Advice on Decibels and Dust Extraction please

[keithy1959]

I have a basic Charnwood chip extracter linked up to a Thein seperator in the corner of the workshop connected to some 38mm hose and it makes a horrible din, so today I enclosed it in some 50mm polystyrene sheet and some scrap MDF. Using an Android app, I measured the decibel level before and after, and somewhat puzzled that the before was 72db, and the after was 78db.

I did three readings over 5 minutes before and after, phone in same place , and the readings were consistent

There is a noticeable different in pitch ( not such a whine) making the workshop more confortable, and making the time I spent worthwhile, but I don't understand how the decibels can go up. Its not a big issue, obviously, but any thoughts very welcome.

Richard

 

[Racers]

Uncalibrated microphone with a uneven frequency response would be my best guess.

Pete

 

[thetyreman]

you should be measuring this in dBA so that you are measuring average levels, I use the decibel x app on my iphone which is free.

try measuring again using that method if possible.

 

[Rich C]

Phone mics are terrible for measuring sound levels, they clip at a relatively low level so it's possible it couldn't measure some of the frequencies on the before correctly and was giving a false reading. I have a cheap sound meter and even that is massively better than a phone.

Also 72 dB isn't loud so that seems a bit suspicious.

 

[Osvaldd]

You created a resonant chamber. Think of a loudspeaker vs loudspeaker in a cabinet. You dulled the high frequencies but amplified the low/mids. Does it actually sound louder to you?

 

[Jacob]

They are bloody noisy and speaking as a deafish person I'd definitely advise investing in good ear muffs with all machines or you'll end up the same.
The problem of noise leakage to the outside is often less severe than you might imagine from within a noisy workshop. Check - switch everything on and wander out, with doors windows closed.

 

[thetyreman]

Phone mics are terrible for measuring sound levels, they clip at a relatively low level so it's possible it couldn't measure some of the frequencies on the before correctly and was giving a false reading. I have a cheap sound meter and even that is massively better than a phone.

Also 72 dB isn't loud so that seems a bit suspicious.

they're perfectly fine for measuring noise levels, I only mentioned it as well because most people have access to one and the app I mentioned, saves him having to go and buy an SPL meter.

 

[sunnybob]

Osvald has it.
You have only cut the high frequencies, and a sound meter measures amount of noise power, which is always the base notes.
High frequencies feel louder because they hurt your ears more.
A proper cabinte, made of at least 22 mm MDF, with either diamond foam or old blankets covering the inside will dramatically reduce your noise level. But dont make it airtight, there has to be an exhaust tunnel

 

[Jonathan S]

Is it the hose that is creating the noise?
I would of thought 38mm hose on a chip extractor would make the hose a whistle....



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[keithy1959]

Thanks for all the feedback. I now understand what is going on

I am sure there are issues with a free phone based decibel meter, and I understand that the readings are probably not accurate, but what interested me was the relative increase, and not decrease in "volume". The phone was approx 3.5-4M from the extractor.

I have deafness at some lower frequencies, so I dont think I would hear an increase in volume - but I have noticed a reduction at the top end.

The hose itself doesn't seem to thrum, but there is a fair old whistle at the end of the hose !!

The polystyrene seems pretty ineffectual, so I may try some old blankets if I can find some. One of the outside walls is overlap cladding, and I have a vent above the box, so I'm reasonably confident there is enough ventilation in there.

Thakns again for your comments

Richard