# Room treatment (argh!)



## elite1967 (Jul 11, 2012)

Hi,
I decided to go the DIY route for my room treatment.
Here is the room dimension:
6.9m x 4.9m x 3.0m (speakers on the short wall)
(the room is not exacly rectangular: see attachment)

The frequency response is attached.

I am trying to remove the modals at 35Hz, 50Hz and 70Hz

I built some Helmholtz Resonators but they do not do anything at all.

Here what I did:

1)HR at 35Hz: 
1 Fat PVC pipe (40cm diameter x 120cm height)
20cm port diameter
40cm port lenght 
Empty inside
Q=8.35

It resonate at 35Hz but it does do anything.
I tried to put in the side wall, in the corner, behind the speakers, etc.
No good
Question: 
a) How many of them should I build in order to see any effect considering the size of my room?
b) Should I put something inside the HR? Fiberglass or such?
c) What is the suggested position of the HR to resolve the modal nodes?
d) Building a 35Hz will resolve also the 70Hz problem?

2)HR at 70Hz: 
Fat PVC pipe (31.5cm diameter x 120cm height)
20cm port diameter
5cm port lenght 
Empty inside
*BUT THE REAL FREQUENCY IT RESONATES IS AROUND 57Hz.*
I do not know why...
I measured everything a lot of times and the sizes are correct.
Everything is perfectly sealed.
Attached is a picture of the HR.
a) What could be wrong? 
b) How many of them should I build in order to see any effect considering the size of my room?
c) Should I put something inside the HR? Fiberglass or such?
d) What is the suggested position of the HR to resolve the modal nodes?

3) Another bigger problem is around 80Hz as there I have a deep canyon in the REW waterfall.
Shall I resolve it with HR?
How many?
Where shall I put them?

Thanks to all for your help.


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## bpape (Sep 14, 2006)

Helmholz can work OK but it takes a lot of them to really do the job many times as you're finding out. Another issue is that you're not addressing the decay time in the rest of the spectrum if you're only using these. Generally, these are used as a final addition to a more broadband solution.

Bryan


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