Skyline DIY Size question

[Lefrançais]

Hello,

I really like Skyline design. And I'd like to put a diffuser on my 8m2 wall (86,1f2). My room is 18 m2 (194f2)
I found here this page to calculate the panel size by choosing frequency range.
HiFi Speaker Design © mhSoft <%=year(now())%>
For 60 cm (23,6 inches) width panel, It will diffuse from 688 to 3440 Hz.

But I'd like a bigger diffuser.

1)How can I get all parts size if I choose 100 cm width (39,3') or 120 cm (47,2') width panel ?

2)Will those widths fit my room ?

Thx for help.

[boggy]

Originally Posted by Lefrançais

Hello,

I really like Skyline design. And I'd like to put a diffuser on my 8m2 wall (86,1f2). My room is 18 m2 (194f2)
I found here this page to calculate the panel size by choosing frequency range.
HiFi Speaker Design © mhSoft <%=year(now())%>
For 60 cm (23,6 inches) width panel, It will diffuse from 688 to 3440 Hz.

But I'd like a bigger diffuser.

1)How can I get all parts size if I choose 100 cm width (39,3') or 120 cm (47,2') width panel ?

2)Will those widths fit my room ?

Thx for help.

If you like to build diffuser bigger than 60x60cm, then build two (or more) of them and instal one next to other

Hope this helps

regards

boggy

[Lefrançais]

Originally Posted by bozoel

If you like to build diffuser bigger than 60x60cm, then build two (or more) of them and instal one next to other

Hope this helps

Thanks, I tought if I 'd do that, diffusers may cancel each other, etc...
I don't know a lot about acoustic. But if it's right I'll try this way.

[boggy]

Originally Posted by Lefrançais

Thanks, I tought if I 'd do that, diffusers may cancel each other, etc.......

They will not "cancel" each other if you change orientation (rotate it)

[Lefrançais]

Originally Posted by bozoel

They will not "cancel" each other if you change orientation (rotate it)

Mmm, I'd like it to stay horizontal. And paint it in orange !
Design is important for me
Is there a way to calculate 100x100 cm diffusor parts size ?
But thx for your idea !

[boggy]

Originally Posted by Lefrançais

Mmm, I'd like it to stay horizontal. And paint it in orange ! ....

Look at ceiling diffusers:


I think about rotation in that way... hope I'm clear
Yes, i know that they are 1D diffusers but principle is similar

regards

boggy

[Lefrançais]

But is there a way to built a custom skyline diffusor size, not multiple of 60 cm ?

[Nordenstam]

Yes!

QRDude: Quadratic Residue Diffuser calculator
QRD diffusers

and the diffuser sticky in this forum.

[Lefrançais]

Originally Posted by Lupo

Yes!

QRDude: Quadratic Residue Diffuser calculator
QRD diffusers

and the diffuser sticky in this forum.

Thanks, I think it's too complicate for me ! I don't know where to enter "width" and where to get the results.
I'll stay with 60x60 cm ...

[Nordenstam]

Originally Posted by Lefrançais

Thanks, I think it's too complicate for me ! I don't know where to enter "width" and where to get the results.
I'll stay with 60x60 cm ...

It IS easy.

Number of wells is the number of unique depths across a 1D diffuser. The prime 7 is the most common one. If you want it to be 60 cm wide, you'll have to divide 60cm by seven. That's about 8.5cm per well. So you enter 85mm in the "well width" field over at the right hand side. Click the "scorecard" and see what it says. It'll have useful tips if you've done something that may lead to less than ideal performance. If you want to go bigger than 60cm, using a higher prime number is probably a good idea.

[Lefrançais]

Originally Posted by Lupo

It IS easy.

Number of wells is the number of unique depths across a 1D diffuser. The prime 7 is the most common one. If you want it to be 60 cm wide, you'll have to divide 60cm by seven. That's about 8.5cm per well. So you enter 85mm in the "well width" field over at the right hand side. Click the "scorecard" and see what it says. It'll have useful tips if you've done something that may lead to less than ideal performance. If you want to go bigger than 60cm, using a higher prime number is probably a good idea.

First I'm trying to read the QRD diffusers page you gave me but it's full of math ! but I get the idea .

1) It seems better to gather several panels in order to get the size I need.
In QRDdude calculator, HF cutoff is set to 3440hz, I have a flutter in my room. Don't know exactly but it sound higher. How can I change HF cutoff ? to 6000 Hz for ex.

2) What is "Fin with" ? is it the angle at the top of the block ?

3)In this page I can choose frequency but the diffusor plan (below) shows only 12X12 wells, do you know why ?
thx

[Nordenstam]

Originally Posted by Lefrançais

In QRDdude calculator, HF cutoff is set to 3440hz, I have a flutter in my room. Don't know exactly but it sound higher. How can I change HF cutoff ? to 6000 Hz for ex.

The high frequency cutoff is the width of the wells, over at the right hand side. The low frequency cutoff is the well depth at the left hand side.

Originally Posted by Lefrançais

2) What is "Fin with" ? is it the angle at the top of the block ?

It's the width of the dividers that seperates each well in a 1D diffuser. If you're bulding without dividers, set it to 0.

Originally Posted by Lefrançais

3)In this page I can choose frequency but the diffusor plan (below) shows only 12X12 wells, do you know why ?

It's a BBC diffuser that uses several smaller diffusers layed into a 12x12 grid. A similar QRD diffuser would be a 13x13 grid.

[Lefrançais]

In this exemple, the diffuser won't "work" above 4300 Hz and below 650Hz ? that why frequency range option is for ?

[SAC]

They don't state the assumed limits and conditions!

If you want to continue to use that particular calculator, please do so, but you are limited to the information and the data they give you! Why do you keep asking us to debate what they list - especially as a solution has already been suggested multiple times? Given that, how long will we beat that horse?

An alternative QRD calculator (QRDude) has been suggested and linked to which is arguably one of, if not the best available for public use, which also provides much more flexibility, information, and an explanation of the underlying theory and of the variables in the calculator itself! Additionally there are many here who have and actively use it who can provide info as necessary.

And the QRDude page is NOT "full of math"! But if you want to understand the QRD design that is literally BASED upon a mathematical sequence and you keep asking how various limits are derived, this involves math!!!! The effective cutoff frequencies are listed for QRDude and you do not have to understand math to appreciate them as they are clearly explained in the documentation.

Play with it! You can't break it and it even gives indications when you enter invalid values and suggestions as to why they are invalid or problematic! QRDude is not only a marvelous calculator, it is perhaps the best interactive tutorial on QRD 1D and 2D design available as well!

I do Not mean any disrespect, but please take the hint! Use QRDude! The foundational concepts and math are discussed and disclosed on the information page, the info displayed in the application is both useful and based upon careful reasoning, and the variables as flexible as can be!

[Yiannis]

I would like to ask if the width of the wells separators matters.

If yes how do I find the correct width?

If no is there a usuall width?

[SAC]

Yes. Theoretically the well dividers/fins should be as thin as possible,
But they allow you to design the unit specifying real world material thicknesses!

And no, there is no 'set' "correct" well width that should not be varied. But there are practical limits that will impact behavior.

Read:
QRD diffusers

I think you will find just about all of the practical information necessary to move forward. Beyond that you move into the math itself...

[Yiannis]

Nice,

thank you

[Lefrançais]

Originally Posted by SAC

An alternative QRD calculator (QRDude) has been suggested and linked to which is arguably one of, if not the best available for public use, which also provides much more flexibility, information, and an explanation of the underlying theory and of the variables in the calculator itself! Additionally there are many here who have and actively use it who can provide info as necessary.

How can I know QRDude is better than others ? I thought they where all the same... I choose the one above because variable I could "play with" was frequency range (that is impossible in QRDude, isn't it ?). I was wondering, in other terms, if frequency range had to be the widest as possible and if the diffusor only worked in this range.

In QRD, I also don't understand what is "design frequency in Hz" parameter.

Sorry I'm really new at this. I bought 6 Gik bass traps and I wanted to add a beautiful "modern art" work on the opposite wall if it could also be something useful for my brand new home studio....bingo ! ... and made by myself ! (then proudly posted in the Gearslutz sticky... )

[SAC]

You specify the "design frequency" and depending upon the configuration, it indicates the "HF (high frequency) cutoff" frequency as well as the "Estimated LF (low frequency) cutoff frequency". These values and how they are determined are explained in the link that was provided.

And this is the effective frequency range of the diffusor...

Additionally you have allot of control over ALL of the variables and a myriad configurations of the QRD.

You have complete documentation as well as examples on the QRDude webpage, as well as a number of threads here where there are literally pages of information regarding the 'method to the (inspired) madness' behind the tools. May I suggest you take some time and print our the QRDude user page and read through it as you play with the downloaded application. You will see that all of your questions are pretty easily answered in doing this, and you will also discover what is IMO the most elegant tool for calculating and tailoring both 1 and 2D QRDs of which I am aware. And in the process, not only will you gain an understanding of how QRDude works, but you will also gain an increased knowledge regarding QRDs and the theory behind them.

Just about every question you have asked can be quickly answered by perusing the QRD user page link. And all you have to do is to search for "QRDude" to find MANY threads with more detailed information about a myriad topics relating to QRDs, PRDs and QRDude itself. And you benefit as there there are many here who know quite a bit about QRDude.

Regarding the mhsoft calculator, the only reference provided is the link to the BBC paper on the mhsoft website. And there is no information provided for an end user to see how things are implemented under the covers. And when you ask questions about it, we simply have to go to the website and read the usage notes or the BBC paper the same as you should do first to ferret out the particular information - assuming this was followed in the tool's design. So, if you (or anyone else) want(s) to use that one, good luck, as you are pretty much 'on your own'.

[Lefrançais]

Thank you very much for your answers (Bozoel and Lupo too !). I'll try to understand the QRDude user page. I know there are a lot of thread about this and read several of them. Learning step by step. But like any complex new subject, it takes time ... too much time ! I wish I could find a "How to built a diffusor" summary instead of picking up informations all over the forum or between math formulas.....lazy I said and too much in a hurry ! but I think in a few days, thanks to you guys, I'll be able to get my "blocks " at the wood store and start my beautiful work !

[Nordenstam]

Hello!

Originally Posted by Lefrançais

How can I know QRDude is better than others ? I thought they where all the same... I choose the one above because variable I could "play with" was frequency range (that is impossible in QRDude, isn't it ?).

Making a guess here.. It may be that this is reduntant, it may be that this is where you miss out on the frequency range controllers in QRD. The thing is that the frequency ranges are physically locked to the dimension you choose to use. A soundwave is about 343 meters/second at 1 Hz, ten times less at ten hertz, 3.43 meters at 100 Hz, 0.343 meters at 1Khz and so on. The physical depth of the QRD diffuser sets the lower cutoff. The physical width of each well sets the higher cutoff.

Diffusers work a bit like real instruments in that they have a fundamental frequency of operation, with the theoretically ideal performance achieved at that frequency and integer multiplies thereof. So if the base frequency is 500 Hz, you'll get the wanted performance at 500, 1000, 1500, 2000 Hertz, and so on, til you hit the upper cutoff frequency. The scattering between these center frequencies is still much better than a flat wall. The scattering below the design frequency is somehow better than a flat wall, at least to an octave below the design frequency. This is why QRDude sets the low cutoff at half the design frequency.

[gremmy]

As mentioned above, the frequency range of a diffuser is directly tied to its depth and well-width. The deeper the diffuser, the lower the frequency it will diffuse. And the narrower the wells, the higher the frequency it will diffuse.

Try changing these dimensions in QRDude and you will see the frequencies change accordingly.

The handy-dandy scorecard page even shows you if you've violated any of the mathematic principles in your design. QRDude is pretty much idiot proof.

[Lefrançais]

Here is the wall I'd like to put the diffusor (at the of the GIK panel):