Australian/New Zealand Luthiers Forum

Thanks to all who participated in this – greatly appreciated.

First, a few more details about the guitars:

Both are falcate braced.
Both have live backs
The bridges are near identical; consecutive slices off the block, same mass (11.5 grams)
The strings are the same; Savarez 540J (High tension, “carbon”), however, the bass strings on the EIR guitar had been on my string test rig (I ran out of new strings when I needed them and these were the best I had, but this explains the slightly “rubbery” sound in the bass on the EIR guitar; slightly loose windings, methinks)
Action is 4mm and 3mm, both guitars (at least when no capo is applied)

The recordings were made on the same day, probably ~half an hour apart, so humidity change wasn’t a factor (though guitars can sound different at different humidities, for sure)

So, the difference?

The EIR guitar has mass loaded sides and that is responsible for the majority of the sound difference. As well as the tuning benefits (placing of the T(1,1)2) the major acoustical differences are in projection (which I don’t think anyone will be able to detect from the recording) and more “punch” which gives greater articulation and separation at the expense of a slightly slower attack (which to my ears tends to be masked by the extra clarity). The Palo Dorado guitar, live, sounds more like a conventional classical guitar of fan braced ilk, whereas the extra mass in the sides of the EIR guitar gives it a different tone, that could be described as “purer”, having an emphasis on the lower order string harmonics whilst still keeping enough of the higher harmonics to ensure good separation and articulation.

When heard live, the majority of people go for the EIR guitar. However, the Palo Dorado guitar, being lighter, shakes you around a bit more as you play it and some players like that, although it doesn’t do the audience any favours (less volume out front).

And to Ro’s question:

MBP wrote:How come it has nothing to do with B&S?

Well, the methods I use ensure that the resonant frequencies of the panels end up more-or-less where I want them, irrespective of the wood species used. That straight away eliminates the majority of the acoustical variables in the wood species mix. The bit that’s harder to control is the sound spectral absorption, which differs by species. Measuring Q or log dec gives a measure of sound spectral absorption at a particular frequency, but I don’t know of a good method to get a spectral view of that. With the side mass thing, you can, of course, put them in or leave them out, so it’s easy to hear the before and after. Putting mass in the Palo Dorado guitar makes it sound very much more like the EIR guitar.

For those interested, we had three Fuji cameras available for the video recording, all “still” cameras with video and sound recording functions, producing .avi files. However, we only used one. The sound was recorded using a single Behringer C-1 condenser mic, phantom power (and nothing else) from a mixer panel, then straight into a Mac running Garage Band. For these two takes the mic was in the same position (you can just see it bottom left of the vids). The sound from the video take was used for syncing the track from Garage Band, which was spliced onto the video using iMovie. The video sound track was then suppressed, leaving the video in sync with the Garage Band track which was then exported to YouTube. Thanks to Damien Geraghty who was playing and Alan Lloyd whose studio, mic and mixing gear he so kindly allowed us to use.

How far down did you drop the top renonance with the side mass loading?

5Hz

Trevor,

Going by what you say about eliminating the difference between wood species what is your preferred wood choice?
Other than getting very consistent guitars do you think it makes them sound better?

Personally, I like very responsive guitars, because on the rare occasions I get to play I'm a "bare hands" finger picker on steel strings (but more frequently classical, these days). However, it really is horses for courses.

For a steel string finger picker I get highest monopole mobility and lowest damping using WRC. Engelmann comes in close behind. I really like the type of SS in the pics above. You can tell what grade of paper you finished buffing yours nails on when you hear one of those!

I got to play "the shed guitar" tonight at the AGMS dinner and have got to say it's a beauty. I'm now a convert....no more expensive tone woods for me. I was also impressed at Trevor's generosity in sharing his knowledge.

Hi Dekka...Please forgive my ignorance but what is the AGMS?.....

...and your right about Trevors generosity!...its AAA+

...the Shed Guitar wowed us too when we saw it at the course we did at Stratos School in January...

John

Hi John,

Australian Guitar Making School.......(Strato's place)
I think it used to be called "Lakeside guitar making school"
He has an annual dinner where we all display, play and talk guitars in between Food and booze. It's a great opportunity to see the diversity of approaches to making, not just guitars, but mandolins, ukes, etc. There was even a beautifully made violin. Some of the wood-work is stunning to see and gives kindling butchers like myself something to aspire to.

Thanks Dekka....Sometimes I can be thick! Acronyms are not my strong point! I should have recognized it!...Anyway there you go...
Thanks

John

Well, not sure if this is going to work (for a whole lot of reasons)...but anyway, here, I think, is a recording of me playing "The Shed" guitar, with dead strings. Maybe...

If you hear anything, the left channel is from a condenser mic and the right channel is from the K&Ks. If you don't hear anything, it's because I haven't yet figured out how to run all this software...

Hi Trevor,

Thanks for your post. I'm unfortunately unable to discern one side from the other but it sounds sweet all the same. (I'm not sure if it's my industrially deaf ears or a mono computer setup.)

Dekka

Well that is certainly proof that Pinus radiata and meranti can make great sounding guitars. I had my Pinus radiata mandolin at the National Folk Festival, and a lot of players could not believe it had a Pinus radiata top.

Peter

Dekka wrote: I'm unfortunately unable to discern one side from the other...

There's not much in it, Derek, that's for sure! The difference was quite a lot clearer before it was MP3'd, but on headphones I can still hear the different channels, mainly because the mic is picking up the sound of the rain on my tin roof (left channel)!

Peter, I'm not sure I'd be classing radiata as a fine tone wood yet, but if one had a few pieces to pick through, I'm sure it would be possible to select some good stuff to make a pretty decent SS guitar at least.

Trevor, what are "mass loaded sides"? Just heavily built ribs or something more elaborate?

matthew wrote:Trevor, what are "mass loaded sides"? Just heavily built ribs or something more elaborate?

Something more elaborate!

There's some more details here: http://www.goreguitars.com.au/main/page ... sides.html

A slightly more technical explanation: A guitar has a "main wood" mode of vibration at around 180-200Hz, and it it this mode that is responsible for much of the sound radiation from a guitar, even well away from its resonant frequency. This mode has a ring shaped node line typically 40mm in from the ribs on the lower bout. There is vibration either side of the node line, but the area outside the node line radiates sound 180 degrees out of phase with respect to the area inside the node line and so some sound cancellation happens. It can be regarded as a sort of concentric dipole. If you can move the node line outboard you get more positively radiating area and less negatively radiating area and the instrument gets louder. Mass loading the sides makes this happen. The frequency of the main air mode also changes.

The full technical explanation, mathematical modelling, experimental results and how to exploit the effect in the instrument are explained in "the book". This effect is one of the ways that Smallman guitars get their volume - their heavy "chassis".

thanks Trevor. i only do double basses, so cogitating on whether a similar approach would have a positive effect on this instrument. i have a feeling it would. problem with basses is they are much slower to build, so less scientific experimenting is possible in a lifetime!

I guess it should work - the laws of physics tend to be universally applied - but I've next to zero experience with B-doubles. And, even with their size, once the box is closed, you can't get your hands in!

trevtheshed wrote:I guess it should work - the laws of physics tend to be universally applied - but I've next to zero experience with B-doubles. And, even with their size, once the box is closed, you can't get your hands in!

Yeah, usually ...



But I'm not sure how I'd go about loading the sides with mass from the insides anyway. I guess I'll have to get your book to find out.

We have a ring mode (mode 5) that extends cross the upper and lower bout with the center decoupled from the ribs to an extent by the FFs. The idea of pushing the node line outwards by adding mass to the ribs seems like it may work. But of course, a heavy instrument already, a heavy DB an be a liability no matter how great it sounds!

Ahhh, a B-dub with a manhole and crawl space. What next?

Not sure whether it's a good place or not, but there's probably enough wood in the lower bout corner block to screw something into, if you feel you have sufficient longevity.

Ah so you're talking just MASS, like a lump of lead, as opposed to carefully lining the ribs with gold ... and I have six blocks to screw into ... oh, fun

Yep, lead is pretty massy.

I thought you bass builders liked lining your ribs - preferably with silk. Though I do agree that gold lined would be a bit of one-up-manship on James Ham.

matthew wrote: [...] to carefully lining the ribs with gold ...

Matthew, I think this might be the way to go if you want add side mass without opening the box!

No Trevor most of us bass builders basically leave the ribs alone, maybe a few linen or spruce cross strips as crack-stoppers. Rarely silk.

Some people make timber laminated ribs, its a good idea if for no other reason than basses get banged into doorways and stages. That bass shown below has laminated ribs. I didn't build it though, i just made the access port and the removable neck conversion.

Jim Ham is the only one I know of who regularly laminates silk INTO his ribs for strength and light weight. Timber-silk-timber, not just a silk lining.

If all goes according to plan I'm going to do a DB workshop with Jim Ham and 20 other bass nuts at Oberlin in June. Looking forward to that. Just one little hurdle to overcome first :-/

I hope you get to enjoy the workshop with Jim, Matthew (and hear what he has to say about mass loaded sides! )

Things cleared a bit for us ... So I'm off to Ohio in June! getting excited. Jim is running an acoustics workshop in parallel with the bass maker's workshop I am attending. We'll meet up with that bunch for dinner each night, and there will no doubt be mutual brain-picking going on.