SUMMARY:  The original plans shown here were a target, the final dimensions I ended up with, that has been documented here, is I think visually better. Also the final result is not a perfect linear scale nor probably should it be.  Also discussed.


Couple comments about the shape and size of these baffles:

Quote:




This is the starting point. Notice there is no spec for thickness. That's because you don't know how thick your wood will be until you machine it. The thickness will be determined by how much twist there is in the worst board of the bunch.

The board widths of the Wenge and Paduke in the drawing above were determined by eye and were targets. There was no way to know how close to these board widths I would be able to achieve until after all the lumber is machined. As Archie noted, these things are complicated for as simple as they are, especially when you have to puzzle-piece all the wood together to match a particular pattern. Solid Paduke (or any hardwood) would have taken less than 1/2 as long.

I did the arc in the drawing by eye using a 3 point measurement... it is how I've always done it. Usually I will cut a piece of wood or metal that is just stiff enough to strongly resist being bent and then bend it into shape by applying pressure at both ends and let nature and the pressure of my tumb tips define a perfect arc, which I can bias positive or negative just by adjusting the pressure at either end and then looking at the arc. When I see it, I just know it, and then I freeze the shape and mark it on the board.

In this case, since a router would be used with a jig, the arc would be perfect. Still I remember how I set the radius, and it was again done visually as I adjusted the swing to hit the top and bottom at the particular point. That point was determined by the amount of Wenge I wanted to show so it visually matched Randy's baffles he made for me. During this process I recall becoming intrigued that the radius was around 42 inches as is the height of the baffle.  

I had already marked the cutout diameters for the driver so I was also referencing that visually as I set the arc. The final shape of these Big Betsy Baffles was the result of all of the above. Interestingly, when I had to saw two of the wide Wenge boards into strips and glue them back together I lost about 1/2 inch -- that I stressed over because I wanted as much Realestate to work with as possible before I set the final shape and dimensions.

Nevertheless my final shape that I ended up with is slightly more stubby which from an artists eye better serves the 15 inch driver I planned to put in it. So if I measure my pair of Big Betsy Baffles, the actual width came to 33.75 inches. The width at the top and bottom were 22-13/16 and the height came to 42-1/8.  

I think if this actual dimension were scaled back down and the original Betsy Shape was modified to match it would not serve the 8 inch driver as well as the original shape does... if not sonically, visually.  And I think the opposite is true as you go up in size.

Quote:



It's some good stuff.  The first recording of the stringed instrumental was stunning, it bent my brain.  The second song which I stopped at 34:53 sounded like Spong Bob playing flexible speaker baffles.  In contrast, the same track on the F15 loaded Big Betsy would have simply crushed it.  I have experimented with foam as a baffle for a real speakers and it's a no-go.  As a panel for a Dayton transducer it has some honorable qualities and good efficiency without a lot of or in the case of the ceiling tile, any resonance of it's own.

Nevertheless, the insight is invaluable.  It makes me wonder if the different dynamics of the woods (Wenge and Paduke) are doing a similar thing but in an inverse sort of way.  Each would clearly have a different frequency balance, and both would probably be good, but combined would likely be better.

BTW, congrats on the new house and large shop area! We'll be expecting a pair of something out of you soon!

Steve

Quote:


Hi Steve,

This is true ..... based on the baffles I have built over the past couple of years, the larger the surface area of an open baffle, the more bass it produces.  One of my audio buddies (Derek) built a pair of 4' x 4' baffles using the original Betsy drivers and called them the "Donkey Kongs".
They made enough bass in his listening room to make my knee caps buzz .....

It's a balancing act though ..... too much bass response can overwhelm the mids, or at least obscure them. I also believe that the size and characteristics of the listening room are part of the equation.
In a larger room, the Donkey Kongs would probably have been more "balanced".

Of course, the shape and materials used in your BIG BAFFLES would have a big effect on the overall sound ..... so the 8" drivers in those baffles might be totally killer .....

Best wishes,
Randy

My drivers are scheduled to show up Monday.  I'm nervous in my anticipation to hear if only Steve is blessed by the Audio Gods.  I'd hate to think a week's worth of work could be in vain.

After reading Steve's build details I see that I basically have a baffle that is 1 inch narrower than his.  If that inch, maple instead of his exotic blend of HW and my painted surface makes a difference then Steve ought to be buying lottery tickets since his intuition/luck is beyond belief!  

Watching more of LR's video link, MDF is not more "dead" than plywood.  So, what could be going on with Dank's MDF baffles and the lack of bass?  Maybe it has to do with the lower stiffness of MDF which would lower its resonant frequency which could interfere with bass production?

All just a guess.

Disappointing  >:(

Keep it smooth Donnie. Keep it smooth.

Here is another video by the speaker builder LR originally posted.  https://www.youtube.com/watch?v=CKIye4RZ-5k

He's making flat panel speakers and I think that some of what he's analysing is applicable to OB speakers.  At 8:25 he talks a bit about shape and at 12:50 he talks about where to put the actuator.  Interestingly, he uses a 3/5 2/5 rule.  Randy and Steve seem to be using this vertically.  Steve's driver center of 25 1/4" in a 42.125" baffle is 3/5 up.

His whole point with the shape and driver offset is to break up panel resonances.

I like the physics as a point of interest but generally I just follow guys who've figured stuff out already, like you and Steve.  The idea of an aesthetics or beauty to what works is more often true.  But beauty is in the eye of the beholder, as they say, which lends me to believe that it can take intuition to see the beauty.  (Steve's Audio Gods)

When I worked in the Aerospace industry there were guys who would "conceptually" design like an artist and the real thing ended up looking like the conceptual design even after all the in-depth analysis was done.

UPDATE 7-27-19

Despite the magic soundstage and overall frequency balance that I get from the Array, I will be putting the F15 drivers back in and running them solo prior to DECFEST 2019.

Why? It should be understood that in the Big Betsy Array -- by design you can not hear the large baffles unless you put your ear up to the speakers. They were designed to support the Betsy Alnico with the utmost subtle amount of sound so they would not detract from the Betsy Alnico speakers in any way and they do it exquisitely well. However by comparison to what the large baffles do with the F15 drivers, I feel like it's almost a horrible waste of such a great large baffle despite how incredible it does sound in the subtle roll it plays in the Big Betsy Array configuration.  It is so right, that it is a new personal reference as of right now.

I have run the F15's in the Big Betsy cabinets with a 12dB passive 90Hz crossover and paired that with the Betsy Alnico to create a similar array and while not as seamless or organic, it did actually work rather well. Problem with that was that using the F15 as a subwoofer felt like a horrible waste of such a great full-range speaker.

Clearly the best bang for the buck is the Big Betsy fitted with the F15, because what those two things do when paired together is more than memorable.

So this puts me back in my original dilemma, in that the speed and sound in general of the Betsy Alnico speakers takes the midrange and top end to another more realistic level in my room. I want that sound, just with more scale and ideally from a single pair of baffles... but with some of the Big Betsy Slam which exceeds any speaker I've ever heard that was actually listenable.

So I have been pondering the Lii-Audio Crystal 10 drivers at $1000 for the pair based on the performance and build quality of the F15 I don't think I'll feel like the drivers were over-priced once I get a pair, so I have ordered them tonight.

Meanwhile I've been working on a new baffle design for these specific drivers. With a lower QTS they obviously want a box and not an open-baffle. The Crystal 10 has a QTS of about 50 whereas the F15 has a QTS around 70 or more. A higher QTS woofer is desirable for open baffle, because the magnet strength is lower to allow the driver to move more at its resonant frequency (fs). This creates a bass boost at resonance that helps offset the cancellation of low bass that the baffle creates by letting the rear wave from the driver come around and cancel the front wave from the driver. This happens at and below a frequency determined by the size of the baffle.

To get a lower QTS driver to work, a larger baffle would be needed and or some bass boost equalization. Let's talk about the baffle size first.

When I scaled the Betsy up for a 10 inch driver, I just felt the size wasn't big enough to give any of that Big Betsy thrill, especially with a lower Q driver that has somewhat elevated highs.



So on the left is the baffle scaled for the 10 inch driver. Next to it is the Big Betsy. The next two are sizes I was trying to pic from and the last one is the original Betsy size. This gives the eye a sense of the scale.  I choose the one that is colored light blue in the picture.  It's going to be about 34-3/4 inches high and about 28 something wide.

The Audio Gods are guiding this one, as I am investing a lot of time and money into it without knowing for sure what will happen. I'm usually rewarded for such faith so we'll see what happens.

Now lets talk about bass boost equalization. You might think at first "no way" not a purist move, etc, but consider this...  the lower Q driver has a stronger magnet hence more bass control, i.e. tighter, faster. There is more control at resonance, which btw, in the case of the Crystal 10, will be in the mid 30's, not 49Hz like the F15. So adding some bass equalization will restore the missing bass from the low Q driver while the drivers stronger magnet will keep that bass even tighter and better controlled. That makes the whole key the EQ. This is were most would botch the concept, but a single-ended class A triode running all by itself with zero negative feedback could easily achieve this with total transparency. Ironically the perfect curve and adjustability for this can be found in a product we already make called the ZROCK2.

So once the speaker is completed I will be pairing it with a ZROCK2. My hope is that this will get me somewhat close to the stock Big Betsy F15 speakers, but with sound that I would fully expect to best the Betsy Alnico drivers on every level.  If this is successful, it will be my personal holy grail of open-baffle loudspeakers.  

If I don't run into problems, these will be done prior to DECFEST and can be compared to the Big Betsy with the F15.

I will of course document the build with pictures as before.

I spent the day today making some of the boards from a stash of really old walnut that was my dads. I'm shooting for a thickness of 1.5 inches. The walnut boards are 6 or so inches wide by 36 length to start. They will be glued up into a total of four 11 inch panels to start things off.  The center stripe will be 5 inches... the radius of the driver.

It was a lot of jointer action since these boards were all over 2 inches thick with a lot of twist to them. In some cases a 1/2 inch in 3 feet.  Between the jointer and the planer, I filled up my dust collector bag past the top and half way into the top bag before I realized it! Trying to get the bag off the dust collector when it's that full is not an easy task. Nevertheless I freed the bottom bag and then about 10 gallons of dust dumped on me from the top bag and like Mt. Saint Hellions it emitted a dust plume that had documentable devastation to not only me but a large part of the shop. Had I known I would write about it, I would have taken a picture of what I looked like. I know that orange haired Bob can relate to this ; )

Anyway, after getting all that cleaned up, the day finished with all the walnut boards I think I will need to make the two baffles. The center strip will be either maple or AAAA+ figured oak.  Something lighter for contrast but with striking grain since it and the driver will be the focal point.

I have some insane figured oak already in stock but it's 4/4 not 8/4 so I would have to glue it together, which I probably will, because I have it.  I want to create something equally stunning to look at as the Big Betsy baffles, in this more manageable but still substantial size and weight.

On a side note, I spent some more time examining the roller guides on my new band saw that are nearly an 1/8 away from the blade which BTW is why the saw dropped an F-Bomb when I tried to cut the Wenge. I discovered they rollers are camed (sp) and figured out how to adjust them to a few 1000's from the blade so now it cuts Wenge just fine, and cuts walnut literally like it was styrofoam! So with this new confidence I ripped all the 8/4 to width on the Bandsaw instead of the table saw.  No noise, no dust, to wasted wood, same precision and same speed. Amazing! Yes, I admit it, I'm getting off pretty frikin hard on my long overdue wood shop. My whole life as a contractor and hobbyist and then union carpenter and eventually speaker designer was tormented by twisted and or crowned boards that you had to wrestle into submission and sand the shit out of to make anything halfway presentable... so you can image what a thrill it is to be able to take tormented wood and make it perfectly flat, perfectly square and perfectly straight... really I can't emphasize how erotic a sensation this is, instead of suffering I'm tripping!


Steve

 

OK, I'll wait before I rush in and make new drawings. Lol
Good tools, aligned and sharp are a pleasure to work with. It is so nice to be able to produce what your minds eye can conceive.
Steve, do you have room for a CNC router? New levels of precision and speed are available.
Also I noticed on the Lii Audio website that if you buy a pair of Crystal 10's you get a pair of F15's for free! A twofer.
What could someone come up with for both pairs to be used in one speaker?? Hmm....
Edit:
Steve you really should look into additive manufacturing (3D Printing) talk about freeing your mind from conventional thought. If you can dream of a shape you can make it.

Steve (and all other contributors to this thread), thanks for sharing your development process on this project. This is the type of nitty gritty that I drool on. It also takes courage and confidence to lay a project bare from the beginning not knowing the outcome, but everyone learns so much from. Both from the little successes as well as the little mistakes along the way.

Quote:




.....

And the other side.

So I'm going to call this one the BESTY10 for now.


It starts with the wood, and this stuff is old. I started with 8 pieces of 1.5 x 6.5 x 36 inch boards, which I made. This morning I realized two of them would have to be rejected. One was too good and one was too bad, so time to make two more. Sadly that's all the wood I'll get from this plank by the time it is machined.



On the table you can see the one that didn't make it. You can see the fault line... even though it wasn't actually cracked, it has a high probability so it's just not worth it.

 

For those who aren't into woodworking, trying to figure out which way to flip the boards and how to deal with knots and misc issues makes it challenging and time consuming. If the wood was perfect it would be a simple experience, but when you have to make the wood perfect from imperfect wood and still have enough to do the project, it is a real puzzle.  This is why it takes so long, and costs so much, but the end result is just that much more appreciated since we know it didn't come easy.

I will say that as I put these panels together I can get a good sense of the size which now feels a lot smaller to me than I though they would be judging from the sketch where I choose the size. I probably should have chosen the size above this one for better performance. The thing is there are about a million people who will not ever buy a pair of Big Betsy speakers because they will think they are too big. This will be a far more manageable size that fall somewhere between an original Caintuck Audio Betsy Baffle and the Big Betsy Baffle shown earlier in this thread.

The difference between 1.5 inch and 1.75 inch, the difference between 35 inches and 42 inches, and the difference between Wenge/Paduke and Walnut/Oak are huge. Compared to the last project this seems like half as big. I won't have any problems lifting this baffle, even when fully assembled. The Big Betsy is a BEAST by comparison.

I could probably cut the arc on my bandsaw, which btw, is kicking ass now that I figured out how to adjust the guide rollers. I used it for all rips today and yesterday. I haven't turned on the table saw one time so far during this project. It's so amazing that the speed of the cut is the same as the table saw, but there is no noise, no dust, and no waste. It rocks!

Archie, Great baffles! Also I looked at the link for the jointers, holy crap! A 24 inch jointer! Just imagine that! I suppose when surfacing a 24 inch wide panel on one, you would have someone sit on the panel as you push it through ; ).

My jointer is a Grizzly 8 inch wide with a serpentine belt, and spiral cutter head. It is my favorite tool in the shop. I love it's precision. I love the feeling when I have just made a pass with a 6 or 8 inch board and go to pull it off the cast iron out-feed table there is a suction from it being so flat! I love that there is no snipe unlike a planer. I love that I can run any hardwood through it backwards against the grain with no tear out. I love that I can put the most highly figured dense hard wood through it and not only is there no tear out, or chipping, there are no marks and it has the finish of something that has been hand scraped.  Sanding it would only make it rough. It actually shines. That really gets me off hard, you just have no idea how much!

Happy listening!

Steve

Steve, a spiral cutter would be nice!  I always do my best to orient the wood grain slant correctly through the jointer and planer but often it goes both ways!  Maple seems the worst.  You have more patience than I when it comes to glue-ups.  I typically do it all at once.   And of course, for anyone wondering, IMO a good jointer is the key to any woodshop.  Although I knew a cabinet maker that didn't use one.  He had a sliding table on his table saw and some amazing blades.

FWIW, I used my bandsaw to cut my arcs and while I'd likely do it that way again, when belt sanding the edges smooth, there is a slight tendency to develop a bit of a bevel in the edge.  For a perfectly square edge, the router is probably still the best way to go.


Pal, how is the top end so far?  I'm wondering if these will benefit from a super tweeter.  What kind of break-in are you thinking?  I know I'll have a hard time resisting the urge to CRANK!

It's interesting that with the 15" driver you tried a sub but not a tweeter.  I would have thought just the opposite.

Wow!

Actually, the low base was why I was looking at the Crystal-10s.

Do you have a ZR2?

I'll be interested in hearing what my ZR2 does with the F15s.  I don't have huge subs now but with the ZR2 my HR1s put out some very low bass.

Archie wrote on 07/29/19 at 17:30:03:


Mine does too. I have one in both of the systems I use most, and both those systems now also have a ZBIT. The one with the 25th Anniversary mods took the longest to break in of any of the Decware components I have but boy does it sound fantastic.

Sorry, I don't know how to make the pictures post smaller.

The footers:

Black paint shows everything and the paint job isn't the best but my total cost was under $500 since I had everything on hand but the drivers, paint, footer pads and driver screws.

Talk about bang for the buck!  Or maybe dB?

I do agree with it.  The sound is so big that for the first time, they have the potential to put the piano in my living room.  And I have one there so I know the difference.

I've found that Steve's "hype" generally exceeds my experience (I'm sure it's my fault) but with the ZR2 he doesn't talk it up enough.  I think he should incorporate the circuit in every amp he sells.

I can't do four feet from the wall but I can see where more distance might benefit.  Do you toe your OBs?