DIY Bass Diffuser

[Andrei]

The problem with bass traps is that most of them are plain ugly. Here is a DIY diffuser. It does not actually trap sound-waves but reflects them.

http://i1279.photobucket.com/albums/y530/Andrei_nz/Diffuser1_zps5f345078.jpg

I have used an 8mm thick sheet of native timber. It is rimu and comes up very well when polyurethaned with a matt polyurethane. It also responds well to varnishes and oil.

http://i1279.photobucket.com/albums/y530/Andrei_nz/Diffuser4_zps96d34f06.jpg

The raised pieces are 18mm dowel that I have had cut to length and angled at about 20 degrees. The pieces have been glued on with PVA.

http://i1279.photobucket.com/albums/y530/Andrei_nz/Diffuser3_zpsbb688471.jpg

I have spaced all the dowel 27mm apart. When it comes to materials you don't have to use dowel but I chose it because it is round.

http://i1279.photobucket.com/albums/y530/Andrei_nz/Diffuser2_zpsb6a9762c.jpg

From the closeup you can see that the cuts are not perfect. If you want to try this then after you have done your calculations for the amount of dowel you require it would pay to order one and a half times that amount. Partly to allow a margin for error, but you will find that a lot of the cuts are not perfect and so there will be quite a few rejects.

http://i1279.photobucket.com/albums/y530/Andrei_nz/Diffuser5_zpsf8147a7d.jpg

The rear is not a thing of beauty but just to show a couple of horizontal pieces of wood. They are added to strengthen the board but also to make it easier to hand on the wall.
Although this was a DIY project I have had a joiner make the cuts. He will need accurate measurements. I tried hand-sawing them but it takes too long and is not as clean a cut. It cost only $20 to have the joiner do the cuts.
Final tip: do not be stingy when it comes to choosing your varnish or polyurethane. It is quite shocking how poor some products are, so get advice if you need it.

As for the size of the dowel, the angle you set it at (on both sides) - the world is your octopus. It is satisfying working with natural timber because its own beauty means that this sort of project can hardly be fouled up.

[Audio Al]

Interesting idea , I like this

It will do two things ,

As you say a bass reflector and a modern work of art , nice to have hanging on the wall

I made something similar some years ago from a MDF base board and British Yew timber

http://img.photobucket.com/albums/v240/bigboobs/IMG_1692.jpg

http://img.photobucket.com/albums/v240/bigboobs/IMG_1700.jpg

http://img.photobucket.com/albums/v240/bigboobs/IMG_1693.jpg

My one is purely visual

[Andrei]

That is gobsmackingly gorgeous! It gives me inspiration to experiment. What wood is that?

[Gordon Steadman]

That is gobsmackingly gorgeous! It gives me inspiration to experiment. What wood is that?

Al is probably off pishantoing, so I'll answer for him - its Yew, my favourite wood (good job as I still have two whole tree's worth to turn in the barn!!)

[Rothchild]

Nice job! Very Pretty.

Did you do any calcs to tune it?

There's a really handy calculator here for skyline diffusors (which is pretty much what this looks like to me) http://www.mh-audio.nl/DiffusorCalculator2.asp you can put in the target frequency spread and it will tell you what depths you need and give you a cutting list and layout plan. I'm not sure how it translates with having dowels and a flat back thought to be honest.

[YNWaN]

Looks good Andrei, but surely it isn't big enough to do anything very much - not at bass frequencies any way?

[Andrei]

Looks good Andrei, but surely it isn't big enough to do anything very much - not at bass frequencies any way?

Right you are there Mark. I don't have a serious bass problem anyway: carpets, drapes, bookshelves, couches etc. However there are a few bare surfaces and I am thinking of doing a larger one and also a set of three smaller ones. For the set of three smaller ones I will probably keep to the same design. For the larger piece I could some variation eg, different lengths of dowel, two different angels, maybe a different timber (wish I could get hold of some Yew).

Marc: 'fraid that website is way over my head. No calcs as such for the job. However the 'long' side of the vertical dowel 24 mm and the 'short' side was 18mm so my trigonometry from school had to be re-engaged. That formula was 6/18 Tan-1 which comes out at 18.435 degrees. The joiner boasted his machine could 'cut the toes off a gnat' so I sent the smartarse the angle to three decimal places!

Gordon: How the hell did you do the one called 'Boxwood form'??

[Rothchild]

Heh, nice one!

I think I linked the wrong calc, it's this one: http://www.mh-audio.nl/DiffusorCalculator.asp it should just have 2 boxes that you put in your target frequencies, so say you want to control some flutter / combing right up high you could put in 7000 and 9999 and it will give you the dimensions of all the bits you need:

Diffusor width 20.64 cm
max. Column length 2.46 cm
Column width 1.72 * 1.72 cm

0 0 cm
1 0.615 cm
2 1.23 cm
3 1.845 cm
4 2.46 cm

and a plan showing you where to put all the bits:

http://www.mh-audio.nl/gif/DiffuserPlan.jpg

It even gives you a cut list:

38 pieces [1] 23.37 cm 38 pieces [2] 46.74 cm
40 pieces [3] 73.80 cm 15 pieces [4] 36.90 cm

As you come further down the spectrum (towards mid and bass) the lengths you need get really silly and you end up with difusors that look like the ones in the pictures on that site.

[Gordon Steadman]

Gordon: How the hell did you do the one called 'Boxwood form'??

Ah well, you want me to give away all my trade secrets huh? If I was to tell you that it was all one piece of wood, you probably wouldn't believe me. Well, it wasn't all one piece of wood, it was two:)

Usually when I am turning, I have absolutely no idea where its all going to end up, the voyage of discovery is all part of the fun. I knew with this one roughly where I wanted to go but it just sort of told me what to do next as I went. The really interesting bit was the captive ball right in the middle:eek:

Basically, once I have an initial shape, I get out the high speed rotary tool (sort of dentist's drill on a compressor) and hack. The ball took a bit of fiddling I admit. That's all there is to it.

[Stubies]

Andrei

Very nice, i like building with wood myself.

Where did you imagine putting it? It might go well on a wall, perhaps as a set of three behind your listening position?

[walpurgis]

With all due respect, the pictured item may have an effect on higher frequencies when close to the source, but it will have no influence on bass. The wavelength at low frequencies is big and would not be impacted by small projections on a board.

[Andrei]

Andrei
Very nice, i like building with wood myself.
Where did you imagine putting it? It might go well on a wall, perhaps as a set of three behind your listening position?
I don't have to worry about behind the seating position as the listening room is very long and the seating position is half way down. I will use one behind one speaker, another on a 'point of first reflection' and the set of three on a blank (ish) side wall.

Gordon:
I see, I see, or at least I get the concept. Are you an octopus? One hand to hold the inner part, one to hold the outer part, one one to hold the drill. That's three for starters and then you need one more to hold the glass of wine that assists in keeping the other hands steady!

[Andrei]

With all due respect, the pictured item may have an effect on higher frequencies when close to the source, but it will have no influence on bass. The wavelength at low frequencies is big and would not be impacted by small projections on a board.
Surely all sound waves have to follow the same principals of reflecting at the angle of incidence. So far I have not noticed a difference and as noted by another the one I have done is by itself unlikely to be sufficient. I have read that a bookshelf nearby is a good thing and this diffuser would have to be at least as effective as that. The proof will be in the pudding no doubt.

[Gordon Steadman]

Gordon:
I see, I see, or at least I get the concept. Are you an octopus? One hand to hold the inner part, one to hold the outer part, one one to hold the drill. That's three for starters and then you need one more to hold the glass of wine that assists in keeping the other hands steady!

Yup, you got the general principle, particularly the wine bit, it helps steady the hand no end:cheers:

[walpurgis]

Try it Andrei. hold the diffuser in front of a speaker, you'll likely notice that higher frequencies are affected, but not lower ones.

[Stubies]

Try it Andrei. hold the diffuser in front of a speaker, you'll likely notice that higher frequencies are affected, but not lower ones.

I have tested sound 'absorbing' material simply by kind of 'yelling at it' - seems too simple but it works pretty well, chaning the pitch of your voice etc. - (pls dont call the guys with the coats just yet! )

Here is an idea:
Since the objective is to change the reflection pattern off the wall - it may be possible to test it by first: stand next to the wall and listen to the 'sound bounce', and second: hold up the diffuser (or have someone else hold it up if you dont want to block the sound path)

That might give a clear result too

[walpurgis]

Here's a link to some interesting info on the subject:

http://www.soundonsound.com/sos/dec07/articles/acoustics.htm

As is implied, absorbtion/damping of bass reflections is the way to go, Diffusion being more useful at higher frequencies.