hi everyone, it's been a long time since i've posted. our studio was built last year with tons of great help from this forum (i still need to post finished pictures).
i've been treating our control room a piece at a time over the last few months, and after some testing, i still have some modal issues floating around 100Hz (due to our ceiling height of 11ft). the room is pretty balanced otherwise, and i'm interested in experimenting with a tube type helmholtz resonator to even out the response in this frequency range.
i've been reading everest's book and understand the concepts pretty well, but i have yet to find an equation to determine the dimensions of the tube and diameter and depth of the neck. can anyone here enlighten me? perhaps it might be more prudent to attach a tuned perforated panel to the ceiling? any advice would be greatly appreciated! thanks for your time and this wonderful resource!
-nick
tube-type helmholtz resonators
Originally posted at johnlsayers.com, topic 11426.
Just convert the flat panel equation to work with the volume instead of the depth.
Andre
cool. so if i understand you correctly:
f=200 x square root (p/(V)x(t)
where
f=frequency (Hz)
p= perforation %
t= effective hole length (inches)
v= volume of tube (i'm assuming cubic inches?)
so, if i buy a 12"x48" cement forming tube (volume 5,428.67 cubic inches)
and i build the lid with .5" plywood (12" circle area is 113.1 square inches)
and i want the resonator to center at 100Hz, the equation looks like this?
100=200 x √((y/113.1) x 100) / (5428 x .5))
where y= hole area
or:
100squared= 200squared ((y/113.1) x 100) / 2714)
then:
10000 = 40000 x ((y/113.1)x 100) /2714)
then:
10000 x 2714 = 40000 x ((y/113.1) x 100)
then:
27,140,000 = 4,000,000 x (y / 113.1)
then divide both sides by 4,000,000:
6.785 = y/ 113.1
then:
6.785 x 113.1 = y = 767.38 = hole area
767.38 / π = 244.26
√244.26 = 15.63 inch radius hole? i'm not sure where i made a mistake. i think i missed a conversion for the depth and the volume. i'm not a math head, can anyone see the mistake?
ooh that hurt my brain.
sorry to subject you to this.
thanks for your help!
-nick
sorry, can anyone help me with this? i'm trying to find the proper equation to build these resonators. thanks in advance for any help!
"EFT" the room measurement software, has a helmholtz resonator disign page in it's help section.
See the Device Designer page.
http://www.acoustisoft.com/index.html
or PM me.
Hi, I am looking for a formula for a cylindrical helmholtz resonator/absorber also. I am very impressed with the taming of the lowest mode found on pages 228 etc. of The Master Handbook of Acoustics. I wish to try this on my room. I assume the classic 'bottle' calculations would be incorrect if we have the smaller tube tucked inside the larger. I reckon many people must have done the calcs on this already but strangely I can't directly find it.
I cannot find that Device Designer on the Acoustisoft site at all. Does it still exist, perhaps this is a Mac Safari thing?
Andre, I am afraid my Maths would be quite rusty and I would probably go wrong trying to convert. Given the variables, e.g. stuffing with fibre etc. do you reckon the 'Bottle' forumula would suffice?
Best Regards, Dan FitzGerald
Lookie here: Acoustic Calculator --EthanHi, I am looking for a formula for a cylindrical helmholtz resonator/absorber also.
Of course it is good. It is the origin of the slat equation! AndreGiven the variables, e.g. stuffing with fibre etc. do you reckon the 'Bottle' forumula would suffice?
Hi Guys, thanks for the thoughts.
Ethan, that's exactly what I wanted. I don't have one, but I will run the numbers on a neighbour's PC. It will be useful to play with the 'what ifs' of different port diameters, Q, etc. to at least get into the ball park.
Andre, Maths and Arithmetic are not my Forte, it's not laziness, I just get it wrong, so I tend to use help of any type. I also suspect that the classic formulae will not take into account:-
1 the slight detuning due to fibrous stuffing.
2 the slight detuning due to the Port or 'neck of the bottle' being within the container.
So for those reasons I wanted to use Doug's Device Designer or such , on the assumption that he had taken these factors on board. Perhaps I will ask Ethan to Design a Device for me in ETF5 when I have my materials in place.
Do you reckon I am correct in these detuning assumptions? The experiment I intend is very specific. It is almost identical to Pages 228-229 in The Master Handbook. Doug assures me that data is true, it did happen. I am stunned by the huge reduction in length of the low mode and hope to achieve similar here, albeit at 37Hz. I am also curious as to how this will sound.
If the device can achieve such a change in mode length I am sure it will detune the mode slightly also. What I need is a Slide or Bottleneck Helmholtz resonator!
Most of the studio rooms I have treated so far have had such a singular large anomaly. I am hoping that careful application of this old chestnut will be a useful tool in the future. I will document the experiment and post it here in any case.
Best Regards, Dan FitzGerald
Here's a useful version of the Helmholtz formula for a Tubular device.
http://forum.studiotips.com/viewtopic.php?f=20&t=150
and
Q ~= 2*π*sqrt[V*(L'/S)³]
Got my Tub and tube, will do the experiment shortly.
DD
I like this. It's easy to use.
http://www.mediafire.com/?k2hjmoh2rmu