Drum riser: poor man's floating floor? *DONE! WITH PHOTO!*

Eric_Desart wrote:

This is based on the approximation (correct for linear bahavior): fo = 15.8/sqrt(d) d=(15.8/fo)^2 fo = resonance frequency d = deflection in mm

Thanks Eric for the most valuable info. I though the thickness of the spring material had something to do as well. Here's the Sylomer P data : (link fixed) According to this, more thickness (two layers of 25mm Sylomer) means a lower resonance frequency. Now I guess a thicker material would deflect more, hence the lower resonance frequency ? According to the formula, the target resonance frequency at Galaxy Studio was 3Hz. Pretty impressive... Let's get a bit silly : to achieve the same 3 Hz resonance frequency with Rockwool, maintaining deflection within 5% (2.5 mm deflection on 50 mm rockwool) you will need a rockwool layer of 560 mm :shock: ... springs were making more sense :D Michel

Michel,

msikio wrote:

Thanks Eric for the most valuable info.

Many thanks for these gentle words

msikio wrote:

I though the thickness of the spring material had something to do as well. Here's the Sylomer P data :

External image, not preserved — original: http://www.studioquatrechemins.info/Images/Sylomer_P_fréquence_propre.GIF

According to this, more thickness (two layers of 25mm Sylomer) means a lower resonance frequency. Now I guess a thicker material would deflect more, hence the lower resonance frequency ?

Your conclusion is correct. Basically for any material there is an optimum workload which can be translated in a % compression. This has to do with aging and elasticity. In order for a material to continue doing it's job it must return (+/-) to it's original thickness after removing the static load. Otherwise it proves that you damaged the material somehow, altering the spring (dynamic stiffness) properties. This of couse also includes material fatigue, chemical interaction with surroundings etc. Since you don't want to overload that material, but want to have a lower resonance frequency (read higher deflection) you just increase the thickness of the initial material. Hence Getzner sais: to get a lower resonance, rather than overloading our material (with the negative short or long-term effect), use a thicker initial thickness. In fact you can compare this DIRECTLY with the cavity in a double leaf wall (drywall). Increasing thickness equals weakening spring, equals enlarging cavity in double leaf wall.

msikio wrote:

According to the formula, the target resonance frequency at Galaxy Studio was 3Hz. Pretty impressive...

Correct calculation since helical steel springs act very linear in function of load. Hence for this type of solution the formula is more correct than for synthetic or other materials that react less linear. However in the typical working load range of a resilient material the material will react rather linear as well, making this formula a good to very good approximation. But when critical one always should resort to the data as presented by the producer.

msikio wrote:

Let's get a bit silly : to achieve the same 3 Hz resonance frequency with Rockwool, maintaining deflection within 5% (2.5 mm deflection on 50 mm rockwool) you will need a rockwool layer of 560 mm :shock: ... springs were making more sense :D

:) Yes but it's also a matter of material quality and mechanical properties of course. One must be sure that after 50 years that thing still does exactly the same as the first day. Steel springs also have a very low internal damping, which also means a maximized decoupling rate in the target range. In function of material fatigue these springs are peen shotted, which means that any tension is removed caused by/during initial production. Hence one could say that they are aged before using them. If you analyze these spring pictures you'll notice that also thin layers of sylomer are used. This is because a spring also causes resonances withing the wire of the spring itself. Hence you design towards a target frequency, but get a free (unwanted) higher resonance within the spring itself. These thin sylomer layers do have an acoustic function. In fact the high price for Sylomer is not that it should be acoustically be better than any other material with the same defection, but the aging properties and the enormous amount of testing related to that. They also have different types for the same workload with different internal damping which results in different types of decoupling curves. For non-critical decoupling purposes where one can easily replace material, one can do with whatever cheap material as long as one takes the deflection in a good workload range into acount. This workload range can differ between material types. Therefore I mostly give rule of thumb ranges covering most materials. For critical projects however one should check these properties as given by the producer. I relative recently checked this with rockwool itself. In fact they allow a very small defection %. Hence they don't trust there own material in function of aging very well for critical purposes (and the symetry in material properties isn't maint for such use). Therefore they use a lot of safety margin. This relates with the fact that this fibre in function of dynamic load can more or less degenerate and break. Hence it should be plain stupid to use such material for a project like Galaxy. PS: your link doesn't seem to work.

Eric_Desart wrote:

I relative recently checked this with rockwool itself. In fact they allow a very small defection %. Hence they don't trust there own material in function of aging very well for critical purposes (and the symetry in material properties isn't maint for such use). Therefore they use a lot of safety margin. This relates with the fact that this fibre in function of dynamic load can more or less degenerate and break.

Very interesting.... at the same time they do have special floor products like Rocksol2 (150 kg/m3) made to be used under a 40 mm concrete slab. In the light of the research you've done, do you think 5% compression if safe and reasonably durable for rockwool ? 2.5 mm deflection leads to a 10Hz resonant frequency. TL enhancing starts at f0 * sqrt(2), around 14 Hz for f0 = 10 Hz. Should be good enough for drums. But in the case of a drum riser like the one we are discussing here, especially if you build an air proof frame around it as suggested by Rod, the platform acts as a regular wall panel absorber with another (higher) resonant frequency ? Do you calculate that resonant frequency the same way as for a wall panel ? For two layers of 19 mm mdf at 80 mm from the boundary I find 40Hz. It means there will be a decrease of TL at that frequency. Am I correct ?

Eric_Desart wrote:

PS: your link doesn't seem to work.

Done ! thanks for letting me know... servers don't like accented characters

The one where you said: "Here's the Sylomer P data". That links to a picture but doesn't show up for me.

msikio wrote:

2.5 mm deflection leads to a 10Hz resonant frequency. TL enhancing starts at f0 * sqrt(2), around 14 Hz for f0 = 10 Hz. Should be good enough for drums.

:) I mostly know what I say and why ..... I know that most Rockwool and fibreglass brands have floating floor boards, normally for a chape/cement topfloor that's even less dense than 150 kg/m3. These higher densities they use mostly for less stiff, lighter top floors (which acoustically is indeed reversed resulting in a worse floor, but done for practical reasons). But to obtain that they use a much lower deflection (the safety I referred), which means that they get a rather high MSM (resonance). I didn't say they didn't use it, I said they build in a much higher safety margin (much lower deflection percentage). Please read the sentences I write. From an acoustical point of view one could say that they UNDER-load that material as safety precaution. The allowed % of deflection seems to differ between fibreglass and rockwool and I can imagine between brands and even types. For Rockwool (brand) floating that's even less than this 5 % (can't remember exactly but was relative little). The others I don't know (haven't checked). For materials as Mineral wool you should stick to what they tell you. You can go to more in less critical applications, since when something happens you can easily replace materials. Hence Rockwool is no ideal material for heavy concrete floating floors in studios, since within the restrictions they give, that resonance remains too high for studio purposes. I checked one brand and with 5 cm initial thickness, if remembering correct the lowest resonance within the restrictions given by them was 48 Hz or something. With Sylomer and comparable you can go down roughly to ca 8 a 12 Hz (depends on design and shape factor) for the same initial thickness. Note that such standard materials and applications are designed in function of the common European standard range of 100 to 3150 Hz (+/- , can possibly differ a bit between national standards). Say roughly covering all standards including US between 100 and 5000 Hz (US lots go from 125 to 4000 Hz). Such applications don't bother about studio applications and very low frequencies. I referred somewhere to a post I wrote at Studiotips here related to rockwool versus fibreglass. And with the airspring you're right. Basically this are 2 parallel springs. Hence closing them off as Rod suggested isn't necessarily a very good idea. At the other hand leaving this open won't make that much difference, certainly when there is a large coverage with mineral wool. But you have to calculate the TOTAL mass including the musician and instruments when calculating the air spring effect. An open edge will weaken that spring somewhat. Using perforated material should acoustically be ideal for a riser. You neutralize that air-spring. As you noticed the questioner didn't really respond to my related comments in function of weight and stiffness (pressure distribution) of that floor. Therefore I adviced to make this topfloor heavy and I did advice to stick to the 80 mm. This combination will give him a good riser even when he closes these edges as Rod suggested. And I can't give a complete course acoustics on every individual question. Maybe I once make a complete page with a better oversight.

Hello Eric, Here's the image without the "é" in the file name, it should work this time for everybody : Again thanks a lot for the info. Most on this info is not readily available elsewhere : even the Rocksol lab report doesn't mention deflection and resonant frequency. I actually understood your point fully. I mentioned floating floor boards as a reference point.

Eric_Desart wrote:

And I can't give a complete course acoustics on every individual question.

You're helping a lot already, thanks again. Michel

Hi again The riser is done ! I will post pictures tomorrow ... As I can say (I am not a drummer) the sound is really better inside the studio .... will have to wait for a real session to see whether it is better or not about sound transmission ... I have between 2 and 5 mm (depending on space ... my ground is not totally perfect) but I think I respect the whole idea was quite easy to do it (but MDF is so heavy ;-) pictures coming soon bye

Here are the pictures, sorry for the quality (quickly done with the phone) http://img511.imageshack.us/img511/5362/dsc00104oo0.jpg http://img511.imageshack.us/img511/2646/dsc00105qj5.jpg http://img505.imageshack.us/img505/4692/dsc00106yn6.jpg http://img505.imageshack.us/img505/1277/dsc00107pu5.jpg http://img523.imageshack.us/img523/4668/dsc00108ox2.jpg thanks for all advice not yet finished .. need to hide this flumroc ... maybe I will fix some pieces of wood directly on the MDF ... (dont want to use more space for this riser so I wont use the solution of adding a frame)

I am about to build one of these 6'x8' riders you guys have been discussing here. I have some extra mass loaded vinyl barrier (some call it sheetblock I think) sitting around from an older studio buildout. Would I benefit from sandwiching a layer of this stuff between the two layers of MDF? Would it help to dampen any resonant frequencies, etc.?? Just trying to put old materials to use...and clean out the basement :) Thanks, Steve