Hi, I'm building some skyline diffusers.  I'm using 32mm Tas Oak and my maximum length is 420mm (calcs says it's good down to 400Hz).  Im building a 12x13 grid and Im making 12 of them.  I will be arranging them on a pair of 2x3 grid.  I was planning to glue them to a 15mm mdf board approx 84cm x 170cm.  Th actual diffuser make up 84cm wide by 115cm high so with the 170cm. board I end up with the centre of the diffuser at the height of my tweeter / mid driver.  I was planning to make a box out of the bottom remainder of the 170cm (so 55cm) as a diffuser so it stands up by itself.  I cant wall mount because Im building this for my first reflection point and that directly in front of a window one side and door the other. (don't use door but its got a glass panel).

 

My question is will 15mm mdf be sufficient on its own, the diffusers (6x) will weigh 150Kg, I will leave a 100mm gap between the box at the bottom and the start of the diffuser.  I have the option of using some square steel tubing on the back of the panel as bracing if needed.  (I have some 20mm tubing).

 

Any suggestions, thoughts?

 

 

Edit: This is the calculator I used. http://www.oliverprime.com/prd/?show=calculator

 

Just enter a block width of 3.2cm and a lower frequency of 400Hz and thats what Im making.  Ive cut all the wood.

 

 

 

Edited August 7, 20232 yr by DVDHack

2 hours ago, DVDHack said:

Any suggestions, thoughts?

Good work, watching on with a lot of interest (in the middle of similar work, building 4 off, 1200 x 2400 x 200mm limp membrane bass traps ATM)

 

The MDF backing/height of the diffuser under 1200mm at 15mm thick, should (don't quote me) be ok, although 19mm might hold up a little better over the years. 15mm, with the aid of some steel might end up a little lighter, with a box as a stand. I'd be a tiny bit concerned it would bend from the top toward the room, if tall, say 1800mm, but they won't be.

Employing some little screw on trolley wheels might make them easier to move about, cheap. I use them on pretty well all my bass cabs.

 

Good luck there on your job. 

48 minutes ago, playdough said:

I'd be a tiny bit concerned it would bend from the top toward the room

Yes, that was my concern.  I had thought that I might just put in a couple of prop pieces of wood between the longer bottom diffuser members and the top of the box.

 

I was hoping to use 15mm because I bought a bunch of it for some absorption panels (bass traps) I'm also making.

Edited August 7, 20232 yr by DVDHack

1 hour ago, playdough said:

Good work, watching on with a lot of interest (in the middle of similar work, building 4 off, 1200 x 2400 x 200mm limp membrane bass traps ATM)

Hadn't heard of those so just looked them up.  Interesting idea.  Seems to me that you could make an arrangement where the depth could be adjustable with an outer sleeve with the membrane sliding over an inner box.  Then it could be tuned to the frequency if the calcs etc aren't exactly right?  What are using as the membrane?

28 minutes ago, DVDHack said:

hoping

 Should be ok, might be like limp biscuit however when you pick it off the bench as completed. See how it goes. All fun

😃

Edited August 7, 20232 yr by playdough
off and of are different words

14 minutes ago, DVDHack said:

adjustable with an outer sleeve with the membrane sliding over an inner box.

Now that's technical !!!! It'll be actually built like that. Inner outer frame.

Edited August 7, 20232 yr by playdough

15 minutes ago, DVDHack said:

aren't exactly right?  What are using as the membrane?

I;ve a thread in this part of the Forum, 

Got the roll today. 10m 80Kg.

5 minutes ago, playdough said:

Now that's technical !!!! It'll be actually built like that. Inner outer frame.

The reading I did said that microphone measurements weren't ideal to base the design on, room mode calculations were preferred.  I might consider some of these instead of the bass traps I was considering, just as easy to knock up.  Knew I shouldn't have sold my table saw but I still have the Triton workbench.

 

Have you made a sample and tried it?

1 minute ago, DVDHack said:

sample

Yea, I've made a few. Good results. When you get over 12m2 area of heavy limp membrane into a listening lounge, makes the bass sound clean and clear, can't be understated really, from experience. 

 

Just now, playdough said:

Yea, I've made a few. Good results. When you get over 12m2 area of heavy limp membrane into a listening lounge, makes the bass sound clean and clear, can't be understated really, from experience. 

 

I was just reading your thread.  I was amused by the 'low profile' description of your 2400x1200x200 build...  

Modelling

Nothing like getting a tone generator into your speakers, and going up down round and  around the room with an SPL Meter, see where the summation is prevalent .

2 minutes ago, DVDHack said:

amused

Nothing is small in there, or light, except the power amp. 

😅

2 minutes ago, playdough said:

Nothing is small in there, or light, except the power amp. 

😅

'My mate asked me how I was going to move this diffuser when it's built, should weigh in at close to 200Kg with the framing.  I told him that's what the tractor is for...

Any photos of actual work, tractor episode ?

 

Have all the pieces cut but waiting on delivery of glue to form the skyline.  Hoping for delivery tomorrow but it's unlikely, more likely next week.

pva for sticks

7 hours ago, playdough said:

pva for sticks

I ordered Titebond III Ultimate, it's supposed to be very good for MDF, which is my backboard.  There's no hurry, I only want to do them once.  I'm working on the other room at the moment hanging treatment.

 

Im amazed at how little treatment makes such a big difference in this room.  The wall behind me is the kitchen area, I'm using the excuse of better diffusion for not tidying it up...

1 hour ago, DVDHack said:

how little treatment makes such a big difference

Indeed, yes, agree.

To add, you can acoustically control an area within a larger open zone (preferred option)

This becomes obvious, with treatment elements, overhead and on the floor, being between the elements "in the zone" High and or vaulted ceilings become a challenge, however there are ways. of suspending treatments and make them look nicely decorative.....

 

A friend gave me a pencil yesterday to mark out some fresh painted plaster walls as he saw me with a sharpie texter, said "no" use the pencil.

1 hour ago, DVDHack said:

at the moment hanging treatment

Design and frequency target ? Substrate ?

I'm all ears.

1 hour ago, DVDHack said:

I ordered Titebond III Ultimate, it's supposed to be very good for MDF, which is my backboard.  There's no hurry, I only want to do them once.  I'm working on the other room at the moment hanging treatment.

 

Im amazed at how little treatment makes such a big difference in this room.  The wall behind me is the kitchen area, I'm using the excuse of better diffusion for not tidying it up...

You will have a very short work time with the glue. It’s very strong and the bond is such that the mdf will pull apart before the glue fractures.

The room has windows on 2 sides, kitchen on back wall and bare walls on remaining long side.  The floor is tiled and it measures 12.8m x 6.5m x3.1m.  I was given a bunch of panels that consist of Martini Prime insulation.  So far I've just hung a panel above and behind the TV, put a bunch of panels in the front corners and propped up a couple of panels to the side which sit directly over a sub on each side.  I've modified 4 panels to make the suitable for ceiling mounting and they're 1.8m x 0.6m, they'll be positioned to cover the first reflection point on the ceiling.

 

This is a secondary room not my main listening room, it currently has JBL S4700s and 2 x PerListen D15s subs.  I have a minidsp SHD as crossover and source (Roon).  When done I'll apply Dirac Live but that's last.  The objective is to get the room to be an enjoyable listen not immersive listening like in my main room.  I haven't measured it yet, no point before doing some treatment, just need to clap hands together or have a conversation to know it was bad.  With temp propping it's pretty good.  The room doesn't really have bass issues with sub placement, the mains run full range.  I sit at about the 40% position, which was just dumb luck.

 

See picture, excuse mess it's a working area.

 

8 minutes ago, klm said:

You will have a very short work time with the glue. It’s very strong and the bond is such that the mdf will pull apart before the glue fractures.

I was counting on that, I only want to put a small spot on the bottom of each piece of wood and then position it.  I was worried if I used a normal wood glue I might end up with the glue squeezing out and getting in the way of a tight fit.  I have nearly 2000 pieces to glue.

3 hours ago, DVDHack said:

I was counting on that, I only want to put a small spot on the bottom of each piece of wood and then position it.  I was worried if I used a normal wood glue I might end up with the glue squeezing out and getting in the way of a tight fit.  I have nearly 2000 pieces to glue.

If you are hanging these, you need to consider that MDF has the ability to split as it’s weakness is in the sheet layering effect in manufacture and so loading weight on the surface layer and vertically suspending that weight could lead to a failure in the MDF sheet. Ply would be a significantly safer option in the same scenario.

18 minutes ago, klm said:

If you are hanging these, you need to consider that MDF has the ability to split as it’s weakness is in the sheet layering effect in manufacture and so loading weight on the surface layer and vertically suspending that weight could lead to a failure in the MDF sheet. Ply would be a significantly safer option in the same scenario.

My plan was to make the board 1.7m high, the actual diffusers will be 1.15m x 0.83m and the remainder of the sheet, 55cm, will form a box at the bottom and have absorption in it.  I'll also put a 5cm gap between the bottom of the diffuser and the box, a small 5cm block will be inserted between the box and a diffuser block to stop the diffuser sagging forwards.

 

Does that sound Ok?

I would go to 19mm hardwood DAR at 120mm wide boards, if hanging or self supported, one each side

A  MDF 15/19mm sheet backplane glued between the hardwoods, laminate it together back sheet for the diffuser.

Wouldn't move, or shouldn't

Nice timber beautiful all round, ends look nice varnished. 

 

Mentioned is Ply, would be alright, MDF alone, meh, might bend, good damping factor though.