[JLM]

I have never liked a speaker cabinet designed to resonate with the drivers.  You want the driver to stay in one place and resonance means it can move.  I do not like boxes, so open baffle speaker need a stiff, low resonance material to work well.  Hence the reason that most use 1.5" baffle thickness of different stiff but damped materials.  The damping is just as important as the stiffness.  Building a speaker out of steel that is not damped is like making a bell, same for boxes that resonate.

Open baffle designs are just extremely poorly supported cantilevers (they'd be a functional cantilever if they were bolted to the floor) which are free to vibrate orders of magnitude more than braced enclosed cabinet panels.  Open baffles remind me of a tuning fork or a diving board - something asking to vibrate.  Without being firmed secured to the floor it's just a matter of comparative masses, driver versus baffle, Newton's Third Law (action/reaction).

[HAL]

There is also another material which is basically a half pressed Panzerholz called Delignant that I've looked at it's about half way between BB and Panzrholz and is used to line the decks of semi trailers and is far more reasonable price wise.

Don

Don,
Very interesting.  Would love it if a scrap sample is available. 

[WGH]

Insulam EH (Densified Laminated Wood) is similar to Panzerholz and is made in the US
https://www.ckcomposites.com/

Richlite is made in Tacoma, Washington and is a paper/resin composite available in many colors and thicknesses. The material is used in counter tops, I got a lot of free scraps from a local supplier.
Check out Richlite's sample page, the Large Prototype Samples are available in thicknesses up to 2":
https://richlite.com/collections/samples

https://richlite.com/



More info plus photos of my MDF/Richlite resonance control panels (which work very well):
https://www.audiocircle.com/index.php?topic=92198.msg914854#msg914854

[HAL]

Very interesting.  Have seen Richlite fretboads on guitars.  Look a lot like ebony. 

[gab]

Some interesting work & measurements here (from 1977):

BBC RD 1977/3
Factors in the design of loudspeaker cabinets

https://www.bbc.co.uk/rd/publications/rdreport_1977_03

[HAL]

Thanks!  Will check out the link.

New test jig for sample testing.

[Elizabeth]

On thing about a resonant frequency is in any material, size matters... and there must be sizes the reduce the resonant peak, and sizes that max it out.

[Early B.]

Open baffle designs are just extremely poorly supported cantilevers (they'd be a functional cantilever if they were bolted to the floor) which are free to vibrate orders of magnitude more than braced enclosed cabinet panels.  Open baffles remind me of a tuning fork or a diving board - something asking to vibrate.  Without being firmed secured to the floor it's just a matter of comparative masses, driver versus baffle, Newton's Third Law (action/reaction).

I'd like to see and hear more evidence of this. If this were entirely true, OB speakers, in general, would sound horrible compared to box speakers.

[HAL]

The nice thing about using planar drivers above 200Hz is that there is very little motion to overcome with the open baffles.

The H-Frames are robust construction with MEDEX frames for 200Hz and lower.
 

[JLM]

On thing about a resonant frequency is in any material, size matters... and there must be sizes the reduce the resonant peak, and sizes that max it out.

Even the earth resonates.  It's called earthquakes.

[gab]

I'd like to see and hear more evidence of this. If this were entirely true, OB speakers, in general, would sound horrible compared to box speakers.

http://www.linkwitzlab.com/conclusions.htm

I especially like:     "It is difficult to screw up an open baffle speaker design to where it sounds worse than your typical box speaker."

gab

[HAL]

I agree with that statement.  Hence the materials investigation.

[HAL]

New test setup is running.

Had to design a simple variable length pulse control system with an Arduino and BJT/Power MOSFET driver for the solenoid.  This lets you make the shortest hit on the material before the solenoid will no longer actuate. 

The results are similar, but the level is much more stable so easier to compare the samples.

Now waiting on some sample material to test.   

[Peter J]

Rich, are you waiting for folks to send you stuff or do you have a supply? I could provide pieces of several different materials from the woodworking and countertop worlds. Sample size and an address is all it takes.

[HAL]

Peter J,
I have some samples coming, but if you want to send some for testing will be happy to test them.

Hopefully having a MEDEX sample coming for test at some point.   Would be interesting to try the composite materials.

I have been using 1.5"w x 3"h x 0.5"d samples with the system.  Will PM address to send samples.   

[shadowlight]

At $900+/sheet of PH plywood for material, not looking to go there as it comes from germany and shipping cost is insane.

Rich,
There is Canadian distributor for Panzerholz in case you are interested - http://www.bkbindustrial.ca/

[HAL]

Deepak,
Will check into it. 

Last time I checked it was around $900.00 for a 4'x8' sheet.

 

[HAL]

Peter J sent a big box of material samples to test!   

Will get the test setup running and see what I find.

[FullRangeMan]

Keep us posted on these

[mgalusha]

More fun with materials, starting at about 26 minutes in.

https://youtu.be/EEh01PX-q9I?t=1564

The whole video is worth the time but 26:00 to about 45:00 is on this subject. CLD for the win.