Measuring machine noise, effective soundproofing, etc.

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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:
  • 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.
 

xy mosian

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Eric, Hats of to you for highlighting this problem. =D> =D> =D> =D>
I am very sorry to hear of your failing sensitivity to sound.
xy
 

Jacob

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Yes to protection. I now have hearing aids - I should have listened to the advice!
It can be very isolating because what you tend to lose first is fairly high frequencies which means the s and t sounds go which makes speech very difficult to interpret, though everything else can be OK ish.
You also lose directionality - becomes difficult to tell direction and distance of sound source, which can be a safety issue too.
PITA all round - put your ear muffs on!
PS normal healthy hearing is incredibly sophisticated - not just the frequencies but also the 3D sound world. You don't know what you've got til its gone and even the most expensive hearing aids won't bring it back
 

HappyHacker

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My hearing was stuffed 30 years ago when I went on a clay pigeon shooting course for 1/2 a day. I was not offered ear protection and was stupid enough not to ask. Afterwards while I could hear people speaking I could not understand them. A week later it was slightly better when I went to see the doctor. He said "You have not perforated your ear drum but you have ruptured blood vessels on your ear drum which has stuffed your high frequency hearing. You won't be stupid enough to that again will you? " I also now suffer from tinnitus.

He was right. Since then I have had great difficulty understanding anyone with a high pitched voice and cannot hear sibilants which make understanding speech very difficult. I have hearing aids but while they help they are nowhere near as good as proper hearing.

Listning to most programs on the TV is almost impossible due to perceived mumbling and background noise. Even turning up the volume does not help.

I now wear ear protection for any noisy activity but being already deaf I do not always recognise how loud things are.

So protect your ears.
 

ColeyS1

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HappyHacker":1vyxc6pg said:
My hearing was stuffed 30 years ago when I went on a clay pigeon shooting course for 1/2 a day. I was not offered ear protection and was stupid enough not to ask. Afterwards while I could hear people speaking I could not understand them. A week later it was slightly better when I went to see the doctor. He said "You have not perforated your ear drum but you have ruptured blood vessels on your ear drum which has stuffed your high frequency hearing. You won't be stupid enough to that again will you? " I also now suffer from tinnitus.

He was right. Since then I have had great difficulty understanding anyone with a high pitched voice and cannot hear sibilants which make understanding speech very difficult. I have hearing aids but while they help they are nowhere near as good as proper hearing.

Listning to most programs on the TV is almost impossible due to perceived mumbling and background noise. Even turning up the volume does not help.

I now wear ear protection for any noisy activity but being already deaf I do not always recognise how loud things are.

So protect your ears.
Not sure if this is any help but I fiddled around with my mum's TV the other day. I noticed it had several options in the sound menu, one of which was 'hard of hearing' . It seemed to make the speaking parts sound clearer and the other sounds quieter. Might be worth having a looksie.

Sent from my SM-G900F using Tapatalk
 

HappyHacker

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ColeyS1":2nwdnw4m said:
Not sure if this is any help but I fiddled around with my mum's TV the other day. I noticed it had several options in the sound menu, one of which was 'hard of hearing' . It seemed to make the speaking parts sound clearer and the other sounds quieter. Might be worth having a looksie.

Sent from my SM-G900F using Tapatalk

Thanks for the tip but unfortunately my sound comes from a Freeview box via a sound bar and neither have decent sound control.

There are also a number of comments on the interweb about a whole range of modern programs where the current artistic method of acting requires realistic dialog, this requires the actors to mumble and whisper as in real life. I am sure to a 30 year old sound engineer with perfect hearing and monitor quality speakers in a quiet room it sounds OK but to a deaf old fart like me I can't understand a word.

I quite like the foreign programs where I can read the subtitles as I don't have to try and understand the spoken word.

Protect your hearing!
 

Fidget

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HappyHacker":1ph8hyrm said:
ColeyS1":1ph8hyrm said:
.......I am sure to a 30 year old sound engineer with perfect hearing and monitor quality speakers in a quiet room it sounds OK but to a deaf old fart like me I can't understand a word.

As one of those said engineers (although I am not 30 any more) I can tell you a couple things.

We don't sit in a nice quiet room, we are usually on location, usually cold and usually somewhere noisy where we listen on headphones.

I have lost count of the number of times I have talked to the director about unintelligible dialogue, occasionally he will listen to me and ask the actor to speak up a bit, but more often than not, having an intimate knowledge of the script and having already heard the words multiple times, he/she will say that he can hear the dialogue perfectly well and he/she wants to 'preserve the actors performance' I then have to sit down again and record more mumbled and whispered dialogue knowing that there will be a problem later on when it is too late to do anything about it.

I believe it is a fashion amongst actors at the moment who believe it makes their performance more real!!
 

Arron

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I am 35 with bilateral otosclerosis and suffer mild (thankfully) tinnitus.
Serving as an engineer on submarines for 17years only compounded the problem! (I was medically discharged 2 years ago for....my hearing ;) )

Anyone who wears heating aids will know how dreadfully artificial they sound.

As pointed out, the problem with being hard of hearing (without knowing it) is you don’t realise just how loud things are!

Wear your hearing protection guys, you will miss your hearing when it’s gone ;)
 

Arron

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P.s

Thank you Eric for taking the time to do this, IMO this is what makes forums an amazing place to learn, I appreciate you taking the time to sit down and educate us all!
 

Claymore

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Very interesting post and after years playing guitars (rock) and similar number of years riding motorcycles without ear protection my hearing is certainly muffled and also slight tinnitus....when your younger you know it all and basically say won't happen to me but it can and will unless you protect your lugs early.
I had to stop both the guitars/bikes due to my hand probs but the damage has been done.
Regarding noise i read recently in a local paper about a white van driver who drives his van for 10 hrs a day usually on motorways and he has just won a court case to do with damage to his hearing caused by the droning road noise inside his van and they tested various vehicles to see just how loud the noise was and the van peaked at 102db a Honda Motorcycle with the rider wearing just his helmet (no earplugs) was 83db.........various cars also were very high (a Punto on the motorway was louder than a mx5 convertable .....they said it could be the start of more claims for hearing damage while using works vehicles. I was shocked really because for years people told me how noisy my bikes were lol
 

Chris152

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Great post Eric, thanks - definitely want to know more of your thoughts on reducing noise - it's the reason I don't have some of the kit I'd really like to have.
 

AES

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Good info EtV, thanks for posting.

I'm by no means knowledgeable on this subject, but one thing I always understood is that it's not only the positioning of the "noise meter" (in relation to the machine) but also the surface/s nearby that play a big role in whatever machine you measure. You mention this indirectly in terms of anechoic chamber measurements, but for all practical purposes, such facilities are not available, even to manufacturers, let alone to hobbyists, just as you say.

So the little I learnt about this is that if, for example, you measure the noise of a machine in your own shop which has, say, concrete walls and floor, the same machine measured at the same position will not give the same measurement when installed in, say, a wooden shed. I'm not sure if, in practical terms, it's possible to overcome this difficulty.

But I do fully endorse your point about hearing protection.

In the early years of my working life I was working close to running jet engines but did not wear hearing protection. Although ear defenders were available none of us used them, the reason being that in those days, military aircraft did not have the flashing red warning lights to show the aircraft had engines running, as they all do today. So with a line of 6 or 8 aircraft parked closed beside each other, some with engines running, some not, the only way to tell which had engines running, which not, was to use your ears! (Walking nearby in front of or behind an aeroplane with running engines was much more dangerous to your immediate life chances than long-term hearing damage was going to be)!

Anyway, you're dead right, always wear hearing protection, I definitely have hearing loss which cannot be repaired! Nowadays in the shop (no jet engines nearby any more) I only wear hearing protection if using a powered router or a mechanical sheet metal cutting tool. That's just daft probably, but I just think that in may case, it's too late now.

Thanks for posting, I look forward to "hearing" more from you (sorry :D ).

AES
 

Jonzjob

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Cheers for the post Eric. All good stuff mate. I, like AES was in the R.A.F. and working on jet aircraft although mine were big transports like the Bristol Britannia, Comet 2 & 4c and VC10s I started in the early 60s through to the mid 70s and as an aircraft electrician and working on an alternator underneath a running VC10 RR Conway engine the ear defenders hadn't a chance. Now I have high tone deafness and rather nasty tinnitus. My normal (?) hearing is not too bad, but when in a group or high ambient noise I just can't make out conversation.

I always used to use ear defenders, but they just were not up to the task. I still have a pair of ex R.A.F. jobbies and they are superb for the sort of noise we create, but not for jet engines.

As for the neighbours, I always try to be as quiet as I can and choose my time to do any noisy jobs. Not that I can do anything yet after our move. I can hardly turn around in our shed cause it's chocker block full of dammed boxes and my lathe is in about 5 boxes!!!

By the way

HAPPY NEW YEAR I SHOUTED IN CASE YOU COULDN'T HEAR ME :roll: :roll:
 

TFrench

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I'm very conscious of my hearing - I work mainly in noisy factories, when we're in our unit we're bashing metal about and when I'm doing my hobby ( DIY/woodworking) its pretty damn noisy too! Always have a pair of plugs tied to my hard hat or around my neck. Proper earmuffs using the tablesaw and planer too.
 

Jacob

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Jonzjob":3lrxjw4h said:
.....
As for the neighbours, I always try to be as quiet as I can and choose my time to do any noisy jobs. Not that I can do anything yet after our move. I can hardly turn around in our shed cause it's chocker block full of dammed boxes and my lathe is in about 5 boxes!!!....:
Actually the good news is that the high frequency screeching you get in the workshop travels least well and won't be as much of a problem outside. You may need ear defenders but your neighbours probably won't.
I found this out dramatically when I was making a planning app. There had been a lot of fuss about noise so I arranged a demo for the planning committee - had them in the workshop with all possible machines switched on, someone working at a bench etc. Very noisy.
Proceeded outside, then with all doors and windows shut, it was very quiet - so much so that some of the committee thought I'd rigged it and had arranged for stuff to be surreptitiously switched off!
This was a stone building with modern single glazed timber windows and fire doors. Heavy construction no doubt reduced sound transmission - light weight trad joinery would not be as good I suspect.
If you are worried about the neighbours try it out for yourself, you may be pleasantly surprised.
 

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