[Bob in St. Louis]

.....Also large square foam blocks. Like the one's a florist woud use in the bottom of a pot to stick the fake flowers into. That would be easy to form/mold.

Bob

[JohninCR]

Bob,

Thanks for reminding me about paper mache.  I thought about it about 6mo ago and forgot.  Florist foam is fairly close, I'd just want a little finer texture and stronger.  I can see that stuff crumbling and rattling within the construction.  The foam used for surfboard cores would be ideal in 1/2" or 1" sheets.

[goo]

Bob good idea Paper mache..cool
John,
good luck finding blanks that thin...well 1" maybe 2" is more like it..yet again it's been a long time since I have played with making surfboards

mcgsxr;
sorry if I hijacked your thread dude

q

[mcgsxr]

Continued no worries about the thread direction, I asked for new ideas!

[Bob in St. Louis]

Florist foam is fairly close, I'd just want a little finer texture and stronger.  I can see that stuff crumbling and rattling within the construction.  The foam used for surfboard cores would be ideal in 1/2" or 1" sheets.

I was thinking more of using it as a "waste" form. Build the paper mache around it. Let it "set", then break away the foam. Then you'd line the inside of the paper mache with fibreglass.
.....Or, just coat the foam with the fibreglass, then break out the foam inside.

Bob

[JohninCR]

Bob,

I don't really follow, but I was thinking make what I want out of paper mache, then just coat that with fiberglass and epoxy or fiberglass resin for strength.  I'd just use plywood for the driver mounting baffle for these prototypes.  In 2 days I could probably whip up 3 or 4 different pairs....Paper mache one day and fiberglass the next.  Then once I get happy with how I'm manipulating the front and rear waves, I can spend more time doing a pretty set or just one to use as a mold to make it easily repeatable.

[Bob in St. Louis]

Well, I'm probably talking out of my butt again.
I've never done it, but I believe one method is using wax. It's called "the lost wax process". Basically what's molded in the first step become a waste byproduct in step #2 and your only left with the final product. The first step is just to make the basic shape.
Like a 'negative' so to speak.

Bob

[goo]

Butt aa Bob How ya going to melt the wax dude...
I know were you are going it could work. How about Green sand casting....nope got to make a form first
I was thinking about a local gal that does pottery, I've built some stands for her... hmmm. Start with a lump of clay and shape and fire it..might ring like crazy without some special coating
anyways
cheers
q

[guest42212]

Bob,

I don't really follow, but I was thinking make what I want out of paper mache, then just coat that with fiberglass and epoxy or fiberglass resin for strength.  I'd just use plywood for the driver mounting baffle for these prototypes.  In 2 days I could probably whip up 3 or 4 different pairs....Paper mache one day and fiberglass the next.  Then once I get happy with how I'm manipulating the front and rear waves, I can spend more time doing a pretty set or just one to use as a mold to make it easily repeatable.

[JohninCR]

Hitsware,

Right now I'm exploring some extreme tangents of OB's where modelling programs
are little to no use, dipoles (equal front and back) with midrange waveguides to
improve directivity in the midrange and U-baffle shapes (more extended to the rear)
to achieve the smallest footprint for a given bass response.  With the waveguides
I'm trying to avoid horn loading, while pursuing directivity, so horn modelling programs
aren't useful.

Bass response is easy.  That's only about delaying the rear wave and to some extent
placement and room.  Then as we start to do things to manipulate more delays in the
rear wave, those things affect higher frequency response through edge diffraction and
the how the front and rear waves combine in the higher frequencies.  This is where
curves and big roundovers come into play, and since computer modelling won't really
help, I need a quick way to prototype different things to understand their effect.

[Jade East]

Blue foam insulation sheets maybe a good material to
play around with for making waveguides.

[JohninCR]

Blue foam insulation sheets maybe a good material to
play around with for making waveguides.

Yes, but the climate is so ideal here that it's not available.  The only foam I've found here
is styrofoam from someone who imports large blocks and hotwire cuts the sheets you want
to order.  It's the normal big beaded stuff that is impossible to make smooth.  It's also more
rigid, so bending like is possible with the blue construction foam, is not an option.

[Jade East]

You could use the foam but cover it with an auto body filler like "bondo".
Although you probably don't have auto body filler because your cars never rust.

[JohninCR]

Of course cars rust here, and Bondo and other body fillers are available.  It's just that a lot of construction materials that are available stateside aren't available here.  Very little insulation type products aren't available because they aren't needed.  My problem with Bondo is that it's not cheap, and it hardens way too fast.

[guest42212]

I get a kick out of 'sims'
My 'Boxplot' OB kludge makes me proud
Accurate enough for government work and
(IMO) a way viable approach ......
Way more accessable than what few OB simulators
exist.........

[JohninCR]

Hitsware,

Sims are fun, but I'd rather just start with the manufacturer's IB response and subtract 6db/oct from the estimated Fequal point.  Simple and accurate.

[guest42212]

Hitsware,

Sims are fun, but I'd rather just start with the manufacturer's IB response and subtract 6db/oct from the estimated Fequal point.  Simple and accurate.

Presysamundo !
How do you calculate "Fequal" ?
Bassed on Fs,Qts,bafflewidth
AND !
Does "Fequal" ~ Fc? , F3? , Fb ,
........ad Fnium

[JohninCR]

Fequal is where you have delayed the rear wave by 1/4 wavelength, so it neither reinforces nor cancels the front wave.  It's only baffle dependent.  You already know the driver's response.  Bass is pretty straight forward.  The problem with the big baffle you use is what it causes to happen above Fequal.

[guest42212]

Fequal is where you have delayed the rear wave by 1/4 wavelength, so it neither reinforces nor cancels the front wave.  It's only baffle dependent.  You already know the driver's response.  Bass is pretty straight forward.  The problem with the big baffle you use it what it causes to happen above Fequal.

So you could model it as an 1/4 wave pipe with 0 length ?
Don't work ...
PERHAPS !
A horn with infinite expansion ......... ?

[JohninCR]

Fequal is where you have delayed the rear wave by 1/4 wavelength, so it neither reinforces nor cancels the front wave.  It's only baffle dependent.  You already know the driver's response.  Bass is pretty straight forward.  The problem with the big baffle you use it what it causes to happen above Fequal.

So you could model it as an 1/4 wave pipe with 0 length ?
Don't work ...
PERHAPS !
A horn with infinite expansion ......... ?

I don't model it.  IB response -6db/oct below Fequal is all I need.  Above Fequal, use The Edge or something similar.  I'd recommend looking at those posts on the Fullrange forum about how the rear wave interacts with the front wave.  Once you truly understand how they interact at the listening position, the lightbulb will go off, and you'll see just how easy it is.   Then maybe you'll stop using those junky drivers with thimble sized magnets.  Fullrange isn't possible unless you delay the low frequency portion of the rear wave enough that it actually reinforces the front wave through most of the bass range, like with my OB-RLH cab.