Can I use room boudaries as a bass trap?

Hello.

That yellow dash i think just a line to say it is a bass trap boundaries, but notice the opening is in the back.

I am asking if I can use room boundaries such as wall concrete as part of the low freq bass trap. For example, in the front of the room, there is a another small room, full of rockwool, separated by brick wall. There are holes in top corner as a bass trap entrance. Will this work?

Thanks

lets say 2 holes @ 1m x30cm in each corner, will it still not help much?

I need to learn to make membrane trap for low freq bellow 100hz. I have tried tim limp before.

I want to step up the game with steel sheet as a membrane.

www.mh-audio.nl/Acoustics/PResonator.html

will this be a good calculator? Can you recommend me other resource?

Thanks

^Really a brilliant article. It's Ethan's writings that's saved me hundreds of thousands of dollars (in debt) by convincing me a little insulation goes a long way. The lucidity of these writings maintains their value even a decade after he published them; even if their message is lost on many. Reviewing it, the device for identifying SBIR peaks and nulls lines up with my most recent learnings. Genelec also emphasizes the first 1/4 wavelength but they don't go into the harmonic progression of further peaks and nulls. Also, I've never seen a good explanation of LBIR anywhere else.

I have a question. If 2" (5cm) rigid insulation fully absorbs 400Hz, why is that? 1/4 wavelength of 400Hz is 8.44" (21.44cm) and I heard that an absorber needs to be 1/4 wavelength to *fully* absorb a frequency. I understand that partial absorption is possible in additional to full absorption of various frequencies and that this is related to absorber thickness. What I'm unclear about is whether an absorber needs to be 1/4 wavelength thick to fully absorb a given frequency.

Thanks.

I'm finding this tread interesting. When I first joined this site, I had a similar question asking if insulation in a closet would affect the acoustics in the room on the other side of the wall or closed closet door. It seems obvious now but it didn't before. Thanks to Ethan, his forum and all the other contributors, I think I now have a pretty good basic idea of what's going on with sound in "small" rooms. (seems to me, priorities seem to change in "medium" and "large" rooms so I'll have to leave that for another day...most of us don't have those size rooms anyway. But now that I think about it, stano's room is on the big side for a "Small Room" and may be entering the "Medium Room" territory. IDK) 

So, the OP, stanodx5, asks: "Can I use room boundaries as a bass trap?"

Well, the answer is no. A solid, rigid, reflective room boundary will not absorb and reduce room modes (to any significant degree if at all).

One suggestion is that if the OP wants or needs low freq bass trapping on the rear wall, fill the space with insulation (2,5m is pretty deep so that would be a very effective bass trap). The fill need only be low density fiberglass since the space is so deep. Let's use the idea of 1/4 wave length as theory of the depth to frequency relationship even though actual acoustic measurements may give us even better results. We can calculate freq of 2,5m quarter wavelength to be 34.4 HZ.

So if you build a wood stud wall, (or steel stud for fire safety) and fill the 2,5m space behind it, then cover the stud wall with acoustically transparent material, there you go!

Now, in addition, Ethan has mentioned the rear wall being a good candidate for diffusion too. Ethan builds combination absorber/diffusors. I think the idea is that the low freqs go "through" the diffusor into the bass trap. So the question is "What are the properties of the diffusor material that will work for this purpose?"

If you are going to build DIY diffusors, hopefully Ethan can share or suggest a material for this purpose... if of course it's not proprietary info. (sorry, Ethan may have mentioned this already in a post but IDK or just forgot:(

"Just one more thing..." (no this is not a Columbo episode:) I notice the dimensions before and after are both well outside of the "Bolt-area" amcoustics.com/tools/amroc?l=953&w=730&h=350&r60=0.6 but even with that, the node distribution looks pretty good and the size of your room pushes the fundamental mode frequencies quite low. The ceiling/floor is, as usual, the highest first node (47Hz) and the idea of a well treated fully transparent ceiling trap is also as usual a good idea too.

Hmm, that's interesting. Right, I looked at the absorption coefficients and it's true that materials less than 1/4 wavelength have ratings of 1.0 for a given frequency. My guess is that this is due to the sound not arriving completely perpendicular to the absorber i.e. some comes in from an angle, some from the side, and some possibly goes "through" the absorber and bounces back and becomes totally absorbed.

On one hand, acoustics can be dead simple. On the other hand, pandora's box.

Hex, you have been a terrific resource in this forum. And I'm still grateful you caught the error in my music theory video, where I confused a flat 5 for a minor 3.