I know you asked Scott. Hence he will certainly jump in.
The best absorbers we know in the DIY world are the super chunks.
You can find info in Scott's FAQ here in the forum with absorption data.
In the commercial things there are many now as well in foam as mineral wool versions.
Without being complete:
Mineral wool (fiberglass or rockwool)
Auralex: the Mega LENRDs seem a bit better than the super chunks
But recent years there came a lot of foam producers, some good some less good.
Jude3 wrote:If large waves are a problem in small rooms aren't the ones at the bottom like 30 cycles the most problem?
How about 60 cycles then. Do absorbers go that low?
The question is also does it cause a problem in your room?
Often there isn't much energy in these very lows. Most smaller full range speakers discussed in studio groups cut off around 40 Hz. I think that a lot of studio guys don't use sub-woofers (but don't know for sure).
It's not because a Church organ can go down to about 16 Hz that a room should be designed as such. It also depends on room measures and shape, not just frequency numbers.
60 Hz seems roughly to be the border line with such modular absorbers that influence acoustics. But in fact one is at the boundaries of can be measured in a reverb room. These low frequencies and the effect of absorbers seems very defined by the use in the room.
But it's all a matter of degrees.
It's not because you have an absorber somewhere in a corner going down to x Hz that all problems down to x Hz are solved.
I have build rooms linear down to 30 Hz but the amount of treatment and space needed is extreme (in DIY notions).
Then one doesn't speak anymore about putting some absorbers in some corners, no matter how good they are.
In a non-environment room it's very well possible that the visible used volume in the room is less than 60 % of the real existing volume enclosed by the physical acoustic boundaries (walls, floor, ceiling) of the room where the height is a grateful spot to build as bass absorber.
But this also means that the build measures of such room are adjusted to make that possible.
There really is no magic absorber that with only a few items can solve all low frequency problems.
I can't remember the exact number, but as I understood Ethan Winer has somehow > 40 traps in his living room.
It should be very clear that with such an amount it becomes more logical and efficient (from cost + acoustic point of view) + architectural and aesthetic pleasing to design the absorption and treatment of the room as an integrated part of the room, rather than trying to push in > 40 individual elements.
Such an approach is used to make a point in function of the effect of the amount of trapping and for commercial reasons. Not taking these motives (however valid or not) into account one could hardly define this as a professional approach.
And that's valid for all of them.
These standard absorbers are a very easy and cost effective manner to solve room acoustic problems to a certain degree.
Exceeding that degree and you don't integrate standard elements anymore but you design the whole room, including the treatment as a complete concept. This is less true for live tracking but certainly for highly absorptive control rooms.
And there is no one single right way to do it. Many paths will lead to the desired result.
And it's also a matter of degree.
Paul Woodlock's studio is a +/- non-environment room. That are no separate absorbers. He made absorption part of the design.
Most typical John Sayers slat type absorption studios are integrated entities.
The advantage of these modular absorbers is the ease of use and flexibility, certainly in the DIY world.
You state you get confused by reading all this stuff anywhere.
I should be surprised you wouldn't. You look for the simple straight forward guidelines.
You can about find them by choosing a principle and applying the guidelines promoted by the people using that principle.
Don't try to compare what's done at the John Sayers forum, with what is promoted here. Even experienced acousticians will have a hard time doing that. And this does not relate to good, better, best, worse or bad.
And you can not expect to know/understand/feel acoustics as people with a related formal education and/or a live time of experience.
Some guys follow the forums for many years to get a better understanding.
And some will start educating others. Some without or hardly knowing what they talk about with what I call "slogan acoustics
", others with a lot of responsibility. Bob Golds is an example of the latter ones. And of course any in-between combination.
The biggest problem for laymen searching for understanding on the net is how to distinguish one from the other.
And a rather unique example is Rod Gervais who wrote a book becoming a must-have for anyone building his own studio.
A book which is a combination of Rod's extensive background in Engineering and acoustics learned via the same channel many others do on the net (but with responsibility, analytic approach and additional studying).