Myths about Soundproofing
1) There is no such thing as perfect silence. In an anechoic chamber what you hear is the blood and other bodily function noises.
Moral of the story......You can't escape from yourself...
2) Take a buzzer and float it just above the surface of a table. Ring is and measure how loud it is. Get a large tin can or plastic bucket and put it over the buzzer and seal it air tight to the table. Ring the buzzer again and measure how loud it is. The metal or plastic might have an STC of maybe 15 to 20 dB. But it measures just about the same as it does without the bucket. Why? Because inside the bucket the noise level can't escape and isn't absorbed so it just gets louder until it is 15 ot 20 dB louder than it would have been if there was no bucket on top of it and then the sound leaks our just as before. 80 db + 20 dB room gain - 20 dB STC = 80 dB.
Moral of the story....for sound containment block the noise and then absorb the noise you just blocked, and then you get sound containment.
3) I agree, people frequently mistate and confuse the difference between soundproofing and sound conditioning.
4) Sound canceling unwanted outdoor noise is a myth. If you use sound to cancel sound you actually are introducing twice as much acoustic energy into the space where you are located. If there is a sound cancel (phase cancel) effect in one place there will be a t4 times more powerful sound (phase add) effect + 6 dB in another place. So far, sound cancel pretty much only works in pipes or ducts or windows, but not in the open space.
5) When sound canceling is used in a pipe, less sound goes out the open end of the pipe and more sound returns back upstream towards where the sound comes from.
6) Lady complains that she hears sirens at night but every time she opens the window she can't hear the sirens. Why? Window twangs at a resonant frequency. City noise causes it to twang making the siren sound.
7) What happens when you add heavy walls to keep sound inside your music practice room? It's stays inside your room,, getting louder and louder until the loudness times the wall friction equals the sound power being fed into the room.
Is a sonic boom louder inside your house or outside your house? Inside: Because the boom hits your roof and shakes the whole house, which makes a lot more noise that the boom by itself, outside.
9) Does sound come out of the sound hole of a guitar? No. The sound hole is an opening into the volume of air inside the guitar. At the lowest tone, the fundamental frequency for the guitar, the guitar acts like a Helmholtz resonator, with air moving in and out of the hole (sound cancel effect) and the air pressure inside the guitar is so strong it bulges the guitar surface out and sucks it in. the moving guitar surface makes the sound.
10) Noise Annoys
11) Sound is twice as loud (+10 dB) inside compared to outside
12) There is no such thing as a sound wave. Sound is the pressure (Potential Energy) part of an acoustic wave and the other part is the inaudible velocity (Kinetic Energy) part.
13) The condenser mic measures the pressure part and the ribbon mic measures the velocity part of the acoustic wave.
14) Classic organ music is written and played so that each new note harmoniously blends with the reverberations of the previous few notes.
15) How can the snapping of a playing card by the spokes of a bicycle replicate the low frequency varoom of a Harley motorcycle? Flutter echo. 50 snaps per second stimulates the 50 Hz part of the cochlea, even though the snap is only made up of high frequency sound. It is called a pseudotone.
16) STC is called Sound Transmission Coefficient but it really should be called Speech Transmission Coefficient because it is based only on 1/3rd octave bands in the vocal frequency range: 125 Hz thru 4000 Hz
17) Sheetrock on either side of wood studs has STC of 25, Add one layer of sheetrock, STC 20 and the result is STC 25 + 20 = STC 45? No, it is about STC 25 + 2.5 + = STC 27.5. +2.5 is the mass law for the wall that accounts for the increase in the wall weight.
18) If you are having a hard time hearing the radio clearly, what to you do? Turn the radio louder or quieter? Most people turn it louder but turning it quieter makes it sound better. Quiet sound has less bass compared to treble than in loud sound where the bass and treble are about equal in loudness. Turning the sound level down improves the treble to bass ratio which makes sound more easy to understand.
19) Sound masking is a way to fight sound with sound.
20) The best noise for sound masking is a scrambled version of the very same noise you don't want to hear.
21) To erase the late night beat of distant music, add a similar sounding random beat to it. You will create a composite noise that sounds like the gurgling noise of an underwater motorboat exhaust and the beat totally disappears.
22) Everyone thinks the mass law is great. But a limp mass wall looses 6 dB of soundproofing power each time the frequency is reduced by half. If a limp mass wall is STC 35 at 500 Hz, it is STC 29 at 250 Hz, STC 23 at 125 Hz, STC 17 at 63 Hz, and STC 8 at 31 Hz. There is another soundproofing term in the soundproofing equation......
23) Two layers of quietrock on studs with insulation might give STC 40. But add OSB to one side of the studs, insultion and then quietrock to both sides. You'd expect the soundproofing to be even more but it significantly less. Air isolates sound between the two layers of quietrock. Adding wood underneath a layer of quiet rock conducts all the sound that gets through that layer into the studs and out the other side. You get maybe STC 30.
24) If someone is playing a radio station of TV show next door and it's driving you crazy, tune the show in on your own set and now you've got great sound, turn it down almost as low as you want and you still don't hear the neighbor, till they change stations.
25) the reason old timer "lath and plaster" houses sound so solid, so great is because they didn't use twangy sheetrock for wall surfaces. The lath and plaster was made out of sand and horse hair and a lot of other stuff thrown in. The surfaces of the walls had a huge amount of internal friction and just didn't twang the way sheetrock twangs. Something like double layer sheetrock with damping compound between.
26) If noise is coming thru the bedroom wall and bothering you, reverse your bed position, get your head as far away from the noise conducting wall as possible and out into the middle of the room.
27) If the ceiling above is vibrating from music or foot fall and you can't stand it. Get a stick that is just a little longer than the ceiling height. Press one end of it against the ceiling where a floor joist is located out in the middle of the room, and gently sidekick the other end along the floor until the stick is pressing hard against the ceiling joist. Presto, quiet ceiling.
28) If you are playing music and the apartments upstairs or downstairs are being bothered, do the same stick trick and your bass boom thru the floor or ceiling will go away. Cheapest soundproofing trick ever invented.....(by me...thank you, thank you)
29) Last one. Get a couple coffee beans and put in old medicine bottle. Shake them and listen to the noise. Now, leave the cap on the bottle and do anything you want to the bottle beside hitting it with a hammer. You thing you are a whiz at soundproofing? Try to soundproof that bottle in such a way that you can still shake the beans in the bottle but you can't hear them rattle. You can't do it...
OK, that's all the diddies I can muster up at this sitting. Hope you enjoyed some of them....I hope I didn't stray too far off topic...to much.
Art Noxon, Acoustic engineer
Pres of ASC - TubeTraps/WallDamp
