# DIY Bass Trap Evolution in Layman's/Simple Terms



## louiein99 (Jun 9, 2013)

This is Home Theater specific and is in very general terms regarding Bass Traps--not Acoustic Panels for reflection points or higher frequencies. I realize there are many highly sophisticated designs, resonators and frequency specific traps out there commercially; but, in all honesty, the average Home Theater Enthusiast is looking for something he can build in his garage and meet the WAF. These are generalizations in what one can find online these days (the dates are just to give a reference based on the dates of threads and previous posts).

90s: 4"-6" Panels mounted across corners. Buzz Word tended to be OC703 (3pcf).

Early 2000s: Denser panels are better. Buzz Word tended to be OC705 (6pcf).

Mid-2000s: Super chunks in the corners. Buzz Words: "Denser is better" seemed to be common sense. Most tend to be 17"x17"x24" or 24"x24"x34". Other brands start grabbing attention since OC stuff always seems tough to source in many areas.

Mid-2000s: Membranes added to the front of panels or chunks absorb the lows, but rejects the highs, which helps keep the room from being too dead. Again, front of the trap only. Buzz Words: FRK, FSK, kraft paper, foil (not sure if this includes aluminum foil, or if it is referring to something else).

Mid-2000s: Due to the cost of OC703/705, many forum experts recommend sticking with OC705FRK or equivalent Panels in lieu of Corner Super Chunks since chunks require at least 33% more material at a minimum. Plus, panels have a full 24" wide face where the typical (17x17x24") super chunk has only a 16" wide face with at least 4" of material

Mid/late 2000s: Limp-Mass Membranes become the buzz words. Still not sure what all materials that are readily available that qualify as this for us DIY-types.

2010s: Super Chunks appear to work more effectively with less dense insulation (but still add a membrane on the front only). For thinner bass absorbing panels, "dense makes sense," but the deeper the trap, the less dense the material needs to be. Many even infer that using cheaper Roxul Safe n Sound and even the pink fluffy stuff works effectively in Super Chunks, which makes the previous cost factor void. Plus, these materials are far more readily available. This doesn't mean that dense wall-mounted panels are out of vogue, it just opens up more possibilities.

So, in 2013, where are we at now? Here are a sampling of questions that I see people ask over and over again. So, let's try to get answers to them with reference to Dedicated Home Theaters.

1) "You can never have too many bass traps." I hear that a lot, but most of the forums with audio experts tend to be referring to Listening Rooms or Mixing Rooms which are typically looking for a flat response. I am hoping that the members of this forum can determine if this adage holds true when I am watching the opening scene of Star Trek or any Michael Bay movie  Let me be clear. I am not disputing this quote. I just want to ensure that it holds true for movie watching--not listening to music.

2) Pink Fluffy Stuff/Roxul Safe n Sound/or equivalent can be used if the Super Chunk Corner Trap is deep/big enough...then what constitutes deep or big enough? Does the typical 17x17x24" chunk work with this less dense material, or does the corner trap need to be 24x24x34". Due to space considerations and WAF for many of us, it sure would be nice to get a few experts/big wigs weigh in on this.

3) What can the average Joe use as a membrane? As I mentioned above, I have read about kraft paper, foil, FRK or "faced" insulation. I have even read that plastic bags or even cling wrap will have some effect, although I cannot imagine they provide much assistance. 

4) Several people have asked whether the membrane should be applied with spray adhesive or just placed between the insulation and the fabric covering in order to allow it to flow freely. The consensus from the posts I have seen say that the spray adhesive is preferred and doesn't cause the membrane to be "solid." What are the thoughts here?

5) Speaking of fabric covering. Unlike early reflection absorbers, it has been said that Bass Traps can use less transparent materials. What are some of the favorites in the DIY community?

I am sure there are other general questions that people have, so please add them if you would like. Bottomline, there are hundreds of Bass Trap threads, but depending on when they were written, as you can see above, the information may be outdated. I am hoping that some of the audio experts will jump in and help set us DIYers straight for what is the most accepted generalizations for 2013 and beyond.


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## bpape (Sep 14, 2006)

When you listen to a consensus, you'll get an average response with some correct and some incorrect. Pretty much all of what you have outlined above have their place pending the specific situation. 

The 2 I would disagree with.

1. Denser is better. Absolutely NOT true

2. You can't have too many bass absorbers. While it is more difficult than having too much mid and high absorption, you can absolutely have too much. Every room has a target curve to shoot for.

Bryan


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## louiein99 (Jun 9, 2013)

Hi Bryan,

Thanks for your response. I appreciate you taking the time to read over this post. 

I am hoping to build a thread where someone can go for the most current and relevant information on lower frequency control. I am no expert, but after scouring hundreds of bass trap threads, I realized that the same questions were being asked over and over; and many of them derive from posts that tended to be 5-10 years old. 

For instance, several years ago, the rage in DIY bass traps seemed to be using OC 705 or denser equivalent; but now, depending on the thickness many experts (including you if I read this and others of your posts correctly) now agree that less dense materials are more beneficial. I found a couple of threads where the OP basically states that, "I used OC705 when I built these a few years ago; before I knew it was better to use less dense material in my super chunks." 

That just illustrates how as technology changes, and experts in the field like you do more testing, the information out there needs to be updated. Problem is, if someone stopped looking after reading a Mixing Room site, or read posts from 2008 they might end up spending more than necessary with less benefits for watching movies.


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## bpape (Sep 14, 2006)

With the density, what happens is that a few 'experts' look at the numbers at 4" thick and see that the 705 (6lb) does slightly perform better. They then extrapolate that out to thicker panels. honestly, even the density isn't the be all, end all answer. It's really about gas flow resistivity. That said you can safely use a 3lb rigid fiberglass board for pretty much any absorber and get very good results. Sometimes you can use it on the surface and less dense behind it pending hte situation.

As I said, every situation is different. Each material has a 'hump' in absorption in different places if it has one. Some are more flat that others. This can be good or bad pending the usage. 

All of this is looking at relatively broadband absorbers. Even those with a facing on them to minimze mid/high absorption are still very broadband. Then you get to a point where the membrane's mass starts mattering such as in a limp mass or damped membrane. In those cases, the membrane should NOT be bonded to the absorptive material. These will be good for several octaves.

Then you come to a more tuned type of absorber where the membrane must be air tight (cavity too) and the membrane stretched. These are good for maybe 1/2-2/3 octave total.

The last type of absorber is the Helmholz which is a series of slats or holes and is narrower yet.


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