Rehearsal Space in Katy Texas

First of all, this is a great forum and I have been lurking in here and researching for a long time. I have dreamed of having a personal home rehearsal space/ drum room and this site along with Rod Gervais’ book has given me the inspiration to pursue that dream. I have a preliminary design for an addition to the property I currently own, but first, the requisite background information: I am located in the suburbs of Houston, Texas. I am in an unincorporated area of the County so inspections and permits will be pretty non-existent. I play drums in a heavy rock/ progressive metal band and I have a neighbor on one side about 55’ away. I took some measurements with a sound pressure level meter during band practice in a similar size room and got about 100 dB on the A weighted scale. I measured the ambient noise level at night at my property and got about 45 dB on the A weighted scale. Using the inverse square law to take advantage of the distance, I get an isolation requirement of 11 dB on the most critical side and less required in the other directions as shown on the first exhibit below. I am working on a budget with a contractor to accomplish as much of the construction as possible so I will guess at $40,000 for now without acoustic treatments and some of the other isolation details to be completed by myself, if necessary. I am planning on the room within a room (mass spring mass) construction technique with wood framing for achieving the isolation. The detail I have given the contractor so far is for double stud wall with double layers of sheet rock and green glue on both leafs. These are my initial questions: Do these figures seem to be reasonably correct? 11dB of isolation requirement seems very minimal, is the inverse square law not appropriate for low frequencies? If it is correct, it seems that I am seriously over-designing with the double wall, double sheet rock with green glue construction with an estimated STC rating of 73 in accordance with green glue’s information on their web site. The isolation requirement is not the same in the other 3 directions. Can I reduce the specification on those 3 walls and save some cost? I need to make sure I am understanding the isolation requirements properly to move on to the next issue of specifying window construction details to have a nice view of the pool. More exhibits and pictures below to help explain. Thank You, Erik

The exhibit below is the first detail sent to the contractor for room within a room construction. I backed off the isolation a little bit and only included green glue between the 2 layers of sheet rock on the inside leaf.

The 100 dB measurement seems off. I will try to get new measurements. I didn't buy the $25 piece of crap SPL meter, but maybe it was a $50 or $75 piece of mediocrity. The room in which I measured our band practice was very open with high ceilings and sound was escaping to other rooms. From all of the research I was fully expecting 115dB and the need for 40 - 60dB of isolation requirement. Until I can justify less and feel comfortable with it, I will still plan on the wall construction detail provided so far. I may try to make some sense of Desart's spreadsheet to help me out as I work through this as well. Some more pertinent information: I will attempt to get a 9' ceiling height in the proposed drum room/ rehearsal space making the re-framing of the existing garage roof a little more interesting. I am a civil engineer and have some do it yourself skills and some cad drawing skills. Pictures of the existing situation now. Erik

I took new measurements at band practice and obviously the previously stated measurement of 100 dB was incorrect. The correct maximum measurements are 118 dB on the A weighted scale and 126 dB on the C weighted scale. I will plan on needing around 30dB of transmission loss (using the A weighted measurement as the basis) or better for the design. The cross section posted previously should well exceed that requirement which is just fine with me. Now on to providing more details to the contractor. Erik

I also found the answer to my question about making 3 sides different from the side with the highest isolation requirement while researching posts in this forum:

The idea with studio isolation is to have consistent isolation all around the room, on all sides, with no "weak links" at all.

Erik

Hi Erik, and welcome to the forum! :)

I took some measurements with a sound pressure level meter during band practice in a similar size room and got about 100 dB on the A weighted scale.

Great! But you should use "C" weighting for loud music, since that better resembles the way people perceive loud music. C weighting for typical rock drums would be around 115 dB.

I measured the ambient noise level at night at my property and got about 45 dB on the A weighted scale.

That sounds about right. It probably would have been a little higher on "C", but that's fine for getting an estimate.

Using the inverse square law to take advantage of the distance, I get an isolation requirement of 11 dB on the most critical side...

I'm not sure how you got to 11, but simple math is what you need here: In order to get the same level of 45 outside your room when you are playing at 115 inside means you need 70 dB of isolation. If all you need is 11 dB of isolation, you could get that from a thick cardboard box! 70 dB is the real number, assuming that you do need to get down to 45 dB outside your walls. That would still be barely audible: you might think that if you reduce your drums to 45 dB when ambient is also 45 dB then your drums would be inaudible, but that isn't the case: our brains and ears have an amazing ability to pick out sounds that are much quieter than the ambient level. That's why you can listen to a conversation on the other side of a crowded room, such as at a cocktail party: even though the conversation is far away, and well below the overall ambient sound, if you concentrate hard you can pick it out. In fact, we can hear things that are about 15 to 20 dB below the ambient level. So your drums would still be slightly audible outside the wall, under the right conditions. Of course, the inverse square law does apply here. But there are other mechanisms that can carry sound a long distance with very little attenuation, and inverse square law assumes a point source: your studio might or might not act as a point source. On the other hand, 70 dB of isolation is a pretty tall order. Realistically, you can probably get 50-something, maybe 60 if you are lucky.

I am working on a budget with a contractor to accomplish as much of the construction as possible so I will guess at $40,000 for now without acoustic treatments and some of the other isolation details to be completed by myself, if necessary.

Your budget sounds reasonable for a small building, assuming you'll do most of the work yourself to save on labor. The best way to get an accurate estimate of the total cost is to find out what the going rate is per square foot for building an upscale house in your area, add about 20% to that, and multiply by the number of square feet of floor area you plan to build. so for example, if the going rate in your area happens to be US$ 100 per square foot, add 20% to get US$ 120, then a building of about 350 square feet would fit your budget.

11dB of isolation requirement seems very minimal,

Right! Hence my ramblings above... Also, you should start form the more realistic figure of 115 dB, which is about what a drum kit puts out when played normal to hard. Add in a bass cab and a few other things, and you can be approaching 120 dB inside. Inverse square would get that down to about 85 dB at 100 feet, but you need to get to 45 for ambient level, so you need 40 dB of isolation, minimum. And allowing for the ability of our brains to detect patterns as I mentioned above, allow another 10 dB for safety. 40 + 10 = 50. so you should be aiming for about 50 dB of isolation, which is do-able on your budget for the size of building I mentioned above.

double sheet rock with green glue construction with an estimated STC rating of 73 in accordance with green glue’s information on their web site.

Yes, but that's STC, which is not much use for measuring the isolation of studios since it does not consider any low frequencies at all. It is quite possible to have a wall rated at STC-73 and still hear the drums very clearly, since STC does not measure sound reduction of typical drum frequencies. On the other hand, it is possible to have a wall rated at STC 53 that drastically kills the drums... STC rating is not much use for studios.

The isolation requirement is not the same in the other 3 directions. Can I reduce the specification on those 3 walls and save some cost?

Unfortunately not, and especially for low frequencies, which are not directional. Once sound gets out of your room, it expands in all directions. The loner the wavelength (lower frequency) the more noticeable this is.

The exhibit below is the first detail sent to the contractor for room within a room construction.

Your ceiling is a three-leaf system there. Are you aware of the issues associated with triple-leaf construction? It might well turn out that 3-leaf is the only way to do it, but that does increase your total building costs. If you could figure out a better way to do your roof so you can get it down to two-leaves, that would likely save you some money.

I backed off the isolation a little bit and only included green glue between the 2 layers of sheet rock on the inside leaf.

Have you considered replacing the first layer of drywall with OSB? That greatly increases the structural integrity of the wall, especially in sheer, and has the added benefit of providing a nailing surface around the entire room, so you don't need to go stud-hunting to attach treatment...

The 100 dB measurement seems off.

It might be because you were using "A" weighting and "fast" measurement. Use "C" and "Slow" to get a more realistic measure. And yes, use a good meter! Those cheap Chinese things are often junk, and the numbers they show can be far from reality. Get a good Extech or Galaxy meter, or something along those lines. Around US$ 80 to US$ 100.

The correct maximum measurements are 118 dB on the A weighted scale and 126 dB on the C weighted scale

OK, so you are LOUD! :shock: That's a bit more than I would have expected, but quite possible, and much more realistic than 100 dB!

I will plan on needing around 30dB of transmission loss (using the A weighted measurement as the basis) or better for the design.

A normal house wall will get you 30 dB, and I absolutely guarantee you that you will NOT be happy with a room that gives only 30 dB of isolation! That's about the same as you get from any typical interior house wall, between two rooms. I would suggest that you shoot for something much better than that: 50 at least.

I also found the answer to my question about making 3 sides different from the side with the highest isolation requirement while researching posts in this forum:

Right! :thu: - Stuart -

Thank you for the reply Stuart. I will plan on designing for 50dB of isolation or better. Great idea on using the OSB for the first layer on the inside. My detail had drywall on the outside leaf in error. That should be OSB on the exterior as well. Making corrections to my drawings and details. Since my area in Texas has high heat, high humidity, high chance of mold, I am not comfortable not having soffit vents and ridge vents for the roof. I received some advice to investigate channel and clips to get a vaulted ceiling with two leafs. Revised details and more details will follow.

Since my area in Texas has high heat, high humidity, high chance of mold, I am not comfortable not having soffit vents and ridge vents for the roof.

That makes sense, for sure! And is what I expected. so you do need a 3-leaf ceiling, which means more mass on the middle leaf to compensate, plus also a larger air gap, if you can spare the lost ceiling height for the final inner-leaf ceiling.

Revised details and more details will follow.

Looking forward to seeing that! - Stuart -

So now that I understand that the roof ventilation (soffit vents to ridge vent path) is requiring 3 leafs for the ceiling, I have two options that I can see for the 3 leaf configuration. Option 1 is a ceiling within a ceiling construction supported by the wall leafs. Option 2 is a suspended ceiling with clips and channels. A typical section view of the two options are shown below. I have added the recommended additional mass on the middle leaf by making it 3 layers of drywall. Option 2 gives me more ceiling height so I really like this option. However, the drywall has a lot of labor intensive cuts involved in placing within the rafters, notching around the ceiling joists, etc. So my next questions are: Does anyone see a constructability issue with option 2? Or, a significant increase in labor cost or difficulty keeping the air tight seal? The clips I found RSIC-1 EXT04 do not give me that much extra space between the leafs (4” extension + 2” inside rafters). Is there a better way to get more space? Erik

Both of those options are possible, but the second one is a lot more work, and there are issues that you are not considering, such as having nailing surfaces behind the edges of the drywall, not just in the center. That complicates things more... I'm still not clear if this is just going to be a modification to the existing building, or a total new build from scratch? If it is a new build, then maybe scissor trusses or some type of gabled truss would be the best solution for your roof. - Stuart -

I'm still not clear if this is just going to be a modification to the existing building, or a total new build from scratch? If it is a new build, then maybe scissor trusses or some type of gabled truss would be the best solution for your roof. - Stuart -[/quote] Let me try to clarify with the roof framing plan and sections below. The rehearsal room is a new build from scratch adjacent to the existing garage. I am re-framing the northern half of the existing garage roof to tie in the roof of the new room. I am extending the slopes of the existing hip roof of the garage and that is controlling my available height.

Soundman2020 wrote:

Both of those options are possible, but the second one is a lot more work, and there are issues that you are not considering, such as having nailing surfaces behind the edges of the drywall, not just in the center. That complicates things more... - Stuart -

I was thinking that scabs could be added inside the rafters for nailing surfaces. I am going to get a contractor to price the build, so if this is something that will add a lot of cost for minimal gain, I appreciate that advice.

Since the western wall of the new rehearsal room has to be pushed eastward to avoid the pool equipment, I gain extra height on the west side of the room by raising the top plate of my wall up to the rafters. I can set the height along the north side to match. On the east side I am coming back down to match the existing wall top plate and dealing with the bathroom as well. I received some advice to use clips and channel rather than ceiling within a ceiling. That got me thinking about a vaulted ceiling. With the comment about the extra work involved, maybe it would make more sense for me to look into vaulting the east side of the room only.

Here is an east-west section view showing the ceiling within a ceiling option and the difficulties with a lower ceiling height and incorporating the bathroom. The ceiling joists would run north-south across the smaller dimension of the room. Erik

The pieces seem to be falling into place easier with the clip & channel flat ceiling across the majority of the room. I added ledger boards and checked to make sure I have nailing surfaces for all the drywall. Revised cross section details to follow. I think the framing and basic idea for the isolation is just about set unless someone sees any issues here.

Here is a north-south section view that shows the existing garage and proposed room.

Now that the ceiling and framing design seems to be taking shape, I wanted to verify that the different components (wall, ceiling, window) have an equal amount of isolation, especially in the lower frequencies around 40 Hz. The acoustic mass law equation is simple enough, but only applies to a single leaf of mass. I found some equations for approximating the transmission loss for a double leaf wall with an air cavity for a given frequency, but it seems to be pretty negligible in the lower frequencies. I cannot find an equation to approximate the transmission loss for a triple leaf and I cannot find any test data for these configurations for low frequencies in the 40 Hz range. I also cannot find a way to account for the green glue in these situations. It appears that transmission loss prediction software would be required to get the exact answer to find out if I added enough mass and air space in the triple leaf to make up for the negative effects of the triple leaf. It is not practical to purchase such an expensive software for one DIY project, so I am settling with assuming that the following components are roughly giving me equivalent isolation for what I need. Here are the different components as they stand now and the transmission loss amounts using the mass law only as well as the resonant frequency of the cavities. Erik

more detail

It seems that the next important step to take at this point is to submit an application to the neighborhood homeowner's association for their approval. I had to take some time to prepare plans, elevations and material and color samples. I don't expect too much of an issue since the addition to the back of the garage is mostly hidden from the street and everything will match the existing materials and colors. However, this is a critical step. I thought I would post the elevation views here. The proposed addition to the garage is shown in red. Erik

Meanwhile... since the sound isolation room addition will result in the demolition of a wooden deck and covered area for a table and chairs by the pool, my wife only agreed to this plan if a new sitting area/ flagstone patio would be constructed in another part of the backyard by the pool. So, an area had to be cleared out for the new patio area. A 25' tall river birch tree was removed that was in conflict with the proposed room addition. Also, a 30' tall bald cypress tree, 15' crepe myrtle tree, 10' bottle brush tree, bed full of fern, and rock retaining wall were removed. We hated to see some of these established trees go, but it is necessary for the project. Also, this happens to be the path for the sanitary sewer line from the proposed bathroom to the existing sewer main. The utilities will have to go in the ground before the flagstone can be set. Erik

Great news! The homeowners association approved my plans. So, now onto more research, planning, and design to make sure I don't make a big mistake somewhere. I have been wondering about a few things and kind of getting stuck. I have focused so far on a single room for mainly just rehearsal purposes. But I can envision my interest and understanding of recording growing and later finding myself wanting a separate control room. This could easily be accomplished in the existing garage space as shown in the plan below. I understand very little about the gear, cabling, patch bays, and other necessities that I will end up figuring out later. Any advice for planning for the future by running conduit under, or in, the new slab to the garage for cables would be greatly appreciated. Or, even running conduit to different locations within the phase 1 rehearsal room for recording within a single room with gobos for separation. This also somewhat coincides with my HVAC planning, which is another very important component at this time. I know the answer is the mini-split ductless system and separate ventilation system. I am trying to avoid putting holes in the walls and run whatever I can under or through the new slab. Is it possible to run the refrigeration lines (with the cable) from the outdoor unit through a conduit under the slab and up into a bass corner trap to avoid running through the wall and using the corner trap to cover it? Mount the indoor unit on the frame of the corner trap? Is that overkill? I need to start talking to my contractor about these types of details, but I would like some better understanding going into the conversation. Erik

HVAC plan

HVAC plan

So you plan to use another room as an exchange chamber, but you also plan to use that room as the CR in the future: what will you do then for ventilation? When that room becomes the CR, you will have to tear down part of the LR in order to re-do the HVAC... (!) So it would probably be better to do the HVAC correctly now, then you can avoid that "tear-down and rebuild" later. Just my $0.02... - Stuart -

Soundman2020 wrote:

HVAC plan

When that room becomes the CR, you will have to tear down part of the LR in order to re-do the HVAC-

Good point. Did not see that. I will put the ventilation unit in a better spot out of the way of the possible future control room. I would like to still exchange air with the current existing room in the initial phase to help cool it down a little bit. After researching the Mitsubishi mini-split some more, I found the unit that has the ability to have multiple indoor units. I changed the design to add one more indoor unit in the initial phase in the bathroom as requested by the wife and a third one can be added to the future control room. I also see that this unit has condensation drain lines, so yet another hole through the isolation. Right now, I am planning on running the line set refrigeration lines from the outdoor unit to the indoor unit through a conduit under the slab then up the wall hidden by a bass trap, then through a hole in the ceiling. Also thinking about running the condensation drain line through the slab for the indoor unit closest to the neighbor. Erik

Back to the conduit under the slab issue, I have a preliminary idea for running multiple conduits to different locations under the slab for all types of future cable flexibility. I did not put a size on them yet. I am guessing 2 1/2" conduits maximum. Maybe a few can be smaller. Erik