The subject of bass regulators and hollow stocks came up in conversation the other day (while we were drinking tea and musing over the state of the colonies) and it was mentioned that bass regulators can do damage to the stock over the years, plus it can dampen the resonance of the hollow stock. Is this true?
DavidG
Any mass added to a vibrating body will lower the frequency of vibration of the entire body. However, like drone reeds, if you added enough mass, maybe the stock would pick up the next harmonic and take off with it. If the wall thickness is thin enough that the stock can vibrate in a localized area, and project the vibrations, the added mass may cause some loss of “buzz”, but probably not noticable to anyone more that a couple of feet (~.6096m 
) away. The reeds would still benefit from being in a common chamber, as far as the frequency locking aspect.
dave boling
Geek-at-large
Thanks Dave, my thoughts pretty much are in line with what you say, but it’s good to have the confirmation of a geek-at-large Have you ever seen damage done to a hollow stock caused by a bass regulator?
DavidG
I’ve seen it, and certainly the hollow Kenna stock in SRS v2 had considerable (repaired) damage from the bass bar (which did not appear to be original).
I think it should be possible to attach a bass bar safely to a hollow stock[1], but not with the usual screws or bolts, something that puts less stress on the timber would be better.
Bill
[1] I mean the cylindrical thin-walled sort of hollow stock, as opposed to the various “chambered” types of hollow stocks.
If you are making a hollow stock, and think to do it before the “top” is glued on (or make a screw-on top if you really want to get involved on the lathe), you could through-bolt the bass regulator plate to a matching plate on the interior of the stock. This would spread the loads imparted to the bass regulator to a much wider area. Of course, some punter at a session could send the whole set flying with the reg attached like the handle on Scottish throwing hammer 
dave boling
This is along the lines of what I’ve been thinking; with glove-leather linings inside and out. Both plates would be machined to match the inner and outer diameters of the stock, respectively.
Hi Bill. Yes, that is what I had in mind as well. When I think about how little anchorage there is for such a long pipe, particularly with staight separator bar, it is conceivable how over the years any minor twisting (ie see-saw/teeter-totter) action, up and down lengthways of the regulator could eventually cause damage at the anchor. Perhaps as well as the two plates that you and Dave talk about, another anchor further along somewhere (but where?) could help? Dunno.
The one reservation I would have in putting a metal plate on the inside relates to what David Quinn has said regarding metal tubing (in bass drone bends). The wood will shrink over time, and if the metal constrains it from shrinking in one direction (toward the middle of the circle), it will shrink in another direction, i.e. draw apart/split. Considering that wood shrinks at different rates according to species, and grain direction, if you oriented the wood in the stock just so, it would delay the inevitable somewhat. If you’re really worried about the stock failing, I’ll turn you one from aluminum that will take (or give) a good beating. We could even get it anodized in your choice of bright colors. 
dave boling
The difference is that the plate would only span a small fraction of the circumference. Wood has a good bit of flexibility in that direction (i.e. towards ovality in any direction), so the resulting tension stress would be very very small compared to the situation where wood is constrained to fit over metal with “nowhere to go”.
In other words, it shouldn’t be a problem because as the wood shrinks, it’s free to move against the leather gaskets, provided the bolt holes are oversize enough to allow for wood movement.
Bill
Perhaps as well as the two plates that you and Dave talk about, another anchor further along somewhere (but where?) could help? Dunno./
along with increasing the tenon depth of the bass regualtor, this is a good idea if you are trying to stabilize the “arm” of the bass regulator - you’d have to make the plate much larger (longer) or install two plates that connect the bass bar to the stock - at points as far apart as possible. looking at my D stock right now, of the 5 1/2" of “usable” surface, only 2 1/2" is covered by the plate, at the back, with the setting screws about 2" apart. with a second plate - or a single, longer plate, this setting distance could be doubled to 4" - even more. this would greatly increase the “fixity” of the connection. in my case, i think the connection could be made stronger by simply moving the same plate down the stock 3" or so - reducing the moment arm of the regulator. measured from center of plate to the lowest keypad, this reduction would be nearly 1/3rd.
the double plate idea - shaped to fit, inside and out - sounds like it’d be much more stable than the standard single plate on the outside, but without making the connection larger (longer, along length) the resolution of all mechanical forces are still concentrated to the same small area of wood, in the end and the results might be the same - after a few decades.