Portable Gobos w/ window design

[SoundMoves]

I am looking for a design for portable gobos. 4ft X 8ft approx with wheels. With window and without window. I have seen a few designs but the specs are a little vague.

Thanks for your help.

[giles117]

Sjoko's oage has a gobo design on it..

Here is the graphic and hotlink



http://johnlsayers.com/Studio/Mainpage/MP-Sjoko.htm

[SoundMoves]

Yes I have seen this one, and it comes the closest to what I need, so far. Any ideas what the material in the middle is, with the holes cut out? It says to cover with plywood. Does this mean the center is not plywood? Any ideas on one with a window? to create a make shift vox booth etc. so the musicians can see each other. I would like it to be around 6' tall by 4' wide. I will need some major support on the bottom so it does not fall over. Any ideas?

Thanks for your help

[giles117]

You should be able to adapt this to fit your uses with a piece of plexi or something for you glass.

I never noticed that the holed structure caption made it seem as if it wasnt plywood. i alwasy assumed that was a piece of plywood. John should be along to clarify his design any moment.

My assumption is that is a sheet of MDF with holes cut into it, adn then a sheet of thin plywood over it. I assume the cutouts are to reduce the wieght of the unit. and the plywood to cover it up (make it solid) because that is the original intent to have a solid board with insulation on either side that is sturdy enuff. /4" plywood is rather flimsy.

Loks like a 1x8 frame around this MDF.

So I see no reason why you could not alter it to have a window in it.

[SoundMoves]

Bryan,

Thanks for your help. I will also wait to see if John pipes in to verify that is indeed MDF.

Any ideas on the footing with going 6'tall. Seems the center of gravity would knock this thing right over.

Thanks,

Michael

[d2k]

hi everyone...

I have few questions that are bothering me and I am sure there are people here that can help me.

At the full pdf of SJOKO Gobbo design there is an variation at the end where is suggested that middle structure can be angled by which the center section of a slat side would have smallest depth and both ends would have greatest depth...

1) how this affects the frequencies absorbed relative to the gap? because the values that are enclosed are being connected to 4" depth? How to position rockwool then? angled aligned with center divider?


2) can i use fir or spruce for the framing/slats and plywood for the filling the holes as suggested?

3) for mobile vocal booth purpose should i use 40kg/m3 density rockwool?
how such a combination will perform for drums?
what would happen if I put rockwool in a very thin plastic folia (to eliminate the rockwoll getting in the air over the years)? To which extent that would affect the upper high range? not a good idea i guess?

4) when I want to assemble a mobile vocal booth out of 2 pieces of these, height of 4'2" or 130,5 cm is insufficient... what happens if I rotate it for 90deg with wheels on the shorter side?
What do I do with slats? Can overall design stay the same with just rotating it so slats would run horizontally or it is better to keep them in vertical orientation?

Many thx in advance for possible answers!

d2k

[Soundman2020]

hi everyone...

I have few questions that are botherin gme and I am sure there are people here that can help me.

At the full pdf of SJOKO Gobbo design there is an variation at the end where is suggested that middle structure can be angled by which the center section of a slat side would have smallest depth and both ends would have greatest depth...

1) how this affects the frequencies absorbed relative to the gap? because the values that are enclosed are being connected to 4" depth? How to position rockwool then? angled aligned with center divider?


2) can i use fir or spruce for the framing/slats and plywood for the filling the holes as suggested?

3) for mobile vocal booth purpose should i use 40kg/m3 density rockwool?
how such a combination will perform for drums?
what would happen if I put rockwool in a very thin plastic folia (to eliminate the rockwoll getting in the air over the years)? To which extent that would affect the upper high range? not a good idea i guess?

4) when I want to assemble a mobile vocal booth out of 2 pieces of these, height of 4'2" or 130,5 cm is insufficient... what happens if I rotate it for 90deg with wheels on the shorter side?
What do I do with slats? Can overall design stay the same with just rotating it so slats would run horizontally or it is better to keep them in vertical orientation?

Many thx in advance for possible answers!

d2k

d2k, there is an announcement at the top of the forum about what to do to assure getting as many responses as possible. The announcement leads to this post (click here). Actually, several people on this forum who are experts will most likely not reply if you don't do what is written in that post. Many others who are very helpful, will probably not reply out of respect for the moderators' wishes. You have been a member for many years, you have made several posts, and on most of those you have been reminded about this rule. I don't understand why you do not wish to comply...

- Stuart -

[d2k]

Stuart,

i am very sorry... i know it looks like i am ignoring the rules, but it seems i simply overlooked that all together...
honestly, i do not understand myself why my location was not indicated when it is clear that it was indeed yourself that warned me...
one of the reason could be that i changed two countries since 2010 and 2 continents since 2000. but its not an excuse.

all i can say is that it was not intentional. sorry...


for the rest, i don't think it is super important that i describe my studio, heights and stuff, as i have specific question about movable gobbos I found on this forum.
for the sake of completeness i can say that height in studio room is 3 meters, 3 walls are 5m x in length, with control room propagating in studio room braking it in kind of irregular shape. it is not finished yet as I need to layer rockwool and celenit boards on the false ceiling.
walls are natural historic stones and there are curtains planned of 500g/m2 with the distance of 30cm from the walls. in that way stones can be exposed or not.
this is also not finished. metal construction rails are placed and waiting for some income for celenit, rockwool and curtains.
instead of curtains i made 3 layers of blankets and using that at the moment.
as i get more work in connection with speech and overdub, as well as some vocal work, I am going to make gobos that i'm gonna need anyway.

sorry once again for obvious ignorance - i am not sure what was it...
looking at my first post, the very first one is missing. i do not get that as well.

i am rarely visiting this forum... it is just that i am preoccupied... sorry... eh...

d2k

[d2k]

hi all,

this looks like I am banned for good or?
I expressed my apologies, it was not intentional and I do not feel good about all of this.

d2k

[Soundman2020]

Sorry about the delay, d2k. It's a really busy tome of year, I have several projects that I'm working on in parallel, and very little time to deal with the forum.

middle structure can be angled by which the center section of a slat side would have smallest depth and both ends would have greatest depth...

1) how this affects the frequencies absorbed relative to the gap?

You can use any slot-wall calculator to tell you what the frequencies will be, assuming that it really is built as a series of Helmholtz resonators. There is a good one on Cris Whealy's web site. However, there does not seem to be any sealed cavity in there, so they are not tuned to anything! They won't work as slot resonators if there's no sealed cavity behind.

2) can i use fir or spruce for the framing/slats and plywood for the filling the holes as suggested?

Yes. The type of wood is not that important, acoustically. It is mostly for aesthetics.

3) for mobile vocal booth purpose should i use 40kg/m3 density rockwool?

That would be about right, yes.

what would happen if I put rockwool in a very thin plastic folia (to eliminate the rockwoll getting in the air over the years)? To which extent that would affect the upper high range? not a good idea i guess?

That is a good plan, as it ensures that the gobo is not to dead for high frequencies.

4) when I want to assemble a mobile vocal booth out of 2 pieces of these, height of 4'2" or 130,5 cm is insufficient... what happens if I rotate it for 90deg with wheels on the shorter side?

You can do that if you want, as log as you make sure that it is stable and won't fall over!

What do I do with slats? Can overall design stay the same with just rotating it so slats would run horizontally or it is better to keep them in vertical orientation?

You can do it either way. Slats can be vertical, horizontal, or even diagonal. It makes a bit of difference for diffusion, but it can sound good both ways, and it can also look good both ways.

- Stuart -

[d2k]

hi Stuart!

Sorry about the delay, d2k. It's a really busy tome of year, I have several projects that I'm working on in parallel, and very little time to deal with the forum.

No worries, I understand... I was more concerned with being kicked out of here because ignorance was not my intention.

middle structure can be angled by which the center section of a slat side would have smallest depth and both ends would have greatest depth...

1) how this affects the frequencies absorbed relative to the gap?

You can use any slot-wall calculator to tell you what the frequencies will be, assuming that it really is built as a series of Helmholtz resonators. There is a good one on Cris Whealy's web site. However, there does not seem to be any sealed cavity in there, so they are not tuned to anything! They won't work as slot resonators if there's no sealed cavity behind.

Huh, I surely understood that there IS a sealed cavity because only solid structure has holes which are covered by plywood and all joints sealed? Otherwise ofcourse there could be no point in slats and slots described. My question was more on the fine detail of having constantly varied depth, which would surely change the intended absorption, but that difference is probably minimum.

what would happen if I put rockwool in a very thin plastic folia (to eliminate the rockwoll getting in the air over the years)? To which extent that would affect the upper high range? not a good idea i guess?

That is a good plan, as it ensures that the gobo is not to dead for high frequencies.

I do not see people do that often. I yet have to find absorption/reflection data for very tin plastic foil but sturdy enough to hold rockwool.


For all the rest you confirmed my thinking.
Thank you.

Happy New Year and lot of success to you and all forum members.

Cheers,

d2k

[Soundman2020]

No worries, I understand... I was more concerned with being kicked out of here because ignorance was not my intention.

No problem. Just a very heavy workload right now, and not much time to be checking the forum. My paying customers have to get first priority...

I surely understood that there IS a sealed cavity because only solid structure has holes which are covered by plywood and all joints sealed?

It does not have to be a sealed cavity, for a typical Gobo. The only reason you would create a sealed box there is if you wanted to have some type of resonant device built in. But reading though John's notes about that gobo, it actually is a sealed cavity, so yes, the slats do create Helmholtz resonators, and the device is tuned. With the angled or curved inner panel, it will be a broadband device, that covers a wide range of frequencies.

Otherwise ofcourse there could be no point in slats and slots described.

There is still a point! I often use slats over un-sealed cavities in my studio designs, when I need reflection and diffusion, but not tuned absorption, or even when I just have a fabric surface that I want to protect from damage. There are many reasons to use slats, apart from just as a tuned slot wall.

My question was more on the fine detail of having constantly varied depth, which would surely change the intended absorption, but that difference is probably minimum.

The difference will not be minimal. The depth of the cavity is one of the key factors in tuning a slot wall. If the depth changes, so does the tuning. With a curved surface like that, there will be large differences in tuning. It will flatten the Q of the device, making it absorb over a broader range but at a lower level. For a gobo, that's a smart thing to do.

I do not see people do that often. I yet have to find absorption/reflection data for very tin plastic foil but sturdy enough to hold rockwool.

People actually DO do that, very often. It is a recognized and common method for ensuring that the insulation does not absorb too much of the higher end of the spectrum. If you look around the forum, you will see that many people do that, and they chose the thickness of the plastic to get the frequency range they want.

There is a reflection curve for foils (plastic is a foil too, acoustically) that defines the point where foil of any given surface density will be 80% transparent to sound (allowing 80% of that frequency through to the other side, reflecting back 20%, or coefficient of reflection = 0.2). The curve rises to about 99% reflection above that, at about 6 dB/octave, and falls off to practically 0% transparency below that, at the same rate:

F = 90 / m

F = The frequency at which the foil transmits 80% of the sound
m = The surface Mass of the foil in kg/m2




Happy New Year to you as well!

- Stuart -

[d2k]

great answers Stuart!

THX!