QRD Prime + Period Question (Live Room)

[terry j]

Originally Posted by collo

Ah, there lies the confusion.

Maybe it is. It could be I grabbed the wrong end of the stick.

Originally Posted by Jason Jones

or you can use a diffuser and for your "second" diffuser you flip the diffuser so it is oriented the opposite way of the first, or you could use diffusion and an absorber. Jason

Originally Posted by terry j

Found this last night, on ethans forum!! Thanks ethan

Jason has already answered it, but this earlier reply from ethan's forum fleshes it out a bit

We need two different diffusers for this to work. It can be the diffuser and the same diffuser "upside down"...or it could be a 7 well diffuser and a 5 well diffuser. Pick one of these (or one configuration "right side up" or "upside down"). This will be diffuser 1. The other diffuser or configuration will be diffuser 2. Set them up like this:

1112212 or 2122111

You have now modulated your sequence. Stand up with pride and make that
"Star Trek V thingy" with your right hand.

Jason

As I said, I could have completely misunderstood it, but to me that says 1234567 goes to 7654321.

I remember it did confuse me just a little, as I had kinda seen your explanation drawings in THE BOOK

Originally Posted by terry j

In the cox book when they give the example of the -1 of the barker code, well I guess a good enough word would be 'the inverse'..and stangely enough it starts behind the normal ones, ie goes deeper. Heck, may as well make all of them deeper and diffuse lower! if you follow.

Which shows the need for the extended fins.

But the trouble is, I can't interpret Jasons comments and get your answer. Not saying you or he are wrong, only that I just can't see any other way of understanding what he said, which I take to mean rotating the existing qrd as described before.

Your drawings (from memory) are exactly as in The Book, with the reverse qrd 'behind' the others and fins extended to the same level.

It would be good to clear this up. For whichever reason I have that interpretation from Jasons comments (my money is on I am an idiot, coupled with what will no doubt turn out to be a humourous misunderstanding) none-the-less it is from an 'authority', so is kinda sticking.

I presume you made those drawings to illustrate (ie did not use qrdude) as in qrdude I simply do not see those super fins in the proper inverse panel. Does that mean then that when we build an inverse per qrdude, it is not 'proper' in every way, it too has some compromises?

Dunno whether it's worth trying to explain what elementary point I am missing, I am happy to just follow 'rules', once we know what the rules are that is!

And so on that front, I am still stuck with my interpretation of Jasons posts.

[Xenon]

Hi Collo,

Good news. I'm still considering one alternative option, though at the moment, yes, my plan is to left-shift the zero-well of each N. The issue is there remains a dimensional 'gap' to consider, in that the N19 is 80.8cm L and the space inside my frame is 91cm. I wanted to avoid making a non-standard frame ...

There is this other possibility, though it voids the Barker code -- but does it, in function? Which would be:

N23 N23 N11+N11 N23

Looking at the ripple tank images in this thread, that Lupo made, the paired N11 seems a 'similar-difference' to the N23 dispersion. It looks as though the mirrored N11 functions as one larger unit -- almost as much as the single N23. (if so, in functional practice it would not void the Barker code). What do you think of this idea?

PS I couldn't find that menu option?

Originally Posted by collo

That sounds OK.
If you left-shift the N19[+3] by 4 wells, you get a zero-depth well on the left end of all panels.

As you alluded to earlier, this lets you use the trick of moving a half well to the right hand end of each panel. The frames of adjoining panels, plus any packing if required, form the zero-depth wells. (QRDude has this as a menu option)

[terry j]

Originally Posted by Xenon

PS I couldn't find that menu option?

Mine is not open now, but it is one of the options (advanced?) listed along the top. You check the one that says something like 'move the last well half a place so they can join'

[Xenon]

Do you mean in

Options > "When first well is zero-depth, show half moved to the right end of panel, for symmetrical build"

This brings up a good point -- since splitting a left-side zero well is allowable, the need for spacers becomes 2.1 cm on each side. (An N23 with 4.25cm well-segments = 97.75cm in a 93.5cm (3') frame needs an extra 4.2cm total = a little less than one well).

Why don't I just make 97.75cm frames? It's because the plywood sheets are best cut at 91cm (they are actually 92.1cm x 183cm). Using 91cm, I can get square frames (183/2 = 91.5 - 0.3 for a saw cut = @91cm, voila), which means these panels can be laid vertical or horizontal in the same space. It's much easier to deal with a square frame than an almost square frame...

Anyway, 2cm spacer strips on the sides is no big deal. If I was building only N23 and a lot of them, I would spend more and build 97.75 frames, but it will more than double the price of the backing plywood to do this.

As I'm also making half-frames of N11 (4 in the live room and 4 in the mix room), you can take one 183 x 92cm panel and get 4 pcs., 44.5 x 91cm. This reveals why I went with 91cm backings, it's easy to stack 2 44.5cm units = 91cm, so it's modular. Keep in mind that the framing wood has to be longer than the backing. Anyway, it gets tricky. Also, for making fins and well faces, each saw cut loses 3mm in a panel. FYI, frame depth = 13.75cm, fin depth = 13.5cm, face 'depth' (for cutting purposes) = 4cm.

In four frames of 4cm wells, it's 80 fins, 80 faces or thereabouts. Lot's of cutting. I have the big cuts done at the Building Center ($0.30 each cut, and they will stack 5 sheets of 2.5mm = 1 cut). The small cuts I also did at the center for the first unit, but will give it a try at home.

Originally Posted by terry j

Mine is not open now, but it is one of the options (advanced?) listed along the top. You check the one that says something like 'move the last well half a place so they can join'

[collo]

Terry,

the way I see it, the statement from Jason, and the comment from Ethan's forum are talking about two different things.

Jason's comment:
or you can use a diffuser and for your "second" diffuser you flip the diffuser so it is oriented the opposite way of the first

I interpret this to mean turning through 90 degrees, so that the fins that are normally vertical are now horizontal. (the key word being "oriented")


From Ethan's forum
We need two different diffusers for this to work. It can be the diffuser and the same diffuser "upside down"...

I interpret this to mean using the back of the panel for the inverse as I described above with the drawings.

The statement only makes sense if you imagine the panel lying flat on the floor. Of course once you put it on the wall, "upside down" infers what you took it to be.

From Ethan's forum
Pick one of these (or one configuration "right side up" or "upside down"). This will be diffuser 1. The other diffuser or configuration will be diffuser 2. Set them up like this: 1112212 or 2122111

The number sequence described is the modulation sequence for the panels, not an indication that the order of the wells of one panel is a mirror image to a normal one.

Maybe everyone should adopt a convention such as....

I wonder what terms NASA uses to describe the motion of the space shuttle.



The drawings done a couple of posts back were done by hand to illustrate the point.


When QRDude draws a normal panel, it assumes you will be leaving out the unused section between the build depth and the design depth (shown in grey in recent versions), so does not draw fins in this area.

It does however draw the inverse panel correctly. You might be still using an earlier version that did not draw the fins.

[collo]

Originally Posted by Xenon

Do you mean in
Options > "When first well is zero-depth, show half moved to the right end of panel, for symmetrical build"

That's the one...

All that mental arithmetic to find sheets that you can actually buy and work with makes me feel great that someone else is going on ahead...

[terry j]

Originally Posted by collo

Terry,

the way I see it, the statement from Jason, and the comment from Ethan's forum are talking about two different things.

Bugger, I have that horrible sinking feeling you are right. Why sinking? Cause I already made a multi qrd!

Jason's comment:
or you can use a diffuser and for your "second" diffuser you flip the diffuser so it is oriented the opposite way of the first

I interpret this to mean turning through 90 degrees, so that the fins that are normally verical are now horizontal. (the key word being "oriented")

Hmm, have my doubts. It WAS said in the context of applying the barker code, so I cannot imagine three (say) vertical qrds of 2m long (for exaggeration) then one single qrd horizontally of 2m, then another vertical qrd.

From Ethan's forum
We need two different diffusers for this to work. It can be the diffuser and the same diffuser "upside down"...

I interpret this to mean using the back of the panel for the inverse as I described above with the drawings.

The statement only makes sense if you imagine the panel lying flat on the floor. Of course once you put it on the wall, "upside down" infers what you took it to be.

this is the crux of it all! Upside down, back to front, flipped over etc. Hah, I often fail at it, but trying to be clear is half the reason for my infamous long posts. As my long posts often makes it less clear kinda defeats the purpose!

I wonder if Jason could chime in. (don't want to give the impression I think I am necessarily right here, just trying to sort wheat from chaff)

From Ethan's forum
Pick one of these (or one configuration "right side up" or "upside down"). This will be diffuser 1. The other diffuser or configuration will be diffuser 2. Set them up like this: 1112212 or 2122111

The number sequence described is the modulation sequence for the panels, not an indication that the order of the wells of one panel is a mirror image to a normal one.

I know that, it is the 'proof' that what was being discussed was the barker code (1112212 or 2122111), which rules out the interpretation of fins horizontal vs vertical.


Gee last thing I want to do is bog down this in minutiae, but as the barker code has assumed the level of importance given it here, it would be good to nail down once and for all.

It DOES have quite a real practical importance in terms of ease of build...

[Xenon]

Thanks for the thumbs up,

Yes we are building from next Monday here.

I'm still contemplating whether to go with the N19 or 2x N11 for the -1 panel. (There will be drums in front of it...)

In the room, right now my friend Jeff and I (we are doing this together) are discussing whether it's better to build our entire wall of diffusion, which would include horizontal N11 units on top --

Or to build, from the floor up (240cm H wall):

1) 32cm H x 13cm D absorbers on the bottom,

2) 187cm H (2 frames) of diffusion

3) 32cm x 13cm absorbers tilted to the ceiling

the alternative is no absorption
and

1) 187cm H (2 frames) of diffusion vertical
2) 48cm H 1 half frame N11, horizontal

We will be mic-ing koto (among other instruments), which is set on the floor. Best mic position is about 20cm off the floor, pointing mostly horizontal, fyi.

So one question remains about the N11+N11 vs. N19. Another concerns whether it's better to go all diffuser on the wall, or go top/bottom absorption for the floor/ceiling corners.

Your thoughts appreciated -- anyone care to chime in?

Originally Posted by collo

That's the one...
All that mental arithmetic to find sheets that you can actually buy and work with makes me feel great that someone else is going on ahead...

[terry j]

mon eh? good luck. make sure you publish the final design before you start.

one thing (might not be good for looks) that has not yet been tossed around re the barker code, is to substitute absorption at the inverse point.

[terry j]

one thing that has only just occurred to me, have you wondered yet about making a diffractal?

very few have the space available for such an ambitious build as this, hey why not make it super duper??

[Xenon]

Originally Posted by terry j

... substitute absorption at the inverse point.

Pagan.

[Xenon]

Terry,

Originally Posted by terry j

one thing that has only just occurred to me, have you wondered yet about making a diffractal?

It's not hard to wonder about. Like putting flutter strips inside your wells. There's a fellow who made his own, over at hometheatreshack (scroll to the bottom and continue for a few pages). In particular, this pic. He's quite a carpenter and that shop looks $$$. Hardwood, router, perfect dimensions... That's some beautiful work. My thought, don't attempt this at home, unless you really know what you're doing and have the space, good tools, and time. There's "SoundScapes" in The Netherlands, who built them in 2006-07, using mostly MDF (he writes that his ceiling diffusion alone weighs 3000Kg). More (utilizing 'Google translate'): "There are a number of fractal diffusers and bass traps in all used a solid-QRD diffuser profile (9.4 x 3 cm), as shown in the picture above. A total of 700 linear meters needed in this space and that alone weighs around 1200kg. The total project is estimated at over 6000 pounds mdf processed." Unbelievable. Go here and take a look at "design065.jpg" > "design081.jpg" to see the process. "design090.jpg" > "design096.jpg" shows his QRD construction, and pics "096a.jpg > 096d.jpg" show the diffractal construction. Note the size and weight of these. It's really something.

[terry j]

collo, only just saw you rotate and flip pic earlier, was not there when I answered before.

nasa? pitch yaw and roll I think.

Originally Posted by Xenon

Terry,



It's not hard to wonder about. Like putting flutter strips inside your wells. There's a fellow who made his own, over at hometheatreshack (scroll to the bottom and continue for a few pages). In particular, this pic. He's quite a carpenter and that shop looks $$$. Hardwood, router, perfect dimensions... That's some beautiful work. My thought, don't attempt this at home, unless you really know what you're doing and have the space, good tools, and time. There's a fellow in Germany who's also making them, using MDF possibly (don't have the link).

yeah, have a few posts in cinema mad's thread. In fact, that was were I first came across the dutch site on qrds. Two different posters with the pics, but they do show not only how expensive those strips are for raw materials alone, but all the tools and passes required.

Oh, if only there were some bright creative genius (and unbelievably handsome I might modestly add..oops, did that pass my lips or did I just think it?) who could come up with a way of making those quickly, simply and cheaply.

I made these in lengths of 1.8m, took half an hour per length.



Just mucked about for the photo and was arranging them different ways to check the funky looks, just docked the long length to whatever I wanted.

Anyway, they are exactly the same flutter strips made in the thread you linked to.

So, that begs the question, leaving aside any thoughts you may have about the difficulty/tools required to make diffractals, if you in fact could, would you now consider it?

Without checking, I imagine your first post would contain sentiments like 'best possible' etc.

Hey, collo seems always bored and wanting to play with that great calculator of his, he may just as a theoretical exercise have a look at a workable diffractal. Heck, I'd be interested too!

Lupo gave a tentative one in my thread, but I think quite a few bits of extra data have surfaced since so an updated design incorporating correct panel widths etc would be interesting to compare.. or wait until we also have the flat panel effect as well.

[Xenon]

Terry,

Originally Posted by terry j

I made these in lengths of 1.8m, took half an hour per length.

Hard to see from the pic there. You'd have to give more detailed information... so..? How..? Type of wood, depth, dimensional specs?

[Xenon]

Fyi,

Using the Barker code, panel size of 93.5cm, 4.25 well-segment, for anyone with a 500cm wall, it's possible using N11^2 and N17^4. Just one needs to tack on a separate small frame of about 25.5cm, containing 6 wells, on the right side (or change frame sizes, see below).

Barker code
7 [-1 -1 -1 +1 +1 -1 +1]
-1 = N11 (4 periods)
+1 = N17 (3 periods)

N11 (constant +2) 811LF (405.5 eff. LF Hz)
N17 (constant + 4) 972LF (486 eff. LF Hz)

22 wells (4.25 well-segment) fit into a frame (23 possible with a small spacer).
Shift all N17 zero wells over by 3 places, making a zero-well at position 11.

PATTERN
N11 N11 N11 N17 N17 N11 N17 (can be reversed)

For 4 frames (+alpha):
F1 = N11+N11
F2 = N11+ first 11 wells of N17
F3 = last 6 wells of (F3) N17 + (F4) N17
[small spacer]
F4 = N11+ first 11 wells of N17
Fa = last 6 wells of N17 (25.5cm)

Imagine a 500cm wall, and in the corners you want a 60cm (2') sheet of 10cm/4" rockwool/fiberglass to straddle them. This means you need 43cm of each side of the 500cm wall for it (= 86cm from the 500cm used).

So max length for diffusion = 414cm.

The N11/N17 panels above = 403.75cm in length, giving +5cm (1") of play on either side -- in other words a perfect fit.

A perfect fit, perfect Barker code, standard (3') frames, plus alpha. An easier build than higher primes, in terms of measuring, though less resolution.

But if the Barker code is crucial, for the size needed, and with easier construction, if you don't mind spanning frames (and losing mix and match modularity). So, yet another solution.


If you wish to build 4 frames, 2 larger 4' frames, of different sizes, etc. (for a 16'6" wall or so). No position shifting is necessary, as all N-periods are self-contained in a frame:

F1 = N11 + N11 (93.5cm/3')
F2 = N11 + N17 (121cm/4')
F3 = N17 + N11 (121cm/4')
F4 = N17 (74cm/2'4"ish)

This seems to fit a North American 4' x 8' better than the cm sizes I get, where (93.5cm2) 3' x 3' works well.

[terry j]

Originally Posted by Xenon

Terry,


Hard to see from the pic there. You'd have to give more detailed information... so..? How..? Type of wood, depth, dimensional specs?

dimensions etc are exactly the same as in cinema mad's thread, and this document

http://www.kineticsnoise.com/interio...true%20QRD.pdf

and this design is also exactly the same as in Alton Everests book, so presumably straight from RPG

How? secret for now

wood, who mentioned wood.

[Nordenstam]

Originally Posted by collo

Lupo is the only person we know that could actually afford the book!

Well.. Umm... It's a quite steep price for a book, but it's only a couple of restaurant dinners, a weekend of good life, a fraction of anything practical worth using in audio, etc etc.. The question you should ask yourself if you're interested in gaining the best return from the _many_ hours that's bound to be spent DIY'ing acoustics..: Can you afford not to have the book?

It's not only covering diffusers and reflectors in all sorts of shapes, all types of absorbers are also described in the same extremely deep style. Including the interesting prospect of using QRD wells to extend the range of low frequency absorption (getting the 4/7 advantage in a bass trap).

The price is, in any case, a normal price for a fact book. This isn't crime, it'll never sell big. What we pay for is a low volume pressing of extremely specialized information. Most educational books do have a hefty price tag precisely for that reason. Of the thousand or so books I have, the most expensive facts books are usually also the ones that I keep refering to over and over and over again. So I don't have much of a problem justifying the expense of such books.



Have been skimming this thread and it seems you guys are handling this very well! So I think I can leave this to you geeks, while I'm practicing the get a life thing. Got three concerts in two cities next two weekends! Will keep up with the other threads whenever there's time, possibly not until next weekend is over.

Can give a small try at ooohmm'ish speak: all engineering decisions are trade offs. If there isn't an if and a but to a particular suggestion, it's probably time to meditate the subject for a while longer.

Am frankly more confused now than ever before when it comes to diffusers. It seems the only way to get it at least halfway right is to build something specific for a certain array size and listener distance. The large number QRD's needs a longer distance to the listening position for all the waves in the diffuser to blend.

I'm also a bit sceptical to the idea of having large amount acoustical treatment that only works in certain frequency bands, leaving other bands as good as a flat wall with random (sticky )objects thrown at it. While some bands again, and certainly the entire non-effective direction of the QRD, are literally as good as a flat wall. I would try to spread the frequency response of the things out on different parts of the spectra. Both with regards to base QRD response to design frequency and integer multiplies thereof, and the flat plane frequency.

As for the Ohm-diffractal, it still seems like a good idea to me, to have the effective frequencies overlap. Ie, a 500Hz diffuser works at 1000, 1500, 2000, 2500, 3000 and so on. So if it stops at 3000Hz, it seems logical to have the smaller diffuser take over that series at 3500 Hz and continue upwards from thereon.


Argh! Trying to give the image of a c00l musician too busy to think about these things, but I guess I can just forget the idea of not being an utter nerd.

Anyways, lovely work guys! Looking forward to seeing the development.

PS: Collo - the calculator now stops exactly AT a design frequency*n. (n is integer) It's cutting off exactly at the frequency it's trying to effect. I would put some margin in there, if it was my QRD build.


Cheers,

Andreas Nordenstam

[Xenon]

Intriguing ...

Originally Posted by terry j

dimensions etc are exactly the same as in cinema mad's thread ... How? secret for now wood, who mentioned wood.

Thanks for the pdf link. By the way, could you post a link to the "cinema mad" thread? I missed that. Hope to hear more in time.

[terry j]

Originally Posted by Xenon

Intriguing ...



Thanks for the pdf link. By the way, could you post a link to the "cinema mad" thread? I missed that. Hope to hear more in time.

It was intriguing eh? The 'International Man of Mystery' strikes again!

Must be some wires crossed at the exchange, the cinema mad thread is the one you linked to at the shack. Just so happened that I was aware of it, that's all.

With all the work he was doing with the flutter strips I thought he might have been interested in anything I had to offer....he must have decided I was a mad man. And that was without seeing a photo of me, which would have clinched the decision!

Hi lupo, and happy ostkaka day. Re the omdiffusor (tm)...normal businesses have the omnidiffusor, we are better than that...would it not make more sense to overlap (in your example) 500 hz downwards rather than above?

As there are no rules to cover this (that I know) think I will do that anyway, the 'tip' you gave was multiples of the design frequency.

I did mention to someone that you take breaks every now and then, I said it was because you obviously had a life. That was wrong, per you you are trying to get a life!

NOW you mention using qrd wells to extend the effectiveness of a bass trap, you waited till you saw I was committed to the space coupler didn't you!

Good luck with the gigs and let us know how they go.

[Xenon]

We shall soon purchase materials for our QRD project.

I have narrowed the choice of design to two possibilities:

N23 | N23 | N19 | N23
Length = 374cm
3 periods, N23
1 period, N19

or

N11 + N11 | N11 + N17 | N17 + N11 | N17
Length = 409.5cm
4 periods, N11
3 periods, N17

Both follow the Barker code.
The wall opposite wall is 345cm (11'4") away.

My question, which is the better choice?
It seems intuitive that a shorter period length will 'cohere' or "blend" in less distance?

PERIOD LENGTHS (4.24cm well-segments):
N23 period = @100cm
N17 period = @ 72 cm
N11 period = @ 47 cm

QRDUDE Calc, listening minimum-distances:
N11(c2) = 254cm
N17(c4) = 212cm
N23(c0) = 208cm

According to QRDUDE above, I can bring my mic CLOSER to the N23, and must be most distant from the N11. This seems counter-intuitive.

Lupo writes:
"The large number QRD's need a longer distance to the listening position for all the waves in the diffuser to blend."

Can anyone clarify this point?
Thanks in advance.

[collo]

Originally Posted by Xenon

My question, which is the better choice?

I would probably build the first choice of N23 | N23 | N19 | N23 because it gives you frames that could be utilised as stand-alone panels if your circumstances change.

I would guess that the distance to the opposite wall would not be a problem.... (only my opinion on that though)

Originally Posted by Xenon

It seems intuitive that a shorter period length will 'cohere' or "blend" in less distance?

Lupo writes:
"The large number QRD's need a longer distance to the listening position for all the waves in the diffuser to blend."

I would like to see a link to where this info came from.

Originally Posted by Xenon

QRDUDE Calc, listening minimum-distances:
N11(c2) = 254cm
N17(c4) = 212cm
N23(c0) = 208cm

According to QRDUDE above, I can bring my mic CLOSER to the N23, and must be most distant from the N11. This seems counter-intuitive.

The recommended minimum distance to the seating position equals 3 times the wavelength of the LF cutoff frequency.
I can only assume you are basing the N11 on a lower design frequency than the N23

Whatever way you go, enjoy the build....

[Xenon]

Collo, thanks,

I was hoping to get your input.
So, I get the sense that listening distance isn't a big factor between the two designs, to your mind... A good point concerning the N23 design. absolutely, modularity is always a big big plus.

Well folks, there you have it:
The design is N23 N23 N19 N23 for the wall.
If anyone needs more specific information, let me know. I'll be posting pics on this thread from the build, which will take place next week.

Also wanted to mention, the units are 'diffsorbers' to the extent that the EPS (aka "blue styrofoam"; Expanded PolyStyrene) we are using seems to be the same material Lupo used in his 2D skylines.

Lupo reports here that, "The blue styrofoam is 32kg/m^3 and the lightest wood is about 2-300kg/m^3.. Quite a difference! The foam reflects down to about 500Hz where it starts absorbing, having a crossover zone with both reflection and absorption extending 1 to 1.5 octaves below that. Absorption works down to about 150Hz on this.

The N23 will hold quite a bit of EPS, which we are using to fill the wells. The EPS here seems likewise 32kg/m^3. Not sure how the EPS will affect our "effective" LF -- though it would seem that 80kg/m^3 fiberglass/rockwool or higher is a preferred material. RealTraps mentions they use a membrane to reflect mid-HF in their (diff)insulant. EPS, while having much lower density, also reflects to 500Hz... We are just really happy that it makes the build easy and it's relatively cheap. Unfortunately we can't measure the effect as we have no access to a lab and the room, being highly reflective now, may show little difference with just a diffusor array on a wall (and no additional treatment).

Collo,
On the idea about period length vs. 'blending' I was just contemplating that say 2 N11 take up about the same space as 1 N23. Since a period functions as a tuned unit, so to say, there must be some relationship between the blending of the period reflection and the physical length of a period?

You're exactly right on the N11, it's LF is lower than the others I listed.

Thanks for your time, help and interest!

Originally Posted by collo

I would probably build the first choice of N23 | N23 | N19 | N23 because it gives you frames that could be utilised as stand-alone panels if your circumstances change.

I would guess that the distance to the opposite wall would not be a problem.... (only my opinion on that though)

I would like to see a link to where this info came from.

The recommended minimum distance to the seating position equals 3 times the wavelength of the LF cutoff frequency.
I can only assume you are basing the N11 on a lower design frequency than the N23

Whatever way you go, enjoy the build....

[terry j]

the 'best' most of us can do is simply measure the room before and after.

We might not get such a golden opportunity again, what are the chances of you doing a recording before and after???

Trouble is, recordings by their very nature vary from one take to the next, but still I wonder.

[Xenon]

Sorry,

When we get the wall in and have probably some traps, we will begin to measure to see where we want to go. But we're not going to measure from 'zero' due to time factors. I think, considering how bad our room sounds now, I think the difference would be obvious. Between 'better' and 'better than that' is our goal. We'll do some basic stuff first.

Thanks for your interest, I'll be posting some build shots within 7 days...

Originally Posted by terry j

the 'best' most of us can do is simply measure the room before and after.

We might not get such a golden opportunity again, what are the chances of you doing a recording before and after???

Trouble is, recordings by their very nature vary from one take to the next, but still I wonder.

[Xenon]

Hi everyone,

Here are some links to the N23 build -- the first test array.

Construction plan (dimensions & image)

Photos

Foam cut sheet for seven N23 arrays (approx 94cm x 94cm, or 3' x 3' each)

Building 12 N23 and 4 N19, the next four+ days
We have made some improvements to the frame.
Due to white glue, our length was 8mm longer than dry fit (which was perfect).
As a result, we are using wood-scrap spreaders to thinly spread the glue (will report back on this).
Tried rubber cement --it eats the XPS foam. White glue has the advantage of cost (very cheap) and if a mistake is made, it can be remedied within about 24 hours.

FYI, total cost per N23 panel is under $50., and N19 is projected at just under $40. Though we spent $600. in air tools (haven't you always wanted that compressor?). Highest cost construction items for us are XPS ($11.20./panel) followed closely by fins (dividers). Even including the cost of air tools, we will comple our diffusion plan for the live and mix room for about $1300., which matches our hoped for budget. We will need less $$ in DIY absorption (though acceptable rockwool is almost 2x the price in the USA), with no extra tool costs (and use the air tools to advantage).

[terry j]

does the foam stay? (ie fill the void below) or just spacers till the glue dries.

What you will see is the 2.5mm ply yeah?

[Xenon]

Hi Terry,

Each well is completely filled with XPS foamcore (to depth - 2.5mm), and then (to be) faced with 2.5mm ply (40mm x 915mm) faces. Faces were cut at the home center; we cut our own fins. I will post more pics in the next few days. If built so that the bottom of the well is 'down,' as long as the frame and backing are level, yes the foam stays, and in the right depth and place. It helps to use bar clamps to keep things neet, and we also 'tamp dowm' every so often, because there is a bit of movement when you are working on it. We put some glue on the inside of the frame, and there is glue between the foam and divider(s).

The spacers (additional XPS 40mm chunks) are necessary to keep the fins square, especially with the deep wells, but we found also with the medium wells. All will be removed (easily, with a couple of pallet knives one on each side) after the glue dries, yes.

The faces will be glued and we need to put some weight on them while drying so they don't curl. We will use scrap wood for this, or small rocks (less than 4cm). After the array is complete, a radius plane (hand tool) will radius the frame (can be done before too). Then we use an air sprayer to shoot stain (dark walnut). The type we have gets shinier with each coat.

So with luck the arrays will look more pleasant in the end. I am also considering shooting lacquer or poly over the dried stain, but this is likely overkill and could create issues. Though it might look sharp.

Originally Posted by terry j

does the foam stay? (ie fill the void below) or just spacers till the glue dries. What you will see is the 2.5mm ply yeah?

[Xenon]

6 N23 arrays built now.

I am adding to the original page of photos (post #55). (Direct link here.) I'll add shots of the N19 later, and units, installed. I have a copy of REQ and hope to get room measurements, prior/post installation.

If we did this again we'd change the frame design to include all wells, and still have the first and last cover left/right frame members. We are able to cut up to @ 0.5mm accuracy on the table saw, at the limit -- 1.0mm is more reasonable using a metal T-square.

An important point: We needed to add 0.6mm for each well-segment to the length, for actual fit. So our total length is 13.2mm over theoretical. We had to adapt the frames a bit. We no longer need bar clamps -- a brick inside keeps things in place. It takes about 2 hours to fill a frame, and perhaps 45 minutes to face it (with everything pre-cut). And a lot of glue.

The fronts are pretty, the depths accurate to about 1mm. We don't have a scale but an array is easily picked up. 8-9kg (17-20lbs.)? Questions, suggestions?

* Note to Collo -- your post #19 presents an elegant solution using N17/I17. I didn't choose it for two reasons. First, those frames are small at 72.25cm (extra work, time and cost building smaller frames). Though it's possible to put 1.5 periods in a frame, just not so easy (or modular). The second issue is how well 5 periods are going to perform in a small room, say compared with the N23/N19 combination. I felt that, with a short mic-to-diffusor distance, individual (and neighboring) arrays might have a greater effect, as there isn't room for a wavefront from the entire array to cohere before hitting side walls, absorption, and what-have you. I leaned toward the possibility of higher resolution (a more polar pattern, possibly) with the N23/N19. This is just intuition or a whim, as I have nothing more to go on. From my reading, it seems that, short of actual trials and room measurements, a 'best' solution is unclear. And there is a limiting factor in that the room is rather small to begin with (not ideal). Our main goal has been to create a sense of a larger space, better micing than with a flat/absorber wall, and to balance absorption with diffusion so as not to create too dead a space. Diffusion arrays in small rooms -- hmmm.

[collo]

Those panels are looking nice. Once the stain and possible clearcoat is applied, and they are mounted on the wall, they should look fantastic.

Your build technique using the foam to hold everything in place may well become a popular one! These discussions are producing some great innovations.

The question of how to best arrange multiple panels is indeed one which seems to have no definitive guideline. Your approach is, I suspect, as good as any, with the added advantage that we all get to see those lovely N23 panels!

Well done!

[Xenon]

Thanks Collo,

Couldn't have done it without your input. Your advice raised my game enormously. And QRDUDE is an awesome tool. Yes N23 is very pretty

I'm not sure about innovations here, but can say that 1) using XPS (EPS) blueboard foam seems an excellent solution: cheap, light, easy enough to cut, and measure. And it's difficult and very time-consuming to 'block up' heights with wood spacers (we tried--lots of extra cutting/measuring). Wells are perfectly sized and spaced and the well volume 100% filled with acoustically absorbant material! Also with XPS some LF absorption is gained below the effective diffusor LF. Another key point is that attaching 4cm x 91.5cm faces of 2.5mm becomes a simple affair, and the result is a perfectly flat face along its length. We used white glue for everything. This is not the best for the faces as the ends can curl up. We had to use 'spacers' and occasionally a little weight, while curing. Rubber cement reacts with XPS, and we don't have ready access to other cost-effective glue options. In North America, there's construction adhesive or liquid nails, which might be better face glues, if they don't react with XPS foam.

Using a well (vertical) length = to the foam panel width makes for a nice looking and well fitting unit. The key is cutting the frame and fins pretty exactly. We cut our fins 1mm less high than the frame (frame inner width = 91.5cm, foam width = 91.5cm, fin height = 91.4cm).

If I were doing this again, I would redesign my dimensions with the face wood-depth in mind. We must minus -2.5mm for every face (wood-depth), and had to work with -0.5mm in measurements all the time. Better to make, for example, the zero-well depth 13.75cm (frame depth = 14.cm). This means foam depth (a cut) for a zero well = 135mm. (not 132.5mm as in our case, since we must subtract for the face depth). We designed with nice round numbers for well depths in QRDUDE, but this wasn't the best approach! For those with more money to invest or time, nicer frame wood and 45deg. corners would look very sharp.

2) Using the frame member as part of the first/last wells: With successive periods, this way, there is no 'frame gap' between them. This seems a good thing. Looking at various N periods, most can be arranged so that a zero-well and near-zero well are at the ends. For our N23 we have a zero-well, and a -7mm well at the ends. So we rip the left-right frame sides (and use 30mm foam instead of 40mm foam for the wells, as the frame takes up 12mm). To do this nicely, you want the top/bottom frame members sized for the entire length, while left/right frame members fit inside these top/bottoms (this would be very difficult to do with 45deg. corners).

Another thing to mention -- we are using a 2.5mm backing (advantages are best-max.-well-depth, and lightness). We had problems with it flexing during assembly. 3) So we tacked three frame boards vertically behind (one left/right, one middle). This kept the backing even. Also it's important to work on a flat surface. After assembly we take them off, place a flat ply panel behind the unit and bungee cord everything together, and place over bricks, for at least 18 hours after gluing. (Take a look here.) One concern is that with a 13.75cm deep frame, there is some bowing of the long frame members. This will disappear when mounted vertically, but would be a concern if the frame was longer/deeper (requiring a top-to-bottom wood strip cross-member in a well of near-zero depth, near the middle of the frame, lengthwise). Using plenty of glue and the overnight bungee method resolved this issue for us.

And we 4) had to add 0.6mm length for each well-segment over the theoretical, according to actual fit.

Collo -- come to think of it, The ability to input an 'actual fit' well-depth constant would be a handy advanced feature in the QRDUDE Calulator.

I think overall, 12mm plywood is a great choice for a frame if the depth isn't too deep or long, but for larger/deeper units, I will go with something thicker or try finished lumber. I'm also thinking that 5) it would be easy to build a double-length frame if you have (near) a zero-well near the middle. Use your frame cross members for the (near) zero well in that case -- and bowing problems would be solved. I'll add that we got all the wood but the fins cut at the home center, which saved us time -- however, some trimming here and there may be involved. We cut our own fins and foam -- which wouldn't be so easy for one person, at least with our table saw.

If I could, I'd start over, with a somewhat better (easier and faster-to-build) design. Maybe this information will help someone avoid the errors we made. I think for the DIYer in ya, 6) our final-result N23 unit is 99cm x 94cm (@ 3'3" x 3'), weighs 11.7kg (25.7lbs.) and cost @$49.USD equivalent, in materials, in Japan.