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QRD Diffuser Options


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I've been wanting to add some (about four) QRD diffusers to my listening room but when I see the price of the commercially available ones I go into palpitations. I'm not that flash at woodwork so I have not ventured down the DIY path in this instance.

I did come across these two options and was wondering whether anyone had tried them and whether they would be any good.  They seem to be reasonably priced so what do you think?  Are these my best options?

 

http://www.ebay.com.au/itm/Skyline-QRD-Fractal-Sound-Acoustic-Diffuser-Diffusor-Panel-Absorption-Treatment-/232091714480?hash=item3609be83b0:g:3k4AAOSwOyJX5FMA

 

http://www.ultrafonic.com.au/Shop/cat/2/pid/36/Studio-Acoustic-Products/Diffuser-Kit-Qrd/prd.htm

 

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The Ultrafonic one should be ok, but if you talk to Andrew who owns Ultrafonic (I have) he will probably suggest some other form of diffusion because the QRD are not a true broadband diffuser, they diffuse in a number of relatively narrow bandwidths across a broad spectrum so tend to come with their own 'sound'.  I really would suggest calling up Ultrafonic and talking through what you need.

 

EDIT:  the uneven diffusion is a trait of all QRD diffusors, not just the Ultrafonic ones.

Edited by acg
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  • 1 month later...

As the guys above said, talk to a pro about diffusion, absorbtion, bass trapping, etc

 

Surprisingly, the Ultrafonic 1D diffuser (known as Schroeder diffusers) kits are quite reasonably priced at about A$200 (unfinished chipbrd?) and the fact that you need more than one, makes you pause before buying, but a $1k investment in this sort of room treatment is possibly the best audio 'add-on' you can get for a domestic listening room, not just for 'pro-audio' - unfortunately, you'll need a bit more with some absorbers to complete the 'fit-out' (easy to make with the Polymax) and possibly bass traps

 

There are a couple of reasons for this - one is that you'll physically play around with the things and make substantial changes to the sound in the room (both good and bad!) and the second is that you'll just absorb/learn a lot in a big rush about your listening room without having to use a Berhinger (for example) or a room measuring program in your computer

 

That 'top' link is a bit of a misnomer (?!)

Skyline QRD Fractal Sound Acoustic Diffuser Diffusor Panel Absorption Treatment - from Latvia, about A$50/piece, free postage and 600mm x 400mm - they're not Skylines (an RPG product name) and they have little absorption qualities

 

They're a styrene moulded version of Tim Perry recent design called  "Leanfusers" - does the same job, or better, than a basic 1D Shroedder diffuser and they're possibly more effective than a standard 1D diffuser like those Ulfasonic kitsets.

As they're only a single panel (600 x 400 wide), you'll need a few more of them to work properly (ie on the back wall behind the listening position) so you'll still need to outlay quite a few hundred $s, unfortunately (similar to using the Vicoustic panels, for example) and you need to seal the surface of the styrene with a quite solid paint/polymer for best performance

 

You can go to Tim Perry's website called Arqen Acoustic Design and download basic diffuser blueprints and with a 'hot wire knife', cut your own out of sheet styrene from building site offcuts - the guys in Latvia have probably done just that

 

I hope this has been useful and pretty certain that they'll enhance your sound of the Maggies but, as I mentioned above,  you will need some absorption mixed in with the diffusers for best results - fortunately, quite a few guys from 'up north' in your area have purchases the Polymax sheets and will possibly have some over - there's a thread here about this with contacts ... 

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download and muck with QRDude (free) - it will show the diffusion capabilities QRDs.

http://www.subwoofer-builder.com/qrdude.htm

 

The finless fractal diffuser in the 1st link provides more diffusion and to higher freq than a QRD - it's a QRD on steroids

 

both links your provided are examples of 1D diffusers - ie diffuse in 1 plane only

 

14 hours ago, jrhill said:

 

That 'top' link is a bit of a misnomer (?!)

Skyline QRD Fractal Sound Acoustic Diffuser Diffusor Panel Absorption Treatment - from Latvia, about A$50/piece, free postage and 600mm x 400mm - they're not Skylines (an RPG product name) and they have little absorption qualities

 

They call them "skylines" as they have no fins between the blocks (compare to the fins or cutlery drawers of the Ultrafonic), and the 2D version looks like city sky scrapers.

The term skyline diffuser generally refers to any finless 2D QRD/PRD (Primitive Root Diffuser).

 

Fins increase efficiency, but swings and round-abouts when comparing a finless fractal design and finned QRD.

 

If you want to learn more read anything by Cox and D'Antonio (RPG) - they own this space.

 

mike

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Hi Mike,

Yeah, thought the Agostini book (Cox & D'Agostini!) pretty good - Filled in a lot of gaps not covered by Toole, etc

It's a pity the price hasn't come down to somewhere reasonable, or an 'ebook' - still well over $150 2nd hand, I think - Everest's Master Handbook is more affordable and Moore's Psych of Hearing is also not too bad - this last one is really helpful too.

 

I built the 7 array version of the basic Leanfuser out of 9 and 12mm plywood - about 3 metres across - weighed a lot but worked like a charm - at present, I'm organising some foam ones with 3mm ply surface but using 50mm width and some 5 element ones - it'll be interesting how they turn out - am a bit tempted by those 'fractal' ones from Latvia but even only $50 odd per 600 segment adds up pretty quickly - if I can get my 'hot knife' cutter to work well enough, I'll have a go at these ones too - not capable of to doing them from wood

 

I went looking for the round fibreglass to make some bass 'tube traps' - know if it's still available, or what it's called these days?    

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16 minutes ago, jrhill said:

 

 

I went looking for the round fibreglass to make some bass 'tube traps' - know if it's still available, or what it's called these days?    

Its called SPI (Sectional Pipe Insulation)

 

I got mine from a local insulation installer.  He got it from Fletcher Insulation, who won't sell direct to the public.  Many sizes available but they will have to be ordered since they aren't a stock item.

 

http://insulation.com.au/product/glasswool-sectional-pipe-insulation-spi/

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Guest Peter the Greek
15 minutes ago, aechmea said:

Its called SPI (Sectional Pipe Insulation)

 

I got mine from a local insulation installer.  He got it from Fletcher Insulation, who won't sell direct to the public.  Many sizes available but they will have to be ordered since they aren't a stock item.

 

http://insulation.com.au/product/glasswool-sectional-pipe-insulation-spi/

 

Well that makes life pretty darn simple! thanks for sharing!

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12 hours ago, Peter the Greek said:

 

Well that makes life pretty darn simple! thanks for sharing!

There is a Fletchers regional office/warehouse at Beresfield.  They would be able to tell you of a local installer through whom to buy.

 

I used Hayes Insulation at Medowie.  The owner used to be the manager at Fletcher.

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On 25/02/2017 at 7:10 PM, Bilbo said:

I want to add some diffusion behind my Maggies so what are the better options for this purpose?

 

What exactly are you wanting to achieve, B, with diffusion behind your Maggies?  (And what Maggies.)

 

I ask because in my last house, I radically improved my sound field depth by putting DIY "Room Tunes" just off the front wall, in line with the reflected 'ray' from my ribbons ... bouncing off the front wall ... to my ears.  :thumb:  (I had my tweeters in, in that room.)

 

It was quite remarkable - I could lay the Room Tunes down and the depth disappeared; stand them up again ... and the depth returned! Underneath the 'socks' are 3x 50mm plumbing pipes (which are not exactly parallel) ... they serve to diffuse the reflection of the ribbon tweeter.

 

Attached is a pic of the Room Tunes in that room.  Unfortunately, in my new house, I can't use them.  :(

 

 

Andy

 

Final Frankenpan Pics 020.jpg

Edited by andyr
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@andyr

I currently have 1.7's (and planning on upgrading to the 20.7's as a retirement present to myself).

I have been reading other folks experience with absorbers or diffraction and it appears that the Maggies may be better with diffusers. Since my first post I have been looking at poly cylindrical diffusers as a cheap option and within my limited wood working skills. 

Your DIY room tunes however would be even easier to build and pipe sizes from 50mm to 90mm are available. Your experience with their effectiveness encourages me to give them a go.  One question though - would the larger diameter pipe give more diffusion or even a mix of say 65mm and 90mm pipes?

Has anyone else got experience with this style of acoustic device?

 

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21 hours ago, Bilbo said:

@andyr

I currently have 1.7's (and planning on upgrading to the 20.7's as a retirement present to myself).

I have been reading other folks experience with absorbers or diffraction and it appears that the Maggies may be better with diffusers. Since my first post I have been looking at poly cylindrical diffusers as a cheap option and within my limited wood working skills. 

Your DIY room tunes however would be even easier to build and pipe sizes from 50mm to 90mm are available. Your experience with their effectiveness encourages me to give them a go.  One question though - would the larger diameter pipe give more diffusion or even a mix of say 65mm and 90mm pipes?

Has anyone else got experience with this style of acoustic device?

 

 

You would need to experiment with the different diam pipes.  I simply followed the recipe that a guy called Jon Risch had put up on Audio Asylum.  (Which, unfortunately, is no longer there.)

 

He was trying to reproduce the official 'Room Tunes' - so chose the same pipe diameter.  The 'real' Room Tunes only had 3 pipes but I suggest 6 or 8 in a line would do more than just 3.  And I can't see why a mixture of diameters would do any harm.

 

The intent is to diffuse the rear reflections of the tweeter (tweeter & supertweeter, in the case of your 1.7s).  If you are planning for 20.7s then I would suggest the following:

  • make the pipes as long as 20.7s are high.
  • it's important not to have the pipes parallel.  At, say, 1.8m long (longer than mine), there should be 1cm gap at one end and a 3cm gap at the other.
  • you need to make some sort of base - to hold the pipes upright.  With only 3 pipes I used 2x 50mm thick slabs of wood; with 6-8 pipes maybe 10mm steel would be needed?
  • I also drilled holes to be able to put a rod through all the pipes, at the top, and glued the rod in place.  This stops the pipes from moving sideways.
  • then how do you fix the pipes to the base?  In my case that was easy - core holes in the wooden slabs so that the pipes slot in.  With a steel base ... rout some 50mm long wooden plugs which match the ID of the pipes you are using and screw these to the base.  Then the pipes simply fit over these plugs.
  • Get some dense-but-stretchy material from Spotlight (colour to suit your wifey's taste  :) ) and get some 'socks' made up which you can pull down over each pipe array.

Good luck - please post your experiences of the sound with - and without - the beasts!  :thumb:

 

Andy

 

Edited by andyr
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@andyr

 

17 hours ago, andyr said:

 

You would need to experiment with the different diam pipes.  I simply followed the recipe that a guy called Jon Risch had put up on Audio Asylum.  (Which, unfortunately, is no longer there.)

 

 

I tried googling Room Tunes and came up with nothing so I now know why!

 

I was going to fix the pipes at the bottom using a gutter dropper outlet upside down (see picture) screwed onto a wooden base. Packing one side would provide some tilt as required.

GutterOutlet.JPG.150d94626e1bd17acb1cb411ebc9fe4c.JPG

 

That should make it easy to get them to be non parallel so I would end up with something like this.

Pipes.jpg.95cc362fa54d623f0884c718d078698f.jpg

 

To hold them in position I was going to use some small diameter PVC pipe cut half way through and glued at the top of the (near) verticle pipes which should make it rigid enough.

Is that what you mean by non-parallel when viewed from the front or do you mean when viewed from the side?

Also are the pipes closed or open at the top and are they stuffed with anything?

Edited by Bilbo
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15 minutes ago, Bilbo said:

@andyr

 

 

I tried googling Room Tunes and came up with nothing so I now know why!

 

I was going to fix the pipes at the bottom using a gutter dropper outlet upside down (see picture) screwed onto a wooden base. Packing one side would provide some tilt as required.

 

 

That should make it easy to get them to be non parallel so I would end up with something like this.

Pipes.jpg.95cc362fa54d623f0884c718d078698f.jpg

 

To hold them in position I was going to use some small diameter PVC pipe cut half way through and glued at the top of the (near) verticle pipes which should make it rigid enough.

Is that what you mean by non-parallel when viewed from the front or do you mean when viewed from the side?

Also are the pipes closed or open at the top and are they stuffed with anything?

 

That's exactly right, B - viewed from the front / back.  However they are much closer together (I know yours was just a sketch to illustrate the concept).  So for 60mm OD pipe, I would suggest 30mm for the wider gap ... and 10-15mm for the smaller gap.

 

The pipes are open; in the original design, the Room Tunes were filled with polyester batting for about a 1/3rd of their length.  This was to make them act as a Helmholtz resonator as well as a diffusor - however, the maths is flakey as their effectiveness as a Helmholtz resonator is influenced by the height of the ceiling, relative to their length.  But putting some stuffing in them would tend to damp the tubes - so it's probably a good idea.  So I would say fill the tubes about 1/3rd of their length, with the 'plug' located at different heights.

 

 

Regards,

Andy

 

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On 05/04/2017 at 3:19 PM, Bilbo said:

Cheers Andy - this will make a good Easter project.

 

Good luck - don't forget to let us all know what effect you heard (with & without).  :)

 

Andy

 

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On 2/25/2017 at 6:06 PM, acg said:

 other form of diffusion because the QRD are not a true broadband diffuser, they diffuse in a number of relatively narrow bandwidths across a broad spectrum so tend to come with their own 'sound'.

I'm not aware of any diffusers that are broadband.

 

QRDs generate diffusion over a well defined range, but have a minimum seating distance so you don't hear "artefacts" - Cox and D'Antonio recommend 3 x the lowest wavelength the QRD operates to - in small rooms this can be an issue - especially if trying to diffuse to lower frequencies - you can't get far enough away from the diffuser for the diffuser to generate a "diffuse" sound field.

 

Fractal diffusors are the next generation after QRDs, and simplistically are a mini QRD on each well of a QRD - the manufacturing cost is higher but this may reduce with 3D printing and other technologies.

The minimum seating distance is the same as QRDs - as it's defined by the lowest frequency of operation - the fractals at the bottom of the wells don't change this.

 

Binary Amplitude Diffusers (BAD panels) don't generate the diffusion that QRDs produce - so the minimum seating distance is less (but poorly/not defined) - I've not been able to find the upper and lower diffusion limits of BAD panels.

If you want proper diffusion use QRDs (or if you have the money Fractal QRDs).

If your room is getting too dead and want to keep some higher frequency energy in the room but proper diffusion is not a big deal use BAD panels.

 

If you want to learn up on diffusion seek out anything by Cox and D'Antonio (the guys that run RPG) - they own this space.

"Acoustic Absorbers and Diffusers: Theory, Design and Application" is a great start.

 

cheers

Mike

Edited by almikel
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8 hours ago, almikel said:

I'm not aware of any diffusers that are broadband.

 

QRDs generate diffusion over a well defined range, but have a minimum seating distance so you don't hear "artefacts" - Cox and D'Antonio recommend 3 x the lowest wavelength the QRD operates to - in small rooms this can be an issue - especially if trying to diffuse to lower frequencies - you can't get far enough away from the diffuser for the diffuser to generate a "diffuse" sound field.

 

Fractal diffusors are the next generation after QRDs, and simplistically are a mini QRD on each well of a QRD - the manufacturing cost is higher but this may reduce with 3D printing and other technologies.

The minimum seating distance is the same as QRDs - as it's defined by the lowest frequency of operation - the fractals at the bottom of the wells don't change this.

 

Binary Amplitude Diffusers (BAD panels) don't generate the diffusion that QRDs produce - so the minimum seating distance is less (but poorly/not defined) - I've not been able to find the upper and lower diffusion limits of BAD panels.

If you want proper diffusion use QRDs (or if you have the money Fractal QRDs).

If your room is getting too dead and want to keep some higher frequency energy in the room but proper diffusion is not a big deal use BAD panels.

 

If you want to learn up on diffusion seek out anything by Cox and D'Antonio (the guys that run RPG) - they own this space.

"Acoustic Absorbers and Diffusers: Theory, Design and Application" is a great start.

 

cheers

Mike

 

Think about my meaning of  "broadband" as a diffusor that diffuses all the frequencies in its operating range.  A QRD is like a series of notch filters and does not diffuse all of the frequencies in its operating range.  Let's say it has 'peaks' at 500Hz, 600Hz, 750Hz...at these peaks it is diffusing quite a lot of the energy it receives but in the ebbs between the peaks it is not diffusing much energy at all circa 500Hz, 675Hz et cetera thus colouring the sound.  QRD's alter the tonal balance of reflections.

 

 

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  • 3 weeks later...
On 4/8/2017 at 0:52 PM, almikel said:

I get that but what sort of diffuser are you referring to that doesn't have the lobing?

 

I missed your reply Mike.

 

The answer is parabolic diffusors.  Have a listen to this to see how diffusors can change the sound...

 

 

...and then have a look at the polar plots here to see the difference.

 

Just like the old Castrol tagline, diffusion ain't diffusion.

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9 hours ago, acg said:

 

I missed your reply Mike.

 

The answer is parabolic diffusors.  Have a listen to this to see how diffusors can change the sound...

 

 

...and then have a look at the polar plots here to see the difference.

 

Just like the old Castrol tagline, diffusion ain't diffusion.

the link to the polar plots is broken, but from the auralex site

http://www.auralex.com/tools/testing-data/performance-data/diffusion-testing-results/

The plots are very impressive and shows how far diffusion has come since the earlier QRDs.

 

The GeoFusor sounds quite different to the T'Fusor - would be interesting to hear them next to a QRD and no diffusion.

 

Auralex lost some cred IMHO when stating the amount of diffusion would change by filling the back with absorption, with their tiny "bass" traps, and with a bit of foam between the speakers to reduce 1st reflections (sure below the baffle effect you get first reflections from the front wall, but thin foam isn't going to help

 

I quite like their diffusers

I'm dubious on the effectiveness of their foam absorbers compared to simple poly/fiberglass batts with similar gas flow resistivity.

The fancy shapes help the manufacturer use less foam, but only reduces absorption (compared to constant thickness and no fancy shape).

 

Mike

 

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