New designs for a diaphragm pickup (yet another ampeg baby bass thread)

[Steve Conner]

Titanium is a really light, strong and springy metal. It's roughly as light as aluminium, but as strong and elastic as steel. Seems like just the thing for making a diaphragm out of.

It's expensive too, but you wouldn't need much of it.

[xxxchange]

Where is "over here"? Please update your user profile to give the city and country, as it helps greatly when answering many kinds of questions.

Done, by the way, updated my real name... I don't give it away so easily, but I think this blog deserves that level of transparency.



I live in beautiful Alsace, by the German border, but -thanks to both WW and all their participants- now under French rule. Quite a beautiful place, especially if you were born in a big, dirty and grey city -as in my case-.

[Joe Gwinn]

Done, by the way, updated my real name... I don't give it away so easily, but I think this blog deserves that level of transparency.



I live in beautiful Alsace, by the German border, but -thanks to both WW and all their participants- now under French rule. Quite a beautiful place, especially if you were born in a big, dirty and grey city -as in my case-.

French food and German beer - good combo.

[David King]

Alsace wine and southern German food, not bad either..
I've made the train trip from Paris to Basel many times. Pretty countryside as you get closer to the border.

So instead of titanium, why not spruce and/or carbon fiber cast in a bowl shape? Pure Ti isn't very strong, only the Al4V6 alloy really has the characteristics you want. You'll probably want to experiment with other fibers like kevlar and spectrol to get the unique sound profile that fits the music. That said, spruce is a well understood material that's readily available.
Don't discount that fiberglass body as a part of the sound of the babybass.

[Bruce Johnson]

Don't discount that fiberglass body as a part of the sound of the babybass.

David, have you ever looked closely at the construction of a Baby Bass? The body is a thin clear plastic shell. It's about 1/16" thick, and is actually Uvex, which is like a Butyrate. The color of the instrument is painted onto the inside of the shell halves before they go together, and then it's completely filled with expanding urethane insulating foam. If there's any "tone" from the body it would be measured in milliseconds!

Running down the center is a 3' long piece of 2" x 2" x 1/16" wall aluminum tubing. The tang of the neck plugs into the top, the whole diaphragm pickup assembly bolts to front partway down, and the tailpiece and peg fit into the bottom. The acoustic structure of a Baby Bass is an aluminum tube surrounded by hard foam, a blend of ding and thud.

It could qualify as sophisticated engineering or cheezy construction, depending on your viewpoint

[Dave Kerr]

French food and German beer - good combo.

Stage Actress to George Bernard Shaw: "Oh Mr. Shaw, I think we should have a child together. With my looks and your brains our child would be the envy of all."

Shaw's reply: "Ye gods woman, what if it had my looks and YOUR brains?"

..

[David Schwab]

"A reasonable man adapts himself to suit his environment. An
unreasonable man persists in attempting to adapt his environment to
suit himself. Therefore, all progress depends on the unreasonable man."
-- George Bernard Shaw.

[xxxchange]

French food and German beer - good combo.

Well, actually I'm not very fond of German beer, it's too bitter -IMO-. There's one unfiltered one, hefeweizen, which is sort of acceptable -always my own personal opinon-, other that it's so thick you don't know if you should have it with a spoon.

It's not the beer man talking here -more like the red wine in my case- but the ones I like the most are Belgian. I've been to Brugge for a concert once, and the Belgians have some really tasty beer (and quite strong, also).

Moving to French food, well, certainly not bad at all, but overrated. I like France a lot, but if you go to Italy you can eat a thousand times better for the same price.

Anyway, I don't need anything too fancy looking for dinner. Having been born in Argentina, I'm used to eating meat twice a day, with only salt as seasoning... let's better change the subject or I'll get homesick.

[xxxchange]

Alsace wine and southern German food, not bad either..
I've made the train trip from Paris to Basel many times. Pretty countryside as you get closer to the border.

You really need to see the Alsatian countryside at least once, this place looks as if taken from a fairy tale. You take the wine route, from Riquewihr or Ribeauville northward, and you'll see really nice little towns that are almost untouched since many centuries past.

Regarding wine, I am completely surrounded by vineyards, beyond where my eyes can reach. People grow vines even within the town, in every little corner. Too bad their speciality is white wine. They have some reds too, but they are not like the stronger ones that fit my personal taste better.

So instead of titanium, why not spruce and/or carbon fiber cast in a bowl shape? Pure Ti isn't very strong, only the Al4V6 alloy really has the characteristics you want. You'll probably want to experiment with other fibers like kevlar and spectrol to get the unique sound profile that fits the music. That said, spruce is a well understood material that's readily available.
Don't discount that fiberglass body as a part of the sound of the babybass.

Thanks a lot for the tips. All that hi-tec stuff seems quite interesting. I heard there is an Australian guitar builder that uses carbon fibre to reinforce his lattice-style bracing.

Is all that stuff at the reach of a complete profane? If anyone knows where to get that stuff within the European market, please let me know.

Regarding spruce, that would be the most classical approach. The thing I don't like about it is that if you want a rugged instrument, a diaphragm of spruce, thin enough to vibrate, would be quite delicate.

[David Schwab]

I've been to Brugge for a concert once, and the Belgians have some really tasty beer (and quite strong, also).

I love unfiltered Belgian ales!

I just finished a Hoegaarden.

I like France a lot, but if you go to Italy you can eat a thousand times better for the same price.

Yes, Italian food is great. We ate at some great little places in Rome.

[xxxchange]

David, have you ever looked closely at the construction of a Baby Bass? The body is a thin clear plastic shell. It's about 1/16" thick, and is actually Uvex, which is like a Butyrate. The color of the instrument is painted onto the inside of the shell halves before they go together, and then it's completely filled with expanding urethane insulating foam. If there's any "tone" from the body it would be measured in milliseconds!

Running down the center is a 3' long piece of 2" x 2" x 1/16" wall aluminum tubing. The tang of the neck plugs into the top, the whole diaphragm pickup assembly bolts to front partway down, and the tailpiece and peg fit into the bottom. The acoustic structure of a Baby Bass is an aluminum tube surrounded by hard foam, a blend of ding and thud.

It could qualify as sophisticated engineering or cheezy construction, depending on your viewpoint

Yes, it's sort of an instrument designed NOT-to-resonate.

I have read somewhere that the thing of filling the hollow with urethane insulating foam was to avoid the dreaded feedback problem that any air cavity could produce. Since it seems they didn't pick the materials for their "nice sounding" qualities, it would be pointless to leave that air space within the bass.

That being said, the new baby basses, or copies on the original model, that are being built today in all the salsa-zone are mostly made of fiber-glass. I don't know if they still fill them with something, but I guess it's very likely.

You could reverse the original design principle and try to build an instrument with some resonances. It would be like a dobro baby bass, with the diaphragm doing some acoustical work, appart from driving the microphone.

But most people want the baby bass not for it's unplugged sound anyway, but for its ability to produce heart-stopping pops and warbles, in your words, that you can amplify at any sound level without the hassle of feedback. (People that would go through the hassle of amplyfing an acoustic instrument, they'll probably pick the traditional double bass anyway)

[David Schwab]

But most people want the baby bass not for it's unplugged sound anyway, but for its ability to produce heart-stopping pops and warbles, in your words, that you can amplify at any sound level without the hassle of feedback.

Nothing sounds like a Baby Bass.

No doubt that people that want more of a real upright tone can use something like an NS bass, but those don't do what the baby Bass does either.

I guess the body was cosmetic, huh? The bass was pretty much a metal pipe with a neck!

Is the bridge/pickup mounted to the pipe or the body?

[xxxchange]

Nothing sounds like a Baby Bass.

No doubt that people that want more of a real upright tone can use something like an NS bass, but those don't do what the baby Bass does either.

I guess the body was cosmetic, huh? The bass was pretty much a metal pipe with a neck!

Is the bridge/pickup mounted to the pipe or the body?

As far as I know, but Mr. Johnson would most certainly have a more definitive answer, the Baby Bass PU is mounted on a pentagonal shaped metal plate, I believe it's cast aluminium. All the "static part", the two coils and the magnet, are also attached to that plate (with a couple of screws that also adjust the "voicing" of the PU).

That plate, I believe, is bolted on the body of the instrument.

I didn't know of the existence of that pipe until Mr. Johnson brought it up.

[xxxchange]

Cancellation problems.

I have been doing some research on how the bridge vibrates.

It seems that the diaphragm pickups, as wired on the Baby Bass, rely on the two feet adding up, so in the case of one going up as the other goes down, destructive interference will occur.

From what I have seen on the web, on analysis of how an acoustical instrument vibrates, the main motion of the top plate, where the bridge is standing, is up and down. Rocking or lateral motion of the bridge might be present, but I guess it is not what sets the plate into motion. So as a whole the Baby Bass design seems adequate, in that it assumes that both feet will move sort of "together", and not one against the other.

I have found something that relates to this. I have been checking the book "The Physics of Musical Instruments", and it seems as if the two feet of an acoustic instrument bridge vibrate more or less with the same intensity for lower frequencies, but then some differentiation occurs, when a certain frequency is reached. That seems quite weird at the beginning, but then not:

This might be due to the effect of having a bass bar in one foot, and a soundpost in the other one... not our case...

I guess no one ever conducted any testing on how the two discs of a Baby Bass vibrates... although it could be done, maybe with some stroboscopic device or laser sensors.

Anyway, the rocking motion of the bridge, however important or not it might be, can never be sensed by the Baby Bass PUs.

[Bruce Johnson]

Yes, the whole pickup system is assembled to the cast aluminum plate, including the diaphragms, coils, controls, output jack, and wiring. The plate appears to attach to the body with 3 screws, but if you look inside, there are three bent aluminum brackets which are bolted to the aluminum tube spine, and come up under the body skin, providing the pads and threaded holes for the screws. It's solid metal from the pickup to the spine. Inside, the brackets are usually partly surrounded by the sprayed-in foam. If you took the brackets out, the body would cave in under the string load.

As I said, the front and back of the body are made from thin flexible plastic. I believe they were vacuum-formed. A serious problem with Baby Basses is that the plastic has become brittle over 40+ years. On many of them the body starts developing serious splits, and there's really no good way to repair them. You can put in glue and patch plates on the inside, and then it just splits again right next to it.

Yes, many of the recent Baby Bass-style clones, such as the ones by Steve Azola and Ray Ramirez, use fiberglass for the body shells. It's simpler to make in low volume, and more repairable. Steve's Baby Basses were the most authentic in construction, with the aluminum tube spines and foam insulation. I think Steve only makes the Baby Basses on special order these days. His main business is all kinds of his own design electric uprights, with wooden bodies.