John Sayers' Recording Studio Design Forum Archive

Hi Keith,

If I do the rough sums with your data I will only need to use one 4"x4"x1/2" puck for the whole riser which of course will not work.

My sums are:

materials, drums, person = approx 350-450pounds

your compression test on one 3 1/2" x 1 1/2" x 1/2" rubber = average of about 500pounds for 10% compression

so what gives, or am I doing the sums wrong somehow.

I will need at least one puck every square foot or so to actually make the platform stable but according to your tests and my sums this will be about 600o%!! overkill that will defeat the purpose of doing it as the rubbers compression is the key to the riser actually working.

I suppose my question is roughly what size do I need to cut each puck of 1/2" 60duro rubber too so I can use more pucks to make a stable riser and still get the desired rubber compression.

Bet there's not many replies to that one!!

JG

I hadn't done the math, John, but I feared that would be the case for you.

60 duro rubber is pretty darned hard, as the data shows. In order to allow for more pads for less weight, you need a softer rubber, or smaller pads, or both.

Bear in mind that if you cut a puck in half, you will probably be able to apply more than twice the weight to it. That's because of the nature of this elastomer -- it spreads out in its deflection. The smaller the puck, the greater the "edge surface to face surface" ratio (I'm sure there's a technical term for that, but I don't have enough -- meaning any -- letters after my name to know what that would be), and thus the more it deflects under the same weight proportion.

--Keith

No problem Keith,

I think what I will do is cut them into 25mm x 25mm x 12mm (1x1x1/2) cubes, start with 2 foot square placement and then add or subtract as required before I glue them down.
Gotta finsh the room first!! - starting ti get ahead of myself!!
JohnG

Couple of problems I see with using rubber for something this small/light - one you've already mentioned, getting the pucks small enough to be able to use enough for stable support. Two, with the possible exception of Butyl and Sylomer, the damping of rubbers such as neoprene and EPDM isn't very good at all - so without some sort of damping in the form of insulation "caressing" ALL the MDF or other flooring, you will very likely get more ringing/boom than you bargained for.

Since this means that you would need to use insulation ANYWAY, it just seems easier to throw down a 2" thick chunk of mineral wool and lay your double thickness (offset seams) of MDF on top. You've already heard from the thread originators that this works well both for isolation AND for sound quality... Steve

Point taken Steve,
Just trying to find a use for $100 worth of rubber pucks I brought when I thought floating a floor was my thing!!
JohnG

The smaller the puck, the greater the "edge surface to face surface" ratio (I'm sure there's a technical term for that, but I don't have enough -- meaning any -- letters after my name to know what that would be

As taught by Eric D: it's the shape factor.

Ha -- I'm happy just to be able to paraphrase that genius correctly! Thanks, Florian!

Hi !

Finally I am going to do the Steve solution ! (yes I am slow


Got one question about density of the rockwool :

Can you tell me if the 2,5 PCF = 48 kg/m3 or 60 kg/m3 ?

And other question : dont you got rockwool "in the air" at each drummer kick ? little afraid about laying rockwool with "no protection" ....

thanks for any response

pulse wrote:Hi !

Finally I am going to do the Steve solution ! (yes I am slow


Got one question about density of the rockwool :

Can you tell me if the 2,5 PCF = 48 kg/m3 or 60 kg/m3 ?

And other question : dont you got rockwool "in the air" at each drummer kick ? little afraid about laying rockwool with "no protection" ....

thanks for any response

If you're doing this freestanding in a room - just build a simple 2x frame flush to sit on the floor that's with the top of the riser - make it 3/4" larger (in both directions) than the riser - then just set this so you have a neat 3/8" clearance all around the riser - attach to the existing floor with angle clips - and use backer rod and caulk to finish the edge seal.

Neat clean edge finish - doesn't stop free movement of the riser itself - and solves your concerns about kicking fibers in the air...........

BTW - just for reference - 3pcf 703 (or equivilent) rigid fiberglass is acceptable from a bearing point of view with the rockwool if it's more readily available to you.

Sincerely,


Rod

hi rod

thanks for the quick response ! I plan to do the work friday so I want to be sure to command the right material

for me the prob is that I have plenty of choice between mineral wool with lot of different density ... it begins from 30 kg/m3 to 160 kg/m3 and I dont know what density corresponds to 3 PCF ???

thanks also for the idea of the frame around the riser .. but maybe I can do what is in the picture in this thread (make a trim that goes near the ground but that doesnt touch it ... should be enough ... it is not in a room, it is in my studio, so it doesnt have to be perfect clean but I dont want to inhale wool at every session

and also 4'' corresponds to 10 centimeters and I wanted better to use 8 cm, do you think I have to use 10 cm or 8 should be enough ?

pulse wrote: it begins from 30 kg/m3 to 160 kg/m3 and I dont know what density corresponds to 3 PCF ???

This link downloads a free (freeware) and rather good unit convertor.
It's easy if you are used to think in metric units on sites dominated by American units to have something like this on your desktop:
http://joshmadison.com/software/downloa ... ertExe4.10
You can find this typical conversion under the tab density. You can calculate both ways.

3 pcf = 3 pound/cubic feet = 3 pound/feet3 = 3 lb/ft3 = 48 kg/m3
There are several manners of writing the same. PCF is normally not written in capitals (in as far as I know).
2.5 pcf = 40 kg/m3
1 pcf = +/- 16 kg/m3

HUGE thanks to Eric !

Endly I have THE answer about that pcf thing !

so I have to find another product ... I was going to buy 60kg/m3 ... It wont do a "correct" ressort ? (in the mass-ressort-mass system)

or maybe I can use 8 cm of 60 kg/m3 instead of 10 cm of 48 kg/m3 ?

is the 4'' dimension a minimal one (for being in th 100 Hz area) or just an example ?

Looks like Steve was giving all these precious infos without having them tested in real ?

Density is one thing. One can have boards with higher density and still feeling softer than others with lower density.
It depends on brands and types of material.

The basic idea is: Whatever you use, you should have a deflection of ca 2.5 mm under static load (riser + drum + you). The lesser the deflection the worse your decoupling will become. With 2.5 to 3 mm you have a rather perfect decoupling (is relative of course) of your drums.
You also need enough cavity (> 2.5 cm better 5 cm) since the air also acts as a spring. If you acoustically close the edges then more than this 5 cm could be advisable (but it all depends of mass of this top floor).

Making a riser in itself as heavy as possible (top floor) will make it less sensitive to the difference in load, with and without musician, and the exact position of drums. The riser becomes more stable be making it heavier.

If you have mineral wool which is too stiff to obtain this 2.5 mm (or more) deflection you can solve that by cutting stripes of this mineral wool and use less than 100% coverage, as such that the total static load is carried by less mineral wool and as a result will deflect more.

I saw (I think here in the forum) someone using tennis balls to obtain the same effect (sounded as a good idea to me). You could use pucks, pieces of foam, whatever.

However you do it, try to get this 2.5 mm deflection under load, and if using pucks or tennis balls fill the empty parts with mineral wool or fibreglass (absorption in cavity), without that wool carrying load.

If you directly use mineral wool, that part is taken care of of course.

thanks for these infos

so you mean I need to have this 2,5 mm of "move" between riser without drums and drummer and riser with drums and drummer ?

I planned to add some piece of wood behind the drums in order to maintain a bit the sound ..

well I think that the only way now is to try !

if i dont have these 2,5mm reduction when I arrange the drums I should remove some material

thanks again for the advice !