Eric The Viking
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Warning: If you don't like complexity, or long explanations, please don't waste time reading this.
There's a thread going on spiral cutter blocks on planer/thicknessers, and one of the issues, especially for us amateurs, has to be the machine noise - are spiral blocks actually quieter? I think both from a theoretical perspective and actually hearing traditional and spiral side-by-side, that spiral-block p/ts are quite a lot quieter, but that's not the whole story.
I'm posting what follows because of the rampant nonsense about noise measurement, misunderstanding of how you measure sound, and silly, meaningless specifications from machine makers in their published information. If it's of interest, I'll develop it to include some of my own thoughts on reducing noise, etc.
On measuring sound loudness:
There's a lot of rubbish out there on this subject, and even more rubbish on sales web pages.
Decibels (dB) are a practical logarithmic scale, and only a ratio. They're used in many different engineering fields to measure ratios and relative changes-- Shock horror: you cannot measure loudness in dB. In order to talk meaningfully about sound levels other issues have to be considered:
OK, relatively boring bit over, so what's the point?
We know we are poorly served by machine reviews, either on web sites or in print. There are many reasons, including the too-close relationship between the writers and the machine manufacturers. It's understandable, and, having worked closely with journalists in the past, I'd be the last to criticise - it's hard enough for them to make a living as it is, and even if there was the equivalent of Egon Ronay's guide for machinery, few people would pay for it - unlike restaurants, we gain nothing from using a different machine every week!
So what are the practical things?
Hearing protection, but from what?
Writing as an amateur woodworker, living in a built-up area of the country, I have two issues of concern: protecting my own hearing and not annoying my neighbours with the noise I make. Thankfully the hearing one has a fairly simple remedy: only ever use machinery and noisy tools when you are also using hearing protection.
Apparently hearing damage is cumulative, that is, it all adds-up over a lifetime. and there is no such thing as "normal" old-age deafness. It's either some illness causing degeneration, usually inherited, or it's the result of environmental noise damage. Even audiologists (the professionals who do hearing tests) often don't know this -- I met one the other day in hospital!
Forty or so years ago, researchers decided that the edge of the Sahara was probably the quietest place in the Western world, so they went there and tested the hearing of the inhabitants: old people had hearing that was as good as that of the young, and as good as teenagers in Europe and North America but there was almost no environmental noise to cause damage!
And in the old Soviet Union, the Russians also contributed some useful research in the same period: They found a small village, in Siberia (IIRC), with basically only one industry, where steel was drop-forged. This is a noisy business! The inhabitants either worked at the forge or they didn't. Testing those comrades' hearing gave a stark result: exposure to the sound of the forge for less than one year cause significant and permanent hearing damage, even in the young. Significantly, it "notched" the response of the ear at exactly the part where we pick up speech sibilants (that's important for recognising the hard consonants of T, S, P and B, etc.).
There is no substitute for hearing protection, used on every occasion when sound may be damagingly loud. That includes rock concerts, using machinery, and loud power tools, and you might also include long-haul flights, on motorbikes and even the London Underground -- tube trains are better than they used to be, but they are still VERY loud. If you're an astronaut, all bets are off!
As I said, the most damaging sound is from percussive actions - stuff hitting other stuff. You'd be surprised how much of that there is in a workshop or on a construction site. For example, many power tools are percussive in some way - planers/thicknessers and routers, nail guns (obviously!), any percussion drills, but even circular saws and big bandsaws - how much so depends on the feed rate really.
As an aside, the loudest natural sounds, probably, that we might ever encounter, are waterfalls, volcanoes and thunderclaps. In all cases, these are predominantly LOW frequency sounds, unless you're right next to them. The ear has a built-in protection mechanism for them too: it loosens the tension on the tympanic membrane (the eardrum), and you go "protectively" deaf for the time you're exposed to the sound (if it's loud enough). Come back into a quiet environment and your ears' sensitivity recovers, in minutes, usually.
The problem with percussive sound (that we create) is that, almost by definition, it has no pitch. In fact it contains noise at many frequencies, mostly higher pitch, and against this the ear has no defence. Add-in the fact that it is usually high energy (think of the drop forge!), and you can see why impulse noise is dangerous to your hearing. Drummers go deaf, and so do other musicians. So, too, do their sound engineers!
How long do you expect to live, and how much of that time are you happy to be deaf for? I'm 57, my hearing is damaged (I think), and it's horrible, more so as I used to make my living from my ears (as a trained audio engineer). I have a good memory of how things should sound, but I can't hear them like that any more. :-(
If you don't care, that is your privilege, but remember that it may also affect your safety, and those of others around you ("So, Mr. Smith, you didn't hear the shouted warning and you kept going...?").
It doesn't have to be that way. Protect your hearing, religiously. Have lots of sets of ear defenders around (they re cheap enough!), so you can't lose them all and they're easy to find. Hang them on noisy machines to remind yourself, or around your neck (good on cold days!). Travel with soft earplugs, and keep a box in the workshop for visitors. when ear defenders break, replace them.
OK, it's obvious, But generations past simply didn't know for sure how hearing damage happens. Now we do, without any doubt, and it's avoidable, even if it seems too late for people like me.
More to follow, if anyone is interested, later in the week. I'll move on to soundproofing, and what does and doesn't work.
Happy, and quiet, New Year,
E.
*It is a theoretical design objective for stereo imaging. Blumlein's work (IIRC) assumes perfectly omnidirectional radiators at all frequencies. The higher the frequency, the harder the task becomes. in practice, nobody really wants speakers that fire just as much at the wall behind them, so the task becomes a bit easier, but we still talk about on-axis response and plot circular graphs showing how the sound changes depending on direction. It does matter, and in the context of woodworking kit and power tools, it matters a lot.
There's a thread going on spiral cutter blocks on planer/thicknessers, and one of the issues, especially for us amateurs, has to be the machine noise - are spiral blocks actually quieter? I think both from a theoretical perspective and actually hearing traditional and spiral side-by-side, that spiral-block p/ts are quite a lot quieter, but that's not the whole story.
I'm posting what follows because of the rampant nonsense about noise measurement, misunderstanding of how you measure sound, and silly, meaningless specifications from machine makers in their published information. If it's of interest, I'll develop it to include some of my own thoughts on reducing noise, etc.
On measuring sound loudness:
There's a lot of rubbish out there on this subject, and even more rubbish on sales web pages.
Decibels (dB) are a practical logarithmic scale, and only a ratio. They're used in many different engineering fields to measure ratios and relative changes-- Shock horror: you cannot measure loudness in dB. In order to talk meaningfully about sound levels other issues have to be considered:
- The dB(A) scale includes an absolute calibration value and a response curve that roughly matches the sensitivity of the normal human ear. Without the "(A)" suffix, you can be pretty sure any numbers are meaningless. But on its own, even that isn't much use...
- For machinery (or any other sound emitter really), the distance that the measurement is taken, away from the machine, is very important. An inverse square law applies - doubling the distance reduces the sound power to 1/4 the previous value. This should be specified whenever anyone has had a serious go at measuring sound, as it really matters.
- Hardly anything emits sound even close to the same loudness from all angles (omnidirectionally). Loudspeaker makers try to make this happen*, but can't, even though they intend this (theoretically) from the outset and they have powerful computers to help with the design. With things like p/t machines, there will be an enormous difference in the sound output from different angles.
- Meaningful measurements of sound emitters (machines) need to be made somewhere where reflected sound doesn't affect the results. Technically this is known as an "anechoic" chamber (one with no echoes), and it doesn't have to be completely soundproof, but it's still a hard thing to build, and expensive. Machine manufacturers aren't going to do that! And they're very unlikely to send a unit off to be measured, either. So at best you'll have someone arbitrarily pointing a sound level meter (not designed for that task), at some arbitrary distance from the machine, and writing down the reading. Worse than useless, because people subsequently believe it.
- As a guide, a difference of 3dB is roughly a halving or doubling of whatever-it-is, in our case sound power (at the measurement point), compared to another measurement. But you have no idea if two measurements have been made with enough consistency for the result to be meaningful, so even if you remember the 3dB rule, you usually don't have enough confidence in the numbers to be able to apply it!.
OK, relatively boring bit over, so what's the point?
We know we are poorly served by machine reviews, either on web sites or in print. There are many reasons, including the too-close relationship between the writers and the machine manufacturers. It's understandable, and, having worked closely with journalists in the past, I'd be the last to criticise - it's hard enough for them to make a living as it is, and even if there was the equivalent of Egon Ronay's guide for machinery, few people would pay for it - unlike restaurants, we gain nothing from using a different machine every week!
So what are the practical things?
Hearing protection, but from what?
Writing as an amateur woodworker, living in a built-up area of the country, I have two issues of concern: protecting my own hearing and not annoying my neighbours with the noise I make. Thankfully the hearing one has a fairly simple remedy: only ever use machinery and noisy tools when you are also using hearing protection.
Apparently hearing damage is cumulative, that is, it all adds-up over a lifetime. and there is no such thing as "normal" old-age deafness. It's either some illness causing degeneration, usually inherited, or it's the result of environmental noise damage. Even audiologists (the professionals who do hearing tests) often don't know this -- I met one the other day in hospital!
Forty or so years ago, researchers decided that the edge of the Sahara was probably the quietest place in the Western world, so they went there and tested the hearing of the inhabitants: old people had hearing that was as good as that of the young, and as good as teenagers in Europe and North America but there was almost no environmental noise to cause damage!
And in the old Soviet Union, the Russians also contributed some useful research in the same period: They found a small village, in Siberia (IIRC), with basically only one industry, where steel was drop-forged. This is a noisy business! The inhabitants either worked at the forge or they didn't. Testing those comrades' hearing gave a stark result: exposure to the sound of the forge for less than one year cause significant and permanent hearing damage, even in the young. Significantly, it "notched" the response of the ear at exactly the part where we pick up speech sibilants (that's important for recognising the hard consonants of T, S, P and B, etc.).
There is no substitute for hearing protection, used on every occasion when sound may be damagingly loud. That includes rock concerts, using machinery, and loud power tools, and you might also include long-haul flights, on motorbikes and even the London Underground -- tube trains are better than they used to be, but they are still VERY loud. If you're an astronaut, all bets are off!
As I said, the most damaging sound is from percussive actions - stuff hitting other stuff. You'd be surprised how much of that there is in a workshop or on a construction site. For example, many power tools are percussive in some way - planers/thicknessers and routers, nail guns (obviously!), any percussion drills, but even circular saws and big bandsaws - how much so depends on the feed rate really.
As an aside, the loudest natural sounds, probably, that we might ever encounter, are waterfalls, volcanoes and thunderclaps. In all cases, these are predominantly LOW frequency sounds, unless you're right next to them. The ear has a built-in protection mechanism for them too: it loosens the tension on the tympanic membrane (the eardrum), and you go "protectively" deaf for the time you're exposed to the sound (if it's loud enough). Come back into a quiet environment and your ears' sensitivity recovers, in minutes, usually.
The problem with percussive sound (that we create) is that, almost by definition, it has no pitch. In fact it contains noise at many frequencies, mostly higher pitch, and against this the ear has no defence. Add-in the fact that it is usually high energy (think of the drop forge!), and you can see why impulse noise is dangerous to your hearing. Drummers go deaf, and so do other musicians. So, too, do their sound engineers!
How long do you expect to live, and how much of that time are you happy to be deaf for? I'm 57, my hearing is damaged (I think), and it's horrible, more so as I used to make my living from my ears (as a trained audio engineer). I have a good memory of how things should sound, but I can't hear them like that any more. :-(
If you don't care, that is your privilege, but remember that it may also affect your safety, and those of others around you ("So, Mr. Smith, you didn't hear the shouted warning and you kept going...?").
It doesn't have to be that way. Protect your hearing, religiously. Have lots of sets of ear defenders around (they re cheap enough!), so you can't lose them all and they're easy to find. Hang them on noisy machines to remind yourself, or around your neck (good on cold days!). Travel with soft earplugs, and keep a box in the workshop for visitors. when ear defenders break, replace them.
OK, it's obvious, But generations past simply didn't know for sure how hearing damage happens. Now we do, without any doubt, and it's avoidable, even if it seems too late for people like me.
More to follow, if anyone is interested, later in the week. I'll move on to soundproofing, and what does and doesn't work.
Happy, and quiet, New Year,
E.
*It is a theoretical design objective for stereo imaging. Blumlein's work (IIRC) assumes perfectly omnidirectional radiators at all frequencies. The higher the frequency, the harder the task becomes. in practice, nobody really wants speakers that fire just as much at the wall behind them, so the task becomes a bit easier, but we still talk about on-axis response and plot circular graphs showing how the sound changes depending on direction. It does matter, and in the context of woodworking kit and power tools, it matters a lot.
) 
