My Helmholtz Worked - How much should i fill them?

[junya-eskimo]

Hi all,

I have a few posts before where i mentioned was building some tuned helmholtz traps.

Well i built 2 dummy traps so see if they worked,, And they did.

HUGE traps. 120 x 80 x 30.5(deep)//.. 59 and 52..

the 52 hrtz actually hit 51.4 hrtz.. but the 59 was 58.8 hrtz... so great/

Now i have the fiber glass. On sunday we put it in.. I have enough to fill the traps i will be making..12 inches deep..

But i ask.. should i fill all the way??

I know air space is needed in some designs, but in the case of tunes helmholtz does it also apply?

If so, what sthe best amount to fill it with and if you have tested this, Please tell me the most effective amount and air gap please... if any..

Cheerz

John

[Jens Eklund]

The addition of porous material will change the centre frequency. How much depends on how much (how thick), where it’s placed and what flow resistivity it has. Use this tool to simulate the effects:

Porous Absorber Calculator V1.58

[junya-eskimo]

Originally Posted by Jens Eklund

The addition of porous material will change the centre frequency. How much depends on how much (how thick), where it’s placed and what flow resistivity it has. Use this tool to simulate the effects:

Porous Absorber Calculator V1.58

Ok.

i tried this, but can you help me out please..

I dont know what to fill in these parameters:

Repeat Distance
Open Area ( i just realized this is the %).



Also, its not creating any graph..It launched a message saying something about my security level settings are too high and i should turn them down...

I am on a friends PC.. I use mac.. She got this AVG for security...

Anyway.. is it to do with that? or is there a "calculate" button or command i missed?

Cheerz

john

[Jens Eklund]

“Repeat Distance” = the distance between the holes (centre to centre).

I haven’t used the PAC for some time now (since I now use SoundFlow) but I don’t recall that you need to fill in the “Open Area”. This should be calculated based on the repeat distance and hole area (radius).

You need to allow Excel to use macros in order to use the PAC plus some other things; Please check the prerequisites on the site for PAC before trying to run it. It will straighten out all of your question marks.

[junya-eskimo]

cool

lowed the macro security..

cool, distance.. that makes sense..

i guess i will toy with it..

out of curiosity, you have anything to share with resuts you have gotten with traps tuned when it comes to amount to fill?


Cheerz

J

[junya-eskimo]

But how can it calculate the percentage without entering the panel size???

Mine are based on 90 x 60

[Jens Eklund]

Originally Posted by junya-eskimo

out of curiosity, you have anything to share with resuts you have gotten with traps tuned when it comes to amount to fill?

I usually fill them completely (or close to completely) assuming the appropriate wool (relatively low flow resistivity) is used.

[Jens Eklund]

Originally Posted by junya-eskimo

But how can it calculate the percentage without entering the panel size???

The sheet should calculate this for you. The only parameters you need to input in regards to this, is “repeated instance” and “hole radius”, and the open area (perforation percentage) should be presented. It is assumed that each opening has the same underlying air volume related to it.

[junya-eskimo]

Originally Posted by Jens Eklund

The sheet should calculate this for you. The only parameters you need to input in regards to this, is “repeated instance” and “hole radius”, and the open area (perforation percentage) should be presented. It is assumed that each opening has the same underlying air volume related to it.

I do think it can. Or at least its not on mine.

1.1% of 90 x 60 will be different to 1.1% in any other size..

[Jens Eklund]

Originally Posted by junya-eskimo

1.1% of 90 x 60 will be different to 1.1% in any other size..

Why?

[junya-eskimo]

i mean..

my panels are 90 x 60.

8 Holes, 3 cm big.. with 15 cm distances.

The Size of the panel would alter both the size of the holes regarding % on a different size panel..

I have other traps that have 15 holes also and 77.

I picked an even number of holes for the size of wood. Then i used the equation backwards to tell me the size of the hole i need.

I bough a detailed drilling kit so i can hit almost any hole size down to .0 mm's... for example.. 2.78 cm.. if i needed. i will have 2.8

[Jens Eklund]

If the repeat distance and hole area is kept constant, the perforation percentage (“open area”) will also be constant, regardless of panel dimension.

[junya-eskimo]

ahhhhhh

I think i have been giving myself a ton of work then,..

I was planning all my traps to be equal gaps between the holes AND the sides..

Not just the holes..

[junya-eskimo]

still does not make sense to me..

I can tune it with different amounts of holes... So number can chage with same result.

anyway..

I am still gettinng no graph reading its all flat,, i guess i will check the site

[junya-eskimo]

got it workinng

Interesting..

The RESONANT FRQUENCY it says is wrong..

BUT the graph is bang on... so i guess i am right..

also i see if i leave a 50mm air gap at the panel end it will be much better..

cool little sheet this..

nice one