Hello;
I am working on an isobooth with two door (inner and outer with a a couple inch airlock in-between)
I scored two doors cheaply, one solid (mdf core) one hollow core.
1) I would like to use the solid door as the inner door the hollow core door as the outer door. Is this OK? I can't imagine why it would make a difference. Sound has to get through both of them to get outside, right?
On to the next question:
I will be beefing up both doors with a layer of 3/4" plywood and 3/4" MDF.
2) Is it OK if I make the order of the layers (from inside to outside) MDF - Ply - Door? Aesteticly it would look best this way as the door is a great honey maple and the MDF is paintable. The plywood is rough and would be the center layer. Any reason why the order should be anything else? (example door sandwiched between the ply and mdf?)
Thanks again.
Linus
Two questions regarding doors: solid and hollow core.
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linus
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z60611
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I think that having a thin door and a thick door it doesn't matter which is on the noisy side, unless one of them rattles. My gut feel is that the solid core on the noisy side would be better.
Since you've only got an inch or so between the doors, the hollow core door might be a triple leaf wall, no matter what you cover it with.
Since you've only got an inch or so between the doors, the hollow core door might be a triple leaf wall, no matter what you cover it with.
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knightfly
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Linus, by using a hollow core door in conjunction with a solid one you create a triple leaf barrier, which will actually WORSEN the amount of isolation you get - the hollow core door is itself a mass-air-mass structure, which is the ideal usage of material for sound proofing. However, it's a really CRAPPY version of mass-air-mass, because it has very little mass and a narrow air gap.
IF these are both pre-hung units, I would forget about the hollow core one and see if you can either sell it or trade it for another solid core. Then, the two doors would be your two masses, and the space between them would be your air space.
The concepts are the same, whether building walls, ceilings, floors, doors or windows - this page probably explains things best; note the diagrams at the bottom - see that sometimes REMOVING material can actually IMPROVE results -
http://www.domesticsoundproofing.co.uk/tloss.htm
If you don't have a second solid core door available, I'd wait until you can - it really makes that much difference... Steve
IF these are both pre-hung units, I would forget about the hollow core one and see if you can either sell it or trade it for another solid core. Then, the two doors would be your two masses, and the space between them would be your air space.
The concepts are the same, whether building walls, ceilings, floors, doors or windows - this page probably explains things best; note the diagrams at the bottom - see that sometimes REMOVING material can actually IMPROVE results -
http://www.domesticsoundproofing.co.uk/tloss.htm
If you don't have a second solid core door available, I'd wait until you can - it really makes that much difference... Steve
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z60611
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Here's where I get a little shaky on triple leaf concepts.
Clearly having a 3" air space between the doors (room for a door knob) and a 1" space in the hollow core door is a bad thing because the 1" space has a higher resonance frequency than the 3" space.
But what if they were equal?
Let's say
a) the hollow space in the hollow core door is 1".
b) and after adding MDF (around the door knobs?), the hollow airlock space is 1"
Does it still have an effect?
(Of course I'm just speaking hypothetically. For a $100 or less, a new solid core door can be purchased, and well established rules apply -- and also solve worries about possible door structural failure. Also there may be little point in building an air lock with only 1" of space).
BTW, a suggestion for linus: glue/fasten some 703 to the back of one of those doors in the airlock.
Clearly having a 3" air space between the doors (room for a door knob) and a 1" space in the hollow core door is a bad thing because the 1" space has a higher resonance frequency than the 3" space.
But what if they were equal?
Let's say
a) the hollow space in the hollow core door is 1".
b) and after adding MDF (around the door knobs?), the hollow airlock space is 1"
Does it still have an effect?
(Of course I'm just speaking hypothetically. For a $100 or less, a new solid core door can be purchased, and well established rules apply -- and also solve worries about possible door structural failure. Also there may be little point in building an air lock with only 1" of space).
BTW, a suggestion for linus: glue/fasten some 703 to the back of one of those doors in the airlock.
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AndrewMc
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I have a metal essentially exterior hollow core door. It has 3/4" MDF on it and the door closes like an airlock & is very soundproof. My internal doors are solid core doors with MDF and they work well too.
I would just work with what you have - if you add MDF to the door it will help a lot.
The whole 3 leaves making it worse thing is a miss-understanding of what the comparisions mean. In the standard diagram that shows the 3 leaf being worse - what this is saying is you get better performance by maximising the mass on the outsides and making the air space as large as possible. -ie all things being equal that is the best placement of a constant amount of mass. But - regardless of any configuration, no matter how many leafs - adding mass will improve sound reduction. If you can just keep it to mass-space-mass - that way you get the best bang for your mass
I would just work with what you have - if you add MDF to the door it will help a lot.
The whole 3 leaves making it worse thing is a miss-understanding of what the comparisions mean. In the standard diagram that shows the 3 leaf being worse - what this is saying is you get better performance by maximising the mass on the outsides and making the air space as large as possible. -ie all things being equal that is the best placement of a constant amount of mass. But - regardless of any configuration, no matter how many leafs - adding mass will improve sound reduction. If you can just keep it to mass-space-mass - that way you get the best bang for your mass
Andrew McMaster
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AndrewMc
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It's probably better if you can put the mass either side of the door rather than all on one side - especially if the door is hollow core
But....in the real world....adding that extra mass is going to help significantly no matter where you put it - in the final assessment balance what you do with what makes sense for your situation - ie don't build a rocket ship to mars if something else is a a lot easier fit for a marginal difference.
But....in the real world....adding that extra mass is going to help significantly no matter where you put it - in the final assessment balance what you do with what makes sense for your situation - ie don't build a rocket ship to mars if something else is a a lot easier fit for a marginal difference.
Andrew McMaster
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knightfly
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Andrew - your comment, "But - regardless of any configuration, no matter how many leafs - adding mass will improve sound reduction." - is simply NOT true - if you look at the tested designs illustrated at the bottom of the page here -
http://www.domesticsoundproofing.co.uk/tloss.htm
And, if you work from right to left (backwards to most of us) from the 57 dB wall, note that the 50 dB wall is achieved by adding another leaf to the 57 dB wall, which LOSES 7 dB STC in the process - now, if you take the 50 dB wall (triple leaf) and add yet another leaf, you get the 40 dB wall (going from 3 leaves to 4, and losing ANOTHER 10 dB -
The physics is the same, whether you're talking about walls, windows, doors, floors, or ceilings. The only improvement I've seen from using more than two leaves in ANY barrier is in the midrange, but it's ALWAYS at the expense of low frequency isolation.
As yet I don't have modeling capabilities for multi-leaf barriers (considering the full version of Insul, but it's over $1000 so may have to wait a bit) - however, when you look at studies such as the link above, the differences in efficiency are obvious - mass-air-mass is the only sensible way to spend your money, unless spending money is your main goal... Steve
http://www.domesticsoundproofing.co.uk/tloss.htm
And, if you work from right to left (backwards to most of us) from the 57 dB wall, note that the 50 dB wall is achieved by adding another leaf to the 57 dB wall, which LOSES 7 dB STC in the process - now, if you take the 50 dB wall (triple leaf) and add yet another leaf, you get the 40 dB wall (going from 3 leaves to 4, and losing ANOTHER 10 dB -
The physics is the same, whether you're talking about walls, windows, doors, floors, or ceilings. The only improvement I've seen from using more than two leaves in ANY barrier is in the midrange, but it's ALWAYS at the expense of low frequency isolation.
As yet I don't have modeling capabilities for multi-leaf barriers (considering the full version of Insul, but it's over $1000 so may have to wait a bit) - however, when you look at studies such as the link above, the differences in efficiency are obvious - mass-air-mass is the only sensible way to spend your money, unless spending money is your main goal... Steve
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AndrewMc
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My point is that all these charts are perfect situations and there is equal data that questions any set of of data you look at. For example - BBC report 1995-06 page8 - shows the sound reduction across 2 walls - not by STC but across the frequency range. Wall 1 is a mass-large airspace-mass - wall2 is mass-space-mass-space-mass.
Wall1 is better by about 20db at around 80Hz - but beyond that they are equal and above 250Hz wall2 is significantly better. Is this data correct? Who knows, it's the BBC - so I have some faith in it.
The large airspace is going to be better on the lower end - and it makes sense to do that if you can - but you have to balance anything with what is practical. If its simply more practical to have mass-space-mass-space-mass then I wouldn't fret over it (especially on a door where any airspace inside the door is too small to matter anyway) - the reduction will still be decent & if you can bulk up the mass in that arrangement - there is a point where even at the low end it will better than mass-space-mass that has lower mass - with such a small air space that point is probably reached well before the mass of 1 sheet of MDF.
Wall1 is better by about 20db at around 80Hz - but beyond that they are equal and above 250Hz wall2 is significantly better. Is this data correct? Who knows, it's the BBC - so I have some faith in it.
The large airspace is going to be better on the lower end - and it makes sense to do that if you can - but you have to balance anything with what is practical. If its simply more practical to have mass-space-mass-space-mass then I wouldn't fret over it (especially on a door where any airspace inside the door is too small to matter anyway) - the reduction will still be decent & if you can bulk up the mass in that arrangement - there is a point where even at the low end it will better than mass-space-mass that has lower mass - with such a small air space that point is probably reached well before the mass of 1 sheet of MDF.
Andrew McMaster
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PD
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I believe that a specific interpretation of Andrew's statement might indeed hold water- just giving it a shot, the interpretation goes like this:
"..regardless of any configuration, no matter how many leafs - adding mass to any existing leaf will improve sound reduction."
The report from custom audio designs clearly shows that in some cases, going from zero leaves in a specific part of the wall to one or more leaves can in fact reduce the transmission loss, something you definately don't want.
But beefing up any already existing leaves, even if there are more than two, should increase the transmission loss, shouldn't it? Again, that's adding mass to leaves that already exist, as opposed to adding that mass in the form of creating additional leaves.
I'm disappointed they didn't show what would happen if you add layers of sheetrock to some of the walls on the left, at the bottom of that report. Moot? Maybe not..
In the example of that report with the wall sections at the bottom, the 3rd example shows a wall with sheetrock on both sides next to a wall with sheetrock only on the farthest side from the first wall. The Rw rating is 50dB. Say that the wall section on the left with sheetrock on both sides is an existing wall in a rented house and cannot be disturbed, so you're stuck with it. Let's say it has antique wallpaper on it with original teak chair rail molding. You can neither touch that wall nor attach any mass to it in your quest for better isolation (this almost describes my situation, btw). Putting up a wall frame with only insulation (absorption) and no sheetrock is not going to give the folks on the other side of that wall much isolation from my noise. Extrapolating from the first two examples at the bottom of that page of that report, a wall of insulation alone may add maybe 3dB of additional isolation, whereas adding another sheetrock leaf onto a new wall section with insulation will add 14dB of isolation from just the original insulated wall rated at 36dB. And, as far as adding mass, that report tells me that if my new wall had sheetrock on both sides, it will not isolate as well as a new wall with only one leaf of sheetrock on it, on the inside of the control room. But wouldn't adding mass to that one leaf, making, say, a total of three sheets of drywall instead of one, sandwiching one 1/2" layer between two 5/8" layers, wouldn't that have to increase my TL even more?
Is it ever possible that adding mass to a leaf that's already there can cause a loss of TL or even a perceived loss of TL? In other words, with that extra third leaf beefed up (as OPPOSED to adding mass in the form of an additional leaf), would it still improve blocking only part of the frequency spectrum while not affecting the other part of the frequency spectrum (i.e., in the "already unwanted third leaf" scenario, could the extra loss of higher frequencies due to extra mass of that leaf exceed the extra loss of lower frequencies. thus giving an overall perception of lower TL from the other side simply because one narrow part of the frequency range leaks through more than the rest of the frequency range)?
My situation is actually even more complicated than that, and because it is, I need to solve some of that here before refining the design stage of the project.
My design so far (which has now been changed to one single control room taking up the whole room space, but to be built as a room within a room):
http://johnlsayers.com/phpBB2/viewtopic.php?t=1862
And the complication is this: starting from the inside of my neighbor's kitchen, the layers are: plaster, wood slat backing, stud cavity, sheathing, exterior wood siding, exterior wood siding (our houses touch), sheathing, stud cavity, wood slat backing, plaster. Effectively three existing leaves, I guess.
NOW what do I do? I need maximum isolation without touching the walls or ceiling of my present (haunted) dining room!
This post proves it's time for me to get some sleep..
Perry
"..regardless of any configuration, no matter how many leafs - adding mass to any existing leaf will improve sound reduction."
The report from custom audio designs clearly shows that in some cases, going from zero leaves in a specific part of the wall to one or more leaves can in fact reduce the transmission loss, something you definately don't want.
But beefing up any already existing leaves, even if there are more than two, should increase the transmission loss, shouldn't it? Again, that's adding mass to leaves that already exist, as opposed to adding that mass in the form of creating additional leaves.
I'm disappointed they didn't show what would happen if you add layers of sheetrock to some of the walls on the left, at the bottom of that report. Moot? Maybe not..
In the example of that report with the wall sections at the bottom, the 3rd example shows a wall with sheetrock on both sides next to a wall with sheetrock only on the farthest side from the first wall. The Rw rating is 50dB. Say that the wall section on the left with sheetrock on both sides is an existing wall in a rented house and cannot be disturbed, so you're stuck with it. Let's say it has antique wallpaper on it with original teak chair rail molding. You can neither touch that wall nor attach any mass to it in your quest for better isolation (this almost describes my situation, btw). Putting up a wall frame with only insulation (absorption) and no sheetrock is not going to give the folks on the other side of that wall much isolation from my noise. Extrapolating from the first two examples at the bottom of that page of that report, a wall of insulation alone may add maybe 3dB of additional isolation, whereas adding another sheetrock leaf onto a new wall section with insulation will add 14dB of isolation from just the original insulated wall rated at 36dB. And, as far as adding mass, that report tells me that if my new wall had sheetrock on both sides, it will not isolate as well as a new wall with only one leaf of sheetrock on it, on the inside of the control room. But wouldn't adding mass to that one leaf, making, say, a total of three sheets of drywall instead of one, sandwiching one 1/2" layer between two 5/8" layers, wouldn't that have to increase my TL even more?
Is it ever possible that adding mass to a leaf that's already there can cause a loss of TL or even a perceived loss of TL? In other words, with that extra third leaf beefed up (as OPPOSED to adding mass in the form of an additional leaf), would it still improve blocking only part of the frequency spectrum while not affecting the other part of the frequency spectrum (i.e., in the "already unwanted third leaf" scenario, could the extra loss of higher frequencies due to extra mass of that leaf exceed the extra loss of lower frequencies. thus giving an overall perception of lower TL from the other side simply because one narrow part of the frequency range leaks through more than the rest of the frequency range)?
My situation is actually even more complicated than that, and because it is, I need to solve some of that here before refining the design stage of the project.
My design so far (which has now been changed to one single control room taking up the whole room space, but to be built as a room within a room):
http://johnlsayers.com/phpBB2/viewtopic.php?t=1862
And the complication is this: starting from the inside of my neighbor's kitchen, the layers are: plaster, wood slat backing, stud cavity, sheathing, exterior wood siding, exterior wood siding (our houses touch), sheathing, stud cavity, wood slat backing, plaster. Effectively three existing leaves, I guess.
NOW what do I do? I need maximum isolation without touching the walls or ceiling of my present (haunted) dining room!
This post proves it's time for me to get some sleep..
Perry
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AndrewMc
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PD - Yes that is what I am referring to. If you add mass to a configuration that you are stuck with, or is un practical to change to mass-large airspace-mass then you will improve the TL by adding mass.
Knightfly is absolutely correct that mass-large airspace-mass is going to give you much better TL at the low end - especially around the kick drum frequency range - but the key is the large airspace. If the airspace is tiny then you are not going to see the benefits - the only way to improve is add more mass where you can.
Knightfly is absolutely correct that mass-large airspace-mass is going to give you much better TL at the low end - especially around the kick drum frequency range - but the key is the large airspace. If the airspace is tiny then you are not going to see the benefits - the only way to improve is add more mass where you can.
Andrew McMaster
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PD
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Andrew a configuration I'm "stuck with" is definitely how this situation feels at this point. I hope I can work with it.
Steve, thanks for asking- yes, I should have my new concept up within a day hopefully, and I'll post it in this forum; I would really appreciate your help on this wall/floor/ceiling thang. I believe my restrictions-to-target ratio is a little wider than most any plan I've seen here (NO concrete, no ability to tear out or add to existing walls/ceiling, and high hopes for isolation.. AND Mrs. Kravitz on the other side of one wall.
Perry
Steve, thanks for asking- yes, I should have my new concept up within a day hopefully, and I'll post it in this forum; I would really appreciate your help on this wall/floor/ceiling thang. I believe my restrictions-to-target ratio is a little wider than most any plan I've seen here (NO concrete, no ability to tear out or add to existing walls/ceiling, and high hopes for isolation.. AND Mrs. Kravitz on the other side of one wall.
Perry
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knightfly
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Andrew, thanks for clarifying what you meant - you're absolutely correct in your interpretation. BTW, the example you gave from BBC report 1995-06 page8 doesn't disagree with tested results from others, and also agrees with any calculations I've seen. More mass, more air gap, better bottom - adding a third, intermediate leaf will help midrange isolation but hurt low freq. No contentions I can see.
Sometimes you just gotta go with what you have, and make whatever improvements you can - still, it doesn't hurt to know what will help and what is just wheel-spin... Steve
Sometimes you just gotta go with what you have, and make whatever improvements you can - still, it doesn't hurt to know what will help and what is just wheel-spin... Steve