Helmholtz Resonators


#1

In our ongoing series about building a new Music Room at PS Audio and installing the legendary Infinity IRSV’s in that room, the subject of bass comes up a lot - especially concerning the IRSV since very few loudspeakers on the planet have such bass as do the IRS and their 12 12" woofers, 3000 watt amps and servo control.



You need a room to handle these monsters that is free from boominess caused by peaks in the room’s response. To make that happen we’ve found where the bass peaks will occur and are building resonators as tuned filters to eliminate the peaks and get a flat response.



If you’ve ever wondered what a Helmoltz Resonator is and does, give this short video a watch.



http://www.youtube.com/watch?v=Ck-fZJvf39M&feature=youtu.be


#2

Very cool!



As a physics/music nerd I first read On the Sensations of Tone when I was 12 or 13. I am very pro Helmholtz. :)


#3

No hardhat with the salad dressing bottle.


#4

Very interesting indeed. No way I could ever build such beasts but it’s fascinating to watch.


#5

Love the videos Paul. Very interesting indeed. Looking forward to the next episode of “This Old Sound Room.”


#6

@euphonite Thanks!


#7

@stevem2 You really don’t need to build beasts to make this work - everyone has extra space in their walls and if you know the volume in each wall cavity - basically the area between the studs - you can figure out a way to do this without building anything.


#8

That would be interesting to see how this could be done is non dedicated listening rooms. - Great thread.


#9

i’ve got few of theese: http://www.vicoustic.com/vn/Homecinema/produtoinfo.asp?Id=78

it actually works :slight_smile:



then when space is concern, membrane resonators come to rescue :slight_smile:

http://gikacoustics.com/product/gik-acoustics-scopus-tuned-bass-trap-t100/

those are not variable, although they can make you one by your specs…


#10
@stevem2 You really don't need to build beasts to make this work - everyone has extra space in their walls and if you know the volume in each wall cavity - basically the area between the studs - you can figure out a way to do this without building anything.


Not quite everyone Paul. My house, which is a semi-attached townhouse (with the speakers nearest the common wall, undoubtedly to my neighbor's delight) turned 100 this year and was an early experiement in the use of precast concrete. The walls are concrete with plaster on top. They are actually hollow in the middle of the panels but I don't think opening them up is feasible. Maybe I could just poke a hole into a cavity and tune that, if I could find it and determine its volume. The corners would be solid and one side wall is mostly windows so the cavities many not be in the right places to begin with. Plus my wife would probably kill me. Interesting concept, though.


#11

@maniac Those are cool, thanks for the info. Problem with these is, as you point out, they are not variable. So one of the pitfalls we have is that as you move things around in your room - or add/subtract furniture or speakers - the needs change and then you’re hosed.



After studying all this I am tempted to build some portable Helmholtz Resonators and sell them - there’s a huge need. The Q or width of frequency for these can be easily controlled as well as the frequency. L-)


#12

Paul is you do a simple frequency sweep in the listening room do the peaks and valley tell you what frequencies are at issue? Is so how many db of variance can be tolerated before it truly affects the system sound?



thks


#13

@magicknow one thing is frequency response and other thing is reverb (how long the tone stays on room when playback stops).



i’d suggest to try REW:

http://www.hometheatershack.com/roomeq/



you would need calibrated microphone (for eg. UMIK-1 from http://www.minidsp.com/products/acoustic-measurement/umik-1)



i’m now waiting for delivery of some additional traps. till the moment i have installed 2 vari-bass-es in corners few movable acoustic foams in reflection points and 3d diffusers on ceiling (damn i hate working with glue :smiley: )



i was surprised how the sound changed (mostly for better) :slight_smile:


#14

^:)^

You made it sound like you were going to just wall off the corners in your previous video. Now THAT’S what I’m talkin’ about! …on steroids!!!


#15
@magicknow one thing is frequency response and other thing is reverb (how long the tone stays on room when playback stops).

i'd suggest to try REW:
http://www.hometheatershack.com/roomeq/



you would need calibrated microphone (for eg. UMIK-1 from http://www.minidsp.com/products/acoustic-measurement/umik-1)

i'm now waiting for delivery of some additional traps. till the moment i have installed 2 vari-bass-es in corners few movable acoustic foams in reflection points and 3d diffusers on ceiling (damn i hate working with glue :D )

i was surprised how the sound changed (mostly for better) :)


thanks I will order it


#16

@magicknow I use pink noise and a sort of simple spectrum analyzer to see the bumps and irregularities.


#17

@maniac - the vicoustic devices look great - were they easy to setup up and dial-in?



#18

@Paul, very interesting video ! Thanks !


#19

@david yes it’s really easy to dial it trough the frequencies. Mine two are set to about 45-55Hz and other two I’m waiting for will be set to around 70Hz to get rid of nasty null I have.



But honestly the varibass units are quite expensive when one considers the flaky materials used. One of the units I have sometimes spontaneously retracts due to gravitation and too low friction (the tuning mechanism is base on rubber to “wood” friction). It may happen over the time i will have to use duct tape or something else to keep them set on desired frequency :slight_smile:


#20
maniac said:
then when space is concern, membrane resonators come to rescue :)
http://gikacoustics.com/product/gik-acoustics-scopus-tuned-bass-trap-t100/

I have had great experiences with GIK and recommend looking into their products.