# Questions about tuned Helmholts resonator



## frd (Nov 5, 2009)

Hi i just started to post and become active here ...
i have a room with a strong 61hz mode so i m planning to make a tube helmholts resonator which is tuned for 61 hz.

In ETF 5 software it was a calculator to set a port length and other parameters
and i need a Q of 1 for it but 

the problem is that i need to increase the diameter of tube to near a meter to get near Q=5 so i was wondering if its correct or i need to consider something else ?

anyone has a better Calculator which i can use ?

thanks


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## Home Theater Guy (Jul 18, 2009)

Hi. I can't help much with the helmholtz resonator construction, but I did want to ask what other means you have taken to address the sound issues in your room.

Could you tell us a bit about your system, as well as the dimensions and layout of your room? Much can be done to alleviate acoustic problems (moving speakers, seats, etc.) before having to resort to building helmholtz resonators or other specialty devices.


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## frd (Nov 5, 2009)

Hi , hometheaterguy ...
I have done a lot and I'm planning to get myself a free time and make my page of home audio and show the works i have done ...just to mention I have solved the basic problems.
But the helmholts resonator is something that really interests me. that is going to be my next playground.
why no one here ever tried it ?


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## MatrixDweller (Jul 24, 2007)

I think the reason less people try the Helmholtz route is that they are a little more difficult to build and only tackle one problem frequency. They also require pretty accurate measuring. Being off just slightly can change how it behaves.

If you want to build one maybe a panel type would be less intrusive. It could be relatively thin, but wide and tall.

Have you seen this site and it's calculators?
http://www.mh-audio.nl/Helmholtzabsorber.asp


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## frd (Nov 5, 2009)

Thanks Matrix .
I have seen the nl audio Calc . the problem for me is not the difficulty of making it.
for instance the calculator in software ETF5 suggest not to make it boxy(due to resonance of box) and when I try it with low Q(2-5) it ended up with big dimension of tube(1meter tube with one meter height ends up Q=5 for 63hz)... . and in Nl audio its more likely to see the numbers but I am doubtful how it going to turn out.
Nl audio I can make a box(height:70cm width:50cm depth:30cm) which gives the Q=2 for 63hz

I have seen some formulas about calculating the Q of resonance but it doesn't necessarily indicated that the shape of the volume leads to different calculation. it was only the air volume and the neck of port dimension and its length.

please correct me if you see any mistake


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## MatrixDweller (Jul 24, 2007)

Probably another reason, and why I am not much help, is that there are fewer experts and/or mathematicians on this forum who know this subject.

My only point was that comparing tubes to boxes, tubes will have a larger diameter (than width) of a box for the same volume and are not as flexible with their dimensions. A 1m high by 1m diameter tube has a volume of ~0.785 m³ where as the same volume in a box could be achieved with 1m x 1m x 0.785m dimensions or variations thereof in a rectangular box.

You could however bury or partially conceal your tube resonator in another room, in a wall or in your ceiling (etc) with a "port hole" attaching to its port. Or you could make it into an end table or some other type of furniture or piece of artwork to conceal it.

I have read that to tame really deep frequency room modes you need to use a Helmholtz resonator. Bass traps help, but become less effective at lower frequencies. What would be interesting, and I haven't seen any, is a post or blog showing before and after graphs of a room using REW with and without the addition of just Helmholtz resonators.

Things keep getting in the way of me obtaining a SPL meter so that i can run my own tests on my room and start building panels. Either my car needs repairs or the dog needs emergency vet treatment or other money draining annoyances. It seems to be my curse.

Maybe in the near future I can graph my room and build some resonators to see what their effect is. According to room mode calculations I might have a doozey at about 55Hz. Of course my room is not a perfect rectangle so I'd have to do some measurements first to identify the true room modes.


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## MarkusBonk (Jun 5, 2010)

Here is a link to a site in Germany which has a formula for calculating the Q

http://www.tmr-audio.de/faq.htm#al7


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## frd (Nov 5, 2009)

Thanks Marcus...

I think somehow I realized how to use them. the only remained question is :
when I have the 63 hz mode in my room i don't maybe need A TUNED FOR 63HZ helmholtz ? I can tune it to higher frequency of Q which the F1(low) is near 63 hz ? and place it in high pressurized 63 tone ?

:T


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