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H.R.Fisher

Base bar question

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I  am interested in understanding the tonal effects of various  weights, heights ,shape and position of the base bar. Thank you in advance for your responses.       

                                                    Henry

 

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15 minutes ago, H.R.Fisher said:

I  am interested in understanding the tonal effects of various  weights, heights ,shape and position of the base bar. Thank you in advance for your responses.       

                                                    Henry

 

I am too.....

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20 minutes ago, Jerry Pasewicz said:

I am too.....

From what I've heard as well, the jury is still out on what parameters do what as far as the bass bar goes. 

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My thoughts: 

bass bar helps support the left bridge foot and distributes vibrations into the bouts. Should be as light and strong as possible (within reason)

don’t want to dampen vibrations, so there should be enough height so as to minimise contact with the belly. 

Want to be springy, so the height should drop off quite steadily. I make sure the height drops the same distance each fraction of the way to the end. Heighest point at the bridge will ensure that vibrations are given weight, allowing a continuous vibration to build up, producing a good sound. 

Aside from that, I don’t know much more. 

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1 hour ago, Jerry Pasewicz said:

I am too.....

Sheesh, Jerry, I thought you were supposed to know a lot! :lol:

It shouldn't be too light, too heavy, to high, too low, and the shape and position need to be very close to perfect. :)

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30 minutes ago, Anthony Panke said:

1.  Should be as light and strong as possible (within reason)

2. don’t want to dampen vibrations, so there should be enough height so as to minimise contact with the belly.

1. I disagree. If the bass bar is too light, it will be moved too easily by high-frequencies, and motion on the bass bar side doesn't contribute to radiation of high frequencies very well.

Think of it like a speaker, with a crossover between the woofer and tweeter. On one extreme, if all the energy goes to the woofer,  the high-frequency end will be severely attenuated. If all the energy goes to the tweeter, the low-frequency end will be severely attenuated. So I think of it as trying to set up a mechanical crossover (rather than electronic).

(The above is a metaphor, and may or may not have anything to do with the way violins vibrate.)

2. I'm not understanding that, so could you please elaborate?

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1. if the bass bar is strong, then the high frequencies should be dampened, shouldn’t they?

im not as experienced as you on this, so I’ll trust your judgement. 

2. If I make an 8mm bass bar, the contact with the belly would be large and dampen vibrations. If i strengthen the bar via height, it doesn’t dampen the vibrations as much, as well as the shape being intrinsically stronger in that direction. ( think of a 5.5mm high bar which is 12mm thick, compared to the other way round)

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27 minutes ago, David Burgess said:

1. I disagree. If the bass bar is too light, it will be moved too easily by high-frequencies, and motion on the bass bar side doesn't contribute to radiation of high frequencies very well.

Think of it like a speaker, with a crossover between the woofer and tweeter. On one extreme, if all the energy goes to the woofer,  the high-frequency end will be severely attenuated. If all the energy goes to the tweeter, the low-frequency end will be severely attenuated. So I think of it as trying to set up a mechanical crossover (rather than electronic).

(The above is a metaphor, and may or may not have anything to do with the way violins vibrate.)

2. I'm not understanding that, so could you please elaborate?

I found that a stiff bass bar reduces the amplitudes's of the lower frequency resonance peaks such as A0 while not affecting the high frequency resonance peaks much.

So a stiff bass bar gives the perception of a brighter sound by decreasing the low frequency output rather than by increasing the high end as is often mentioned.  

Another impression is that it takes a big change in the bass bar height to have a noticeable sound character change.

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26 minutes ago, Anthony Panke said:

1. if the bass bar is strong, then the high frequencies should be dampened, shouldn’t they?

2. If I make an 8mm bass bar, the contact with the belly would be large and dampen vibrations. If i strengthen the bar via height, it doesn’t dampen the vibrations as much, as well as the shape being intrinsically stronger in that direction. ( think of a 5.5mm high bar which is 12mm thick, compared to the other way round)

1. I don''t see it that way. Refer back to my speaker crossover metaphor.

2. I see the mass of the bass bar as being important, not just the strength. There are many different ways to adjust the the ratio between mass and strength, from a light carbon fiber bass bar with some lead weight added, to a heavy bass bar with the sides hollowed out to reduce the weight.

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I see now, that the energy of each frequency needs to go to it’s most effective amplifier. The ideal weight of the bass bar then depends on the relative weights of everything else, the desired frequency response and the position of the soundpost, along with the type of strings, level of tension etc. At this point, the number of variables is too large to comprehend, and I just go by intuition and consensus. 

The bass bar is still a little in the dark for us. We therefore make it as clandestine and mysterious as possible. 

there was an interesting article in the strad recently about an innovative bass bar. Can anyone verify its success?  It tapered the other way,narrowing towards the belly,  8mm wide at the top with very narrow gluing area and a flat profile. 

 

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