Longer Scale Axes: Flat Top vs. Induced Arch vs. Carved Arch

**Ed Goist** · Jun-10-2012, 8:59am

Bill, actually I am really enjoying all the thought-provoking discussion here.
One thing I'm getting out of this is that there does not seem to be a clear demarcation between 'flat-top' and 'archtop'. For example, at what point (radius) does it become appropriate to call an instrument an archtop (20', 17', 15', something else)? Or, should the term archtop be reserved for carved instruments only? From a consumer standpoint I think this is an important question.

**Jim Garber** · Jun-10-2012, 10:11am

Yes, definitely a derailment...

**Tavy** · Jun-10-2012, 11:10am

Originally Posted by Ed Goist

Bill, actually I am really enjoying all the thought-provoking discussion here.
One thing I'm getting out of this is that there does not seem to be a clear demarcation between 'flat-top' and 'archtop'. For example, at what point (radius) does it become appropriate to call an instrument an archtop (20', 17', 15', something else)? Or, should the term archtop be reserved for carved instruments only? From a consumer standpoint I think this is an important question.

Normally only carved top instruments are referred to as "arch op", but the line does get blurred when dealing with pressed tops....

**foldedpath** · Jun-10-2012, 12:00pm

Originally Posted by Ed Goist

One thing I'm getting out of this is that there does not seem to be a clear demarcation between 'flat-top' and 'archtop'. For example, at what point (radius) does it become appropriate to call an instrument an archtop (20', 17', 15', something else)? Or, should the term archtop be reserved for carved instruments only? From a consumer standpoint I think this is an important question.

Speaking as a consumer (and with only enough knowledge about construction to be dangerous), I think there is one bright line of distinction between "flattop" and "archtop" as descriptions. It gets muddied with the bent/induced arches, but I think this is the main dividing line:

A "Flattop Mandolin" has a a uniform top thickness, usually with additional bracing underneath, more or less like the way a flattop guitar is built.

A "Carved Archtop" mandolin has a top plate resembling that of a violin, with (usually) some recurve or thinning near the edge, and (usually) a thicker center section. The thickness is not uniform in cross-section: it's more like a violin plate, not a guitar top.

To me, those are very distinct categories. Each is represented by a large number of existing mandolins, and the tonal differences are usually fairly obvious.

As we've seen in this thread, there are many different ways to split the difference and make an "arched top" from single-thickness wood plates that are bent with steam, or induced into arches with bracing or edge-stress, or glued from tapered plates.

It gets even more complicated if you include the different methods of loading the bridge, whether it's a glued bridge where the strings terminate and cause a twisting force to apply vibration, or the top-down force of a floating bridge and tailpiece.

As long as the description "Carved Archtop" is reserved for mandolins with a violin-type top plate, I think we'll know what we're talking about. "Archtop" used alone can mean anything, and needs further elaboration in the description.

**nkforster** · Jun-11-2012, 3:25am

Originally Posted by Bill Snyder

Like I say, I don't know how they did it. I do know that Paul Hostetter and I believe Rick Turner have both stated that they think they were steam bent or pressed into shape.
Given their credentials and the fact they have both had several in hand I am inclined to think they might know what they are talking about.
Jim your posted photos really show the sharp transition of the hump very well.

That seems fair enough to me, the thing is, we can't know how they were made unless we worked for Howe-Orme at the time or have spoken to an employee. And as Howe-Orme were around along time before any of us were even thought of so we are left with observation, and experimentation, opinion and speculation, informed or otherwise.

Now I know Rick Turner has quite a collection of these things so his opinion is certainly to be considered. I don't know how many he has made but I've read in an interview that he'd love to build them.

I only ever saw one - a guitar (oh, and I wish I'd bought it!) but it made quite an impression on me, as a result I've made many instruments in this style too.

So steam bent or pressed? Wether you steam bend or not, you do have to press. Well, mine are pressed. Without steam. When you take a soundboard down to 2mm as I do for these instruments it takes very little pressing to get the top to conform between the fitted struts and the curve in the former. How much do I have to press? I asked Rick Taylor a few years ago about the depth and build accordingly. To some extent you are limited not by the willingness of the spruce, which will bend to a surprisingly tight radius but by the depth of your bridge blank! After all you have to fit the underside of the bridge to the curve and if you go too far you run out of height.

It's possible steam may have been used, it's just my experience tells me it's not required.

I'm actually in the process of writing my second guitar book, and this one is all about making cylinder top guitars. It's a design that is very closely related to the way in which Sobell instruments are made (I worked for Stefan for many years) and it's a design I've explored quite a bit recently - most of my orders for "flat top" instruments are now made this way. Stefan was totally unaware of the existence of Howe-Ormes when he developed his guitar design, and to the casual eye they look VERY different, but in principle there are many similarities, it's just that the execution of the principle is different. Fascinating stuff - for the likes of me anyway!

Anyway - this is how they tend to come out - enjoy!:

n

http://www.nkforsterguitars.com/nkfo.../the_book.html

**Bill Snyder** · Jun-11-2012, 10:28am

Well no matter how Howe-Orme did it your way certainly seems to work well. That thing rings forever and your workmanship appears to be top shelf.

**gypsy1** · Jun-13-2012, 11:59am

I build my instruments with an induced arch, this arch is also thinned from the top side, (similar to Brian Dean's, as mentioned by Otterly). The top is left thicker in the middle and thinned towards the outer edges. The combination of tension and thinning increase the instrument response and adds to volume/projection.

I do not pretend to be simulating a carved top instrument, the principles are entirely different as are the tone and instrument response.

The point I, along with other induced arch builders in this thread are trying to get across is in my opinion, there are several tops used consistantly in western stringed instruments.

Dome: like acoustic/classical guitars
Cant: mandolin, Greek bouzouki, etc
Arched: induced or shaped
Carved: Violins, etc. and some mandolin family instruments

Walt

**Jim Garber** · Jun-13-2012, 1:26pm

Walt: What is the difference in construction between "dome" vs. "arched"? Wouldn't a pure induced arch (no additional thinning of the top) be the same as what is used for acoustic guitars?

**gypsy1** · Jun-13-2012, 2:13pm

If you look at the traditional variations of Torres style bracing, (fan w/cross bracing), no. The dome is slight and directly beneath the bridge and created by the fan style bracing, which is below the cross brace at the soundhole.

The induced arch uses variations of X style bracing, single, double, triple and oddities lattice.

Walt

**Jim Garber** · Jun-13-2012, 2:31pm

It sounds like the principle is the same but the specifics of the application change. In other words, the shape and configuration of the bracing determines the shape of the top. Correct?

**gypsy1** · Jun-13-2012, 4:07pm

The shape and configuration of the bracing does determine the shape of the top, hence arched, not to be confused with carved.

We who arch the tops on our instruments are tuning it by adding tension for both tone and volume, to understand this a bit clearer, think of the instrument like a drum head, you tighten it to tune it.

It is really quite different in principle than the variations of ladder style bracing found in classical guitars and cant top instruments

Walt

**Jim Garber** · Jun-13-2012, 4:22pm

Interesting, Walt, however, my experience with cant top mandolins is that there is still, however slight, a longitudinal arch. I know this from trying to fit a bridge to the top. In fact I would think, esp for instruments with tailpieces and movable bridges that the downward pressure would, by necessity, require some sort of arching to counteract that pressure.

I will have to take a look at the bracing on my Brazilian bandolim and see how they do that particular instrument.

**gypsy1** · Jun-13-2012, 6:28pm

That is correct Jim, my point is the classical and ladder style bracing though having a slight arch is not serving the same purpose that an induced arch is, similar, but not the same..The induced arch in my opinion inhances volume and tone.

So many ways..all good..

**NG53** · Jun-13-2012, 10:14pm

I agree. An induced arch gives the instrument more volume and perhaps a drier sound. My Paddy Burgin bouzouki has a very slight induced arch to give it strength. The induced arch on it still gives lots of clear trebles but it gives the trebles a deeper bell-like sound.

**Jim Garber** · Jun-14-2012, 8:26am

All right... so at what point does a slight arch become an induced one? Can you measure the radius of your induced ones? I know your instruments certainly sound lovely. Not to belabor the point... but technically aren't the arches induced by the braces in all cases and the difference is largely a matter of degree and the use of different bracing patterns to create different tonal characteristics?

**gypsy1** · Jun-14-2012, 9:29am

At the point when it eclipses structural and becomes tonal...hence the common term 'flattop' vs. 'induced arch'.

The truth is ALL arches are induced, carved or not, it is a method of tone and strength. One induces an arch from a block of wood or forms it to a frame.

**TijnBerends** · Jun-14-2012, 1:07pm

Originally Posted by nkforster

I'm actually in the process of writing my second guitar book, and this one is all about making cylinder top guitars. It's a design that is very closely related to the way in which Sobell instruments are made (I worked for Stefan for many years) and it's a design I've explored quite a bit recently - most of my orders for "flat top" instruments are now made this way. Stefan was totally unaware of the existence of Howe-Ormes when he developed his guitar design, and to the casual eye they look VERY different, but in principle there are many similarities, it's just that the execution of the principle is different. Fascinating stuff - for the likes of me anyway!

I'll be sure to buy that book when it comes out

I really like te first one, for the information as well as the stunning pictures it has. I'd never heard of Stefan Sobell before, had a look at his website and I can recognize much from your instruments in his!