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In the Forum: Audio Discussions
In the Thread: The ULF cannel for my new listening room.
Post Subject: I am inclined to agree with them...Posted by anthony on: 8/2/2018
 Romy the Cat wrote:
I engaged is a discussion about my IB project with some guys who do IB for a while: 
 
http://ibsubwoofers.proboards.com/  , the My Projects Section, I think you need to login to get it… 
 
What is interesting is that they claim that “rubber and foam do nothing to decouple the manifold from the structure” because it will be “tremendous amount of vibration from the sound waves”. I certainly respect what they advise but it does sound not intuitive to me. I know that there are some builder at this forum, what is your take on the subject?


I did not bother signing on to that forum to see your thread, but no foam is going to decouple 20Hz, not even close.  Part of the design criteria of my my Bass Cannons project is to try to limit the transmission of low frequencies through the floor of my room down to the house below.  Speaker cabinets at those frequencies do not attenuate the volume very much and even with my rather inert, damped, very rigid and pre-tensioned Cannons sound leaks through like water through a sieve.  The transmission of sound causes vibrations in the cabinet walls which is then efficiently coupled to the floor which vibrates in sympathy which causes sound transmission to the rooms below.  I looked at all kinds of ways to isolate these speaker vibrations from the floor, but in the end I used industrial pneumatic isolators similar to those you have in you Vibraplanes (but much less expensive).  Part of the reason that I used those mounts is so that I can level the stack of Cannons, but there are other low frequency mounts that you may be able to use if levelling is not required.

Look for the resonant frequency of the mount (Fs) that is sufficiently below the frequency that you wish to isolate above.  Multiply Fs by the 1.41 and that is the frequency from which the isolator will start isolating:  so if Fs = 5Hz then isolation begins at 7.07Hz.  

Have a look at these mounts.  Note that they have specidfied a minimum and maximum load:  to get best isolation you have to load them near their maximum (same with all of these mounts I will link you to).  These are the pneumatic mounts that I used.  Under the DSET power supplies I needed something that was relatively inexpensive but capable of isolating reasonably low frequencies so that I could keep floor vibrations out of the power supplies:  I used these.

I hope this is of some use Romy.


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