naymi
MM Forum Member
Posts: 14
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Post by naymi on Oct 3, 2014 8:22:20 GMT
Je, je. Deuce, I already own a MM Blues, but I am afraid to mess around with it and ruin it.
Resonatorman, that's an interesting fact, I didn't know. Always had the idea that the single cone came first.
Regards.
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Post by bod on Oct 3, 2014 10:02:19 GMT
... One small clarification, however, as Davey compared it to the process in a phonograph or trumpet. I may be wrong, but I think it's actually different. It is a matter of impedance, as Tark said, but in the case of a trumpet or phonograph horn, the moving air particles forming the sound wave collide into a progressively increasing amount of new particles as they advance through the horn shape, preventing them in this way from "bouncing back". (This is well explained in one of the articles of the page that Bod provided). But in the resonator cone, the sound waves don't actually travel THROUGH the cone (in fact, I believe the cone is covered in the smaller end). Rahter, they are CREATED by the movement of the cone. (This is just so you know what I mean, being precise we'd have to say that they are actually created by the vibration of the strings, and then transferred onto the cone). .... You are right, the phonograph horn is rather different to the resonator cone, but I think that is because it (the horn) does a different job; I suggest the horn is more akin, in function, to the resonator body construction (sound wells / baffles) than the cone. On the other hand, the phonograph sound-box (or reproducer) is rather more like a resonator's cone, bridge and saddle assembly (the needle moves the diaphragm, inducing vibration in much the way that the bridge and saddle transfer vibration to the resonator cone).By 1925 Victor had evolved 'Orthophonic' sound-boxes which even had a spider to transmit the vibrations from the needle to the newly developed aluminium diaphragm. These even look kind of familiar:
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Post by tark on Oct 3, 2014 15:34:15 GMT
The soundboard of a regular acoustic needs to be less stiff than a resonator body. Its not attached to any flexible surrounds - it needs to vibrate. Resonator bodies should be as stiff as possible - there are not supposed to vibrate really. The soundboard of a regular acoustic and the cone of a resonator do the same job - they are both supported by the guitar body and transfer the vibration from the strings to the surrounding air. The ideal construction for both is that they should be as stiff and light as possible with a flexible surround. The conventional soundboard does this by being made from a light but strong wood - spruce, pine or cedar. These woods have straight grain and a high strength to weight ratio. They are strongest along the grain, so cross braces are added to increase the across the grain strength and stiffness. These braces are always tapered off towards the edges of the soundboard leaving it at its most flexible around the joint to the rims of the guitar body. There are two design approaches to building an conventional acoustic guitar body - either make the back and rims as stiff as possible so that most of the vibrational energy goes into moving the soundboard and making sound OR allow some vibration in the back and rims in order to modify the tone of the guitar. Resonator guitars follow the first approach and certainly the wood body resonators have generally very stiff bodies. With the metal body resonators the bodies do vibrate quite a bit and that colours the sound. The reason that resonator guitars are so loud is because they are more efficient than conventional acoustics. The lighter and more edge flexible you make a soundboard the louder the guitar, but take it too far in that direction and the top is too delicate. The soundboard is easily damaged and the tension of the strings tends to tear the guitar apart. In the resonator guitar, because the cone is not a structural element and does not support all the string tension it can be that much closer to the to the edge of destruction. In old resonator guitars it is not unusual to find that the cone/s has/have collapsed. But one of the features of the design was that the cone or cones could easily be replaced. Replacing a collapsed wooden soundboard is not so easy. The Dopyeras likely used 3 cones because the tripod arrangement produces a rich sound and is both strong and self levelling. It was George Beauchamp who insisted on a simpler, cheaper single cone and the Dopyeras did not agree with his method of doing it, they wanted a more complicated and expensive system, which was really missing the aim of a cheaper guitar. That is partly why they left National and went off to make Dobros.
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naymi
MM Forum Member
Posts: 14
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Post by naymi on Oct 3, 2014 16:30:02 GMT
Tark, very interesting stuff! Thanks.
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Deleted
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Post by Deleted on Oct 3, 2014 18:33:55 GMT
Here are some images of an acoustic guitar and where the vibrations aree. You can see the vibrations are in the middle areas of the soundboards, some with several vibating areas - little or no vibration at the edges, with the vibration reducing towards the edge at an exponential / logarhythmic (or whatever) rate. The edges are essentially inflexible, like pivots - doubly fixed in place, with kerfing to keep them more rigid / set in place. Granted the kerfing might not be 'solid' but thats just so 'work hardening' doesn't destroy the glued planes.
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Post by mitchfit on Oct 3, 2014 19:15:21 GMT
^^^
slide496, remember when you asked about microphone placement, and the general consensus was that there was no correct answer...
keep locating them ~everywhere possible~ until large grins emerge.
mitchfit
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Post by mitchfit on Oct 3, 2014 19:20:40 GMT
oops, almost forgot---thanks for posting deuce.
very interesting stuff there. any idea about model of guitar used as a test platform?
mitchfit
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Deleted
Deleted Member
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Post by Deleted on Oct 3, 2014 19:58:50 GMT
Just some classical guitar or other I think mitchfit. TT
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naymi
MM Forum Member
Posts: 14
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Post by naymi on Oct 9, 2014 8:44:16 GMT
I just read the thread about the dual-olian in the Talking Blues section of the forum, with an interesting project and infor about the two cones. Since we briefly discussed the two cones in this thread also, I thought I'd post the link to the other thread, in case someone hasn't read it. Regards.
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Post by tark on Oct 17, 2014 0:56:12 GMT
Here are some images of an acoustic guitar and where the vibrations aree. You can see the vibrations are in the middle areas of the soundboards, some with several vibating areas - little or no vibration at the edges, with the vibration reducing towards the edge at an exponential / logarhythmic (or whatever) rate. The edges are essentially inflexible, like pivots - doubly fixed in place, with kerfing to keep them more rigid / set in place. Granted the kerfing might not be 'solid' but thats just so 'work hardening' doesn't destroy the glued planes. Your post prompts me to say that perhaps I wasn't clear enough in my description of an acoustic guitar soundboard. Yes you are right to say that the very edges of the soundboard are fixed to the rims and the joint is reinforced by the linings (apparently kerfing really refers to the method of multiple partial cuts through the strips of lining to make them easier to bend around the curves of the rims / sides) making the very edges of the soundboard rigid, but the area of the soundboard between the edge and about 3 cms inward is rendered more flexible than the centre of the soundboard by tapering the bracing. Some guitar makers even taper the thickness of the soundboard towards the edges. Yes the centre of the soundboard moves more than the edges because it is being driven from the centre by the bridge, but the edges do need to be more flexible than the centre in order to allow that to happen most efficiently. Perhaps I should also clarify that loudspeaker cones are usually designed to work more like a piston with a clearer division than a guitar soundboard between a rigid centre (the cone) and a quite flexible surround. Resonator cones more closely resemble loudspeaker cones than they do acoustic guitar soundboards. You have the centre cone, in Nationals case with embossed spirals to add a degree of rigidity, and the cone is supported on a 'concertina' folded, relatively flexible rim to allow the cone to vibrate up and down. Rather than move like a rigid piston the acoustic guitar soundboard bends and flexes and as the images you posted show, operates in many different vibrational modes. On more expensive guitars the bracing is often tapered or scalloped on more central sections as well as near the edge to control the overall flexibility and enhance these modal patterns of vibration.
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Post by mitchfit on Oct 17, 2014 19:31:25 GMT
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svento
MM Forum Member
Posts: 3
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Post by svento on Aug 18, 2019 22:33:03 GMT
I'm into a solid-body bass guitar project. It's meant to be an more or less regular electric bass, but I would like it to have somewhat more acoustic output volume than standard solids. I'd also like it to have some of that typical semi-acoustic sound when amplified.
It actually does have a lot more air inside the body than a true solid. However, it doesn't seem to affect the sound. The chambers do not seem to get involved.
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Already from the start, the idea has been to boost the acoustic output with some kind of resonator system.
Been thinking about some different approaches including sympathetic rods (or should it be 'Rhodes'...?), pipes and spiral springs, metal membranes, tiny bells and cymbals, reflectors and horns.
The bridge will be a dense and rigid construction.
The challenge is how to transfer the ringing of the bridge so that some acoustic tone will be projected in those body chambers and amplified there.
Many of my ideas are related to the the principles of old phonographs and horn fiddles. A needle which is an extension of the bridge, stimulating some kind of membrane, maybe a system of pipes boosting the output like a wind instrument, and finally some reflector, cone or horn will be amplifying the vibrations.
Problem is the constructing of the unit transferring energy from bridge to resonator box.
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However- I do have this alternative idea.
It will look very much like a typical guitar cone-resonator system, but it will probably operate in a completely different way.
I happen to have this spherical chrome brass floating switch. The housing consists of two halves held together by eleven small screws.
They're only some 4" ΓΈ and they're rather stiff and heavy. They're not flexible and they can't behave like regular Dopyera style cones, but they do have very pleasant tone. A lot darker than expected.
In the middle of the lower bowl, there's a vertical needle that's more likely to actually vibrate, and my idea is to make use of that object.
The bowl would be mounted bottom down, like a spider bridge cone rather than a biscuit bridge one. Located typically under the bridge, firmly locked to the solid body by eleven small screws.
So far it will probably work as an extension of the bridge - adding extra mass - thus contributing to sustain and preserving some overtones - though probably not increasing acoustic volume.
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To make it involved in the acoustic power, I intend to place some kind of cymbalic disc under the bridge. This, I believe, will probably be the actual resonator unit.
I also hope that energy from the bridge will get the needle vibrating and tease the disc.
The ringing of the cymbal will then be projected inwards, amplified in the bowl and reflected outwardly.
The housing bowl will probably resemble the function of a resonator well, rather than a resonant Dopyera type cone.
The bottom of the bowl will also be fixed in some kind of resonant unit. I will likely use a bottom-up candy tin.
The bottom will then hopefully function as membrane, and the rest of it as an amplifying well. This, I hope, will project some sound out to be amplified further in the cavities of the instrument body, then leaking out through holes in the surface.
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Opinions about this?
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Post by Pickers Ditch on Aug 18, 2019 22:49:10 GMT
You are probably aware of the Ampeg bass mystery pickup - if not I suggest you check it out. See: www.pressreader.com/
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Post by Pickers Ditch on Aug 18, 2019 23:00:11 GMT
...or the Stromberg Electro pick up which appeared in 1929? There is an article written by Lynn Wheelwright in a 2008 edition of Vintage Guitar magazine about it which is available on line. See; www.vintageguitar.com/3657/stromberg-electro/
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