What acoustic treatments for vocal booth?

Posted: Tue Dec 17, 2002 1:48 am

"Leafy Green Substance" ???

Jeez, Fats, I've been eating broccoli most of my life, and NEVER have "Senior Moments"...

Endless Mind Farts maybe, but NEVER Senior Moments...

That WAS the Leafy Green Substance you were referring to, right??? Steve

Posted: Tue Dec 17, 2002 10:36 am

Hello guys,

Special thanks to John Sayers-who had to understand quickly most of the posts and helped a lot by confirming Steve's choice...
One question for John:In this room,do you really think broadband absorbtion will make a good job mostly above 100hz?If so,is it going to be a defect for a vocal recording or not?
I'm also using guitar recording there from an acoustic guitar with a condenser mic in front?
(detail:I have to remember how to calculate the length of a given frequency...speed of sound/frequency=length?)
it's true that the big problem was the boominess;i put off some foams and the sound got brighter,but maybe not enough,because of the low standing waves.So i'm definitively seduced by the broadband low mid absorber!
Ahh...Seems obvious to build the broadband absorber on the ceiling,but i definitively don't have enough space yet,7,19' is a minimum...(and i'm not so tall!)

By the way,Steve,i was just wondering about these low frequency problems you refered to:67hz,140hz,220hz.Sorry,but ...
I had calculated that there were some clusters around 90hz(89hz,91hz),180hz(178hz,180hz,181hz),and 270hz(267hz,273hz).
You primarly had posted the 76hz,177hz,266hz which corresponded more or less to what i had found by myself,but are these last result corresponding to another dimension?Maybe the basic dimension of the room LESS the broadband absorber dimension?(which should be anyway taken into account!).That was just the new part i didn't catch-Important for me to undestand the results in order not to make a few mistakes when i do the broadband absorber with so much precise work ...
Thanks,
Greg

Posted: Tue Dec 17, 2002 11:22 am

Greg, I'm not sure where the 67 hZ came from - 78.58 is the lowest modal freq. for your booth with a 7.19 foot ceiling. Musta been yet another of my "brain farts" at work...

You never mentioned whether you have Excel on your computer? If so, I hope you've downloaded both roomtune and modesV2 - if so, look at the formula (in roomtune, the easy one I wrote) in cell E-2 - Freq=1130/2L, where L is the dimension between any parallel pair of walls. 2x, because the sound has to make a round trip. 1130, because that's the speed of sound @ sea level, in feet per second.

Basically, what I would do is figure the room dimensions using the AVERAGE distance from the splayed trapwall - (if min.=5' and max=6', use 5.5')

Then, using John's sheet for slat resonators, calculate slat and slot width and depth, for each of three lowest center frequencies of each group of modes. That's what I did, but I may have gotten the lower one wrong, don't remember what freq. I used.

The values I get for a room 6.35x5.5x7.19 are:

1st harmonics of lwh - 88.97 102.73 78.58
2nd harmonics - 177.95 205.45 157.16
3rd harmonics - 266.93 308.18 235.74
4th harmonics - 355.91 410.91 314.33

If you tune slat/slot/depths at the center of each of those ranges, leaving out the 4th harmonic, that will give you specs for left, center, and right sections of the slat absorber - John's suggestion of using 2" 703 on the ceiling should take care of the 4th harmonic and higher.

The 1" foam will only absorb really high freqs, so I'd pull as much of it off as possible, maybe tripling it on the surfaces you leave foamed.

I'd be really careful when (finally) using the booth, NOT to place mics dead center between ANY two surfaces - a standing vocalist shouldn't be a problem, but a sitting guitarist needs to make sure the mic is NOT @ 50% of ceiling height - same goes for 1/3 or 1/4 of any room dimension. These positions will cause comb filtering, giving really unpredictable results. Re-read the Doublehelix thread for my comments on this part.

If you have trouble with the spreadsheets, or don't have Excel, post back and I'll re-run everything with current info for you... Steve

Posted: Tue Dec 17, 2002 12:16 pm

Steve,
It's true i didn't mentionned i don't have Excel on my computer,even if i did downloaded Roomtunes.anyway i had looked for another way to do it and finally found a similar program on the internet,tha's the one i finally used to find the results for a room 6,35x5,57x7,19.
Now it seems like we do have the same way to work out ,i just have to be sure about the right dimension of the broadband absorber:You went first with 150mm(0,49') thus giving 5,71' (6,2-0,49)for one width / and 300mm(0,98') giving 5,22'(6,2-0,9 Cool

for the other width.
So we would have 5,46' for the average distance...Should we be so precise or not?
If not,i will keep your last posted dimensions,but still there i've got a doubt:If the fake wall will break parallels between the two walls,do we still have to worry about the room modes we have found for THIS width??Furthermore,if we admit that we don't have these room modes anymore(but still the other ones for length a height),that means that we will have MORE distance between the actual modes,thus a different dimension/position choice for the slats/slots to do?
That's really the big question right now for me,i'm sure you'll know...
Otherwise,very good thing to know the "dangerous" positions in a recording room like that!-thanks
Greg

Posted: Tue Dec 17, 2002 10:27 pm

Greg, sorry to hear you don't have access (pun) to Excel - starting tomorrow I have to work 2 12-hour days followed by 4 12-hour night shifts, so I will be kinda not here much - I've copied your last post to my laptop, and will try to find time to work out final dimensions and post them back. This may take a few days due to the above reasons, but I'll get back to you as soon as I can.

Oh, and the non-parallel walls do NOT get rid of modal frequencies, they just spread them out a little, which makes them less noticeable but NOT gone - It's best if you calculate the short and long dimensions between the walls, take the average, and balance things out among all three. I think I did that for the first set, but I'll double check this time around.

yeah, it helps sometimes to understand WHY a mic sounds better in one location that another, rather than just "move it til it sounds good" - same thing with the sound SOURCE.

Give me a few days, and I'll have some new dimensions for you - two weeks work in one weeks time tends to slow things down a little... Steve

Posted: Wed Dec 18, 2002 10:03 am

Steve,

Don't worry if you've got so much work these days;anyway i'm still in contact with knaufalcolpor to get crown slabs panels and waiting to locate a dealer nearby....Good luck for your job and see you soon !

Posted: Thu Dec 19, 2002 4:13 pm

OK, Greg, I got a little time I wasn't expecting, so here goes - I rounded off the depth of the cavity to 1 foot and 6", just to make this easier to build. This gives the following dimensions, in feet and tenths.. Johns spreadsheet is in metric, so I'll calculate in metric and post BOTH dimensions when I'm finished.

OLD - L=6.35 W=6.2 (-12" or 6", avg 9", which =305mm, 152mm, avg 228 mm) H=7.19
NEW -L=6.35 W=5.2 to 5.7, avg 5.45 H=7.19

For 5.2' dimension
H1,L1,W1 = 79,89,109hZ - H2,L2,W2 = 157,178,217 hZ - H3,L3,W3 = 236,267,326hZ
For 5.7' dim. 79,89,99 - - - - - - - - - - - - -157,178,198 - - - - - - - - - - - -236,267,297hZ

I'm calculating for the center of each group of nodes, so f/o will be 89, 187, and 266 using the longer dimension(5.7ft), or 95, 187, 281 hZ using the shorter dimension (5.2 ft)

If you stretch the response out to cover the lowest center freq of the lows and the highest center freq of the highs (3rd harmonics) you would center the responses at 89, 187, and 281 hZ - in practice, there are enough variables that we can round things a litle either direction and not notice the difference. This is good, because building tolerances are hard to hold this tight even if you were machining steel parts instead of wood. Especially true of the slot width, where 0.5mm makes a noticeable shift in frequency.

Sooo, here are the values, assuming that you use 2x4, 2x8, and 2x12 (US dimensions in inches, which are NOT actually those dimensions but in reality 1.5" thick and 1/2" narrower than the stated width - I recommend ripping each board at least enough to get rid of the rounded edges (I calculated the slat width based on 3.25", 7.25", and 11.25", based on using US dimensional lumber with 1/8" ripped from each edge, which gives a sharper edge so it's easier to measure the slot width, which is VERY particular.

- - - - - - - - -89 hZ - - - - - - - -187 hZ - - - - - - - 281 hZ
SlatWidth - 11.25"/286mm - - 7.25"/184mm - - 3.25"/82.5mm
SlotWidth - - .060"/1.5mm - - - .177"/4.5mm - - .236"/6mm
SlotDepth - - 1.5"/38mm - - - - - 1.5"/38mm - - -1.5"/38mm
DepthToWall - 12"/305mm - - - 9"/226mm - - - 6"/152mm

Anyone trying to deal with this in inches - use the metric values for SlotWidth - fractions of inches won't get you close enough. Even 1/64" increments don't come out right, although if you have access to Excel you could always recalculate once you understand what I did based on the rest of this post...

You need to try to maintain the calculated slot width to less than 1/2 mm from spec. I'm hoping you have access to a table saw, radial arm saw, or joiner, or this could get really difficult. This trap might be buildable using thinner boards, but the other dimensions would change. For example, using half the thickness of boards with no other changes, raises the low freq from 89 hZ to 112 hZ. To get that back down to 89 hZ, you would have to increase the cavity depth from 305mm to 650 mm!

Given the dimension of the wall you intend to put this trap on, I'd probably recommend that the slats get mounted horizontally over studs spaced, NOT on 24" centers, but with a 24" space BETWEEN them. This way, the framing should come out about even with a stud at each wall and two more in between. That would allow you to place 24" wide insulation board between the studs with no cutting to width. Remember to caulk any gap except the ones between the slats...

I'd put the wide boards/narrow gap at top and bottom, the medium ones next, and the narrow boards/wide gaps in the center (vertically) The variable cavity depth will smooth out the response of each slot.

My reasoning behind this is that low freq's build up at boundaries, which would be floor and ceiling. High freq's have a much shorter wavelength and so are not as sensitive to placement between boundaries. (walls) This way, the lower freq's would see a slot tuned to their freq. where the pressure is greatest, therefore the best absorption.

You'll still need ceiling absorption and possibly another bass trap - John's comment about these absorbers not working much below 100 hZ means you may need to put something like a corner trap between the ceiling and the wall opposite the trap. This would impact your available floor space the least.

As low as the ceiling is, the 2" 703 John mentioned would be the best way to absorb the ceiling with minimal height loss. This treatment should take care of the 4th/5th harmonics of room modes, which aren't taken into account with the slat resonator. It will also help flutter echoes from the vocalist/mic being too close to the ceiling as John pointed out.

If you felt you could afford lower ceiling height at the rear of the booth (away from the door) you could mount the 2" 703 at an angle similar to the slat resonator - this would give more absorption @ lower freq's, lessen flutter echo, and might lessen, or even eliminate, the need for the second trap I mentioned in the previous paragraph.

Keep in mind, that over 90% of my recommendations come from STUDY, not reality - The fact that John seems to concur raises my confidence factor significantly, but still I would recommend that if you have ANY doubts you contact a professional acoustician before you build this trap. It is a lot of work to go to on someone else's say-so.

If it's of any help, I would personally build this if I had the same size booth and wanted to treat it - in fact, I'm saving this post for my own future reference, so I'll remember how I got there... Steve

Posted: Fri Dec 20, 2002 4:16 am

Hello Steve,

The theorical thing seems to be clear right now for me,except the practical part ,i.e. the slats positions and dimensions;
"Sooo, here are the values, assuming that you use 2x4, 2x8, and 2x12 (US dimensions in inches, which are NOT actually those dimensions but in reality 1.5" thick and 1/2" narrower than the stated width - I recommend ripping each board at least enough to get rid of the rounded edges (I calculated the slat width based on 3.25", 7.25", and 11.25", based on using US dimensional lumber with 1/8" ripped from each edge)"
...Euhh... 2x4..do you mean,original or actual slats dimensions ? 1.5" thick...I'm sorry but it looks like i'm really lost there between inch/metric and us/french language conversions !

OK,let's resume what i understood so that you correct me,right?
1)We've got 3 different slats dimensions for each 1/3 part of the fake wall(24"each),1 slat =center of 1 of the 3 groups of frequency
2)I suggest we call the 3 types of slats/slots placements :S1/S2/S3 for low/medium/high frequency slats/slots...
So S1=top+bottom
S2=next
S3=middle
Means that looks like a mirror position,right?

Ok,i'm stuck there....If i put the slats horizontally means wall frequency division is ...vertically?And what about 24" division...?My brain has stopped there,tryin' hard to figure out...Even tried to sketch it ....wwhhaaoouuh!

Posted: Fri Dec 20, 2002 2:05 pm

Greg, you do much better with English than I EVER will with French - and the metric/English thing is a bona-fide nightmare...

First I'll try to explain how/why dimensional lumber, as purchased in the US, isn't what it claims to be - when sawmills first started standardizing on dimensions for sawn boards (as opposed to "go cut your own, flatten it with an adz or a draw knife, build your cabin, fight off the indians") anyway, at that time when you bought a 2x4, you got a rough-sawn board that was really 2 inches by 4 inches. At that time, near as I can tell, the "board foot" measurement came into being, for purposes of pricing. One board foot (at that time) = 12" x 12" x 1" thick. Using that value, 1 foot length of a 2x6 = 1 board foot (BF)

Then, somebody decided they would be easier to work with if they were smoother, so then you could buy either rough sawn (really 2 icnes by 4 inches) or S4S (Surfaced 4 Sides) which STARTED as a 2 x 4 but ended up about 1/8" smaller on each surface, or in reality you got a board that was 1-5/8" x 3-5/8" -

Finally, someone discovered that they could get more boards out of the same log by using more precise milling methods, so they started ripping 2x4's to about 1-5/8" x 3-5/8", and only planing them down to 1-1/2" x 3-1/2" -

Now, here comes the crass commercialism part - they still CALL it a 2x4, and guess what? They still CHARGE you by the board foot, based on what they CALL it, not what it REALLY is - so, a 2x4 gets charged for as if it really was 2" x 4", or 2/3 of a board foot per lineal foot.

The reality, for actual building purposes, is that US dimensional lumber is really 1/2" LESS in either dimension than its name would suggest.

This is why I settled on 1-1/2" for slat thickness (slot depth) - it was the closest depth to the requirements of this particular trap that wouldn't require thickness planing - a job that any but the most dedicated woodworker would not be equipped to do, and would have to hire it out.

Now, as for slat WIDTH - since a 2x4 is really only 3-1/2" wide, and since it has been planed and the edges radiused, it will not react the same to impinging sound waves at its edge as it would if it were perfectly square-cut. If you don't think this makes a difference, ask a few high end nearfield monitor manufacturers WHY they radius the edges of their speakers... Anyway, if you want to get rid of the rounded edges on lumber, you have to rip a small slice off each edge to get back to a perfectly square corner. Usually, 1/8" is enough, so that would reduce the width of a 2x4 from 3-1/2" down to 3-1/4" - same for the other sizes - they would end up at 7-1/4" and 11-1/4" respectively.

"So S1=top+bottom
S2=next
S3=middle
Means that looks like a mirror position,right?

Ok,i'm stuck there....If i put the slats horizontally means wall frequency division is ...vertically?And what about 24" division...?" - Yes, you appear to be thinking the way I was - see the next paragraphs -

As to construction, if you first build a frame with 2x4's, positioning the side of the frame that is toward the open area of the booth at 6" and 12" from the wall that will be inside the trap, that will establish the variable depth of the trap. I would fasten a 2x4 (laid flat) to the floor, and another to the ceiling, that runs from a point 6" from the wall at front, to a point 12" from the wall at the rear - You will need to cut these plates at an angle on their ends, so that they fit firmly against the wall on both ends. An adjustable carpenter's protractor will be invaluable here - adjust it for the angle you need and mark both ends of the floor/ceiling plates. If you flip the protractor over for opposite ends of the board, you will get the two end angles such that the board ends will be parallel but NOT square.

IMPORTANT: before you start construction, obtain the caulk you plan to use, along with some construction adhesive - here in the US, one brand is called "Liquid Nails" - it is VERY important that you test these on an actual (scrap) piece of the insulation board you're using, allowing the test piece to "cook" for at least 3-4 days - if the sample shows any signs of deterioration after that time, find a DIFFERENT brand/formula of adhesive and try again. The LAST thing you want to do is put everything together with an adhesive that is going to MELT your trap from the inside out...

Lay a bead of caulk (either flexible silicone or butyl) about 1" from each edge of the 2x4 BEFORE you place the board - press the board down firmly, then fasten to the floor (or ceiling) with screws that will penetrate far enough to hold well - preferably into framing members behind the floor/ceiling covering material. Cut 4 2x4's long enough to require tapping into place between these "plates" on floor and ceiling. These will be your framing "studs" - place one of the studs against the wall, at the 12" deep end of the trap - make sure the 2x4 is square with the base plate - since the angle of the baseplate to the wall isn't square, the inside edge of the vertical 2x4 will touch the wall while the outer edge will NOT. To make it easier to caulk this joint, I would run a heavy bead of caulk along the edge of the vertical stud that will touch the wall BEFORE you fasten this first stud.

Use a piece of the 24" wide insulation board for a guide, place it against the first stud vertically, and locate the second stud up against the insulation board. Toenail the second stud in place, using caulk on the ends of the stud. Continue this until you reach the other ends of the floor/ceiling plates - The last stud will be at the 6" depth, and only the FRONT edge of the stud will contact the wall (all the studs need to be square with the plates, or the slats will not mount firmly to the studs.)

The last opening between studs will probably NOT come out exactly 24" wide, so the pieces of insulation board will most likely need to be trimmed to fit. A razor knife can work for this, if you use a board for a straight edge guide - if you try to saw the insulation board, have a dust mask and a vacuum cleaner handy - not a good idea.

Once the framing is complete, I would mount the insulation boards in between the studs, placing them back from the outer edge by at least 1/4", preferably 1/2" - one way would be to cut some 1" cleats and place them flush with the INSIDE edge of the studs, floor to ceiling - run a bead of construction adhesive all the way around the cleat, then press the insulation boards up against the cleat. Wait a day or so (check the label on the adhesive for recommended cure times) then caulk around the edges of the insulation board with silicone or butyl caulk. At this time, the only way for air to get inside the trap should be THROUGH the insulation board. Make sure EVERY seam is caulked, without the caulk getting in the way of the flush front of the frame.

Now, since the bottom 1-1/2 inches is already blocked by the floor plate (ceiling too) I would start at both bottom and top with a horizontal 2x2 (not really 2", see the first part of this post) - you can use the factory-radiused edge toward the floor, since it will be caulked, but one side of the first real "slot" will be formed by the upper edge of this bottom board, so the upper side should be square cut. If you rip one 2x4 in half, you could use half at the bottom and the other half at the top. These, allowing for a 1/8" kerf width (typical table saw blade width) would end up being 1-11/16" wide, or 1.6875", which is just under 43mm.

To simplify, here are some definitions, after which I'll refer to the simple name to save space and typing ;

For SLATS, NOT STUDS - (studs are left at nominal purchased dimensions, or 1.5" x 3.5")

2x2 = 1.5" x 1.625", or 38mm x 67mm (the dimension you get when ripping a 2x4, minus the 1/8" kerf)
2x4 = 1.5" x 3.25", or 38mm x 82.5mm (1/8" ripped from each side)
2x8 = 1.5" x 7.25, or 38mm x 184mm (1/8" ripped from each side)
2x12 = 1.5" x 11.25, or 38mm x 286mm (1/8" ripped from each side)

From bottom to top, here are the #'s I came up with -
2x2, 1.5mm slot, 2x12,1.5mm slot, 2x12, 1.5mm slot, 2x8, 4.5mm slot, 2x8, 4.5mm slot, 2x4, 6mm slot, 3 more 2x4, each with 6mm slot between, then a 6mm slot and an "adjuster" slat, which will be about 5.2" wide, this is the last slat to be placed - Now, starting from the TOP, a 2x2, 1.5mm slot, 2x12,1.5mm slot, 2x8, 4.5mm slot, 2x8, 4.5mm slot, and the previously mentioned "adjuster" slat.

If your 7.19 foot height dimension is accurate, these #'s should work. If not, you will need to adjust the width of the "adjuster" slat, but keep the same slot widths. Any variation of slat width on this one board will only help broaden the response, which is fine.

Again, the variable depth of the trap will smooth out the gaps that would be caused by only 3 slat/slot widths - I would cut the "adjuster" slat LAST, after all the other slats are in place and fastened down with countersunk 3" brass wood screws - measure between the lower board of the top part, and the upper board of the bottom part, subtract 10.5 mm and that is the width of the "adjuster" slat. Place that last slat with a 6mm gap from the 2x4 below it, and the gap above should come out to 4.5mm.

Also, in answer to one of your questions, since sound PRESSURE is at maximum at boundaries and high frequencies have several wavelengths between walls, It isn't real important that the different slots are placed vertical or horizontal. The design of this trap makes it a pretty broadband device, with more absorption at the 3 lowest modal groups of this particular size booth.

When attaching the slats, I would run a bead of caulk under each slat where it contacts the studs, and then screw it down with 2 screws per stud for narrow boards, and 3 or 4 screws per stud for the wider ones. The caulk will keep the slats from rattling later. The ends of the slats should be caulked, and carefully cut to extend the full distance between walls. You could glue and nail a small cove moulding vertically at the junctions between slats and walls for a more finished look.

What I SHOULD have asked you before I even STARTED, is what actual sizes of dimensional lumber are available to you at YOUR location, and then used those dim's for calculation - if you can get that information, post it back here and we'll start over. (When I can get some more time)

I'm not sure how much more to tell you, other than do everything as if you were building a boat and didn't want it to sink - A lot of the reason it is expensive to hire a proper studio built is this serious attention to detail. An average framing carpenter would waste your time, money and materials if you asked him/her to build such a structure - minute gaps in construction are no big deal for most houses, but can totally negate the initial plan for anything involving acoustics.

Gotta go, graveyard shifts start tonight... Steve

Posted: Fri Dec 20, 2002 5:12 pm

Hello Steve,

One more time i have to thank you for that big time you're giving to all these explanations and instructions...
Even if you're right when you say that it would be better to start with these lumber dimensions that i have to check in my location,all instructions from your last post are clues helping me to see if i'm figuring out the right thing or if i made a conceptual /translation mistake from the beginning(which would mislead myself for the next details...).
So first,yes i have to go and see what kind of lumbers i will purchase here and then start from their dimensions if they are different from yours;
But before i have to be sure about one thing:when you say "lumber",do you mean a piece of wood like a "rafter"?Important to know to understand other things:
1)do 2x4's lumbers mean lumbers with 4" width,2" thick and...length...?(so the base would be...rectangular?)
2)"Cut 4 2x4's long enough to require tapping into place between these "plates" on floor and ceiling.
These will be your framing "studs" - place one of the studs against the wall, at the 12" deep end of the trap - make sure the 2x4 is square with the base plate - since the angle of the baseplate to the wall isn't square, the inside edge of the vertical 2x4 will touch the wall while the outer edge will NOT. To make it easier to caulk this joint, I would run a heavy bead of caulk along the edge of the vertical stud that will touch the wall BEFORE you fasten this first stud."
Means that we've got 2 lumbers placed horizontally at the bottom and the top,and as much as needed vertical plates(=lumbers) going BETWEEN these 2 lumbers?(LENGTH=7,19'-2x2"?)
Then means that the open angle due to the slope between wall and plate should be caulked as much as possible,putting the "glue" before the plate to improve the result(That outside angle at the max cavity depth means that you put the 12" cavity on the left side of the wall,right?)
3)"Once the framing is complete, I would mount the insulation boards in between the studs,"
Means that the first time we had put the insulation board was just to check the studs position?And right now,we do put them,BETWEEN the stud and not ON them?
But if i"build a frame with 2x4's, positioning the side of the frame that is toward the open area of the booth at 6" and 12" from the wall that will be inside the trap",and if insulation board is put BETWEEN,then the cavity would be shorten as much?
I'm sure i have missed something,cause i'm still confuse with that:"placing them back from the outer edge by at least 1/4", preferably 1/2" - one way would be to cut some 1" cleats and place them flush with the INSIDE edge of the studs, floor to ceiling - run a bead of construction adhesive all the way around the cleat, then press the insulation boards up against the cleat."Euh..
4)Steve,just wanted to check to your previous post:
"I'm calculating for the center of each group of nodes, so f/o will be 89, 187, and 266 using the longer dimension(5.7ft), or 95, 187, 281 hZ using the shorter dimension (5.2 ft)"
I'm not sure but...i always find 177hz instead of 187hz(longer dimension).Am i wrong?

Whaouh...I really hope i won't make you repeat things ,if only i could have a pen and send you a drawing of what i can visualize now,things would be much easier for me and for you...
Just hope i'm not too far right now from reality and that i'm not making you spend much more time than you expected to spend with all that !
Thanks
greg

Posted: Sun Dec 22, 2002 8:52 am

“when you say "lumber",do you mean a piece of wood like a "rafter"?”

Yes. In John’s country, apparently the word is “timber” - normally, a
general term for building materials which means “ solid wood, direct from trees, cut to
a specific cross-section such as 2”x4”, called “dimensional lumber” here in the US.

“do 2x4's lumbers mean lumbers with 4" width,2" thick and...length...?"

I know this gets confusing, but read my last post again - the one where I explained
how/why
a 2x4 really is NOT 2” x 4” … and, yes the length of lumber
(boards,
or timbers) must be specified when you buy them - normally, such boards come in
even
lengths of feet in the US - such as 8 foot, 10 foot, etc… You usually figure
out what you need, ]
and sometimes buy lumber that is twice as long as what you need if the price is
better -
you then just cut two pieces from the one long one…

“Means that we've got 2 lumbers placed horizontally at the bottom and
the top,
and as much as needed vertical plates(=lumbers) going BETWEEN these 2 lumbers?(LENGTH=7,19'-2x2"?)”

Sort of - I’m not sure where you got the “-2x2” part.
Also, at least in the US, the carpenter’s terms are: a PLATE is the
horizontal framing member of a wall which is in contact with the floor on
which the wall is built. The STUDS are vertical framing members, such as
the 7.19’ pieces (in the case of your vocal booth) that go from
the plate on the floor up to the horizontal member on the ceiling; these
ceiling horizontals are normally called CAPS (like the cap you put on your head)

“Then means that the open angle due to the slope between wall
and plate should be caulked as much as possible,putting the "glue" before
the plate to improve the result(That outside angle at the max cavity depth
means that you put the 12" cavity on the left side of the wall,right?)"

Correct.

“the first time we had put the insulation board was just to check the
studs position?"

Yes.

“we do put them,BETWEEN the stud and not ON them?"

This is what I would do - if you mount the insulation board on TOP of the frame,
then mount the slats over the insulation board with screws, it would be nearly
impossible to maintain the critical slot width since the insulation board can flex
and compress. That would change the angle and position of the slats, relative
to each other. Since this is where the slot dimension is formed, merely
tightening some screws more than others would pull the slats one way or the
other, changing the slot width.

By mounting the slats DIRECTLY on the frame and placing the insulation board
BEHIND them, you have a hard surface joint between frame and slat, and can
set them very precisely, for example by using the spacer method I mentioned
at the first of this thread.

“if i"build a frame with 2x4's, positioning the side of the frame that is
toward the open area of the booth at 6" and 12" from the wall that will be
inside the trap",and if insulation board is put BETWEEN,then the cavity would be
shorten as much?"

Effectively, no. The outer surface of the slats determines the surface to be
used for modal calculations. The depth of the trap is not nearly as critical as
slot width/depth. As long as the insulation board is close to the slats, it will
serve its purpose of broadening the response of the trap and increasing the
amount of absorption. The air that is attempting to pass thru the insulation
still has to get past the slots, which, along with the slat width and depth
behind the slats, combine to determine frequency response.

“i'm still confuse with that:"placing them back from the outer
edge by at least 1/4", preferably 1/2" - one way would be to cut some
1" cleats and place them flush with the INSIDE edge of the studs, floor
to ceiling - run a bead of construction adhesive all the way around the
cleat, then press the insulation boards up against the cleat."Euh..”

A cleat is just a smaller board, normally fastened to a larger one to act as
a “stop” for some OTHER piece that needs to be accurately
located, with a surface you can glue or fasten to. Normally used in furniture
making, to support shelves, seats, etc. - In your case, these would be strips
of wood approximately ¾” to 1” square in cross section,
fastened to both sides of each stud lengthwise at the innermost edge, so
that you have a surface that will act as a “stop” and also
a glue surface for the mounting of the insulation board.

“I'm calculating for the center of each group of nodes, so f/o
will be 89, 187, and 266 using the longer dimension(5.7ft), or 95, 187,
281 hZ using the shorter dimension (5.2 ft)"
I'm not sure but...i always find 177hz instead of 187hz(longer dimension).
Am i wrong?"

177 is the second harmonic of the 6.35 foot dimension, which doesn &
#8217;t get changed. 187, however, is the AVERAGE between the lowest
and highest frequencies for second harmonics, when using the 5.2 foot
dimension caused by the deeper side of the trap. I picked that freq just
to be centered between the two extremes of the second harmonic so t
hat all 3 modes are covered. Given the variable depth of the trap, it won
’t make any difference to change things by 10 hZ. No, you&#8217
;re not figuring it wrong, just different.

Greg, if you haven't already been there, you REALLY need to look at John's
drawing of a trap. It explains almost exactly what I've been trying to explain,
other than the cleats. Click on this link -

http://www.saecollege.de/reference_material/index.html

Then, click on Absorbers, then click on the tab marked Mid Frequencies,
and look at the drawing. The only difference in what I'm recommending is the
variation in slat width and slot width, the values of which I posted just prior to
this.

From your questions, I'm not sure if you are just struggling with the translation
(again, much better than I ever could) or if you're not very familiar with building
techniques - if inexperience is the case, you would be wise to buy a book on basic
carpentry, including tools, skills, and methods.

This book,

http://www.amazon.com/exec/obidos/tg/detail/-/0865735778/ref=lib_dp_
TFCV/002-1300918-3303229?v=glance&s=books&vi=reader#reader-link

has the basics of carpentry, and would be a good beginner book if you haven't
yet learned about it...

just some food for thought; have you discovered what lumber sizes are available
in your area yet? Should be interesting comparing the two... Steve

<small>[ December 23, 2002, 01:38 PM: Message edited by: Cedar Flat Fats ]</small>

Posted: Sun Dec 22, 2002 8:57 pm

.......actually my bathroom works quite nice...depending on how I hang the towels.

Sorry folks....you guys are going into some great depth here..I love it!

Posted: Mon Dec 23, 2002 12:11 am

Hey Bill, glad to see ya here - funny you should mention that, I was just considering whether to "throw in the towel", as it were... :=) Steve

BTW, does anybody know what terms are used for the various parts of a building in France? Just a little unsure of how to 'splain some of this in a language I can barely recognize, let alone speak... Steve

Posted: Tue Dec 24, 2002 5:03 pm

I like bathrooms for vocals because the outboard reverb deteriorates the quality too much..
Hang those towels where you need them.

(I got cha)