Ethan/All, bass trap design improvisation help.

I was going to follow Ethan's Deep Bass Trap plans: http://www.ethanwiner.com/BTPlans.gif but instead of using 703 I decided on Mineral Wool. As you can see by my other post I have, I ordered 8lb density by mistake. I have 2" and 4" 2'x4' panels. My ceiling is 9' tall. I'd like to build traps that are not connected to the corner walls sorta like realtraps. Do you think the 8lb will be good and should I still follow the deep bass design plan and substitute plywood backing for the existing wall? Should I possibly cut the wool down to 1" or go with the is 2" or 4"?

Hey dude. Welcome again to this side. The 8 lb will work just fine in ethans DEEP bass trap. Consider this, his deep trap has a plywood (reflective) surface. You'll be fine. I am trying to visualize the "not connected to the corener thing" I am sure Ethan understands it as it is his trap. :) If the facing of the unit is a reflective surface then the 8# will work just fine. Hope that helps.

Thanks for the Welcome! The face would be reflective. I plan on using Ethan's 1/4" plywood face with 1" of air space between the ply and wool, then the mineral wool, not sure how deep though, Ethan suggests 1"... then another 2" of air space from the wool to the back... now the confusion... Ethan's traps are connected to an existing wall flat on from what I can tell in the linked diagram. I'd like to make the traps more like Realtraps in the sense that I can move them around. My purpose is that I move often and I'd like to take them with me when I do. I'm keeping everything I make removable for this reason... so...from what I can tell I need to either build a 4" 2'x4' frame, ply front, with some sort of back, maybe just fabric?????, mounting them in the catty-corner so that the back wall resonates into the trap ---or--- build some kind of tall triangular box and work from there creating air and lots of wool inside.

Now there is the question. This is a membrane absorber which requires the enclosure to be sealed. TO use it as a corner bass trap as in a real trap the unit should be built like a hi-bass absorber with an open (cloth-covered) back. But in that config you might wanna do what Steve suggested. Put a layer of fluffy stuff in front of the 8# to counteract the reflectivity of the 8# density. of course on the side facing the room :) And voila a nice bass trap. sturdy and moveable. I'd use 1x4's to construct it and keep it as light as possible.

Getting closer...How about with 1x4 2'x4' panel I do the following: 1) leave 1" of air space on the back 2) follow it with 1" of 8# wool 3) follow that by 1" fiberglass insulation 4) leave 1/2" of front air space That would give fill the 3 1/2" 1x4 space. Please modify if you can improve on this. Note: I am not sure if I need the hi bass absorber in the corners being I plan on building hi end absorbers too for the front and real walls. I'm sure you know much better than I do so I will follow your advise.

Does this revised desing still include a plywood front face?

Oops! Yes, it should. So, let's see, that makes a 1/4" ply on the face so the panel will total 4" depth. As you can see I'm a confused individual. Is the air space really needed front and rear or will I reap the benefits from more wool and/or fiberglass?

Panel resonators work by vibrating the front panel, which moves the air inside the (sealed) trap, which gets then absorbed partially by the insulation inside - bass losses occur first when expending the energy to move the front panel, then again when trying to navigate the interstices of the insulation. A light rear panel messes up the calculations, making it nearly impossible to predict the results. Probably the best and easiest FIRST thing to do to most rooms is to forget the "bass trap" paradigm, and just build some NON-backed frames (4' wide if possible) - large perforations in back board, cloth fronts, heavy/light insulation as before, and just stand them catty corner in the corners. Floor to ceiling if possible, two halves work as well as one tall one if it's easier to build/move. If tippy, a couple of screen door hooks and eyes or something to hold them against the wall; pieces of foam between frame and wall to kill rattles. If you need absorption at lower than maybe 200 hZ, and still want portable, build the panel traps to specific room mode frequencies but use a heavy (at least 3/4") MDF back so your calculations aren't totally out of whack... Steve

If you think I was confused before you should see me now! :shock: :shock: :shock: I was basing my simple design of Ethan's 2x4 realtraps which I believe his plan (link in first post) reveals. I basically wanted to modify that a bit for my room, which by the way is 15x20 with a 12' cathedral ceiling (will have mid/hi absorbers there). Everywhere I read people seem to rave about "Realtraps. I'd like to buy some but just can't afford them presently. I figured what ever I came up with would be better than nothing. I spend quite a bit of time laying out Bryan's plan and pulled together a material list. I was going to start with 6 traps and see the results and go from there... Now I have 2nd thoughts. If I forget the "bass trap" paradigm and follow your advise can you please clear up a few points for me: 1) Would 3' wide be okay? 4' is pushing it for me. 2) How deep? 3) Any air space needed inside them and how much 8# wool and fiberglass to use? 4) I'm really confused here "build some NON-backed frames (4' wide if possible) - large perforations in back board" Is the back board you mention actually the front board? you did say use Non-backed. Can I use peg board? 5) Are you saying these traps won't be effective with frequencies below 200Hz? Woah, that's a lot of questions! :roll: Sorry I just want to get it right! Have a great Weekend! Johnny

Sorry, I know how you feel - every time I make the mistake of thinking I'm getting smarter about acoustics, I learn something new and more confusing. If I keep it up(and live long enough), I'll eventually graduate to "complete idiot" status... Even Ethan has discovered in recent years that broadband trapping is more effective in smoothing out a room than panel traps - his newer mini traps are totally different than the ones plans are available for. The simplest way to do your corners is to just put 4" material diagonally across them, preferably floor to ceiling, and as wide as you can get away with - the depth will be dictated by the width, wider/deeper is better but 3 feet will help a LOT. As on the other thread, if you can put a few inches of lighter weight fiberglass in front it will help for higher frequencies, which will improve stereo imaging. Anything else for these corners is just to hold the material in place, although you don't want solid backing if you build any sort of frame - typical pegboard has too small holes and will reduce low frequency absorption - one way to accomplish holding the absorbent in place might be to use 3-4 boards about 4" wide, running horizontally near top, middle and bottom of the trap across the back - mount impaling clips on these and just push the insulation onto the spikes to hold it in place - http://www.acousticalsolutions.com/prod ... _clips.asp These can be found locally at insulation contractors, or ordered from that link. In a pinch, you could just drill holes through the back boards slightly smaller than a 16d nail and angled slightly up toward the front, then drive 16d nails through from the rear and push the insulation onto them from the front. If you don't drill first, you might split the boards. I would drive 2-3 nails in a cluster, placed at each side and in the middle, and use 3 of these boards - bottom, middle, and top of a 4 foot high trap, two traps stacked per corner. flat against the wall versions of this, placed either side of the room on the walls, halfway between speakers and your head, will treat early reflections - finally, a "cloud" of the same material overhead does the same for the ceiling. More of the same on the wall behind you, preferably spaced several inches away from the wall, and you're ready to rock. If you need a sketch to visualize any of this, let me know... Steve

I think I'm finally getting the picture. Thanks tremendously for the info. I think I can manage from here. I also was going to build 4 broadband gobos/trapping, use them as Gobos for tracking (mostly done with headphones) and use the Gobos for front/back wall treatment when mixing. In other words Movable Walls/Gobos. Make sense? 2 or 3" wool with 3 1/2 fiberglass. I thought that one side of these should be broadband absorption and the other side reflective, maybe 1/2" ply or possibly the back of the 8# wool would do the reflective job? I'd like the Gobos to be about 4'x6', 2 for the front wall and 2 for the back, possibly even treating the back wall ones a bit differently, maybe with built in diffusion? Thoughts? Johnny

Sure, there are as many variations of this as there are builders - I'd be careful with diffusion in a small room, it takes about 8-10 feet distance from a diffusor (most of them, anyway) before you get consistend diffusion. Making one side of plywood can be good - one application would be to put two of these, plywood facing inward, one on each side of the mix position, and splayed inward at the fronts by about a foot - this can get rid of side reflections without deadening the sound, especially if the room already has enough soft stuff to kill higher freq's - Another thing - a couple of these units built with predominantly open backs can be spaced to different distances from walls to increase lower frequency absorption when necessary. I saw one design somewhere, where they built the frame from 1x4 or 1x6 (on edge, like a shadow box) and made stands from pipe floor flanges and lengths of pipe - a wider base (like 1x8 or 1x10) at the floor would help stability. Looked something like this... Steve

I feel like I'm finally getting somewhere. I just drew the plans for building them. Thanks again! I more than likely will build 2 with plywood backs and leave 2 open with the 4# wool. I'm wondering how much more reflective the plywood would be over the 4# mineral wool. Any idea?

Yeah, quite a bit different; the plywood will reflect down to fairly low bass frequencies - there, the plywood should act somewhat as a panel resonator, frequency dependent on the thickness of the plywood mainly. It would be hard to calculate, I don't have formulas for open panel traps. Angle of incidence would also come into play. Two of these with plywood backs could be used during mixdown, one on either side of the console with plywood toward you, angled toward the rear of the room by about 25-30 degrees - this would fix early reflections from the sides, and the absorbent on the rear would tame reflections from other elements in the room that shouldn't be there acoustically. If you use the pipe stand idea, be aware that there could be unwanted resonances involved - I would plan to leave a pluggable hole in one end for filling with sand if necessary - you can find out about this a simple way; just hook up an audio oscillator to your monitoring system, crank it up to about 90 dB SPL, and slowly sweep from 20-20kHz - this will find any room rattles or resonances. Steel pipe will have them in the upper midrange, possibly as high as 5-6 kHz. If you don't have access to much in the way of audio test gear, here's a place you can get a few vital pieces in software, FREE - http://www.moonaudio.com/softwar5.htm Happy material mutilating... Steve

You are definitely the man! Plywood it is (on 2). Tomorrow I start gathering the materials and will build them this week...a million thanks to you! :D johnny :D By the way, thanks for sticking with me through the many changes in this post. I read it is it's entirety and boy was I drifting all over the place.

All these softwares for testing a room are all for pcs, are there any free ones for mac users.

Maybe something here - http://www.google.com/search?biw=1014&h ... gle+Search Another possibility - if you find yourself asking that question very often, look into Virtual PC - a google search should bring it up, Microsoft bought it a while back. My son's a graphic designer and has used Virtual PC with really good results; just a thought, don't remember the cost... Steve