Hanging Panel Bass Trap vs Plywood Front Bass Trap

Ok...What's the difference between the two bass traps below? Is one more effective than the other? Thanx!

Maybe part of the answer is here... http://www.johnlsayers.com/phpBB2/viewt ... p&start=15 Seems the volume level you plan to listen at may or may not give you the need to have hanging panels according to Steve.

Camistan - they are very different. The panel absorber is reflective. It only absorbs around the frequency it's tuned to. i.e. 1/4 plywood would absorb lower than 1/8" plywood over the same airspace as it has a lower resonance frequency. The amount a panel absorber absorbs in a room is relative to the size of the absorber, i.e. it's surface area. the more area the more absorption. Your rear wall on the other hand is a broadband absorber - it's absorbs the high end as well as low end AND it has a large surface area not only on the wall but within itself, when you add the surface area of all the hangers you can see what I mean. What I suggested before was to add a reflective front to your wall, like I did in the drum room, to stop all the highs being sucked up by the wall.

may not give you the need to have hanging panels according to Steve.

I disagree with Steve on this - they are absorbers and the volume of the playback is not relative. 50hz is 50hz at any level and it's ratio to 10khz and the other frequencies stays the same. cheers john

I really question the value of those hangar traps. Has anyone done some conclusive testing and found that they were significantly more effective than rockwool/fiberglass alone? The reason why I question it is that a mass swinging on a string stores energy fairly well, and in order to remove bass from the room you need to waste that energy in the form of heat. Pendulums can swing for quite some time with only an initial energy input. Also, consider that the frequency at which a pendulum vibrates is a function of it's legnth. I looked at some simple pendulum equations and found that if you wanted your absorber to resonate at 20Hz, you'd need a rope that's less than 1 cm long (and that's to the center of mass). That doesn't appear practical, so most of the design for hangars that I've seen are resonating at very low frequencies. Are they effective? What is damping the vibration of the hangar (lets face it, it's vibrating, not really swinging)? I just don't see how these traps are worth the effort....any dissenting opinions? I'm happy/willing to be totally wrong here! Cheers, Kris

I'm not certain its a pendulum effect or its simply increasing the surface of dense (or varying density) materials. it would seem that a large volume would move the hangers, but I think the suspending rope is more of a decoupling function and somewhat of a positioning function as well. given the effect of insulation alone versus dense materials and insulation, it would seem intuitive to be more effective. I'd argue that the efficiency of hangers is probably improved by their relationship to the opening which guide the sound into the area - angled versus straight - and the size and density of the plates has some resonance quality that improves the trapping as well. It may be that properly configuring the hangers to increase the free travel of sound into the hanger space (sort of like a maze...) would increase its effectiveness (easy in, hard out) but would be more complex than simply hanging a bunch to increase surface area.

Kris - the hanger was invented by Tom Hidley of Westlake Audio back in the 70s. If you check the plans of a later Hidley studio, under his later company Eastlake Audio, you will see that he bases the control room plan on a 35' x 35' square. The angled control room shape sits inside with over 1/3rd of the floor space, 4 - 5 ft depth, taken up with hangers behind the walls. There are big hangers behind the walls, smaller hangers in the ceilings. He specifies that his rooms are flat down to 20hz. I've built them into various studios and they do work - don't ask me how, but I've witnessed them working many times. The hangers Hidley built (I've seen 3 - 4 different Hidley studios during construction) are made of soft fiberboard wrapped with insulation and hung by two wires. If you move one the others will move in sympathy ;) A bass trap under this definition is an area full of hangers where the sound enters via an opening, travels through the hangers and is reflected back out through the hangers again, that's if it is still going ;) This can also be above a false ceiling with ports around the edge opening into the space above. They can also be hung into a corner where the hanger increases in width as it get into the corner, same effect, the sound has to travel through the hangers and back out again. I hope this helps cheers john

I thought it best to pick up an existing thread, instead of starting a new one. I realize this system being under debate without any substantial research to back up any point of view... but based on your experience, how would one go about designing the use of hangers within a given room? I mean, can the range of effect be estimated by the hanger's dimensions (much like would a resonator panel) or is it power-by-numbers (the more hangers, the broader the effect)? I ask cause the concept speaks to me and I'm willing to give it a try in our new radio / live combo studio. http://www.johnlsayers.com/phpBB2/viewtopic.php?t=10037

"I disagree with Steve on this - they are absorbers and the volume of the playback is not relative" John, I doubt I said exactly that - my understanding, which I thought I'd gotten from you, was that hangers were developed from the need for better bass absorption due in part to the trend toward higher mix volumes in studios during that time period. If I said something to indicate that they wouldn't also work at lower volume levels, it was unintentional, mis-quoted or worded unclearly on my part. I don't think treatments beyond the "basics" of first reflections, clouds (also first reflections) and rear traps should be built by anyone not experienced in this field (myself included) without a LOT of listening/testing as you go - it's too easy to build two "identical" devices that are NOT, just from differences in materials, fasteners, glues, etc - this includes WALLS since the "normal" wall is typically gypsum over studs, which is a panel trap in disguise. It's been proven that it is nearly impossible to build a panel trap to a specific resonant frequency without allowing some sort of "soft surround" and screws to adjust tension, etc - and this is something that is PURPOSELY built. Imagine the variations in a wall, where screws may be different lengths/spacing/damping, etc... Steve

Point taken. 8)

The hangers Hidley built (I've seen 3 - 4 different Hidley studios during construction) are made of soft fiberboard wrapped with insulation

can anybody post a picture of soft fiberboard? i realy don't know what it is, and look's like. Maybe somebody have a link, for ordering these material in europe??? cheers Mika :D

Mika - it is also called homosote here's a picture of it.

Thanks John :D Before i thought it is also possible to use MDF plywood for hangers, but now i found a manufacturer in germany called homatherm. this is the link to the stuff i think, it is the same which you mean!? : http://www.homatherm.com/int/produkte/h ... ibung.html cheers Mika

It doesn't look like it's the same - but it does look similar :) here's the US site http://www.homasote.com/products/440-Soundbarrier.aspx

Hm John, why do you want to get me frustrated? :cry: I can't find something similar here in europe/germany. Do you think some kind of very rigid galsswool will do the same job, or more something like plywoodboard or gypsumboard? Do a hanger need something porous or just a kind of membrane? please help me to understand this important element of basstrapping :wink: cheers mika

Mika - it's a common product - it's made from recycled paper and usually comes with one side painted white as it's main use is for notice boards because you can stick drawing pins into it easily.

I hope that i found the right material now :roll: What about this: http://www.modulor.de/shop/oxid.php/sid ... ttype/list cheers mika

I want to build hangers in my front corners. I was suggested this calculation for hangers previously on this forum. f=344/7x(l+s) l- length of the wire from the top to the board s-the length of the board (see the picture below) So I want to build hangers for 60Hz that makes l+s= 344/7x60=0.819m=81.9cm Is this calculation right? Normally I see already made hangers and almost always they are from the top to the bottom long and by this calculation my hangers should be only the third of the height of the ceiling If I am wrong please tell me how to do it right. Thank you very much. Cheers, Joka :D