Hardwood for OB baffle - bad idea?

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dkmooers

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Hardwood for OB baffle - bad idea?
« on: 11 Mar 2012, 03:03 am »
I'm planning to build a pair of GR Super-Vs, but I really go nuts over figured hardwoods, and my dad makes musical instruments so I have a good wood source.

Is making the baffle out of solid hardwood a bad idea? I know the Orions are solid hardwood, and the latest version magnet-mounts the mid driver to decouple it from the baffle. I don't know if Danny's P-Audio driver can be magnet-mounted, considering it's coax... but maybe some kind of rear basket mounting? Then maybe I could do a thinner baffle.

I could also just mount the driver the standard way (straight to the baffle), and use 1.5" or 2" thick hardwood for the baffle. Is a piece of solid wood this thick going to significantly color the sound? I thought OB speakers were not supposed to be as dependent on construction material, but I really don't want to bugger the cabinet design and turn it into a vibrating musical instrument.

Also, what about the side panels and bass baffle? I'm open to using MDF/ply for the subwoofer frame, but can I do hardwood for the side panels? Do those matter much in terms of acoustic re-radiation?

Advice?

vilbig

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Re: Hardwood for OB baffle - bad idea?
« Reply #1 on: 12 Mar 2012, 03:41 am »
One of the main considerations for open baffle designs is to make sure there are no baffle vibrations which result in reduced output. I would think about a lamination of your hardwood of choice onto mdf or Baltic Birch ply. Just my 2 cents.

Rudolf

Re: Hardwood for OB baffle - bad idea?
« Reply #2 on: 12 Mar 2012, 09:38 am »
If open baffles vibrate or resonate, it is not due to the air pressure in the first place, but due to drivers mounted rigidly on the baffle. You could always mount the drivers on a separate spine and let them just "look through" holes in the baffle. In that case a rather thin (not flimsy!) baffle would be sufficient.
If it is no OB any longer, but something like a U- or W-frame with side walls, some bracing between opposite walls goes a long way to subdue vibrations (by moving them outside the frequency range in use).

Simply making the baffle thicker is always a valid approach, but always a "no brainer" in the derogative meaning of that phrase too. And your father could tell you that having the right orientation of the wood fibers in that piece of would will make a lot more difference vibrationwise than doubling the material thickness.

Rudolf

Angaria

Re: Hardwood for OB baffle - bad idea?
« Reply #3 on: 12 Mar 2012, 10:34 am »
With thick baffles you want to avoid creating a resonant chamber within the bandpass.  Basically as long as you chamfer it, you should be fine.

http://techtalk.parts-express.com/showthread.php?t=216510 for examples of hardwood OB's

zmyrna

Re: Hardwood for OB baffle - bad idea?
« Reply #4 on: 12 Mar 2012, 12:00 pm »
magnet mounting or sand filled baffles are the two best options.

Gothover

Re: Hardwood for OB baffle - bad idea?
« Reply #5 on: 12 Mar 2012, 03:13 pm »
One of the main considerations for open baffle designs is to make sure there are no baffle vibrations which result in reduced output. I would think about a lamination of your hardwood of choice onto mdf or Baltic Birch ply. Just my 2 cents.

I agree with laminating for additional dampening.

Dave

dkmooers

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Re: Hardwood for OB baffle - bad idea?
« Reply #6 on: 13 Mar 2012, 07:58 pm »
Thanks for the tips everyone! Are there other problems with baffle vibration besides lower output? Do the baffles re-radiate stored energy and color the sound output of the drivers?

Also, is it possible to get the benefit of the constrained layer baffle (solid wood backed with, say, birch ply or MDF, maybe with a layer of sound-dampening material in between) without using glue? Might be crazy, but I look forward to a world where large manufactured items can all be disassembled with hand tools and recycled/repurposed. Would attaching the hardwood to whichever sound-dampening backing with a bunch of bolts do the trick? (could give a nice look, too... a bunch of polished round-head brass bolts rimming a curly koa baffle.)

doak

Re: Hardwood for OB baffle - bad idea?
« Reply #7 on: 25 Mar 2012, 04:53 pm »
See this thread and others about the Hawthorne Reference Series on the Hawthorne Audio forum:

http://www.hawthorneaudio.us/forums/viewtopic.php?f=2&t=4324

THWO

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Re: Hardwood for OB baffle - bad idea?
« Reply #8 on: 14 Apr 2012, 06:51 pm »
Thick baffles may be stiffer than thin ones... but may also cause new problems, if they lead to smeared radiation of the drivers, especially mids and treble. Those need free space around them on the front as well as on the back side.

A sandwich of different materials is a great idea to keep the wall thin(ner). Magnet mount woofer(s) with "floating" fronts should help to keep the baffle calm. If your design consideration allow to go for a combination of both, you may have found a nice solution...

Regards
Till

S Clark

Re: Hardwood for OB baffle - bad idea?
« Reply #9 on: 14 Apr 2012, 06:55 pm »
"Bad idea?"- yes.  Veneer something acoustically dead.  Using hardwood, you are just asking for an inherent resonance problem. 

Hank

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Re: Hardwood for OB baffle - bad idea?
« Reply #10 on: 25 Apr 2012, 12:53 pm »
The other thing about solid hardwood is that it will move over time, based on two things:
1:  ingress and egress of moisture
2:  internal stresses that play out over time
Both the above could result in cracks, splits and warps
I've always used MDF and veneered it with exotic veneers like padouk (for Danny's original LSA-1's), rosewood (my favorite), makore, etc - even oak for a customer.
I'm contemplating an OB Line Array and thinking about constrained layer dampening - using a sandwich of MDF and and void-free birch plywood.  Another thought is a sandwich of MDF and vinyl sound dampening sheet.
Veneer MDF with your choice of exotic veneers and the result can be absolutely beautiful.
« Last Edit: 25 Apr 2012, 02:43 pm by Hank »

jparkhur

Re: Hardwood for OB baffle - bad idea?
« Reply #11 on: 25 Apr 2012, 01:37 pm »
Make it 1.5 inches..  2 x 3/4 inch laminated, you will be fine....

lowtech

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Re: Hardwood for OB baffle - bad idea?
« Reply #12 on: 25 Apr 2012, 01:56 pm »
Advice?

Any reason why you don't wish to build them based on the manufacturer recommendations?  I assume there are some since this is (or should be) a key aspect of the design.  Swaying from them will have ripple implications that will need to be addressed, assuming that you want to build something that it true to the designers' intentions.

D OB G

Re: Hardwood for OB baffle - bad idea?
« Reply #13 on: 26 Apr 2012, 06:53 am »
I've had great results with barium loaded vinyl sheets.
Vinyl, mdf, vinyl, mdf, vinyl may seem like overkill, but is very effective.
The one I use has a sort of tooled leather surface, if you want to make a speaker with a "sonus faber" type of look. :)

Regards,
David