DIY Absorbers for the Less-than-Handy Man: Part One

[Audioholics]

<P><FONT face=Arial size=2>Thomas Andry doesn’t profess to be an acoustical engineer or some sort of sound guru.<SPAN style="mso-spacerun: yes">&nbsp;&nbsp;</SPAN>He's a normal guy, married with a kid, who has recently purchased his first house.<SPAN style="mso-spacerun: yes">&nbsp; </SPAN>Having been an audio nut for years with very little money to invest, he's picked out systems for friends and family all the while listening to a mishmash of different speakers (timber matching, what’s that?) with an old analog <FONT face="Arial, Helvetica, sans-serif" size=2>Onkyo</FONT><FONT face="Arial, Helvetica, sans-serif"><FONT size=2> receiver.<SPAN style="mso-spacerun: yes"> </SPAN>His wife (if she had her way) would almost never turn the TV on, and when she did it would be either the news or the weather channel (with the occasional American Idol and 24 thrown in).<SPAN style="mso-spacerun: yes">&nbsp;</SPAN>However, she recently agreed to allow Tom to purchase all new equipment and gave up a whole room. Out of need for improving the sound fo the room, Tom decided to attempt DIY sound absorbers. Here is Part 1 of his adventures.</FONT></FONT></FONT></P><P><FONT face=Arial size=2>[Read the Article]</FONT></P>

 

[Francious70]

Very good article. Very well written too.

Paul

 

[Josuah]

I've got construction photos of the panel trap I built using rigid fiberglass. I picked them up from a local industrial/commerical HVAC company that had some extras from a job.

 

[JohnA]

Great Article, very informative and helpful! I do have one question....how did he determine where to place the panels? Like Tom I just bought our first home, moving from an apartment, poor, and don't have audio measuring tools...Unlike Tom (no offence) am very equipped with power tools, and I know how to use them ...so DIY panels here I come. But how do you determine location of the panels...

Thanks for the help!

 

[Josuah]

Easiest way to determine panel placement is to sit in your primary listening location and have someone else move a mirror around on the walls. Wherever you can see a speaker reflected in the mirror, you should have a panel.

You may also want to do this for the ceiling or floor too. Myself I just have a rug on the floor, and an ottoman in front (tables bad). Nothing on the ceiling.

 

[JohnA]

Thanks Josuah,

That helps alot!

 

[warnerwh]

Go to Rives audio and/or Realtraps and read. You are on the right track to truly good sound. Remember that bass traps help alot too. They're actually a necessity as your room as well as everyone else's has problems in the bass somewhere depending on the dimensions. Bass traps will make your bass more pronounced and at the same time make the midrange more clear! Well worth the effort. Many diy traps online. Just found this, excellent info:
http://www.ethanwiner.com/acoustics.html

Cheers

 

[Tom Andry]

I do have one question....how did he determine where to place the panels?

To answer your question, I did not have all that much choice of location. My room is fairly open, so I essentially place panels on every available wall. The advice above is all very good. Also, remember that a primary reflection point other than the side walls (which the mirror test is good for) is the ceiling. I tried to convince my wife to let me mount some up there but it was a no-go. I will post pics of my panels very soon.

 

[HookedOnSound]

safety first...

Great article,

I am tempted to try building in some in the near future but I must admit that I am a little bit concerned about it.

I know that fiberglass insulation is used quite extensively to insulate homes but how safe is it to install in living spaces? It's one thing to install behind walls with relatively low air circulation but what about fiberglass panel behind nothing more than light woven fabric?

From what I know, fiberglass is an irritant and is not good for the lungs which is why they always recommend working it in ventilated environments and with a respirator masks is always advised.

Can anyone reply? I am sorry if these questions are dumb but I would rather be safe than sorry.

Thanks,

 

[Tom Andry]

First of all, I don't think your question is dumb.

When I researched creating the panels, just about all of the designs I looked at suggested that a cotton batting layer between the fiberglass and the fabric would be sufficient to contain any escaping fibers. If you are concerned about the fibers escaping into the air, I would follow the design but add additional layers of the cotton batting until you feel reassured that it is thick enough. The batting is acoustically transparent so you won't affect the sound or effectiveness of the panels in any way. If you are still concerned, use thicker material for the covering. This will reduce the absorption at higher frequencies, but your piece of mind is probably worth it.

If you have never seen rigid fiberglass boards (as I had never before this project), you’ll notice that they stay together really well unless you crush or cut them. I’m no expert on fiberglass, but I don’t see how they would shed that much without abuse.

Lastly, nearly all of the professional acoustical products are made of either foam or fiberglass with fiberglass being the more popular choice. Many of the products, from what I could tell, are simply fabric wrapped fiberglass panels with treated edges that keeps them from deforming during the wrapping process. There may be a layer of something between the fiberglass and the fabric, but given the size and the need to be acoustically transparent, I can’t believe it’s that much different from the batting I used in my panels.

If there are any fiberglass experts out there that can shed some light on this subject – please chime in.

Hope this helps.

 

[HookedOnSound]

Hi mrnomas, thanks for the response.

What you said makes senses, knowing there is a barrier between the fiberglass and acoustic fabric would definitely put my mind at rest.

I have a back wall behind the couch I am tempted to experiment with an 4' x 8' (h x w) DIY absorber.

Again, thanks.

 

[Tom Andry]

If you decide to try it out, post pics and let us know how it went.

 

[Tom Andry]

I have recieved a few PM's recently with this question:

I am still confused as to how you mounted the rigid fiberglass to the frame? Did you build two frames and sandwich the fiberglass in between? Or did you simply put the fiberglass overlaid on top of the frame (with batting) then staple the fabric over it?

I figured I would respond here as well to clarify for others.

I address this on Part 1, page 2, second paragraph. Basically, I simply made the frame so tight that the fiberglass was held in place by the frame. Since I used the fiberglass to measure the boards, the frame was an exact fit to the fiberglass. When I constructed the frame (meaning inserted the screws), I always had the fiberglass in place so that when the frame was completed, the fiberglass was already mounted. I wouldn't want to try to remove the fiberglass and reinsert it into the frame. I imagine that this would damage the edges so much that the fiberglass may not be held in as tight.

Understand that while rigid fiberglass board is not as stiff as plywood, it's a heck of a lot stiffer (heh, heh, stiffer) than that rolled fiberglass everyone sees at the store. It will support its own weight as long as it is not abused too much.

I have seen other designs that have used an "L" bracket with a long screw and washers. Essentially, the "L" bracket is attached to the inside of the frame overlapping the fiberglass. The screw is attached to the bracket and pushed through the fiberglass. The washers are used so that, when you tighten the nut, it doesn't push through the fiberglass. Just make sure that you don't tighten it too much or it will push through no matter what. Hope this helps.