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isolation for recording guitars, acoustic instruments

Discussion in 'Room Acoustics / Isolation / Treatment' started by CGL, Dec 23, 2014.

  1. CGL

    CGL Active Member

    Dear all,

    This is my first post. Thank you all so much for an invaluable resource! I have read the rules, searched for a similar post but nothing was quite like I was looking for so here it is!

    Ok so I'm planning to build a small studio at the bottom of my garden (in South East London. UK). My original plan was to have it built out of blockwork (concrete bricks) I got some quotes and the price was far too much for what I could afford so I had to go to plan B. As well sound engineering I have been a carpenter for a few years. Although I specialise on fitted furniture I have done some building work so I have decided to build it myself (timber structure) hiring some help for some stages.

    My plan is as follows:

    - Building size would be 5.5m x 3.5m x 2.6m

    - Due to cost, ease of installation and environmental impact I have decided that rather than having a concrete slab laid I would like to use a system called Swift Plinth:


    -The building's base would be made out of 10x2 treated timber sitting on the swift plinth

    - My thought was to build the walls using 4x4 timber 600mm centres. The exterior would be covered with a layer 18mm osb board, a layer of 18mm external grade plywood and cladding.

    - The cavity would be stuffed with insulation. 100mm Rockwool?

    - The interior would have a layer of plywood and two layers of plasterboard with green glue between layers and caulking all gaps. Finally the interior would be plastered.

    - The roof/ceiling would have same treatment as the walls.

    - For the floor I would have a layer of 18mm plywood, a layer 22mm T&G chipboard flooring, A layer of flooring insulation and finally some T&G 18mm engineered flooring.

    - I would like to have two top level windows (approx 400mm x 1000mm) Each window would have two panes of double glazed 6mm glass (I might sack this idea if it proves impractical and just do with no windows)

    - I'm planning to have two doors. Each one made gluing 3 x 18mm pieces of plywood and using rubber seals all around

    My main question here is about isolation. The room would be one open plan room. Generally I monitor at medium level with short loud bursts. I don't plan to record drums. Just acoustic instruments and guitar amps. For these I would build an enclosure so they don't make too much noise.

    My nearest neighbour is 25m away.

    My main questions are:

    - Does this sound like something viable? In your opinion would I get enough isolation?

    - Since the base frame would be slightly elevated would it be worth stuffing the cavities of the frame to stop it resonating? Would it be better to just have a concrete base laid?

    - Do I make any sense?

    Any help MUCH appreciated. Thanks in advance!!

  2. DonnyThompson

    DonnyThompson Distinguished Member

    I strongly urge you to buy this book:

  3. CGL

    CGL Active Member

    Hi Donny. Many thanks for your reply. I already have the book. There is lots of good advice there but also wanted to see other people's opinions. Also the book focuses more on building within an existing structure which is not something I'll be doing.
  4. Space

    Space Well-Known Member

    I wouldn't, here is why.

    While I suspect the cost of this system with the framed floor will just about match what a concrete floor would cost it is not my only reason for dismissing it as viable. The main reason is that you will build an elevated wooden deck that will have a resonant frequency higher than a concrete substrate. That means the wooden floor will vibrate more readily than a solid concrete floor and will introduce frequencies at the resonant frequency of the less weighted wooden floor that can and will be a distraction while trying to record.

    Essentially, a drum head is what you will build with this system.

    An Earth damped concrete slab is the best first line of defense you can have in this type of consideration.
    kmetal, pan60, DonnyAir and 1 other person like this.
  5. CGL

    CGL Active Member

    Dear Space,

    Thank very much for your advice. I thought that might be the case but hoped hat being outside etc it might be less of an issue. Having said that I totally agree with you. Swift Plynth is ditched!

    Regarding the rest o the construction do you think that the outlined plan would be sufficient to keep the sound in bearing in mind the surroundings etc? Would you advise to build a secondary room within the main building? Thanks in advance!
    kmetal likes this.
  6. Space

    Space Well-Known Member

  7. CGL

    CGL Active Member

    Hi Space,

    Thanks for the link. I did read that thread before I posted and thought I was abiding by the rules. I did search for a similar post beforehand and couldn't find anything similar enough or with relevant advice. Also I haven't done any sound measurements because I'm not building within an existing structure. The plan is to build something from the ground up so I'm not sure what and how I need to measure before there is a building in place. In regards of how picky my neighbours are to be quite honest this building will be at the bottom of a vey long garden and the closest neighbours are those whose gardens mine backs onto. They live in a different street in a very populated area so I don't know them at all and probably never will. I thought I had given enough detail about how I plan to build the studio. I used measurements and materials. Am I missing anything?

  8. Space

    Space Well-Known Member

    What types of bands do you plan to record.

    if you were mixing only, what sound levels do you anticipate you will be mixing at?
  9. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Are the interior walls/ceiling going to be independent from the external ?

    Also, any of the concepts in BLTP are the same whether it's new or existing construction, and it's very likely that you'll encounter some of the same situations, reguardless of new or existing construction.
  10. Space

    Space Well-Known Member

    Exactly. The exterior of the structure, while important, does not get as much attention as the interior. So it could be new, remodel, retrofit or any number of things.

    Good call Kmetal.
    kmetal likes this.
  11. CGL

    CGL Active Member

    Hi Guys, thanks very much for your interest. Please read bellow. Perhaps worth mentioning that I use nearfield monitors (at the moment quested F11)

    My original plan is to build one single room rather than a room within a room. One of my questions is whether this is viable or should I be looking at building an external structure and then a secondary one within?

    Many thanks
  12. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Room within a room can give you a very significant amount of isolation, as opposed to the single leaf option, Especially in a wood framed structure. If you where using solid concrete block, double walls might not be necessary, some would weigh this when figuring costs of labour and materials. This is another area (double walls) where a concrete foundation comes into play, since in most typical cases I know of, both the outer shell and inner shell share a common foundation. And while this is a flanking path for sure, if your wood farmed walls make 4-6-8" of concrete foundation the weak link in the ISO, yr doing quite well.

    Usually where a lot of people go wrong in your case CGL, is they want to force a control room and a tracking booth in inadequate cubic footage. Sinnce studio double walls usually average at around least 10-12" thick, your smart to keep your area wide open, because Imo it's better to have one really good room, than two compromised ones. And honestly I work in comercial facilities ( modest ones) and w out an assistant it's a real annoyance to set levels, and walk thru two rooms to move a mic, listen, rinse repeat. Planning for this w some remote qwerty keyboards mouses and screens would attack this. Keyword there being planning lol, fortunately that oversight is an easy fix.

    I'm not familiar w the f11 model, but the questeds 8" mid fields, I have used in the past go LOUD. Obviously it's not a drum kit so you can turn them down, but that's really tough to say, unless you could give a rough idea of the DB level you typically use. And just for the sake of the fletcher Munson curve, I personally would never want to build from scratch anything that didn't allow me to listen up to the 90ish db range, without incident. Even the db meter free apps, will get you a rough ideA of SPL, my iPhone/pad meters read about 10db louder, or softer, ugh I forget which, than my radio shck meter. One thing to consider is that isolation or TL values, change with frequency, which is why SCT ratings aren't the best thing to go by. 80db at 60hz is a much more difficult to contain, than say 600hz, or 6k. If I rememeber the rule of thumb is isolation values are halved, with each drop in octave. Sorry too lazy to look it up :) but u get the idea. I use a free app from JL audio that has a db meter and RTA, obviously taken w a grain or 3 of salt, but not completely terrible.

    Do you record vocals? With condenser mics? I only ask because, this is a consideration for keeping outside noise out, which in your case doesn't seem to be an issue.
    CGL likes this.
  13. CGL

    CGL Active Member

    Dear Kmetal,

    Sorry about my slow reply. I have been away for a few days. Your input is very much appreciated.
    To answer your question yes, I would be recording vocals but you are right to assume that outside noise is not an issue. I am more worried about trying not to make too much noise! At this point I am tempted to have some more quotes for having the building done using concrete blocks. If I factor in the time it would take me to build it (not getting paid) and materials I might not be making a great (or any) saving. I will have a good think about it. I will also visit a colleague's timber framed, single leaf studio which he claims delivers pretty good isolation and will report back!
    kmetal likes this.
  14. CGL

    CGL Active Member

    Dear all,

    It's been long but I finally managed to go and take a look at the aforementioned friend's studio. He built it in his garden using the following method:

    - Concrete base
    - 3m width, 3.5m length and 2.4m height single leaf timber framed building
    - He used 4x2" timber for the walls and 6x2 for the roof. The building is sitting on 4x2" joists (which are sitting straight on the concrete) and a layer of 18mm plywood.
    - Externally covered with 18mm external grade plywood (walls and roof) Compacted rockwool in the cavities. Inside it has one layer of plasterboard, one layer of iso rubber (on walls, ceiling and floor), a second layer of plasterboard and some floor boards on the floor.
    - For the door he glued two fire doors together. There are some attempts at sealing on the door jambs
    - There is one window about 600x1000mm with two panes of double glazed glass. Not quite properly sealed.

    This is as much detail as I could get out of my friend!

    Ok so I followed Kmetal's advice and downloaded the JL audio app. Turned the music up (very loud) and metered 95db in front of the speakers. Stepped out of the room into the garden and on the door and window side it read 55db 1m away from building and 50db 2m away. I went around the only other side I could access (the other two were right by the garden's boundaries) where there are no doors or windows and it metered 48db 1m away.

    Personally I thought the isolation was pretty good. I believe that with a couple of tweaks (better door and better sealing) it can be improved and bearing in mind that the nearest house to my studio would be about 25m away that level of isolation should be sufficient. I would rarely play the music that loud anyway.

    Apparently the iso rubber was fairly expensive. In your opinion is this a crucial element? is there a cheaper alternative/method? What do you gentlemen think about all of the above?

    Many thanks!
  15. Space

    Space Well-Known Member

    "The building is sitting on 4x2" joists (which are sitting straight on the concrete) and a layer of 18mm plywood."

    Except for that, sounds good. A concrete Earth damped floor is all you need. Any addition to this floor in an attempt to construct a mass/air/mass assembly should have matching mass. Concrete is roughly 98 pounds a cubic foot and the addition of a wooden deck does not have the same mass. And as we discussed before, its a drum head.
  16. CGL

    CGL Active Member

    Yes! I did think about hat at the time! so do you suggest that the walls should be sitting straight onto the concrete base?
  17. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Nice! Good stuff, barring the wood deck design. Curious how it sounded in there, and if you got to hear any recordings in there?

    Sealing is very important, and the main objective is that the seal makes contact along the whole length. Fortunately glazing tape, and weatherstripping is fairly painless to install, and most people could do it well if they take watever time they need to be neat. That said doors are a major source of agony for me an I don't have them down to an exact science. The double/triple seals help eliminate the chance that their is a breach in the exact same spot three times. From what I've gathered the actual material of the seal isn't particularly important as long as it seals, but different types will wear differently. If I remember correctly dark pines (madmax) used stuff like this for his secondary seals, on his doors, but it might have been another build, or he may have gone w something different.


    Windows are cool because they don't move lol, so a bit easier on that front, but glass is heavy too, and expensive, so maybe equally as painful?

    One way to do it is build directly in the concrete. since it's one room you don't really have to run ducting in the foundation, but it could be useful maybe. The general idea is that the concrete does not transmit sound well, like wood does. there's different variations on slab designs that range from simple to elaborate. I guess in its simplest form it would be a basic reinforced slab, probably require some special appointments, based on the additional load the ISO construction will impart. Pi really don't have any hands on experience with new foundations, or purpose built ones, so I dontnknow the finer details of that. Inhave been in a couple modest studios with rooms built in foundations residential and comercial, and it never seems to the weakest link.

    I think the idea is that if a wooden deck is going to be used it needs to be dampened so it doesn't resonate. I've only used sand filled decks for the couple booths I've need to and it seems to be fine, and operate as advertised. If I didn't need one I wouldnt put a wooden deck in If for no other reason than saving money and labor. I think in general it's basically a wash acoustically if it's deadend.
  18. CGL

    CGL Active Member

    To answer your question Kmetal I listened to some heavy rock for metering purposes. As far as I could tell it sounded pretty good. One interesting thing the owner mentioned is that when he recorded drums in the room (using an electronic kit) the kick drum was clearly audible outside. I imagine that must be caused by the wooden deck!

    So it is decided. I will build it with the walls sitting straight on the concrete. Perhaps I will have a course or two of bricks laid for the walls to go on as a damp protection measure.

    Any thoughts on the iso rubber? In your opinion is it a must do?
  19. CGL

    CGL Active Member

    Also, for the door I was thinking about glueing three layers of 18mm plywood together with perhaps some sheet lead sandwiched in between. Does that sound like a good idea or is it a bit silly?
  20. Space

    Space Well-Known Member

    Is it a solid core door?

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