"Scalloping" The BOTTOM of Electro-Acoustic Saddles

BillDL · October 2021

I have a strong feeling that this question might attract a few strongly differing opinions, but I am keen to see what others think.

All the electro-acoustic guitars with under-saddle piezo transducer strips that I have bought new and 2nd-hand over the years have had saddles with flat bottoms EXCEPT for one that I bought new and sold again. That guitar had the flat brass looking piezo strip with segmented rectangles visible rather than the type made from an oval or round piezo cable. The artificial bone substitute saddle on that guitar had shallow arches cut into it in between where the strings make contact on the crest on the top, so it was like a long railway bridge with shallow arches and solid piers or buttresses. The arches were VERY shallow, but would be just enough to sit above the piezo strip while the piers made full contact with it and the downward pressure of each string directly on top of each of the piers would be transferring differing amounts of pressure depending on the string tension.

Way back in the early to mid 80s I bought and fitted a Shadow piezo saddle that comprised a 2.3mm wide brass trough containing a piezo strip and individual plastic saddle sections, so it was similar in some ways to having material removed from the bottom of a solid saddle to give separate footprints on the piezo element for each string.

Conventional wisdom with a non-electrified acoustic is to have the saddle slot and the bottom of the saddle absolutely flat so that the saddle can mate perfectly with the bottom of the slot to maximise transfer of vibration. That wisdom should still be carried forward to a piezo-electrified acoustic in that the bottom of the saddle slot should continuously support the piezo element along its length. This is something that Dan Erlewine is emphatic about:

https://www.stewmac.com/video-and-ideas/online-resources/learn-about-guitar-pickups-and-electronics-and-wiring/acoustic-guitar-pickups-installation-problems-to-avoid/

As I was inspecting that saddle I first noticed arches on I could see why it might be a good idea to have a smaller footprint of each string's own vibrations on a piezo saddle strip, but the more I thought about it I couldn't see any sense in that because all the raw signals generated by the vibrations of all of the strings are merged into only one signal anyway.

When replacing plasticky stock saddles in some of my my electro-acoustics for Tusq or bone I replicated the arches on the bottom by filing into them a bit with a rat tailed file. The problem with knowing whether there is any perceptible improvement in the electrified sound of a saddle with arches on the base is that I didn't do a before and after test using the stock and UN-scalloped Tusq/bone saddles. The ones I did this for also have the thin cable type piezo element rather than the flat strip.

I now see that Graphtec sells what they call a "MicroBalance" Tusq saddle designed for use with under-saddle piezo pickups:

https://graphtech.com/products/tusq-microbalance-12-radius-saddle

Rather than oval or round arches it has square notches cut out of the base.

All they can say about it (and I see the web designer also has a dodgy "H" key that misses strokes like my keyboard) is:

"... allows you to fine tune he output for each string".

That lack of trumpet-blowing and lack of supporting data or testimony is unusual for something that is being marketed as an "upgrade". Kind of understated really.

How can you "fine tune" the output unless you are using separate piezo elements for each string and applying EQ or volume control on each before merging them into one signal?

What do others here think about notched vs flat-bottomed saddles in guitars with under-saddle piezo strips?

sev112 · October 2021

I thought it was to do with “balancing” the various frequencies of the 6 strings, so just one cable but different levels of each frequency can be caused / generated by inconsistent / different contact stresses.
but I’ve never thought about it any more detail than that.
my only experience of anything like it was when after changing some strings I couldn’t get the tuner to work on the top 2 strings, so I loosened them all off again and made sure the saddle was seated properly on the piezo strip, and then when tensioned the strings up again they all all were picked up by the tuner.

im an engineer but not an electrical eng

BillDL · October 2021

When you describe it like that it does make sense. Different levels of different frequencies from each string but then blended - kind of like a cocktail made more acidic or sweeter by the addition or subtraction of a couple of components from the finished blend. It's impossible to see from the photos of the Graphtec "MicroBalance" saddle, but I wonder if those "bridge pedestals" are of fractionally different lengths so that some make "harder" contact with the piezo strip, or if they intend for end users to do that. I have had the same issue you describe quite a few times, and it invariably is caused by the round cable type piezo pickup being sideways in the saddle slot that is wider than the cable.

WezV · October 2021

Personally, I think its a fudge to get around the issues of making a perfectly fitting slot and saddle, but it is a fudge that works

Pressure is focused on certain points, not spread across the whole strip. The total pressure is focused on smaller areas ensuring the good contact needed for piezo to work Differences in string tension/pressure at the top are evened out on the notched edge underneath. It probably also helps the saddle distort to fit with something like tusq

WezV · October 2021

I picked up this book the other day after it was mentioned in the acoustic section
https://www.amazon.co.uk/gp/product/1912677059

Here is the snippet on piezo imbalances

BillDL · October 2021

I think you're right Wez. An aftermarket saddle made to compensate for poorly fitting parts. While you were posting I found a guitar-related forum where somebody was asking about a thinner sound from some of the strings. Somebody else mentioned a fudge method of smearing a thin later of superglue on the bottom of the saddle in the area where the strings were thin sounding, or inserting one or more tiny bits of paper on top of the piezo element in that area to add thickness and allow the saddle to press down more on the element. The notches would certainly allow a small amount of flexibility, and therefore artificial levelling out, with an otherwise stiff saddle, and that's something I hadn't really thought about.

WezV · October 2021

the book also talks about the way saddles are shaped in the factory, and suggests the sanders used create a slightly concave bottom on many saddles, giving better contact on the outer strings.

If you swap one of those for a notched saddle giving 6 points of firm contact, you would notice a definite improvement. The graphtech solution will likely give a noticeable improvement for a lot of people

Keefy · October 2021

I once had a Godin Acousticaster that suffered very poor string balance. The top E string was particularly quiet. Based on online advice I rolled a thin flat strip of self-hardening clay, laid it in the saddle slot and refitted the saddle and strings. This evened out the string balance but I had to shim the neck to compensate.

This method worked by forcing the clay to fill the space between bridge slot and saddle. The method described by the OP seems to give the saddle just enough flexibility to make good contact with the bottom of the slot under each string.

BillDL · October 2021

Thanks for that info Wez. I hadn't refreshed the page to see your additional posts referring to the book. I've heard the author's name mentioned, but I can't be sure where and when because I have read a lot of books of that nature. So he mentions cutting away the area right below a string to reduce the contact pressure. The pre-notched Graphtec saddle would allow for this by shortening that "leg", but I think it would be a bit like giving somebody a haircut for the first time, i.e. "whoops, I took off too much there so I'll have to take off more all round .... whoops ....".

It certainly confirms that it could be a useful fix for problematic setups and perhaps even an improvement on good setups. Self-adhesive "metal tape" is mentioned to pack out the depth in a small area. That doesn't compress like bits of paper might, and I would guess that the self-adhesive backing on copper screening foil is probably pretty thin. I used to use the smooth sides of Fray Bentos pie tins as partial saddle shims because it is very thin and easy to cut accurately into strips with an old pair of scissors and tap flat with a fretting hammer, but it would be too thick for piezo saddle setups.

I wonder how they sand the saddles in factories. I always have to be very careful with consistent hand sanding motions or I end up with a convex curve on the bottom.

BillDL · October 2021

Hi Keefy. It's a strange coincidence you mentioned clay, because I was just pondering the best way to check for evenness of a saddle slot without having a Dremel router base to skim a narrow bit across its surface. One of my Yamaha electro-acoustics has the same issue you describe, but with the low E. I was just wondering if I could check the base of the slot accurately enough with a digital vernier in "plunge" mode and had a thought about somehow making a cast. The modelling clay would be a good packing agent because it dries very hard.

Keefy · October 2021

I suppose the best way to create a flat-bottomed slot would be with a router working from a known flat surface.

ICBM · October 2021

Personally I think it's a bodge, but I have resorted to it sometimes when with a saddle that I've made perfectly flat, there's still a balance problem. It can be tricky to get right even then, and you can get into a real rabbit hole of chasing the problem around. At the end of the day I've always found the *best* balance is with a perfectly flat saddle slot floor and a perfectly flat bridge, but getting the slot floor flat if it isn't already machined like that from the factory is tricky.

Actually, at the end of the day I've always found the best solution is to remove the piezo, throw it away as far as possible, and replace it with an internal contact pickup or a magnetic soundhole pickup... but that's not always an option unfortunately

.

Funkfingers · October 2021

I avoid piezo undersaddle transducer problems by not using 'em.

My preferred solution is an internal microphone à la L.R. Baggs. My friend and musical collaborator likes the Taylor system.

One of these days, I'd like to try the Baggs i-Beam doobrie to determine whether it is up to snuff.

For parts that will sit in the background of a mix, Roland VG99 modelled acoustic guitar sounds sometimes suffice.

BillDL · October 2021

I suppose if I was making a living or even earning from playing acoustic guitar I would be inclined to justify the expense of the internal microphone kit, but I am not and will have to live with piezo and external mic for now.

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"Scalloping" The BOTTOM of Electro-Acoustic Saddles

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