My first diffusor

[spm_gl]

Well, actually Thomas', my partner. He's the handyman of us two. But I designed it, so I guess that counts too.

I chose a double-7 configuration, for speedy building and good bass response.
More pictures here: The first diffusor – DIY | Spreemusik Blog

It's made of pine boards, 18mm thick, 20cm wide, well width is 45mm

[mobius.media]

how does it sound?

[spm_gl]

A bit woody, at the moment
Still need to build a second one and then mount them on the wall. And put up the curtains, and install the speakers, and and and. But we're getting there.

[terry j]

well done Thomas!

Oh ok, and Jan

They would be pretty heavy? Which leads to, any particular reason for the thick wood??

Now listening impressions.

This is what I don't know. How many of these does it take to make a noticeable difference.

Let's use a panel trap as an analogy. We know trapping works and helps in the room, BUT if a person threw 'one' up somewhere, I doubt it would really help, and he may conclude that 'all this trapping talk is a load of rubbish' if you follow me.

Same here, TBH I doubt 'one' qrd thrown in a room will make much difference. There is a big difference in effort between making a qrd and throwing a bit of fibreglass around!!!

So it could be kinda scary to make a qrd, put it in and 'not hear a difference', yet be confident enough to say to yourself 'it is because I need to build more'...and then build them!

Not sure if that made sense, but anyway yeah, I too am interested in your listening impressions!!!

How long did it take to make.

[spm_gl]

They were originally meant to be nearly room high, that's why we used the "thick" planks. And because they were available (we're out in the country here). Only took 4 hours or so, the main time factor actually being the cutting to length. Weight is around 40kg or so (I think).

I don't expect it to make a huge difference, it's more part of the whole acoustical room concept. So the question should be, does it play it's part? And I'll only know that once the rest of the acoustics are done. The diffusors are pretty close to the surround speakers, which could be a problem, or an advantage. We'll know in a few weeks, when the speakers can be put in.

[SaSi_SiDi]

Nice work. But a bit overworked - perhaps.

Theory dictates that the fins between wells need to be as thin as possible provided rigidity isn't sacrificed and resonances not introduced. 2mm sheet metal could be a good choice as well as 3-4mm plywood. I would assume that 4mm plywood would make a much cheaper and lighter.

It's also a good idea to fill that construction (of 4mm plywood) with fluffy fiberglass or mineral wool to reduce resonances.

Also, you must make sure the joints are glued well and become airtight, as any open joints will form a slatted tuned absorber. Now that could be bad or nice, if it happens they are tuned to a problem frequency.

Or you could "engineer" the slats into the design to combine diffusion in upper frequencies and absorption in the lower, modal frequencies.

[spm_gl]

I remember reading a paper that states the fins don't need to be as thin as possible, but I've forgotten where. But as I said, we're very dependant on what we can get here. And it definitely sounds better than a blank wall. I need to manage the amount of high frequency absorption carefully, because we need a complete curtain front (the windows must be accessible).

We'll fill the gaps later, once the second diffusor is done. A coat of transparent lacquer, and a decorative border to finish the looks. If I feel really crazy, I might just stick some LEDs into the top and bottom of the wells. But I doubt I'll find the time...

I doubt we have a problem with resonances, the wells are made of 18mm strong slats, and the back is not airtight.

BTW, I've seen a QRD that had holes in the slats, to work as a helmholtz resonator. Nice idea.

[spm_gl]

It's up! Mounted nicely on the wall. This time the pic is in our build thread and of course some more on our blog: Hang ‘em higher | Spreemusik Blog