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terry j
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corner traps, how high do they need to be?

Hi Ethan

assume you (at least) will reply!!

Once I finish my speakers, I will be able to get around to room treatment, and prob the easiest to do in the corners are super chunks type absorbers.

BUT, my ceiling height is about 17 feet. BTW, tri corners are out for treatment (tho I mainly mean the ceiling, could imagine getting away with the floor).

OK, 17 foot ceilings (5.4 metres), no doubt it would be best to do the full height but am a bit reluctant for mainly aesthetic reasons.

What would be a good compromise for the height?

(and just to stir the possum for funs sake, I also use digital eq for room correction. Having said that, I feel the best solution is both rather than one or the other)

Basically no other treatment, except for rugs on the wall to stop the echo that you get in a big solid room (about 9m by 5m, with a very deep and wide bay window, about 2.4m deep). My main concern would be bass traps, and then investigate diffusion behind me. I think I can get away without first reflection treatment, mainly as there is at least 1.5 m between the walls and speakers, and also I sit diagonally to the corner so the room 'falls away behind me'.

ethanwiner
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Re: corner traps, how high do they need to be?

Ideally you'd treat all 12 corners fully, plus the reflection points. But this is a very large room, and large rooms don't have the severe bass problems smaller rooms have. Can you post a photo or two?

--Ethan

terry j
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Re: corner traps, how high do they need to be?

12 corners??

Yeah, it is a large room, I am very lucky. Trouble is (this particular room was built in the 1870s) the builders completely failed to take into account the sonic implications of my stereo..not happy! grrr heh heh

Ignoring the bay window which is very large, the ceiling height and the width of the room are quite close, as I say about 5.4m vs 6m or so, for sure the bay deepens the width for 30% of it but still. I have not plugged those figures into a calculator, but the room has a very strong 110 hz or so peak no matter where you are or where the speakers are. Prob a result of the 5-6m dimension.

This is a bit of term term planning, as the room itself has to be renovated so I can incorporate the treatment at the same time. In most cases I will not 'fix' the treatments in place, I do have to be aware of the heritage/architectural implications of whatever I do.

Will try and rustle up a photo, sure I have a few sitting around.

One thing I could possibly do is build panel absorbers(terminology?), you know the sealed units with a wooden front panel with f/glass inside it. The room next door will have the 1.5m or so wooden panels that line the wall (we were lucky to find some old cedar ones that we can retrofit to the room), so with a bit of arm twisting I may be able to talk the boss into letting me build something similar for my room, but designed for an acoustic purpose.

That would have the advantage (as it would be around the entire periphery of the room) of a lot of surface area that also looks good. Trouble is, they might not be broadband? And it might not happen if the construction, to be effective, has to be six inches or more thick. that might look odd which negates the purpose.

Ok, just took a few quick photos, now to work out how to embed them

think that worked. hope it is not too big, but this shows the height of the corners, the reason why I cannot do any treatments at the ceiling wall junctions, and shows a bit of the bay to give an idea of how it fits in the room.

this is the room I have done up, my actual listening room is the same (mirror rooms). This would be a shot in my room from the speakers looking back at the LP

I prob need a better camera to be able to get the 'entire' room into the shot, this camera is not able to give the feel of the room in it's entirety.

BOY! It took me so long to take the photo and upload it that my reply timed out!

ethanwiner
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Re: corner traps, how high do they need to be?


Quote:
12 corners??


Yes, four where the walls meet, four more where the walls and ceiling meet, and four more where the walls and floor meet.

You should see my living room.


Quote:
One thing I could possibly do is build panel absorbers


Yes, that's a good choice for bass traps in a room that large. You could even put the same paint or wall paper on them to match.


Quote:
Trouble is, they might not be broadband?


Yes, you need traditional broadband absorption too, especially at reflection points.

--Ethan

terry j
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Re: corner traps, how high do they need to be?

Ok, depends on the definition used for corners, should have realised you meant junctions, sorry

So how high in a room like mine ya reckon? It's also a bit of an artistic thing perhaps, 'what height also gives a nice proportion' type of thing, ie a bit more than just 'acoustic function'.

Put it another way, emotionally I can grasp why some people look for room treatments that are 'invisible'...might be a market there for you Ethan ha ha

Re the wall lining, I could always make varying sized panels in an attempt to at least have differing bands of operation, and yeah it would all be done to look in place, except have the hidden acoustic function. But again, depends on the depth required to get decent absorption.

I should have perhaps shown a pic of my room with the speakers (only showed that one cause the lighting is better and also to show exactly why I can't treat wall/ceiling junctions etc) cause you again mentioned first reflection points.

What is the cutoff point distance wise where you may not need first reflection absorption? My memory is a bit vague, but basically it's all to do with the timing of the reflection vs directed yeah?, which is directly related to distance. Or are you saying basically 'in any conceivable domestic room I cannot envisage one large enough that first reflection absorption is not warranted'

I do have some of those movable office divider type things beside each speaker where the first reflection would be. Lightweight and flimsy, but in any case can't say I notice any difference with it there at all. If they are effective I doubt they'd absorb very low.

So is it also a case for FRA (got sick of typing first reflection absorption) to absorb as low as you can?, ie even there use as thick an absorber as possible? Ideally in FRA how low should you be able to absorb to

Jan Vigne
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Re: corner traps, how high do they need to be?


Quote:
Put it another way, emotionally I can grasp why some people look for room treatments that are 'invisible' ...

http://www.synergisticresearch.com/

terry j
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Re: corner traps, how high do they need to be?

thanks Jan

umm, that WAS what I was referring to (and the like), and I hang my head in shame that I was being tongue in cheek (to ethan) and you tried to help me.

sorry about that

I like the latest discovery in room treatment, blocks of tape (as in masking tape thickness)in the corners of the room, sigh.

It is an 'outgrowth' of the enable treatment, seems nothing that the magic of those bits of tape cannot fix. Wait, don't want to give the idea that they are magic tape a la May or anything, no normal tape but in a magic pattern.

Oh well, think I have no choice but to stick with physics, it seems to have some sort of bearing on our everyday lives doggone it.

ethanwiner
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Re: corner traps, how high do they need to be?


Quote:
So how high in a room like mine ya reckon?


The more total corner surface you cover, the better. Always. It's that simple. However, you can use a little science to find which locations will benefit most from a small number of traps:

Pink noise aids placing bass traps


Quote:
depends on the depth required to get decent absorption.


Two inches for reflection points, and at least four inches for bass trapping.


Quote:
What is the cutoff point distance wise where you may not need first reflection absorption?


A 20 foot difference in distance between the direct and reflected sound. Sound that arrives within 20 milliseconds of the direct sound is considered early. And when the distance is farther the reflection are also weaker.

Another metric for this is aiming for the reflections to be at least 15 dB softer than the direct sound.


Quote:
is it also a case for FRA (got sick of typing first reflection absorption) to absorb as low as you can?


Yes, though this is mainly a mid/high frequency issue that affects imaging and clarity. But you can never have too much bass trapping, so thicker is better.

--Ethan

terry j
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Re: corner traps, how high do they need to be?

thanks ethan, you know I feel a little embarressed, of course you're correct, the answer is 'as much as you can', duhh, sorry I should have thought a little more before asking. thanks for taking the time anyways

two inches for reflection points, well straight away that makes any conclusions I have about my thin office dividers as FRP absorbers totally invalid. well worth the time and trouble to try it properly.

I must admit I've seen varying times that people feel are early, I think from very poor memory that 20 ms is at the high end of those figures. Still, what is important is that it is the difference rather than 20 feet from speaker to wall and then wall to LP, 20 feet (or even 10) difference is a LOT.

Can you tell me just HOW you can measure the db difference between direct and reflected?? Another thing I've often wondered about (again, check my terminology), the transition point between near field and far filed listening.

There is some sort of 'formula' that tells you were that point is, dunno, when the two energies are equal (?)

Anyway, I've only just started to wonder cause I now find (after much trial and error to find my 'magic speaker and chair placement) that any slight change of chair or speaker positioning seems to produce big changes. I must be on some sort of 'knife edge', and am wondering if I have found (for my room etc etc) that transition point?

Anyway, similar to my question above, can you tell how it is you manage to measure the direct sound vs 'combined sound' (if that is the basis of what I'm talking about)?

It's all well and good that these terms are thrown around, but unless we can practically measure them they just stay 'terms bandied about' if you follow.

edit

thinking about how to measure how far down the reflection is
I think you need to look at the impulse graph? You should see a 'peak' that represents the initial pulse from the speakers, then at a later time another peak, which I presume is the first reflection.

close?

KBK
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Re: corner traps, how high do they need to be?

Beautiful house, BTW.

If it is horsehair plaster and slatboard underneath..then you have most of the issue solved already. If it has been removed and replaced with drywall, then shoot the guys who removed it. Drywall is the worst. Drywall is easy and cheap to install....it is not good for acoustics - at all. However, it is good for those who have to go in and repair acoustics. The best solution is for the acustics and mechanical expert to be there before the plans for the building are finalized, but so few people know how little such a thing could cost at that level and so few know how vital it is.

When putting together ANY building that people have to be inside of, having an acoustician and mechanical design expert as part of the team at the planning stage can save $100's of thousands-and on bigger projects..easily into the millions.

Looking at the picture again, it is just too dang perfect to be anything but modern drywall construction. Unless there was a very fanatical owner involved in restoration, it is going to be drywall. If that really is the original walls..and the builders were THAT good....then it already is a good sounding room, with not to much to fix. Not too difficult.

The bay window is an excellent bass trap so your problem is immediate reinforcement by width height issues, not long term boom or pressure loading.

You should spend time going for speaker placement FIRST before heading for treatment, as due to the big bass trap that the window itself is.... treatment is not going to do as much is it normally would in a sealed room. Check the floor for excitation. check the walls for the same. If they are 'firing up' then corner treatment is not going to solve all that much of the issue.

110hz is getting near the difficult range (lower frequencies) for traps to be effective with, and any traps used will suck out frequencies that are above it in frequency as they are more effective in that upper range. This will not fix the 110hz issue -- but will exacerbate it at the same time it sucks the natural, workable and beautiful 'life' of the room dry. More will be taken out at the upper mid-bass ranges than in the ranges you desire--and the acoustical tilt will be worse, not better. What I'm saying is that the last thing you want to do to the room is to use the usual suspects of acoustical treatment and make the room sound like some shitty box theater in a local shopping mall area.

If it is acoustic space resonance related, it should be possible to find the excitation zone by speaking in a very loud and bassy voice and simply walking around the room. You will know it when you hear it. I'm leaning toward it being a floor resonance/flex issue. If you stomp on the floor and get a boom, then that is where most of the issue is at.

If you have ventilation like as in older houses have with the floor and wall plates for thermal flow, then the room and adjoining spaces could be the issue as they would then be coupled acoustic resonators.

Is there a basement or crawl space? Crawl spaces can create this sort of an issue. Hard reflections can be the issue there with the floor being fired up as the secondary point.

ethanwiner
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Re: corner traps, how high do they need to be?


Quote:
thinking about how to measure how far down the reflection is I think you need to look at the impulse graph?


Yes, exactly, and you do that with room measuring software:

ETF, Windows, $150

FuzzMeasure, Mac, $150

Room EQ Wizard, Windows and Linux, Freeware

This article explains how I use ETF, but the principles apply to all such programs. This article doesn't get into measuring impulse response, but all of the above software can do that.

--Ethan

JoeE SP9
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Re: corner traps, how high do they need to be?

Thanks Ethan, I'm going to give Room EQ Wizard, Windows and Linux, Freeware a try. I've already downloaded it.

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