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There's another storm brewing!

#341
Was out of town the last week, so was viewing this on my phone. Back home now, and thee larger images just amplify the design quality of this bass. Simply stunning work so far.
But would expect so, coming from your previous.

Could you not tape the cavity, and leave a "tail" that would extend to an out of view area, that would mate to the cover which is totally covered except for the visible edge? (apologies if this is a dumb question...)
 
#342
I tend to think of myself as a pretty "outside the box" thinker, but every time I visit this forum I am astonished by the kinds of ideas that are out there — things I would have never conceived on my own.

This thing is so awesome. I love the shape of the instrument, and of course that lamination is something to behold. Even in this state, where there's still a lot of shaping to do, it still looks fantastic.
 
#344
wraub - Thanks. If I understand correctly, this would leave be replacing exposed copper at the edge with an air gap at the edge. I'm looking for something where there's no interruption at all. I think my solution will do it, but I was also looking for others' ideas.

Brett - Thanks. I think the shape does look nice, basically I'm ending up following the same path Sheldon Dingwall did, that is to say I got rid of the kink (or "cello hip") at the lower bout. I just hope the laminations don't look to over the top when it's done. This thing may not have started out conservative in its construction scheme, but there were only three woods in it. It now has two close primaries, but five spectral secondaries.

lowsound - The angled edge of the cover (with the blue/black stripes on the body) has a dovetail bevel. The edge along the neck beam does not, it is straight perpendicular. So this is pretty different from SK1 where the cover is trapped between two bevels. I will put in more magnets than the last one, to get a good grip on the cover. If that's not enough I have some ideas in my back pocket that hopefully not be needed.
 
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#345
So about that cover... I am looking to not have any copper over the lip area, either on the cover or on the body, so as not to cause the problems mentioned previously. The laminations on the cover are not done, so I can hide the magnets in there. I have the lamination done already on the body side, so there's no way to hide the magnets. So, if they'll be visible, I think it should be a design element.

So here's the current plan for the cavity. For the heck of it I tried doing a render in SWX, and I got decent quality really easily. I rarely do renders at work, as I'm not trying to sell anything. The back plate has the grain running the wrong direction, but NBD.
cavityrendering_zpsbb5a0a02.jpg
 
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#348
I agree with the Cellist... To much magnetic force going on there..! What you could do if you want them invisible is to install them a bit deeper and then glue round pieces of matching wood on top of the magnets. With your skills I'm sure you can make those small round pieces almost impossible to see. If it's thin veneer you should still have enough magnetic force to hold the cover.

Regarding the shielding, I noticed that you mention not wanting copper foil visible when looking at the edge of the bass... (way back I'm an electronic engineer, so this is actually something I know a bit about). When shielding for hum (low frequencies) it does not matter if the shielding does not cover 100% as low frequencies does not ''creep in'' through small holes not covered. Had it been high frequencies we wanted shielding for it would be an entirely different matter and the shielding had to be extremely tight and cover 100%. What I would do would be to just let the copper foil cover the area similar to the hole that you have routed, meaning the foil will not be on the ''edge'' and it will not be visible. You then need to connect the foil on the underside of the cover with a ground wire to the foil inside the cavity. This can be soldered, or if you don't want the cover to be permanently connected to the bass you could install a small connector on the ground wire and the other half of the connector at the bottom of the cover, with connection to the foil. Does this make sense in writing? (English as a second language can sometimes mean that I'm writing nonsense when it get's technical)... Let me know if it does not make sense and I will upload a drawing...
 
#350
pilotjones said:
So about that cover... I am looking to not have any copper over the lip area, either on the cover or on the body, so as not to cause the problems mentioned previously. The laminations on the cover are not done, so I can hide the magnets in there. I have the lamination done already on the body side, so there's no way to hide the magnets. So, if they'll be visible, I think it should be a design element.

So here's the current plan for the cavity. For the heck of it I tried doing a render in SWX, and I got decent quality really easily. I rarely do renders at work, as I'm not trying to sell anything. The back plate has the grain running the wrong direction, but NBD.
cavityrendering_zpsbb5a0a02.jpg
Click to expand...
Lots of cooks in the kitchen here when it comes to the magnet issue, so I'll just add a little nugget but with it simply being something to consider.

What about mounting the magnets on the vertical walls of the control cavity? You could then mount the opposing magnets on the cover and have them inset way inside the perimeter so they line up.
 
#351
Splods said:
Got enough magnets?
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IntrepidCellist said:
If those are neodymium, that's going to be VERY difficult to move!
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Morten_B said:
I agree with the Cellist... To much magnetic force going on there..!
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Well, the thing is, I did a test. The effect of having the .020" gap from one veneer is pretty significant. And with .040 it's even worse. So I'm going to stick with either what I have modeled, or possibly a bit less.
Regarding the shielding, I noticed that you mention not wanting copper foil visible when looking at the edge of the bass... (way back I'm an electronic engineer, so this is actually something I know a bit about). When shielding for hum (low frequencies) it does not matter if the shielding does not cover 100% as low frequencies does not ''creep in'' through small holes not covered. Had it been high frequencies we wanted shielding for it would be an entirely different matter and the shielding had to be extremely tight and cover 100%. What I would do would be to just let the copper foil cover the area similar to the hole that you have routed, meaning the foil will not be on the ''edge'' and it will not be visible.
Click to expand...
Yes, that is exactly what I will be doing. I had a pretty good idea that LF-EMI couldn't fit through small gaps, but I'm glad to hear it confirmed. Can you tell me how large a gap has to be to be significant, for frequencies in maybe the 600 Hz range, which would be an upper harmonic of line frequency such as you pick up from fluorescent lights?
Morten_B said:
Or... You could install a metal spring at the bottom of your cavity, pointing up, and connected to the foil. The metal spring will press against the foil at the underside of the cover when you put the cover on. The spring will then be the ground wire...
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Actually, I'm going with some of the metal fabric covered conductive foam EMI gasket material that is used in enclosures. Less spring force involved, and it should look cool (at least to the nerdy people :) ). I got the idea when I was disassembling a friend's old Bondi Blue iMac to pull out the hard drive.
Brett Zeppelin said:
Lots of cooks in the kitchen here
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No problem!
when it comes to the magnet issue, so I'll just add a little nugget but with it simply being something to consider.

What about mounting the magnets on the vertical walls of the control cavity? You could then mount the opposing magnets on the cover and have them inset way inside the perimeter so they line up.
Click to expand...
Interesting idea. I think you're talking about bar magnets? Not sure what you mean.
 
#352
pilotjones said:
No problem! Interesting idea. I think you're talking about bar magnets? Not sure what you mean.
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Well, what I mean is any type of magnet that could be mounted to the walls inside the cavity. I would think something that is a bar shape would make the most sense since you'd have a flat surface any way you looked at it. To visualize, take your recent rendering. Imagine that 9V battery you drew is a actually magnet instead. Something like that, in three or four places around the cavity walls. The topmost surface of those magnets would be level with (or slightly below) the cavity so that the cover could still sit flush. The magnets on the cover would align to those cavity wall magnets.
 
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#353
@magnets... Yes, your're right... if they don't actually touch their power is much less. If it's a priority for you that the magnets are invisible on both the bass and the cover, and you cover them with veneer, I think the number of magnets you have modelled is fine.

@Shielding... It's not critical. Actually copper does not shield well against low frequencies. Copper is just used because it's soft and easy to get into the shapes we need, and it's easy to solder on. So already by using copper the shielding is less than perfect. (Mu metal would be a much better shielding, but it's harder to shape and it's very difficult to solder on). Often when doing low freq shielding (of electronics) it's enough just to use a ground plane on the circuit board meaning just a ground on one side. In this case that could be just to have a ground plane at the bottom of the cavity - nothing more. I'm not saying that you should shield as little as possible, I'm just saying that it's not that critical when working with low freq. So if you shield the cavity bottom and sides with foil, and then do one piece of foil at the underside of the cover that just fit's inside the cavity you should be more than ok.

@A bit more on shielding... I have repaired numberous instruments for friends who had hum. They had then tried to install several layers of foil etc etc, but the problem has in all cases been the ground connections. It does not help to have a shielding if there is no ground connection, or if the ground connection has bad solderings etc etc. Related to your set-up, the important thing will be to have effective ground between the cavity ground and the underside of the cover ground.
 
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#356
IntrepidCellist said:
To be fair, though, I'm not exactly sure *why* the magnets have to be covered by veneer. The control cavity, and cavity cover, will cover them from external view anyway.
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He does not want the magnets to be visible... I would not even think that magnets hidden behind a cover would be a ''visual problem'', but that's just me, and I don't do work on this level so close to perfection...
 
#357
Brett, I see what you mean. A different idea, but I'll stay with disks since they're already ordered.

Why cover them? Just more elegant/understated. Plus people wonder where the screws are. :)

Actually I'm looking at having the magnets exposed on the body, and hidden on the cover. When I tested I found that going through one layer of veneer was ok, but I didn't like the effect with two. Also I think any patch I would do there, matching or contrasting, would be no better looking than the magnets themselves.

Lisa, I thought about holding the battery with a magnet, too. It's an interesting way to do it. Electrons flowing through a magnetic field would be deflected, per the right hand rule--but I don't think it would have any significant effect. Hmmm. I've got some nice little 1/8" cube magnets, four of them at the corners might do the trick nicely. Or two discs.
 
#359
pilotjones said:
Lisa, I thought about holding the battery with a magnet, too. It's an interesting way to do it. Electrons flowing through a magnetic field would be deflected, per the right hand rule--but I don't think it would have any significant effect. Hmmm. I've got some nice little 1/8" cube magnets, four of them at the corners might do the trick nicely. Or two discs.
Click to expand...

I've noticed that every time I put a battery in one of mine or move it for some reason it usually gets pulled to the magnets near it. They'd probably keep it in place nicely.
 

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