Okay, so I went down to Carpet Right today (that's right I know how enjoy boxing day
) I asked them if I could have a few of their Helmholtz resonators that the carpets come on and they said yes!
So I now have two 4 meter 10cm diameter strong cardboard tubes which I can play with.
I entered the numbers into that helmholtz calculator on the site technobear gave and it said that if I use 1 meter of the 10cm diameter tube with a 10cm length of 4cm diameter tubing for the neck then it will resonate at a frequency of 68hz. Which is just what I need! Woohoo!
It still needs to be put into practice but that should not take too long. I'll do it in the next few days when I have some time and let you all know what happens.
Oh, the 4cm diameter neck tube is just the standard size of plastic tubing used for plumbing sinks and so on. Very cheap and I had some in the shed.
One thing though, in order to make this a broadband absorber I have read that all you have to do it put a thin air filter between the body and the neck. Does that mean like.. just a layer of fabric starched over the hole or something? This is what the site says -
Is that really al there is too it? Because if having a broadband absorber like that means that it will smooth out dips and peaks then I might make a lot of different ones for all the frequency range! Remember that the higher the frequency the smaller they can be so... it sounds pretty good.

So I now have two 4 meter 10cm diameter strong cardboard tubes which I can play with.
I entered the numbers into that helmholtz calculator on the site technobear gave and it said that if I use 1 meter of the 10cm diameter tube with a 10cm length of 4cm diameter tubing for the neck then it will resonate at a frequency of 68hz. Which is just what I need! Woohoo!
It still needs to be put into practice but that should not take too long. I'll do it in the next few days when I have some time and let you all know what happens.
Oh, the 4cm diameter neck tube is just the standard size of plastic tubing used for plumbing sinks and so on. Very cheap and I had some in the shed.
One thing though, in order to make this a broadband absorber I have read that all you have to do it put a thin air filter between the body and the neck. Does that mean like.. just a layer of fabric starched over the hole or something? This is what the site says -
To make the resonator a more useful sound absorber, it is necessary to broaden its frequency range. This can be done by making the "air piston" lose more energy. The most effective way to do this is to add a thin air filter between the neck and body of the resonator. Now, a lot of extra energy is needed to move air back and forth through the air filter. The resonator is still most efficient at absorbing sound at its resonant frequency, but the added resistance caused by the air filter makes it an efficient absorber at other frequencies too.
Is that really al there is too it? Because if having a broadband absorber like that means that it will smooth out dips and peaks then I might make a lot of different ones for all the frequency range! Remember that the higher the frequency the smaller they can be so... it sounds pretty good.