Hi All,

I've bought a little (9cfm / 50l) workshop compressor and as with all
the cheaper jobbies it's not exactly quiet (I've also heard noisier).

So, I thought of making a cover / enclosure for it, probably 18mm MDF
that will probably just sit over the top, plenty of clearance, with a
foam seal where it touches the floor (to make it sit still and steady
more than anything else).

I was going to make suitable ventilation holes with sound baffles at
the back and a lift off front panel at the front (also with holes and
baffles) and possibly a Perspex viewing window (to see the gauges).

The front will easily lift off (magnetic catches?) to allow the
compressor to be wheeled out for use elsewhere, oil checks and water
draining etc.

If it seems to get too warm in there I could also make it thermostatic
/ fan assisted (120mm PC style but 240V fans etc).

So, assuming someone hasn't already tried similar and found it doesn't
work, or has an easier alternative [1], is there a cheap but good
sound absorbing material I could line this box with please?

All the best ..

T i m

[1] There is nowhere else (like outside) I can easily put this (atm
anyway).

T i m wrote:

So, assuming someone hasn't already tried similar and found it doesn't
work, or has an easier alternative [1], is there a cheap but good
sound absorbing material I could line this box with please?

About the cheapest is to use a double-skin plywood construction and fill
the gap with dry sand. It makes it very heavy, so you'd not want to move
it.

A lot of noise will still escape via the ventilation and you would need
baffles to suppress the noise.

Less cheap, but more effective, is the acoustic foam/lead sandwich used
to soundproof engine compartments on boats. There's also a version with
a plastic interlayer rather than lead, less effective but cheaper and
lighter.

You could, at a pinch, try the bituminous "anti-drumming" panels fitted
to cars to reduce noise. I've tried using the butuminous self-adhesive
underfelt that goes under roofing felt and while it makes a compartment
"dead" it doesn't provide much isolation.

The basic requirements are mass, some ability to move with the sound
wave but to damp that movement rapidly, and a substance that doesn't
reflect sound.

Oh, BTW, when you design your enclosure, check the flywheel of the
compressor. These are usually designed to act as a cooling fan as well
as a pulley/flywheel. You will need to exhaust the hot air and provide
for admission of cold air, preferably directed onto the warm bits.

On Wed, 13 Aug 2008 10:43:26 +0100, (Steve Firth)
wrote:

T i m wrote:

So, assuming someone hasn't already tried similar and found it doesn't
work, or has an easier alternative [1], is there a cheap but good
sound absorbing material I could line this box with please?

Hi Steve,

About the cheapest is to use a double-skin plywood construction and fill
the gap with dry sand. It makes it very heavy, so you'd not want to move
it.

Hmm, that sounds like it would work well but might be a bit ott for
now.

A lot of noise will still escape via the ventilation and you would need
baffles to suppress the noise.

Understood. I was going to just place another piece of (say) MDF over
the exit hole so the air could get out freely but the sound might not
(so much). What I'll probably design by mistake is a tuned port AT the
main frequency of the compressor! :-(

Less cheap, but more effective, is the acoustic foam/lead sandwich used
to soundproof engine compartments on boats. There's also a version with
a plastic interlayer rather than lead, less effective but cheaper and
lighter.

Oh, not heard of that one before? So would this still be used as a
lining Steve or is it something I could actually build the enclosure
with?

You could, at a pinch, try the bituminous "anti-drumming" panels fitted
to cars to reduce noise.

Ah, I've got some of them and have successfully used them to 'deaden'
PC / Servers etc.

I've tried using the butuminous self-adhesive
underfelt that goes under roofing felt and while it makes a compartment
"dead" it doesn't provide much isolation.

Ah, and that's the bit I guess I don't fully understand.

The basic requirements are mass, some ability to move with the sound
wave but to damp that movement rapidly, and a substance that doesn't
reflect sound.

Ok, right, so the last bit (reflection) could be dealt with by using
egg boxes type of thing? Is there an alternative to egg boxes that
would be in more of a panel form .. like that 1/2" thick pin board
material (or is that still too flat)?

I understand the mass bit (concrete bunker etc) but I wasn't aware of
the 'ability to move with the sound' bit (although it makes sense).
This is like a crumple zone on a car, absorbing the energy before it
can get to the important bits (but non sacrificial)?

Oh, BTW, when you design your enclosure, check the flywheel of the
compressor. These are usually designed to act as a cooling fan as well
as a pulley/flywheel. You will need to exhaust the hot air and provide
for admission of cold air, preferably directed onto the warm bits.

Understood (and good thinking) but this is one of the direct drive
types with no obvious flywheel Steve. Coweled motor with built in fan,
air from that generally also blowing over the twin cylinder pump. I
would arrange the exhaust at the top back (in this exhaust airflow)
and the inlet at the front bottom, so convection would also help keep
things cool. If not then extra fans to be added to push or extract (or
both).

All the best and thanks. ;-)

T i m

T i m wrote:

On Wed, 13 Aug 2008 10:43:26 +0100, (Steve Firth)
wrote:

T i m wrote:

So, assuming someone hasn't already tried similar and found it doesn't
work, or has an easier alternative [1], is there a cheap but good
sound absorbing material I could line this box with please?

Hi Steve,

Good Morning/Afternoon T i m.

[snip]

Less cheap, but more effective, is the acoustic foam/lead sandwich used
to soundproof engine compartments on boats. There's also a version with
a plastic interlayer rather than lead, less effective but cheaper and
lighter.

Oh, not heard of that one before? So would this still be used as a
lining Steve or is it something I could actually build the enclosure
with?

It's just a lining so you would have to build an enclosure.

http://www.marinemegastore.com/categ...undproofing-EN
GIMP004.htm

Has some examples of the material.

It's really not cheap, so probably won't meet your requirement.

[snip]

Ok, right, so the last bit (reflection) could be dealt with by using
egg boxes type of thing? Is there an alternative to egg boxes that
would be in more of a panel form .. like that 1/2" thick pin board
material (or is that still too flat)?

There are things like strawboard (which used to be used as pin board)
which absorb some sound. Like egg boxes they could be a fire risk.

I understand the mass bit (concrete bunker etc) but I wasn't aware of
the 'ability to move with the sound' bit (although it makes sense).
This is like a crumple zone on a car, absorbing the energy before it
can get to the important bits (but non sacrificial)?
[snip]


Yes that's what you're after. Some movement but quickly damped so it
doesn't travel from the inside to the outside of the enclosure. An old
technique where there's room to do it is to have a series of hanging
curtains of sound absorbent material. That won't work for an enclosure
though.

In message , Steve Firth
writes
It's just a lining so you would have to build an enclosure.

http://www.marinemegastore.com/categ...undproofing-EN
GIMP004.htm

Has some examples of the material.

It's really not cheap, so probably won't meet your requirement.

We built a boat, so I was familiar with this lead or plastic foam
sandwich lining material. Didn't actually use it on the boat, but did
use some to assemble a soundproof box for a PC. The 'design' was
basically a chimney of lined ply with top and bottom 'labyrinth' air
intake/outlets that could be lifted off for access.
Normal sound level meters don't work at low levels for this sort of
application, but we measured the attenuation with a decent microphone
into some audio software. I can't remember the figures, but they showed
that it worked well.
The material that I used was bought from a boat jumble as offcuts. I
think, but am not certain, that you need to seek out big enough offcuts
to use a single sheet for each panel. I certainly didn't pay prices
anything like those shown on the website referred to here.

This acoustic box showed that it could be done, but made access to the
PC a bit awkward ( e.g. the chimney had to be lifted off if access was
required to the CD-writer). Now when I need to run a noisy PC, I remote
control it from a laptop in the studio and put it as far away as
necessary.

Hope this is of interest, if not help.
--
Bill

On Aug 13, 10:22*am, T i m wrote:
Hi All,

I've bought a little (9cfm / 50l) workshop compressor and as with all
the cheaper jobbies it's not exactly quiet (I've also heard noisier).

So, I thought of making a cover / enclosure for it, probably 18mm MDF
that will probably just sit over the top, plenty of clearance, with a
foam seal where it touches the floor (to make it sit still and steady
more than anything else).

I was going to make suitable ventilation holes with sound baffles at
the back and a lift off front panel at the front (also with holes and
baffles) and possibly a Perspex viewing window (to see the gauges).

The front will easily lift off (magnetic catches?) to allow the
compressor to be wheeled out for use elsewhere, oil checks and water
draining etc.

If it seems to get too warm in there I could also make it thermostatic
/ fan assisted (120mm PC style but 240V fans etc).

So, assuming someone hasn't already tried similar and found it doesn't
work, or has an easier alternative [1], *is there a cheap but good
sound absorbing material I could line this box with please?

All the best ..

T i m

[1] There is nowhere else (like outside) I can easily put this (atm
anyway).


I've done this several times with various equipment, and its not hard
to get very good NR figures.

A really effective sound absorbing box needs a few features.

First it needs as much rigidity as possible. Any bending that occurs
conducts sound from inside to outside, so you want to minimise that.
So the first thing is to start with a stiff material. MDF is poor in
this respect, 1" chip would be better.

Now no liftable wooden box is going to be fully rigid, so the next
thing to do is to damp it. The cheapest material I've found works well
for this is triplewall cardboard. Its free and very easy to work with.
2 layers of standard twinwall also works similarly. Another option is
2 layers of carpet, which does an additional job described later, so
is more effective.

Now that you've got your stiff box, the next job is to make the input
and output airpaths go round as many corners as possible. Each time it
turns a corner the sound level drops. Baffles are the main way. You
can also add something I dont know how to describe in words... its a
ring of thin (eg half x half) wood around the inside of any air port,
and this wood is all quarter to half an inch away from the box rather
than against it. It makes much of the interior noise turn another
corner or 2 to get out.

Finally, and importantly, you want the air in the box to go through a
sieve like structure to further quieten it. This can be achieved by
lining the box interior with 2 layers of carpet. Where its ok
appearance wise, another exterior carpet lining creates further small
scale baffling, adding more NR.

Last time I did this I was very surprised by how much NR resulted, and
my best guesstimate was about 40dB. I had designed a more elaborate
structure, but once this first box was in place it was clear nothing
more was needed.

Where fire risk is an issue, rockwool is fireproof. Improved box
rigidity is achieved by gluing bits fo sheet material onto the box,
inside or out. These can be just scrap pieces and don't need to be in
any way accurately cut, if you have an offcut and it goes on, just
glue it on. A few screws hold it while the glue sets.

Perspex has litle rigidity and cant be lined. The thicker the acrylic
the better, and a double glazed window would perform better than
single.


NT

On Aug 13, 3:46*pm, wrote:
On Aug 13, 10:22*am, T i m wrote:



Hi All,

I've bought a little (9cfm / 50l) workshop compressor and as with all
the cheaper jobbies it's not exactly quiet (I've also heard noisier).

So, I thought of making a cover / enclosure for it, probably 18mm MDF
that will probably just sit over the top, plenty of clearance, with a
foam seal where it touches the floor (to make it sit still and steady
more than anything else).

I was going to make suitable ventilation holes with sound baffles at
the back and a lift off front panel at the front (also with holes and
baffles) and possibly a Perspex viewing window (to see the gauges).

The front will easily lift off (magnetic catches?) to allow the
compressor to be wheeled out for use elsewhere, oil checks and water
draining etc.

If it seems to get too warm in there I could also make it thermostatic
/ fan assisted (120mm PC style but 240V fans etc).

So, assuming someone hasn't already tried similar and found it doesn't
work, or has an easier alternative [1], *is there a cheap but good
sound absorbing material I could line this box with please?

All the best ..

T i m

[1] There is nowhere else (like outside) I can easily put this (atm
anyway).

I've done this several times with various equipment, and its not hard
to get very good NR figures.

A really effective sound absorbing box needs a few features.

First it needs as much rigidity as possible. Any bending that occurs
conducts sound from inside to outside, so you want to minimise that.
So the first thing is to start with a stiff material. MDF is poor in
this respect, 1" chip would be better.

Now no liftable wooden box is going to be fully rigid, so the next
thing to do is to damp it. The cheapest material I've found works well
for this is triplewall cardboard. Its free and very easy to work with.
2 layers of standard twinwall also works similarly. Another option is
2 layers of carpet, which does an additional job described later, so
is more effective.

Now that you've got your stiff box, the next job is to make the input
and output airpaths go round as many corners as possible. Each time it
turns a corner the sound level drops. Baffles are the main way. You
can also add something I dont know how to describe in words... its a
ring of thin (eg half x half) wood around the inside of any air port,
and this wood is all quarter to half an inch away from the box rather
than against it. It makes much of the interior noise turn another
corner or 2 to get out.

Finally, and importantly, you want the air in the box to go through a
sieve like structure to further quieten it. This can be achieved by
lining the box interior with 2 layers of carpet. Where its ok
appearance wise, another exterior carpet lining creates further small
scale baffling, adding more NR.

Last time I did this I was very surprised by how much NR resulted, and
my best guesstimate was about 40dB. I had designed a more elaborate
structure, but once this first box was in place it was clear nothing
more was needed.

Where fire risk is an issue, rockwool is fireproof. Improved box
rigidity is achieved by gluing bits fo sheet material onto the box,
inside or out. These can be just scrap pieces and don't need to be in
any way accurately cut, if you have an offcut and it goes on, *just
glue it on. A few screws hold it while the glue sets.

Perspex has litle rigidity and cant be lined. The thicker the acrylic
the better, and a double glazed window would perform better than
single.

NT


PS you can also get more NR by damping the parts of your equipment
that dont need to dissipate heat away. The pressure vessel acts as a
sounding board for the compressor, and damping can much reduce that.

I cant imagine mag catches doing the job, not tried them though in
this app

On Wed, 13 Aug 2008 07:58:58 -0700 (PDT), wrote:


So, I thought of making a cover / enclosure for it, probably 18mm MDF
that will probably just sit over the top, plenty of clearance, with a
foam seal where it touches the floor (to make it sit still and steady
more than anything else).


Well, thanks very much Steve, Bill and NT (so far) ;-)

I think I've got the idea of what's needed now and will get some bits
together and experiment.

Luckily a mate is a carpenter and will have his table saw up soon so
I'll be able to get some nice panels cut up easily. I'll make a point
of not throwing away the off cuts. ;-)

Also it seems I can do this in stages to some degree, starting with
the box then looking at internal and possibly external coverings.

I'm not looking to make this thing silent and I'm also aware I still
need to let it breathe and have access to it myself, so as normal it's
bound to be a compromise.

Anyway, thanks again and I'll post back my real life results as / when
I can. ;-)

All the best ..

T i m

On Wed, 13 Aug 2008 10:22:56 +0100, T i m wrote:

I've bought a little (9cfm / 50l) workshop compressor and as with all
the cheaper jobbies it's not exactly quiet (I've also heard noisier).

Listen to your compressor. Why is it noisy? Which part of your
compressor is making the most racket? No point in silencing something
that's already quiet in your case.


Remove the air filter (if it's a nasty plastic thing, throw it away)

Replace it a length of steel pipe into a large heavy vessel (recycled
fire extinguisher shell works) then a length of pipe into a filter box,
either the original or something recycled from a car scrapyard.

What you've made here is a buffer chamber to even out pressure changes
in the inlet. Much of the inlet noise is because of the "pulsing" effect
of this on the inlet holes of the filter from the atmosphere. Less
pulsing, even though the total airflow remains the same, can be much
quieter.


Unbolt the compressor / motor from the tank and fasten them to a welded
steel subframe (unless it's a direct drive) and mount this subframe on
the old tank-mounted frame via some anti-vibration. I use strips of
rubber / canvas coal mine conveyor belt. This stops the tank being a
soundboard. Make sure the subframe is rigid, as a compressor that rocks
back and forth is not only noisy, it can also fracture pipe.


As for a soundproof enclosure, then that's a last resort. Needs to be
big if it's not to overheat. If you have a solid brick wall handy, put
it on the other side of that and run some extra plumbing. It's easier to
make an outdoor shed than an indoor sound enclosure.


--
Cats have nine lives, which is why they rarely post to Usenet.

On Thu, 14 Aug 2008 03:01:01 +0100, Andy Dingley
wrote:

On Wed, 13 Aug 2008 10:22:56 +0100, T i m wrote:

I've bought a little (9cfm / 50l) workshop compressor and as with all
the cheaper jobbies it's not exactly quiet (I've also heard noisier).

Listen to your compressor. Why is it noisy? Which part of your
compressor is making the most racket?

The motor and pump mainly, although the cooling fins on the pipe
between the pumps and cylinder buzz a bit (but that is less energy and
could be silenced quite easily).

No point in silencing something
that's already quiet in your case.

Indeed.

Remove the air filter (if it's a nasty plastic thing, throw it away)

There are two, with foam inserts.

Replace it a length of steel pipe into a large heavy vessel (recycled
fire extinguisher shell works) then a length of pipe into a filter box,
either the original or something recycled from a car scrapyard.

I understand your logic here but part of why I bought this model was
that it was portable (in the wheelbarrow use of the term).

What you've made here is a buffer chamber to even out pressure changes
in the inlet. Much of the inlet noise is because of the "pulsing" effect
of this on the inlet holes of the filter from the atmosphere. Less
pulsing, even though the total airflow remains the same, can be much
quieter.

I think it's the pump itself making most the noise in this case.


Unbolt the compressor / motor from the tank and fasten them to a welded
steel subframe (unless it's a direct drive) and mount this subframe on
the old tank-mounted frame via some anti-vibration.

I did think of isolating the dd motor / pump from the cylinder but
would then need a flexi hose on the outlet from the pump.

I use strips of
rubber / canvas coal mine conveyor belt. This stops the tank being a
soundboard. Make sure the subframe is rigid, as a compressor that rocks
back and forth is not only noisy, it can also fracture pipe.

Understood.


As for a soundproof enclosure, then that's a last resort. Needs to be
big if it's not to overheat.

Yup. I was going to make a box as big as the space at the end of my
bench allowed. It would roll into it like a dog going into a kennel
then the door goes on after.

If you have a solid brick wall handy, put
it on the other side of that and run some extra plumbing. It's easier to
make an outdoor shed than an indoor sound enclosure.

I have some solid pre-fab concrete garage panels g but no space
around it for anything external (it's at the bottom of the garden and
the full width of said garden). The back goes onto a private access
way.

The good thing about this particular model is it's pretty fast, so
from switching on to being up to pressure is less that a minute.

http://tinyurl.com/5pv8zf

From low pressure back to full about 10 seconds. My mate has a much
bigger cylinder and once his has cut back in it seems to clatter away
for hours, even with no air being drawn off.

No, all I'm trying to do here is just take the edge off the sound as
much as possible without making it project 1874532 in my ever
lengthening list. :-(

All the best ..

T i m

I agree, and external brick built enclosure would probably be the best
noise wise (for me in the garage anyway) ;-)