Saturday, 4 April 2009

A body that preserves vibration

With the addition of a body to the T-beam bass, it begins to resemble an instrument.

The body is a 3 mm (around 1/8") acrylic (or plexiglass) shield, cut with a saw and an angle grinder, polished, and bent in shape with a hot air gun. As with almost everything else on the bass, it is not intended as the final version. For this, I will use thicker (probably 5 mm) acrylic sheet and have the leg rest further to the back.

The acrylic shield is slightly bowl-shaped so it follows the contours of my body. It's a fairly deep bowl shape ;-) It has a leg rest bent into the lower part and an arm rest created by folding back a wing on the upper part. It quite looks like the body of an Ovation Breadwinner, though that was not the intention originally. It's very comfortable, and I expect it to be even more so when I've moved back the leg rest.

The four mounting supports that connect the shield to the stick will have to be replaced with a central support mounted on one of the two places where the stick has least vibration. A so-called node. I located the node by suspending the stick on two springy foam blocks, pouring salt on the stick and tapping it with a knife handle. As predicted in the marimba literature, the salt would gather to show the location of the node. Luckily, the node is somewhere in between the mounting supports, which makes construction easy. BTW; marimba and vibraphone builders do a lot of interesting research into the acoustics and vibration of wood; something that the guitar builders might draw upon in their work.

The reason for having the shield mounts on the node is to preserve vibration in the stick and not have it travel through the body and into the all-absorbing torso of the player. The node does not vibrate - or at least it vibrates less than other areas of the stick, meaning that less vibrations will be transferred from this point to the shield than from any other areas. I expect it to have a pronounced effect on sustain, and perhaps also on tone.

Some sort of leaf spring suspension mount might give even better isolation between the shield and the stick, but that will have to wait for a later version.

12 comments:

Kaspar said...

Nice bass building series!
At the beginning of this year I too had an idea to build a simple bass, but initially I thought of building it from rectangular pipe aluminum profile.

As I gathered some background information to start building, I came about your blog.
Long story short - I changed my mind and started to build a T-beam bass instead :)

My build is still in process, but I wanted to share some pictures of slightly different solutions:
http://www.kaspartorn.eu/alubass/nut_back.JPG
http://www.kaspartorn.eu/alubass/nut_front.JPG
http://www.kaspartorn.eu/alubass/tuners_back.JPG
http://www.kaspartorn.eu/alubass/tuners_front.JPG

Thanks!

Kaspar
------
http://www.kaspartorn.eu

Alexander Gorm Øst said...

Hi Kaspar

How nice! I am very glad that somebody besides me likes the concept enough to build one.

It'll be interesting to know more about your build. How do you plan it to be? Will it have a body? Wooden neck sides? Piezo or magnetic pickups?

It looks really well made, with nice and clean slots for the strings. Did you use a milling machine? Plus, it's an ingenious way you've fastened the string eyelets to the vertical flange at the head end.

Do you plan to post about the project on your own blog? If not, I'd be happy to post about it here.

BTW, I've thought about using a box profile myself... one of the great things would be that you'd be able to mount a sliding pickup inside the box, completely hidden. I haven't yet devised a proper way of positioning such a pickup, but it could be another fun project some day.

Kaspar said...

Alexander Gorm Øst: Will it have a body? Wooden neck sides? Piezo or magnetic pickups?

My plan was to keep it without a body, just wooden or plywood sides.
Maybe a spike at the bottom to play it upright-style.
I found that it's very well suited to upright position (although I've never played one :)).
Right now I don't have a pickup attached, so I found that to be able to hear the low B-string at all, I had to place the bass on a wooden box - that gave it a nice sinister tone :)

Right now my plan is to use a regular guitar pickup.
If I decide about the position, then I thought of cutting a hole for it in the T-s vertical beam, so that the pickup is right under the horizontal part of the T.
Then drill holes in the horizontal part for the pickup's pole-screws.
It's just an idea, don't know yet if it'll actually work well.

Alexander Gorm Øst: It looks really well made, with nice and clean slots for the strings. Did you use a milling machine?

I wish I did! :)
They may look better on the pictures than in real life.
I just drilled holes in a row and then filed them together to make a slot.
Milling machine would make a lot of processes easier.

Alexander Gorm Øst:
Do you plan to post about the project on your own blog? If not, I'd be happy to post about it here.

I don't plan to write a blog, so I'd be happy too if you did it.
After all it's very similar to yours.

Alexander Gorm Øst:
BTW, I've thought about using a box profile myself... one of the great things would be that you'd be able to mount a sliding pickup inside the box, completely hidden.

That was my reasoning too. What stopped me though, was the unability to find the right profile at a reasonable price - either the inside dimensions were too small for the pickup or too large for the hand or the wall thickness was too small to give proper strength according to the calculations.
Even for the T-beam the minimum amount to buy was 5m :)

Alexander Gorm Øst said...

I've tried playing mine upright, and it worked good for me as well. Nice idea with the box... one might even use one of those Cuban box drums to get a really nice sound.

What sort of guitar pickup do you plan to use? My guitar humbucker turned 90 degrees worked well, considering that it was used for another purpose than than it was designed for. But I would like to try a good bass pickup. I would imagine the P-bass pickup would be straightforward, since it's in two parts. As long as you mount it _above_ the strings.

For mounting the pickup below the strings, keeping the top flange intact sounds like a really good idea, as does the idea of holes for the pole pieces. The pole holes will look amazing if they're going to be in-line with your string slots. How far is the distance between your strings, BTW? Mine is 18 mm, same as the two pole rows on my humbucker.

5 meters of T-beam is a lot! But then, if you mess up, you can just cut a new piece;-) Where do you get your metal from? I've used willmsmetall.de and metallstore.de. Both are good, Willms Metall is generally the cheaper one. If you know other reliable metal suppliers within the EU, I'd like to know. (I assume from your site that you're in Estonia).

I'll prepare a post about your build. Do you have improvements planned, which I should wait for?

Kaspar said...

Alexander Gorm Øst: What sort of guitar pickup do you plan to use? My guitar humbucker turned 90 degrees worked well, considering that it was used for another purpose than than it was designed for.

My plan too is to use a 7-string guitar humbucker, as I have a couple of those lying around.


Alexander Gorm Øst: For mounting the pickup below the strings, keeping the top flange intact sounds like a really good idea, as does the idea of holes for the pole pieces.
How far is the distance between your strings, BTW? Mine is 18 mm, same as the two pole rows on my humbucker.

Thanks about the compliments! It'll be a pain though to get them perfect with a hand held drill.
It's about the same - 17.5mm, I chose this spacing because of the pickup.


Alexander Gorm Øst: 5 meters of T-beam is a lot! But then, if you mess up, you can just cut a new piece;-) Where do you get your metal from?

Yeah, I have the future to be T-beam basses stacked under my bed :)
I bought mine from http://www.sapagroup.com/en/, they have a branch here as well as in Germany.


Alexander Gorm Øst: I'll prepare a post about your build. Do you have improvements planned, which I should wait for?

Well, first there are the improvements that have to be made to be able to call it an instrument and then there are the bonuses.

The basics:
1) Pickup
2) Trimming the beam to correct width/height.
Haven't yet found a suitable blade for the type of jigsaw that I have. Doing the sawing by hand isn't a very inspiring thought.
3) Wooden/plywood sides
4) The bolt used to fix the strings at the nut needs to be of a bigger diameter, where possible.
If it's the same diameter all the way (that fits the string ends) then it isn't strong enough and bends.

Bonus:
1) Detachable box(es) for an optional acoustic bass
2) Foldable spike - for better upright playing height
3) A hole/hook/stand for storing - the "spike" might have a multifunctional design that would serve as a stand if in another position.
4) Some way to finish the aluminum so that it doesn't get your hands dirty :)
Anodizing was an custom option but too expensive if made in Sapa.

The timeline for all of this uncertain because "instrument building" is a sub-hobby of my main hobby ;)

PS: What did you use for the 3D?
I'm using SolidWorks.

Alexander Gorm Øst said...

With fourteen holes for pole pieces to drill, it might be worthwhile to make a drill jig. It could be a piece of steel, as wide as the T-beam with two holes, 17.5 mm apart, drilled in it. These holes would guide the drill, so you'd only have to worry about getting the holes right lengthwise. After drilling a two holes, you'd move the jig the necessary couple of mm down the neck, clamp it, and drill the next set of holes. And so on. With the drill bit securely guided by the holes of the jig. I haven't tried it myself, but I wish I had made one before drilling the holes in my own T-beam. It might have made it much easier.

Regarding a post about your project: How about if I make a short post about your bass as it is now, and when you make substantial improvements, I'll make follow-ups?

Re. getting a suitable jigsaw blade for trimming the neck: I read somewhere that if you're sawing in a soft alloy (often AlMgSi a.k.a. 6063 aluminium), you're actually better off using a wood blade.

Plywood sounds cheap but can look very interesting as shown here: http://projectguitar.ibforums.com/index.php?showtopic=39130&st=30
I've been thinking about making a shield in steam bent plywood to replace the acrylic one I've got on now. Still, there's a lot of other things I want to do before that.

A detachable sound box could be nice. I thought about sacrificing an old acoustic guitar... cut of the neck, cut a channel through the body for the vertical flange and bolt the beam to the bridge and heel. It would be a quick way to try the idea.

My drawings are made in Google Sketchup. I haven't used modeling programs before, but I found it pretty easy. I do however miss a way to turn my models into technical drawings.

Kaspar said...

Alexander Gorm Øst: Regarding a post about your project: How about if I make a short post about your bass as it is now, and when you make substantial improvements, I'll make follow-ups?

OK. That would be great, as I'm not sure how soon I'm able to "finish" my project.

Alexander Gorm Øst: Plywood sounds cheap but can look very interesting as shown here: http://projectguitar.ibforums.com/index.php?showtopic=39130&st=30
I've been thinking about making a shield in steam bent plywood to replace the acrylic one I've got on now. Still, there's a lot of other things I want to do before that.

Yes, the plys can make very nice patterns.
Regarding the bent plywood body, I suggest you also look into this thing called "3D veneer".
It differs from regular plywood - you can bend it more easily in two directions.
Here's more info on it:
http://www.reholz.de

Kaspar said...

Regarding pickups, these could make an interesting choice.
Or if the idea could be developed further - the bass could *be* the pickup:

http://lacemusic.com/electric_pickups/bass/bass_specs.php

Alexander Gorm Øst said...

That could be fun to try. If I understand the construction of the Alumitone correctly, you'd have to make two parallel slots across the top flange and isolate the piece in between from the vertical flange. And then add some sort of secondary coil. It could be doable while maintaining structural integrity.

I have absolutely no idea what it would sound like. One of us should try it. You've got 5 meters of spare T-beam so you're a good candidate ;-)

Seriously: it's a really fascinating idea. It might sound terrible, but then again, it might sound incredibly good.

BTW, have you seen this?
http://music-electronics-forum.com/pickup-makers/5447-low-impedance-pickup-research.html#post43064

Kaspar said...

Alexander Gorm Øst: BTW, have you seen this?
http://music-electronics-forum.com/pickup-makers/5447-low-impedance-pickup-research.html#post43064

What is it?
I get a "Error 404: Page Not Found" with this link.

Alexander Gorm Øst said...

Sorry... part of the text was missing.
http://music-electronics-forum.com/t4881/

It's a pickup design using a primary and a secondary coil like the Alumitone. It is even flatter than the Alumitone and might lie beneath the strings with no or little modification to the top flange.

I don't think it's useful in relation to your suggestion of using the whole beam as the pickup body. But still interesting for a stick-type instrument such as ours, where you don't want to cut holes for pickups.

Alexander Gorm Øst said...

Whoops, that was a wrong link. This is the right one:

http://music-electronics-forum.com/t5447/