I've read myself into confusion

[jude3]

I thought I had it till I started reading it again.

I am getting ready to start the acustical treatment for my CR.

I thought I had it in my mind to contruct a braodband absorber but now I'm confused.

Are there different types of braodband absorbers?

[Scott R. Foster]

What are you reading?  [context pleease]

[jude3]

What are you reading?  [context pleease]

The stuff on all the studio constuction sites. I am sure you are familiar with them all.

In small rooms aren't you suppose to just use broadband absorbers on the walls and some bass traps in the back corners?

But there seems to be several ways to build them and I am confused about which ones to use.

Can a bass trap absorb down to 30 cycles?

[Scott R. Foster]

Back corners are a good place to put broadband absorbers.

Why 30 Hz?

Do you really have a 30 Hz problem?

[Eric Desart]

Can a bass trap absorb down to 30 cycles?

Yes you can.  :) If you have space enough.
Maybe they exist lower in frequency, but the largest wedges I personally know for anechoic rooms are guaranteed and measured to 50 Hz (covering the total 1/3 octave down to lower cutoff) having a total mounting depth of 1450 mm.  But they fulfill very strict requirements at straight incidence. I assume they will be good too, down to 25 to 30 Hz in control room circumstances with a more chaotic soundfield.
 Now Bob starts calculating.

You can have good results down to 30 Hz with less thickness as well for practical use, but you will still be close to roughly about 1 m (cavity + wool).
I've once tried to build a membrane absorber around 30 Hz., damped enough to "not be the cause of trouble in itself". While getting it well tuned to the desired frequency the damper forgot to absorp sound that well, as if telling me: "you can't get it all ......." That was a lot of money, manpower and time spent to know it didn't work that well.
To make such a membrane absorber more sensitive you need a lot of space (read volume) as well in order to keep the TL of the membrane itself low enough.

The more important question is Scott's: Do you need to go down to 30 Hz?
.

[Terry Montlick]

Can a bass trap absorb down to 30 cycles?

Yes you can.  :) If you have space enough.
Maybe they exist lower in frequency, but the largest wedges I personally know for anechoic rooms are guaranteed and measured to 50 Hz (covering the total 1/3 octave down to lower cutoff) having a total mounting depth of 1450 mm.  But they fulfill very strict requirements at straight incidence.

If this is the anechoic wedge design that I think it is, it is radical new technology.  It was co-developed by Leo Beranek before 1946.

Regards,
Terry

[Eric Desart]

[Terry Montlick]

:D

I just checked Beranek and Sleeper's original 1946 paper. Their design, the "Harvard Linear Wedge," had a depth of 56 3/4". That's 1441.45 mm, which is coincidentally very close to your 1450 mm.

I just love this old literature! Their main anechoic chamber, built using 19,000 of these wedges, was operational at Harvard by at least 1943. They had tested almost 1000 different designs using an impedence tube in order to find an optimal one.  :bang

[Eric Desart]

 The company I worked for did it with less than 1000 (as far as I know or can imagine)
 But I humbly admit we seem 8.55 mm less efficient.

I wonder the exact history of these things.  I have a paper here telling that the first designs (and use) were made by: von Meyer, Buchmann und Schoch for the anechoic room of the "Heinrich Hertz" Institute in Berlin, and that since then the principle spread over the world.  That room should have been treated in 1939, hence these pictures referring to 4 old different main wedge designs date from before that.

There is a ref of the original publication, but I first need to find an amplification glass to read it exactly (old, mini text, bit fased out and my eyes aren't that good anymore). Check tomorrow.

Now communication between the old and new world wasn't probably that flexible those days.

 Let's become chauvinistic ..... We invented these things, NO we did. Damned we, No we.


http://handlers.sans.org/wsalusky/rants ... boxing.GIF

I leave it open (for now) who is who .....

Serious, should be fun to know this history more exactly. Who was first, with what, or was it just parallel running stuff.
.

[Terry Montlick]

I wonder the exact history of these things.  I have a paper here telling that the first designs were made by: von Meyer, Buchmann und Schoch for the anechoic room of the "Heinrich Hertz" Institute in Berlin, and that since then the principle spread over the world.  That room should have been treated in 1939, hence these pictures date from before that.

There is a ref of the original publication, but I first need to find an amplification glass to read it exactly (old, bit fased out and my eyes aren't that good anymore). Check tomorrow.

Now communication between the old and new world wasn't probably that flexible those days.

Yes, the Beranek and Sleeper paper cites a 1940 paper in Akustische Zeits. by Meyer, Buchmann and Schoch. Beranek tested this design against theirs, the two being quite similar (long, linearly tapered wedges). According to a graph shown, the Harvard design had improved performance at the very lowest frequencies -- 100 Hz and below. Bereanek and Sleeper also say that the first anechoic chamber design in the literature was by E.H. Bedell in 1936.

The Harvard work was funded as part of US government war research, which would explain the post-war publication date. So I don't suppose there was a lot of scientific collaboration at the time with Berlin.

Regards,
Terry

PS - The Beranek and Sleeper paper describes the Meyer, Buchmann and Schoch room as containing "pyramidal-shaped muslin bags stuffed with loose rock wool," and as "lined with thousands of acoustical stalagmites and stalactites projecting from walls, ceiling, and floor." I don't have access to the original German publication or its translation, so perhaps Eric can clarify.

[jude3]

Back corners are a good place to put broadband absorbers.

Why 30 Hz?

Do you really have a 30 Hz problem?

What kind of broadband absorber? One with slats or fabric on top?

If large waves are the problem in small roms then shouldn't all snall rooms want to dampen that low?

If large waves are a problem in small rooms are'nt the ones at the bottom like 30 cycles the most problem?

How about 60 cycles then. Do absorbers go that low?

[Eric Desart]

Jude3

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)
Ready Acoustics
GIK Acoustics
RealTraps

Foam
Auralex: the Mega LENRDs seem a bit better than the super chunks
RPG
But recent years there came a lot of foam producers, some good some less good.

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).

Eric

[jude3]

Thanks Eric. That helps alot.

I'll just sum up what i have learned and build it.

It should be ok.

I have completed all the sheet rock and fooring. I will be starting on the baffled walls and ceiling next week.

Maybe you can stick around to help me.

I am splaying the side walls 6 degrees and the ceiling from front to bach 12 degrees.  I hope my carpentry skills can be good enough. I have been designing it in my head for two months.

I still don'tknow how i am going to fasten all the boards together but I'm jst going to go for it.

Thanks

[Scott R. Foster]

Jude:

I suggest you read for general background, but focus on specific advice for you project in your posted questions.  Define your project and its limitations and ask how to best to address acoustic treatments.  That method won't obviate your exposure to differeing opinions that may cause confusion, but at least all proper responses will be targeted at your particular needs.

To do otherwise is to send every query you post down a cliff into a sea of infinite confusion and disagreement on core design philosophy... which could never really pragmatically help you on your project's design.  If you don't have 4,000 cubic feet of volume available for your 2,000 cubic finished room, then why muddle your threads exploring such design options?  If you do, and wish walk that path, then why bother discussing modular solutions... just build all you treatments into the room [SuperChunks Baby!].

My $0.02

[Eric Desart]

PS - The Beranek and Sleeper paper describes the Meyer, Buchmann and Schoch room as containing "pyramidal-shaped muslin bags stuffed with loose rock wool," and as "lined with thousands of acoustical stalagmites and stalactites projecting from walls, ceiling, and floor." I don't have access to the original German publication or its translation, so perhaps Eric can clarify.

Terry,

I don't have this original publication, and even don't know (for now) what the "Akustische Zeits" is or still exist as a magazine or whatever.
I have a bunch of papers related to anechoic rooms, some from 1965 which refer to this original papers and describes stuff.  It must exist, but therefore I'll need some Sherlock Holmes qualities.
As I can see it here they investigated wedges and pyramids, and decided to use the wedges not pyramids for that "Heinrich Hertz" institute.  Hence the picture shows it flat, hiding the fact if it are wedges or pyramids, and the text states that they concluded (very free translation) that the wedges showed more favourable absorption values.
I must look further, it's not really conclusive here.

With the stalagmites and stalagtites they most likely refer to the visible impression of those long conical dripstones in caves where the stalagmites are the standing up ones (growing up) and the stalactites the hanging ones (growing down).

We remember the difference with the French words: The t in stalactites are from tomber (to fall) and the m in stalagmites from monter (to rise).
.

[Terry Montlick]

Thans for the sleuthing, Eric. I'll poke around a little more for clues on this side of the pond.

With the stalagmites and stalagtites they most likely refer to the visible impression of those long conical dripstones in caves where the stalagmites are the standing up ones (growing up) and the stalactites the hanging ones (growing down).

We remember the difference with the French words: The t in stalactites are from tomber (to fall) and the m in stalagmites from monter (to rise).
.

In America (and I presume, the UK) we use a different mnemonic. Stalactites are on the ceiling, while stalagmites are on the ground!  :mrgreen:

Regards,
Terry

[Zaphod]

In America (and I presume, the UK) we use a different mnemonic. Stalactites are on the ceiling, while stalagmites are on the ground!  :mrgreen:

I can use this  :mrgreen:

[Eric Desart]

 :oops:

Do you know Terry you learned, without knowing it, me to write Dutch correct?

Without your post I should have written stalagmieten and stalagtieten (Dutch) only distinguishing between the t and m.
Seeing your post, I thought: "Strange guys these USers, why do they use a g and a c?

Hence I checked.
 As more than poor excuse I can tell I have no stalactites and stalagmites at home.
But I checked our dictionary, and come to the conclusion that I must have written stalactieten wrong as long as I can remember.
Now I'm really glad I have a very poor/short memory (for selective stuff). Or that cheese between the holes is disolving faster than I hoped.

Stalactites = stalactieten = from Greek stalaktos (must have written or assumed this a million times wrong as stalagtieten)
Stalagmites = stalagmieten = from Greek stalagmos (that I wrote always correct).

 Stupid Eric, learning Dutch from a USer  :mrgreen:
.

[bert stoltenborg]

Yeah, get your own language, Belg!
 :mrgreen:  :mrgreen:  :mrgreen:

[J.F.Oros]

Yeah, get your own language, Belg!
 :mrgreen:  :mrgreen:  :mrgreen:

Common Albertus, he's just polishing his Eriqueze ...  :mrgreen:  :mrgreen: