John Sayers' Recording Studio Design Forum

Hi guys

I did some listening test in my CR, you may check my construction thread here : http://www.johnlsayers.com/phpBB2/viewt ... 9955#59955

I would need some cues on what you guys think is happening with this room, and what action should be taken.

Thanks

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Eric
Orange Numerik
Montreal

Technology is just faster ways to do things we didn't have to do before !

Sorry, I don't have time to plow through six pages of that thread. But I can offer this:

Have you optimized the speaker placements, and the listening position to the 38 percent "rule?" Read more about that here:

www.realtraps.com/art_room-setup.htm

The main null I find in most rooms is related to 1/4 wavelength (and its multiples) distances from the rear wall behind you. For this reason you want to put traps on the rear wall as well as straddling as many corners as possible.

--Ethan

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The acoustic treatment experts
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Orange,

I'm not surprised that so much of your low end is accumulating in the rear corner, since your room is shaped to aim all sound reflections back there. You're definitely going to want to build as big a superchunk as possible in that back corner.

If it were my room, I'd probalby go with a huge superchunk in the rear corner, more absorption along the 2 rear walls, slot resonators on the 2 side walls. I'd probably go slot on the front wall as well.

Orange - I'd build something like this in the rear corner

cheers
john

John, thanks for piping in on this. Interesting about the bass hangers, I know you're a fan of them. Do you think they will be more effective than filling the entire area back there with absorptive material? Well, you must or your wouldn't have suggested it....

I just wonder about the differences between the two approaches.... could you maybe say more about why you prefer that approach?

I'm interested too because I know little (okay, nothing) about slat absorbers and I should!

--Ethan

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well - the main addition was not the hangers per se it's the angled drywall walls.

Most control rooms have a bass buildup in the rear of the room, possibly because of the angled walls directing all the signal to the rear of the room.

see attached pic.

I remember an article way back in the 70s in REP discussing this and the author offered the triangular rear wall solution. It does work - Guruland has a triangular rear wall sot resonator and there is no bass buildup in the rear. Unfortunately it takes up space but in the corner room like this it's space well spent IMO.

cheers
john

Thanks guys, thanks John

Very informative info here. At first i was shocked by John proposition but the more i looked at it, the more i thinks i get the way it works. I must say that i am not a big fan of the hangers principle, but i've seen them so many time in many studios, i may give it a try.

four question for John :

1-Does the added "solid wall with drywall" has to be as massive as possible and sealed or just one layer of 5/8 gypsum will do ?

2- The center frequency of the slat resonators on the side walls can only be determined by testing the room with measurement gear ....right ?

3-When you say "heavy insulation" for the rear walls do you mean "Thick" or "high density" (4pcf and up). As we speak i have 3" of RW spaced 3" from the walls 4ft high X 8 ft wide centered at hear height.

4-


So if i get this straight, in my case i can't built a triangular rear corner slat resonator because i don't have enough distance between the listening point and any reflective rear surface, so the rear corner has to be absorbent, right?

sorry if those questions are just obvious but i am a bit discouraged and i need approval that i am on the right track.

jwl wrote:


I plan to have two slot resonators on the front wall over and under the main window, that is for sure. But i still don't know if i will use the front wall corners to soffits the monitors, or as bass traps or even slot resonator... hum

Bonus question : When building a bass trap, am i right to think that higher RW densities is prefered. I always tough so but i seem to read just the oposite from time to time. I am using Roxul Safe n"Sound 3" (3pcf) for all my traps.

Thanks to all this is great info.

_________________
Eric
Orange Numerik
Montreal

Technology is just faster ways to do things we didn't have to do before !

I'd use two layers for extra mass - it is low end we are dealing with here.


Not really - you are aiming for the low mid frequencies that the insulation doesn't absorb , i.e 100 - 350hz.


yes - that's the pcf but I'd do the whole wall, niot just an 8' x 4' area.

4-


correct.


cheer up mate - It's not brain surgery


Roxul Safe n"Sound 3" (3pcf) is fine.

BTW The further forward you can build that rear wall unit the better, work out where the rear wall works best and built it out to there.

cheers
john

Interesting, John. Thanks for taking the time to explain the angled wall. Very good idea.

I'm still curious about the bass hanger vs. absorptive mass/superchunks approach. It seems to me that the greater mass of absorptive material from a superchunks approach would provide more absorption that the bass hanger approach, and therefore would flatten out the low end more effectively.

But then I still don't quite understand the theory of the bass hanger approach.

What if you built the small angled wall as you suggest above, then fill the spaces behind the false wall and around the angled wall with absorption?

Or perhaps asked a bit more succinctly, what advantage does the bass hanger approach have over a superchunks (or fill-the-space-with-absorption) approach?

These are all good questions jwl, i'd like to know too.

BTW thanks to John for answering all my questions so fast, it's really appreciated.

_________________
Eric
Orange Numerik
Montreal

Technology is just faster ways to do things we didn't have to do before !

good question - the superchunk is a new method for me so I'm making assumptions here.

The hanger traps have never been officially explained as far as I know - they were an idea put forward by Tom Hidley in his studio designs. The only explanation for how they work was demonstrated to me one day when I was down by the river - there were oyster pots hanging in the water by the river and a boat went past creating a wave - as the wave passed through the oyster farm all the hanging oyster pots moved together and the wave was absorbed and didn't make it to the shore.

I realise this is not a scientific explanation but it's the only one I have - perhaps Eric could offer a better idea.

The advantage I see in hangers over superchunk would be simply less materials. Filling the whole corner using the superchunk method would use up a lot of insulation, and I mean a lot!! hangers on the other hand would probably use less than a quarter of the amount. Also corners are not the only place you want to absorb low end. How about in a ceiling? are you going to fill a whole ceiling using the superchunk method? I think not.

cheers
john

I confirm John here.

I never found a real conclusive explenation and have been discussing this at the Catholic University Leuven.
I do have measured them and compared with other alternatives.

There is one real study I know about (a book of 127 pages which was a dissertation submitted for the degree of Master of Science from the
University of Southampton
Faculty of Engineering and Applied Science
Institute of Sound and Vibration Research
Dated 1990 by L. E. B. Soares

It has costed me (period 1989-1991) A LOT of effort to 1) discover the very existance of such study and 2) to get me a hard copy of that (AFAIK non-published) thing.

An extract from the opening summary:

....... The results present no significant evidence of low-frequency absorption by a vibrating process. The mechanisme responsible for the effects observed in real studio control rooms is therefore still a paradox, and further research is needed.

This is an extensive study, directly related to the hangers as described here, where one searched for the supporting theory and tested in a special for this purpose build scale model at 1:10.

I have done numerous measurements in real life and in the lab on hanging baffels, with and without core, as applied in more industrial applications. These measurements do not confirm these low frequent qualities.

Possibly, but here I'm assuming, has this to do with the smaller distance between the hangers in studios, causing a damped 1/4 wave resonator effect when close to a reflecting wall and a 1/2 wave resonator effect when rather distant from a wall (+ whatever other and in-between phenomena).

I also have a baffel study from the Cath. Univ. Leuven where they investigated positioning from these thing, edge effect, screening etc.

At one point in time someone here quoted a book where the author ice-cold told these things could be calculated including the low frequent cutoff, but without explaining how, nor refering to any source whatsoever.
I really should be interested in more physical or mathematical data.
When hearing/reading that here I could only smile and don't trust such an author anymore.

I've seen a lot about this stuff and analogies with baffels. I still don't know anyone (serious) who told he had the final answers.

It's like aspirine. One knows it works, but it's not very clear how or why.

But the explenation I often read here about that vibrating core, is found to be not or little defining as per the referred study.
Measurements I personally executed in the lab with baffels with and without core also didn't show any significant influence in the low frequent absorption.
Hence the answer must be found elsewhere. I'm sure this core is important but related to their mutual and array positioning.

Note that that guy got his Masters degree with as end conclusion that the effects as observed in control rooms is still a paradox.

It's because I didn't understand either what I was looking at when I saw these hangers at first that I wanted to test them, just because I didn't trust things I couldn't explain/understand enough or wasn't sure about.
But that still does NOT mean that I fully understand why they do what they do.

_________________
Best regards - Eric Desart
My posts are never meant to sell whatever incl. myself, neither direct, nor indirect.

Eric - when I hang hangers in the ceiling I put the first one at the halfway point between two parallel walls. I then divide that and keep dividing until the hangers are around 8" - 12" apart. In other words at the nodes. I also vary it with hangers in the opposite direction by 90 degrees for the other walls..





here's the verbtime of that room

cheers
john

Thanks John,

Do you have before/after measurements? (with exclusion of other possible altered, more or less significant influencing elements).

In numbers? If so, combined with some data of the room itself one could calculate a rough estimate of the absorption per piece or m2 ceiling surface.

_________________
Best regards - Eric Desart
My posts are never meant to sell whatever incl. myself, neither direct, nor indirect.