My home made diffuser

[4 the Max]

I am following the absolutely wonderful plans and photodiary by Jake Hartsfield:

DIY Acoustics III: I Did It - You Can Too by Jake Hartsfield (TuneCorner)

In studing his and other QRD builds on gearslutz, almost everyone is using luan (wood) for the fins and wells and pine whiteboard for the frame and well spacers, including DecWare's kit ($150 for single unit):
http://www.decware.com/p1324.htm


Like many of us on gearslutz, I just can't afford to purchase multiple $500 commercially-made QRD units.

I was thinking of using 3/16" foam-core for the fins;
and either 3/16" foam-core OR 1/8" matte-board (used for matting photos in framing) for the wells

Questions:
Is there some acoustically significant about
1. using luan (wood) vs. foam-core for fins and over OC 703 in the wells?
2. using foam-core vs. matte-board over the Owens-Corning 703 in the wells?

I was thinking that the matte-board over the wells might be better because it's thinner allowing more bass trapping by the OC703 beneath the well

The diffuser weighs and costs less than using luan:

Foam-core/Matte-board materials:
A.C. Moore, a local crafts store, sells
white 3/16" 20" x 30" foam-core for $2.69
colors 3/16" 20" x 30" foam-core for $5.99 (beige speckle, white speckle, gold, cyan, green, yellow, red, tan, gray, navy blue, orange)

3/16" 32" x 40" foam-core for $7.99
1/8" 32" x 40" matte-board for $7.99

In speaking to a cabinet-maker/carpenter who manages the local Home Depot contractor's desk, luan would require purchasing a 10" Ryobi table saw ($119), 10" 90 tooth blade ($40), and push shoe for safety ($20) besides all of the luan

The matte-board and foam-core can be cut with a utility knife and drywall T.

Aside from acoustics, wood QRDs look beautiful hanging on a wall. However, my main consideration is acoustics not aesthetics. However, if the wood build is acoustically better than foam-core/matte-board, I'll use luan despite the extra cost.

Thank you.

[mhch]

Originally Posted by dr jazz

Thanks for the advise but I'm not sure Gator board Exist here in France...
Perhaps it has another name?
If anybody has an idea...

May be use balsa and harden the surface with paint !! Utilises du balsa et rends la surface reflechissante avec de la peinture ... (yes I'm French too)

It's a good idea to fill the inner part of each slot (below a thin wood piece), using absorbing wool, as this also provides some extra bass trapping, specially if the diffuser is large.

[Jens Eklund]

Originally Posted by mhch

It's a good idea to fill the inner part of each slot (below a thin wood piece), using absorbing wool, as this also provides some extra bass trapping, specially if the diffuser is large.

Diffuser with bass trapping?

[Xenon]

Hi,

I built a couple of QRD walls for my live room, seen at the thread here:

QRD Prime + Period Question (Live Room)

There is nothing like QRDUDE free software to help you:
QRDude: Quadratic Residue Diffuser calculator

After some research by utilizing "blueboard" in the well gaps (40mm width wells, N23), there is some absorption between 150Hz-500Hz. Filling the wells involved a substantial amount of blueboard (you can calculate it based on the well width x height x depths). The blueboard was just the thing to keep the well widths uniform.

Keep in mind the absorption is not bass trapping. I think the amount of absorption has benefit, but the absorption is tangential to having a non-resonant acoustically absorbent material in the wells behind the front slats.

Look into corner bass trapping for instance (or Heimholtz corners, etc.) to achieve effective trapping (our live room has corner bass traps and 48Kg rigid fiberglass above/below the QRDs, and we built 15cm ceiling absorbers, with about a 5cm gap below the ceiling).

Our project studio live room can be seen here:

BigFish — Studio

Good luck. A lot of work but very cost-effective and totally worth it.

[DaggerToe]

YouTube - DonketasLoveOrgan.MOV

How would you connect all this together?

[localhost127]

Originally Posted by Jens Eklund

Diffuser with bass trapping?

Jens,
pardon me if i may have missed it in your previous explanations, but while styrofoam may not absorb as one would assume, is it still useful to be permanently used as a cavity filler for the diffuser wells?

or would you recommend simply using it as a guide, and then removing it and filling the well with fluffy insulation. (if the goal is only to minimize resonance within the wells, not to perform any additional overall absorption).

thank you,

[Xenon]

though you are asking Jens, I would like to say that as a diffuser is made of a dense material designed to reflect sound waves down to a certain Hz, and "fluffy" insulation at the volumes we are considering, absorbs HF/MF, its seems there is little absorptive benefit, as you are reflecting the wavelengths prior to the absorption, right?

The blueboard I mentioned has absorptive properties below the typical LF cutoff of all but really deep QRDs (check QRDUDE). So there is some benefit, though it is limited. Of course as mentioned you want to fill the void with something to prevent resonance. It needn't be fiberglass though.

Originally Posted by localhost127

Jens,
pardon me if i may have missed it in your previous explanations, but while styrofoam may not absorb as one would assume, is it still useful to be permanently used as a cavity filler for the diffuser wells?

or would you recommend simply using it as a guide, and then removing it and filling the well with fluffy insulation. (if the goal is only to minimize resonance within the wells, not to perform any additional overall absorption).

thank you,

[Jens Eklund]

Originally Posted by localhost127

Jens,
pardon me if i may have missed it in your previous explanations, but while styrofoam may not absorb as one would assume, is it still useful to be permanently used as a cavity filler for the diffuser wells?

or would you recommend simply using it as a guide, and then removing it and filling the well with fluffy insulation. (if the goal is only to minimize resonance within the wells, not to perform any additional overall absorption).

thank you,

EPS can be used in two ways: Either as the actual material of the diffuser if relatively dense (approx. > 25-30 kg/m³);

Diffusors: opinions about EPS polystyrene?

or as a build guide when making them in wood DIY-style. Provided that the wood is glued to the EPS, it will not absorb noticeably but any diffuser will naturally absorb more or less due to other reasons.

[localhost127]

Originally Posted by Xenon

though you are asking Jens, I would like to say that as a diffuser is made of a dense material designed to reflect sound waves down to a certain Hz, and "fluffy" insulation at the volumes we are considering, absorbs HF/MF, its seems there is little absorptive benefit, as you are reflecting the wavelengths prior to the absorption, right?

no, the absorption within the wells is strictly to address resonation inside the wells --- not to be used as any part of an absorber in the classical sense.

much like the use of fluffy insulation between wall cavities.

[secret secret]

Thought I'd share a couple pics of my newly finished DIY skylines. I used 1x1s and stained them a bunch of different colors. I glued each row together first, then glued the rows together to make 2 12x12 panels, then glued the two panels together.

pic here: The Studio

[soundoff]

Secret Secret - What plans did you follow to build those skylines?

I'm considering building some 1X1's myself... just wondering how much background research you did. Is there a huge difference between skylines built with 2x2's vs 1x1's?

Also... out of curiosity... how far away from your primary position do you have that diffusor?

thanks,
soundoff

[chadking]

Just finished up my first skyline style diffusors. These are adjustable on the stand and easy to move. It was my first set, so I learned a lot. Next sets should have a bit better fit and finish.

Thanks everyone for the inspiration!

[localhost127]

Originally Posted by chadking

Just finished up my first skyline style diffusors. These are adjustable on the stand and easy to move. It was my first set, so I learned a lot. Next sets should have a bit better fit and finish.

Thanks everyone for the inspiration!

nice work! i like the gobo/stand idea.
i did the same thing (installed wheel casters on the bottom so it was mobile) ... but i also installed 4" OC703 on the backside.

this quickly lets you switch between a diffused surface and an absorptive surface, depending on what your needs are

something you may want to consider

[Cegor]

All of the diffusers look great so far. Any size(s) that's recommended for the fins?

[localhost127]

Originally Posted by Cegor

All of the diffusers look great so far. Any size(s) that's recommended for the fins?

1/8" luan ply

[Adhoc]

Hats off and a salute to Boggy Petrovic! His MLS sequence, a binary series of slats and slots, has helped me to increase T60 from about 0,1 s at about 150-4 kHz to about 0,2 s in the same range. (Jens Eklund has provided some other stuff, even more important and for the same purpose. I might show that in another thread)

An easy trick to add more life to a “dead” room is to add slats on top of resistive absorbers. The most common advice on GS seems to be to follow Newells 3-5-4 series of slats and slots, giving about 50% absorbtive area and 50% reflective area. Boggys MLS series provides the same ratio as Newells as it is a binary series. I prefer Boggys as it should add some more diffusion and is more versatile. The BIG plus is that it is so much easier to calculate it into a “tailor made” version for your available wall area and one can buy one and the slat dimension at the lumber yard. –No need to cut up different widths of slats. Calculation for an optimation is quite straight forward but boring and tedious, so I wrote an excel spread sheet in which all the variables are easily varied to one´s own wishes. I also added a new variable “end correction”, to simplify planning and symmetry in the room. The spreadsheet is quite self-explanatory and is added below.

Background: Treating an underground concrete bunker into an enjoyable listening room is not an easy thing. It needs a lot of absorbtion to tame the modes. Lots of resistive absorbtion in turn leads to a room too dead to be enjoyable. -But that is where one may have to start and then from the too dead room move on to make it more live. So, that’s what I did and to some degree is still striving for.

What I started out with was a room 7,86 x 4,19 x 2,25 m. Three walls, towards the garden, 20-25 cm (8-10”) of concrete, dirt up to half height of the room, remaining wall towards the rest of the building about 50 cm (20”) solid concrete and brick. Ceiling and floor also concrete. Good thing: I knew the problems in advance and the room was very close to symmetrical making it suitable for a control room design regarding treatments. Bad thing: A nightmare acoustically if not heavily treated because of the extremely rigid room boundaries.

Front end of room. About 1/3 of room length has 95 mm equivalent of O C 705 closest to concrete, added on top towards the room is fluffy 45 mm Isover Piano (= Behind the burgundy coloured fabric) At floor level, behind the black fabric are limp mass membrane absorbers. At the front wall are 45 mm Isover Piano + 60 mm O C 705, behind the resistive absorbers from floor to ceiling are more limp mass membrane absorbers, distance for resistive absorbers to concrete is 160-250 mm.

Before MLS-slats, T60 is about 0,1 s, 150-4 kHz:



After, with 106 segments of the series 127 segments. T60 is about 0,2 s 150-4 kHz (there are also some other additions not shown here to lengthen the time). Total error in theoretical calculated panel length versus actual panel length turned out to be about 2 mm (< 1/8") along the L-shaped length of 3,533 m (12' 7") on both sides of the rooms symmetry line => pretty good!

[jeremycox]

Originally Posted by Adhoc

Hats off and a salute to Boggy Petrovic! His MLS sequence, a binary series of slats and slots, has helped me to increase T60 from about 0,1 s at about 150-4 kHz to about 0,2 s in the same range. (Jens Eklund has provided some other stuff, even more important and for the same purpose. I might show that in another thread)

An easy trick to add more life to a “dead” room is to add slats on top of resistive absorbers. The most common advice on GS seems to be to follow Newells 3-5-4 series of slats and slots, giving about 50% absorbtive area and 50% reflective area. Boggys MLS series provides the same ratio as Newells as it is a binary series. I prefer Boggys as it should add some more diffusion and is more versatile. The BIG plus is that it is so much easier to calculate it into a “tailor made” version for your available wall area and one can buy one and the slat dimension at the lumber yard. –No need to cut up different widths of slats. Calculation for an optimation is quite straight forward but boring and tedious, so I wrote an excel spread sheet in which all the variables are easily varied to one´s own wishes. I also added a new variable “end correction”, to simplify planning and symmetry in the room. The spreadsheet is quite self-explanatory and is added below.

Background: Treating an underground concrete bunker into an enjoyable listening room is not an easy thing. It needs a lot of absorbtion to tame the modes. Lots of resistive absorbtion in turn leads to a room too dead to be enjoyable. -But that is where one may have to start and then from the too dead room move on to make it more live. So, that’s what I did and to some degree is still striving for.

What I started out with was a room 7,86 x 4,19 x 2,25 m. Three walls, towards the garden, 20-25 cm (8-10”) of concrete, dirt up to half height of the room, remaining wall towards the rest of the building about 50 cm (20”) solid concrete and brick. Ceiling and floor also concrete. Good thing: I knew the problems in advance and the room was very close to symmetrical making it suitable for a control room design regarding treatments. Bad thing: A nightmare acoustically if not heavily treated because of the extremely rigid room boundaries.

Front end of room. About 1/3 of room length has 95 mm equivalent of O C 705 closest to concrete, added on top towards the room is fluffy 45 mm Isover Piano (= Behind the burgundy coloured fabric) At floor level, behind the black fabric are limp mass membrane absorbers. At the front wall are 45 mm Isover Piano + 60 mm O C 705, behind the resistive absorbers from floor to ceiling are more limp mass membrane absorbers, distance for resistive absorbers to concrete is 160-250 mm.

Before MLS-slats, T60 is about 0,1 s, 150-4 kHz:



After, with 106 segments of the series 127 segments. T60 is about 0,2 s 150-4 kHz (there are also some other additions not shown here to lengthen the time). Total error in theoretical calculated panel length versus actual panel length turned out to be about 2 mm (< 1/8") along the L-shaped length of 3,533 m (12' 7") on both sides of the rooms symmetry line => pretty good!

Is it normal to want to get stoned down there?

[Adhoc]

Getting stoned? If you are a New Yorker from Brooklyn, possibly. Personally, I keep to alcohol.


Guests bar section, on the right hand side of the room




Owners bar section, on left hand side of the room



Actually, the “bar sections” are some SBIR-fixes which improved some dips pretty well, about 8-9 dB or so.

[jeremycox]

Looks great ;-)

[Adhoc]

Thanks. I believe function comes before looks though, always. The “bar sections” work well against SBIR for me. A combination of absorbtion and steering 1 st reflection sound waves towards backwall.

Before, some quite deep dips at about 150 and 250 Hz (old curve with 1/6 octave resolution, 300 ms range), the 2 dips are moving around a bit in frequency, 10-30 Hz, depending on placement of speakers and listening position. Still, the 2 dips are there all the time.



”Bar section” installed + some smaller change of placements, previous SBIR dips are gone so bass curve has been improved between 25-300 Hz. A mode dip at 22 Hz and the "bump" at 44 Hz, I can live with (curve = 1/12 octave resolution, 300 ms range)



Enough of OT as this is a diffuser thread. Sorry.

[matt thomas]

I never posted some I made (and sold) years ago. I made 22 of these, and 6 low and 6 high bass traps for about $1500 USD.



Note that they only have 6 wells, this is because the side of the diffusor, when jammed up against another diffusor, functions as the 7th well.

I used "tri-board" for the frame and backs of the slots, and MDF for the slats. Tri-board is basically a chipboard sandwiched between two layers of thin MDF. Mostly designed for cheap shelving I think. I bought a whole lot of off cuts cheaply, which I designed the dimensions around, to maximise coverage and effectiveness vs cost. They are 18.3 cm deep. I also had the wood cut professionally, by my neighbour at the time who was a cabinet maker, so he gave me a good deal too. Took him aaages with all those slices, 25 pieces for each diffusor! All held together with gorilla glue.

I also made matching membrane bass traps of two different depths. They cost a bit more to make than the diffusors because of the plywood and rockwool.



Matt

[SKD]

[QUOTE=jhbrandt;3938166]
(I have actually succeeded in making excellent qrds with foam board. :D like Formular 150. - but I used 1 1/2 inch board and made the wells 1 1/2 inches wide.)

Were the fins using this or did you use something else a bit thinner?

Would any high density foam do?

Is there a minimum sheet depth you wouldn't go under?

I'm thinking of making diffusers that are as light as possible. For example could I make a diffuser out of the foam sheets I could get in an arts and crafts shop?

In my case I am mainly concerned with higher frequencies, I know that the low end is out of reach.

Steve

[kasmira]

Originally Posted by SKD

Would any high density foam do?
(...)
I'm thinking of making diffusers that are as light as possible. For example could I make a diffuser out of the foam sheets I could get in an arts and crafts shop?

In my case I am mainly concerned with higher frequencies, I know that the low end is out of reach.

Steve

Standard EPS (expanded polystyrene foam) will work great for diffusers. You can make large diffusers without having to worry about mounting very heavy panels to the ceiling very securely so that they do not fall on anyone (or yourself!) Same with walls, etc.

Many companies make diffusers out of EPS. Jens Eklund's Optiffuser is one example. GIK's VersiFusor/GridFusor is another. Etc, etc.

[djmj]

I´ve found blueprints on QRD 734.
"The QRD® 734 has proven to be the most popular and versatile diffusor in the RPG® product line."

Not all the measurements was in the blue print, but I used the blueprint in a cad software and used it as an underlaying layer. Then it was easy to make everything in correct sizes.
Bounding box is 1´-11.625" x 1´-11.625" x 9.125"
I can measure from the 3d model the caves, depth and width atc...

Just a simple render. Light and dark wood with coating.



Looks good/simple enough to build. So this is gonna be my wall diffusers.
Cheers
Johan

This was updated, and thanks for the help Schaap. The nail holes in the drawing fooled me.

[Schaap]

Originally Posted by djmj

I´ve found blueprints on QRD 734.
"The QRD® 734 has proven to be the most popular and versatile diffusor in the RPG® product line."

Not all the measurements was in the blue print, but I used the blueprint in a cad software and used it as an underlaying layer. Then it was easy to make everything in correct sizes.
Bounding box is 1´-11.625" x 1´-11.625" x 9.125"
I can measure from the 3d model the caves, depth and width atc...


Looks good/simple enough to build. So this is gonna be my wall diffusers.
Cheers
Johan

You want to DIY the QRD 734? The 734 has a '0' at the sides and inside the 7 'elements' there are no 'sloping' but flat bottoms.
Or is this your own design?

Henk

[djmj]

Originally Posted by Schaap

You want to DIY the QRD 734? The 734 has a '0' at the sides and inside the 7 'elements' there are no 'sloping' but flat bottoms.
Or is this your own design?

Henk

Thanks for letting me know Schaap. Ofcourse you where right. Here is the blueprint if anyone has a need for it



Cheers
Johan