Official Luthiers Forum!

[QUOTE=TonyKarol] Is the goal to max the cross dipole, or make the cross and long even between each other ??? Early on Ervin mentions that good sounding guitars exhibit all three modes in balance does he not ???

Cross dipole gives long range volume/projection, long dipole close range volume correct ... thats why classical guitarists want cross dipole, to fill a small concert hall. Whats the goal for long range projection in a steel string ??? [/quote]

Hi, Tony and all of you out there: The goal might be to max the cross dipole. It all depends on what you want to get from the final product. In general, the rule is that you want plenty of everything . . . so maxing something necessarily means not leaving any other thing on the insufficient side. The player will very likely sooner or later be very annoyed by this. Actually, what I said was the opposite of what you've written: I said that the cross-dipole is associated with loudness in proximity to the guitar and the long-dipole would be associated with projection or cutting/carrying power. Classic guitar players want a good long-dipole, whether they think in terms of this or not; flamenco players tend to really appreciate a good cross-dipole. The thing to remember is that these are not either-or quantities, but more a question of balance and emphasis. The monopole, cross-dipole and long-dipole are mostly convenient abstractions whose best uses are for our carrying on better conversations.

The steel string guitar is a different critter than the Spanish guitar because it typically (that is, much more typically than the Spanish guitars) gets played into a microphone and/or otherwise is amplified. As such, the luthier's building-in of projective capacity is not so important an issue.

However, if one wanted to talk about it, then one would have to focus on the steel string guitar's long-dipole. Why? Because high-frequency signal travels farther on a limited energy budget than low-frequency signal does. Sharp, high-frequency sound is the guitar's cheap-bang-for-the-buck sound, compared to low-frequency sound. (It's actually everything's cheap-bang-for-the-buck sound. That's why you can hear a puny chihuahua squeal and bark from across the street, and why you can simultaneously hear a lion's roar equally easily from the same distance. Different projective-energy levels, different frequencies, same distance of travel.) I hope this short explanation makes some sense. Cheers, Ervin Somogyi

Brock Poling39095.0308101852

Yep, agreed .. I had it wrong the first time, but looked back and corrected the statement in another post - even from a logistical look it makes sense .. the longer dipole will have more staying power, more throw - thus long range volume.

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Most of this conversation is way over my head but having watched the Ervin's videos I can grasp these concepts intuitively. I see from his website that his fan fret places the straight fret close to the body, thus shifting the steepest angle down to the nut so he can incorporate the off-set saddle into a “normal” footprint for the bridge and thus maintain the integrity of his symmetrical bracing (at least that's my guess). So, my question is: would on off-set bridge requiring an asymmetrical bracing pattern affect the long/cross dipole vibrations adversely, or does it really matter so long as the irrigation ditches provide a good balance of energy distribution, which I presume is the goal?

(Hi Tony – yes, you've corrupted my mind for life!)

Hey guys, where can I download these videos you are talking about? I found the origianl thread, but the link to download was removed...

Is the chihuahua thing why mandolins are so much louder than guitars? It seems one of the important goals of any self respecting bluegrass player would be to be heard at the same level as that loud little instrument. Excuse my lack of intellectuality.
Also. In my utter confusion I noticed that one guitar up there had a drumhead thin top. How does this relate to how a banjo top works I wonder? I am an absolute beginner but believe it or not I've been attempting at least to think about this subject for a while, and am now aware of parabolic bracing for instance. I just read that Ignacio Fleta was known for his obsessive voicing of tops, which were of constantly varied thicknesses. Of couse this has little to do with the chihuahua though.
I think it would be interesting to build a guitar with the drum concept in mind, not that it hasn't been done I'm sure.

_________________
"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

   I would like to apologize if I was veering off the point or trying to joke around too much. I was up late last night reading as much as I could of Ervin's wonderful website after that post and am a bit better informed now. I am very interested in the course and would like to find the videos to better understand cross dipoles. Also I'm not really an absolute beginner. I guess I'm on my third guitar now, my first being a strat copy.
That Bridge plate on the guitar pictured above seems very large, and I notice how it purposefully connects to the x and other braces. This is good on steel string guitar I seem to understand now. A smaller plate would give better bass response but might cause too much top weakness. Is the plate made of brw? mahog or Koa?...Interesting choices. Large plate and tighter bracing allow for a thinner top perhaps. I like how it's all stitched together and am curious about that neck block area...
Seems these days a steel string is the ideal singer songwriter home recording guitar, and in this situation "tinny sounding" or just smaller guitars are often preferred, because they don't cause the microphone nightmares of dreads. The Smallman strikes me as primarily an air pushing device, almost like a stringed bagpipe of sorts, concerned mostly with what goes out of the hole. In recording I've found it best (and have read this) to put one mic toward the end graft and another closer to the neck, and not directly over a hole. I'm not sure how this relates to cross dipole exactly but I'm trying here.   

_________________
"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

Since what happens on a guitar top is so difficult to actually see.   I go back to a couple of visual examples that keep sticking in my mind.

There was this experiment in my high school physics class that had a shallow pan of water about 2' in diameter. Attached to the side were a couple of vibrating gizmos, basically a small ball on the end of a stick, that were placed on the surface of the water. You could vary the frequency of the vibrations and you could also move the vibrators to different places on the pan. It was interesting to see the different wave patterns you could get. You could see how waves reflected off the sides and how they reacted with each other. Sometimes cancelling each other and other times reinforcing each other depending upon frequency and position. You could also get patterns that look like Chladni patterns, where small "peaks" of water would shoot straight up. I think a guitar top is very much like this, but the oscillations are much smaller and faster.


Another example is the caribean steel pan drum, like this one.



It must have taken alot of experimenting to figure out the size and placement of the "bumps" to get different notes all out of one piece of steel. But there is a pattern.

What I get out of this is that for every surface that vibrates, there are adjacent node points. And on the other side of the node is another surface vibrating opposite the first surface. Just like the first harmonic on a guitar string, the two halves of the string are oscillating in opposite directions with the node in between.

Sorry for being long winded, but I'm fascinated by this and I'd like to hear more of what others have to say.

Ok I'll shut up now.    

Kirt

_________________
Horton, MI

Hi, Nick F. and Kirt Myers:

Good comments and thinking on both your parts. The Chihuahua phenomenon does explain the cutting power of the mandolin, I think. The chihuahua and the mandolin are both high-frequency tone generators, as a direct function of their most basic design parameters. That is, they're made for producing high-frequency signal, and not particularly made for producing any low-frequency signal: their "speakers" would have to be bigger to do that, and the larger speakers would require a more powerful generating impulse. If the chihuahua could somehow manage to produce a low, roaring sound, for instance, all of its driving energy would result in a very quiet low frequency sound. I imagine this would sound more or less like a hoarse whisper out of such a little animal. This is a comedic image, naturally, but I think an accurate one. On the other hand, the same smallish amount of energy can produce an astonishingly far-traveling high-frequency signal. I think of high-frequency signal like being really, really cheap gasoline: it can drive your car far per dollar cost, but your engine performance will be bad. To play with the metaphor some more, imagine a rottweiler (with huge lung capacity, of course)with the voice-box and vocal cords of a chihuahua: what do you think would happen? You'd get a large-sized tone generator that would instantly be overdriven by an mount of energy that the "speaker" cannot handle. If that speaker weren't to blow out, the rottweiler would have to essentially bark very quietly. A definite mismatch there, between driving energy and speaker capacity.

And as for top thinness and fragility . . . that's an interesting area to think about too. It might help to think of the guitar as a sailboat that's more or less efficiently pushed by a wind. The sailboat will navigate its waters as a function of [1] its mass (it'll take more wind to push a heavy boat than a lightweight one), [2] its design (you really want to minimize friction, drag and resistance), and [3] the size of the sail. If the sail is limited to being a given size, then you'd think you'd be better off having (4) a sail that's as delicate, light and thin as possible without being torn apart by the force of the winds you expect to encounter [NEWS FLASH: SALES OF MARINE-GRADE PLYWOOD SAILS PLUMMET SINCE MYLAR CAME ON THE MARKET!!!], combined with (5) a mast and rigging that will hold that same sail out against the forces of the winds, but [6] equally without being so overheavy or overmassive that the sailboat's performance is negatively impacted.

In other words, if the sail is going to tear, that's no good; and it's no good either if the mast bends over (or breaks!) and doesn't support the sail in its wind-catching work; and neither is it going to work if the mast weighs three tons just to make sure it will hold up against the wind. Can you visualize that the sail would be an analogue to the guitar top and the mast and rigging would be analogues of the bracing? It takes an optimal balance of both for the system to work. And you do need both in systems that either drive air or are driven by air (wind). [If you wanted to generate some giggles you might think of the guitar as a chihuahua-sized wind generator.] But regardless of the words you use, the mast in the sailboat is useless by itself, and so is the sail. I hope that helps. By the way, I do think it's useful to think in terms of "other" systems and examples: irrigation ditches, steel drums, sailboats, chihuahuas vs. rottweilers, etc. It's kind of fun, too. Cheers, Ervin Somogyi

Ervin, thanks for the insight.

I have a question/comment. For the same energy (same amplitude), the low frequencies travels further than high frequencies, due to less absorption by the medium. Also, since they both have the same amplitue they have the same amount of energy.

So in plain physics wise, I think, one frequency is not really louder than others (although way they excite the medium "air" does get affected by the frequency and and perceived power delivery I think).

But in this case why chihuahua or madolin sounds louder is not because they are higher pitched and have more ernergy (it doesn't), but the way our ears perceive loudness.

If you look at the Fletcher-Munson curves (scientific test done by Bell Labs scientists. here is a pitcture http://www.webervst.com/fm.htm), our ears are extra sensitive at certina frequencis (1-6 Khz)

I don't know the frequnecis of guitar and madolin perfectly, but I think it falls within this range.
Guitar 80-1280 Hz
Mandolin 200-3200 Hz

Mandolin falls under the curve that our ears are more sensitive to than the guitar. So, even if my open G chord on my guitar pumps out the same amount of energy as the open G chord on the Madolin, Mandonlin will sound much louder. (I bet also the small body tend to favor louder overtones, therefore making it seem even louder).

So, maybe we perceive chihuahua to travel further, because the loss over the medium is more than enough to be compensated by our sensitive to that particular frequency.

If this is really true, I think guitars with a lot of loud overtones would do better at projecting far (because those frequencies will fall under the frequencies that we are more sensitive to). Do you know if this is a one of the hallmarks of "concert" classical guitars?microsmurf39101.7428587963

   Supposedly great violins vibrate similarly as the human voice, but of course we're talking different instruments here. I think there is definitely something spiritual to the best tones and frequencies, in how they can touch the soul so to speak. This is why singing is so important in churches (I think I've said that before). It is actually a form of channeling. The best guitars I have ever played seem to make my whole body become part of the instrument itself, and thus form a vibrational connection that is "moving". In recording a guitar also makes the room part of its instrument. There's got to be a balance between dampening and free vibration I would imagine, to prevent either wash out or muddiness. I personally don't like when a guitar sounds like a haunted house after purposefully stopping a string from ringing either. I bet this has something to do with top tuning and cross dipole.

_________________
"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

Interesting point Nick, i always thought that the magic related to the sound and the soul was connected in a spiritual way, maybe are we on to something here?

A lot of people will say that a well equipped luthier shop will need this hand tool or this power tool to help build great guitars but let's not forget what Mr Charlie Hoffman wrote on his website, your hands and surely your brains are the most magical tools when coupled with your spiritual beliefs.