Bridge height

[Brian Baker]

(Please bear with me on this fairly lengthy post...)

On my 15th anniversary vacation, I snuck off to the Bluegrass Center in Asheville NC and sampled their mandos... Played an F9, two F5Gs, a Weber Gallatin, a Weber Bitteroot, an Eastman 615, an Eastman 605 A-style, and a Morris F5.

Big variety in volume and tonal quality, as expected, but an odd thing that I noticed was the great variety in bridge heights. All the mandolins were set up for reasonable action, but in order to achieve that action, some of the mandos had the bridge wheels cranked up so high it looked like the top half of the bridge would fall off!

One of the F5G's (which I thought had the best sound of any mando in the store) had the bridge way up high, and tilting. Then I noticed that in this case, the top appeared to have sunk a bit. Myself and another mando player in the store brought it to the attention of the staff, and suggested they have the boys at Gibson take a look at it.

So I understand that due to the apparent top sinkage, this mando needed the bridge cranked way up. But a couple of the other mandos were this way as well. And my personal A9 has the bridge down almost all the way, and the strings are not close to buzzing.

So my questions (finally!) are:
1. What factors affect the bridge height necessary for "decent" action? My guess would be it is mainly related to the neck angle and the amount of arch in the top.
2. Do neck angles vary a lot much from maker to maker? And from instrument to instrument?
3. Is a high bridge height always associated with higher string tension, and thus more volume? If so, is it best to find a mando which, when set to a low action, still has a high bridge setting?

Alas, my brain is all a-flutter with questions... Any help from the experts would be greatly appreciated!!!

Thanks
Brian

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[Fretbear]

IMHO:
1: Yes, those two things.
2: Yes, for instance the '25 ferns produced after the Loars ended up with a shallower neck angle, some say because the worn out carving template was changed, and some players (like Jimmy Gaudreau) had their neck joints "shimmed" by as much as 1/8" to create more bridge height.
3: Generally, yes, but there is also more to it than just volume; tone, playability and feel are also to be taken into account &
Yes, I personally prefer an "easy" action, with enough bridge height to play "plenty" loud when required.
Also all bridges are not created equal; Steve Smith of Cumberland Acoustic makes and sells high quality Loar style bridges with options such as a "Tall-Boy" for mandolins that require a higher bridge, and so you don't run out of post-thread.

[AlanN]

I had a Duff F-5 with the neck angle so severe that the bridge needed to be sky high just so the strings could clear the frets.

[GTison]

2. yes from instrument to instrument. When I went mando shopping (wheather right or wrong) I was looking for a higher bridge setting while having good action and adjustability (up or down). I played about 15-20 new Gibsons of various models, about 6 Collings and about 15 or 20 other makers like Webber, Horner, Rigel etc. There was lots of variation between brands. Even within the Gibsons there was variation of maybe 1/8-1/4 inch in bridge height.
Your comment about the G having a collapsing top made me think of some of the Gibsons I have seen had the peak of the arch of the top was back of the saddle. This seemed odd to me, but I have seen it more that once and on other mandolins besides Gibson. It can make the top look like it is sinking.
I'm not sure what the average height of the Loar bridges were as compared to the post Loar "fern" bridges. It'd be interesting for someone in the know to compare and contrast that.

[VernBrekke]

When an instrument is built, the main factors that determine bridge height are the neck angle and the height of the fretboard from the body of the instrument.

After the instrument has been sold, humidity changes can be a significant factor in either direction for the bridge height depending upon the characteristics of the top wood. Even wood of the same species can have very different characteristics for soaking up water.

A sinking top will also affect bridge height. This can happen if the neck angle has been set too high, the top has been graduated too thin or if the bracing is inadequate. Usually a combination of all three. A high neck angle with a thin top and minimal bracing can produce an instrument that sounds great right out of the box. Unfortunately, it may be destined for a relatively short lifespan for the top wood. It's a challenge that every builder must meet in their own way. Standard graduations can get you into the ball park, but only an experienced luthier can pull the most out of each individual piece of wood. It's one reason why instrument making is an art.

Hope this helps,

Vern Brekke
Sound To Earth, Ltd.

[Moose]

Very informative - Thank you, Mr. Brekke - (ain't this CAFE great!!!) http://www.mandolincafe.net/iB_html/non-cgi/emoticons/mandosmiley.gif http://www.mandolincafe.net/iB_html/non-cgi/emoticons/laugh.gif

[Brian Baker]

Thanks for the great answers, folks!

The mandolin is a more complex beast than it seems at first glance!

-Brian