QRD Prime + Period Question (Live Room)

[Xenon]

Hi Terry, Collo,

I just jotted a quick email to Trevor Cox at Salford U., on the question of 'inverse' and phase difference. I also queried him on the RPG-4311 and viscous losses. Perhaps there will be a reply.

Fyi, my wall is 500cm L and I'm building (up to) 4 N23, 99cm/period (outside frame dimension). So 4 periods of N23 = 396cm, leaving 57cm on each end for corner bass-trapping. Also I'm building 8 arrays, as the height of one period = 94cm. So the two rows of arrays (one on top of the other) all together are 188cm H x 396cm L, on a wall 240cm H x 500cm L. Note that I have absorption above and below the diffusors; 30cm below and about 30cm above, which is tilted 45° onto the ceiling.

[collo]

It gets a bit harder to compare when you pick a left shift that maximises the difference with the standard panel (as you suggested)

[collo]

Even with a 5m wall you would want to introduce variation using the Barker code. (I think that as you increase the number of periods, it becomes more important in the fight against the dreaded lobe)

The panel width vs design frequency on the scorecard was making sure that the period width is at least equal to the design wavelength. If you're sticking near the recommended well width, this requirement is generally met once the panel order gets above 7.


Out of interest, I've attached my take on the 4311..(the forum software wont allow the .qrd extension so delete the .txt from the end of the filename)

[terry j]

Good call xenon, tho Trevor will probably say 'just buy the bloody book'!

which I will do, maybe an early xmas present.

Originally Posted by collo

Even with a 5m wall you would want to introduce variation using the Barker code. (I think that as you increase the number of periods, it becomes more important in the fight against the dreaded lobe)

The panel width vs design frequency on the scorecard was making sure that the period width is at least equal to the design wavelength. If you're sticking near the recommended well width, this requirement is generally met once the panel order gets above 7.


Out of interest, I've attached my take on the 4311..(the forum software wont allow the .qrd extension so delete the .txt from the end of the filename)

The hampster has a message for you, he's upset. (in fact, he's sulkin')

haha, no, what I find interesting is the words you used..'the dreaded lobe'.

Have you ever heard a qrd in action, and if so, have you actually heard the 'dreaded lobe' in action?

gee, as i get older I think I get more cynical or 'wary', but I have learned to take a lot of things with a grain of salt. Especially internet lore (ok, granted this prob came form cox et al) but you know what I mean.

heck, if I followed all the important things in audio I read, then I would not be working on the room but getting the best cables I can!!

For sure, as I say getting old and crabby, but I at least don't want to be responsible for passing on, without personal inspection, unexamined stuff.

So, the question is, how much are we tying ourselves up in knots here? And anyway, it is really interesting that we can look at the same thing, and come to completely different conclusions!! (tho I do tend to defer to your opinions on technical matters, have much more confidence in them than mine!!)

I tried to have a look at your file, but couldn't delete the .txt..will try again but just a heads up that there are idiots (like me) out in internet land.

[collo]

I agree with you - we're chasing our own tails. Or as a friend of mine says, revin in the mud!

I must confess that I've not encountered the dreaded lobe, but you must admit, it's got a certain ring to it....

[Xenon]

Hi Collo,

Thanks for all these images! By the way, I think I fixed my earlier image, if you check. Looks like your post#92 just above shows about as much of a difference as possible. And also my left-shift-18 looks pretty good. I was able to load your N43. Very elegant design and only about 120cm (4'). so much work went into that... In your 'left-shift-5' above I notice the phase vectors at the center seem to be fairly divergent, compared to the standard 0-shift N23. Looking into this idea further, I wonder if periods like N19 or N17 might have better results?

Also going to N29 (shifted down either 9 or 16 for depth savings), you can see quite a variance in that layout, internally. That would be pretty nice in a larger room (like at least 25' or 750cm).

N17 seems more self-similar, looking quickly at it.

In general, you've got 'turret' sections and 'stepped hemisphere' sections. If you realign turrets over the position of hemispheres, you get divergence. I think the point or the question is, does this break up the lobing. (I think following a Barker code is smart, the problem of symmetrical periodicity seems well documented.) Interesting, your idea to let the design Hz float in building a (Barker) -1 (realigned) N23.

As for a write-up, sheesh, I was thinking the photo links, construction sheet, cut sheet plus this thread would be enough. If you have a thought though let me know. I was hoping to spend my 'extra' time in getting some room measurements, though I doubt they will say much that's good, until I do a lot more acoustic treatment (which will take a couple more months).

I'm thinking seriously of trying one of these realigned N23s instead of N19... (e.g. Shift Left-5, and split the left well (5) which is only 8mm deep in my design, between left and right, so the frame members can be utilized in the well construction). [Edit: No! See below]


Edit !:
Better add to this, after looking at the sections that can be seen in googlebooks here (in Acoustic Absorbers and Diffusers: Theory, Design and Application By Trevor Cox, Peter D'Antonio), pages 289-329. It seems from this that the Modffusor is likely a 'sampled' N-73 PRD (not QRD), which is why it is asymmetric and why it has 8 wells (see below). The example given (on page 311) is for a modified
(asymmetric) N-7 PRD with 6 wells (ratios: 132645), which can be flipped (to 546231), rather than inversed, in creating multiple periods (according to the Barker code).

The concept of inversing is explained here on p. 248: "The curse of periodicity", in part:

"A QRD needs periodicity to form its optimum diffusion of even energy lobes, yet the periodicity lobes cause uneven scattering."

I learned that techniques of altering symmetrical periodicity in however many arrays, is called "a modulation scheme":

"The modulation works best at multiples of the design frequency. Only at these frequencies do the diffuser and its inverse create exactly opposite pressures. At other frequencies, the modulation is likely to help with the scattering as it breaks up periodicity lobes, but in a more uncontrolled manner." (p. 251)

Which implies that you would want to keep the same the design frequency, whatever (inverse/flip/different N-prime) was used, but with the caveat that altering the design frequency will still be effective in the primary goal of breaking up lobes.

It's stated that QRDs are not mathematically asymmetric. And further in the chapter optimization is mentioned (e.g. autocorrelation) and this interesting statement, leading to my supposition as to the Modffusor, on p. 302:

"Consider a primitive root sequence based on prime 73; this will be of length 72. By taking every ninth sample from this sequence, a shorter-length 8 sequence is formed....the flat plate frequency will be at nine times the frequency that a more normal number theoretic diffusor would achieve."

Well, the above could certainly be the Modffusor, couldn't it? A sequence of 8 wells, based on each ninth well of an N-73?

The basic principle of optimization is to "get the computer to search for a sequence with minimum side lobe energy..." A modified primitive root sequence based on N43 (mod. PRD) is mentioned on p. 318. It seems that quite a lot has been done with PRD modification, since Alton Everest, and since the 90s. Then there is this patent on aperiodic repetition of arrays on a wall, "Embodiments of aperiodic tiling of a single asymmetric diffusive base shape," (issued August, 2004) which may relate to our current discussion. And also see p. 248 of the above book. I downloaded the patent (public domain), and you can grab the PDF here and the full text of the patent, in html form, verbatim, here. It's in the patent that,

"The sound diffusor of claim 14, wherein said series includes said first and last half wells of depth zero, and seven wells there between having respective consecutive depths equal to or proportional to the following amounts in inches: 3, 67/16, 37/8, 51/16, 211/16, 45/8, and 13/16."

Can you source it from an N73 PRD of a certain depth? Anyway the point most relevant to our discussion concerns aperiodicity. Reading over the work of Angus, as mentioned in "Acoustic Absorbers and Diffusers," it seems best to work with "two base shapes" as a best 'less-technical' solution to the problem of periodicity -- a problem explained at length in the patent. It seems there is much to explore for the intrepid.

[Xenon]

The above information has helped me pragmatically, in that I will return to this arrangement:

N23 N23 N19 N23

But I will change one element. My max well depth of the N23 is 135mm = 994Hz design frequency. If I make the N19(shift-3) max well depth as 127mm (losing 8mm of depth), the N19 design frequency = 994Hz, matching the N23.

[collo]

Originally Posted by Xenon

The concept of inversing is explained here on p. 248: "The curse of periodicity", in part:

"A QRD needs periodicity to form its optimum diffusion of even energy lobes, yet the periodicity lobes cause uneven scattering."

I learned that techniques of altering symmetrical periodicity in however many arrays, is called "a modulation scheme":

"The modulation works best at multiples of the design frequency. Only at these frequencies do the diffuser and its inverse create exactly opposite pressures. At other frequencies, the modulation is likely to help with the scattering as it breaks up periodicity lobes, but in a more uncontrolled manner." (p. 251)

Which implies that you would want to keep the same the design frequency, whatever (inverse/flip/different N-prime) was used, but with the caveat that altering the design frequency will still be effective in the primary goal of breaking up lobes.

That link is the best one we have for the issue of modulation. (Unfortunately for me, the Google display hides one of the pages right in the middle of the section we're interested - will have to wait for the book, which of course, is the intention of the publishing scheme, and fair enough!)


Anyway, having the same design frequency for both diffusers used in the modulation scheme is only required when the exact inverse is used.
If the second diffuser is not the inverse, but a normal panel of a different order, you will not get the advantage of exactly opposite pressure described in the bold text.
In that case, you may as well allow different frequencies into the mix, giving the ability to match the build depths.

Speaking of matching build depths.....
If you are prepared to do away with zero-depth wells, (meaning no nice half-width ends), you can often find advanced panels that have the same build depth as their inverses.
Examples are N7+4, N11+1, N11+4 (the best of the three N11's), N11+9 etc.
Because the inverses have a smaller build depth than their non-advanced counterparts, you pick up savings in well width.

I see this type of design as the main strength of QRDude.


As far as the modfusers go, I'll leave you and Terry to duke it out - my little brain is liable to explode if I stray too far from the QRD arena...

[Xenon]

Hi Collo, you wrote

Originally Posted by collo

Speaking of matching build depths.....
If you are prepared to do away with zero-depth wells, (meaning no nice half-width ends), you can often find advanced panels that have the same build depth as their inverses. Examples are N7+4, N11+1, N11+4 (the best of the three N11's), N11+9 etc. Because the inverses have a smaller build depth than their non-advanced counterparts, you pick up savings in well width. I see this type of design as the main strength of QRDude.

For sure! I have a further question -- do you find anything similar with the higher primes, N17 N19 (not N23 I gather) N29?

PS One thing I'd like to mention in terms of a build is you can split non-zero-depth wells. Any well can be split, but it's obviously preferable to select a well that is as close to zero-depth as possible. Often the well next-closest to zero is only a few millimeters deep, so it won't affect the frame strength to cut the left-right sides down a bit.

[Xenon]

Hi guys,
I received these replies from Trevor Cox. One thing I take from this is that a well width of 4cm is "standard" and not an issue in QRD builds in general (I think there needs to be more definitive research into well-width vs. well depth before making firm minimum recommendations). See what you think, I'll put the letter here verbatim, October 2, 2009:

The first question concerns viscous losses in QRD designs. RPG in the 1990s built QRD-4311 (16" depth/1.1" well width). Schroeder's recommendation would be for a well width of 4 3/4", in our understanding, so,

Q1: Didn't the QRD-4311 experience substantial viscous losses due to the narrow wells?

Trevor: You would have to see if RPG has measurement data. I've only measured wider diffuser well widths for absorption (about 4cm)

Would you have a recommendation on (or formula) for max well-depth/well width -- or even general guidelines?

Trevor: The build quality is probably as important as this ratio

Relevance: in the project studio, where QRD max. well depth may be only 15-20cm, we would like to build for maximum HF bandwidth, so well-widths as small as reasonably possible. My own unit has 40mm wells (with 2.5mm dividers), but some say this well width is too narrow. Could you comment?

Trevor: 40mm doesn't seem very narrow to me, pretty standard in the commercial world.

The next question concerns the Barker code in multiple arrays (in a project studio say with rectangular walls about 500cm x 460cm or so). In a 4 or 5-period array of QRD N23, Barker calls for:

+1 +1 -1 +1
or
+1 +1 +1 −1 +1

Concerning the -1 period, we gather the best choice is N23i (inverse) but max. well depth suffers. Another option is selecting a different N-period, like N19. But, and here's the question, it's possible to shift the N23 wells so that the well-phase at a given period length is changed, as shown in the following two images here:
http://www.gearslutz.com/board/4633435-post88.html

Q2: We are wondering what you think of the above idea of well (phase) shifting as a Barker code solution, in a small (realistic cost) project studio live or mix room.

Trevor: Good idea, although the big gains are probably doing some modulation, and then what type you choose to do is then of less importance.

[collo]

Originally Posted by Xenon

Hi Collo, you wrote For sure! I have a further question -- do you find anything similar with the higher primes, N17 N19 (not N23 I gather) N29?

PS One thing I'd like to mention in terms of a build is you can split non-zero-depth wells. Any well can be split, but it's obviously preferable to select a well that is as close to zero-depth as possible. Often the well next-closest to zero is only a few millimeters deep, so it won't affect the frame strength to cut the left-right sides down a bit.

Here are a few more....
N7+4
N11+4
N13 +2 ..... better mix with N13+6, but not quite same depth
N17+6
N19 +1 ..... better mix with N19+5, but not quite same depth
N23+6 ..... better mix with N23+2, but not quite same depth
N29+11

Good point about being able to split any well......

[collo]

Nice to see a reply from Trevor Cox.

I see the following:

- no real comment on the 4311
- build quality is important - ratio can probably be a bit less than Shroeder without too much worry (don't know by how much though)
- 40mm wide wells are fine, but no info on smaller ones
- With Barker modulation, the fact that you modulate is more important than the actual second panel used .... probably the gem of the letter!

[Xenon]

Hi Collo,

Yes, you've done a nice wrap-up -- I would add that it was mentioned, 40mm wells are common in commercial applications. It would take some fieldwork to locate and scope out the many varieties of commercial diffusers, but I have to imagine that most are at least in the 16cm-22cm depth range (8" is spoken of as a reasonable depth minimum in commercial applications). I personally feel that builders should carefully consider the bandwidth benefits of 40mm wells, and feel there is perhaps no big issue with this size well-width used in deeper units (my supposition from Trevor's reply).

Originally Posted by collo

Nice to see a reply from Trevor Cox.
I see the following:

- no real comment on the 4311
- build quality is important - ratio can probably be a bit less than Shroeder without too much worry (don't know by how much though)
- 40mm wide wells are fine, but no info on smaller ones
- With Barker modulation, the fact that you modulate is more important than the actual second panel used .... probably the gem of the letter!

I asked a follow-up question, and got a reply today. Here's the text,

Me: My question is a simple one. My N23 design freq. = 994Hz, MWD = 135mm. With this arrangement: N23 N23 N19 N23 (Barker code: +1 +1 -1 +1) To make N19 design freq. = 994Hz (max well depth 127mm) or disregard the design Hz, and just build to the same depth (135mm) as the N23? I ask, in that from reading it seems that matching the design Hz is preferable -- though some on the board disagree, stating that a mismatch is actually preferable, in terms of modulation. Could you clarify this point?

Trevor replies: Probably impossible to answer the question without a few predictions. But given you are using relatively large N primes, flat plate frequencies are not a worry, so choosing the same design frequency is OK (choosing a different one is probably OK as well!)

A rather sphinxlike reply -- can you intuit anything from it?

[Xenon]

Hey Collo,

I have a question about this:

Originally Posted by collo

Here are a few more....
N7+4
N11+4
N13 +2 ..... better mix with N13+6, but not quite same depth
N17+6
N19 +1 ..... better mix with N19+5, but not quite same depth
N23+6 ..... better mix with N23+2, but not quite same depth
N29+11

Taking N23+2 (at 135mm MWD), when I switch to Inverse mode, if I go to N23i+4, I get a MWD of 132mm. What do you think of this approach?

Originally Posted by collo

Good point about being able to split any well......

There is a point where it will look strange or weaken the frame, but you could split a well that is say as much as 25% of MWD I think.

I'd like to add another question, related to my build. I am using 3 N23 arrays (plus a 'modulation' array--this is the one I'm not sure on). I plug in my MWD (135mm) into QRDUDE, then toggle to "design frequency", hit "Switch to Inverse Panel" then (here's the trick) reset my "Deepest well" as 135mm, and start scrolling through the Inverse panel permutations. I find that:

N23+0: design freq. = 994Hz = 135mm MWD
N23i+4: design freq. = 1055Hz = 135mm MWD

Design Hz are not that far apart either. Do you think this is a fair application of the Inverse panel in a modulation scheme? If so, it would be a good solution for me.

[collo]

Decoding the sphinx....
Where plate frequency is a limiting factor in the bandwidth (really only a problem for lower order panels), you can use a different design frequency for the 2nd panel so that when one panel is acting as a plate, the other is diffusing properly. (This is from the link you presented earlier on periodicity)
Trevor seems to say that because your order is high enough for this not to be an issue, you can take your pick....

The use of 40mm wells is anectdotal at this stage. Will need to think more about it before allowing qrdude to move that far from the Shroeder ratio.

Taking N23+2 (at 135mm MWD), when I switch to Inverse mode, if I go to N23i+4, I get a MWD of 132mm. What do you think of this approach?

Once you rotate the phase wheel after shifting to the inverse, you generate a new normal/inverse pair. Switching back to the normal panel, you'll see its not the one you started with.

The N23+2 / I23-2 pairing was the closest match for build depths.

[collo]

Originally Posted by Xenon

I'd like to add another question, related to my build. I am using 3 N23 arrays (plus a 'modulation' array--this is the one I'm not sure on). I plug in my MWD (135mm) into QRDUDE, then toggle to "design frequency", hit "Switch to Inverse Panel" then (here's the trick) reset my "Deepest well" as 135mm, and start scrolling through the Inverse panel permutations. I find that:

N23+0: design freq. = 994Hz = 135mm MWD
N23i+4: design freq. = 1055Hz = 135mm MWD

Design Hz are not that far apart either. Do you think this is a fair application of the Inverse panel in a modulation scheme? If so, it would be a good solution for me.

The I23-4 is not the inverse of the N23+0
Having said that, you are maximising the "free ride" for both, thus getting the lowest design frequencies for each.
Given Trevor's earlier comments downplaying the importance of having an exact inverse, this is should be as good as any other non-exact arrangement.

[Xenon]

Yup, got it!

Yes, the 40mm well width is anecdotal for sure, though expertly so. I suppose it will take more voices and some digging to learn more. It's too bad that a fair degree of LF bandwidth is sacrificed, between the N23 and N23+2...

Well I am on to building the N19+3 as my modulation period. Reading over the design Hz/MWD discussion, I surmise that, if plate Hz isn't an issue (as with larger primes), then, if it's not otherwise problematic in the space, matching the design frequency between +1/-1 panels is a good thing, and as the difference for me is only a matter of 8mm shorter, it's easy to accomplish (I can use my same frame as with N23, but my max wells will be 127mm not 135, which means they will have 5.5mm spacers under them (plus 2.5mm faces). When the modulation panel is a bit shorter the design execution is easy.

Originally Posted by collo

Decoding the sphinx....
Where plate frequency is a limiting factor in the bandwidth (really only a problem for lower order panels), you can use a different design frequency for the 2nd panel so that when one panel is acting as a plate, the other is diffusing properly. (This is from the link you presented earlier on periodicity)
Trevor seems to say that because your order is high enough for this not to be an issue, you can take your pick....

The use of 40mm wells is anecdotal at this stage. Will need to think more about it before allowing qrdude to move that far from the Shroeder ratio.

Taking N23+2 (at 135mm MWD), when I switch to Inverse mode, if I go to N23i+4, I get a MWD of 132mm. What do you think of this approach?

Once you rotate the phase wheel after shifting to the inverse, you generate a new normal/inverse pair. Switching back to the normal panel, you'll see its not the one you started with.

The N23+2 / I23-2 pairing was the closest match for build depths.

[Xenon]

Originally Posted by collo

The I23-4 is not the inverse of the N23+0
Having said that, you are maximising the "free ride" for both, thus getting the lowest design frequencies for each.
Given Trevor's earlier comments downplaying the importance of having an exact inverse, this is should be as good as any other non-exact arrangement.

That's what I was thinking too! This seems useful, in that now there are two decent modulation options beyond the IN23. I can use an N19, or the I23-4. In terms of studio decor, the I23-4 will look much better and cover a larger area.

Here are 4 completed N23s in the live room (still unstained). There will be another row on top of these (#3 will be Inverse N23, Shifted up 4 depth units, left 8 wells, the left well (-7mm), split):

[terry j]

just had a crazy thought...seein as how Trevor is willing to communicate, I wonder if he'd cast a critical eye over the qr dude page and the calculator in advanced mode???

[Xenon]

Originally Posted by terry j

just had a crazy thought...seein as how Trevor is willing to communicate, I wonder if he'd cast a critical eye over the qr dude page and the calculator in advanced mode???

I've written him offering thanks for his time and promised not to pester him... If Collo feels like sending an email, why not? QRDUDE is a great piece of software.

[Xenon]

Update:

We are now in the staining phase.
We are using a Vaton "dark brown" indoor wood stain, sprayed with an inexpensive $35.00 HVLP sprayer, off our 2hp 39Litre air compressor.

Good results with 60%/40% stain/paint thinner.
For a look at our sprayer, go to amazon.com and this keyword:
Tool Force A-C1 50 PSI 2-in-1 HVLP Spray Gun

(Another company to look at is "Advanced Tool Design" (at amazon or spraygunworld). Nice color, we are happy (we ended up not using the regulator that came with the gun, as our air tank reg works perfectly well).

Gloss finish
We are unhappy that in Japan at least in our area, while spray can acrylic lacquer is plentiful, a commercial size (3.5L would be fine) is unavailable. Frustrating. The common thing here is to spray polyurethane, and we are likely forced to do this to get a gloss finish. A benefit also is that the unit is less likely to degrade or shift in any way -- one benefit of poly though is the super-hard, acoustically reflective surface, plus joins (between faces and fins) will be filled or smoothed by the poly (if we shoot it to our satisfaction).

Glue
We do have some white glue drops on some pieces. If we could do it again:

Once you are sure of your frame size length, assemble & glue the faces on at the same time as fins are assembled, not later.

And if possible, get the glue into a caulk tube or find a way to apply it directly with (something like) a caulk gun. This would have solved our issues (mistakes). Also we found out a bit late that if you keep wet-damp rags around and use them liberally on missed glue, you can wipe it off wood pretty well, if done immediately.

In the USA, liquid nails or constructive adhesive in caulk tubes may be the better choice, though I can't say for price. I think white glue works very well in the build, I like that we can bungee and tighten our frames overnight, and that the glue remains flexible for some hours. If a more targeted application method is found, it would be perfect.

From an engineering standpoint, we have all well depths within 2mm and many within 1mm of spec, and the widths are spot on (due to the foam being a stable 40mm width).

Spray materials use
It's way easier to stain/seal last, the sprayer works great, with a little help from a stain-soaked rag for deep areas and smoothing. We go with one spray coat, then wait about 15 minutes and do some spray touchup if needed. An N23 uses between 300cm-350ml of stain, so it's pretty economical. Spraying a unit takes perhaps 10 minutes, and touchup another 5. The time involved is in setting up an outdoor spray station, pouring and mixing, getting the gun set up right. We had no experience shooting stain before, and it wasn't too hard to figure out. We also shot polyurethane, which isn't that different.

For costs, we costed our N23 at $49. each. In Japan stain and poly aren't cheap.

$60. for 3.7L of stain (x2?) $120.
$45. for 3.5L of poly (x2?) $90.
$ 9. for 3.5L of paint thinner (x3) $27.

$237. (and a lot of stain and some poly left over). We built 14 units (4 are N19s) so altogether we add $17. to the cost of each unit, bringing the cost up to $66.USD per unit. (We have enough extra to build the remaining 4 N23s for the mix room ...)

I don't have pics yet, but soon --

[PaulP]

Beautiful work thumbsup

What are your first impressions on how it sounds ?

Paul P

[Xenon]

Thank you Paul,

I'll have some pics in a few days -- it was raining today (Sunday). We won't know how it sounds for some time, as all the units are outside the room now. After shooting poly in maybe two weeks, we need to let the smell desist -- so 10-14 days in the garage 'curing'. Meanwhile we want to test the bare room with REQ to get a baseline, and be building frames and applying absorption. We will run acoustic tests with only the diffusers in place, but don't expect very much difference, with plenty of reflective surface (no absorption). We suppose that, until the absorption is in place, we won't see the major benefits of diffusion.

So we are likely still looking at another two months, as we can only work weekends on this for a while. Or course it is pleasant to talk in front of several units. Like looking at delicious, ripened fruit.

Originally Posted by PaulP

Beautiful work thumbsup
What are your first impressions on how it sounds ?
Paul P

[PaulP]

Originally Posted by Xenon

Or course it is pleasant to talk in front of several units. Like looking at delicious, ripened fruit.

Speaking of talking, what do you think would be the effect of having a
similar sized diffuser, say one or two or your units, on a wall alongside the
long side of a dining room table ? I ask because my rear wall is also the
wall of the dining room and I've been thinking about putting a large qrd
along that wall. Is speech in front of one of your units clearer or does
the diffuser add some strange effects close up, like 1-2m away ?

Paul P

[Xenon]

Paul,

I recommend you check out these videos from RealTraps -- I think they will help answer your question. And I'd be curious as to your impressions. Check 'em out. The first is probably the most directly relevant:

1. ALL ABOUT DIFFUSION

2. HEARING IS BELIEVING:
THE ULTIMATE SMALL MIXING & MASTERING ROOM

3. MINITRAPS DEMONSTRATION

4. HOW TO SETUP AND TREAT A LISTENING ROOM

5. THE ULTIMATE HOME STUDIO

Originally Posted by PaulP

Speaking of talking, what do you think would be the effect of having a
similar sized diffuser, say one or two or your units, on a wall alongside the
long side of a dining room table ? I ask because my rear wall is also the
wall of the dining room and I've been thinking about putting a large qrd
along that wall. Is speech in front of one of your units clearer or does
the diffuser add some strange effects close up, like 1-2m away ?

Paul P

[Schaap]

Originally Posted by Xenon

Update:

We built 14 units (4 are N19s) so altogether we add $17. to the cost of each unit, bringing the cost up to $66.USD per unit. (We have enough extra to build the remaining 4 N23s for the mix room ...)

I don't have pics yet, but soon --

Nice work, would love to see the pics!

Originally Posted by PaulP
Speaking of talking, what do you think would be the effect of having a
similar sized diffuser, say one or two or your units, on a wall alongside the
long side of a dining room table ? I ask because my rear wall is also the
wall of the dining room and I've been thinking about putting a large qrd
along that wall. Is speech in front of one of your units clearer or does
the diffuser add some strange effects close up, like 1-2m away ?

In the living room we have a pair great (2' by 4') QRD7 and some skylines and Flutterfree kind of diffusers along with GIK 242 and 244 panels. The room(5 x 6 x 2.7 meters) have all concrete walls and ceiling and a hardwoodenfloor. Without treatment it sound horrible and harsh. One of the first things I put in there was GIK panels and the great sized QRD. Both helped a lot.
The last things I made were those 'antiflutters' and that's really the 'finishing touch' for music and speeche.
Last Christmas we had the family here with some 80+ with hearing aid and they always had trouble to follow the conversation mostly by the 'reverbpickup' and the 'directions' in the room of the spoken words. We put some extra GIK panels and diffusers from the studio in the room and after dinner we asked if they noticed something during the conversations. The 80+ers all said no; they just participated with conversations as they used to do. Then suddenly they realised that was not the case in the previous years.

Henk

[PaulP]

Originally Posted by Xenon

Paul,

I recommend you check out these videos from RealTraps -- I think they will help answer your question. And I'd be curious as to your impressions. Check 'em out. The first is probably the most directly relevant:

1. ALL ABOUT DIFFUSION

2. HEARING IS BELIEVING:
THE ULTIMATE SMALL MIXING & MASTERING ROOM

3. MINITRAPS DEMONSTRATION

4. HOW TO SETUP AND TREAT A LISTENING ROOM

5. THE ULTIMATE HOME STUDIO

Thanks for the links Xenon. I've actually watched these videos maybe a
month or two ago but it's worth seeing them again. Now I have some idea
of what Ethan's talking about . It looks like I might be better served with
a shallower diffuser with narrower wells than your big ones, though I
suppose the best would be something like yours but with smaller ones
inside each well (like the 'fractal' ones). I'm a part-time woodworker
with the necessary tools but my shop hasn't yet been unpacked since
our move. Your work is inspiring.

Paul P

[PaulP]

Originally Posted by Schaap

Last Christmas we had the family here with some 80+ with hearing aid and they always had trouble to follow the conversation mostly by the 'reverbpickup' and the 'directions' in the room of the spoken words. We put some extra GIK panels and diffusers from the studio in the room and after dinner we asked if they noticed something during the conversations. The 80+ers all said no; they just participated with conversations as they used to do. Then suddenly they realised that was not the case in the previous years.

Thanks for this story. I've gotten so caught up in thinking about music that
I forget about speech. It makes perfect sense that a nicely balanced room
for music would also be great for speech. Funny that no one suggests you
treat the rooms of your house so you can enjoy better quality conversation.

Now I think I have a good reason to treat the entire dining room, seeing as
it's mostly the rear half of my music room. Much easier to get approval if,
instead of saying it's for my music room, I say it for everyone's enjoyment
around the dinner table . Just gotta make it look good.

Paul P