Best open baffle material?

If you were to build an open baffle that would house a big bass driver as well as the mid and tweet, what would you make it from?

I've thought about a few things - Thick MDF is easy to work and easy to finish but not the least resonant at low frequencies. Concrete board is heavy and stiff but near impossible to get a good finish on. A layer of phenol board between two of MDF would give a good surface to finish as well as super strength, but phenol is damn difficult to work as it blunts tools super quickly. Perhaps the same idea but with chipboard in the middle, as it is stiff and less resonant than MDF. Again difficult to finish the end grain though.

Any good ideas?

 

On ported enclosures I've been somewhat pleased with this:

Don't know what it is called in the UK but in the US we have "particle board" most often used as a construction material for underlayment floors, roofs and decks. If you look closely at the edge you will see it is compressed at the surface and is quite hard, but somewhat less dense in the middle -- actually pretty soft so it doesn't hold screws very well. In theory, this difference in density **might** spread the resonance peak a bit compared to MDF. Don't know if this is indeed true.

Compared to MDF particle board is usually quite a bit cheaper so you can make thicker panels for the same cost. Adding particle board and MDF together might also spread the vibration spectrum out a bit while making the MDF surface on the outside easier to finish.

As an trial I used a three layer panel: 19 mm (3/4 inch) MDF as an outside layer, a thin sheet of EDPM rubber roofing membrane in the center, and another 19mm (3/4 inch) particle board on the inside surface. The three are glued together using regular water based wood glue with screws to get enough pressure for the glue to work and to add additional stability.

I use high pressure laminate ordinarily used for countertops as a final surface so the edges are simply filed flush, laminate applied, then the edges finished with a router. Don't have to worry about cocktail glass rings.

Also helpful are cross braces joining the side panels to each other and the front panel. The braces resist in-phase vibrations between panels if placed near the center of the panels.

A good rap on the surface produces more of combination of "thud" and "think" sound rather than a "bonk". Not too scientific but works for me.

 

Marine ply, decent stuff.

 

How about a light weight stiff material? Ceramic honeycomb board?

 

Could do, it depends on whether your priorities tend towards spunking loads of money on high tech materials that give you no sonic improvement but allowing you to move your speakers without putting your back out, or hitting some balance of costs vs potential measured improvement.

 

I would be tempted to build something with a slight curve - laminated from thin sheets of birch ply and then finished with twin skins of melamine. I would then brace it on the rear with full width teardrop shaped braces and a single vertical brace that would also form part of the support (braces to be made from birch ply, phenol board or aluminium).

 

ply wood density of width will depend on size of drive unit's

 

Will it...ermm..perhaps it will, who knows...I'm sorry Nando, but I genuinely haven't a clue what you mean. The density won't be affected in any way by the drive units.

 

fine the best desing on open bafle was made by tannoy, what ever.

 

Oh, was it?

 

Metal foam.

 

I see that foamed metal is very in vogue at the minute.

 

How about Jesmonite (otherwise called by Celestion as AlphaCrystal in their Kingston speakers - so they could say it was special rather than readily available).

It's a water based resin (www.jesmonite.co.uk) that you can either form shapes with by pouring into a mould or I think you can use a thickener so it can be plastered onto a shaped mesh. The Celestion Kingstons were made using moulds and loaded with granite agrigate so it had a specled finish.

You could make a curved mould with ribs going across at points to strengthen and flat mounting baffles for the drivers.


Otherwise, how about some rolled sheet metal (i.e. so it's curved for strength) covered on the inside with some carpet and then plaster worked into the carpet pile - that's what Townshend Galstonbury speakers are made of and I'm sure you could make an open baffle in a similar way.

Or.. have you ever rapped your knuckles on some gaffer tape or electrical tape? Hard as stone. Make some speakers entirely out of layer upon layer of tape! Perhaps make a basic frame and go round and round and round with a hundred reals of tape (at £5 a pop!)..

Or go the whole hog and get rid of the baffle completely - hang the drivers at the correct depths from the ceiling and anchor them in place with guy ropes so they don't swing about.. Put in some really strong fixings (or get a piano frame) and use ratched straps to tension the lines (or make the ratchet straps the lines themselves).

Am I being silly now or stumbled across an amazing idea?

What would happen if you did do away with the baffle? Have just one I beam pointing upwards and bolt the drivers on it's edge. Is the baffle there for sonic reasons or just to afix the drivers in space?

 

Open baffle material

Quote:
Originally Posted by nando
ply wood density of width will depend on size of drive unit's


Will it...ermm..perhaps it will, who knows...I'm sorry Nando, but I genuinely haven't a clue what you mean. The density won't be affected in any way by the drive units.
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100% Analogue

If you simply substitute "thickness", i.e. number of plies, for "density" you will find it makes perfect sense.Big speakers = thicker wood,little speakers = thinner wood
Not always easy in another language,is it?
In answer to the original question I would say plywood.With the speakers mounted anywhere other than the middle of the board.If you have to think about more specialised materials then you're probably not constructing the right speaker mounting system in the first place.

 

You mean like this -


Taken from this thread - http://www.diyaudio.com/forums/multi-way/175745-three-way-nude-swinging-dipole-thread.html

The baffle helps to give the bass driver an easier time, since as frequency goes lower it will cancel itself out from front to back more easily. True di-pole behaviour also causes notch filtering in the response, so a lot of open baffles are big enough not to actually be di-pole in the mid upwards.

 

Not being a member of that forum and being confused enough by this one, I can't see the pictures.However,if the pictures I conjured up in my mind from the descriptions given are even remotely accurate, I am sure that the speakers wouldn't be the only things suspended on sky-hooks in my house.

 

No, I appreciate that it is not easy in another language - hence my comment 'sorry Nando'. How very kind of you to come along and clarify the above for me - most thoughtful (and a very creative interpretation too).

I disagree (in short).

 

Quote:
If you have to think about more specialised materials then you're probably not constructing the right speaker mounting system in the first place.


I disagree (in short).
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100% Analogue

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You're absolutely right to disagree with my previous comment about materials.I had forgotten at the time that I made that statement about a very nice sounding open baffle that I heard auditioned sometime around the mid to late 1950s.
I used to shop at that time in H.L.Smiths in the Edgware Road and it was there that I heard a Wharfedale SFB3.The SFB stood for "sand filled baffle"and the 3 for the number of drive units.The construction as I remember it was of two sheets of ply filled with sand in between them.To me it sounded great but at a cost of the best part of £40 (about 4 weeks pay for me at the time) I could'nt afford it.
So I guess my original comment should have read "2 sheets of plywood with a filling of sand between them"
Pete.

 

It's a bit of a dumb ass question in the first place, there is no 'best' material, you have to look at what it is being asked to do and why. if the question was 'what's the best material to make this baffle for this speaker out of' then there is a likely right answer which gives the least amount of colouration.

But certainly theres more to good design than just speccing 'A' material.