So maybe you don't need glue - Cohen Content

**fatt-dad** · Sep-08-2010, 9:29pm

Just showing what Dr. Dave is up to; an engleman spruce, maple, carbon fiber mandolin (neck) with a screwed on top and back. He's using it for research and let me take a photo. Wonderful sounding mandolin. There is a companion neck that he can also interchange, the companion being the more conventional maple with CF reinforcement.

I just love his work and study. Fun to visit too!

f-d

**Folkmusician.com** · Sep-08-2010, 9:42pm

That is cool!

**F-2 Dave** · Sep-08-2010, 9:50pm

Cool. Wow, that bridge looks tall. Is it one of his designs?

**fatt-dad** · Sep-09-2010, 7:11am

Yes, Dave makes his own bridges and they are very light weight. It may be some perspective on the photo, but it's not tall when the instrument's in hand.

**farmerjones** · Sep-09-2010, 7:40am

judging by the deployment clasp, is that a daytona?

**fatt-dad** · Sep-09-2010, 10:03am

No, I'm wearing my Belair, which is a couple-hundred dollar, Swiss analog quartz. On par with a Swiss Army watch. Comfortable watch though.

Mandolins, guitars and watches - got a few. Big gaudy rings - only got one of those.

f-d

**Willie** · Sep-09-2010, 11:00am

In some real old copies of Frets Magazine Siminof told about a mandolin that he built with a removable top so he could try tops made out of different kinds of wood...I wish I had kept all of those old copies so I could go back now and read some of the things that were being tried back in the `60`s.....If Roger posts on here maybe he can chime in and tell us all about it....Willie

**Ivan Kelsall** · Sep-09-2010, 11:20pm

Well darn me !. In a thread in the 'builder's' section re.experimental tops / back,a while back i put forward the idea of a removable top & back & asked if anybody had done it. John Hamlett chipped in & said that a certain builder (can't remember who) had actually done something like it - & here we are,the full blown edition - brilliant !!,
Ivan

**Bill Snyder** · Sep-09-2010, 11:26pm

Mario Proulx has also done something like this. I don't remember if the top and back plates were both removable or just the back, but he has mentioned it in some previous threads here and possibly at the MIMF as well.

**fatt-dad** · Sep-10-2010, 6:47am

Just to point out, the neck is bolted on also, without any glue.

f-d

**Dave Cohen** · Sep-10-2010, 7:49am

I built what Fatt-dad calls "opus I" back in 2000-2001, and that is the mandolin to which John Hamlett was probably referring. It has a redwood top plate and eastern black walnut back/sides/neck. The back plate of opus I is held to the body with 60+ #2x3/8" wood screws. I finally got around to doing the experiments for which opus I was intended in early 2005. In Rossing's lab at NIU, I did a series of holographic modal analysis experiments, followed by sound and accelerance spectra, on the opus I mandolin with four different bracing patterns. The mandolin started out with "tone bars". After doing the holography and spectra, I added a Virzi thingy made from the GAL drawings (done by Ted Davis) and repeated the experiments. After the Virzi iteration, I carved out the bracing and put in an X-brace a'la Gilchrist, and again repeated the experiments. The last iteration was my "wacky braces".

The mandolin sounded the same to my ears regardless of the bracing pattern. That will have to remain an anecdote, though, as I did not do any objective auditions with numerous listeners, and my own auditions of each iteration were 24 hrs apart. The holography and spectra, on the other hand, were legitimate data. The differences were small, as I have posted many times here on the 'Cafe. Imo, the experiments and my own audition corroborated each other, supporting my contention that mandolin bracing patterns have at most a small effect on the sonic qualities of the instruments. That made sense with the hindsight of Meyer's two 1983 papers. One of Meyer's conclusions was that differences in the exact positions of classical guitar braces did not make a noticeable difference in the sound of the guitar. He had numerous knowledgeable auditioners listen to the various iterations of classical guitars in 'blindfold' listening tests, and among other things, they were not able to observe any sound differences attributable to the positions of braces.

To clarify just one thing in Fatt-dad's description, the companion neck for "Opus II', above has a conventional adjustable steel truss rod, but no CF composite reinforcement.

http://www.Cohenmando.com

**Markus** · Sep-10-2010, 8:06am

Thanks for that detailed post, Dave ... some of us are new around here and it's great to have you help catch us up.

**M.Marmot** · Sep-10-2010, 8:45am

Originally Posted by fatt-dad

Just to point out, the neck is bolted on also, without any glue.

f-d

That reminds me of those instruments made by the Turkish company Cumbus, where they manufacture different necks, Guitar/Bouzouki/Banjo/Oud/Mandolin which can all be attached to their standard instrument bodies... kinda neat-o

**Rick Turner** · Sep-10-2010, 11:41pm

The Cumbus is also a nice rice cooking pot in an emergency. I wouldn't want to try that with one of Dave's mandos...

Hmmm, got to get my Cumbus back together.

**Paul Hostetter** · Sep-11-2010, 12:38pm

Originally Posted by M.Marmot

That reminds me of those instruments made by the Turkish company Cumbus, where they manufacture different necks, Guitar/Bouzouki/Banjo/Oud/Mandolin which can all be attached to their standard instrument bodies... kinda neat-o

Also reminds me of Martins and Mozzanis and Howe-Ormes and, for that matter, lots of American banjos, all of which predated the cümbüş.

**Jim Rowland** · Sep-11-2010, 4:29pm

Paul,is that top image of the "clock key" system which allowed the action to be adjusted by changeing the rake of the whole neck?
Jim

**Paul Hostetter** · Sep-11-2010, 5:17pm

Yes, they're all three variations on a theme, much like the cümbüş. And as with banjos, the necks could be removed and swapped if anyone wanted. Primarily they were about adjusting neck angle though.

Here's a cümbüş violin I made for a guy a few years ago.