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PostPosted: Thu Apr 25, 2019 1:45 am 
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Location: Los Angeles California USA
Good Morning All,
I'm new to the forum so please forgive if I'm posting this in the wrong place. I've built a rehearsal studio for my son in our back yard. He's a drummer. I started out with a 10'x12' Tuff shed built on a gravel bed. the floor rests on a metal frame. The floor material is fiber board. The walls and ceiling are plywood with wool insulation between the studs and thick drywall covering. On the dry wall I've hung moving blankets. On the floor I've also got moving blankets. Inside the Shed I've assembled a Iso Booth https://drumperfect.com/index.php/silen ... ert60.html . The Iso booth has greatly reduced the drumming sounds except for the lower frequencies; bass drum, floor toms and some of the rack toms. I'm looking for a solution to reduce the lower frequencies. Will building a platform for the kit to separate it from the floor do the trick? Should I try to find something to fill the gap between the floor and the gravel bed? Any help would be greatly appreciated. My neighbor would also be thankful. Cheers.
Peace,
Michael Mintz


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PostPosted: Thu Apr 25, 2019 4:37 am 
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Hi there Michael, and welcome to the forum! :)

As you already figured out, isolating drums is hard. Actually, it's the hardest of all instruments to isolate! For four main reasons: 1) it's the loudest of all them all: a typical drum kit can put out 115 dBC when played moderately, and higher when played hard-and-fast. 2) Most of that energy is in the low end of the musical spectrum, below about 300 Hz. 3) The "low end of the spectrum" is the hardest part to isolate, due to the laws of physics. 4) Low frequency sound travels better over long distances than high frequency sound.

So for drums, you have the perfect storm of conditions working against you.

The ONLY way to stop sound, is with mass. There are several ways that can be enhanced, but in the end, it all boils down to mass. That implies heavy building materials. The heavier, the better.

In fact, there's a simple principle of physics that describes exactly how well any give mass will stop any give sound, and that principle is called "Mass Law". The equation goes like this:

TL(dB)= 20log(M) + 20log(f) -47.2

Where:
TL is the "Transmission Loss", or how much isolation you get, in decibels
M is the surface density of the panel (mass per unit area (kg/m²) ), and
F is the center frequency of the third-octave measurement band

Any scientific calculator can be used to figure out how much isolation you will get from any type o material like that. As a point of reference, here's the "absolute density" of several common materials:

PLYWOOD: - 560
OSB - 610
DRYWALL - 680
MDF - 720
CINDER BLOCK 1700
BRICK - 2300
CONCRETE - 2400
GLASS - 2500

All of those are rough averages, in kilograms per CUBIC meter (kg/m3). To get the "surface density" (which is the mass per unit area), of your actual materials, multiply by the thickness. For example, it says above the drywall has a density of 680 kg/m3, so if you have a sheet of drywall that is 10mm thick; 10mm is 0.01 meters, so multiply 680 x 0.01 = 6.8 kg/m2. That's the surface density of a sheet of 10mm drywall. For 16mm drywall (5/8"), it would be 680 x 0.016 = 10.9 kg/m2. For 19mm MDF (3/4"), it would be 720 x 0.016 = 13.7 kg/m2, and for a 6" thick concrete wall (150mm), it would be 2400 x 0.15 = 360 kg/m2.

If you plug in any of those to the equation above on a scientific calculator, you can find out exactly how much isolation you would get for any frequency that you choose.

If you do that, the first thing you will notice is why I gave you rule #2 above: For low frequencies, you need a HUGE amount of mass to get decent isolation. The second thing you'll notice is that, for any frequency you choose, doubling the mass only increases isolation by 6 dB, which is not very much. You need an increase of 10 dB in isolation before most people would say that the sound is "half as loud". 20 dB makes it "one quarter as loud". 30 dB "one eighth as loud". etc.

All of the above applies to having one single "barrier": in other words, a wall that has only one "leaf" of mass in it, such as a brick wall, or a stud wall with plywood on one site of it. That mass itself can be built up from several layers, but still all together in once place, with no air gaps. For example, a wall that has a layer of plywood, then a layer of MDF, then a layer of drywall, all nailed together on one side of the stud frame, still counts as a single "leaf" of mass, even though there are several layers in there. Mass Law describes how that "single leaf" barrier blocks sound, no mater how many layers you put on it, or what materials you use in each layer. Just add up all the individual "surface densities"

It turns out that if you put TWO such leaves separated by an air gap, you can get MUCH better isolation. So, for example, if you have one leaf that consists of plywood with siding on the outside, then another leaf a few inches away that consists of two layers of drywall, you can get really, really good isolation: Much better than what Mass Law allows. In fact, the mass law equation no longer applies to two-leaf walls. There's a more complicated equation for that.

But there's a catch: the two leaves must not touch each other, or have anything that ties them together. If there is something that connects the two leaves, then you are moving back towards Mass Law again. Not quite as bad, but not as good as "fully decoupled".

So they CANNOT be on the same stud frame. You need to have separate independent frames for each "leaf", and those two frames cannot be connected in any way. The only exception is that they can rest on the same floor, provided that the floor has very high mass (such as a concrete slab, for example).

Now, you might think "Well, if one leaf is bad, and two leaves is good, then three leaves must be better!". And you'd be wrong! Curiously, in one of those strange quirks of acoustics that is not intuitive at all, three-leaf is WORSE than two leaf for low frequencies. It's better for high frequencies, yes, but not for lows. And highs are not a problem in any case! If you get good low-frequency isolation, then you will always have excellent high frequency isolation, regardless of how you did it. It's the lows that are a problem.

Here's a simple graph that shows it the three systems, very clearly:
Attachment:
TL-graph-isolation-of-single-double-triple-1-2-3-leaf-walls-SML.jpg

The green line shows the isolation you would get from a thick concrete wall, that is a single leaf. That is pure mass law for a very high mass single-leaf. The red line shows the case of a simple two-leaf wall, where there are two stud frames and each one has two layers of drywall on just ONE side of the studs. As you can see, the isolation is pretty good: not as good as the 400mm thick concrete, but take into account that this is MUCH less mass, and much thinner as well, yet it performs nearly as well, and gives you very good isolation. The blue line, however, is the three.laf case, where there is one stud wall that has two layers of drywall on EACH side (total of four layers), and right next to it is another stud frame that has two layers of drywall on just one side. That's the same total thickness as the red-curve wall, and 50% more mass, but looks what happens for low frequencies: it does far, far worse than either of the other two walls. Below about 250 Hz, it gets really bad. Even though the blue line is great in the highs, it is terrible in the lows, and the extra isolation it gives in the highs is no use, since both of the others were already very good in the highs: It's the lows that count, and 3-leaf is not good for lows.

So, to summarize: one leaf is "mass law", and not very good. 2-leaf is much better. 3 leaf is bad again, especially for low frequencies. And 4 leaf is even worse.

OK, all of the above explanation is necessary for you to understand the implications of what I'm about to say:

You have built a three-leaf wall.

You have a very similar situation of the blue line above. You have a coupled two-leaf wall, and also the drum booth, which is the third leaf. And thus you say: "...has greatly reduced the drumming sounds except for the lower frequencies; bass drum, floor toms and some of the rack toms.". The problem is the laws of physics. With your 3-leaf system, you cannot get good isolation, because physics is working against you. You got great isolation in the highs, yes, but not in the lows, because that's what 3-leaf walls do. It's all related to resonance in the wall systems, and I could explain it in detail if you want to understand WHY this is happening, but you are probably more interested in "what to do about it".

(By the way, the moving blankets: are not doing anything useful to isolate here. It's a common misconception that moving blankets are good for sound isolation: they aren't.

The answer is fairly obvious, now that you understand the underlying reasons: )

Quote:
The walls and ceiling are plywood with wool insulation between the studs and thick drywall covering.
There's your problem! That's the basic reason here. What you should do, is to take off that drywall, cut it into strips that fit in between the studs, and push it in place up tight against the plywood outer-leaf. Don't nail it, and don't glue it: just push it in place up against the plywood, and caulk around the edges to get an air-tight seal, then use simple cleats to hold it in place, nailed sideways into the studs. This is often referred to as "beefing up the mass" on a leaf. It puts all of the mass where it needs to be, in one single "leaf", not two. Do the exact same thing for the walls and the ceiling: Put all of your existing mass on the outer leaf, carefully sealed, air-tight, using caulk.

Now, having said all that, you still might not be out of the woods. This should give you an improvement in isolation, but still might not be enough, for various reasons. One of those is that the drum booth is too far away, and the mass is too low, to work properly as a two-leaf system. You might still need to create a different type of 3-leaf system, that DOES isolate. If you find that, after doing the above you still are not getting the isolation you expect, then I would suggest adding isolation clips, hat channel, and another two layer of drywall. There are several different types of isolation clips, such RSIC, Genie Clips, Isomax, etc. They all do basically the same thing: they allow you to put up another layer of drywall on your same studs, but they decouple that from the studs. They have special rubber pads in them that disconnects the hat channel from the studs, so there is no direct mechanical connection. So put up the clips on the studs, then put in the hat channel on the clips, then screw the two layers of drywall onto the hat channel in the normal way, but "staggering" the joint between the layers, so the joints in one layer do not line up with the joints in the other layer. Caulk the joints in both layers.

If you really want to go as far as you can with this, then also use something called Green Glue Compound" between the two layers of drywall, to improve the low frequency isolation even more. There are no substitutes: Green Glue is the only product that works, despite the claims of their competitors. It's not cheap, but it is good stuff. It is specially formulated to create something called a "constrained layer damping" or CLD interface between the two layers of drywall, that improves low frequency isolation.

So, that would be the plan of action here. At least, that's what I would do if that were my studio, and I had that problem. That's also what I would recommend to my clients in a similar situation.

However, there's still one aspect that I did mention briefly, but that needs more discussion: the floor. All of the above assumes that you have a concrete "slab-on-grade" floor, with the walls resting on that. That is not your situation at present. There are some things that you can do to your floor system to help, and perhaps building a proper drum riser (such as Gulffo's design) would be useful, but there might also be other issues involved. Unfortunately, I'm out of time right now, so 'd have to get back to that later, assuming that you are prepared to do what I'm suggesting above. If you can't see yourself doing all that extra work, then there's no point in fixing the floor either.

Unfortunately, there are no simple fixes for your situation: it's going to take at least the above to get it usable, and I do "get it" that it's a lot of work, so you might not be willing to do that, and just prefer to live with the problem. But at least you now know WHY you have the problem, and you also know the best way of fixing it: it's just up to you if you can justify all that extra time and expense.

- Stuart -


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PostPosted: Thu Apr 25, 2019 6:13 am 
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Thank you so much, Stuart. You've given me a great wealth of information. I'm going to take a few days to digest and figure out if I'm going to have at it again. You mentioned Gulffo's design for building a proper drum riser. I'm not familiar with that. Is it possible for you to please send a link for that design. Thank you. If I do this I'll probably build the riser first and then do the hard work over a few weekends. Thanks again for all your help.
Peace,
Michael


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PostPosted: Thu Apr 25, 2019 6:23 am 
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Location: Cork Ireland
Risers are quite common, but in general I am not convinced about the supposed benefits or purpose.
They are sometimes said to add resonance, but in my experience, unless they are really booming, they instead remove LF tone.
In your case they may reduce the LF the hard ground reinforcement of the drums by creating a distance and introducing an LF absorber.
It should also isolate the structure borne LF from drums to ground to neighbour. That is, IF there is a such a path at play.
Overall, playing drums in a warm climate near other humans is an unreasonable ask IMO. Isolation, HVAC, would be so difficult to do fully and properly that one would would have to consider the options IMO. Like Pianos and Organs, Virtual drums have come a long long way. A Mesh Head Kit has many benefits over a real kit.
Even Aerodrums have benefits in practicing. Let us not forget Noise Induced Hearing Loss.
DD


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PostPosted: Thu Apr 25, 2019 7:24 am 
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Location: England, Bristol
DD
I might have to try some of those new virtual drums, the only electronic kit I’ve played was an SDX in 2000 ... it left me wanting : )


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PostPosted: Thu Apr 25, 2019 1:17 pm 
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msm24p@gmail.com wrote:
You mentioned Gulffo's design for building a proper drum riser. I'm not familiar with that. Is it possible for you to please send a link for that design.
Sure!

Exploded view:
Attachment:
GLENN-example drum riser 2-Exploded.jpg


Completed view:
Attachment:
GLENN-example drum riser 2-Full.jpg


The main purpose is to decouple the drum kit from the floor, in cases where the floor is not isolated. They do work, but it's not the same as fully decoupling. What it does do, is to keep the impact noise from getting into the floor: the sounds of feet stomping on pedals, and other mechanical vibrations. It can help a little with the actual kick drum reverberance too, but don't expect that it is a magic wand: it won't do anything for isolating plain airborne sounds: it is primary mechanical decoupling. If you look closely, the entire unit rests on the insulation, not on the wood: the wood around the edge is just a decorative skirt that hides the insulation, but does not touche the floor. Simple principle.

Oh, and as you can see from the image, it works with electronic drums too... they have the exact same impact noise issues as acoustic drums... :)

- Stuart -


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PostPosted: Thu Apr 25, 2019 10:22 pm 
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Soundman2020 wrote:
You have a coupled two-leaf wall, and also the drum booth, which is the third leaf.


With the drum booth well out in the room does it still become that third leaf?

Steve


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PostPosted: Fri Apr 26, 2019 1:14 am 
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SGleason wrote:
Soundman2020 wrote:
With the drum booth well out in the room does it still become that third leaf?
Depends on how close it is to one or more walls. Technically, it is always a third leaf: the issue is how low down the MSM resonance is tuned. With very large air gaps, it would be tuned too low to be of concern, and the air spring would be so weak as to not be of concern.


- Stuart -

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PostPosted: Fri Apr 26, 2019 7:23 am 
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Structure borne sound may make it from your drums to the walls and roof. Pedals especially as Stuart pointed out.
But the floor you described strikes me as somewhat isolating already. I don't know what fibreboard is specifically, but any board on a metal frame is probably 'springy'. Gravel underneath should prevent any ground borne spread. A layer of fibre damping in the void may be very helpful.
SDX? Simmons? That is way way old. Modern Roland and Yamaha Electronic Kits sound and play really well.
The cymbals are probably the most disappointing element, so you could easily do a Hybrid.
Even existing drums can have triggers and mesh heads fitted.
Best to borrow a set and get into them for a week or two.
For space reasons in my small CR, I moved on from the 'rubber' drums to aerodrums.com
A really great practice tool.
Don't be put off by the obvious....... Watch Richard bouncing and rolling here. https://www.youtube.com/watch?v=iF8296Aai9k
DD


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PostPosted: Sat Apr 27, 2019 8:27 pm 
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I’ll have to try some out, out of interest... the Aerodrums seem interesting, also have to try that!

yes it was a Simmonds SDX... it was a good upgrade from a bluebird typewriter on its edge as a kick drum, quality st. Tin with stuff in for a snare and tin lids for hi hats and cymbals! I was about 10 though... and my Dad would use the sdx turned on... I just went in for a tap as it was more realistic than the alternative: )


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 Post subject: Kids
PostPosted: Sun Apr 28, 2019 1:41 am 
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LOL, been there. My first snare was a five gallon plastic petrol can, with a thick wad of newspaper taped on to make the snare wire sound.
My record player was a turntable chassis in a box, piezo cart playing into the family Philips Valve Radio.
Things were so much better then, pre Digital....... Not!

https://www.youtube.com/watch?v=nzmhRKB7Qdo

DD


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