Soundproofing/Studio Construction Questions
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A. Do I need to soundproof my home studio?
A. Not an easy question to answer. Maybe Yes, Maybe No. Let's ask another question. What is soundproofing? A lot of people confuse soundproofing with creating an acoustical enviroment. Soundproofing is keeping the sound in the studio from leaking out.This way your neightbors won't call the police when you're in the studio. Creating an acoustical enviroment is making the room have the acoustics you want, ie having sound of a gym (with it's ringing, delays and boomy sound) or having no ringings, boomy, etc sound at all (Speaker companies build such rooms called anachic chambers).
Q. I have an band and I want to record/practice without having the police show up.
A. This is where you want to seal the room so sound doesn't leak out. There are basically two types of leakage, SPL and STC. SPL (Sound Presseure Level) is your basic "I can hear it" while STC (Shock Transmission) is the kind you feel (very low frequency stuff like your neighbor three doors down banging with a hammer). STC is the kind that will result in a visit from the police.
To soundproof a room all you do build a room from massive, limp materials that is airtight. What we want is to make a room with as much mass as possible (in it's walls, ceiling and floor) and hang it from a skyhook so it floats in the air. The easy thing for Pro studios to do is float a slab on mounts and then build the room on top of it without touching anything else.The cost of that is beyond most people.
The solution for the average person is to increase the mass of the walls/ceiling and to patch up any leaks from windows, doors and vents. Replace hollow core doors with solid doors and weather-strip around them. Seal any air leaks in the windows then cover the windows with plywood (put soft packing form, loose fiberglass or some other insulation between the glass and plywood) and add sheet rock over the plywood. If you have a window air conditioner build a baffle around it pointing the air stream away from any neighbors (couple of 90 turns with diffusers would help if they are close). You can also put a cover over it on the inside and sweat in an extreme case. If you have central heating/ac, your ducts should have at least two 90 degree turns with diffusers to help keep the sound out the rest of the building. (If you can add central heating/ac for just the studio would be better.)
If you can, build a room in a room using 2x4s for the frame. The idea is to avoid providing any path for vibrations to pass between the two walls. Make sure not to attach the outside walls to your inside room. You will have to attach it to the floor (make a floating floor if you can). Make the inside walls and ceiling as thick as you can (use sheetrock or Durarock, a mesh reinforced cement type board). You could also sandwich 1 3/4" fiberboard between two layers of 1/2' sheerock then apply the sandwich layer by layer to the frame. Inside the 2x4 frames put loose fiberglass, this will impede the movement of the air without actually transmitting any vibrations. Seal all cracks with drywall tape and spackle. When you're finished, seal the cracks again including nail holes with butyl rubber caulking or similar caulking.
Now the floor, no matter what you do to the walls, the floor will conduct sound at a certain level. This is why we need to float the floor (having the floor attached to rubber mounts on top of concret pillars that are not connected and go directly to the ground is how the pros do it.). Since we can't do that we can build a platform for the drummer or make the platform the whole "floor". You make a frame with 2x6s, plywood top and bottom, filled it with sand and float it on a 1-2" rubber mat (this is for best isolation if your budget allows it). If weight is a problem use as light and dense loose material (like loose fiberglass) as you can.
If this is a recording studio then you need to add to the number of rooms. A drum room, main room and control room may be required. You need to do the same things for each room. Remember none of the walls, ceilings or floors of the rooms should touch each other, if possible. To go between the rooms, you can use double pane sliding doors (a pair of them with 6-12" of space between them if possible). They can also double as windows so everybody can see each other.
If you can't do the room within in a room, the same ideas still apply. Increase the filler in your outside wall if possible and add to the mass of the wall like above. Also seal all the windows, etc so there is no air leaks. If you have to leave the windows uncovered, you can either make the covers removeable or use doublepane windows.
Q. I have a home studio where it's just me and maybe a couple friends recording one or two at a time. I can't do any of what you've suggested above. Help!!
A. If you have a large enough closet that you can convert into an insolation booth, then you're inbusiness. The conversion doesn't have to be extensive. If possible run a heat/ac vent into the closet so you can seal the door. Hopefully the door can replaced with a solid core one. Drill holes though the door or wall or run the wires (headphones, mics, etc) under the door. Cover the walls with Sonex, heavey curtains or similar material. This will give you a place to do vocals, record live guitar (put the amp in the closet), etc.
If the closet isn't workable then you can use an adjacent room and just run the wires needed to record the drums, vocals, guitar, etc. If possible, hang up blankets, etc to dampen the room. If want to spend some money there are portable Isolation booths that can be purchased
Q. I put Sonex on my walls in my apartment but the neighbors still complain. Why?
A. Sonex and other such products as well as curtains, etc dampen sound (SPL) but don't stop the sound from traveling through the walls (STC). You use Sonex help control your acoustical enviroment, ie what the room sounds like. If you turn up the gain on a mic that's on in a room and listen to the background sound after hitting a snare or clapping your hands you'll then hear the acoustics of the room. Back in the old days before EFX processors, etc you had to find a room that sounded right for your recording, find the right mic and place the mic just right. Elvis recorded in a stairwell in order to get that effect on his voice for those early Sun recordings. The drum sound of Led Zepelin were recorded with a single mic in a hard surface room. In order to stop the sound from traveling you need mass, see the above about soundproofing. It also is possible to get lead panels (soft ones) to hang on the wall and cover them with Sonex.
Q. I mix my song at home and it sounds just like I want but when I take it my friends, it sounds a lot different, Why?
A. There's a lot of possible reasons for that. One is the room you mix in. Speakers, amps, tape recorders, CD players all can have effect as well. An acoustical neutral room with acoustical neutral speakers and amp is ideal for mixing. That rarely happens unless you first test your room acoustics. After finding out where hot spots (places where certain frequencies find sympathic vibrations causing added volume to those frequencies, if you ever heard more bass in one part of your room from the other then you know what a hot spot is), low spots (those dead spots where the bass disappers) and the natural reverb or ringing are in the room, you fix them. The pros use a spectrum analyzer and frequency generator (or a test audio CD) to discover the hot,low spots etc. If you don't have this equipment, you can use your ears and a synth. In either case you sweep the room for individual frequencies (have the synth play the lowest to highest notes with a simple waveform like a sine wave by sticking a key down, you will have to transpose the keyboard to get all the frequencies). You then stand in all the listening areas of the room checking to see if there's any problems and take notes of what you find. Pros then use a 31 band stereo EQ (the best available) to adjust the response in the room to eliminate those spots. You finalize the room EQ by playing some records, CDs that you really know well to see if the spots are gone or at least minalized.
By using Sonex (or other acoustic foam products), curtains, rugs you can control or eliminate the ring of your room.The ring (a long enough one becomes reverb) is caused by standing waves. Standing waves happen when sound bounces back and forth between to parallel walls repeatedly before dieing out. If you ever threw a rock into a still pond or pool and watched the waves bounce off the edges and run into each other and off the opposite side, then you've seen what we hear as standing waves. In order to cut out the standing waves which cause the ring you only actually need to fit Sonex, etc onto two adjacent walls and the floor (ie. on just one of any pair of facing surfaces) this can save some money and may provide enough control.
Also there are "traps", portable devices designed to fix specific acoustic problems like bass traps. Taytrix, ASC, the Acoustic Space from Folded Space Technology and others make such devices. If you don't want to tune your room (that's what finding and fixing those hot spots is called), these can help fix those problems
The floor can be treated by laying a good quality carpet on a hairfelt pad (plastic foam pads are not good as an acoustic absorber).
Q. If I'm building a home studio from scratch, besides the above recommendation on soundproofing and my acoustical enviroment, other tips?
A. Your construction techniques are most important if your really building from scratch. There is nothing like lots of mass for providing sound isolation. A good solid brick outside wall (or preferably a outside and inside wall with a cavity between) is the ideal. Follow the rest of the room with in a room instruction for each room needed for the studio.
Another solution for those situations where construction from the ground floor is not possible, which has been succesfully used by the BBC is a Camden partition. (First used in the Camden Theatre in London in the 1940's). The following description of the construction is from the BBC Engineering "Guide to Acoustic Practice" (ISBN 0 563 36079 8). (They include drawings in the book.):
" ....the (Camden) partition consists of a layer of 12.5mm (1/2") plasterboard (sheetrock)... backed by a 12.5mm thick sheet of softboard (Softboard is a kind of compressed cardboard material, soft enough to compress if squeezed between thumb and finger, which is often used for noticeboards) fixed on either side of a 76mm x 50mm (3" x 2") softwood stud framing. The vertical members of the framing are spaced at 0.6m centres (2ft) and the horizontal ones at 1.2 m centres (4ft) with hairfelt carpet underfelt all round the edges where the Camden abuts another structure. Structural necessity often demands that the partition be tied to the adjacent structure but such fixings must be resilient. The softboard which serves to damp the resonance in the plasterboard as well as partially isolating the plasterboard from the timber frame, contributes a significant proportion of the mass and therefore increases the sound insulating properties of the partition."
"It is essential that there are no weaknesses acoustically and the softboard and plasterboard must be butt jointed only on timber members. All plasterboard joints must be properly sealed, with taped joints and with a skim (thin) coat of plaster applied to the surface."
"A single Camden partition provides approximately 35dB average sound pressure level difference over the frequency range 100hz to 2.5kHz a double Camden 52dB and a triple leaf Camden partition 87dB average all over the same frequency range." (The isolation is greater at higher frequencies.)
The BBC publication gives the disclaimer that although adequate for talks and discussion studios these partitions are not suitable for music studioswhere higher levels of sound isolation are required at the low frequencies. But they are refering to studios used for Big Bands and Symphony orchestras. Your home studio might be fine, built this way.
A double version of this partition was used in a small radio studio which was in an alcove at one end of a third floor open office area for a University Journalism department. The rest of the floor was the general teaching and editing area. It was full of loud college students exchanging information about the previous night's extra curricular activities. The partition,which incorporated a 2 inch air gap between the walls, included an observation window and a door. It was built by a carpenter who had no previous acoustic experience, working from instructions based on the BBC book, and the level of isolation which was achieved was impressive.
The window for this studio consisted of two separate frames, one in each partition with two different thicknesses of glass, one of 1/4 inch and one of 3/8 inch. This avoids a common resonant frequency which would allow transmission acros the cavity. When you are installing any windows in a studio it adviseable to angle the glass down from the vertical by about 5 degrees so that any reflections are sent down into the carpet instead of straight back.
The door frame was fitted into the inner partition (studio side) and the gap between the partitions partially covered over in the door recess with a timber lining fixed to the outer partition leaving a quarter inch gap to the door frame which was sealed with expanded neoprene rubber to preserve the isolation. The door was fitted with magnetic seals around three sides. and a neoprene compression seal to a hardwood threshold which was bedded in mastic and fixed to the floor.
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