In response to comments from the reviewers and some user questions, I
have reworked my Helmholtz calculation spreadsheet - particularly the
sheet for slotted absorbers.

This tool can be downloaded from
http://www.rmmpnet.org/members/ChrisW/index.html

The main difference between this spreadsheet and other Helmholtz
spreadsheets is that I calculate an absorption curve rather than just
the device's resonant frequency. An absorption curve will give you a
much better appreciation of the performance of the absorber over an
eight octave range than a simple resonant frequency value.

As with any prediction, this is the theoretical absorption of normal
incident sound (not random incidence which would also be useful...). So
the prediction offered by this spreadsheet serves only as a guide. The
actual performance of the absorber will only be known once it has been
built and tested in situ.

I hope however, that prediction and reality are acceptably close!

Regards

Chris W

--
The voice of ignorance speaks loud and long,
but the words of the wise are quiet and few.
--

"Chris Whealy" wrote in message
...
In response to comments from the reviewers and some user questions, I
have reworked my Helmholtz calculation spreadsheet - particularly the
sheet for slotted absorbers.

Thanks! This is a very easy to use implementation.

How much detail does Cox and Antonio's book go into about this calculation?
Does it take into account resonant modes which involve more than one hole or
slot? I can see I will have to buy this book but it would be nice to know
that while I am saving up.

Also, the calculation depends on knowing the flow resistance of the damping
material. Is there any handy place where one can look up the approximate
flow resistance of commonly used mineral fibre materials?

Finally a word of warning. The panel thickness can be set as low as 1 mm.
In most configurations panels only a few mm thick would be far from rigid
and, depending on the intended frequency of operation, that could have a
very major effect on the performance.

--
Tony W
My e-mail address has no hypen
- but please don't use it, reply to the group.

Tony wrote:
Thanks! This is a very easy to use implementation.

:-) Useability always takes more effort to implement than the actual
calculations, but I think the effort is worth it!

How much detail does Cox and Antonio's book go into about this calculation?
Does it take into account resonant modes which involve more than one hole or
slot? I can see I will have to buy this book but it would be nice to know
that while I am saving up.

They go into lots of detail. The chapters are generally structured such
that they discuss a practical situation, then go through the maths, then
go through a practical implementation using the maths they've just
described. They try to give every equation a practical application,
this is why I like the book so much.

Also, the calculation depends on knowing the flow resistance of the damping
material. Is there any handy place where one can look up the approximate
flow resistance of commonly used mineral fibre materials?

There are a few (small) tables in the book, but what is more useful is
that there is a whole chapter (chapter 5) on porous absorbers, and a
whole section (5.3.1) on the various methods of calculating flow
resistivity.

Finally a word of warning. The panel thickness can be set as low as 1 mm.
In most configurations panels only a few mm thick would be far from rigid
and, depending on the intended frequency of operation, that could have a
very major effect on the performance.

This is true, therefore I have placed a caveat in the instructions that
warn about the difference between theoretical predictions and actual
performance. If I have not made this point clearly enough, then I will
reiterate it.

Chris W

--
The voice of ignorance speaks loud and long,
but the words of the wise are quiet and few.
--

Tony wrote:
Thanks! This is a very easy to use implementation.

:-) Useability always takes more effort to implement than the actual
calculations, but I think the effort is worth it!

How much detail does Cox and Antonio's book go into about this calculation?
Does it take into account resonant modes which involve more than one hole or
slot? I can see I will have to buy this book but it would be nice to know
that while I am saving up.

They go into lots of detail. The chapters are generally structured such
that they discuss a practical situation, then go through the maths, then
go through a practical implementation using the maths they've just
described. They try to give every equation a practical application,
this is why I like the book so much.

Also, the calculation depends on knowing the flow resistance of the damping
material. Is there any handy place where one can look up the approximate
flow resistance of commonly used mineral fibre materials?

There are a few (small) tables in the book, but what is more useful is
that there is a whole chapter (chapter 5) on porous absorbers, and a
whole section (5.3.1) on the various methods of calculating flow
resistivity.

Finally a word of warning. The panel thickness can be set as low as 1 mm.
In most configurations panels only a few mm thick would be far from rigid
and, depending on the intended frequency of operation, that could have a
very major effect on the performance.

This is true, therefore I have placed a caveat in the instructions that
warn about the difference between theoretical predictions and actual
performance. If I have not made this point clearly enough, then I will
reiterate it.

Chris W

--
The voice of ignorance speaks loud and long,
but the words of the wise are quiet and few.
--

Tony wrote:
Thanks! This is a very easy to use implementation.

:-) Useability always takes more effort to implement than the actual
calculations, but I think the effort is worth it!

How much detail does Cox and Antonio's book go into about this calculation?
Does it take into account resonant modes which involve more than one hole or
slot? I can see I will have to buy this book but it would be nice to know
that while I am saving up.

They go into lots of detail. The chapters are generally structured such
that they discuss a practical situation, then go through the maths, then
go through a practical implementation using the maths they've just
described. They try to give every equation a practical application,
this is why I like the book so much.

Also, the calculation depends on knowing the flow resistance of the damping
material. Is there any handy place where one can look up the approximate
flow resistance of commonly used mineral fibre materials?

There are a few (small) tables in the book, but what is more useful is
that there is a whole chapter (chapter 5) on porous absorbers, and a
whole section (5.3.1) on the various methods of calculating flow
resistivity.

Finally a word of warning. The panel thickness can be set as low as 1 mm.
In most configurations panels only a few mm thick would be far from rigid
and, depending on the intended frequency of operation, that could have a
very major effect on the performance.

This is true, therefore I have placed a caveat in the instructions that
warn about the difference between theoretical predictions and actual
performance. If I have not made this point clearly enough, then I will
reiterate it.

Chris W

--
The voice of ignorance speaks loud and long,
but the words of the wise are quiet and few.
--

Tony wrote:
Thanks! This is a very easy to use implementation.

:-) Useability always takes more effort to implement than the actual
calculations, but I think the effort is worth it!

How much detail does Cox and Antonio's book go into about this calculation?
Does it take into account resonant modes which involve more than one hole or
slot? I can see I will have to buy this book but it would be nice to know
that while I am saving up.

They go into lots of detail. The chapters are generally structured such
that they discuss a practical situation, then go through the maths, then
go through a practical implementation using the maths they've just
described. They try to give every equation a practical application,
this is why I like the book so much.

Also, the calculation depends on knowing the flow resistance of the damping
material. Is there any handy place where one can look up the approximate
flow resistance of commonly used mineral fibre materials?

There are a few (small) tables in the book, but what is more useful is
that there is a whole chapter (chapter 5) on porous absorbers, and a
whole section (5.3.1) on the various methods of calculating flow
resistivity.

Finally a word of warning. The panel thickness can be set as low as 1 mm.
In most configurations panels only a few mm thick would be far from rigid
and, depending on the intended frequency of operation, that could have a
very major effect on the performance.

This is true, therefore I have placed a caveat in the instructions that
warn about the difference between theoretical predictions and actual
performance. If I have not made this point clearly enough, then I will
reiterate it.

Chris W

--
The voice of ignorance speaks loud and long,
but the words of the wise are quiet and few.
--

"Chris Whealy" wrote in message
...
In response to comments from the reviewers and some user questions, I
have reworked my Helmholtz calculation spreadsheet - particularly the
sheet for slotted absorbers.

Thanks! This is a very easy to use implementation.

How much detail does Cox and Antonio's book go into about this calculation?
Does it take into account resonant modes which involve more than one hole or
slot? I can see I will have to buy this book but it would be nice to know
that while I am saving up.

Also, the calculation depends on knowing the flow resistance of the damping
material. Is there any handy place where one can look up the approximate
flow resistance of commonly used mineral fibre materials?

Finally a word of warning. The panel thickness can be set as low as 1 mm.
In most configurations panels only a few mm thick would be far from rigid
and, depending on the intended frequency of operation, that could have a
very major effect on the performance.

--
Tony W
My e-mail address has no hypen
- but please don't use it, reply to the group.

"Chris Whealy" wrote in message
...
In response to comments from the reviewers and some user questions, I
have reworked my Helmholtz calculation spreadsheet - particularly the
sheet for slotted absorbers.

Thanks! This is a very easy to use implementation.

How much detail does Cox and Antonio's book go into about this calculation?
Does it take into account resonant modes which involve more than one hole or
slot? I can see I will have to buy this book but it would be nice to know
that while I am saving up.

Also, the calculation depends on knowing the flow resistance of the damping
material. Is there any handy place where one can look up the approximate
flow resistance of commonly used mineral fibre materials?

Finally a word of warning. The panel thickness can be set as low as 1 mm.
In most configurations panels only a few mm thick would be far from rigid
and, depending on the intended frequency of operation, that could have a
very major effect on the performance.

--
Tony W
My e-mail address has no hypen
- but please don't use it, reply to the group.

"Chris Whealy" wrote in message
...
In response to comments from the reviewers and some user questions, I
have reworked my Helmholtz calculation spreadsheet - particularly the
sheet for slotted absorbers.

Thanks! This is a very easy to use implementation.

How much detail does Cox and Antonio's book go into about this calculation?
Does it take into account resonant modes which involve more than one hole or
slot? I can see I will have to buy this book but it would be nice to know
that while I am saving up.

Also, the calculation depends on knowing the flow resistance of the damping
material. Is there any handy place where one can look up the approximate
flow resistance of commonly used mineral fibre materials?

Finally a word of warning. The panel thickness can be set as low as 1 mm.
In most configurations panels only a few mm thick would be far from rigid
and, depending on the intended frequency of operation, that could have a
very major effect on the performance.

--
Tony W
My e-mail address has no hypen
- but please don't use it, reply to the group.