Thread: Dust extractors noise ratings

One needs to be a bit careful about comparing reported Sound Pressure Levels (SPL) especially by DIYers.

In this sticky DRAFT: FAQ - Dust Extraction (Practical Aspects) I describe the problems in comparing DC SPLs - in particular see section 2 of that post.

To make a truly accurate reading these need to be done in an anechoic chamber as the confined situations found inside and even outside sheds can dramatically change the readings by many DBs. Results obtained in a shed are fraught with effects due to multiple reflections and different types of surfaces. This is probably why why DC manufacturers rarely report DC noise levels and they don't want Muggins complaining when their new DC exceeds the specification.

Its one thing to report "I am measuring 85dB" as applied to my particular noise and related hearing effects issue , and saying this is what the DC is making. You could well transfer that same DC to a different shed and get anywhere form 82 to 88 dB depending on how it is installed, where and what rejecting surfaces are used and the length of grandma's nose. Same goes for enclosure sound reduction as there are alway before and after measurements made.

About the best a DIYer can do is to drag their DC outside and get it at least 10m away from any reflecting surface and then measure in several places around the DC. However, I would not expect many people to do that. I have measured 2, 2HP DCs this way and obtained between 82 and 85dB around the DC (all at 1m away and 1m above the ground) - the one that was 85 db became 87 dB inside the shed when placed in an open Colorbond shed corner and 84 db when placed along a wall next to a stack of wood offcuts.

The 3HP Carbatech with the twin bags with the 13" impeller was 87dB on the back lawn (not 10m away from anything). The only noise measurements I worry about now are what's outside its enclosure which is not going to help much in comparing DCs.


Before anyone grabs their mobile phone and starts measuring SPLs I recommend reading the above link so while we may not end up camping apples with Apples, we can at least be comparing fruits, and not apples and puppies. NB I recommend measuring SPLs 1m from the DC and 1m above the ground.

Thanks BobL but I’m just interested in round about figures,80-85 dBA for instance would work enough for me.
I’m pretty well up to speed with acoustics through my job, so I understand exactly what you are talking about but I’m not really concerned about the error it imposes.
TBH I have no idea what noise levels DC run at, so any numbers is a good start


Sent from my iPhone using Tapatalk

Originally Posted by Runningman

Thanks BobL but I’m just interested in round about figures,80-85 dBA for instance would work enough for me.
I’m pretty well up to speed with acoustics through my job, so I understand exactly what you are talking about but I’m not really concerned about the error it imposes.
TBH I have no idea what noise levels DC run at, so any numbers is a good start

Almost all 2-3HP Dcs are in the 80-85dBA ball park. Some DCs use different vane impeller arrangements and are supposed to be noisier but that is often masked by the way they are installed. In 2014 I tested a 20+ year old 3HP "straight vaned machine" and it was 93 dbA at 1m. A few years back a local member, Dave Reed, installed straight vaned DC but he got something much lower than this - I think it was less than 85.

Even the exact same model machine is going to give variable result. It only takes an impeller housing to be half a mm out and this can change things dramatically.and most mobile Most basic phone apps are not going to be that reliable either.

Anyway lets see what pops up.

BobL, Are you in the mechanical services game as your knowledge of acoustics, air volume, fan performance is reminiscent of an HVAC engineer. I’m in that industry myself


Sent from my iPhone using Tapatalk

Originally Posted by Runningman

BobL, Are you in the mechanical services game as your knowledge of acoustics, air volume, fan performance is reminiscent of an HVAC engineer. I’m in that industry myself

I was a scientist that used ultra clean air laboratories. I started using these type of labs in 1979 when myself and a hands on professor renovated an old darkroom into a clean air lab. It was only about 3 x 3 m and had a small (doorway size) air lock entry way, and two 1.2 x 0.6 m 99.97% at <0.3 microns HEPA filters.

After finishing my PhD in 1985 I was employed as a research scientist at the same uni and built a 6 x 4m metal free ultraclean room in a so called cyclone resistant demountable. At the time this was an unusual fit out that no local contractor seemed to understand what we wanted. it had 4 x 1m air lock and 4 x 99.997% at >0.3 micron filters. In that space we dissected polar ice and snow and tiny meteorite grains. It was cheaper to empty me to do all the electrics, metal free fittings for air handling, metal free plumbing etc otherwise I would have to stand and watch over (and argue with contractors). The result was a lab with minimal metal and ~10x cleaner than a hospital operating theatre. There is no way, with OHS etc, this could happen today.

I then went on and refitted/refurbished a number of other labs to varying degrees of dust freeness. I also worked overseas in various dust free labs in Europe and the US.

In 1999 a group of use designed and had built a $2 million 400 square metre x 4m high containment space containing 8 large 6.5 x 4m ultra clean labs inside the containment space. The facility contained over 70, 99.9997% at <0.3 micron HEPA filters. The result was some spaces in the labs were up to 100X cleaner than the best hospital operating theatres. The most impressive KPI was the recovery time. If the building was breached or someone like tradie walked into the facility with dirty clothes and boots the air quality could recover itself in 20 minutes and inside the pods in 8 minutes - normally it takes hours to days to remove The dust.
The main air intake fan delivered 11.2 m^3/s of cleaned air into that 400 sq meter space.
The 70 odd HEPAs recycled and clean 56000 CFM of air 24/7. It had an on-line dust particle monitoring system that could pick up if someone removed their head covering or did something stupid - it was able to pick up several prospective fires before they got started because of plastic breakdown under heat. It was a very fun project to work on.

From all this I learned way more than I needed about HVA and dust control and measurement - it took a while to connect all this to wood dust in my home workshop where I was up to my ankles in it and even lost my sense of smell for 6 week when working with MDF. These days I'm retired, do experiments on ducting and DC etc and consult for free to local mens sheds about dust.

Bob, have you found hose size as a variable in the noise level equation? I recall testing the sound level of my 2 hp CT with 4" hoses as 85 dB. I was surprised when I switched to 5" hoses to experience what I thought was a subjective lowering of the noise level. As I result I measured this again, and discovered that the levels had indeed dropped to about 80dB. Subjectively, with 4 " hoses, the DC was too loud, and yet with the 5" hoses it was bearable without hearing protection (of course the table saw was around 90dB, so it did not make any practical difference).

Regards from Perth

Derek

Very impressive resume young man [emoji106] pioneering PS1and PS2 clean rooms by the sounds of it.
Biggest issue with these rooms is leakage, when built by unknowing Builders, powerpoints and light switches having the biggest leaks.

My most interesting project was air filtration of a contraceptive pill mixing lab, was 100% outside air so the exhaust air was heavily laden with dust, so had to be filtered to be suitable for release outside the building. Apparently the dust when ingested by men would increase estrogen levels and had weird side effects.
Anyway the exhaust air had to be extracted with high pressure fans rated at 2000pa so class F7 prefilters and then HEPA filters could be used. The hepa and pre-filters were within bag-in/bag-out housings, so the filters could be replaced without exposing the techs to the dust. Needless to say, oh&s requirements still required the techs to use fully sealed body suits with body worn scrubbers. Interesting project.

But we digressed lol


Sent from my iPhone using Tapatalk

Originally Posted by derekcohen

Bob, have you found hose size as a variable in the noise level equation? I recall testing the sound level of my 2 hp CT with 4" hoses as 85 dB. I was surprised when I switched to 5" hoses to experience what I thought was a subjective lowering of the noise level. As I result I measured this again, and discovered that the levels had indeed dropped to about 80dB. Subjectively, with 4 " hoses, the DC was too loud, and yet with the 5" hoses it was bearable without hearing protection (of course the table saw was around 90dB, so it did not make any practical difference).

Regards from Perth

Derek

Derek, the larger hose reduces the static pressure on the fan, therefore it works less, and then noise level drops


Sent from my iPhone using Tapatalk

Thanks RM. Interesting. So one of the benefits from increasing hose size (think 6") is lowered noise.

Regards from Perth

Derek

Originally Posted by derekcohen

Thanks RM. Interesting. So one of the benefits from increasing hose size (think 6") is lowered noise.

Regards from Perth

Derek

Indeed, it also lowers motor kW and that lowers running amps which saves your back pocket. Fan is less stressed so lasts longer as bearings aren’t run too hard.
Having said that, too large a hose/duct reduces air velocity which means less dust carrying ability, so there’s a fine line


Sent from my iPhone using Tapatalk

Originally Posted by Runningman

Very impressive resume young man [emoji106] pioneering PS1and PS2 clean rooms by the sounds of it.
Biggest issue with these rooms is leakage, when built by unknowing Builders, powerpoints and light switches having the biggest leaks.

Thanks RM.
Whilst we tried for reasonably air tight all our labs except one were over pressured with super clean air so if they leaked it didn't matter as long as they didn't leak too much and we could maintain sufficient air pressure. Two of the labs were run at between -10 to -18ºC which was where the polar ice cores were decontaminated.

The only lab that was underpressured was one of teh modules where we cleaned the lab ware in baths of dilute nitric acid. The other thing done in that lab was bank of 6 fume hoods where we distilled out own super pure acids. HCl, HF, HNO3 etc. This lab has sincebeen shut down as it has been deemed too dangerous.

My most interesting project was air filtration of a contraceptive pill mixing lab, was 100% outside air so the exhaust air was heavily laden with dust, so had to be filtered to be suitable for release outside the building. Apparently the dust when ingested by men would increase estrogen levels and had weird side effects.
Anyway the exhaust air had to be extracted with high pressure fans rated at 2000pa so class F7 prefilters and then HEPA filters could be used. The hepa and pre-filters were within bag-in/bag-out housings, so the filters could be replaced without exposing the techs to the dust. Needless to say, oh&s requirements still required the techs to use fully sealed body suits with body worn scrubbers. Interesting project.

Sure sounds like it.

But we digressed lol

Unfortunately we do - often

Originally Posted by derekcohen

Thanks RM. Interesting. So one of the benefits from increasing hose size (think 6") is lowered noise.

Of course reducing noise with a large hose means if you can it's tempting to crank up the fan speed which gets you back to square one.

Noise is good reason for using a variable speed fan or a 3P motor with a VFD.
During my recent upgrade to a 3P motor and VFD I set the VFD up with 3 preset speeds.

60, 50 and 40Hz (plus I can dial in anywhere from about 5Hz to 65Hz).

The 50Hz is normal operation - the rushing around of the air especially into open ended Bell mouth hoods is quite loud and somewhat distracting but ear muffs are not needed.

For really dust operations 60Hz really pulls the air through but its loud enough to warrant using muffs just for the air rush noise so it's not used often.

The 40Hz is whisper quiet in comparison but is more than enough for some operations and general ventilation of residual dust.

Originally Posted by derekcohen

Bob, have you found hose size as a variable in the noise level equation?

I can generate an equation for you if you like?
I should have done it while testing all those flexies in 2017.

Hose noise also depends on factors like how floppy/elastic the hose is, and the shape and geometry of the corrugations.
The stiffer the hose is the better less restrictive it is and give other things being equal to less noise - I'd like t explore all that a bit more some time.

Runningman you are probably aware of the cyclones sold by Clearvueoz but if not here is the link.
Clearvueoz.com.au | Dust Extraction & Collection | Woodwork | Air quality
Generally at the top of the food chain of home shop dust collectors. They are based on the work of Bill Pentz.
Dust Collection Research - Home

With your background you might want to skip the ones Carbatec and Hafco market for the better machines. They are louder and most people enclose them to control the noise. There is lots in this forum about that.

Pete
I have a very unimpressive resume.