Thread: More on dust extractor noise

Actually I have just realised, the small holes are actually part of the sound deadening scenario.

Our local primary school has a couple of fairly new transportables and the ceilings in those are made from perforated metal in a corrugated iron (Custom Orb) pattern.
It is very effective too.

Originally Posted by veloaficionado

I used BP's quick and easy muffler on my JET DC1900 blower/homemade cyclone: a 2.5 m length of 6" insulated HVAC flex-tube from the blower to the elbow taking the air outside to the DC bags/ Not too bad.

If this the stuff you are referring to?

If so it is equivalent to using regular flexy and even if it is 6" diam it would be better to use straight PVC and then clad it in that material.
That material acts like regular flexy and loses 3x more pressure than straight PVC. Also two x 45º will be better than one elbow.

Originally Posted by pjt

Over time there could be some dust enter through the holes, essentially tho, as there is (should) be no air flow into the sound absorbing mat'l it shoudn't fill up with dust, if the sound waves carried dust it might be a different matter


Pete

It won't matter if they fill with dust as the sound waves will easily penetrate the small amount of dust in the holes.

Originally Posted by BobL

It won't matter if they fill with dust as the sound waves will easily penetrate the small amount of dust in the holes.

I agree, the way I read Arron's post was not so much the holes blocking up but the dust getting into the sound absorbing mat'l, (most likely fibreglass) and thus loss of sound absorbing ability.


Pete

OK, so one of these days I'm going to sacrifice some mdf to build an experimental muffler. Is there any reason why I shouldnt build it so its one L-shaped muffler replacing the entire 5 inch pipe from impellor housing to dust-bag assembly ?

Originally Posted by Arron

OK, so one of these days I'm going to sacrifice some mdf to build an experimental muffler. Is there any reason why I shouldnt build it so its one L-shaped muffler replacing the entire 5 inch pipe from impellor housing to dust-bag assembly ?

Unfortunately That won't do much for motor noise.

Motor or impellor ?

Originally Posted by BobL

Unfortunately That won't do much for motor noise.

I should have clarified - I meant build a proper muffler with a central tube of pierced metal, layers of acoustic foam and/or sound batts, and an mdf casing.

Sorry
arron

Look forward to your results Arron. It will of course come at the cost of flow, but then again every muffler does, but just like car mufflers some a better than others. Wonder how a truck muffler would go?

Originally Posted by Arron

I read Zelk's long thread below on Reducing d/e noise and realise I need to do something like this. One thing that I noticed though was that his d/c (like mine) is sitting on a pressed steel platform. I was wondering if this contributes to the noise - like siting your d/c on a steel drum. Would it help to replace the steel base with a timber one ? Anyone tried this?
Cheers
Arron

Good Morning Arron

I cannot answer directly as regards a dust collector, but a little anecdotal story may help your thinking.

I have a wooden yacht that has a BMC Captain diesel engine that was rather noisy. The engine was bolted directly to the engine bearers and the prop-shaft was bolted to the gear box. Lots of noise; lots of vibration.

Some years ago I installed flexible mounts on the engine and a flexible coupling on the prop-shaft. These steps drastically reduced the engine noise (halved???) and drastically reduced hull vibration. It seems that the entire hull had been acting as a sonic amplifier and radiating the engine noise.

Later I installed a water-trap on the engine exhaust and this further reduced engine noise, but not as drastically. I no longer worry about its noise; normal conversation is happens with the engine running.

Then the fibreglass noise insulation in the engine box was looking rather daggy so I removed it with the intention of replacing it. The removal made virtually nil difference to the noise level, so I never put any back. The only noise insulant that I know that is really effective is the lead-sponge multi-laminate but at a cost of over $100 per m2 is rather expensive, and noise will get through any holes - not airtight, not noise proof.

It is possible that your engine and fan noises are entering the structure of your dusty and the entire structure is amplifying and radiating that noise.

Fair Winds

Graeme

Originally Posted by GraemeCook

Some years ago I installed flexible mounts on the engine and a flexible coupling on the prop-shaft. These steps drastically reduced the engine noise (halved???) and drastically reduced hull vibration. It seems that the entire hull had been acting as a sonic amplifier and radiating the engine noise.

Very interesting stuff Graeme.
I had a similar problem with my DC attached to my DC housing - I decoupled the DC so that it became free standing and it improved things a little.

Later I installed a water-trap on the engine exhaust and this further reduced engine noise, but not as drastically. I no longer worry about its noise; normal conversation is happens with the engine running.

This has been discussed before but just in case someone has missed it, water trap noise reduction is unsuited for hobby level DCs. Hobby level DCs are high volume low pressure devices and only have about 12" of H20 pressure to begin with and need every inch of that to efficiently collect dust. If water trap is used - even a few inches it will rob the DC of the much needed pressure.

The only noise insulant that I know that is really effective is the lead-sponge multi-laminate but at a cost of over $100 per m2 is rather expensive, and noise will get through any holes - not airtight, not noise proof.

The lead provides a lot of sheer mass in a small volume so if volume is not an issue it does not have to be lead. A thick wall of concrete or really thick wall of wood will be just as effective as lead. A multilayered wood cardboard wall is surprisingly effective especially if care is taken as to how the layers are attached to each other.

Originally Posted by Arron

OK, so one of these days I'm going to sacrifice some mdf to build an experimental muffler. Is there any reason why I shouldnt build it so its one L-shaped muffler replacing the entire 5 inch pipe from impellor housing to dust-bag assembly ?

I would not make it L shaped, bad for airflow, best if made lobster back fashion, the normal thing for making large radius bends in large (500mm+) pipework, google it if you need to see what I'm talking about.

As for how long and whether noise reduction would benefit from being longer I'd say yes but my guess would be that there would be some sort of exponential drop off in actual noise reduced v's length, meaning that the first ft of muffler does more than the 2nd ft and the next two ft does even less than the first two ft, Bob will know I reckon or be able to find a reference/chart or....... say I'm talking absolute shyte which could be.

I reckon your best bet is to look into the best type of sound absorbing mat'l specifically to attenuate (deaden) actual frequency/ampltude produced by the exhaust, there maybe some info on BP's site on this, thickness required, size of holes in side muffler (open area as a % in sheet metal) stuff like that.


Pete

Originally Posted by BobL

A multilayered wood cardboard wall is surprisingly effective especially if care is taken as to how the layers are attached to each other.

This sounds a bit interesting Bob, is this layers of wood/cardboard/wood kinda thing


Pete

Originally Posted by pjt

This sounds a bit interesting Bob, is this layers of wood/cardboard/wood kinda thing

Correct. It's not my idea, it's been around a while and I think it is Chris Parks that tried it with his DC enclosure.

If you look up acoustic bats they make a big deal about how they should installed. This is because acoustic bats by themselves don't do much unless the supporting structure is properly designed and constructed.
One design that produces a very high level of sound reduction is a 3 layer sandwich consisting of
1) a standard plaster stud wall
2) bats attached to an internal stud wall - ie not attached to 1) or 3)
3) a second standard plaster stud wall

Replace bats with cardboard and a similar effect can be obtained.