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#1
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question on small room acoustics.
I'm hoping smart people like Mr. Dorsey will chime in on this one:
I saw this design for an iso booth (it's like a pentagon): http://www.vocalbooth.com/products/diamondseries.html I thought this would be a great idea since there are no parallel walls. But it is roughly approaching a "round" floorplan. And I learned from people that a concave "round shape" is terrible for a room. So would you give this shape a thumbs-up or thumbs-down? (I'm building an iso-booth this week). |
#2
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GP,
it is roughly approaching a "round" floorplan. And I learned from people that a concave "round shape" is terrible for a room. Round and similar shapes are a problem, but that problem goes away if all the surfaces are covered with absorbing material. A small booth needs to be covered mostly or completely anyway, so with enough absorption on the walls that shape will be okay. --Ethan |
#3
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wrote:
I'm hoping smart people like Mr. Dorsey will chime in on this one: I saw this design for an iso booth (it's like a pentagon): http://www.vocalbooth.com/products/diamondseries.html I thought this would be a great idea since there are no parallel walls. But it is roughly approaching a "round" floorplan. And I learned from people that a concave "round shape" is terrible for a room. The reason a round shape is terrible is that it concentrates all the reflections right in the center. An octagonal shape is almost as bad because it has a bunch of parallel walls. The pentagonal shape is much better because you never have two surfaces directly opposing one another, so you don't get direct reflections between them. In the case of the isolation booth, though, your whole goal is to make it totally dead at higher frequencies, so the reflection problems aren't severe except at lower frequencies where they turn into standing wave problems. And I don't think the pentagon will really help to deal with the standing wave issues much anyway. So would you give this shape a thumbs-up or thumbs-down? (I'm building an iso-booth this week). I would give it a thumbs-down, because I am not sure it is really any better than a simple rectangle, and it is a _lot_ harder to build than a simple rectangle. Mitering all those wacky angles will take some time. It might be a little bit better but it's a lot of work for a little bit. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#4
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I thought this would be a great idea since there are no parallel walls.
But it is roughly approaching a "round" floorplan. And I learned from people that a concave "round shape" is terrible for a room. So would you give this shape a thumbs-up or thumbs-down? (I'm building an iso-booth this week). With the right acoustical treatment, I have never had problems with any room, no matter what the size or shape. |
#5
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The reason a round shape is terrible is that it concentrates all the
reflections right in the center. What reflections? Acoustical treatments get rid of reflections. |
#6
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"Truth" wrote in message
... I thought this would be a great idea since there are no parallel walls. But it is roughly approaching a "round" floorplan. And I learned from people that a concave "round shape" is terrible for a room. So would you give this shape a thumbs-up or thumbs-down? (I'm building an iso-booth this week). With the right acoustical treatment, I have never had problems with any room, no matter what the size or shape. I guess we'd have to know what kind of material you record to understand why you make that assertion. IMO, for many recordings the room is an important part of the sound. Further, where that applies, some rooms simply cannot be 'fixed'. Of course, they can be made to essentially disappear from the recording, but that can be a bad thing. If you're recording mostly direct or close-miked instruments you can get away with a lot. Before I had the experience of working day-in and day-out in a really well proportioned studio of sufficient size to provide a variety of acoustic areas, I had no idea how much the room affected the results and how much easier it became to do first rate work. Steve King |
#7
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Truth wrote:
The reason a round shape is terrible is that it concentrates all the reflections right in the center. What reflections? Acoustical treatments get rid of reflections. Not in a tiny vocal booth, and nowhere else, either, except for anechoic chambers. -- ha |
#8
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"Ethan Winer" ethanw at ethanwiner dot com wrote in message ... GP, it is roughly approaching a "round" floorplan. And I learned from people that a concave "round shape" is terrible for a room. Round and similar shapes are a problem, but that problem goes away if all the surfaces are covered with absorbing material. A small booth needs to be covered mostly or completely anyway, so with enough absorption on the walls that shape will be okay. How big could you build a shape like this, assuming that the walls are covered in Auralex or the eqivelant, before you would start to have a problem? jb |
#9
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In article ,
reddred wrote: "Ethan Winer" ethanw at ethanwiner dot com wrote in message ... GP, it is roughly approaching a "round" floorplan. And I learned from people that a concave "round shape" is terrible for a room. Round and similar shapes are a problem, but that problem goes away if all the surfaces are covered with absorbing material. A small booth needs to be covered mostly or completely anyway, so with enough absorption on the walls that shape will be okay. How big could you build a shape like this, assuming that the walls are covered in Auralex or the eqivelant, before you would start to have a problem? Auralex will kill the high end issues, so your first problem is going to be low end resonances. If we figure that the foam becomes pretty useless around 500 Hz, then a round room that is a wave across at 500 Hz is going to start being a problem, right? And that would be... what, about 32 inches? Hmm... anyone care to try a better back-of-the-envelope calculation? This doesn't sound quite right to me, overall. --scott (who thinks there is a special place in hell for architects who design octagonal churches) -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#10
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thanks for the insights, Mr. Dorsey.
the two most important functions of the iso booth will be to record vocals and to record a cranked 4x12 guitar cabinet. would getting some of these RPG "modex corners" actually help? http://www.rpginc.com/products/modexcorner/index.htm i could almost see myself raising up the guitar cabinet and then "surrounding" the perimeter of the guitar cab with these modex things. |
#11
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Scott, I'm killing you here with all these questions.
But since you thought the pentagon shape would only bring marginal gains over the rectangle in this example... do you think a rectangle that adheres to one of the "golden ratios" (1: 1.4: 1.9 for example) would be a better strategy than the pentagon? you have me thinking about standing waves! |
#12
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wrote:
thanks for the insights, Mr. Dorsey. the two most important functions of the iso booth will be to record vocals and to record a cranked 4x12 guitar cabinet. would getting some of these RPG "modex corners" actually help? http://www.rpginc.com/products/modexcorner/index.htm i could almost see myself raising up the guitar cabinet and then "surrounding" the perimeter of the guitar cab with these modex things. I don't know. I'd bet that if there _were_ big standing wave problems in the room, you could compensate for them with placement, in the case of the guitar amp. You can move the amp and the mike around to deal with all kinds of problems. I can't see the RPG gadgets really doing much at the low frequencies where the problems are really going to be. But I might be wrong.... --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#13
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JB,
How big could you build a shape like this, assuming that the walls are covered in Auralex or the eqivelant, before you would start to have a problem? It's not at what *size* you need more than thin foam on the walls, it's what *frequencies* will be sounding in the room. If it's for voice only, the requirements for a booth are not as stringent as when recording a guitar or bass amp or string bass player or drum set. --Ethan |
#14
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GP,
the two most important functions of the iso booth will be to record vocals and to record a cranked 4x12 guitar cabinet. For a cranked guitar cabinet you need substantial absorption at low frequencies. Thin materials won't do that. would getting some of these RPG "modex corners" actually help? RPG Modex bass traps are great, if expensive, but they're not appropriate for this application. Modex traps are available tuned to different frequency ranges, and those ranges are better suited for larger rooms. What you need is broadband absorption that works well down to the lowest frequencies, not just over a narrow range. i could almost see myself raising up the guitar cabinet and then "surrounding" the perimeter of the guitar cab with these modex things. Modex traps are meant to be stacked in corners, not placed out in the room. If you get EQ magazine, the current (January) issue has a review of my company's MiniTraps. The reviewer specifically mentioned how successful MiniTraps are for exactly what you describe. --Ethan |
#15
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GP,
do you think a rectangle that adheres to one of the "golden ratios" (1:1.4: 1.9 for example) would be a better strategy than the pentagon? Yes. There are other good ratios too. If you download my Graphical Mode Calculator (PC only) it lets you play with different dimensions to see their affect. It also lists several "preferred" ratios. Here's the link: http://www.realtraps.com/modecalc.htm --Ethan |
#16
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thanks guys,
Ethan, I have a question for you: Do you make any Realtraps that go way down into the bass range? Those might work out well. thanks for the room calculator link. i figured out a 1:1.5:2.10 that will work with the space i'm playing with. |
#17
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How big could you build a shape like this, assuming that the walls are
covered in Auralex or the eqivelant, before you would start to have a problem? BRBR Small rooms tend to have more problems and are harder to treat than large rooms. A larger room, if nothing else, affords you the space necessary to build proper bass traps. Auralex and the like won't do anything to tame low frequencies, so a round room whether covered with Auralex or not will have gobs (the technical term) of low frequency energy reflected toward its center center. A spectacular example of this is the globe room at the Christian Science Monitor building in Boston. It's a globe-shaped room with a bridge spanning the horizontal axis. At the center you can hear everything anyone in the room is saying. It's really cool, but I wouldn't want to record or mix in it. Joe Egan EMP Colchester, VT www.eganmedia.com |
#18
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On Thu, 30 Dec 2004 10:26:50 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: RPG Modex bass traps are great, if expensive, but they're not appropriate for this application. Modex traps are available tuned to different frequency ranges, and those ranges are better suited for larger rooms. What you need is broadband absorption that works well down to the lowest frequencies, not just over a narrow range. snip I've not attacked this particular problem personally, but what experience I do have with tiny environments would bear this out. When you use tuned "traps" to suck up acoustic energy, it's somewhat of a rule of thumb that as the enclosured space (room) gets smaller, the Q of these devices rises seemingly exponentially. Thus, instead of the relatively broadband trap it would be in a largish room, it becomes a very sharp trap in a small room, thus giving you a "comb filter" effect, which can be VERY nasty. i could almost see myself raising up the guitar cabinet and then "surrounding" the perimeter of the guitar cab with these modex things. snip Hmmm...thus making the tiny room "look" bigger aurally? Not a bad idea, really. Modex traps are meant to be stacked in corners, not placed out in the room. If you get EQ magazine, the current (January) issue has a review of my company's MiniTraps. The reviewer specifically mentioned how successful MiniTraps are for exactly what you describe. snip Smaller trap for smaller room...form follows function. Works for me as a "guestimate," I'd gather! dB |
#19
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"EganMedia" wrote in message ... How big could you build a shape like this, assuming that the walls are covered in Auralex or the eqivelant, before you would start to have a problem? BRBR Small rooms tend to have more problems and are harder to treat than large rooms. A larger room, if nothing else, affords you the space necessary to build proper bass traps. Auralex and the like won't do anything to tame low frequencies, so a round room whether covered with Auralex or not will have gobs (the technical term) Actually "gobs" in itself is not a technical term, it's only when you start breaking it up into "milligobs" & "nanogobs" is when it warrants a tech definition. Neil Henderson |
#20
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GP,
Do you make any Realtraps that go way down into the bass range? Yes, that's exactly what our products are for! The MiniTraps demo video on our site www.realtraps.com shows them making a real improvement all the way down to the 40 Hz lower limit we tested. Our larger MondoTraps absorb twice again more below 100 Hz. thanks for the room calculator link. i figured out a 1:1.5:2.10 that will work with the space i'm playing with. Great. Also, at the urging of a customer I updated my ModeCalc program just yesterday to accept feet and inches instead of only feet with decimals. So now you can enter 13'6" instead of 13.5 feet, or 162" and all other such combinations. --Ethan |
#21
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dB,
When you use tuned "traps" to suck up acoustic energy There are a lot of issues with tuned traps that make them inappropriate for smaller rooms. Not just booths, but bedroom sized control rooms too. The biggest problem is that *all* rooms have peaks and nulls at *all* low frequencies, not just those frequencies related to the room's dimensions. Another problem is bass traps need to cover a large amount of surface. So if you load up the room with traps tuned to match one or two dimensions, you don't have space left to handle all the other frequencies that also need attention. thus making the tiny room "look" bigger aurally? Not a bad idea, really. This is true for all absorption. For example, putting absorbers on the ceiling over a drum set makes the ceiling appear to be much higher. If you think about it, there's no difference between a ceiling that's fully absorbent and one that's infinitely high. Either way, sound that goes up does not come back down later as a reflection. --Ethan |
#22
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"Ethan Winer" ethanw at ethanwiner dot com wrote:
thus making the tiny room "look" bigger aurally? Not a bad idea, really. This is true for all absorption. For example, putting absorbers on the ceiling over a drum set makes the ceiling appear to be much higher. If you think about it, there's no difference between a ceiling that's fully absorbent and one that's infinitely high. Either way, sound that goes up does not come back down later as a reflection. Here's something that's puzzled me, Ethan. I've read that when calculating modes, etc, for a room with an acoustic ceiling, you should measure the height to the actual hard surface above the acoustic tiles. It makes sense that as you APPROACH full absorption, you would APPROACH infinite effective height (i.e. zero reflection). But in practice, these are only approachable limits, not actually attainable, right? Whouldn't any low frequencies that are not fully absorbed be reflected in the same timeframe as if the absorption was not there? Or does the absorption affect phase as well as amplitude? |
#23
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"Ethan Winer" ethanw at ethanwiner dot com wrote in message ... This is true for all absorption. For example, putting absorbers on the ceiling over a drum set makes the ceiling appear to be much higher. If you think about it, there's no difference between a ceiling that's fully absorbent and one that's infinitely high. Either way, sound that goes up does not come back down later as a reflection. Ethan, how do you feel about diffusors above a drum kit or above a listening position, as opposed to absorption? Neil Henderson |
#24
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Neil,
how do you feel about diffusors above a drum kit or above a listening position, as opposed to absorption? I'm not an expert with diffusion, but I can see how it would be useful there. It won't make the ceiling disappear like absorption does, but it will make it seem farther away. The main goal is to avoid the obvious echoes and comb filtering, and good diffusion can do that. Note the word "good" - all of the cheap diffusors I've heard sounded worse to me than a bare wall. But RPG's deep well diffusors are very good if a little pricey. Peter D'Antonio who heads RPG, and is a real diffusion expert, says diffusion is not useful if it's too close to your ears. Dr. D'Antonio says the minimum distance is about 10 feet, but I've heard others say 8 feet is okay. So that probably rules our diffusion as a practical solution in a small control room having a normal 8 foot ceiling. --Ethan |
#25
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Agent,
I've read that when calculating modes, etc, for a room with an acoustic ceiling, you should measure the height to the actual hard surface above the acoustic tiles. Yes. It makes sense that as you APPROACH full absorption, you would APPROACH infinite effective height (i.e. zero reflection). But in practice, these are only approachable limits, not actually attainable, right? Right. You'd need (guessing) about 3 feet of dense rigid fiberglass to absorb 100 percent at 100 Hz. And then there's 60 Hz and 40 Hz etc which would require even more absorbing material. I've been in the large anechoic chamber at IBM's acoustic lab, and they have *huge deep* fiberglass pyramids all over. Even with all that the room is guaranteed anechoic only down to 100 Hz. Wouldn't any low frequencies that are not fully absorbed be reflected in the same timeframe as if the absorption was not there? Or does the absorption affect phase as well as amplitude? Yes, any waves that are not absorbed will get through to the rigid boundary behind and be reflected back. As for phase, I honestly don't know. I do know that waves passing through absorption are slowed down a little. So you'd think that would affect the phase. As you add absorption to a room you actually lower its resonant frequencies a little. This is why loudspeakers have fiberglass inside them, to make the box seem acoustically larger than it really is. So, yeah, phase may be affected, but this is more a theory issue. In practice, just add as much absorption as you can. It will never be 100 percent in a typical size room no matter what you do. --Ethan |
#26
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"Ethan Winer" ethanw at ethanwiner dot com wrote:
Wouldn't any low frequencies that are not fully absorbed be reflected in the same timeframe as if the absorption was not there? Or does the absorption affect phase as well as amplitude? Yes, any waves that are not absorbed will get through to the rigid boundary behind and be reflected back. As for phase, I honestly don't know. I do know that waves passing through absorption are slowed down a little. So you'd think that would affect the phase. As you add absorption to a room you actually lower its resonant frequencies a little. This is why loudspeakers have fiberglass inside them, to make the box seem acoustically larger than it really is. So, yeah, phase may be affected, but this is more a theory issue. In practice, just add as much absorption as you can. It will never be 100 percent in a typical size room no matter what you do. My use of the word phase may have been misleading, but I think you more or less answered the questtion I was trying to ask. I was thinking in terms of the difference in the time it takes for sound waves to reflect back from a high ceiling as opposed to a low ceiling. I was refering to phase only insomuch as it relates to the reflection time, since comb filtering is, as I understand it, essentially a product of phase differences between the direct & reflected signals. Your preference for hard floors & soft ceilings is well documented. What are your thoughts on using a totally soft wall facing a hard wall if one must record in a relatively narrow room ( 12')? |
#27
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"Ethan Winer" ethanw at ethanwiner dot com wrote in message ... Peter D'Antonio who heads RPG, and is a real diffusion expert, says diffusion is not useful if it's too close to your ears. Dr. D'Antonio says the minimum distance is about 10 feet, but I've heard others say 8 feet is okay. So that probably rules our diffusion as a practical solution in a small control room having a normal 8 foot ceiling. Ah, was just wondering... then I may have to trap above my listening position, but I was also considering diffusion as an option. Unfortunately, I've got 8' ceilings in my new room, so if the above is correct, diffusion wouldn't work. I've got some bass traps in the corners & on the back wall, and they help, but I'm still getting some very ****ing annoying low-end buildup - I assume from the low ceiling. Thanks. Neil Henderson |
#28
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Neil,
I may have to trap above my listening position, but I was also considering diffusion as an option. With an 8-foot ceiling you're probably better off with absorption. Note that the important places to treat in a small control room are the first reflection points on the side walls and ceiling. These points are not directly besides you or overhead, but about halfway forward between you and the speakers. I've got some bass traps in the corners & on the back wall, and they help, but I'm still getting some very ****ing annoying low-end buildup - I assume from the low ceiling. Just as you can never be too thin or too rich, you can never have too much bass trapping. What kind of traps do you have, how many, and which corners? And how big is the room? --Ethan |
#29
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A-86,
What are your thoughts on using a totally soft wall facing a hard wall if one must record in a relatively narrow room ( 12')? That can be useful, though I usually prefer to treat both opposing walls in a checkerboard pattern. But having one totally absorbent surface gives you a place to record acoustic guitars and vocals near, to avoid comb filtering. --Ethan |
#30
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"Ethan Winer" ethanw at ethanwiner dot com wrote:
A-86, What are your thoughts on using a totally soft wall facing a hard wall if one must record in a relatively narrow room ( 12')? That can be useful, though I usually prefer to treat both opposing walls in a checkerboard pattern. But having one totally absorbent surface gives you a place to record acoustic guitars and vocals near, to avoid comb filtering. That would be my preference as well. I'm stuck with an immovable ciderblock wall & an immovable (load bearing) 2X6 frame wall about 10-1/2" apart. I was toying with the idea of putting 2 layers of 5/8 sheetrock on the outside, then putting carpet or burlap right over the fiberglass in the inside, without anything reflective. Kind of LSDS (live-side-dead-side) instead of LEDE. Thanks. |
#31
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"Ethan Winer" ethanw at ethanwiner dot com wrote in message ... I've got some bass traps in the corners & on the back wall, and they help, but I'm still getting some very ****ing annoying low-end buildup - I assume from the low ceiling. Just as you can never be too thin or too rich, you can never have too much bass trapping. What kind of traps do you have, how many, and which corners? And how big is the room? Ethan, I have one trap built as per some of your instructions (going to do at least a couple more of those, as I have the O-C 703 on hand, but I wanted to try one first just to see how it went), and I have four Auralex corner traps that I got a good price on used from a local home theater installer... he had them installed in a display at a home show recently. As for the placement, I've tried a number of different combinations so far - I just don't think I have enough trapping yet. It's making *some* difference, but not enough. As for the room size, it's difficult to say exactly what the effective room size really is, because of a couple factors like an alcove on one side, and a large opening that shoots off into another room on another, but the room "proper" is 19' x 19'. Neil Henderson |
#32
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Les,
Why does a rough brick surface* seem so effective at acoustic guitar/singer recording? Great question. I'm sure a brick wall gives the same reflections and comb filtering as any other surface, and probably more and to a higher frequency than bare sheet rock. In a room with carpet a brick wall could be useful in the same way a reflective floor is useful. You get *one* reflecting surface that adds a nice ambience. --Ethan |
#33
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Neil,
I have one trap built as per some of your instructions ... and I have four Auralex corner traps ... I just don't think I have enough trapping yet. I agree. the room "proper" is 19' x 19' Besides the square shape, which requires more bass trapping than usual to counter, that's also a relatively large room. I'd say you need at least a dozen serious bass traps. --Ethan |
#34
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x-no archive: yes
"Ethan Winer" ethanw at ethanwiner dot com wrote: Just as you can never be too thin Wasn't Karen Carpenter too thin? or too rich, you can never have too much bass trapping. She'd have been better off trying to trap fish, yes. Then frying them in olive oil and devouring them. -- ha |
#35
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Ethan Winer wrote: If you get EQ magazine, the current (January) issue has a review of my company's MiniTraps. The reviewer specifically mentioned how successful MiniTraps are for exactly what you describe. --Ethan Some other interesting DIY and commercial solutions: http://www.acoustics-noise.com/AFBsi...erbank002x.gif http://www.acoustics-noise.com/AFBsi...erbank003x.gif http://www.acoustics-noise.com/AFBsi...nPosition2.gif Warm regards Eric Desart |
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