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Wood to use and other related issues
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July 23, 2019 - 5:28 am
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Hello there,
bought my plans in 2018 and know I am getting about to start on my diffusers.
I have red pretty much all off the related Topics and threats in that manner here in the forum. Unfortunately it leaves quite a few question unanswered or some not mentioned at all.
How on earth can anybody make decisions without having the answers needed for this project?

I also think this issues are critical because most people have no idea on how much such issues change/alter performance to the better or worse.

Dennis I hope you are able to answer this for all your customers here in the forum so we really know what is best and what is perhaps not so good to use, thank you in advance.

1. Question – an easier one: The depth of the horizontal dividers is measured from the top edge of the vertical divider to the surface of the horizontal dividers board, I am pretty sure that is what you mean???? ..there are no real explanations in the Manual.
So the inserted supportive wood for the horizontal dividers that gets glued into it has to be measured and cut accordingly in order to provide the 1″ depth total (with divider) or whatever measurement is needed in that particular slut?

Choice of wood:
Although you show MDF sluts in your installation videos it is really not recommended due to sound transfer issues as you said so in the forum yourself – to much absorption of the signal (frequenz), MDF swallows it to a degree instead of giving it back and this makes sense.
It is extremely expensive and difficult to look for “SOLID” wood 6 (1/4″) or 8mm panels in solid wood, nothing is available here, they all would have do be made by a carpenter. (If solid wood is what I think solid wood is and not Plywood, because Plywood is also solid wood for some people but has glue in between the layers which is bad for translations issues regarding sound transfusion and penetration as well as spreading out).
So most of us will have to use Plywood with some form of a veneer because as you said MDF when used need to be veneered – meaning a harder perhaps smoother surface than the MDF so that the frequency does not permeate into the MDF but is bounced back out of the diffuser into the room. I am asking myself what the real prerogatives of a QR diffuser are. It has got to be the kind of wood used whereas Spruce is properly the best you can get due to its low “Raw density” of 441 kg/m3 and a high Elastic Modul of (E-Modul): 12.500 N/mm2 next to Fir with 11.000 N/mm2 same raw density. Also wood is a natural resource and Instruments are built with it and there is a reason. It sounds most natural, but even with wood there are differences. Is it glued or not, what kind is it, Hart or soft wood a.s.o.
What I do think to a degree is that there is no difference between a solid wood surface you use like cherry for your dividers (if your interpretation of solid wood is really solid) that is finished with a clear coat compared to a fine sanded, smooth not veneered surface like Alder or Pine Plywood with a clear coat. I know it is not the same as mentioned before since plywood is layered and therefore looses vibration, transportation of sound waves but if only the bounce back of the frequency is a true criteria with QR diffusers it should not matter, correct?????…because vibration issues regarding the wood should not matter in your QR diffuser because if that is the case MDF with veneer is not an option at all, regardless whether veneered or not…it would just be cheap that is all.

2. What I need to know from you Dennis is if Plywood (perhaps Alder or Spruce) is as good as solid wood for the dividers of the diffuser wood wise?..because surface wise there is no difference, both have the same “Shell hardness surfaces” the difference is the built on the inside of the wood itself or should I say construction of it. The actual surface hardness itself should be the same, because Birch in solid wood is not different than Birch in a Plywood version if the wood comes from the same region and company that makes them for instance?

3. If the built of wood does make a difference because of vibration issues and therefor ongoing sound translation of the dividers in solid wood, solid wood is really the only option if you want high end sound coming out of there, everything else is steps down but of course can still be sounding okay.

4. My last question: it is really very difficult to find 1/4″ Plywood in an intact condition let alone solid wood, all the wood in 1/4″ I saw in the store was bent (storing issues) so would like to go with 8mm (5/16″).. this kind is much more straight at the store and, also glues better due to a larger surface. Would that be okay or is this creating deviations in your calculations regarding (vibration) and translation of the signal within the diffuser? On the QR dude software it changes the “Period width” from 1288 to 1334 but I am not familiar with that and what that really means to the performance of your QR diffusers. If vibration of the dividers is no an issue it should not do anything on the signal itself other than the dividers are somewhat thicker and therefor influences sound waves differently as with a thinner divider. Yes the total area of waves hitting the larger area of wood in the front of the thicker panel will change sound performance, is this critical and is this the reason you recommending 1/4″ although this could be solved by sanding it down in the front to a curve or peak so to speak?

I am really just want to do all this only once and not finding out that it was wrong due to missing information’s to begin with, please advice accordingly and thanks for all the vids and info on the web what you are doing is unique and very appreciated….and please can you go over all (1-4)issues, thanks and take care.

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July 23, 2019 - 7:24 am
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BDA,

Please follow the depths for each well as indicated in the drawings. Plywood can be used for horizontal and vertical pieces. Softer woods are better for middle-range tonal qualities. Keep your well dividers as thin as possible. A 1/4″ well divider is acceptable. Make sure you have your low-frequency issues managed correctly in your room first before applying diffusion. Diffusion will make your room sound worse if you have not managed low-frequency issues.

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July 25, 2019 - 4:07 am
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Hi Dennis, thanks for your replies,

Wood to be used seems to be clear softer is better, I feel the best in regards to numbers will be spruce, so most likely will go with that.

Thickness to be used seems to be clear to me also, when you say thinner is better, so will go with 1/4″ or 6,5mm over here (Wood thickness varies between 6,2 – 6,8mm)

One Thing left to know for sure will be on the finish of the 1/4″ Plywood

So, is it better to have that smoother Surface with Phenolic resin or go for the natural Surfaces of the spruce veneers with a lite clear coat if at all?

Is the main purpose the smooth, hard Surface of a soft wood or all soft Wood in generall or perhaps the combination of the two?

I will send you and Readers this Webpage to better see for yourself/themselves what I mean and also this may be of some real value for all of us …. and if applicable to your QR diffusers.

https://www.wisaplywood.com/siteassets/documents/brochures/handbook-en.pdf

Handbook in all kind of languages available

Finnished phenol formaldehyde glued plywood products exhibit very low levels of formaldehyde
emissions. Urea formaldehyde glued products have slightly higher values but they
still fulfil the requirements of the most demanding European standards relating to formaldehyde
emission and content

Thanks and have a nice day.

P.S.
For all Readers, there are even different Phenolic resins surfaces to be choosen from and the one with 2 smooth very thin, almost glossy finishes is the one I am refering to (Wisa form Beto also Birch). You could not use the one made for Boarding up a floor on a truck for instance (Wisa Trans & Truck) since this one would has thicker Phenolic surfaces and is rough to avoid slipping, it also is waterproof to avoid swelling.

The Wood used or Quality should I say need to be good, at least a Grade BB(III) better Grade S(II) is recommanded I feel but of course your choice. (Hardend Areas in the Wood such as branches causes Sound spreading unevenly to a degree. How much I cannot say in this case but I have done enough work to tell everybody that sometimes even smaller things matter big, especially in things like where Sound waves, vibrations and limitations of them wanted or not is
concerned.) You would not use a guitar bottom or resonance board of any kind with branches in it)

Since Dennis recommanded thinner Fins are better I suspect vibrations are good and wanted and Need to be inspired instead diminished, because the fins need to vibrate with the waves comming into the difuser to a degree. Spruce is therefor very good since it is used for resonance boards of instruments such as Guitars. It reacts fast but does not hold Sound vibrations Long. (We are talking milli/sec. here)

Personally I feel that natural plain Wood surfaces are best since soft natural Wood transfers vibrations better as suspected in the QR fins are equally important. (just like a Speaker so to speak as Dennis says).

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