reso physics

[davidppp]

Prompted by some success at understanding how drumhead physics can account for the biggest differences in sound between banjos and guitars, I thought I'd take on resonator guitars. I know much more about banjos than any kind of guitar, but I do think resos are special.  

"Understanding" means connecting to something you already know.  My approach is pretty physics based  So, it might not resonate with too many folks.  But I know that a few of them are out there.

At this point, I believe that the only important thing about the resonator cones themselves is that they're relatively light and rigid in the lowest relevant frequency range. The rigidity is provided by the conical shape.  The magic is how they drive the rest of the body.

I write things up and post on-line: Resonator Guitar Physics Clue from a Paper Cone

It appears that the biggest difference in timbre between resonator and flat-top guitars is something the resonators do share with banjos. Of course, they are also loud (for an obvious, similar reason), but their overall sound is certainly guitar and not banjo.

Resonator Guitar Physics Clue from a Paper Cone includes sound files, identification challenges, and graphics, even if reading is not your cup of tea. (There are no equations!)

[Pickers Ditch]

I find that introduction to your post a bit insulting.
I'm technically and scientifically educated to a high level but I ain't got a Nobel prize.
I'm like a lot of other people on this forum.
...and I can read too!

I also play bass and guitar but am totally dyslexic when it comes to reading and writing music notation.

Personally I don't care about the physics, chemistry, voudou etc. of an instrument as long as it sounds good and plays well to my taste.

My ears are shot but I can tell the difference between a banjo, a wooden reso and a metal reso - I even have a parlour guitar with a wooden resonator disc.

So I just play the bl00dy things for my (and hopefully others) enjoyment and I really can't be airsed with the hows and the whys to be honest.

[Michael Messer]

Hello David,

Welcome to our forum.

The reaction to your post doesn't surprise me because what you are trying to understand and uncover is something that the great builders and players of these instruments have a perfect understanding of.

Having been close to resonator guitars for around forty five years as a player, researcher and designer, I do have a deep understanding of the whole concept of resophonic instruments, but I am also not a technically minded person and gave up on physics very early on in my life. In some ways I wish I had studied it closer, but I also am very pleased that I didn't, because I use my heart and instinct when dealing with musical instruments. You wouldn't want me designing and discussing an aircraft! I know musicians that study the intricacies of notes, tone, timing and phrasing in a mathematical way and sadly their own playing is technically accomplished, but it completely lacks any soul. I also know instrument makers that are like me and use their heart and soul build a create instruments, and I know builders that rely on calculations and physics to be creative. I know whose instruments I prefer to play.

Having said all that, while I am interested in your research and findings and I know you have said that you may not be using components to some people's taste, but the components you are using to do your tests with are not something that any experienced National / resonator guitar authorities would be able to take seriously. So with those components your tests are a pointless exercise. Here are those components...

First of all the 9.5" National-ish style resonator cone is made of a material far too thick to give a proper resonator tone and it has no spirals, which are also major contributors to the tone and volume of the resonator cone. The cone you are using is basically a piece of junk that cannot give you any correct calculations on how a resonator cone works and sounds.

Then there is the biscuit, which I can't quite tell, but looks to be too thick and might not be maple. Maple is the best and only material to carry the vibrations from the bridge saddle to the resonator cone.

Your bridge saddle is an ebony capped one which does not respond properly at all and gives off a thin tinny and bright tone that is not pleasant at all. The correct material is English Box Wood. This is what the designers of National and Dobro instruments used in the 20s, 30s and 40s, and nothing else gives the warmth and depth of tone. Maple is close, but not as good.

So putting all these bad components together to run serious tests, to me seems a little pointless and lacks the research that should have been done. A resonator guitar using the components you have assembled will sound terrible. It will not be pushing out the right frequencies and because of those shortcomings, comparing that sound with a wood bodied flattop is not a serious test.

You should look into the work and research done by the Dopyera brothers in the 20s and 30s. They designed and patented numerous types of resonators made of various materials in all kinds of weird and wonderful shapes before they settled on their masterpiece and excellence in design that are still being played almost a hundred years later. Even with all the technology available today, the resonator cones made in the 20s and 30s can be equalled by one or two makers, but not bettered.

To ask me if I can spot which guitar is which in your tests is to me a little ridiculous because I have been listening to and identifying types of resophonic guitars on old scratchy 78 RPM records for a very long time, in fact for most of my life. I have heard and played resophonic guitars almost every single day of my life for forty five years, so my ears are pretty well tuned for such things. Your tests might be interesting to some people, but not to me, or for that matter any of my expert friends.

I am not trying in any way to put you down, but I am saying that I think you should have asked some questions before spending so much time putting your tests and ideas into practice.

I would never dare to question or test the knowledge on his subject of a man that has a Nobel prize in physics, but I am surprised that you have gone to all this trouble without doing proper research. Or am I missing something?

Shine On
Michael

[stevie2sticks]

Hi David

I came to music, blues and resonators very very late in life which is something I have regretted. And I practice & practice till I wear the strings out as my time is slowly running out.

Sometimes I study a song or musician with a fierce intensity which is part of my enjoyment as I move along. For me, an easy example is some of the music produced by Ry Cooder which seems almost spiritual.

I’m always grateful that somebody has had the skills, knowledge & tenacity to design & build my guitar. And that a musician has had the skills, knowledge & tenacity to produce music that has such spiritual qualities.

Enjoy the forum.
Kind regards
Steve
Isle of Mann

P.S. Physics, not for me.

[davey]

If a wooden guitar needs metal strings to sound good, why doesn't a metal guitar need wooden strings ? Answers on a postcard please.

[jono1uk]

I agree with everything that has been posted here except the load of old tosh by the OP.
The phrase “if it ain’t broke don’t try to fix it” springs to mind.

Jono

[davey]

"The magic is how they drive the rest of the body." How they don't drive it is more important.

[Michael Messer]

I am not surprised at the response you are getting to you post and I don't know what you expected from a group of knowledgeable people. Nobody is trying to be unfriendly, it is not the nature of the members of this forum, but your posting and paper on the subject of resophonic instruments physics is as I said it would be, not something that can be taken seriously.

Shine On
Michael

[davidppp]

Jul 31, 2023 13:26:38 GMT -7 Michael Messer said:

...Or am I missing something?

Yes, the whole point. The effort has nothing to do with making better instruments or better music.



In the write-up, these spectrograms (www.its.caltech.edu/~politzer/paper-cone/original-volume-spectrogram.jpeg) show something that stands out in terms of measurable frequencies and correlates exactly with the easy-to-do identification by ear of what's a resonator guitar and what isn't. (It may or may not have anything to do with how our brains do it.) The six instruments are intentionally very different. There's a reminder of how frequencies that are unrelated to the pitch of the strings get produced by a pluck, and I'm keen to explore the specific details in this case.

The sound samples are there to show anyone who's never played a resonator that they can hear the difference themselves.

Plenty of folks aren't interested in how things work. Plenty don't like to read. That's OK.  It takes all kinds. Some people like rubber bridges.

[jono1uk]

Tell me this is a wind up? what a load of bollox.

[davey]

Some possibly helpful comments:

The Banjo with cone is strung with five banjo strings, total tension circa 55 pounds. A resonator guitar with six strings will have a string tension of at leat 190 pounds.

To be meaningful, the bridge has to be at the point where it intonates correctly. On your Banjo the cone is in the centre of the pot & the bridge needs to be further towards the tailpiece.

The main difference in sound between a Guitar of any kind and a Banjo is the length of sustain of the note. You could also have a look at a Dobro type arrangement (concave cone)and a National type (convex), which are different again.

Regards, Davey.

[davidppp]

Thanks, Davey.

This is the sound of that banjo-shaped thing, using the same Replogle biscuit, bridge, and cone as on the National in those comparisons: www.its.caltech.edu/~politzer/resonator-guitar/resonator-mp3s/banjores.mp3 .  Getting the intonation about right required the neck extension that you can see in the photo.  (In an earlier write-up, I included lighter biscuit and bridge to get a bit closer to real banjo sustain.)

Sustain and also inherent loudness are, indeed, the immediately obvious banjo/guitar differences.  But I think there's a lot in the timbre.  Banjos put a lot more emphasis on higher frequency components.  Also, banjos "ring."  That's a word that's been used to describe them from as far back as Stephen Foster (for banjos with essentially no metal parts).  Keith Richards said banjos ring in an interview where he described his favorite tuning.  The ringing is something I think they share with resos.  It's not well-understood by people who do very serious acoustics of musical instruments, but it's my favorite open question.  I think it's those "extra" peaks in the spectrograms.  (The "serious" guys don't much like me, either.)

I suspect that the differences people can hear between the two types of single cones are too subtle for my crude methods, but it's an interesting challenge.

[Michael Messer]

I was, while being critical of your tests, also being polite by welcoming you to my forum and to being a part of our community. Your response opened with "..Or am I missing something? Yes, the whole point. The effort has nothing to do with making better instruments or better music"... and that shows me that you completely misunderstood my words and that you could have been a little more friendly.

The Repogle cone which is too thick and without spirals is not giving you the correct reading of a National guitar, or any other instrument that it is put into. It is giving you a nasal tone with clipped highs and lows. The wrong frequencies. The only way you can do these tests properly is with a National cone or something that is equally as good.

I am now beginning to remember why I spent my afternoons in the local guitar and record shops when there were physics lessons at school.

Shine On
Michael

[jono1uk]

Jeeeez RJ,Son House, Honey-Boy,Johnny Shines etc would be turning in their grave , if you are looking at this beautiful "art" in the way your are doing then i don't think it's for you..
My advice.. stop p***ng around trying to "teach your grandmother to suck eggs" buy an MM Blues and play the f**ck out of it.

[bonzo]

Calm down jono calm down 😊 the guys on the forum are on the case!
(MM in particular)! I'm sure the guy has his own agenda, maybe more theoretical than musical perhaps.
I think that because this is a premier forum people do post here knowing they will get a serious response to their theories.
Should be taken as a compliment, and if it gives us pause to confirm our love for reso's then that's a good thing. Over the years I've been a forum member I've seen some interesting posts that while not immediately involving have occasionally made me think 'outside the box'.

Best wishes to you all, John
Ps string types comes to mind.