Acoustic advice

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vox

vox

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Right now I track drums in my living room, it has parallel concrete walls and aproximately the following dimensions - 18' x 30' with roof that slopes from 10' to 14' across the 18' width.

I can't make any physical modifications to the room itself so I'm looking for other solutions, the best one I could think of is to build Gobos which I can arrange around the Drums like a fence or cubicle, however I have a couple questions about their design.

So far the design I have in mind would be a wooden frame about 2' or 3' wide x 7' or 8' tall, filled with Rock (mineral) wool.

1/ Would it be better to add a solid backing to the gobos or to leave the mineral wool exposed on both sides? If I leave it exposed the sound should travel through it, through a 3' airspace to the wall, bounce off the wall and back through the mineral wool. Whereas if I put a backing wouldn't the sound just bounce of the backing instead?

2/ What thickness mineral wool do I need to use, is 4 inch enough, 6 inch?

3/ What weight mineral wool would be best for this application?

4/ I think John wrote that it's ok to seal the mineral wool with plastic, does this mean that I can cover the wool with an airtight plastic sheet in this case? won't that affect high frequency absorption/reflection? does that mean I should use a very light loose plastic covering?

5/ Should I aim to surround the Drums completely with Gobos that latch together with no gaps in between or would I get better results using spaced gobos to not totally deaden the sound?


Any input would be greatly appreciated,

Thanks Guys :)
 
Here's link to a plan I did for sjoko for his drum booth. Check it out, it's a PDF file.

Booth Plan

cheers
John
 
Thanks for posting that. Very similar to something I've been brainstorming on recently. Now I know I'm on the right track.:)
 
Drawing/cad tools

Hello, and I hope this doesn't annoy you. I would like to ask John Sayer a question,( or anyone else who can help) if you don't mind, . I would like to post drawings and pictures on the forum. But I'm missing a few pc's of the puzzle. I'm not real efficient on the net. However, I am a builder, and designer. And I think I can offer some real info in my own way.
First of all, for those of you who post drawings, like Johns above(most of what I've seen) look like they were drawn on Visio, or some program I'm not familiar with. Do you mind sharing with us your drawing tools knowledge. I'm a CAD draftsman/detailer
(for an architectural mill/store fixture manuf.)and would like to draw with more graphic oriented qualitys. I do have Visio, and just loaded it. But learning curves aside...What I could offer for now though, is full blown Cad drawings that any mill in the western nations can build from. However, since autocad files have to be read with Autocad, I don't know how I could post them on the forum. I did hear there is a reader for it. But it seams to me, the server would have to somehow display them as ? thanks for any info, p.s. I can attatch autocad files to emails. But same problem. The reason I'm asking this, is I could show an alternative sometime to building things. Like curved gobos! Or curved suspended absorbers! Thanks now for anything you can help with.
Fitz
 
Fitz,
You mean Autocad doesn’t have a way to export to an image file?

Well, you can try this:

Hit the [Print Screen] key – this copies what you see on your screen to the clipboard. Open Paint or some other photo editing type software and then choose Copy. You should then see a picture of the screen shot you captured. Edit and Save this as a .jpg or .gif (less than 100KB) and post it to the board.

barefoot
 
I think John uses SmartDraw for some of his drawings. I just got it a little bit ago ... it's definitely no AutoCad or ProE, but it's pretty easy to use and relatively feature-rich for the price.
Give the screen print idea of barefoot's a shot first, though ... I'd love to see your CAD drawings! Just hit the "browse" button in the "attach file" section when you make a post, and pick the file you want to attach.
 
test failed

Wow, thats what I like about this forum. Everybody helps. I must be a bonehead. I followed the instructions, and it came up in paint, I saved it as test1.jpg and attatched it to an email to my wife(in her ebay room) but when she got it, there was a logo for the file, but nothing happened when she clicked on it. I didn't want to test here. And the "print screen seemed to save the whole file - 3200kb. I'll ask around, or if you see something I'm doin wrong, let me know. Maybe autodesk's forum can help. Anyway, I'll get it sooner or later. Looking forward to posting this stuff. I communicate much better with drawings more than text. (1 picture= 1000...you know)
but mucho gracias I learned something already-cool, hmmmm now how did I do that.....
fitz
 
Re: test failed

RICK FITZPATRICK said:
And the "print screen seemed to save the whole file - 3200kb.
Click to expand...
3.2MB sounds about right for a full color bitmap of your screen. You might need to crop it and reduce the color depth to make the .jpg file smaller. Some email systems limit the size of attachments. This might be the problem with your wife seeing it. Try .gif as well. Especially if it's a CAD drawing with just a few colors.

barefoot
 
Yes Rick - I use Smartdraw - I tried Autocad but it was toooo complicated for me plus it doesn't draw colour pics like smartdraw. Also smartdraw also saves in a PDF file format which allows most users to read as they all seem to have acrobat reader installed. You can also download a free smartdraw reader from smartdraw.com.

cheers
john
 
Hearty thanks!

Thankyou for the info everybody, I'll look into smart draw, in the meantime I dug up my autocad manual(2" thick, think I'll use it as an absorber-lol)and maybe I can get this going. Till I do I'll keep reading your posts. They are graet!
fitz
 
Wow, thanks for the info John.

Couple questions,
If I wanted to make them taller so that I could use a few of them as a make shift vocal booth as well, should I flip the whole design sideways leaving the resonator slats the same length and just mount them horizontally instead?

Would you advise using plastic to keep the fiber particles under control in your design?

Thanks again.
 
John,

One possible problem I see with your design is that the fiberglass is shown flush against the slates.

A slat absorber is essentially just a damped Helmholtz resonator. http://www.phys.unsw.edu.au/~jw/Helmholtz.html For this type of resonator to work most effectively the air in and around the neck (slat spaces) should have unrestricted flow. This allows low frequency energy to efficiently be stored in, and released from the cavity via the "mass" of air in the neck. Damping material inside the cavity and/or lossy cavity walls can then absorb this energy in the process. In this case I would suggest leaving a 20mm or so gap between the insulation and the slats. From my experience building ported loudspeakers (same principle) I believe you'll get better low frequency absorption this way.

Or maybe I'm missing the point of your design?

barefoot
 
Last edited:
This topic inspired me to write a quick applet to calculate the resonant frequency of a slat resonator absorber. It's on my web site http://geocities.com/twbarefoot2000 It doesn't include the effect of damping material .

Let me know what you think. :)

barefoot
 
good one barefoot except that as I understand it the slat spacing should be the slat width.

cheers
John
 
ausrock said:
A similar thing is already available at:
Click to expand...
I'm also well known for reinventing the wheel.:D

Well, I wanted to tech myself a little Javascript anyhow. And this was a good enough excuse.:)

barefoot
 
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