John Sayers' Recording Studio Design Forum

Hi everyone!
i was just building a slat absorber/resonator and realized that i didn't quite know how to make one. could someone plz give me some tips? i've got all the measurements and stuff but am lost and puzzled as to how its supposed to be built and how it works. like, when you attach the slats onto the wood, wat material r u supposed to put as insulation or absorption? and r u supposed to put material inside the box as well? i'm soooo confused!:(
i would really appreciate any help!:)

Have a look at this awesome animation from Kendale n my thread. I was a bit lost too! By the way. Always put your location in your profile so others know where you are.

Insulation needs to be rigid/semi-rigid. Guys in USA use a product called Owens Corning 703 Fiberglass insulation, commonly referred to here as 703, OC 703 or a 703 absorber (an absorber using 703 insulation or equivalent). You can also use a rock wool based semi-rigid or rigid insulation. My thread has a lot of info for newbies in it cause I was very new to it as well.

There is a standard of how much mass they need to be, I think there is a link to it in my thread, otherwise hopefully some of the more experienced guys put it in here, I don't know off the top of my head, sorry:(.

Cheers

Willo

http://www.johnlsayers.com/phpBB2/viewt ... 8&start=30

thanks, that was really helpful! by the way, does it really matter if the thing is airtight? surely it wouldn't affect it too much right?

The basic idea of a slat resonator is that it is based on Helmholtz principles.
Hence a slat resonator IS an Helmholtz resonator.

An Helmholtz resonator is a mass-spring system or mass-spring resonator.

The mass here is the air enclosed by the slots between the slats.
Hence you alter this mass by varying the width and/or depth of these slots (depth mostly equal to slat thickness in standard applications)

The spring here is the air enclosed by the volume behind the slats.
Hence you alter the stiffness of that spring by altering the cavity depth (in fact more correct is by altering the cavity volume).
This air really works as a spring. Air is even a rather stiff spring.
Take a medical syringe (but remove needle .... can hurt). Press your finger at the end to close it off and try to close that syringe. You feel the extreme resistance of the air acting as a spring.

If you now let the resonator open on one or more sides, this air can escape (as if you should drill some mini to larger holes in that syringe, see sound as pushing and pulling on that piston in that syringe).
Hence you alter the properties of that air spring, which will retune/alter that resonator (difficult to calculate).

But you nowhere told what exactly you want to build (some small resonator, cladding your complete walls, other .......? Narrow band, broad band, other ....?)

i just want to make a small slat absorber built to absorb a particular frequency (800hz) - its for a school experiment. i'm just a bit lost as to how to put it all together but i have all the dimensions - eg. slat depth, slot width ect. btw, can you suggest something, like glue or whatever, that is relatively cheap to make the box airtight? i am also a bit confused as to whether the slat absorber is actually a closed box with slats stuck on to the front of it - is this right? and should i put some material (insulation eg, wool) inside the box as well as where i attach the slats to the front of it?
i'm sorry if i do not sound very clear - this is a new topic for me and there is not a lot of information (that i can find) on the internet.

Kay,

Can you make some sketch how you see this now? And what exactly you're stuck with?
Have you searched this forum? The post and thread referred by Willo?
Have you found the calculator?
Do you now already which slat width and thickness and slot width you need?
What the cavity depth or volume should be?
There isn't any other forum on the web where so much pictures and drawings of slat resonators can be found than here.

Have you learned at school what a slat resonator is in fact? What a Helmholtz resonator is?
Did you understood my explanation?

firstly, thankyou for replying- yes, i did understand your explanation, i have read the thread referred to by Willo, found the calculator, cavity depth etc. and after searching this forum a bit more have a better understanding of what a slat absorber is. I am not too good at building things you see, and was just worried if i was doing the right thing or not. one question - how do you make the cavity air tight?

Just make that box on which you nail, screw, glue the slats (your choice) rather accurate (it doesn't need to be watertight). If it isn't accurate enough use caulk or whatever mastic.

And if you need this narrow tuned at 800 Hz, you don't need any insulation in that box.

thanks for you help - much appreciated.

Just one last thing.

I don't know how accurate this school project should be and if someone will test/measure if you got this 800 Hz correctly tuned.

If that's the case then make that box as described, firm and stable, and make the slat width as such that the 2 edge slats have a 50% width covering the empty space of the more centered slats, but still leave them a bit wider.

Then mount these slats temporary (as per your theoretical calculation) with something you can still adjust it (small nails, not completely knocked in or something).
You'll notice that these formulas are stylized things ignoring some possible side-effects. There can be correction factors not exactly covered by these formulas.
As such you can still easily adjust your tuning by shifting the slats closer together or shifting them apart a bit.

When sure your resonator is correctly tuned then fix the slats better (and adjust width size of edge slats if you want it nice).

If you find someone to help you you can make long-holes in these slats and use screws and washers. As such you can easily retune them. Could be a nice thing to demonstrate the principle in class.

But I don't know the exact terms of your school project of course.
I hope you got a clearer description of what's expected from you than what you gave us here.

i am trying to make the absorber as accurate as possible. can you expand a bit more on these correctional factors which are not taken into account in the formulas? and i do not understand what you mean when you say:
"make the slat width as such that the 2 edge slats have a 50% width covering the empty space of the more centered slats"

Kayb7,

Now it's first up to you.

Can you please make a draft/sketch what you're going to build based on what you know until now?
Who is and how are you or whoever testing the properties of that resonator (if someone is going to)?
I'm not used to make drawings as some people are able to here.

What I'm saying from these formulas that reality is complexer than a simple formula, hence you must take count that you can adjust them somewhat.
And no I'm not going into that math, which is exponentially more complex than that base formula, and which certainly goes far beyond the scoop of your project.
It's much more difficult to calculate then just fine-tuning your resonator in practice.

here's a very quick sketch. you need to adjust the width of the slats, gaps (slots) between them, and depth based on target design goals. it would be sealed to the wall or you could seal it with a plywood backing.
adding insulation causes the Q of the resonator to lower a bit (+/- about 1/2 octave?) from the center frequency.

Glenn,

I sinned ....
Was easier to adjust your nice picture a bit.

Eric - feel free to sin more often all excellent points. could you clarify the edges should have 50% volume? i'm assuming you mean (in this example) the end slots should be (50%) less open than the other slots. if this is correct, could you explain why this helps?

as always, thanks for sharing your knowledge!