Diffraction..? Which direction?

[crisis]

OK so probably more technical than that but I am building a pair of diffraction (I think) panels and wondered which direction I should diffract? Up and down or side to side? They will stand about 1.2 meters tall, just over the top of my speakers at the first point of reflection.

Edited August 28, 2024 by crisis

[Keith_W]

Humans are much more sensitive to left/right direction than up/down. So to the side. 

[Artnet]

Are these to be ceiling mount?

 

If 2 x 600mm square units that could move independently then you could try both in different orientations and hear what happens.  Good luck with the build.

[Kinsella]

Not sure about which way to orient them, but they look great.  Nice job.

[crisis]

On 27/08/2024 at 7:43 AM, Artnet said:

Are these to be ceiling mount?

 

If 2 x 600mm square units that could move independently then you could try both in different orientations and hear what happens.  Good luck with the build.

Cheers. I’m experimenting with them either vertically next to the speakers or also trying absorption pads next to the speakers. Tried the absorption panels , Verbox V Panel Ultra Acoustic Treatment Panel (djcity.com.au) next to the speakers last night and recognised a noticeable improvement in solidity of the imaging. The centre phantom channel really tightened up. There was no appreciable effect as far as deficiencies in any frequencies. Once the diffusers are finished Ill see how they react.

[almikel]

they're 2D panels, so they diffuse both horizontally and vertically - choose which sounds best

[almikel]

Are you building these?

10x10 is not a typical 2D quadratic residue diffuser (QRD) build.

It may be a Primary Root Diffuser (PRD), or some other type of diffuser I'm not familiar with.

 

QRDs are always based on prime numbers in each direction, or a repeated pattern of prime numbers.

 

If you want to build 1D or 2D quadratic residue diffusers (QRDs) check out QRDude

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

A free tool to design QRD diffusers.

 

cheers,

Mike

[crisis]

11 hours ago, almikel said:

Are you building these?

10x10 is not a typical 2D quadratic residue diffuser (QRD) build.

It may be a Primary Root Diffuser (PRD), or some other type of diffuser I'm not familiar with.

 

QRDs are always based on prime numbers in each direction, or a repeated pattern of prime numbers.

 

If you want to build 1D or 2D quadratic residue diffusers (QRDs) check out QRDude

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

A free tool to design QRD diffusers.

 

cheers,

Mike

Thanks. There's a fair chance I wont even understand what is going on there... But worth a crack.

Yes I'm building these, today hopefully.

My original intention was to use two absorbers (as in the pictures) however in a separate thread read that diffusers might be better at the first point of reflection. So I purchased four of those panels with the intention of mounting them and trying both types. That is about as scientific as I got.

The listening room is a bit of a work site at the moment as there is a bit going on....

[crisis]

No craftsmanship to speak of and a few technical difficulties on the first one. Took about 3 hours and the second one about 40 minutes..

Still...

Plan was to glue and paint but I decided to try a dry run first.

Initial impressions is that these are sound much brighter than the absorbers. The absorbers tightened the imaging better but clearly rolled off the hi frequencies and detail to an extent. I swapped back and forth and then tried them together side by side. With the diffusers closer to the speakers this seemed to give the best of both worlds with an impressive spread of sound stage. I will finish the diffusers tomorrow. Paint them and glue the panels in place. 

Still waiting for the bass traps and then see what else from there.

[JkSpinner]

20 hours ago, crisis said:

two absorbers

Those absorption panels are quite deep

[JkSpinner]

Hi Crisis, I am doing the same at the moment, my music room is also a work in progress as well.  I  am playing around with 6 Broadband panels and 2 x Hybrid panels, ( https://soundacoustics.com.au/product/room-kits/hybrid-absorber-diffuser-ha600-75/) also moving each around.  I also tried the Hybrid panels (Diffusion/absorption) and the 1st reflection point and really liked the SQ, however the REW measurement told a different story.  So I am going to try absorption panels at 1st reflection point to see what difference that makes, will also try absorption panels next to the speakers, and the Diffusion panels behind the speakers.

I am interested to learn what you are using as stands.  I was going to purchase some office divides from IKEA for this and somehow attach my panels to it, just so I can move them around, but even the ikea ones are $200 each.

Also - have you taken measurements.  I am not an advocate for measuring, in fact the opposite, but in the end I succumb to the pressure and bought the device.  I don’t think it added much value initially, as I think I had a good idea of what I needed to do, however I am finding it Valuable to measure the changes when moving speakers, and moving panels around etc, and I kind of weigh up the difference of what I hear, and the results, it’s interesting.

 

[crisis]

1 hour ago, JkSpinner said:

Those absorption panels are quite deep

Yes they are these.

https://djcity.com.au/product/verbox-p200-acoustic-treatment-panel/

I didn't realise they were that deep but its all good. They also do 100mm but DJ city no longer list them . You can purchase direct from Verbox but they wont ship to me in SA.

The stands I'm using for the diffusion are home made (badly) and consists of some pine and the Bunnings Prempanel. One cut in half https://www.bunnings.com.au/prempanel-2700-x-600-x-21mm-oak-timber-acoustic-panel_p0455959?region_id=115068&gad_source=1&gclid=EAIaIQobChMIiLDx9qmgiAMVDhaDAx2dywtFEAQYASABEgJ47PD_BwE&gclsrc=aw.ds

Not very well put together but you can reinforce them.

Ive purchased bass traps similar to your absorber diffusers https://soundacoustics.com.au/product/bass-traps/lf65-corner-bass-trap/ but am still waiting on them.

I  like the set up of the absorbers and panels where they are at the moment but as they are portable will continue to experiment. I will probably buy another two absorbers for the back of the room and would like two white 100mm ones for the cieling but don't know how to get them as Verbox wont post to SA. Then maybe some absorber diffusers on on one of my walls.

Haven't got into measuring and as I am not spending thousands am happy just to play around and listen but it is something I might try when I get around to it. Honestly all of those graphs and numbers kind of freak me out.

[crisis]

2 hours ago, JkSpinner said:

Also - have you taken measurements.  I am not an advocate for measuring, in fact the opposite, but in the end I succumb to the pressure and bought the device.  I don’t think it added much value initially, as I think I had a good idea of what I needed to do, however I am finding it Valuable to measure the changes when moving speakers, and moving panels around etc, and I kind of weigh up the difference of what I hear, and the results, it’s interesting.

 

What measuring device did you buy?

[JkSpinner]

50 minutes ago, crisis said:

The stands I'm using for the diffusion are home made (badly) and consists of some pine and the Bunnings Prempanel. One cut in half

That’s perfect, I am in search of ideas for moveable stands, I bought some 3mm ply, and also some pin boards to experiment with.

[JkSpinner]

50 minutes ago, crisis said:

What measuring device did you buy?

The Umnik 1.  It’s only $200.  Like I said, I  thought it was a bit of a waste, but now that I have panels, I am finding it of benefit.

[almikel]

On 01/09/2024 at 6:53 AM, JkSpinner said:

Those absorption panels are quite deep

Any absorption you want to be effective at lower frequencies needs to large (length/width/depth), and preferably with an air gap behind to further assist low frequency absorption, which is why these traps are often deployed "straddling corners".

 

A bit off topic for a thread about diffusion, so I hope @crisis doesn't mind...

...Absorption traps are also called "velocity traps", as they work by slowing down the air particles carrying the sound waves by friction in the absorption trap (reducing the amplitude/volume of the sound wave) - and they work best when placed where the air particles have the highest velocity.

Think about a tennis ball bouncing off a wall - at the boundary, the tennis ball is at zero velocity.

 

In the "modal" region of our rooms, where we have room modes bouncing/resonating around we have a similar effect - air particle velocity is zero at a rigid boundary, and "non-zero" just off the boundary (let's park "non rigid" boundaries for the moment).

In the modal region of our rooms, because we have resonant behavior, the highest air particle velocity is 1/4 wavelength from the boundary, then minimal velocity at 1/2 wavelength from the boundary, then maximum velocity again at 3/4 wavelenth, then minimum again at 1 wavelength etc - ie oscillating between minimum and maximum air particle velocity.

 

It's important to note that pressure and velocity are inversely proportional - pressure is maximum at the wall, minimum at 1/4 wavelength from the boundary, maximum again 1/2 wavelength from the boundary etc.

Our ears react to pressure, not velocity - which is why bass sounds louder at our room boundaries. 

 

Looping back to placing absorption treatment appropriately in our rooms if we wish to absorb bass frequencies...

 

Let's say we wish to absorb 250Hz, which has a wavelength of 1.38m -> the air particle velocity is highest at wavelength/4 = 0.34m or 340mm away from the boundary.

For best absorption performance at 250Hz, you want the middle of your absorption 340mm from the boundary!

 

This is why gapping absorption is recommended for absorbing lower, either offsetting from the wall, or straddling corners, so the absorption is placed in higher air particle velocity regions for lower frequencies

 

Absorbing lower than 250Hz requires larger/deeper absorption again, which is why absorption gets too large/too deep to be practical for fixing room low bass issues.

 

Don't get me wrong - I'm a big believer in using absorption best placed to absorb bass (straddling corners) and avoiding absorbing too much treble (don't put absorption at reflection points) - cleaning up the "in room" sound <500Hz with absorption can make a massive difference to the "in room" sound.

 

It's just that absorption needs to be supplemented with EQ or pressure traps for room bass issues where absorption gets too big to be practical.

 

Mike