Soundproof Your Studio

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Over the past three years I have recommended the DIY Mr. Cool ductless mini split as a viable option for home studios. In this article I am going to explain why I no longer think this is a good option. 

Every once in a while we learn from experience rather than books or videos. This is one of those situations. In theory the DIY Mr. Cool systems are great. They cost about $1200-$1500, you can install them yourself with a few tools, and they can heat and cool a room while staying somewhat quiet. You can always turn them off if they are too loud. Awesome, right? Well here is what happened to me so you can see where things go wrong. 

First, this past fall, three years after my mini split install the compressor stopped working. I think this was due to a a power surge hitting the unit and frying the logic board. The lesson here is to add a surge protector to your condenser. 

Through this experience I learned that most HVAC technicians have never heard of Mr. Cool and needed to call their tech support line. The tech could never get ahold of tech support. In fact, nothing happened until I emailed Mr. Cool and got involved. After several weeks of back and forth they finally decided to send me a new condenser outside unit free of cost except for the cost to ship it and hire someone to install it. 

This was great, minus the three to four weeks I didn’t have any heat in the studio because Mr. Cool’s tech support was not top notch. Then about two to three weeks after installing the new condenser I realized that the mini split was not putting out any hot air. 

I called another HVAC tech to come out and just yesterday he said that I had a refrigerant leak in the line set in my double wall system and that the only fix would be to open up the walls. 

Well, you can imagine that this is not an ideal scenario, so the lesson learned here is do not put your line set with the refrigerant lines where you cannot access them easily. It would have been best to run the line set on the outside of my studio so that we could easily check for leaks. 

This might lead you to wonder how a leak would open up? The HVAC tech said that a screw or nail could tag the line or the vibration of the line itself over time could rub against a sharp edge and open up. This could be what happened to me. We may never know. 

So here I am writing this in my studio with an oil based space heater (just to rub salt on the wound my internet is also out and Google Fiber can’t figure out what is wrong). What is the lesson for you in building your own soundproof home recording studio. 

There are two types of mini splits and to be honest I am surprised at the the number of HVAC techs, contractors and even architects that don’t know this. The mini split I have is called a ductless mini split, meaning there is a condenser unit outside and a mini split wall or ceiling cassette unit on the inside. The condenser outside is connected with a refrigerant line set that runs to the head unit on the inside of your room. 

This system is great for most situations, but it is not great for soundproofing. First, the unit is quiet, but not that quiet. Now that it has not been working I am realizing how noisy it really was. In an ideal world you should not have any mechanical noises in your studio. This means no mini split head and only using solid state hard drives if possible.

The other superior option is to use a ducted mini split. This is a system where the mini split is not attached to the wall or ceiling, but is instead installed in the attic or a separate mechanical room. The mini split unit is an air handler and it pulls air from the room heats or cools it and then pushes it back in the room. Simple right? Well, for a normal room, yes, but for a soundproof room, well it is a different story. More on that install in a second. 

So why didn’t I install the ducted mini split in the first place? Great question and with 20/20 hind site I sure wish I had. The reason I installed the DIY Mr. Cool Ductless mini split is the same reason you would. It is cheaper and seemingly a great option if you have never built a recording studio before. Experience is everything and I am learning that the really really hard way. 

Short of finding a solution to my mini split problem that is an easy fix, I am really stuck between a rock and a hard place. I have to open up my walls and find the leak and repair it, but what if another leak happens? Option two is to run a new line set along the outside of the building and then punch a whole through my outside wall and connect the new line set to the existing mini split head. This is a cheaper solution, maybe, but it requires keeping my noisy mini split in the room and reducing my soundproofing by having a direct hole from the outside to the inside. 

This leads me to option three. Which, I think is the best option albeit maybe a little more expensive. I could buy the Olympus Mr. Cool 9000 BTU ducted mini split. I could install it in the ceiling of my bathroom attached to my studio. Then I could connect that mini split (hopefully) to my existing condenser outside unit. I could then tie in the mini split duct work with my ERV and baffle box system and have fresh hot and cold air supplied to my studio that is also quiet. Perfect right?

The downsides to this solution are what keep most DIY people from doing this set up. The reason? Cost! But, this saying is very very true in recording studio builds. You get what you paid for. I repeat because this is the greatest knowledge and wisdom I can give you. You get what you pay for. All of your problems down the line in your studio will come from taking the cheaper DIY approach. 

So, to install a ducted mini split you must hire an HVAC tech. This will cost you thousands of dollars because those guys really know how to charge what they are worth. Lastly, if you want my best advice. Don’t buy a cheap unit. Buy a Mistsubishi or Fujitsu ducted mini split. Size it correctly for your room and you will avoid so many issues. 

Learn from my mistakes. They continue to cost me time and lots of money. Saving money on the front end doesn’t mean you saved money if you spend thousands of dollars fixing your mistakes on the back end. 

Buy a Mitsubishi or Fujitsu ducted mini split. If you can’t afford those units ask your HVAC installer for the next best option. I would stay away from Mr. Cool. There tech support alone is good reason to avoid them, but their units are cheap for a reason. That reason is that they are not built well and are prone to breaking in my experience. 

If you do use a ductless mini split system, run the line set outside of your studio and do your best to seal up the hole you run through your wall to help keep the wall soundproof. Remember, the ductless mini split should be a last resort not your first option. 

I hope this article was helpful and I hope you don’t go through what I am going through. Learn from my mistakes and you will thank me three to five years down the road. 

FREE Soundproofing Workshop: https://www.soundproofyourstudio.com/acoustic

You read that right, vocal booth, the hallmark of any legitimate studio actually are bad for vocals. How you ask? In this article I will dive deep into the science, cite multiple reputable books and teach you what a vocal booth is really for. 

To record vocals, right? No, they are used to separate the singer from the band when live tracking. Our modern notion of sticking singers in a dead small claustrophobic room with a terrible foldback system (headphone system) is not how final vocals are supposed to be recorded. Don't believe me? 

Richard Hilton who has recorded Diana Ross, Michael Bolton, SImon Le Bon, Tina Arena and many others will record the final vocals in the control room. Everyone wears headphones and can easily communicate and the room itself is way better sounding than a booth (more on that to come)(“RealTraps - Vocal Booths”). Moreover, some producers will even play the music softly over the speakers and forgo headphones all together to get a great vocal recording. 

Another thing to realize is that professional "vocal booths" actually are usually live rooms or fairly large neutral rooms. When you see an artist through the glass in a mulit-million dollar studio they are usually in a fairly large space, and if not it is to the deficit of the acoustics. Let's talk more about that. 

Physics cannot be changed. Small rooms, no matter how much acoustic treatment you put in them will always sound worse than a large room. Why? The first reason is that small rooms cannot support the massive wave lengths of low frequencies. This leads to the bass frequencies getting trapped (especially when the room is soundproof). This leads to a boomy boxing sounding room. You can add as much fiberglass panelling as you like, but those will not fix the low end. Bass traps, sure they can help a little, but they are not very effective below 100 Hz. 

Here is what the Master Handbook of Acoustics says about small vocal booths: "provide very little low frequency absorption. Thus important voice frequencies may be overly absorbed, whereas low frequency room modes are untreated" (Everest and Pohlmann, 480). The smaller rooms make it impossible to absorb low frequencies because you don't have the space for true low frequency absorption, plus room modes occur higher up in the frequency spectrum which means the bottom end of voices will ring out more than the higher end of the voice leading to a boomier and boxier vocal tone. You can spend $10,000 on your vocal chain, but if you record it in a bad sounding room then the vocal will always sound cheap. 

Just to drive this point home, here is an excerpt from Recording Studio Design by Philip Newell:

"Simple attempts at absorption by placing of acoustically absorbent tiles on the walls and ceiling will not suffice. These will tend to absorb the higher frequencies but leave the lower-mid and low frequency modes largely untouched, yielding a room with a heavily coloured ambience which will lack life and add a thickness to the sound, robbing it of much clarity" (Philip Richard Newell, 153).

This is the argument against vocal booths and really small rooms in general.  This is not to say you should never use a vocal booth. If you are tracking live bands then vocal booth are a useful for isolating the vocalist from the band. However, for most situations vocals should be tracked in a larger room. This could be the control room or a live room in a large studio. 

Everest, Frederick A., and Ken C. Pohlmann. “Acoustics of Audio/Video Rooms.” Master Handbook of Acoustics, McGraw-Hill, New York, 2015.

Philip Richard Newell. Recording Studio Design. New York ; London, Routledge, Taylor & Francis Group, 2017.

“RealTraps - Vocal Booths.” Realtraps.com, realtraps.com/art_booth.htm. Accessed 2 Jan. 2024.‌

FREE Soundproofing Workshop: https://www.soundproofyourstudio.com/workshop

When I built my first studio I did not stagger my double wall studs for soundproofing my recording studio. This was a small mistake, but nonetheless a mistake. I am going to give you two reasons why staggering your studs is important with recording studio design. 

I had asked Rod Gervais, the author of Home Recording Studio: Build It Like The Pros about why he recommends staggering studs in a double wall system. His answer was that overtime studs can bend and if they bend inward they could actually touch each other thus short circuiting the system. He did admit, although this is rare he has seen it throughout his decades of building studios. 

Staggered Stud Diagram (16" OC) 

I asked JH Brandt, a well respected and experienced studio designer the same question. Should you stagger studs? He also said it is a best practice in double wall design and the reason is that when studs are not staggered the drywall becomes a diaphragm that vibrates similar to a speaker cone. This pushes the air in the air cavity, which then starts to vibrate the other wall sympathetically. Once this process gets going it creates a bit of a feedback loop as well. This will weaken the system as a whole because sound can vibrate through the system more easily. 

Now, damping materials like MLV or Green Glue can help reduce the vibrations of the drywall, but simply staggering your studs, even by a few inches will reduce or eliminate the sympathetic vibration between your walls. 

One of the reasons we did not stagger our studs in my studio is because we needed an R30 insulation in the walls for our climate. However, R Value is additive, meaning if you need R30 you can use two insulations with an R15 value or one R20 and R10. You get the picture. This means if you don't have the space for R30 you can use two different insulations in each stud wall to make it work. Another option is to use a 2x6 exterior wall and a 2x4 interior wall and this will give you more space. 

Having two well respected studio designers teach me how I was wrong is honestly pretty cool. They both gave great and different answers for why you should stagger your studs. I hope these answers help you decide to stagger your studs when building a studio and give you the understanding on a deeper level to know why it is important. 

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We often here that big rooms sound better, but why is that. Why can't we get a small bedroom to sound awesome. I mean, we see home studios that look awesome online all the time, so why do they have to be big to sound good? 

This article will answer that question with the physics behind acoustics of small and large rooms and how this knowledge can help us understand and design our own studio builds. 

Room modes require their own article, which I wrote here: Why Room Ratios Don't Work...Most of the time. But this article will focus on one aspect of room modes and room acoustics which is room volume. So, to quickly summarize, room modes are certain lower frequencies that create either peaks or nulls in your room. This means that when you walk around your room and play, say a 60hz tone, you will hear places in your room where the tone sounds louder, softer and miraculously even some places where you can't hear it all. I know freaky, but cool! 

This is a problem for your listening environment and your recording environment too. We want to sit where the space in the room is as flat as possible. To get a "good room" we can start with a room that has even spacing of room modes in the lower frequencies below 300 Hz. Notice I said even spacing. It turns out having more room modes more evenly spaced sounds better. Weird, I thought we didn't want room modes is what you are probably thinking. Nope, we do want them and we want them evenly spaced so that none of them really poke out and cause big dips or nulls when we walk around our room. 

Here is a quote from the Master Handbook of Acoustics: " The short dimensions of a small room almost guarantee acoustical anomalies resulting from excessive spacing of room resonant frequencies." (Everest and Pohlmann, 436) Whoa, a lot to unpack there. 

This means the smaller the room the more likely you will have uneven, blurry, muddy sound in the low end due to too much space between your room modes, aka "resonant frequencies."

Here is another quote from the Master Handbook of Acoustics: "...large rooms have the inherent advantage of relatively more modes in the low-frequency region, and hence smoother low-frequency response"(Everest and Pohlmann, 436). The key word in this quote is smoother. The more modes means that the low frequency spectrum doesn't have big modal peaks followed by vast modal valleys where there aren't room modes. Remember, we want more room modes evenly spaced in the low-frequencies, 300 Hz and below. 

Now let's visually look at this using the AMROC calculator. I am going to input three dimensions using the Sepmeyer room ratio. This ratio of 1: 1.28 : 1.54 will get us the best room sound given our different sizes. However, even with an acousticians room ratios we will quickly see the limitations of our smaller room. 

First, here is the axial modes of a small studio with dimensions: 8ft ceiling, 10.24ft width and a 12.32ft length (2.44 m x 3.12m x 3.76m).  The volume is 1,000 cubic feet.

Second, here is a mid sized studio: 12 ft ceiling height, 15.36 width, and 18.48ft length (3.66m x 4.68m x 5.63m) Volume = 3,400 cubic feet. 

Third, let's look at a large studio: 16ft ceiling height, 20.48ft width, 24.64ft length (4.88m x 6.24m x 7.51m) Volume = 8,000 cubic feet. 

Okay, so what does all of this mean? Each of those red blocks is an axial room mode. Axial modes are the most powerful and problematic types of modes so I am showing those. To compare, let's look at 100 Hz and below. 

Small Room = 4 axial modes

Medium Room = 7 axial modes

Large Room = 9 axial modes

Remember, we want more modes in the low-frequency range to smooth out the room's response. Also, notice that the larger rooms go lower down in the frequency spectrum. This is also good because we want that "smooth" response as low as possible. Ideally to the threshold of hearing at 20 Hz. 

Now you know why bigger rooms sound better. The larger the room the more room modes you get in the low-frequency spectrum leading to a smoother more even response in the room, which translates to a cleaner more accurate low end. The high end of a room is easy to fix with basic acoustic treatment. The low end is very difficult to fix. In fact, the Master Handbook of acoustics says that "...anomalies encountered in studios having volumes less than 1,500 cubic feet are sometimes severe enough to make small studio rooms impractical" (Everest and Pohlmann, 436).

Uggh! That totally bums us out right? What about your dreams of the bedroom studio or the small room in your basement. Great music is made everywhere, but know that for an accurate low end you will be always fighting an uphill battle in a small studio room. If you have the luxury of choosing a bigger and really higher ceilings then you should choose that room over the smaller room. This article was meant to give you some more tools in your arsenal of studio design, but not to discourage you altogether. I created amazing music in a very small room for many years and it did not stop me. Now, I create music in a bigger room and it has only made me better. You too can shoot for bigger and better rooms over time. 

Work Cited

Everest, Frederick A., and Ken C. Pohlmann. “Modal Resonances.” Master Handbook of Acoustics, McGraw-Hill, New York, 2015.

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QRD Calculator: http://www.mh-audio.nl/Acoustics/diffusor.asp

One of the most effective and efficient types of diffusers are reflection phase grating diffusers otherwise known as Schroeder diffusers. A type of Schroeder diffuser is the Quadratic Residue Diffuser (QRD) and in this article I will teach you how the diffusers work, the theory behind them, and how to build one. 

Manfred R. Schroeder developed the quadratic residue diffuser by using a series of wells of different depths with a constant width that are separated by thin dividers to evenly disperse sound back into the room. (Everest, 265). He found that a number sequence based on prime numbers can be used to calculate the depth of each well. This number sequence can also be repeated over and over (in periods) to expand diffusion across a wall or ceiling. 

When designing a QRD the maximum frequency for diffusion is determined by the well width and the minimum frequency is determined by the well depth. For example a QRD that needs to cover most of the audible spectrum would need to have very deep wells up to several feet and very thin well widths to cover say from 60 Hz to 10,000 Hz. This is one of the design limitations of QRD and phase grating diffusers in general. 

So don't get scared, but I am going to talk about math. I am not a big math genius, so I always need to break down the numbers in simple terms, ideally, this makes me a better teacher for you! So, the equation behind the number sequence used to build the QRD is: 

Well depth proportionality factor = n^2 modulo p

where n = integer greater than or equal to 0 

p = prime number

If you are like me, you had no idea what the heck modulo meant. Modulo is a calculation in number theory. It is a short cut for the following equation

n^2 / p = x + remainder or residue

n^2 modulo p = remainder or residue

The modulo operation says take the n squared in our equation and divide so there is a whole number and a remainder. It says that the modulo will = the remainder not the whole number. If that still seems confusing let's do an example. 

Let's say we want to build a QRD with a prime number of 11. Now lets pick an integer of 5 in our number sequence from 0 to 11 for the diffuser. Again, I just chose 5 randomly for this example, when building the diffuser you would do 0 then 1 then 2 and so on up to 11. 

So, in our equation: 

Well depth = 5^2 modulo 11 

Well depth = 25/11 = 2 with a remainder of 3 

Well depth = 3 

11 goes into 25 two times, which equals 22 and to get to 25 we have 3 left over. The remainder and residue terminology is interchangeable. Confusing, I know! 

So, the QRD are usually made from the following prime number sequences: 5, 7, 11, 13, 17, 19 and 23. 

Below is a chart from the Master Handbook of Acoustics that shows the well depth ratios for all of those prime number diffusers. 

You will also notice the diagram showing one period or one diffuser length. Notice this period goes from 0 to 1 in the prime 17 sequence. This shows how diffusers can be placed side by side to continue the sequence across a wall or ceiling. 

So, first we must choose a prime number to build our QRD. Each prime number has some benefits and limitations and ideally in a room design you might use a combination of different prime numbers to achieve a diffuse sound field across as much of the audible spectrum as possible. All that is a bit beyond this article. For this example, I will be building a QRD 13 based on the prime number 13 sequence. 

Now, the chart above is great in theory, but it is hard to imagine translating all those ratios to our actual physical diffuser. So, I recommend using a handy QRD calculator. There are a lot on the web, but this one does the trick: http://www.mh-audio.nl/Acoustics/diffusor.asp

I will be doing this example in metric since my design is for a client in New Zealand, but you can do yours in imperial and all the concepts stay the same. 

My design is limited by space, as is the case for many home studios, so I will be working with a theoretical depth of 13 cm. I chose 13 cm because it will make the measurements whole numbers not decimals. I could have done a multiple of 13 like 26 cm, but my deepest well would be too deep for my room limitations. The width of my design should also be a multiple of 13. The reason is that this will make all of my well depths a whole number, so my design will be much easier to measure and build. 

With a theoretical depth of 13cm and a diffuser width of 65cm here are my well depths and well widths for my diffuser. 

Notice, I get nice whole numbers. My well width is 5cm and my well depth are all whole numbers as well. We also get my low frequency cutoff and high frequency cut off. Ideally, I would diffuse from 20 Hz all the way to 20 kHz, but that is not really possible, so instead I am happy with a nice low mid to upper mid diffusion on the back wall of my design. 

This diffuser will help to widen and deepen the sound field when mixing and it will add back some of the life to the room, since I am using a lot of absorption to help control the low end and early reflections in my design. 

Now that you have all the well depths, and well widths you can design your diffuser. Use cabinet grade or marine AA grade plywood so the diffuser will look nice. In my design I am using 12mm marine AA plywood for my back, top, bottom and sides and 6mm marine AA grade plywood for my fins to separate the wells. 

For my spacers I used 50 mm x 50 mm blocks on both the top and bottom of my diffuser to create the right well depth. To fill the wells you can use 12mm plywood to lay on top of your blocks. Here is a diagram to show how to do this. 

Notice the well depth is the distance from the top of the diffuser fin to the to of the 12 mm plywood on top of your block. Each well is 1-13 from the chart above moving from left to right. 

It is good practice to dado out the well dividers on the back, top,  and bottom so that you can simply slide your fins into the grooves. You can then attach the fins with wood glue. To build the top, bottom, back and sides you can use wood glue and some small screws to adhere the box together. Your spacer blocks and spacer faces can be attached using wood glue as well to keep the design clean and free of nails and screws. 

You now know what a quadratic residue diffuser is, how the number sequence is derived, how to calculate your own design and how to build one. I hope this article was helpful in demystifing one of the more complex acoustic tools and allowing you to experiment with your own designs for your home studio. 

Work Cited: 

Everest, Frederick A., and Ken C. Pohlmann. “Schroeder Diffusers.” Master Handbook of Acoustics, McGraw-Hill, New York, 2015.

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I recently had a great long talk with the studio designer JH Brandt. Brandt has been designing recording studios for decades and he mentioned how he never uses putty pads to soundproof. I love the idea and wanted to share how to do it in this article. 

Now, I call this method a pro method because it requires that we build our studio room with an outer soundproof shell and an inner acoustic shell. The two systems work together to both isolate and treat acoustics at the same time. 

This approach also allows us to hide our electrical behind the acoustic treatment and mount the electrical boxes and lights in the acoustic panel wall rather than the soundproof drywall. 

Here is a picture of this in action in one of JH Brandt's designs. 

Notice how the wall protrudes out from the door. This wall is made of lightweight wood and fabric with fiberglass batting behind it. It is not the soundproof wall. The electrical boxes can be framed directly into this fabric wall making it so you don't have to use putty pads. 

The electrical should enter through the front of the room through an electrical conduit pipe. There is an added benefit to this design where the audio electrical and audio XLR cables can run side by side eliminating ground loops, but that is a discussion I will save for another article. In the photo below, again courtesy of JH Brandt's free resources on his website: https://jhbrandt.net/resources/. 

In this photo the piping is coming in from the back of the room, but you could have your piping come in through the front wall. The key is to keep your soundproofing methods in tact when doing this. Run the pipe through the wall and use acoustic sealant where the pipe enters the drywall on each side. 

To increase isolation you can have the pipe enter the outside wall then have the pipe run through the wall for a several feet before having it enter into the inside wall. This makes it so both holes do not face each other in the wall system. 

Lastly, where the conduit enters the pipe you can seal up the opening around the wires with putty pad and acoustic caulk to reduce sound traveling through the pipe it self. 

If you are using lights with low voltage wiring, meaning they use a transformer to drop the voltage from the standard 120V in the United States, then you will need to run the low voltage wiring separate from an electrical that is supplying audio. A good rule of thumb is to run the low voltage wiring on the ceiling opposite the audio line on the floor. If you must cross the wires at any point it should be at a 90 degree angle. 

Attaching all of your electrical boxes to your inside acoustic wall is a great way to increase isolation in a control room or home studio room. This can also be done in live rooms, but you would need an acoustic plan that covers your electrical runs and boxes. This method is not for every design, but is one I am am using more and more with home studio designs. 

Work Cited: 

“Resources.” John H. Brandt Acoustic Designs, jhbrandt.net/resources/.

‌

This week I am doing something a little different. I had a member of our community reach out and ask me to do a reaction video to Home RenoVision's youtube video "The MOST Effective Way to Soundproof any Room." Well, after the watching the video I knew this member was right. I had to chime in on what made know sense in this widely watched video. 

This video goes over: 

Enjoy! 

-Wilson 

FREE Soundproofing Workshop: https://www.soundproofyourstudio.com/workshop

Last week I wrote about how to build a soundproof door part 1, however, after lots of thinking and designing I have scrapped a lot of what I taught in part 1 of this series. This is an iterative process for me as I am designing the perfect doors for my clients. 

In part two of this series I will go over my new findings and my new design. The entire goal is to create an affordable yet solid soundproof door for all home studio enthusiasts. I have borrowed ideas from Rod Gervais, J.H. Brandt and my own building and design experience to create what I think will be a very effective and affordable soundproof door plan. 

First, I found that the WIC isolation clips made by Mason Industries are 1 1/2" wide. Meaning your air gap between your walls must also be 1 1/2" not the usual 1" I recommend. The reason I am recommending using the WIC isolation clips is that they can each hold up to 250 lb and are much higher quality than the usual I-B3 sway bracing clips I recommend. The I-B3 clips hold 38 lb per clip. This said you could still use the I-B3 sway clips for our doors since the doors each weigh 123.5lb. 

The big discrepancy between JH Brandt's door design and Rod Gervais's is in leaving a gap between the double wall or connecting the two with wood. I like JH Brandt's design better because it keeps the integrity of our double wall system, whereas Gervais chooses to bridge the gap at the door with 5/4" wood stock because he feels the doors need the support. I agree with JH Brandt that we can support the doors using the WIC clips and not sacrifice our double wall system. However, if we do leave the air gap, Brandt points out that there will be odors that emanate from the double wall cavity. 

To block the odors we add a rubber seal around all four sides of the door opening. The rubber should extend from the edge of the outer wall to the edge of the inner wall. According to Brandt, you should also place rubber on the floor of the opening and ensure it is sealed against the two sides. I question whether this is necessary and may removed it in future plans, but for now it is part of the design. 

The rubber should be attached with screws, but you also should run three beads of acoustic sealant down the middle and sides of the rubber before adhering it to the studs and floor. You can see the rubber in the diagram below attached to our stud wall and concrete floor. 

*As a side note, in part 1 of this series I had the rubber on the outside of our king studs. I have changed that design because I no longer want to use pre-made door frames. I will explain why later on. 

The actual door, meaning the swinging wood is going to be made from a solid core door that is 1 3/4" wide. This door should weigh around 66 lb (30 Kg). Now a 66 lb door alone is not enough mass to match our double drywall. 

The two layers of 5/8" drywall equals 4.4 lb per square foot (10.7 kg/ sqm). We need our 36" x 80" door to weight at least 4.4 lb x 20 square feet = 88 lb (40 kg). 

To do this I like to add 16 gauge plate steel to and 1/8" plywood to the back of each door. This is the side of the door facing the inner wall. 

16 gauge steel weighs 2.66 lb/ sq/ft. And 1/8" plywood weighs 0.4lb / sq/ft. The steel and plywood will go on the back of each door leaving a 3/4" gap around the door. The gap is to create a bank vault seal as you can see in the diagram below.  

 Because of this 3/4" gap the weight of our added plywood and metal is about 57.5 lb (26 kg). That brings the total weight of the door to about 123.5 lb (56 kg). This is well over the 88 lb we needed to match our walls. Going over is a good thing, because our doors are a natural week point and we want to beef them up as much as possible within reason. 

So how do we attach the door to the door frame. The answer is with our continuous hinge. I recommend using the ABH A110HD Heavy Duty Full Mortise Concealed Continuous Geared Hinge. This hinge will help with hanging the door plumb with the frame and will hold the added weight of a heavy door. 

Lastly, to finish building our doors, we will need a door lockset. Now from part 1 you noticed I recommend a mortise lockset. The reason is twofold. First, we want something that doesn't fully go through our door and second we want a lockset that can withstand the added weight of our heavy door. I recommend buying the Cal Royal NM Series Mortise Lock. This lockest has a 2 3/4" backset, which is just enough room to clear our bank vault seals. It also fits a 1 3/4" door. This is an important detail to note, your added metal and plywood will have to fit around the door handles in this case. This is not a huge deal, but does require a bit more care when cutting the metal and plywood to fit the back of the doors. An important detail is to add some thin closed cell foam that will go over the mortise lockset. Poke holes where the handle lever will be. This will create one more solid seal to prevent air and sound from traveling through the mortise lock. 

That covers the door itself. As a side note, it is a good idea to hang the door with just the solid core door first and then add the metal and plywood after it is hung. You can add the lockset towards the end as well. It might be easier to cut out the mortise for the lock before hanging the door. 

In part one of this series I had said to use a pre-made steel frame, however, after much thought and consideration I have decided to stick with the tried and true method of building your own door frame. Because our doors are so heavy we are going to use 5/4" wood stock to frame our door. The frame will attach to each 2x4 stud in the rough opening and will protrude out 1 1/4" to run flush with the two layers of 5/8" drywall. See the diagram below. 

After we have build the frame we need to add our first set of bank vault seals. I like to make these out of 1x3" lumber. I then attach 3/4" Frost King Weather striping to the ends of the 1x3" to create a tight seal against our solid core door. See the diagram below for an idea of how this works. 

Now that you have the frame, the door, our added metal and plywood on, you are now ready to seal up the door completely. To do this we will use Zero International seals. I like these seal because they are high quality and have excellent acoustic ratings. The seals I recommend are: 

These seals will go over the metal and plywood of the door. See the diagram below to see how the perimeter seal works. 

These perimeter seals can be adjusted to fit snugly against the door ensuring no sound will enter or exit the door. 

The door bottom is a very important part of the this door system. The door bottom I recommend is a drop seal and will seal the air gap below the door when the door is fully closed. See the diagram below. 

Once you have installed the door bottom your door should be air tight and ready to go. You can add some trim around the outside and seal it with acoustic caulk to finish off the door. Now you just have to repeat all the step for the second door and you will have your communicating door system. 

The last step to finishing our doors is to fill the gap between our two stud walls and rubber with rigid 3lb per square foot fiberglass batts. I recommend using either Corning 703 or Knauf Ecose insulation. Cut the fiberglass batts down to size so that the first layer fits snug up against the rubber and the two 2x4's in our framed wall as well as the two headers. 

Next, we will add the second layer of insulation, but this time we will wrap it in acoustic fabric such as Guilford Of Maine. This will fill the gaps between our 1x3 boards around all three sides of the entryway. It has the added benefit of increasing isolation and making our door look nice and clean between the walls. 

 J.H. Brandt recommends adding two acoustic panels on the back side of each door in the air gap. He says this can increase the doors attenuation by 10 dB. I would recommend this if you have the budget and the space between your doors.  

If we add up all the costs not including the framing of the wall itself we get the following: 

Total Cost Per Door = $1,338.53 or $2,677.06 per entryway. 

Could you build these doors cheaper. Sure, you could get a cheap door handle, forgo the added perimeter gasketing. However, every corner you cut is a weak spot in your entire design. I try to balance cost with budget and things like the mortise lockset and perimeter seals are important in my opinion. 

*if you build your doors right, but don't use green glue you will have saved the cost difference anyway and will have a better soundproof room in the end. 

FREE Soundproofing Workshop: https://www.soundproofyourstudio.com/workshop

I have done many articles over the years on soundproof doors. Lately, I have changed how I build them from my earlier videos. I am going to do a multi part series on door design and building over the next few weeks. Today will be all about framing the door and where to source your solid core doors. 

For this example I will be using two interior walls framed with a 1" air gap. The same principles apply if you are using a hat channel system on your walls or have one wall that is interior and one wall that is exterior. 

Below is a diagram of how to properly frame a soundproof door. Most of the framing is consistent with normal construction, however we want to add an extra king stud to support each or our 140+ lb doors. 

I would recommend 24" OC framing if your wall can handle it. You should calculate the max load your wall can handle before framing 24" vs. 16" OC. From a soundproofing perspective the less wood to transfer sound in anyway the better. 

One very strange aspect of a double wall design is how to seal the air gap so that it is still soundproof, but also so that you don't smell or see into the wall cavity between your two doors. The solution is to use rubber. I recommend buying 1/16" x 8" rubber off amazon here in the states. This way your rubber seal will fit your two walls perfectly. Notice the diagrams below. 

The rubber should be attached with screws and acoustic sealant to make sure it is airtight. I place the rubber on the outside king studs, because we will be using a prefinished steel door frame that will wrap around the inner jack studs and two layers of 5/8" drywall. The remaining gap between the rubber and inner door frame will be filled with 1" rigid Corning 703 insulation wrapped in Guilford of Maine Acoustic Fabric. 

Notice I recommend placing the rubber on top of your header and under the cripple studs. This will cover the 1" air gap at the top of your door. The bottom of the door will have a threshold and the studs will be cut away for entry. 

 To keep your walls from swaying with the weight of the door we need to add sway bracing to the interior walls. I like to use I-B3 clips from The Soundproofing Company. Place these clips every 48" OC on the top plate of your inside wall and connect it to the ceiling joists. This will still decouple your wall, but provide much needed support to your inner decoupled wall. 

Over the years, I have moved beyond the Rod Gervais book and have begun designing my own system for soundproof doors. This has led me to a great site here in the states called TruDoor. They have everything we need to order all the door parts in one place. The following is what I recommend for each door. Simply double the materials to get your communicating door system. 

*If you don't live in the States then do your best to find these similar materials in your own market. 

Total Door and Hardware Cost - 1,371.22 

Total Entryway Cost = 2,742.44

If that number shocks you, then you probably have not researched pre-built soundproof doors. Custom Soundproof Doors can reach the $6,000-8,000 range. The lowest price I have found for a quality soundproof door is $3,260/door. So, you can cheap out on some of the items above, but it will sacrifice your level of soundproofing. 

Lastly, this is part one of a multi-part series. The solid core doors only weigh 60 lb so, we will need to add weight to each door. This will add some more costs in materials. We will also need to go over how to install the doors and ensure they are airtight. Stay tuned for part two. 

FREE Soundproofing Workshop: https://www.soundproofyourstudio.com/workshop

I had done a version of this article before, but this one builds on the last and introduces a new mistake or two! In this lesson I will go over three mistakes I made when building my soundproof door that really didn't not become apparent until years into its use. 

Like anyone, we all start with no experience. I only had Rod Gervais's book as a guide and being the person I am, I followed it to a T, you could say religiously. The problem is that Rod's design or more likely, my interpretation of his design did not end up working for me. No shade on Rod, I respect his book and ideas, but my point is that a simple book with a fairly quick run through of how to build a soundproof door never beats the experience of building soundproof doors over and over again and the experience of knowing what happens to that door over time. 

In his book, Gervais explains that he uses GM trunk rubber and magnetic seals to build custom seals around his doors. He does mention a company called Zero International as well. In my experience the trunk rubber he recommended or at least the one I bought using his recommendations to the best of my research ability, was too stiff. The door would bounce of the seal and it was very difficult to get a complete seal around the door. 

So, we took off most of the trunk rubber and used weather stripping we found at our local hardware store. The weather stripping we used is not amazing, but it did the trick. It is called Frost King here in the United States and comes in various widths and depths. You can customize the size to your door design. 

On top of using these Frost King weather seals I also recommend that you buy high end door seals to go on the inside of each of your doors. The seals I recommend are: 

Zero International Door Bottom 367AA

Zero International Perimeter Seals 770AA

These are not cheap and I spent $770 on my seals and am excited to install them in the coming weeks. If you cannot find these specific seals in your country then look for a similar item that is high quality and acoustically rated. 

The second mistake I made was buying a relatively cheap and thus not sturdy door handle and deadbolt for my door. In a previous lesson I talked about buying a door handle with the wrong backset, but that is another story. Today I am saying not to buy a through the door door knob. The reason, mortised locksets don't go all the way through your door, thus improving soundproofing, but they also are usually made for heavier doors and can handle the pressure of a 300lb door. 

I have really enjoyed using a company called TruDoor here in the states. Mortised locks are available all over the world, so check your local supplier to pick the right one. You can also use a closed cell foam to help insulate the door handle from sound. 

It can take a little digging, but getting a pre-hung solid core door is a great starting place. It might be a little more expensive, but you don't have to try and hang a door let alone a very heavy door. If you have not hung doors before it is a very labor intensive process = money/time = money in the end. 

Again, in the united states I really like TruDoor. They seem to have great support and a very efficient website, which is so helpful and worth extra money a lot of the time. 

If you can find pre-hung solid core doors locally then go with that. The install of the pre-hung doors is beyond the scope of this lesson, but that is another pieces of this complicated soundproofing puzzle I will save for another time. 

In the end, buy high quality door seals, buy a mortised lockset, and try to buy pre-hung solid core doors if you can. This will save you time and money in the long run. Remember, I am speaking from years of experience now, so trust me when there are certain corners you just don't want to cut when soundproofing.