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REQ: Low frequency sound absorbtion
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Rene Tschaggelar
science forum beginner


Joined: 25 Aug 2005
Posts: 12

PostPosted: Sat May 06, 2006 6:09 pm    Post subject: REQ: Low frequency sound absorbtion Reply with quote

Hello,

I am trying to make a room as quiet as (reasonably) possible,
especially below 200 Hz.

The room is a laboratory about 6m wide by 8m long by 4m high. The
floor is linoleum, the ceiling is exposed concrete (and lots of ducts
and pipes), and the walls are 12mm sheetrock on metal studs.

There is a scanning electron microscope in the room. The quieter we
can make the room the better images we get.

I have read older posts, especially by Eric Desart, about using rigid
fiberglass panels, such as Owens-Corning 705. This appears to be the
best solution so far. We are also concerned about flammability
particle generation, and outgassing.

I would appreciate any advice on methods and arrangement of applying
the panels and alternative materials.

Rebuilding the walls is not an option at this time but may be in the
future.

Thank You
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Angelo Campanella
science forum Guru Wannabe


Joined: 08 May 2005
Posts: 226

PostPosted: Sat May 06, 2006 7:23 pm    Post subject: Re: REQ: Low frequency sound absorbtion Reply with quote

none wrote:
Quote:
I have read older posts, especially by Eric Desart, about using rigid
fiberglass panels, such as Owens-Corning 705. This appears to be the
best solution so far. We are also concerned about flammability
particle generation, and outgassing.

That will help. At high frequwenies (500 Hz up) any acousical absorber
works fine. But for lowe frequencies, the geomtry of theinstalled
material beome increasingly inpotant as the frequency lowers.
Ultimately, furred materals mus be used, and the furring depth can be
4"-6" and more at the lowest frequencies. "Wedges", though trndy, really
con't help and are certainly never cost effective.
Quote:

I would appreciate any advice on methods and arrangement of applying
the panels and alternative materials.

The ceiling is usually an arguable choice because of logistics, though
the conventional suspended grid acoustical ceiling is always welcome in
these matters. That shuld be your first priority.
Quote:

Rebuilding the walls is not an option at this time but may be in the
future.

Well, there you have it.

Let us know which ceiling configurations your management will tolerate.

If not that, then hanging baffles are your only choice.

Or you can operate late at night when no one is around and you can turn
off the HVAC during critical runs...

se la vie.

Angelo Campanella
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TheGhost
science forum addict


Joined: 09 Aug 2005
Posts: 85

PostPosted: Sat May 06, 2006 7:31 pm    Post subject: Re: REQ: Low frequency sound absorbtion Reply with quote

none <none@none.net> wrote in news:Xns97BB8FEF9315D5454125@69.28.186.121:

Quote:
Hello,

I am trying to make a room as quiet as (reasonably) possible,
especially below 200 Hz.

The room is a laboratory about 6m wide by 8m long by 4m high. The
floor is linoleum, the ceiling is exposed concrete (and lots of ducts
and pipes), and the walls are 12mm sheetrock on metal studs.

There is a scanning electron microscope in the room. The quieter we
can make the room the better images we get.

I have read older posts, especially by Eric Desart, about using rigid
fiberglass panels, such as Owens-Corning 705. This appears to be the
best solution so far. We are also concerned about flammability
particle generation, and outgassing.

I would appreciate any advice on methods and arrangement of applying
the panels and alternative materials.

Rebuilding the walls is not an option at this time but may be in the
future.

Thank You


You may want to consider the possibility that the cause of the problem is
structure-borne vibration. If it is, reducing sound level will reduce an
effect (sound) but will not reduce cause (vibration) of the problem.

If low-frequency airborne sound is indeed the problem, rather than reducing
the level of low-frequency sound in the entire room, you may want consider
the possibility of using active noise cancellation around only the
sensitive area of the microscope.
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Rene Tschaggelar
science forum beginner


Joined: 25 Aug 2005
Posts: 12

PostPosted: Sun May 07, 2006 3:18 pm    Post subject: Re: REQ: Low frequency sound absorbtion Reply with quote

Angelo Campanella <a.campanella@att.net> wrote in
news:zI67g.32861$Fs1.27284@bgtnsc05-news.ops.worldnet.att.net:

Quote:
none wrote:
I have read older posts, especially by Eric Desart, about
using rigid fiberglass panels, such as Owens-Corning 705.
This appears to be the best solution so far. We are also
concerned about flammability particle generation, and
outgassing.

That will help. At high frequwenies (500 Hz up) any acousical
absorber works fine. But for lowe frequencies, the geomtry of
theinstalled material beome increasingly inpotant as the
frequency lowers. Ultimately, furred materals mus be used, and
the furring depth can be 4"-6" and more at the lowest
frequencies. "Wedges", though trndy, really con't help and are
certainly never cost effective.

I would appreciate any advice on methods and arrangement of
applying the panels and alternative materials.

The ceiling is usually an arguable choice because of logistics,
though the conventional suspended grid acoustical ceiling is
always welcome in these matters. That shuld be your first
priority.

Rebuilding the walls is not an option at this time but may be
in the future.

Well, there you have it.

Let us know which ceiling configurations your management will
tolerate.

If not that, then hanging baffles are your only choice.

Or you can operate late at night when no one is around and you
can turn off the HVAC during critical runs...

se la vie.

Angelo Campanella

Thank you for your response.


I suppose we can install any type of ceiling. Do you think a
suspended grid ceiling would be better than hanging baffles? Can
you suggest a link that discusses hanging baffle geometry? This is
a lab so appearance is not very important. We only care about
dampening low frequency sound.

You say the geometry of the panels on the walls is important. Can
you tell me what geometry is best or suggest a link?

By furred, I assume you mean mounting the panels on spacers so
there is space between the sheetrock wall and the acoustical panel
(mounting the panels on furring strips). Is this correct?

A note to Mr. Ghost: We have measured mechanical vibration and it
is not so bad. The problem is mostly noisy machinery in adjacent
labs. After we try acoustical dampening we are going to look at
active vibration canceling.

Thank You
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Tony177
science forum Guru Wannabe


Joined: 07 Sep 2005
Posts: 111

PostPosted: Sun May 07, 2006 5:44 pm    Post subject: Re: REQ: Low frequency sound absorbtion Reply with quote

"none" <none@none.net> wrote in message
news:Xns97BC72FEDFA315454125@69.28.186.121...
Quote:
none wrote:

A note to Mr. Ghost: We have measured mechanical vibration and it
is not so bad. The problem is mostly noisy machinery in adjacent
labs. After we try acoustical dampening we are going to look at
active vibration canceling.

I think you should have an acoustic consultant on board, who should be able
to save you money or at least avoid the risk of wasting money.

For your background information, ceiling tiles can give very cost-effective
low frequency sound absorption if you choose suitable ones and leave an
appropriate spacing (usually 200 -300 mm) from the structural ceiling.
However this will not damp all modes so you will also need absorption on the
walls. The easiest way to make effective low frequency absorption is
usually to have lightweight panels over an enclosed air space with some
damping.

I would reinforce what the Ghost wrote: make quite sure that the vibration
is getting in via excitation from airborne sound, and not by direct
mechanical coupling, before spending money on room treatment. One way to
check this would be to produce sound from a loudspeaker in the room and find
how the sound level relates to deterioration of the image, then compare this
with the sound level from the interfering machinery.

Also consider that unless the room is very reverberant in the relevant
frequency range before treatment, it is not practical to make a large
reduction in reverberant sound level by adding sound absorption. How much
improvement do you need?

--
Tony Woolf
My e-mail address has no hyphen
- but please don't use it, reply to the group.
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Bruce
science forum beginner


Joined: 07 May 2006
Posts: 4

PostPosted: Mon May 08, 2006 10:31 am    Post subject: Re: REQ: Low frequency sound absorbtion Reply with quote

Rene Tschaggelar wrote:
wrote:
A note to Mr. Ghost: We have measured mechanical vibration and it
is not so bad. The problem is mostly noisy machinery in adjacent
labs. After we try acoustical dampening we are going to look at
active vibration canceling.


First, I agree with Tony, you should have an acoustical consultant on board. At least spend a few hundred dollars to make sure you don't waste thousands of dollars on the wrong solutions.

Absorption does not improve isolation. This is a very common misconception. If the room is overly live, then absorption is a good thing, but I don't believe it will solve your problem.
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Dev Null
science forum beginner


Joined: 08 May 2006
Posts: 1

PostPosted: Mon May 08, 2006 9:37 pm    Post subject: Re: REQ: Low frequency sound absorbtion Reply with quote

"Tony" <news@t-onywoolf.co.uk> wrote in
news:dmq7g.65761$wl.51574@text.news.blueyonder.co.uk:

Quote:
"none" <none@none.net> wrote in message
news:Xns97BC72FEDFA315454125@69.28.186.121...
none wrote:

A note to Mr. Ghost: We have measured mechanical vibration
and it is not so bad. The problem is mostly noisy machinery
in adjacent labs. After we try acoustical dampening we are
going to look at active vibration canceling.

I think you should have an acoustic consultant on board, who
should be able to save you money or at least avoid the risk of
wasting money.

For your background information, ceiling tiles can give very
cost-effective low frequency sound absorption if you choose
suitable ones and leave an appropriate spacing (usually 200 -300
mm) from the structural ceiling. However this will not damp all
modes so you will also need absorption on the walls. The
easiest way to make effective low frequency absorption is
usually to have lightweight panels over an enclosed air space
with some damping.

I would reinforce what the Ghost wrote: make quite sure that the
vibration is getting in via excitation from airborne sound, and
not by direct mechanical coupling, before spending money on room
treatment. One way to check this would be to produce sound from
a loudspeaker in the room and find how the sound level relates
to deterioration of the image, then compare this with the sound
level from the interfering machinery.

Also consider that unless the room is very reverberant in the
relevant frequency range before treatment, it is not practical
to make a large reduction in reverberant sound level by adding
sound absorption. How much improvement do you need?


Thank you for your response.

We have had measurements taken by the SEM manufacturer and they
indicate that the mechanical vibration is O.K. (but not great)
except for one peak around 8 Hz of 2 um/s, which is the maximum
allowed.

The noise is quite audible. We have taken measurements that show
sound peaks of ~50 dB at ~60 Hz and ~120 Hz so we would like to
minimize these. This is mostly from a large air compressor that we
plan to move and insulate.

Ideally, we would would like the sound level to be less than 35 dB
A-wtd below 200 Hz.

If I use Owens-Corning 705 panels I assume the best way to install
them is to space them away from the wall as far as possible and
place the panels in contact with each other. I can probably make
the spacers out of the 705 panels.

I would love to hire an acoustic counsultant but the administration
is very resistant about hiring outside people.

Thanks again
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Rene Tschaggelar
science forum beginner


Joined: 25 Aug 2005
Posts: 12

PostPosted: Mon May 08, 2006 9:43 pm    Post subject: Re: REQ: Low frequency sound absorbtion Reply with quote

bcOlson@YOSound-dot-com.no-spam.invalid (Bruce) wrote in
news:445f1f42$0$15474$892e7fe2@authen.yellow.readfreenews.net:

Quote:
Rene Tschaggelarwrote:
wrote:
A note to Mr. Ghost: We have measured mechanical vibration
and it is not so bad. The problem is mostly noisy machinery
in adjacent labs. After we try acoustical dampening we are
going to look at active vibration canceling.

First, I agree with Tony, you should have an acoustical
consultant on board. At least spend a few hundred dollars to
make sure you don't waste thousands of dollars on the wrong
solutions.

Absorption does not improve isolation. This is a very common
misconception. If the room is overly live, then absorption is a
good thing, but I don't believe it will solve your problem.

Thanks for this information.

I think I understand what you are saying but there has to be some way
to isolate a room from external sound sources. We just have to do
this by installing material inside our room.

An acoustical consultant would be a big help. I will suggest hiring
a consultant but I don't have much hope.
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Tony177
science forum Guru Wannabe


Joined: 07 Sep 2005
Posts: 111

PostPosted: Tue May 09, 2006 6:58 am    Post subject: Re: REQ: Low frequency sound absorbtion Reply with quote

"Dev Null" <devnull@foo.bar> wrote in message
news:Xns97BDB3279AE9477894A89C9@69.28.186.121...
Quote:

The noise is quite audible. We have taken measurements that show
sound peaks of ~50 dB at ~60 Hz and ~120 Hz so we would like to
minimize these. This is mostly from a large air compressor that we
plan to move and insulate.

If you are planning to move the interfering sources, why are you proposing
to spend money on other measures that will not be very effective?

Quote:
Ideally, we would would like the sound level to be less than 35 dB
A-wtd below 200 Hz.

The sound levels you mention add up to about 35 dB(A) already, unless those
levels are already A weighted. If they are, you have quite a long way to
go.

You also wrote in your other post:

Quote:
I think I understand what you are saying but there has to be some way
to isolate a room from external sound sources. We just have to do
this by installing material inside our room.

Acoustic design or interior decoration, your choice.

--
Tony Woolf
My e-mail address has no hyphen
- but please don't use it, reply to the group.
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Noral Stewart
science forum addict


Joined: 23 May 2005
Posts: 77

PostPosted: Tue May 09, 2006 11:09 am    Post subject: Re: REQ: Low frequency sound absorbtion Reply with quote

To reinforce what others are saying

It is usually very hard to make major improvements in low-frequency
absorption in a room.

It is difficult to get more than a few dB of noise reduction with added
absorption.

If sound is coming from elsewhere, the best route is to improve isolation -
to prevent the sound from getting into the space in the first place.

"none" <none@none.net> wrote in message
news:Xns97BDB42F7AA935454125@69.28.186.121...
Quote:
bcOlson@YOSound-dot-com.no-spam.invalid (Bruce) wrote in
news:445f1f42$0$15474$892e7fe2@authen.yellow.readfreenews.net:

Rene Tschaggelarwrote:
wrote:
A note to Mr. Ghost: We have measured mechanical vibration
and it is not so bad. The problem is mostly noisy machinery
in adjacent labs. After we try acoustical dampening we are
going to look at active vibration canceling.

First, I agree with Tony, you should have an acoustical
consultant on board. At least spend a few hundred dollars to
make sure you don't waste thousands of dollars on the wrong
solutions.

Absorption does not improve isolation. This is a very common
misconception. If the room is overly live, then absorption is a
good thing, but I don't believe it will solve your problem.

Thanks for this information.

I think I understand what you are saying but there has to be some way
to isolate a room from external sound sources. We just have to do
this by installing material inside our room.

An acoustical consultant would be a big help. I will suggest hiring
a consultant but I don't have much hope.
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