sound board as open baffle

[intojazz]

I have been in the process of completing a pair of open baffle speakers for several months now (hey Glynn). Held up mostly by my tenacious perhaps silly desire to use a particular ribbon tweeter that was NLA in the US. Now that has been resolved and should be hear in about a month so I've turned my attention back to finishing the bass bins and most importantly the baffle. I'm considering building the baffle  very similarly to that of a guitar
soundboard. Specifically a bookmatched jointed panel of split, quarter-sawn spruce. This is all in an effort to allow the full tone of the paper coned mids to come forward. Perhaps this is problematic and not a good choice. It will cost a fair amount to just get a baffle made like this I suspect. I'd do it myself but my skills are limited by the necessary tooling. Not to mention the space needed to do this well. So what do you think of this baffle idea?

best regards,
John

 

[Paul Joppa]

Visually, it sounds beautiful.

Technically, here are a few thoughts:

Remember that guitars are made so the wood will radiate sound. Speaker baffles are made so that the wood will NOT make any sound - just the driver. Two things will reduce the sound radiated by the baffle - mass and damping. A thick baffle has mass; the best place for it is as close to the speaker as possible. Look at the Abby speaker for an example, or the metal rings used by Phy-HP and Fostex. Heavier hardwoods such as maple (used for musical instrument backs and sides) might be a better choice than the spruce used for sound boards. Of course, if you can find some book-matched tapered fletches such as used for violin-family instruments, that would put the thickest part in the center nearer the driver ...  shouldn't set you back much more than the price of a good used car.  :^)  [yes, I am being completely unrealistic here!]

Damping is more problematical; for example MDF has more mechanical damping than quality plywood or solid wood, but most listeners don't like the resulting sound as well. Some kind of vibration-isolating mounting for the driver might be the best place for this, limiting the vibrational energy imparted to the baffle. (Don't let the mounting bolts carry the energy into the wood, either!)

Be aware of the risk of splitting wood due to humidity variations or inadequate drying. Fortunately, a single flat baffle which allows the wood to expand and contract (unlike a box) does provide the best candidate for a crack-proof system. Quality wood will always cost more, but remember that instrument makers seek out wood that has been drying or stabilizing for years. Even wine barrel makers want wood that has seasoned for two or three years.

 

[glynnw]

Hi John - You might take a look at the Linkwitz speaker, which appears to be a more sophisticated approach to the same type of speaker.  He now mounts the fullrange driver from behind, not connecting it to the baffle.  I played around with the idea, but since my speakers are already built it was just too daunting a task.

What type of tweeter will you be using?  This is an area where I feel I could stand an improvment over the Aurun Cantus drivers I am using.  When I put the mic from an RTA on the speaker, it is flat at 1 meter, but after that the tweeter energy falls dramatically with distance.  At a distance of 3 meters, the tweeter reponse barely shows up on the display.  However, it still sounds OK - just not quite a sparkly as I'd like.

 

[Doc B]

I'm with Peej here, as one of the more striking improvements I have heard in the speakers we use in the listening room here came from isolating the midrange driver from the baffle by clamping it into place between gaskets of lossy material. I learned the technique from Andrew Jones, and found recently that Clark Blumenstein is using a similar concept to mount drivers in his cabinets.

 

[glynnw]

Hi Doc - Would it be possible to get instructions on how to mount drivers in this way without violating any privacy agreements among manufacturers?

 

[Doc B]

You just use something squishy and ring shaped on each side of the driver flange - silicone gasket, neoprene o-ring, etc. Make a ring shaped clamp that goes over the front squishy thing and clamps the whole squishy/flange/squishy sandwich to the baffle. The mounting screws for the clamp should not touch the driver flange, it is held in place by compression.

 

[intojazz]

Thanks everyone, good ideas all. Especially like the whole "squishy things" description lol .
John

 

[jrebman]

Hi John,

I too think what PJ said is good advice -- finding a solid piece of spruce that large and a couple inches thick is going to be near impossible anymore, not to mention the price.  I'm guessing you'd also have to go to austria or italy to even find something like that anymore -- that's where a guitar builder friend of mine goes every year on a wood hunting/buying trip for his sound board stock.

Only half- joking here, but if you want to try something a bit different, why not a ferrocement baffle.  At least nobody would be tempted to steal it and it would continue to get stronger for the first 50 years of it's life.  Won't resonate like marble or granite either.

Dan, yes, I found that a very cool idea that Clark is using for mounting the drivers.  BTW, I ordered the Naga system and will be shipping him a slab of koa I hav for the baffles.  Your post was very timely as I had been looking at a number of other speakers in roughly the same price range and yet none of them really struck me as anything terribly special or interesting.

-- Jim

 

[intojazz]

Thanks Jim,
I've decided on a more conventional material, tempting as ferrocement  may be (lol). I've chosen maple as the material for the baffle. Partly because it compliments the color of the Fostex driver so beautifully. This driver has a light yellow tint and I'm keyed on the look of these speakers as well as the sound. I'm open to suggestions for a veneer to use on the bass bins. I'm thinking a dark veneer, walnut perhaps. Ideas welcome. The pic doesn't really show the color of the paper driver very well. Banana paper is what I believe it's actually made of, it's more of a pastel yellow. Actually I have seen cement used in the construction of some bass bins
John

 

[keto]

Looks like a great project. Just an idea. There's a workbench that was available at costco a few years ago, thats 2' x 6', with legs about 3' long. If you could source one and cut it in half, you'd have two 2' x 3' baffles of some nice wood-composite that's about 1-3/8" thick, with 3' "legs" that would extend backwards to hold it all up -- all with the original hardware. Sounds like you're on to an even nicer solution, with the maple, but I thought I'd toss this out there.