Eric The Viking
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- 19 Jan 2010
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I have a telly in the bathroom*. I like to watch/listen to junk TV in the morning (Pick/Quest), as the ad breaks help me time things like washing my eyes, and make sure I don't linger in the bath too long.
But Pick has just started showing series 8 of Wheeler Dealers. This morning one episode was a really nice 1950s Chevy pickup, lovely straight 6 engine, beautiful restoration, but a really, really noisy cab. Edd China applied a sound-deadening kit. The measured results went from 104 dB(A), down to 93 dB(A) after the kit was fitted.
This is that very Chevy - nice innit?
I'm an ex-professional sound engineer ("Eh, what?"), so I understand decibels. But you're an educated lot too, so I'm sure you already know that a measurement in decibels is defined as 1/10 of the log of the ratio change (of anything - the "A" part defines what the 'anything' actually is). It's 1/10th of the log value (base 10, not log e), a deci-Bel, because a whole Bel (yup, really exists) is too big to be practically useful. That's also why the unit is abbreviated to a small "d" with a big "B".
Never mind the detail though, for most of us wot use decibels, the important thing to remember is that a 3dB change is almost exactly a halving (or doubling) of whatever you're measuring**.
See where we are going here? The Chevy's cab got quieter by almost 16 times. Or, to put it the other way round, the sound in the treated cab was 1/16th what it was originally. That's impressive by any measure! And to prove it, they recorded their usual end of restoration test drive in the cab, and you could tell that voices did not have to be raised (at 104dB(A) plus road noise they would have almost needed sign language).
So sound deadening can work really well if it's done properly.
Obviously it can work for woodworking too. One of the important things Edd China did, which is often neglected when the subject comes up, was to block as many holes in the engine bulkhead and the floor that he could. In audio studio construction, this is also closely attended-to. If you fail to do that, you risk the studio being quite limited in its usefulness, because sound leaks through from the control room monitor speakers, and people digging the road up outside. It's the air movement that matters - stop that and you stop the sound.
You can also head the problem off at source, so to speak.
My machines are not expensive. So the sheet metalwork is probably thinner than it could be (on better machines), and its tendency to behave like a drum skin is increased. What can I do? Answer: dampen the vibration and increase the mass of the resonant panel.
There is a cheap and effective way to do this, using a roofing repair material, known as "Flashband". It's basically just heavy gauge aluminium foil with a bitumen coating on one side, that sticks to pretty much anything (and bloomin' everything when you are trying to use it!). You cut it to shape with a Stanley knife or tin snips, peel off a greaseproof-paper type of backing (now thin plastic - I'm ancient!), and stick it down. For really horrifically good adhesion, apply a hot-air gun and a wallpaper seam roller. You can also hide it by, for example, using it on the inside of saw cabinets, metal cupboards, etc., and it really works: It changes the clang of a tinny panel to a soggy thud - way better if you want as much quiet as possible. I've even put some on the back of my parabolic microphone reflector (for long distance sound recording), which stops it ringing like a bell which is, er, unhelpful***.
For bigger "panels," for example up-and-over garage doors, you can use thermal insulation, such as Celotex. It's not very heavy, and doesn't need to be very thick either. Anything that keeps it in place - glue, wire, whatever - will serve.
There is no point doing this for concrete or brick walls as they don't really vibrate from sound in air hitting them, so they don't transmit sound very well that way. But they do bounce sound back around the workshop, so for a nicer working environment, you could still go ahead and put absorbency on the walls.
In this case Celotex won't help as much as open-wool Rockwool slabs - it's the open "weave" that makes it absorb sound well. Rockwool is a standard tool for professionals doing acoustic treatment, and it has the big advantage that it's very fireproof. Bear in mind though that it will collect airborne dust very enthusiastically (think baby elephants and dust baths), so if you want cleanliness too consider something that lets you hoover it yet still keep it out of the dust bag - you might enclose it in chicken wire for example or an open-weave fabric (that's the normal studio solution).
Generally, for a comfortably quiet life inside the workshop, you want as few sound-reflecting surfaces as possible, so consider floor, ceiling and walls first-off, but don't forget acres of storage cupboards etc. (if you're lucky enough to have them).
Deadening the surfaces inside will also make a difference to what's heard outside, but not as much as most people hope it will. So we're back to that Chevy pickup: look for and block-up unnecessary air passages between the workshop and the outside world. That includes at the roof-line, draughty gaps round and under doors and windows, and ventilators or vent ports of any sort that you don't need. You don't want to kill yourself through asphyxiation, so cabin hooks for doors (and window stays), to hold them open in hot weather, are obviously sensible, but if you have to be really noisy you want to be able to close up for a short time, while you get the job done.
But that 11 dB of improvement proves it's easily possible, which ought to be an encouragement.
E.
*in the attic next door, behind glass let into the wall - perfectly safe.
** "Er, not always!" I hear the electronics guys shout in unison. That's true but not relevant. Move along folks, nothing to see here...
*** Flippin' annoying actually.
But Pick has just started showing series 8 of Wheeler Dealers. This morning one episode was a really nice 1950s Chevy pickup, lovely straight 6 engine, beautiful restoration, but a really, really noisy cab. Edd China applied a sound-deadening kit. The measured results went from 104 dB(A), down to 93 dB(A) after the kit was fitted.
I'm an ex-professional sound engineer ("Eh, what?"), so I understand decibels. But you're an educated lot too, so I'm sure you already know that a measurement in decibels is defined as 1/10 of the log of the ratio change (of anything - the "A" part defines what the 'anything' actually is). It's 1/10th of the log value (base 10, not log e), a deci-Bel, because a whole Bel (yup, really exists) is too big to be practically useful. That's also why the unit is abbreviated to a small "d" with a big "B".
Never mind the detail though, for most of us wot use decibels, the important thing to remember is that a 3dB change is almost exactly a halving (or doubling) of whatever you're measuring**.
See where we are going here? The Chevy's cab got quieter by almost 16 times. Or, to put it the other way round, the sound in the treated cab was 1/16th what it was originally. That's impressive by any measure! And to prove it, they recorded their usual end of restoration test drive in the cab, and you could tell that voices did not have to be raised (at 104dB(A) plus road noise they would have almost needed sign language).
So sound deadening can work really well if it's done properly.
Obviously it can work for woodworking too. One of the important things Edd China did, which is often neglected when the subject comes up, was to block as many holes in the engine bulkhead and the floor that he could. In audio studio construction, this is also closely attended-to. If you fail to do that, you risk the studio being quite limited in its usefulness, because sound leaks through from the control room monitor speakers, and people digging the road up outside. It's the air movement that matters - stop that and you stop the sound.
You can also head the problem off at source, so to speak.
My machines are not expensive. So the sheet metalwork is probably thinner than it could be (on better machines), and its tendency to behave like a drum skin is increased. What can I do? Answer: dampen the vibration and increase the mass of the resonant panel.
There is a cheap and effective way to do this, using a roofing repair material, known as "Flashband". It's basically just heavy gauge aluminium foil with a bitumen coating on one side, that sticks to pretty much anything (and bloomin' everything when you are trying to use it!). You cut it to shape with a Stanley knife or tin snips, peel off a greaseproof-paper type of backing (now thin plastic - I'm ancient!), and stick it down. For really horrifically good adhesion, apply a hot-air gun and a wallpaper seam roller. You can also hide it by, for example, using it on the inside of saw cabinets, metal cupboards, etc., and it really works: It changes the clang of a tinny panel to a soggy thud - way better if you want as much quiet as possible. I've even put some on the back of my parabolic microphone reflector (for long distance sound recording), which stops it ringing like a bell which is, er, unhelpful***.
For bigger "panels," for example up-and-over garage doors, you can use thermal insulation, such as Celotex. It's not very heavy, and doesn't need to be very thick either. Anything that keeps it in place - glue, wire, whatever - will serve.
There is no point doing this for concrete or brick walls as they don't really vibrate from sound in air hitting them, so they don't transmit sound very well that way. But they do bounce sound back around the workshop, so for a nicer working environment, you could still go ahead and put absorbency on the walls.
In this case Celotex won't help as much as open-wool Rockwool slabs - it's the open "weave" that makes it absorb sound well. Rockwool is a standard tool for professionals doing acoustic treatment, and it has the big advantage that it's very fireproof. Bear in mind though that it will collect airborne dust very enthusiastically (think baby elephants and dust baths), so if you want cleanliness too consider something that lets you hoover it yet still keep it out of the dust bag - you might enclose it in chicken wire for example or an open-weave fabric (that's the normal studio solution).
Generally, for a comfortably quiet life inside the workshop, you want as few sound-reflecting surfaces as possible, so consider floor, ceiling and walls first-off, but don't forget acres of storage cupboards etc. (if you're lucky enough to have them).
Deadening the surfaces inside will also make a difference to what's heard outside, but not as much as most people hope it will. So we're back to that Chevy pickup: look for and block-up unnecessary air passages between the workshop and the outside world. That includes at the roof-line, draughty gaps round and under doors and windows, and ventilators or vent ports of any sort that you don't need. You don't want to kill yourself through asphyxiation, so cabin hooks for doors (and window stays), to hold them open in hot weather, are obviously sensible, but if you have to be really noisy you want to be able to close up for a short time, while you get the job done.
But that 11 dB of improvement proves it's easily possible, which ought to be an encouragement.
E.
*in the attic next door, behind glass let into the wall - perfectly safe.
** "Er, not always!" I hear the electronics guys shout in unison. That's true but not relevant. Move along folks, nothing to see here...
*** Flippin' annoying actually.
