Double Bass EUB design and build and some lessons learned

[Jaygetsreal]

Post 8 : Strength where it's needed - steel

Mea culpa, I thought a heavy duty roofrack bar would be strong enough. It wasn't. Tuned BEAD it was ok - and kinda fun to have low B - but when I tuned up to EADG there was a very slight bow to the body. (The pro's are shaking their heads in disbelief reading this)

Instinctively I thought "carbon fibre truss rod". Tried that but abandoned it for two reasons - one it is very difficult to terminate securely at each end. Epoxy just wasn't up to the job and I have no contacts in NASA. And two it wasn't adjustable like a truss rod should be.

Although adding quite a lot of weight (and I needed not one but two because the centre line of the bar was already occupied by other parts) I ended up using 3/16 steel rods with stainless nylock nuts at each end. All along their length I placed rubber pads to avoid vibration.

Unlike a truss rod in a BG which I think is straight along the back of the neck, in this case each truss rod is two sides of a long squat triangle, ends anchored as far towards the front of the bass as possible and mid points as far to the back of the bass as possible. Thanks high school physics! [Thought: Has anyone ever made a back-to-back instrument where rear strings provide the compensation for front strings?]

Now thankfully the bass is absolutely straight. I could even, if necessary, adjust the relative tension on each side to match the tension of the E & A and D & G strings respectively! Best thing is that with all structural parts metal it stays in tune beautifully with varying temperature!

 

[Jaygetsreal]

Post 9 : The elusive woody timbre

If you're still reading, here's where I exit my comfort zone and enter an arcane world.

This screenshot is an upright bass pizzicato note from a recording of uber-bassist Lyman Medeiros playing into a Neumann U47a. [Thanks Lyman for the inspiration] [It seems the recording is no longer available online but I suppose I could share it via private message if anyone wants to hear it]

The rich harmonics and the full bottom end are clearly visible. [BTW the screenshot was done in the Voxengo Span VST add-on running in Cubase]. THAT'S MY GOAL, if you like. The sound I wanted to try and achieve.

The next shot is the unprocessed signal I got early on from the piezo using weedwhacker line for strings. Clearly a long way to go!

This beautifully illustrates why I quickly upgraded to proper strings.

My most recent tinkering has been (...pause to allow purists to leave the room) with overdrive pedals! For what it's worth, putting the output of this particular EUB through a Zvex Woolly Mammoth, with all the controls at almost minimum, sounds pretty 'woody' to my ears. I hear "Heretic! Witches were burned for less"!

The MP3 snippet of Cold Cold Heart in Post 6 was recorded like this. I haven't done any screenshots of the sound yet but will post when I do.

I am not sure what other EUBs through other OD pedals will sound like but I'm pretty happy for now.

One more post to come.

 

[Jaygetsreal]

Post 10

Here are a few closeups of non structural parts for anyone interested.

The removable endpin with its thumbscrews.


The removable body brace. Same kind of thumbscrews. (No the bass isn't bent it's just taken with a wide angle lens).


And the coffin!


For an ageing bassist, a fortuitous point to end

 

[delta7fred]

My most recent tinkering has been (...pause to allow purists to leave the room) with overdrive pedals!

Funny you should say about overdrive pedals.

The closest sound I have achieved to a DB out of a BG was a Violin bass clone (with a centre beam, not a full hollow body) into a Zoom B1Xon effects pedal using one of the presets (can't remember which one now but I know it had mild overdrive, chorus, and maybe a bit of octave down). It was strung with chrome flats and played with a pick with heavy palm muting so the notes decayed quickly.

It certainly wasn't going to fool and real DB players but it was a lot closer than my EUB.

 

[alder]

Post 1 : Key Dimensions

I decided to design the instrument in 3/4 scale. Please reassure me that 3/4 is the de facto normal for DBs in jazz so one day I can easily migrate to a real one!

The finished instrument without its removable endpin ended up 1.55m (5 foot 1 inch) long. Nope, I won't be flying with it.

At the very beginning I put together the string geometry for 3/4 a bass from collected internet wisdom. Then I tested it out using weedwhacker line.

This allowed me to emipirically fill in the gaps in the measurements. Pretty soon I had all the string heights, string spacings, curvature radii etc I needed. This step also taught me just how much combined tension the bass has along its length, which helped me to design a strong enough skeleton (See Post #8 coming soon)

A note on weedwhacker line. I used 1.6 2.0 2.8 and 3.5 mm gauges. The sound was...well...thin. And frequent retuning was required. I subsequently upgraded to Helicore Hybrid Mediums which give me good all-round performance - and incredible sustain (which could be a bad thing I suppose)

Anyway, back to the build. Here's a sketch of the key dimensions.


Post 2 is about choosing construction materials.

Could you repost those attachments, the links are broken. Thanks !

 

[Jaygetsreal]

No worries, sorry.

Testing geometry with weedwhacker line:

Key dimensions:

 

[Matt Hoyle]

Just wanted to say thanks for sharing all this, too, Jay. Really interesting.

And love your sketches.

 

[Jaygetsreal]

Update on the quest for that woody double bass sound from piezo EUB.
After much experimentation with compression, overdrive and filtering the simplest solution for me seems to be simply filtering out the upper mid-range at around 800hz. With a graphic eq pedal I pull this frequency down by about 12db and there's none of that honky sound now.
It does depend on the amp though - in live situations it actually seems to sound better direct to PA rather than through my bass rig. Someone might know why?

 

[jthisdell]

Update on the quest for that woody double bass sound from piezo EUB.
After much experimentation with compression, overdrive and filtering the simplest solution for me seems to be simply filtering out the upper mid-range at around 800hz. With a graphic eq pedal I pull this frequency down by about 12db and there's none of that honky sound now.
It does depend on the amp though - in live situations it actually seems to sound better direct to PA rather than through my bass rig. Someone might know why?

Interesting, I usually try to curb the honkiness on my NXT by dialing back the upper mids using the sweepable mid on my TH500. Last night at rehearsal I switched the mid control on my Radial pre to 1,000hz and backed that back a little bit and it sounded really good, big thump, no hnk and enough highs for definition. I'm going to have to experiment with my TH to see if I can fine tune that a little.

Thanks for the tip!