[HAL]

What happens when you put an accelerometer on a piece of MDF and hit it with a ballpeen hammer. Lets take a look.

Audio spectrum 64K point FFT of piezoelectric acclerometer with CLIO.

Love hitting stuff and see what happens! 

[mresseguie]

 

[Elizabeth]

Actually using exotic wood under my equipment has made me a fan of tuning.. Different materials, particularly various exotic wood bits really change the tonal balance of the system, and increase the clarity. And the larger the blocks of exotic wood, the greater the effect. I started with hobby wood turning pens, 3/4" by 3/4" by 5" and moved up to knife blanks 1" by 1 1/2" by 5" and then on to bowl blanks 4" by 4" by 2". Cocobolo. African Blackwood (Mpingo) Bolivian Rosewood (not a true Dalbergia species) Bloodwood, Katalox, Wenge, Brown Ebony, Verawood, etc...
Try hammering some of those.... 

[HAL]

Actually using exotic wood under my equipment has made me a fan of tuning.. Different materials, particularly various exotic wood bits really change the tonal balance of the system, and increase the clarity. And the larger the blocks of exotic wood, the greater the effect. I started with hobby wood turning pens, 3/4" by 3/4" by 5" and moved up to knife blanks 1" by 1 1/2" by 5" and then on to bowl blanks 4" by 4" by 2". Cocobolo. African Blackwood (Mpingo) Bolivian Rosewood (not a true Dalbergia species) Bloodwood, Katalox, Wenge, Brown Ebony, Verawood, etc...
Try hammering some of those.... 

Exactly my point.  What do different materials have for resonance and damping properties.  The samples have to be the same size for comparison, but usually easy to cut a piece to use from raw materials.  I have tested turntable isolation stands in the past with a different setup, but the same measurement system.  Fun stuff!

[Elizabeth]

I just bang two if the same wood pieces together. The harder the wood, the more metallic and higher the pitch in the pen blank size wood. (3/4" by 3/4" by 5")
As an example, I got one type in the Pen blank, and a larger turning blank of 1 1/2" by 1 1/2" by 12" and the pen blank a metallic clock click, the larger block a warm tone rather delightful. hardness of 3400. (that is really high. An ebony type of wood.) most hardwood is hovering around 800 to 1500
And the more interesting tone woods are heavier like 0.75 or higher of weight of water. The scale is compared to water. So my ebony example is 1.10 as much as weight of water by volume. Where a lot of hardwood used in USA is like 0.50 of water, Or less.

[SET Man]

What happens when you put an accelerometer on a piece of MDF and hit it with a ballpeen hammer.

.....

Hey!

   I don't like MDF, it rings. I prefer Baltic birch or even marine plywood over MDF. I actually built my speaker out of plywood and will never build one out of MDF.

Buddy

[WGH]

Love hitting stuff and see what happens! 

Me too! Here is a video I made 8 years ago hitting birch ply, Richlite and MDF

https://www.youtube.com/watch?v=SkSxH40x5SA

[Letitroll98]

I just bang two if the same wood pieces together. The harder the wood, the more metallic and higher the pitch in the pen blank size wood. (3/4" by 3/4" by 5")
As an example, I got one type in the Pen blank, and a larger turning blank of 1 1/2" by 1 1/2" by 12" and the pen blank a metallic clock click, the larger block a warm tone rather delightful. hardness of 3400. (that is really high. An ebony type of wood.) most hardwood is hovering around 800 to 1500
And the more interesting tone woods are heavier like 0.75 or higher of weight of water. The scale is compared to water. So my ebony example is 1.10 as much as weight of water by volume. Where a lot of hardwood used in USA is like 0.50 of water, Or less.

I assume you're using the Janka Hardness Index for the first numbers and specific gravity for the second.  Beware that the specific gravity of wood samples varies wildly depending on moisture content.  A single sample could vary from, say, .5 to 1.10 depending on if it's fully dry, 0% moisture, to green wood.  My dad manufactured wood working equipment for most of my life and there's a really big difference sawing green wood vs kiln dried, which I assume would also impact the sound deadening properties.

[HAL]

The plot I posted is the impulse response of the piece of MDF after FFT processing.   It shows the overall transmission of sound vibration through the sample from the hammer impulse.  Amplitude may change due to how hard you hit it, but overall a good way to test sample.  You typically want something harder than the sample to do the hit.

In the vibration industry they use calibrated hammers (specific mass hammers with an accelerometer attached) and shake tables with accelerometers for this type of testing.  This is my DIY version for trials.

Fun stuff!

[I.Greyhound Fan]

I made a new chassis for my vintage Thorens TD-145 TT out of Cocobolo and lined it with GT-Matt and made the bottom out of true Baltic Birch and lined it with GT-Matt.  It really dampened things and improved the sound.

[richidoo]

A decade ago I used to walk around homedepot knocking on every material in the place, looking for dead materials for the latest diy speaker project. Corian, PVC, ply, etc. My kids were young so they would come shopping with me, and when we traveled on vacation I used to tease my kids that we would stop at HD to shop for "speaker wood" and they would howl in protest - so funny!

I once built a big planet10 horn speaker out of Trex decking. Trex back then was 4/4 thick, polyethylene mixed with sawdust. I glued it together with West Systems epoxy. It seemed totally dead as a long single plank, but built into a speaker with smaller spans the resonance became audible. They were by far the worst sounding speakers I have ever heard, even tho same speaker made of BB was among the best. Fortunately the epoxy failed within a week (nothing can glue PE) so they ended up in the dump quickly, and it took it two people to lift it into the dumpster! It was lots of fun. Gotta do a DIY again soon.

[FullRangeMan]

Hey!

   I don't like MDF, it rings. I prefer Baltic birch or even marine plywood over MDF. I actually built my speaker out of plywood and will never build one out of MDF.

Buddy

Do you recommend Baltic Birch or even Marine plywood for 15'' woofer baffle? How thick?

[Elizabeth]

On the other hand....
Why not build a cabinet, stiff of course, but design it so the cabinet resonance is right at the gap between the port and woofer/midrange gap. (And the sound is pleasant. Using a wood with good resonance properties, musical instrument wood) So instead of support for the woofer just from the port, all three, port, cab resonance and woofer/midrange (plus crossover) all work together. It is really really expensive to make a cabinet that is totally dead.. why not make a cheaper cabinet that WORKS WITH the other devices in the cabinet?
I am sure some successful speakers did this just by accident. Why not build one on purpose.


???

[JLM]

Please explain/interpret the graph and video results because frankly I don't see/hear anything meaningful in them.  And honestly don't know how much can be discerned from uncontrolled/unmeasured banging or knocking on pieces of wood.  And BTW, all solids can resonant.  No wonders outsiders scoff at audiophiles. 

From my very brief research, marine grade plywood is simply plywood made with water resistant glue (usually of better grades of wood).  So it and of itself probably has no inherent advantage to a quality (grade A, no knots/holes) plywood in terms of acoustical performance. 

Note that some speaker manufacturers actually try to work with the resonance of the cabinet to achieve the desired sound (colorations).

[S Clark]

What I see is that MDF doesn't ring especially at any audible frequency (perhaps slightly around 20 Hz), and falls off rapidly above 1800Hz.  Looks like an ideal material for speakers, and very easy to incorporate into a 2 way system with a crossover around 2KHz. Perhaps more important than the above graph would be a look at decay.  That's what would tell more about ringing. 

[HAL]

As stated above, this is a standard test technique for materials resonance properties.  Different levels of striking the piece changes the amplitude, but not the overall spectrum.  The less upper end response and lower amplitude are for better internally damped materials.

The wider the frequency response and higher the amplitude, the more the material resonates. 

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. 

[HAL]

What I see is that MDF doesn't ring especially at any audible frequency (perhaps slightly around 20 Hz), and falls off rapidly above 1800Hz.  Looks like an ideal material for speakers, and very easy to incorporate into a 2 way system with a crossover around 2KHz.

Scott,
Excellent observation. 

I am trying to see if a material is available that will beat MDF, as it does not have enough structural strength for larger line array baffles.  Next I will test the oak sample I have that is the material I made The Megaliths baffle from.  Should be interesting.

Also working on a more repeatable striking method.  Parts are here and time to build it.

[S Clark]

Isn't Panzerholtz (or however it's spelled) the answer to your search?  Where in the world can you buy that stuff anyway??

[HAL]

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

[Endo2112]

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