Room Treatment Impressions

[Ian Mackenzie]

http://www.soundscapes.nu/rb_prd.htm
http://www.soundscapes.nu/rb_dif.htm


Here is something to checkout!

I did a seach tonight in google on QRD diffuser and found the above site.

Despite not being in English it is by far the most comprehensive coverage of diy diffusers I have seen.

Ian

[Hoerninger]

Great!
Thank you.
__________
Peter

PS:
Just "coming back", a listening room for your DD66000 or other speakers:
http://www.soundscapes.nu/!gallery/design/index.htm
And more foto-galleries ("A picture says more than a thousand words"):
http://www.soundscapes.nu/!gallery/

[Andyoz]

I really can't stand the "look" of the 2D diffusers.

For domestic use, I would just stick with 1D diffusers and alternate the orientation.

[Ian Mackenzie]

Yeah,

They are a bit technical. Nice for a ceiling application though.

It is entertaining to see what he has been up to..a diffuser farm!

I will try and scan that doc for you Andy.

Ian

[Andyoz]

Some of those 2D diffuser installations on that Soundscabes website appear to be more to do with "willy wagging" for audiophiles! I mean, painting them in yellow for Christ's sake.

Due to the hearing mechanisms higher sensitivity to lateral reflections. I would concentrate on 1D diffusers in the lateral plane and leave it a that.

[Ian Mackenzie]

Some of those 2D diffuser installations on that Soundscabes website appear to be more to do with "willy wagging" for audiophiles! I mean, painting them in yellow for Christ's sake.

I am surprised some of our Yanky friends have not chimed in on the color. Yellow I mean. In any case it would clash badly with the JBL Blue

One of the images is of a the Harman testing room with 2 D diffusers.

My understanding is its a case by case thing and these devices should be used in critical locations.

That said most of the primitive Root 2D diffusers seem to be used in roof locations and that makes a lot of sense to me when you think about the angle of the incident rays.

The real benefit is they throw off only about half the energy in the same plane as the classic 1D QRD. That in fact could be real plus on the rear wall where they are used as a passive suround sound ambience.

There are some interesting applications using the Omidiffusers in that situation.

The idea of controlling the absorption by using a binary code for applying some absorber material (J Angus) to the 1D QRD does have some merit.

[Andyoz]

Yes, I woud agree re. your comment about placing them on the ceiling (if you can stand to look at them!!).

I like the idea of using a limited area of polycyndrical 'deflectors' though. Not as good as the diffusers, but even the missus would like them . After all, were're not trying to mix super critical music recordings here, just after some happy enjoyment of music playback in the home environment.

[Ian Mackenzie]

I'm having a close look at the Bad panel scrim 12 x 12 bad panels for the rear wall.

This or Arch is RPG's recommendation.

http://www.rpginc.com/residential/pdfs/CineMusic-2007-MSRP-Catalog.pdf

A 1D amplitude phase grating QRD could be fabricated but for the equivalent cost of 9 square bad panels I doubt the result would be a good.

""I like the idea of using a limited area of polycyndrical 'deflectors' though""

Yes they are an interesting creature. I think that might be the way to go on the front wall if I decided not to make a lot a saw dust!

[Ian Mackenzie]

The lead time is months on the Bad panels so I have opted to have a go at the 1 D QRD 17 diffuser for the rear wall.

I did some research during tonight and called up Primacoustics regards their Polyfusers and they are true diffisers except the Minifuser. The reason I called however was to discuss my application. Apparently the diffuser really needs 12 feet from the source for it to work properly. My room just meets that requirement taken from the baffles. The effect of the diffuser can be detected from the rear listening position but the effect is more so on the room overall according to the applications specialist. Similar feedback was obtain from SRL who make a whole line of modified Schroeder diffusors.

My design is based on the Prime 17 Schroder diffusor and has 2 inch wide wells.

In my inital design I took into account the coverage area of the rear wall, about 3 ft wide x 4 1'2 high. The maximum depth is a theoretical 8 inches.

The working range is 798 - 3390 hz although the practical frequency range is about 1/2 an octave above and below these operating points. The design frequency is about 930 hz.

The higher prime number designs have better high frequency characterictics. The prime 17 design suited my rear wall coverage area better than the QRD7 design for the same bandwidth. The important bandwidth from what I have read is 800- 4000hz. The width of the wells does not want to be any narrower than 2 inches in practice to avoid absorption.

I basically decided not to use blades because of construction issues and because at a normal angle of incidence the effect on the diffuser is un important. At wide angles the blades have an effect. Given the location of the diffuser on the rear wall and distance from the source I hope it will not be an issue.

After reading a google translation of the Soundscapes design notes it is apparent that solid construction is critical to correct operation. Given the side walls/blades and have to be ideally thin this makes them mechanically weak while if they are too thick this impairs the diffuser operation.It will also be an order of magnitude easier to make without the blades.

Below are details of the design.

It is essentally very similar to the SRL audio design. Depending on what happens I will consider a similar (larger) version for the front wall.

Ian

[Andyoz]

Excellent work there!

I would take issue with Primacoustics statement that their Polyfusers are a "true" diffuser. I don't think that is really correct under the strict definition of what a diffuser is. The true diffuser scatters sound over a broad area, for a broad range of frequencies and these affects should be (relatively) independent of the angle of incidence.

Cylidrical type "diffuser" also scatter sound but they are sensitive to the angle of incidence and don't have the abandwidth of properly designed QRD designs.

I still like them though.

[Cyclotronguy]

Hey Ian;

You gotta come back over for a visit, listen and some adult audiophile approved beverages. I've set up the listening room with active bass traps.... damn but they are impressive. Will get you some jpgs.

Build as follows:
Ten inch (sorry 3.9 cm) floor to ceiling concrete form tubes, covered with layer of spun glass and linen "socks" to keep the glass fibers out of the air.

At top and bottom are 8" car audio subwoofers looking into the corners of the wall floor and wall ceiling. Looking back at the room are microphone capsules.

Inside the tubes are electronics; Mic preamps, crossovers and chip amps; in addition to twin drivers.

Woofer output the antiphase of any signal the microphones sees below 100 Hz. Gain is set just below where they go into feedback.

Works like glue!

Cyclotronguy

[Ian Mackenzie]

That is one of the reasons I wanted to try this out>

Having printed, read and researched over 100's pages I wanted to see what all the fuss was about.....If something happens...Look , "its full of stars".

I may look at a Diffractal just for grins!

If it clashes with the JBL decor there is always the option of putting some acoustically transparent fabic over it.

[Ian Mackenzie]

Hey Ian;


Gain is set just below where they go into feedback.

Works like glue!

Cyclotronguy

Sniff! Active absorbers..Love it!

"You gotta come back over for a visit, listen and some adult audiophile approved beverages."

I think so.... and catch up with the Diva.

[Hoerninger]

When reading here I got in mind some pictures with details I did not pay attention first.
At the launch of the new Everest in Tokyo there was quite a usage of diffusors. The pictures will show you.
___________
Peter

[Ian Mackenzie]

Making it is not easy...

Using discrete MDF sections and joining is quite complex and difficult assembly..for a prototype.

I will thereforelook at solid timber construction using 2 x 2 and 2 x 4's. The profile will be 4 inches thick in some places so heavy is only downside but has advantage of being solid and no resonance.

Timber will be cut in workshop and then assembled on site like a model plane.