Gobo design help needed

I came accross this : http://www.johnlsayers.com/Stuff/Draw1.pdf while searching about gobos, and I was wondering: which gobo is more effective : 1-One that only has a 4 side frame with rockwool in the middle (like a standing piece of wool, no backing) 2-One that has a 4 side frame with any kind of backing (mdf, cardboard, plywood) filed with rockwool 3-One that has 4 side frame with slats, with a sealed back (like the 2 one) filed with rockwool (just like on http://www.johnlsayers.com/Stuff/Draw1.pdf but without the dead side). If anyone can illuminate me, I would be glad. I am looking for the gobo that has the most bass-mid absorption, or broadband absportion... Well thx everyone

I also forgot to ask, why is there a sheet of plywood with holes on http://www.johnlsayers.com/Stuff/Draw1.pdf I mean, isn't it easier to use only 1 sheet of plywood instead of 2 glueds togeter? Is it for the airgap? thx

tenkas - if you read the page I was replying to Sjoko's question regarding gobos and this is what he had and I offered a solution - hence the cutting out the holes in what already existed. cheers john

Thx for the reply John, I really didn't notice the pdf was written by you :P and for my first question about effeciency, do you believe a gobo without any backing absorbs as much bass (if I put it in the corner of the room) as a gobo with backing? Plus, here is a little plan I wanted you guys to check out also, I don't wanna build something bad, so here it is:

tenkas wrote:

and for my first question about effeciency, do you believe a gobo without any backing absorbs as much bass (if I put it in the corner of the room) as a gobo with backing?

I'm not sure a 2'x15"x3" panel will do enough for bass absorption. Most of the plans I've seen for bass absorption panels have been 2 sheets of OwensCorning 703 2"x4" panels wrapped in a open weave cloth, and suspended from picture hangers. I don't know if it's necessary to wrap a frame around them for added physical support or not, but I don't think so. http://johnlsayers.com/phpBB2/viewtopic.php?t=2930

Thx for the reply! The thing is I am going to build maybe 5 small pannels like this, and I want to "stack" them up (like guitar cabs). Will that be efficient? Also, seems like no one wants to answer my question wetter it is better to put some backing or not... :P thx a lot

tenkas wrote:

Also, seems like no one wants to answer my question wetter it is better to put some backing or not... :P

What are you planning on backing them with?

Well, MDF or plywood

tenkas wrote:

Well, MDF or plywood

My understanding is that basstraps work better when air (and sound) can move all the way through them, so putting a backing on them would turn them into high-frequency traps (John, Steve, feel free to jump in and correct me :-) ).

That was exactly what I have tought! And is it a good idea also to build a panel that has slats in front but has NO BACKING or is it useless because the slats aren't doint anything if there not in a sealed box? Thx

you've got it tenkas - but what do you need bass traps or gobos? With a backing it will act as a gobo - (BTW Sjoko wanted them as gobos to go around his drum booth for isolation.) otherwise sound will go straight through them. Corner bass traps are another animal. ;) cheers john

I need some portable gobos so I can put in the car, visit a client that has NO ACOUSTIC TREATMENT AT ALL and use a few gobos... So I guess I will build some 2 inch panels without any backing, and I will make a few 2 inch panels with slats... do I use the helmotz calculator for the slats? ( 2 inch dept, 2 feet width, 1foot3inch height) thx

I need some portable gobos so I can put in the car, visit a client that has NO ACOUSTIC TREATMENT AT ALL and use a few gobos

ahh - if you'd said that in the first place ...... Why not make panels - with backing - that can either have cloth front or attachable slot fronts.?? cheers john

Would it be a better to build a few panels with slats (I can't go bigger then 2inch deep) and building some with no backing at all? Because I believe that if I put backing on rockwool, it will make it less effective then if there is no backing because I cannot use the airspace behind... Well acoustic is really complicated, so I hope I learned well, and if everything turns right, I should be able to post some pics of the finished product in a week because I just got my wisdom teeth (the 4 of them) pulled out... and OUCH

I just got my wisdom teeth (the 4 of them) pulled out... and OUCH

OOOOO - I can feel that - have a glass of salt water handy mate :) cheers john

Thx John, yeah I just washed my mouth with salted water this mourning, it just tasted YUKY like the sea water! Also, I did an other post about a new design for gobo (new size, etc) if anyone has time to check it out, it's a question of effictiveness in relation with the volume behind the slats. Well thx a lot guys