ths61
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Posts: 22 
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Post by ths61 on Aug 11, 2018 18:49:32 GMT
I have a few questions about the Bass/Panel/Membrane traps described in Ethan's article found here:
- What is the actual thickness of the 1/8" and 1/4" plywood ?
- Can these sealed traps be made free standing so they could be moved and hung on a wall ?
- Can these traps be made to extend the lower frequency coverage by using a thicker plywood (e.g. 3/8" plywood) ?
I noticed that Ethan's design goes from using fabric (virtually no membrane) to 1/8" to 1/4" (0, 1, 2 thickness progression) and wondered if continuing the progression to 3/8" (0, 1, 2, 3) would extend the frequency range coverage to lower frequencies ?
Note (added October 7, 1999): Although it is not stated in the article, the low-bass trap is effective at frequencies between about 80 Hz and 160 Hz, and the high-bass trap absorbs frequencies between 150 Hz and 300 Hz.
I have some uneven brick walls, thus using toggle bolts and straight boards would be problematic for this application. I was wondering if these traps could be made self contained by using 2 layers of plywood, one front and one back while maintaining the internal dimensions?
I have a few RealTraps in my room but still have issues below 100Hz that I would like to address, mainly centered @ 40Hz.
Since the free standing traps would have 2 layers of plywood, they could be made with 1 thickness of plywood on one side and another thickness of plywood on the other side (e.g. 1/4" and 3/8") so the front facing side would chose the frequency range (e.g. dual-range traps). I would assume that the unused side would have to be damped when hung to not encourage additional panel resonance by having both front and panels vibrating in tandem.
As for using 1x4's and 2x2's on the sides, top and bottom, 2x4's could be used with a 1" dado down the center to hold the rigid fiberglass like how floating panel doors are made (with the rigid fiberglass being the floating panel). This would maintain the air space between the rigid fiberglass and the front/back plywood panels as well as grip the entire edge of the ridge fiberglass in the dado groove. The 2x4's should be rigid enough for self-standing structural support as well as stout enough for hanging purposes.
Since the existing design use 3/4" edge to attach the plywood, a 3/4" rabbet cut could be made on the edges of the 2x4's to thin the plywood connecting edge from 1.5" to 3/4" like the existing design if the extra edge width is of concern. If it is not of concern, it will make a more secure gluing/calking/nailing surface at 1.5".
Thanks in advance for your help.
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Post by Michael Lawrence on Aug 11, 2018 19:59:00 GMT
Hello ths61-
Welcome. I'm not exactly clear on what you're asking, but I did give Ethan a heads up about your post so he should be along shortly.
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Post by Ethan Winer on Aug 11, 2018 20:12:09 GMT
Thanks for the heads-up Michael. ths61: 1. The actual thickness of plywood is very slightly less than what's stated. But for thin plywood like this I believe it's the same as stated. More here: theplywood.com/thickness2. Yes, but then you have to make a very thick rigid backing, or at least ensure they are pressed tightly against the wall with no air leaks. 3. Yes. 4. The fabric panels are mid/high frequency absorbers, not tuned bass traps. I really suggest avoiding this type of bass trap. If you'd rather not buy more RealTraps (Fat MondoTraps and MegaTraps target 40 Hz very well) you'll do better with very thick rigid fiberglass. If you get the FRK type all the better. Even if you'd rather treat the room with wood panel traps you'll still need a lot of them. So the same amount of money and effort will go much farther with traps made of rigid fiberglass. |
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ths61
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Posts: 22
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Post by ths61 on Aug 11, 2018 22:57:53 GMT
Thanks Ethan for the quick reply. My take-away from your answer is that the wood panel traps are not as effective as other solutions per square foot for frequencies below 70-80Hz.
Thanks Michael for the heads up, Ethan understood the questions.
I already have Mega, Mondo, Mini and 2 - 6'x2'x4"DIY OC 703 traps in the room which seem to have tamed from 70Hz and up. Also have a pair of 1D QRDs to break up the backwave and tame my strongest early reflections.
The 1/48 waterfall plot below is the left speaker at the listening position (no EQ) with the bass/broadband trapping and QRDs. I have some asymmetry in the back of my room (3 different room lengths), but the right speaker has similar issues in the [30-60]Hz range (and 25Hz). The 40Hz corresponds to my room's axial width mode.
I am looking for a targeted solution for the remaining issues and noticed Ethan's wood panel trap's effective range was @ 1 octave each. I looked at Helmholtz resonators, but they appear to be a much narrower filter than what I need at 1 octave. I don't know if it is a realistic goal to have similar decay times across the frequency range.
The MegaTraps appear to have the most absorption just above my problem area.
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Post by Hexspa on Aug 12, 2018 10:17:52 GMT
Well, ths, I don't see much of a problem. Again, I consider 20dB decay within 150ms to be a reasonable standard. You've got your waterfall set to 45dB which is 50dB of decay for your low peaks. Narrow the dB range and make it relevant to your target. According to an EBU recommendation* for audio rooms, you don't want an even decay across your spectrum but a tapered one. Whether they arrived at this as a nigh inevitable consequence of bass being hard to tame or if it just sounded good, I don't know. In any case, they got super nit-picky with everything and that's why I stick with my first suggestion.
Thanks
*Section 2.3 Reverberation field, p. 6, and Fig. 1
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Post by Michael Lawrence on Aug 12, 2018 13:30:39 GMT
Hexpsa is 100% correct. Generally the preference is towards more decay in the LF. See any of the surveys by Beranek, or the Master Handbook of Acoustics. That's how rooms sound naturally, and what our ears are used to. RT60 flat across spectrum actually sounds pretty weird in a lot of cases.
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ths61
New Member
Posts: 22
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Post by ths61 on Aug 12, 2018 18:28:08 GMT
Well, ths, I don't see much of a problem. Again, I consider 20dB decay within 150ms to be a reasonable standard. You've got your waterfall set to 45dB which is 50dB of decay for your low peaks. Narrow the dB range and make it relevant to your target. According to an EBU recommendation* for audio rooms, you don't want an even decay across your spectrum but a tapered one. Whether they arrived at this as a nigh inevitable consequence of bass being hard to tame or if it just sounded good, I don't know. In any case, they got super nit-picky with everything and that's why I stick with my first suggestion.
Thanks
*Section 2.3 Reverberation field, p. 6, and Fig. 1
Michael,
I have a copy of MHoA and will do more reading.
Hexspa,
Thank you for the link and target goals.
Here are the new plots with a Y-axis set at 25dB range (from doc: "... usually measured over the range from 5 dB to at least 25 dB below the initial value ...", "... measured in the listening room with 1/3rd octave filtering ...").
The paper you referenced indicated the measurements should be taken with 1/3 octave smoothing so I also included that plot.
As for the plot of Figure 1, I am still trying to grok it. It seems to be a gating plot with a knee from 200Hz and below, but there is no corresponding dB references. It does imply that frequencies above 200Hz should be at 50ms (but at what dB drop).
The new plots appear to be mostly within 20dB in 150ms until the 2 lower room modes kick in. The 40Hz mode is product of 2 room modes.
1/48th Smoothing:
1/3rd Smoothing:
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Post by Hexspa on Aug 13, 2018 17:46:32 GMT
Ok, I'm drinking but hear me out. They're talking RT60 and I'm talking RT20. Ethan said that decay is linear. I except low frequencies because even a breeze will make your modes ring. That being said, they want, what, 60dB of decay within 300ms for your 40Hz mode? Bro, you're already down 20dB within half that time. Modes gonna mode. In my opinion, otherwise known as unquestionable fact, you're good. Ya, you can target this issue but at what expense? If you're ready to achieve perfection then I'm ready to eat some  . I'm always inspired by a true renegade sensei. Sláinte
P.S. - Wait, wait. I must be known for editing every one of my posts by now so let me throw something in, real quick. You know why they say '5dB...' in that White Paper as RT60 for measuring a totally unspecified frequency, probably 20kHz?
BECAUSE THEY SPEND OPM*!
This is your room we're talking about that you rando-ly made awesome. This here is exactly why I don't adhere to their jabber - it's pure British Bollocks. We all want perfect, and the so-called experts are ready to inform you. /rant
*Other People's Money
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Post by Ethan Winer on Aug 13, 2018 18:07:04 GMT
Ok, I'm drinking but hear me out. LOLZ. |
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Post by Hexspa on Aug 13, 2018 18:08:20 GMT
Hang on. This deserves its own post:
THEY DON'T EVEN SPECIFY BELOW 63Hz! They're like, "Meh?!"
Ethan gives up at G1 and the English are singing soprano with C2. For godssakes, hespect 'Murica lol
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ths61
New Member
Posts: 22
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Post by ths61 on Aug 13, 2018 19:57:40 GMT
Hang on. This deserves its own post: THEY DON'T EVEN SPECIFY BELOW 63Hz! They're like, "Meh?!"
I saw the gap @ 63Hz as well and included it in my head scratch at attempting to interpret the diagram you referenced.
As for being made "ramdo-ly", I followed the instructions from Ethan's very educational website first and then added the QRD's to address issues specific to my room and speaker combo. It wasn't random, it was 'plagiarism' (for the lack of a better term, maybe "monkey see, monkey do" would be more accurate in my situation), I tried to utilize the published wisdom of others as the starting point.
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Post by Hexspa on Aug 14, 2018 11:36:54 GMT
Hang on. This deserves its own post: THEY DON'T EVEN SPECIFY BELOW 63Hz! They're like, "Meh?!"
I saw the gap @ 63Hz as well and included it in my head scratch at attempting to interpret the diagram you referenced.
As for being made "ramdo-ly", I followed the instructions from Ethan's very educational website first and then added the QRD's to address issues specific to my room and speaker combo. It wasn't random, it was 'plagiarism' (for the lack of a better term, maybe "monkey see, monkey do" would be more accurate in my situation), I tried to utilize the published wisdom of others as the starting point.
Sorry, I need to install an ignition interlock for my keyboard. I meant that in a supportive sense as in you probs don't have their budget or cumulative experience. In other words, good job.
Still, don't be put off by their lack of specification. Like I said, even Ethan stops prioritizing below a certain cutoff. There may be reason to it in that long decay in that range is acceptable.
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. I'm always inspired by a true renegade sensei.