Double Bass That VooDoo that You Did??

[Don Kasper]

I recall hearing (in the mid 70's) of Kolstein's shop re-graduating the tops of basses by taking the top off, inverting it, and sprinkling sand (or sawdust?) on the inner surface, then vibrating that top at certain frequencie(s) and observing the sand-patterns that showed during the vibrations. They would then re-graduate the top, removing some material, and re-vibrate, repeating the process as necessary.
I never heard too much about the results, one way or the other. Have you?
(Also, I don't recall ever dropping Acid during this period, but I could be.....)
Anyone?
Thanks, in advance.
Edited: to include "...sawdust?".

 

[Don Hergert]

It probably requires a special sand. If you want to try this I have lots of cat-box sand you can borrow... Some of it might even be slightly used.

Just sayin'

 

[Don Kasper]

If you want to try this

NOOOOOOO!
Thx.

 

[GretschWretch]

It probably requires a special group to vibrate the sand. Something like the Sandpipers.

 

[GretschWretch]

It probably requires a special group to vibrate the sand. Something like the Sandpipers.

 

[Don Kasper]

It probably requires a special group to vibrate the sand. Something like the Sandpipers.

You disappoint me GW....I was expecting this:

 

[ardgedee]

The inside surface would be dished, right? The sand would all collect in the middle and maybe bounce a little.

 

[GretschWretch]

You disappoint me GW....I was expecting this:

It's a question of emphasis, Don. I was focused on the sand; you, on the vibrations. If Kolstein had had a calligrapher on staff at the time, s/he could have written love letters in the sand.

 

[Don Kasper]

The inside surface would be dished, right? The sand would all collect in the middle and maybe bounce a little.

My understanding (at the time) was that it would still make or reveal some sort of "pattern" that was related to the frequency of the induced vibration...and the structure of the top plate.
I was not there, FYI.
Thx.

 

[Don Kasper]

It's a question of emphasis, Don. I was focused on the sand; you, on the vibrations. If Kolstein had had a calligrapher on staff at the time, s/he could have written love letters in the sand.

Tomato/Tamahto, I guess.
Thanks?

 

[Don Kasper]

The sand would all collect in the middle and maybe bounce a little.

Hmmmm. Maybe it was not sand, but sawdust or a lighter substance.
Good point.
Thanks.

 

[Don Hergert]

Ok, no more cat box humor...

Seriously, I wonder if this would be better done with the back off, keeping the top attached to the sides so it would keep most of the top's playing geometry and contour. Cover the F-holes with tape to keep the sand in. Also wouldn't need to dismount the neck from the neck block.

Then just need a huge variable tempo vibrating table.

I do also wonder if there isn't a more reliable and traditional method for this kind of work.

 

[Don Kasper]

I do also wonder if there isn't a more reliable and traditional method for this kind of work.

Yeah...I'm just posting asking if anyone remembers Kolstein's shop offering this service and using this method.
As I recall, some Pollmann basses were Over-Engineered, and needed top-thinning/re-graduating.
Just askin' about the Kolstein connection - not exploring other methods.
Thanks.

 

[Brent Nussey]

https://www.benningviolins.com/reference/violinmaking-and-chladni-patterns.html

Ernst Chladni - Wikipedia

en.wikipedia.org

CAS Forum Home Page

Chladni patterns are probably what you’re talking about. A woman named Carleen Hutchins was very involved in their use in violin making. Whether Kolsteins used this, I don’t know, but they were talked about as having regraduated a lot of tops

 

[Don Kasper]

https://www.benningviolins.com/reference/violinmaking-and-chladni-patterns.html

Ernst Chladni - Wikipedia

en.wikipedia.org

CAS Forum Home Page

Chaldni patterns are probably what you’re talking about. A woman named Carleen Hutchins was very involved in their use in violin making. Whether Kolsteins used this, I don’t know, but they were talked about as having regraduated a lot of tops

YES! this sounds familiar.
Thanks for your informative reply.

 

[bass player 53]

It’s been brought up on TB before that violinists either prefer new instruments to very famous ones, or they can’t tell the difference.

Marcus du Sautoy explores the symmetry of Stradivari

 

[micguy]

Chladni patterns (we did this in school) with sand require a very flat, level surface to avoid having the sand all run off or collect in the low spots. Nowadays, assuming you have the budget for it, you'd do modal analysis with a scanning laser vibrometer, which works fine on a curved surface.

 

[DJ Bebop]

All I ever hear of was shaving the bass bar

 

[JKoehler]

When Hammond Ashley was mainly a bass shop, they would re-graduate overly thick tops on old German basses. The procedure started with removing the top, and then suspending it with string over a 15” heavy duty speaker. I’m not sure the wattage of the power amp that powered the speaker, but it was well over 100 watts. A tone generator was run through the power amp, usually set at A220 or A110. Glitter from an arts and crafts store was used to show the patterns. To excite the top, the power amp was cranked to bowl loosening volumes with the top suspended an inch or two above the speaker. Neighbors from blocks away could hear the low rumbles coming from the shop.
I’ve worked on some of those basses, and whenever I play an open A, it rattles the shop floor.

 

[ole Jason]

Using Chladni patterns is somewhat common in the building of ouds. It seems to be preferred over modal analysis in some cases. Cool stuff!

http://emirdegirmenli.com/en/musical-acoustics/chladni-patterns/