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:
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:
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?
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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
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
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https://www.amazon.co.uk/gp/product/1912677059
Here is the snippet on piezo imbalances
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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
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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.
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 .
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
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.