I'm in the middle of a 'paper mache' tapered resistance 'rear' for the Coral beta8 sphere's - an attempt at a 'lossy wall' structure to marry up to the graduated damping to reduce intermediate cone damping (directly behind the driver) - an old idea from early 'German Radio' about 80 years ago!
It seemed like a good idea when I started it, but at nearly 10mm wall thickness already, not so sure now!
I'm thinking I should have followed on behind your method, Derek.
It seemed like a good idea when I started it, but at nearly 10mm wall thickness already, not so sure now!
I'm thinking I should have followed on behind your method, Derek.
I have yet to master this bloody Canon digital camera so it'll put pictures where I want them to go!
Not exactly up with a lot of this computer stuff, and that's why I'm playing around with this 'yuck' paper mess!
I'll ask around and get something together over the break - the tapered resistance is pretty standard and the damping in the 'horn' is easier done by ear than the programmed response method, and I'm hoping that the 'lossie' wall material can be a cumulative advance to controlling the higher volume transient pressure waves that are quite hard to limit breaking thru the cone to effect the front response quite drastically - the very light cone adds very little rear <-> front damping, unfortunately.
Incidently, the 'baffle step' produced by the spherical front of the chamber only produces a 3dB variation in the radiated response pattern unlike the usual flat panels and if the size/shape is carefully worked out in combination with the Xover freq, it can be a useful parameter in the design, rather than a hindrance - similarly to the curved panel of the OB style.
Not exactly up with a lot of this computer stuff, and that's why I'm playing around with this 'yuck' paper mess!
I'll ask around and get something together over the break - the tapered resistance is pretty standard and the damping in the 'horn' is easier done by ear than the programmed response method, and I'm hoping that the 'lossie' wall material can be a cumulative advance to controlling the higher volume transient pressure waves that are quite hard to limit breaking thru the cone to effect the front response quite drastically - the very light cone adds very little rear <-> front damping, unfortunately.
Incidently, the 'baffle step' produced by the spherical front of the chamber only produces a 3dB variation in the radiated response pattern unlike the usual flat panels and if the size/shape is carefully worked out in combination with the Xover freq, it can be a useful parameter in the design, rather than a hindrance - similarly to the curved panel of the OB style.
Hello guys.I know Im lacking in finishing the teardrops.Personal matters took priority.
Small update....The same problem happened as to wesayso to his 25 driver tower.One of the enclosures has cracks in it.Have to saw them open and fill with thin modelers ply and glue...dont want to cut them all the way apart and re do some rings...
I dont know what was the cause...perhaos changes in temperature...from hot to cold...
Danny
Small update....The same problem happened as to wesayso to his 25 driver tower.One of the enclosures has cracks in it.Have to saw them open and fill with thin modelers ply and glue...dont want to cut them all the way apart and re do some rings...
I dont know what was the cause...perhaos changes in temperature...from hot to cold...
Danny
Strange, ply is really stable, perhaps there was too much pressure on it from glue up?
I wonder if sealing the whole thing in oil, varnish would help?
I wonder if sealing the whole thing in oil, varnish would help?
Oh No! And you didn't even have any steel rods like me in there...
I'd still blame it on (fast) changes in humidity. When did they crack? In which season?
Ply is very stable in the length and width directions... I'm not so sure about the thickness being that stable any more.
I'd still blame it on (fast) changes in humidity. When did they crack? In which season?
Ply is very stable in the length and width directions... I'm not so sure about the thickness being that stable any more.
Theoretically it should be, but practicalities are another matter & depends on the quality of the materials that went into it -both the birch wood and the glues. Production quality control is generally very good, but occasional flaws are inevitable, and tend to be exacerbated when stressed.
It cracked about 2 weeks ago.
Aleady have advice from dad whi used to restore furniture in museum.
I'm confident that it will be easy fix and strong bond.Perhaps the change in climate from country in middle earth to island
and with high humidity...
Anyway,during weekend will fix it and post pics and procedure.
Danny
Aleady have advice from dad whi used to restore furniture in museum.
I'm confident that it will be easy fix and strong bond.Perhaps the change in climate from country in middle earth to island
and with high humidity...
Anyway,during weekend will fix it and post pics and procedure.
Danny
I have a humidity meter on my wall (installed it when I got my oak wooden floor) and the biggest changes occur due to heating the room on the colder evenings/days.
I noticed swings as big as a 15% change in one day. Outside the humidity over here is still pretty high but with the heating on it changes rapidly inside.
Take your time to do it right. This is just the start of the season that creates the cracks. You're in the UK now right? If I read my floor right it will get a bit dryer indoors the next couple of months.
I noticed swings as big as a 15% change in one day. Outside the humidity over here is still pretty high but with the heating on it changes rapidly inside.
Take your time to do it right. This is just the start of the season that creates the cracks. You're in the UK now right? If I read my floor right it will get a bit dryer indoors the next couple of months.
Last edited:
Yes Im in UK now. And to think of it,your right.The landlord started heating the house a lot two weeks ago.That must be the cause.Anyway will fix it and seal it up as quick as possible.
Danny
Danny
FWIW, some tests have shown that shellac is the best sealer. However, while it can help impede things slightly, it will not prevent wood movement due to humidity changes. It's best to assume that wood will move, and plan for it accordingly.
15% change in one day is nothing. Where I live it can easily go from 15% to 85% in a few hours.
15% change in one day is nothing. Where I live it can easily go from 15% to 85% in a few hours.
Hope it works out for you. What are your sealing plans? Polyurethane 1K coat didn't do enough for me. I agree with Greg, the wood will always keep on moving. Our best work around is "engineering" that movement into the design as best we can.
Epoxy is used in boat building with some success. I imagine the degree of permeability varies with coating thickness.
Jp
Jp
hmm didnt thought of epoxy..you have any particular in mind? how much will it add to the diameter?
danny
danny
I've covered mine in epoxy. With fibre glass weave embedded on the outside. But cut the enclosure in 24 pieces before covering to relieve the stress. Or so goes my theory 😀.
The cuts are filled with closed cell PU foam.
Time will tell. I have high hopes but no real answers yet. I looked into boat building for this as mentioned by sootsboots 😉.
With relative thin matt you can make it close to invisible using epoxy. It does need a clear coat though or a more expensive epoxy that's UV proof. I have color pigment in my epoxy as using wood stain and epoxy would be an experiment at best. So I decided to go for a black finish.
Edit: it adds very little to the diameter, my coat with 300 grams fibre glass weave adds 0.3 mm. In my case the micro balloon layer after that adds a little more.
You could use a lighter/thinner weave, or none at all...
The cuts are filled with closed cell PU foam.
Time will tell. I have high hopes but no real answers yet. I looked into boat building for this as mentioned by sootsboots 😉.
With relative thin matt you can make it close to invisible using epoxy. It does need a clear coat though or a more expensive epoxy that's UV proof. I have color pigment in my epoxy as using wood stain and epoxy would be an experiment at best. So I decided to go for a black finish.
Edit: it adds very little to the diameter, my coat with 300 grams fibre glass weave adds 0.3 mm. In my case the micro balloon layer after that adds a little more.
You could use a lighter/thinner weave, or none at all...
Last edited:
Laminating epoxy can be put on Very thinly even with a brush.
The 'finish coat' of an Epoxy lam surfboard goes on with a brush and we look for about 1.5mm / 1/16" before sanding.
If you spray, less than half the above and sanding becomes more a polishing exercise.
Adding 1 lam off 4oz glass fiber will maybe see the above figures taken to 2 - 2.5mm...... thats laminate / filler / sand coat combined.
Q for wesayso: Did you get much 'substrate suck' or 'blowing off' of the glass?
(I doubt the latter as you'd already stopped the grain / pores)
- Status
- Not open for further replies.