Construction advice

Hi, New to these forums. So may just give some brief relavant information. Live in Channel Islands near UK. Currently own a large warehouse and have built two music rooms and now looking to build a further 4 or 6 rooms. The usable interior area should be around 240 square feet like my existing ones. My current design which was done on the fly simply doesnt block out enough sound and is causing disturbance. Essentially new design is as follows (remember all this is already within the 15,000 square feet warehouse to be built near the centre) -Floor made of thick concrete slab already existing to be carpeted -Wall made from concrete block with heavy wooden fire door - walls to have wooden batons about 30mm thick on them with some form of insulation in between - sound proofing plaster board over the top and then plastered and painted. - Ceiling to be a stud wall which then covered in plasterboard and then plastered and painted. - All walls to be offset a few degrees to reduce echoing Surrounding this room i expect to leave a smallish gap and then build another concrete wall surrounding it and another stud work ceiling going over the top. Thus creating a room within a room. Will try and supply a picture to help explain. Some of my immediate questions are -decent space to leave between walls? -best insulation to use behind the plaster board? -best insulation to leave between the walls? (sand? foam? AIR?) - best way to Ventilate the rooms whilst no sound escaping - advice on doors? -advice on what concrete blocks to use for contruction? James

Hi James. Welcome. Please read the forum rules for posting (click here). You seem to be missing a couple of things! :)

My current design which was done on the fly simply doesnt block out enough sound and is causing disturbance.

If you explain your current design in detail, with photos, then we might be able to help you fix that too, so all your rooms will be isolated to the same level.

Some of my immediate questions are...

Before anyone can answer any of those in detail, we would first need to know the answer to the most basic question here: How much isolation do you need (in decibels)? Walls, doors, windows, ceilings, floors, HVAC, and electrical systems are all specifically designed to provide certain amounts of isolation. You choose the construction materials, thicknesses, densities, types, dimensions, etc. based on the need for a specific level of isolation. There are equations for calculating that. Building a room that needs to be isolated to 60 dB is very, VERY different from building a similar size room that needs to be isolated to 40 dB. There's also the issue of frequency: Isolating a room meant for bass guitar ad drums is very different from isolating a room meant for violins and sopranos, even if the same overall level of isolation is wanted. So your first order of business is to get a proper hand-held sound level meter (not expensive: around US$ 100) and determine how many decibels of isolation you need, and also to describe what types of instruments and what genre you are dealing with. With that number and frequency range, then it becomes possible to choose the wall type, construction techniques, and materials that will provide the right level of isolation. Isolation walls need to be calculated, not guessed. Guessing is a bad idea, and seldom works (as you already discovered... :) )

-Floor made of thick concrete slab already existing to be carpeted

That would be a mistake. The concrete is great, of course, but that's it. Nothing else is needed. Studios are seldom carpeted for a simple reason: carpet does the exact opposite of what is needed in small rooms, acoustically. Small rooms need a huge amount of low frequency absorption, some controlled mid-range absorption and diffusion, and little to no absorption at all in the high end. What carpet does is the opposite: No absorption at all in the low end,random uncontrolled absorption in the mid range, and stacks of absorption in the high end. If you carpet your rooms, they will sound dull, hollow, thunky, boomy, muddy, and unpleasant. Many studios just use bare concrete floors, polished or stained to give an attractive finish. That0s the best possible surface, acoustically. If you don't like concrete, then lay laminate flooring over a suitable underlay. But not carpet!

-Wall made from concrete block with heavy wooden fire door - walls to have wooden batons about 30mm thick on them with some form of insulation in between - sound proofing plaster board over the top and then plastered and painted.

That woulds create a coupled 2-leaf resonant system, which would not isolated well at all! At the resonant frequency of that system, it wouldn't isolated at all, in fact, and could even end up amplifying the sound. You can calculate the resonant frequency by using the equation f = 60 / (SQRT (M x D)), where "M" is the surface density of the plasterboard+plaster+paint, and "D" is the thickness of the battens. Do the math, and you'll see that it's not a pretty picture. Building such a wall would be detrimental to low frequency isolation. Starting at a frequency of 1.4 x the resonant frequency, everything below that would not be isolated at all.

- Ceiling to be a stud wall which then covered in plasterboard and then plastered and painted.

Depending on what is above that ceiling, that probably would not work either. Also, the technical term for the wood framing in ceilings is "joists", not studs. Studs stand up vertically inside walls and support vertical loads in compression, while joists run horizontally across ceilings or floors, and support loads in tension. Exact same material, different use. The overall isolation of a room is only as good as the weakest part (the part that has the least isolation). If you build really good walls that provide 50 dB of isolation, but your ceiling only provides 30, then your total isolation is 30 and you wasted a lot of money on those great walls.... If you wanted 50 dB of isolation overall, then you would need to build ALL parts to 50 dB: Walls, ceiling, windows, doors, HVAC, etc. IF any one of those is not isolated to 50 dB, then the room as a whole is not isolated to 50 dB. The weakest path wins.

- All walls to be offset a few degrees to reduce echoing

Myth. No need for that. It's a very, very common misconception that "angling walls eliminates echo" or "angling walls makes a room sound good". Wrong. It does not. Angling walls is good for one specific thing: it can eliminate a particular type of echo, known as "flutter echo". It does nothing at all for any other type of echo. The reverberation time for a room does not depend on the shape of the room. It depends on only two things: the total volume of the room, and the construction materials. A concrete room with a volume of 50 cubic meters will have roughly the same overall RT-60 times no matter what shape you make it. So angled walls can reduced flutter echo. Great!... actually, not great... In order for that to work, the angle needs to be at least 12 degrees, and you'd need to do it to two adjacent walls as well as the ceiling.... That means you waste a lot of room, and end up with a strange shaped room that looks weird, and is hard to fit people and furniture into. And the kicker is this: it is actually easy to stop flutter echo entirely with treatment panels on the walls, at strategic locations. Since the room will need to be heavily treated anyway (its a small room), there's no need at all to angle your walls. You live not very far from what many people consider to be the best studio ever built: Abbey Road. Take a look at all the rooms in Abbey Road: They are all plain old rectangles. Not one of them has angled walls! So if the best studio in the world works just fantastically without angled walls, then why would yours need them?

Surrounding this room i expect to leave a smallish gap and then build another concrete wall surrounding it and another stud work ceiling going over the top. Thus creating a room within a room.

Assuming you are planning to build this whole thing inside an existing building, then that would be creating a mangled monstrosity of four-leaf walls and three-leaf ceilings! What most people don't realize is that isolation walls are tuned systems. They resonate at specific frequencies. They are actually designed to do exactly that! The resonant frequency is carefully chosen so that is at least one octave below the lowest frequency that needs isolating, because the wall does not isolate at all until 1.414 times the resonant frequency, and only starts isolating decently at 2 times the resonant frequency. The cheapest, most effective, most practical tuned system you can build is a fully decoupled 2-leaf MSM system. 2 leaf, and only two leaf. If you have a three-leaf system, then there are multiple resonances going on at the same time, and the lowest of those is still higher up than it would be if you had used the same materials to build a 2-leaf wall. A 4-leaf wall is even worse still. This is not intuitive: people think that if they put up a single leaf wall that sort of isolates a bit, and then adding a second leaf in front of that makes it isoalte much better, then you'd assume that adding a third leaf would make it even better still, but that simply isn't true. The best wall is a two-leaf wall. Anything else has worse isolation in the low end. It is possible to compensate for that, yes, by adding more mass and using larger air gaps, but why would you? That wastes space and costs money! The lowest cost, most effective isolation system is 2-leaf.

Some of my immediate questions are -decent space to leave between walls?

Back to the same question: How much isolation do you need? (Measured in decibels) Without knowing that, it is impossible to say how big your gap needs to be. The size of the gap tunes the wall.

-best insulation to use behind the plaster board?

If you use mineral wool, then the density should be 50 kg/m3. If you use fiberglass, then the density should be 30 kg/m3. If you don't use either of those, then all bets are off...

-best insulation to leave between the walls? (sand? foam? AIR?)

Sand, foam and air are no use as insulation for acoustic purposes. Technically, the purpose of insulation in a wall is to provide acoustic damping on the resonances that could occur. Technically, you need "porous absorber" materials to do that: things that are fibrous, soft, "fluffy", and that air can move through. In fact, the property of the insulation that actually damps the resonance, is called "Gas Flow Resistivity",and is measured in the unlikely units of MKS rayls. That's a measure of how the material resists the flow of air through it, and it needs to be in a certain range for each type of acoustic treatment. Somewhere around 15,000 rayls is about right for what you want, and you can get that with 50 kg/m3 mineral wool or 30 kg/m3 fiberglass insulation. Sand does not do that. Closed-cell foams do not so that. Air does not do that.

- best way to Ventilate the rooms whilst no sound escaping

With a carefully designed HVAC system that has been properly calculated to provide the correct air flow rate of at least 6 full room changes per hour and 5 liters per minute per person, such that the air velocity at the registers does not exceed 300 FPM (roughly 1.5 m/s), and the insertion loss of the silencer boxes is the same as the isolation level required for the room as a whole, while the static pressure of the entire system does not exceed 0.5 inches WG. You also need to provide sufficient dehumidification and cooling, based on the sensible heat load and latent heat load, such that the relative humidity is kept around 40% and the temperature around 22°C. The latent heat and sensible heat loads depends on the number of people in the room, the equipment they use, the lighting in the room, and the local climate. There's a LOT that you need to take into account when designing the HVAC system! When I'm designing studios, I often spend more time on getting the HVAC right then I do on the design of the room layout, structure, and acoustic treatment together!

- advice on doors?

You will be building two-leaf walls everywhere, so each doorway needs to have two doors in it, back to back, one in each leaf. On door opens outwards,the other opens inwards. Each door must be solid-core (never hollow!), the surface density must be at least as great as the surface density of the leaf it is in, and the gap between the doors must be at least as great as the gap between the leaves of the wall itself. You also need at least two complete, unbroken seals around the full perimeter of each door (sides, top AND bottom), and you might need three such seals on each door if you need high levels of isolation. Doors like this are heavy. Very heavy. You need special heavy-duty hinges (at least four of them, preferably five), and an automatic door closer. It is not safe to try to close such a door by hand.

-advice on what concrete blocks to use for contruction?

Whatever type provides the structural integrity that you need to support the inner-leaf ceiling, and also has enough surface density to provide the resonant frequency that you need (along with the air gap) in order to produce the level of isolation that you need (Transmission Loss in decibels) for the frequency range that you need to isolate. - Stuart - - Stuart -

Hi, (When I say Channel Islands I mean Jersey and Guernsey, so not too easy to pop and see Abbey Road) Thank you for the very long answers! Will spend some time drawing out info that can help me. My rooms are aimed at bands wanting to hire a permanant space that they can use to practice at any time 24/7. My main concern is preventing noise pollution to any local residents. My current design is essentially just the first design without the extra room around it. its in the adjoining warehouse. So its the block wall, batons with insulation then plasterboard and plastered. The ceiling is just a hanging ceiling with a huge amount of rockwool insulation above it. The result was, you stand outside the door and you cant hear anything whatsoever other than the really low frequency stuff. Literally the only thing you can hear is the base. My main issue I believe was that one of the walls of the studio extended out and adjoined onto a residential property. This was still about 50 metres away but seemed to channel the base right into the house. It may be that without this im most of the way there already. ASAP: Also sorry if missed site rules, gonna read those now Gap in between walls. I realise your saying its like asking "how long is a piece of string" but it must be a case of diminishing returns? Currently looking at leaving about 5 inches between the two ceilings and the walls. Thank you for the advice on the rockwool insulation, thats that sorted. well the requirements should be fairly simple seeing as its inside a warehouse, the rest of the building will be self storage which can be planned around the music rooms. My restrictions - Cost: £4,000 to £5,000 for each room as a guide budget. - maximum hight to work with is 3 metres - Maximum surface area 300 sqft, - Desired internal space of the room to be near 200- 240 square feet. - Floor is concrete slab aim of the game? MINIMAL sound escaping the room.