to the discussion on absorption ...

- Stuart -

[phlange]

Please let us all know when you get past the first few chapters of MHoA. Pay special attention to the discussion on absorption ...
- Stuart -

Stu, I 100% am not trying to offend you (all).
I came in here to learn and when I saw pictures of everybody
building the same exact thing, it conflicted with something else
I learned from a very reliable source. Not Winer (though Winer agrees).

Here it is and it'll figure if you laugh or think I'm lying to you:

I live in New York. My block is arranged like this:
My house...my next door neighbor's house....and at the corner,
a two-story recording complex with 8 suites. Artists who
have worked in there include Mariah Carey, Green Day, and
whoever else these new freaks are walking in and out these days.
So today, I simply walked in with a printout of Winer's blueprint
on the THREE types of absorbers, and showed it to the guy
who built the damn place. He agreed. He even elaborared on a few
principles I was doubting as far as sealed membranes.
That's it!

For you to say "let 'us' know when you get to the chapter on..."
I claim no authority. I might read your book.
But I'm pretty confident the guys I met today had practial working knowledge.

[Soundman2020]

The basic problem is that you are confusing two totally different types of acoustic device. You are looking at absorbers, which work very well as broadband bass traps down to very low frequencies, and telling us that they wont work because they are not panel traps, which work on totally different principle. Absorbers work on the velocity component of a sound wave, panel traps work on the pressure component. They do the exact opposite thing from each other, but they both work.

Panel traps are TUNED treatment, which is sometimes what you need in a room and sometimes not. They work on specific frequencies, and should be designed for each room to deal with the problematic frequencies of that specific room. Absorbers are "broadband", meaning that they work across a range of may frequencies, and will therefor work in any room. If you put a panel absorber tuned to 125 Hz in a room that does not have any problems at 125 Hz, but actually has an problem at 90 Hz, then not only did you not help things, you actually made them WORSE: You took out energy at a frequency that was just fine, and you DIDN'T take out energy at the frequency that needed it most! So now your room will sound worse than if you had done nothing at all. That's what you get from trying to fix things through ignorance (no offense) without actually understanding what you are doing, or what people are telling you.

Panel traps should go right up against the walls for maximum efficiency, because that's where the pressure component is highest: they are pressure-based devices, not velocity based. Space them away from the walls and they LOSE efficiency. Absorbers SHOULD be spaced away from the walls for maximum efficiency, because that's where the velocity component is highest: they are velocity-based devices, not pressure based. If you put the up against the walls, they lose efficiency.

Acoustics 101.

The reason I am being so harsh here is because you came into the forum, jumped on the end of a great thread that has been around for years and teaches people how to do things RIGHT, and you start yelling about how it is all wrong and won't work. I cannot allow that to pass unchallenged. This forum is well regarded and well respected precisely because the people who post here actually do know what they are talking about: some of the best experts in the industry drop in from time to time to offer their thoughts. So I'll do my best to ensure that no myths, legends, half-truths or plain old wrong information are spread here. As a moderator, that's part of what I'm supposed to do.

If you aren't sure about how things work, then ask, and folks here will be more than happy to explain how things work. But please don't come barging in trying to teach the experts when you don't even understand the principles.

The absorbers described in this thread actually do work, and they work very well when built and positioned correctly. If you enclose them in "sealed boxes spaced away from the wall" then they will do nothing useful at all (at best) or will even add additional problems to rooms (at worst).

I really do suggest that you buy MHoA. It explains all of these concepts (and many others) very clearly, and gives you the acoustic principles on which they operated, and mathematical equations for calculating their frequencies and performance.

I came in here to learn and when I saw pictures of everybody
building the same exact thing, it conflicted with something else
I learned from a very reliable source.

They only trouble is that you did not understand what your reliable source was trying to tell you, and nor did you understand the devices described here. Out of ignorance you confused the two, and then carried on insisting, over several posts, that you were right and everyone else was wrong, even though I already explained it to you.

Not Winer (though Winer agrees).

No he does not. Ethan sells both absorption based devices and panel traps (among other things). I'm pretty sure he knows the difference, and understands how they both work!

He even elaborared on a few principles I was doubting as far as sealed membranes.

It's a pity you didn't ask him about absorption-based treatment. Maybe you should go visit him again, and ask him what he thinks about superchunks, and what principle they operate on...

But I'm pretty confident the guys I met today had practial working knowledge.

They very likely do! But if you want the correct answers from them, you have to ask the correct questions, and you have to have the basic understanding to grasp what they are ACTUALLY telling you, not what you THINK they are telling you.

If you really did come here to learn, then great! There is a huge amount of information here, most of it solid, sound, correct and based on the real principles of physics and acoustics. There is way more than you could ever hope for, on practically every issue of small-room acoustics. Spend a few months reading over it, like most newcomers do here, and I'm sure you will learn a lot.



- Stuart -

[phlange]

You're right I did just join. You can delete the posts.
But at least I inadvertently got you to passionately impart
information. Sorry about that.

Thank you for clearing up the membrane/absorber question.
I didn't want to go building stuff only to discover I wrecked
my already-sounds-like-im-sitting-inside-the-body-of-an-acoustic-guitar
mixing room.

Delete those horrible posts they dont belong.
-Mike