Hi John,
Thanks
I think only real live measurements, comparisons and investigations can give enough answers. But that means time and money.
I checked that study I referred here again triggered by your reply, to go into some more detail.
To know how such traps ought to be build, they visited some Londen Studios including "Nomis" (a Tom Hidley design) and "Britania Row" (during refurbishment work conducted by Philip Newell) in order to check the details of the employed trapping system. (I believe I can safely assume they did this with knowledge and approval of the designers)
Confidential access*** to construction plans of a major studio, to be build around that time, from "Tom Hidley Designs, Switzerland" were defining in the geometry and disposition of these traps in the scale model. Hence there was direct personal contact between "Tom Hidley Designs" and the guy making this extensive study.
I checked the sub-studies and numerous measurements they performed to make sure the properties of the material used in the 1:10 model matched the scaled real live situation. (can assure you this is heavy stuff).
Hence this whole thing is really based on scaling Tom Hidley's principles and ideas.
Yet the outcome was how I entered before in this thread (questioning this vibrational thing).
I now even start assuming that the fact that this study is nowhere to be found or referred, while Tom Hidley himself (or whoever in his company) was sideways involved, even providing confidential data on that studio in design, must have some reason.
He MUST know that study, and NOT being happy with it.
The quality of this study really is an Univ level end work .....
With everything we collected already about this, I think the only thing one can say is:
Real live applications prove they work, and so and so we got this kind of results, but it's not really clear how they work, hence we're still far from whatever mathematical modeling or quantification, with exception of some empirical analogies.
As per your info it's center core vibration related.
As per me (belly) I assume some 1/4 to 1/2 wave resonance is somehow involved (not in panel). This should need the core. But this are just assumptions, in order to explain something I can't explain.
As per Delta acoustics some anechoic wedge behavior is simulated (not even referring to that center core).
Delta acoustics suggests that no real controlled lab measurements where executed by, or known from the original designer.
Jeff Cooper states in his book that "sometimes" a core is used (meaning: giving it some undefined not necessary function) and that they are meant "To obstruct the sound waves" (whatever that means), and "diffraction".
In his book he refers to a mathematical to be defined critical distance and configuration in function of a project, without having any related math to offer or refer to.
And for now I DO question that cutoff frequency calculation unless I see what that means in some curve(s).
. What's e.g. the cutoff of all these broadband wall traps from the traditional suppliers?
. A cutoff suggests a sudden steep drop related to some phenomenon, above which it must be close to max.
And as per this study I referred (after rechecking triggered by your response, almost certain well known by Tom Hidley, possibly even discussed) they call the observed effects still a paradox needing more investigation, even explicit investigating and questioning this vibrational stuff.
With this in mind I should be careful to divert too much from the main applications as these ceiling traps and large wall bass traps, rather than hoping the principle will work in every corner where undersized models are pushed somewhere hoping they perform their magic stuff.
*** Additional footnote in study: "Private communication from Tom Hidley Designs, Switserland"
thanks for this Eric. its very helpful to consider the relative effectiveness of different types of trap configurations. It is indeed a mystery as to how this type of trap became popular throughout the world if it had no substantiated effectiveness compared to X type of trap (still want to know what is the most effective type of trapping). it points to the need for careful consideration as to when to use a given type of trap based on space vs. effectiveness and what you're trying to solve...
I do remember (having nearly a photographic memory :wink: ) everything about our visit to Galaxy and our conversations. Eric is a kind soul and a bonafide genius (in case anyone didn't know that already...). Respect.
Many thanks Glenn,
My question remains about the use of L (lenght , Height).
Otherwise I've no idea what to do with that cutoff approach.
Can you check my question please?
Glenn wrote:
still want to know what is the most effective type of trapping
my understanding is the length of hanger + hanging distance = about 1/7th of the frequency. so if you have hangers that are 2' long + hang 0.5' for a total of 2.5' your lowest frequency affected (presumably the "cut off frequency") is 64.5hz. presumably smaller hangers are a higher cut off, and longer hangers are a lower cut off.
width should be proportional to the length. you may have some other ideas on how these dimensions play a role.
It is indeed a mystery as to how this type of trap became popular throughout the world if it had no substantiated effectiveness compared to X type of trap
The Hidley design came about because of the high levels being created in the Rock studios at the time. Sure the big bands of earlier times were loud but they preferred a reverberant room and still had dynamic range.
By the 70s the loud rock bands had guitarists with stacks of Marshall Quad boxes, similarly with bass amp stacks. The extremely high spl levels in the studio couldn't be controlled by the standard acoustic treatment of the day (absorbers mounted on wall modules) so Tom and Westlake Audio invented the hanger trap which appeared to work. Up to 1/3 of the studio floor space and most of the ceiling space was taken over by trapping. One area of the studio was devoted to the bass amp - you fired the amp directly into what was called a "bass trap" which was made from hangers. Initially they were open faced but later on Tom started to place them behind walls in an attempt to brighten up the top end of the very DEAD control rooms and studios. It was also the period where he started quoting flat down to 20hz.
For example the live room he designed for Paradise Studios in Sydney in 1979 had angled 3/4" mirrored glass walls floor to ceiling (14') but there was a port at the floor/wall intercept that allowed the sound into the heavy trapping (2' - 3') behind the glass. Similarly the ceiling was false with hangers above. (btw - I actually watched the construction and had access to the plans)
I recorded a few albums at Paradise and for me (and many other engineers) the live room was TOO live ;) so we used to set the drums up next to the open doors of the live room and use it as a reverb chamber whilst retaining a close miked sound. :D
still want to know what is the most effective type of trapping
:mrgreen: Isn't anyone ???
Some related question marks:
Passive or active?
Narrow or broadband?
Space constraints (how much weighs lesser space needed)?
Cost/result ratio?
Simplicity?
Physical/acoustical comprehensibility, predictability and controlibility?
Technical/acoustical best result independent of cost?
without whatever space constraints?
within the smallest space constraints?
Note that the use of membranes or panels are sensitive (more or less important) to the properties of the walls on which they are mounted (they become part of the system).
Well this thread is somewhat dead but sooooo interesting… after taking the time to read all replies as well as other posts regarding the issue of Hangers or Superchunks, based on everything I’ve read, the pros and cons, I finally choose to go with the hangers design, eventhough there is no data as to how they work or why they work. And to stay on the esoteric side on things my guts tell me it’s an idea worth trying :shock: . The graph below shows what I intend to do for my rear corner bass trap, based on John’s idea posted earlier on this thread.
A new frame will be built to hold the two layer of 5/8 drywall in place as well as to hold the hangers, that new frame will then be filled with rockwool on both side. Here's a couple of questions for John if he’s still around , or anyone who have some clues about what I’m proposing.
1)When using hangers in a corner like this what would be the spacing between each hangers, I’ve seen 8” to 12” to barely touching ?
2) Does the spacing between the newly added drywall (purple) corner and the inner wall meet is an important factor in the trap performance, if so, how large should it be ?
2)Again, some contradictory info on this, Light pink stuff (1.6pcf) or rockwool (2.5pcf) for the hangers and the inside of the trap.
Regards
hey there orange,
Looks good, but I have 2 concerns about your drawing.
First, the hangers look close enough together that they are touching. My understanding is that there is supposed to be airspace between them (ie, john settles on 8" to 12" between hangers?)
Second, the new wall-framed "inverse corner" at the back of the room looks to be touching the rear walls, ie, creating a very tiny "room" at the back corner. In John's original drawing on page 1, the new inverse corner did not touch the rear walls, ie, there was space for sound to travel behind it. I don't know enough about this approach to know whether it is right or not, I just saw a discrepancy between the 2 drawings.
Hi JWL
Thanks for answering. Well your concern about my drawing are my questions in my previous post. I know i drew them barely touching because i'm not sure of the spacing, i've read 8", 12" and barely touching. Same for the inverse corner wall, my drawing shows a 1" space, John's drawing shows lots of space between the walls, but how much is a lot of space :roll: i mean is it 3" or 12" or did he just draw it like that so it's clear and easy to understand ? I am willing to do whatever it take to built this monster, i just need some clarifications. Now if you know that John go for the 8" to 12" for the hangers i'll go with that without further questions but again is it 8" or 12" or am i being too picky ? :wink:
Sorry if this is anoying...and thanks again for your answer
Regards
generally, 12" if you have the space. if you're restricted with the amount of space and need more absorption surface area, i'd go with 8". worst case just a couple of inches. i'd also alternate them so they provide a path into the back corner.
Hi Gulfo
OK got it, i'll probably go with 8" then. What are the rules for these spacing ?
i'd also alternate them so they provide a path into the back corner.
Have you look closely to John's design for this trap? It involves building an inversed corner hard wall with dry wall inside the trap, that alone takes alot of space, I am not using all that space for hangers so they can't be placed like in the pict you posted ( although it's a good idea ). Now i'm wondering how large should the "ports" be on each side for this inversed wall.
Regards
no hard and fast rules... if you can use 8" and get the amount of absorption you need, then i'd say use it. if you're space constrained and you have the inner drywall set up, then opt for closer spacing and more even alignment with the idea of trying to get the hangers to provide a face to the opening - which i would think needs to be at least a foot high and a couple of feet across to ensure good flow into the space.
Hi Gulfo, Thanks for taking the time to answer my post your valuable input is always greatly apreciated.
no hard and fast rules...
Well i am always looking for "hard" rules granted but not ...fast... ?:wink:
I am definitely going to try the inverse drywall corner, after reading your last post i think that what i am going to do is this : hangers inside the corner spaced appart at 4" or 8" and the ones outside very close from each other, and hang them in a way that air can easily reach the ports each side of the corner. In other words perpendicular to the ports. Those two ports will be 12" wide all the way from to to bottom. I guess this is what you mean and maybe it was john's idea too. If john could just chime in....
i also have a question about the length and width of the hanger panels.
i have heard of homasote being used for the core of the hanger, and i have found 1/2" 4'x8' panels of it.
my control room ceiling is 11' tall, and there will be a couch in front of the bass trap in the back of the room.
is it cool to have the hangers this length (8')?
should i try to center them in the space between floor and ceiling or hang them relatively close to the ceiling?
also, should they be hung from the ceiling from the center of the board so that it can pivot, or be mounted out to the sides to prevent them from twisting?
any advice would be greatly appreciated! thanks.
Yes, from what i've read so far bigger and deeper will be more efficient in the very low freq range.
also, should they be hung from the ceiling from the center of the board so that it can pivot, or be mounted out to the sides to prevent them from twisting?
Hang them so they cannot twist.
should i try to center them in the space between floor and ceiling or hang them relatively close to the ceiling?
Centered
You may also lined the walls surrounding the hangers with absorbent material. Keep in mind that the orientation of the hangers should be parralell to the sourounding walls where possible.
should i try to center them in the space between floor and ceiling or hang them relatively close to the ceiling?
Centered
I mostly stay out of these individual things. And I still have a problem not understanding how they work.
But I don't believe this is right.
Only I can't prove it, as little as you can prove the opposite.
This isn't meant in a bad way, I really mean what I say here.
Normally the further you bring absorption in a really free-hanging field the worse low frequent absorption becomes.
And I've read some sentences here from whoever, but they are all without any measurement to substantiate this.
Forgive me if I add to uncertainty. I immediately draw back and stand corrected if some data substantiates otherwise.
An analogy with suspended ceilings: you increase cavity and your low frequent absorption improves. You increase cavity that much that it looses a logical controlled wavelength relationship with the fixed boundary and the total absorption diminishes again with the emphasis in the lows.
If distance control shouldn't play a roll you could as well see the height underneath the ceiling as the cavity, since sound does not recognize a floor from a ceiling.
With baffels I have the same experience.
But I admit these hangers are some strange things. But I also believe that a lot of never measured assumptions are made trying to fill in the gaps.
Hi Eric
I'm always impress with all your post, they're always detailed and based on a clever reflexion of the given situation. My hats off to you. Now as for these hanger thing, most of the things said onthis thread (beside yours) are based on unverified but somehow mostly agreed on what one should do to built these hangers. I just hope that some readers do not take this as the absolute truth. Most things read here are based on personal experiences and reasearch based on what's been done before and seem to work. Keeping that in mind i am fully aware that no-ones can explain why these hangers seem to work. But still, i want to built one. This very un-scientific process is more like a collections of mostly used design or way to go than real undeniable data.
regards
Erik,
I wasn't advising against the use of hangers as principle in themselves. It's an accepted approach here. And there are lots of happy people here with their constructions.
I was clearly limiting my comment to your word centered (related to the hanging height between ceiling and floor).
I don't say the have to be direct against the ceiling, but hanging them completely in a free field centered between floor and ceiling sins with about any analogy I know.
Hence I wasn't trying to question the use of hangers. Just the word "centered" triggered me here.
looks like i'll have to get Eric the 2nd edition Newell book :wink: which actually includes a whole section devoted to detailed hanger analysis (acoustic wave guide = board covered with insulation - sounds like a hanger :-)) including absorption and pressure measurements - oddly enough it occurs in front of the hangers as well as behind...
Glenn,
I don't have that book. Hence can't have an opinion.
If you think based on the info you have that centered is better it's OK for me.
I doesn't fit my belly for now.
If that gives good descriptions about the stuff, Ill buy me one.
Does that book includes any comparative measurements which relates to the point I was discussing?
Hi Eric, the appendix 1 is devoted to absorption methods and includes several other mechanisms as well as the hangers and compares across a variety of metrics. i think you will find good information there, but we all believe in the belly of Eric too!
Thanks Glenn,
You're a kind guy,
But you give a very general vague answer.
In a gentle, respectful, but indirect/suggestive manner you question my careful reply (Eric missed something).
I was discussing a very specific point, literally asked for.
I want to hear you say that based on the information you have, you advice to mount these hangers in the center between ceiling and floor.
Which was EXACTLY the point I was discussing.
What you do is diffusing my reply without putting anything as alternative.
Or can you please give some scan, quote or metrics from the part showing the answer for the discussed point.
The general fact that it describes absorption mechanisms, and shows related metrics is no answer.
I do understand absorption mechanisms (I specifically studied physical acoustics remember?), I also have books describing absorption mechanisms and teached engineers about them and acoustics in general.
This doesn't mean that it isn't interesting to me to read more and more and learn from it. I know, no matter how hard I try, I will die with much more questions than answers.
It's just because I didn't (and still don't) understand the metrics of hangers, that I searched as hell to find related stuff and only could come up with a university level study telling it's a paradox.
Does Newell solves this paradox?
This is the first time I tell this so explicit here ....
I'm always EXTREMELY careful about this because this calls for more study, but .......
It's just because I didn't understand the metrics of hangers that .....
As far I can tell from everything I can read on the net, I'm the ONLY guy who EVER really compared/measured hangers versus an alternative solution (thick wool on a cavity using the same space constraints and no, not based on THE 1/1 ratio believe/dogma/slogan).
These hangers were mounted by a master carpenter working for Eastlake audio itself, and he got all materials he asked for, applying the design as applied/intended by Eastlake Audio (can't be much closer to the source of the idea/principle).
This wasn't a scaled model as in that British study, but a real live studio application.
And while such hangers are good (but I still don't understand exactly how, when and why), the result was that I never applied them based on these costly and time consuming experiments.
And these results were discussed with Prof. Dr. Ir. G. Vermeir from the Department Acoustics - Catholic University of Leuven, in order to understand/interpret them.
But I do agree, I do not express explicit statements about them, without further study.
But my belly, while certainly fallible, is based on lots and lots of stuff.
Except for the empirical experiences, described often here (but not detailed studied or compared to whatever alternative), and results referred to by John (from his long and valuable experience), from the theoretical point of view I never saw anything convincing yet referred to in the forum.
Moreover, all theoretical references shown here until now (when explanation could be seen), more point to the lack of available insight and real study.
In fact John with the most real live related experience is very careful (which is a scientific attitude to be admired) in the why and how.
He, not just once said (free wording by me): "..... that's how they told me, and when I move them they ........
It are not rarely the ones with MUCH less experience and knowledge than John, who seem to have the final answers.
This doesn't refer specific to you Glenn, I know you're rather careful. In this case that careful that you in fact don't answer the specific question at hand.
There are designs here, the clear ceiling or back wall treatments and comparable, where I do believe them to be good.
But I also see them handled as some magic where a few are forced behind corner traps or whatever narrow spot and for me, giving me the feel of a questionable application.
It's just because I can't prove most of it, and just have my belly to go on, that I rarely intervene in such cases.
In this case however (the centered height), this is a clear principle being discussed and/or asked for.
if the largest of the hangers are nearly floor to ceiling (and i believe that is size of hangers in the research in Newell's book - but not performed by him - a PhD thesis presented the research). then i would say centered between floor and ceiling. :idea:
Eric - since we're all aware of the shortage of detailed mathematic models and detailed research data, let me turn the question a bit and ask (gently): if you were building this corner trap, what would you use? is there a more cost effective method?