Acoustic Isolation Frame Mounts

In order to achieve maximum acoustic isolation, I had decided to try and decouple the inner room of the studio as far as possible from the outer room. This meant using a resilient layer of EPDM rubber underneath the sole plates of the stud sections, as I have mentioned before. As a reminder, here's a picture of the resilient layer underneath a horse shoe section of frame that I was about to flip upside down into position. The black tape in position is the damp proof course:


Therefore, when it came to fixing the stud frame to the concrete floor I wanted to avoid using a simple bolt, as this would bridge the gap by contacting both the wood and the concrete and compromise the acoustic separation. Therefore I came up with the  solution of using a block of 2by4 as an isolation mount. You can see an example of this below where I was testing out the concept:




The principle here was to use the 2by4 as a "washer" that gripped down on the sole plate of the timber frame (the longer section of 2by4 shown above). I then used M8 concrete screwbolts to fix the 2by4 to the floor. The trick here was to have an interference fit (i.e. physically touching) between the bolt and the isolation mount, but to have a clearance fit between the bolt and sole plate. To this end I drilled a much bigger hole (25mm) in the soleplate so that the bolt wouldn't make contact with it. Two example holes are shown in the left corner of sole plate section in the image above. Then, I used more of the resilient strip between the isolation mount and the sole plate to try and acoustically decouple them.

All of this meant that the bolt didn't bridge the acoustic gap between the walls and the floor achieved by the resilient EPDM layer - or at least it minimised the transfer of sound between floor and wall as far as possible without resorting to actual spring/rubber isolators as would be used in commercial studios. 

NB One alternative solution to this issue would have been to use a rubber washer/bushing instead of having to make a whole wooden isolation mount - but this was a product that I only discovered afterwards!

I therefore made up several of the isolation mounts that I would be needing to tie the frame down at roughly 80cm intervals:



Then I proceeded to mount the frame down, as you can see below:



As I wasn't using shield anchor bolts because I couldn't find any long enough, I had to be careful not to overtighten the M8 bolts with the impact driver, as I did this a couple of times and broke the concrete thread. This, however, only occurred in places where the concrete floor seemed to be weaker, and the whole frame mounting solution worked very well in the end!