Baltic Birch Translam Baffle with MDF Cabinet

[Arctos]

Considering trying something new for my next build. Has anyone done a baffle or baffle and back out of BB translam with the rest of the cabinet made from MDF? My plan would be to just cut 1.25" slats of .75" BB, stack and glue them to the correct width. My intention would be for this to be both esthetically interesting as well as provide a more rigid but still sonically dead baffle.

Does anyone see any glaring issues with this concept?

Does my logic hold true regarding rigidity and good sonic characteristics?

Could this potentially reduce the amount of required internal bracing?

Thanks,

RDS

[billfitzmaurice]

It's a perfectly good concept, but in terms of rigidity a thinner braced baffle is better than a thicker unbraced baffle.

[djg]

http://techtalk.parts-express.com/fo...ay-facet-build

http://www.divine-audio.com/ansonica/

[Chris Roemer]

Here's a story of a translam gone bad - and the fix.

http://techtalk.parts-express.com/fo...vacation/page2

[andy19191]

Considering trying something new for my next build. Has anyone done a baffle or baffle and back out of BB translam with the rest of the cabinet made from MDF? My plan would be to just cut 1.25" slats of .75" BB, stack and glue them to the correct width. My intention would be for this to be both esthetically interesting as well as provide a more rigid but still sonically dead baffle.

Does anyone see any glaring issues with this concept?

Yes. It will be significantly less stiff in the direction between the plys. Maximising baffle stiffness is important because the stiffer the baffle the less the drivers hammering on the baffle will transfer work into the cabinet to then be dissipated via cabinet damping and unwanted sound radiation. Simply gluing two pieces of ply will be superior.

Does my logic hold true regarding rigidity and good sonic characteristics?

No.

Could this potentially reduce the amount of required internal bracing?

No. Bracing the baffle is almost always a good idea but bracing the other walls may be good, bad or indifferent depending on the approach to cabinet design with respect to isolation and damping.

[Arctos]

Thanks all, appreciate the comments and links to some beautiful speakers:

Will certainly take the advice on baffle bracing.

andy19191, I don't entirely understand your first comment. Do you mean that it will transfer energy sideways across the baffle and into the MDF cabinet sides through each layer? My plan was to glue the BB slats so that the layers as well as my glue joints would run vertical. Don't know if this would make a difference based on your comment.

Chris, amazing looking speaker and amazing fix! I would have probably just started over.

So the vibe I'm getting seems to be that it is a viable option for esthetic reasons, albeit not without some potential issues, but regarding sonic characteristics maybe I'm better off sticking with MDF. Correct?

Also, forgot to mention, I was recently looking into a new 2-way speaker project, but moved on to potentially building a pair of Bagby Woofer Modules to augment a pair of Mandolin's. I was considering this method for the modules.

[jhollander]

I think your concept of 1.25 inch thick baffle is good with the laminated BB strips. The thickness will offset the weakness in the parallel to the layer direction. I'd test it for sure as the quality of BB varies. Some translams I've done were crap because of the BB. I've used some rift sawn veneer for close to the same effect as translam. BTW the thick baffle will require attention to back side relief around the woofer.

[Arctos]

Thanks John, appreciate your input. I agree on the woofer relief. In the few projects I've done so far (only built 3 pairs and a bluetooth so far) I've used a 45 degree chamfer bit to open up around the inside of the woofer cutout and just left about an 3/4" unrouted so the woofer screws didn't punch through.

I've been using BB from Rockler (have a local store) for bracing on the last 2 builds and it seems to be pretty good quality. I've also got a Woodcraft store that is close by that could also carry some higher quality ply.

Regards,

RDS

[andy19191]

I don't entirely understand your first comment. Do you mean that it will transfer energy sideways across the baffle and into the MDF cabinet sides through each layer? My plan was to glue the BB slats so that the layers as well as my glue joints would run vertical. Don't know if this would make a difference based on your comment.

Plywood has 2 strong axes and 1 weak . A speaker cabinet requires 2 strong axes to resist bending which moves the cabinet in and out radiating unwanted sound and 1 axis that is less important (actually it is a bit more nuanced but that is the gist). The 2 strong axes and 1 weak determines how plywood is used in constructing aeroplanes, boats or speaker cabinets where the mechanical properties of the material affects performance. This is less the case for furniture and the like where aesthetics may be more important than the material properties.

The stiffer a baffle the less vibrational energy is transferred into the cabinet by the drivers. Recall from school physics classes that energy transferred is the product of force * distance moved in the direction of the force. The force is the reaction on the driver magnet to the motion of the cone assembly and air which is pretty much constant and an unaffected by speaker design. The distance moved however will reduce as the baffle is made stiffer. The stiffer the baffle, the less energy put into the speaker cabinet that will then have to be absorbed by the damping in the structure or radiated away as unwanted sound. Misusing the mechanical properties of plywood by having 1 strong and 1 weak axis to resist bending of the baffle will put more vibrational energy into the speaker and make the radiated sound from the cabinet louder. Whether this cost is less than an aesthetic gain is for you the designer to judge. But there is a performance cost to what you propose and to some eyes there will also be an aesthetic loss not a gain particularly if the viewer possesses engineering sensibilities.

[donradick]

I don't see a problem with the overall design.
Having a 1 1/2 inch thick BB translam baffle will certainly be stiff and non-resonant enough compared to the walls of a box with 3/4 inch MDF.
The drivers will transfer mechanical vibrations and energy to the rest of the box, but they will also transmit acoustic energy from the back of the woofers.
Which is more of a problem? Who knows! The only empirical measurements are corporate IP research.
What most designers use is window braces for the box walls. The advanced guys will use matrix bracing, top, sides and back, although rarely bracing a baffle.

Have fun. A lot of this DIY addiction is just saying "what if I do this?" and finding the answer!

[andy19191]

The drivers will transfer mechanical vibrations and energy to the rest of the box, but they will also transmit acoustic energy from the back of the woofers.
Which is more of a problem? Who knows! The only empirical measurements are corporate IP research.
What most designers use is window braces for the box walls. The advanced guys will use matrix bracing, top, sides and back, although rarely bracing a baffle.

DIYers have the option to perform 3D numerical simulations using open source software, low cost commercial software and sometimes high cost commercial software at work. One or two are starting to do this over on diyaudio but it is early days and they seem to be going about it in fairly inefficient ways but that should improve with experience. Curiously I have seen nobody using what I would judge to be the most useful free and open source software.

For those that don't want to perform 3D simulations themselves studying representative 3D simulations from others should lead to a better and quantitative understanding of the physics relevant to things like the vibration and sound radiation from cabinets. How does energy gets into the cabinet? How to reduce it? What is effective at removing it and what is not? In the absence of evidence from 3D simulations or measurements (which are time consuming and tricky to do competently for cabinet sound radiation) a fair amount of nonsense has been propagated by those with a web presence, enthusiasm but little understanding of the science and engineering. Pretty much the definition of the web I guess. I have started a project to perform and write up 3D simulations relevant to speaker design but it is in the very early stages at the moment.

Have fun. A lot of this DIY addiction is just saying "what if I do this?" and finding the answer!

Spot on. Some derive fun from complex calculations and growing understanding. Others can't be bothered with any of that and just want to cut metal ASAP. So long as fun and satisfaction is being derived the hobby is working.

[Arctos]

Thanks All, and I totally agree with the having fun part!

I look forward to experimenting at some point in the future (probably after I retire, my kids move out and I have more time) but for now I need to depend on tried and true methods or methods that I have a high degree of confidence in. Regardless of which baffle design I go with (translam or MDF) I'll still plan on using atleast one window brace made of .75" BB ply and it will connect all 4 sides of the cabinet (baffle, back and sides). Actually, since this will be a woofer module with a 10" driver I'll probably go with 2 braces just to be safe. Also, haven't seen the designer's cabinet plans yet but will be sure to meet or exceed their bracing recommendations as weill.

And once I decide and move ahead with the plan i'll let you all know and maybe post a few pics.

Thanks again,

RDS

[Arctos]

Forgot to show a photo of the effect I was considering going for. Imagine this but with only the baffle being translam and the rest of the cabinet being MDF with wood veneer, and obviously only having a 10" woofer mounted: