Double Bass Tone Shims Under Bridge Feet

[skychief]

Searched and searched... Nothing came up. Im looking for a darker tone from my bass. I dont want to change the strings, so I was toying with the idea of putting soft-wood shims under the bridge feet to filter out the higher frequencies/harmonics.

Anyone had any success with this? i was thinking of using balsa or maybe cork..or is that too soft? Maybe spruce or pine?? Just wanted some ideas...trying to eliminate some of the experimenting phase.

I fully understand this will almost certainly sacrifice some volume. As the bass is being amplified, this is not an issue.

Thanks in advance.

 

[Jake deVilliers]

Try some sheet cork and report back!

 

[Eric Hochberg]

Frank Tate, bassist with Buddy DeFranco has cork shims and swears by them. Don't remember what he says they do though...

 

[powerbass]

+1 I'ld do this

Try some sheet cork and report back!

 

[gene beauchamp]

My euro spector has shims under the bridge

 

[MostroDB]

An advantage of a cork shim is that it helps evening-out the load across the feet area, and that may help your bass to sound more consistent over time. And it will reduce wear on the top, and make your strings higher.

Under a typical load of about 60psi under the feet of a db, however, I fear many corks will be high up in the hard part of the stress-strain curve. Then you will get some dampening, but maybe not as much as you like. Try & let us know. I don't think you will hear the effect of spruce.

You can also try small o-rings below the strings on the bridge to dampen highs.

 

[powerbass]

I used cork shims under the bridge feet of my DIY EUB with good results dampening harsh tones. There are a few versions of cork to try, auto supply stores have cork w/rubber used to make gaskets, craft stores have sheets of cork to make message boards. Also at craft stores are various types/thicknesses of felt. Bicycle inner tube is pretty thin and might work well

 

[skychief]

Cork it is, then... Thanks everyone!

Ill post the results.

Oh and MostroDB: Funny you should mention the o-ring trick... I recall buying a set of strings a looooooooong time ago that included 4 small o-rings. I didnt know what they (the o-rings) were for so i threw them out! lol.

 

[drurb]

Lycons used to be supplied with "tone filters." They were small rubber rings to be placed between the strings and the bridge. FWIW, this cork thing is just too much "tweaky" stuff for me. The load across the feet of your bridge will be quite even if they're fitted properly to the top. Want a different sound? Switch strings. I can't imagine why that would be less desirable than putting some material under the bridge feet. What's next... a discussion of all the different materials that could go under bridge feet? Rubber? Nylon? Kevlar? Tyvek? I'm just saying that it's not an approach I would take.

I've never heard a luthier recommend this type of modification. I wonder if that's true for the majority of players here.

It'll be fun to hear how this turns out. It's interesting... as long as someone else does it. Whatever floats your boat. To each his own.

 

[MostroDB]

Yeah that's why I thought of it, I once had a set like that too. Thomastik or Pirastro, many many moons ago...

 

[MostroDB]

If the centre line of your bridge is not exactly along the line bisecting the breakover angle, the side of the bridge feet it is leaning towards will be loaded more than the opposite side, regardless of the quality of the fit. A material like cork can compensate for that.

 

[drurb]

If the centre line of your bridge is not exactly along the line bisecting the breakover angle, the side of the bridge feet it is leaning towards will be loaded more than the opposite side, regardless of the quality of the fit. A material like cork can compensate for that.

I think you mean the breakover plane... yes, a detail... I think an uneven load would likely remain even after installation of the cork. That is, given the physics, I don't think the cork will compensate to any meaningful degree the effect you cite.

 

[powerbass]

For my EUB I made the cork shims wedge shaped to compensate for string tension pulling the bridge toward the FB. The auto store cork is quite durable and does allow for fitting compensation. There are numerous ways to alter the sound of a DB, many of the ideas have been posted here - various sound post materials, tail piece material/weight, changing the mass and shape of the bridge etc. Shimming the bridge may have merit as well for certain basses.

 

[MostroDB]

John, possibly the original angle in your bridge feet wasn't optimal then, and this is an elegant way to optimise. Agreed to all you said, and it reminds me of one other thing that may serve skychief's objectives, although it is almost certainly beyond what he wants to do. But it's relevant info, so let's share it.

Maple is a beautiful wood, mechanically, with very little absorption. Tap a piece of old good maple, while holding it in a node, and you get a clear bright tone that lasts reasonably long. In terms of elasticity modulus E, birch has properties not dissimilar to maple, although it is slightly less hard and slightly less strong. But it differs significantly from maple in terms of absorption, particularly for the higher frequencies. Tap a similar piece of birch, and it sounds quite dead. Not the low frequencies, but particularly the high frequencies. I guess birch is not a tone wood.

Anyway, a long time ago I was experimenting to find an optimal location for a pickup integrated in the bridge (for a van Zalinge EUB, actually), and for those tests I made a birch bridge. Scarred & all, the thing ended up in the retirement home for old bridges, for several decades. Until a few weeks back, when I used it as a blank for another test, this time on a conventional DB. I adapted the bridge to a basic shape, with feet fitted, and tested it. The DB I tested it on is a hybrid, with quite a bright sound, yet I noticed quite a bit of these highs were attenuated by the birch, while the lows were virtually unchanged. Actually, particularly for arco, its character improved over the maple bridge. I'm not suggesting we should now all be making birch bridges, it's just a story to corroborate John's point above, tying in with skychief's objectives.

On the spreading of uneven load due to bridge orientation: apologies if I used the wrong word. I meant the angle that the strings make where they break (their straight lines) over the bridge. Agreed, a very thin layer of cork will do very little to compensate for this uneven load (just as it will dampen very little), but given sufficient thickness it will help. It will do that by compacting more in the regions of higher stress, and less in the regions of lower stress. Therefore the high regions effectively become lower, and the low regions effectively higher, carrying more load. It's like putting extra springs in the system. If it helps, think of the extreme of a deformable medium, that's a fluid, below the bridge feet, for instance in small pouches the size of the feet. It may also help to look at the attached stress-strain graph for a highly deformable medium (60psi is about 4 kg/cm). Note that this graph is not for any specific kind of cork, it's just to illustrate what deformable media do when loaded.

 

[drurb]

Mostro, thanks for the clarification. I do understand the theory. It seems we agree that, in practice, cork won't really function effectively as "springs" under the load described.

It's also worth mentioning that, while cork might even the low/high positions, whether it will balance disparate for es through the medium is another thing.

Oh yes, and while liquids are deformable, they are incompressible.

Far be it from me to discourage experimentation. Still, I note that, after centuries of all kinds of trial and error, few players have or desire to have cork under their bridge feet. I still think the OP would be better served evaluating tried and true methods first. Just my opinion.

 

[chopsy]

I'm running cardboard under my bridge just to get it up to a playable height (can't afford the luthier right now) with no noticeable difference in tone.

In fact, I WISH it would cut some of the highs from my twangy G.

 

[skychief]

Still, I note that, after centuries of all kinds of trial and error, few players have or desire to have cork under their bridge feet. I still think the OP would be better served evaluating tried and true methods first. Just my opinion.

As stated in the thread starter, changing strings is not an option... am forced to use Corelli ultra-lights for physical reasons. The soundpost has been positioned by a professional (luthier).

Even tho its a carved bass, it sounds very plywoody to me (and to others). Reminds me of an old Kay i had when i was a kid. Thin and brittle tone when playing pizz. Im just looking to darken it up a bit.

 

[drurb]

As stated in the thread starter, changing strings is not an option... am forced to use Corelli ultra-lights for physical reasons. The soundpost has been positioned by a professional (luthier).

Even tho its a carved bass, it sounds very plywoody to me (and to others). Reminds me of an old Kay i had when i was a kid. Thin and brittle tone when playing pizz. Im just looking to darken it up a bit.

I don't think you'll get very far in your quest with those strings. Your string choice seems likely to be the root of your problem. There are other strings that would likely work in the face of physical limitations that would be a better choice.

I did read and understand your post. I urge you to re-consider the premise that the strings cannot be changed. I'm no stranger to having to be careful about string choice in terms of physical limitations having endured a serious hand injury.

Perhaps you'd prefer not to divulge the nature of your limitation in this public thread. I'd be happy to try to help via PM, if you wish.

Edit-- Thank you for the revealing PM. I understand better now why you are choosing the shim route. It does seem to make sense for you and I wish you success with it.

 

[james condino]

Did this "professional luthier" set the soundpost with you present and try a number of different positions to select the best tone for your ear or did a tonedeaf ex-chainsaw logger with 80% hearing loss who works in an electric guitar shop set it for his ear and just hand the bass over? About 50% of the time I find that regardless of what my ears percieve to be the optimal position and voice, customers ears, hearing, and expectations are different enough from mine that they like another position for the soundpost.

One of Chuck Traeger's books has a section on adding a certain type of polymer shims under the bridge for a specific tone response. 'Gotta agree with Dr Bub that Corelli ultra are pretty low on my chioce for strings...

 

[skychief]

Slid some 3mm pieces of sheet cork (gasket material) under the bridge feet. The brittleness is gone. Success!. As expected, theres a very slight decrease in volume, but i think thats attributable to the fact that all those hi-end harmonics are diminished, not because theres less transfer of string vibrations to the instrument. Im getting a wonderfully woody tone from the D string now (it was the worst offender). The sheet cork is really easy to work with; no sanding or shaping the contours because the material is so flexible, it conforms itself to the top of the bass.

Yah, looks like crap but Im not really concerned with aesthetics at this point. I just want to sound like Im playing a carved bass.

Many thanks to all of you who offered insights/info on this. It started out as a shot in the dark, but because you guys got me pointed in the right direction, my only investment was $8 for the roll of sheet cork (and a little time).