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Post by santodx5 on Mar 5, 2023 4:07:53 GMT
Hi Guys,
I am building a new home theater room. Size is 7.3x12x3.5m. The length is too long so i will make a new concrete wall about 2,5m to make the length about 9.53M.
Can i make this 2.5m new room as a low freq bass trap by filling it with rockwool + dacron and make holes in the corner as "a bass trap entrance?
I attach rough drawing and a plan from FB that inspire me.
Thank you.
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Post by Ethan Winer on Mar 5, 2023 17:21:59 GMT
I'm not sure what you're asking. And what are the yellow dashed lines?
If you want to make the ceiling into a bass trap that's a great idea. But the absorbing material should be fully exposed to the room below. So the entire ceiling should be thick absorbing material. Also, the side-wall reflection areas should be treated with absorption, not diffusion. Diffusers are best used in the rear of the room behind you.
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Post by santodx5 on Mar 6, 2023 1:31:22 GMT
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
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Post by Ethan Winer on Mar 6, 2023 17:31:02 GMT
If sound has to pass through small holes to get to absorption on the other side, that will not help much.
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Post by santodx5 on Mar 7, 2023 3:36:37 GMT
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.htmlwill this be a good calculator? Can you recommend me other resource? Thanks
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Post by Ethan Winer on Mar 7, 2023 16:06:23 GMT
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Post by Hexspa on Mar 10, 2023 3:15:58 GMT
^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.
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Post by Ethan Winer on Mar 10, 2023 19:53:14 GMT
I think the quarter wavelength idea is more theory than practice. I mean, if 2-inch rigid fiberglass measures as fully absorbing 400 Hz, then there's your answer. Of course, we know that spacing the fiberglass off the wall absorbs even better and to a lower frequency. And 1/4 wavelength spacing puts the fiberglass where wave velocity is maximum.
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Post by rock on Mar 12, 2023 16:14:30 GMT
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.
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Post by Ethan Winer on Mar 12, 2023 17:08:17 GMT
The RealTraps diffuser wells are made of Gator Board, a type of sturdy cardboard, with rigid fiberglass behind. So bass goes through the cardboard but mids and highs are reflected / diffused.
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Post by Hexspa on Mar 15, 2023 10:40:30 GMT
I think the quarter wavelength idea is more theory than practice. I mean, if 2-inch rigid fiberglass measures as fully absorbing 400 Hz, then there's your answer. Of course, we know that spacing the fiberglass off the wall absorbs even better and to a lower frequency. And 1/4 wavelength spacing puts the fiberglass where wave velocity is maximum. 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.
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Post by Hexspa on Mar 15, 2023 10:43:45 GMT
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. Ethan and others have noted that, depending on building material, walls can be about 5% more distant acoustically due to their absorptive properties. Often you'll see measurements which reflect this i.e. an 8' ceiling but ringing below 70Hz (or whatever it is). Additionally, the bass traps you add will contribute further to this. Please allow me to take this time to thank Ethan for creating a hospitable environment here - as much as I tried to burn it down . I've been exploring a few other forms and, let me say, it can be tough out there. Thanks, Ethan!
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Post by Ethan Winer on Mar 15, 2023 16:23:15 GMT
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.
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Post by Hexspa on Mar 16, 2023 7:58:27 GMT
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. Haha I don't remember that exact one. The one that comes to mind is where you decided to write the song a perfect fourth higher key signature because "bass players rarely pedal on I-IV" It was unusual, to be fair. heh
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Post by Ethan Winer on Mar 16, 2023 16:45:13 GMT
My flawed example was on the song It's My Life by The Animals. I said "the guitar plays a minor third while singer Eric Burdon goes back and forth between major and minor thirds to avoid a clash." You pointed out that Eric alternates between a normal and flatted fifth.
I don't recall anything about a fourth higher.
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