Blackwood L-00 analysis

[Dominic]

Hey, I’ve had this blackwood L-00 boxed for a while now waiting for bindings and neck fitting. But I got the books in the meantime and went back and did some analysis and study and things slowed down.

Well I just got back to this guitar and took the spectrograph in green in the chart. It has no bridge btw.
The numbers were 100 199 with no back response or a big hole at 240. The back is a 4 brace back but brace 3 and 4 had about 2mm scallop but were still quite tall. They tapper down to nothing at the edge and the back was not moving at about 3mm so I figured I could thin the edge and try and get a back response and this would lower the T(1,1)1 and T(1,1)2 modes.

So I went at the back with a scraper around the edge of the lower bout and used a little wooden plane and took a few mm of the centre of braces 3 and 4 and blended them in and retested. I got a back response that was still a little high and not much else. I still had not thinned the edges of the top so I took them down to about 2mm and blended them back towards the bridge and the guitar opened up a bit and seemed to have much great sensitivity. The T(1,1)2 had dropped a bit but was still up around 196. So I did a little more thinning around the lower bout back tapping while I went to judge the response. And I sanded the tool marks from the braces inside and went back and tested and got the green line, 97, 193, 235. I am going for 95, 180, 220.

I’ll stop there because I still have to add the bridge and the back will get sanded again and cleaned up after the binding are done and that will further lower the top and back freq and the air needs to be a bit lower to get it away from G at 97.99 which just happens to be the soundhole diameter. So could I bind the soundhole if it stays where it is after binding and cleaning up.

But so far this has focussed me much more on aiming for something rather than just kind of using judgement which would have meant I used some lovely wood to make an average guitar. I feel like Trevor has sold these books too cheaply, if this one comes out well I’ve already made the investment back many times.

Anyway, I said I’d share some charts so there you go with my first one. I’ll follow up with more as it get closer to getting strings.

Cheers
Dom

[Clancy]

and got the green line, 97, 193, 235.

I think you mean the 'pink' line Dom
Will it be ready for me to try it out when I'm back for xmas?

[Trevor Gore]

Good stuff Dom!

I sanded the tool marks from the braces inside and went back and tested and got the green line, 97, 193, 235

Sure it wasn't the purple line?

That's a pretty noisy looking trace, BTW. Is that direct into your computer's built in mic? (or even a phone app.?), then Excel? Mine routinely come straight out of VA looking something like this:

SS classical.jpg (89.64 KiB) Viewed 12806 times

(...and Clancy beat me to it...)

[Dominic]

Yes sorry green first, pink second. You all knew what i was talking about I hope.

Trevor, I was using my laptop internal speaker. I have just ordered a half decent samson USB mic with a flat freq response so I'll see if I can clean up the signal. Perhaps I also have the boost turned up too much. I'll muck around and what happening.

Thanks for the tips

Dom

[Trevor Gore]

Sorry Dom, should have said. I'm using a Shure PG57 dynamic mic these days, not too expensive. My old Sennheiser died. I plug it straight into the mic input on my Tosh. Tecra M5 and use the mic boost.

[Clancy]

Just for further comparison, here's one taken with my Samsung laptop's internal mic.
I didn't take too much notice of the values because of the mic & because I was tapping with my finger pad.
(Just testing the method & software)

BW OM FS 105 189 .jpg (43.59 KiB) Viewed 12779 times

Actually, this plot is only up to 500Hz so it probably looks cleaner than it would when looking up to 1kHz like yours

[Dominic]

Hey Craig, I’ve written this email several times and been foiled by the ghost in the machine.

So, I want to ask about the plot you put up. Is it a finished guitar? Are you happy with it and what are the actual numbers for your peaks. Are you planning on doing some tweaking and if so what values might you aim for and how are you thinking of getting there. Have you gleaned any insights into how you build and what to do.

I’ve been setting up to do deflection tests so I can calculate MM. I’ll start putting them up when I have the bugs worked out.

Cheers
Dom

[Trevor Gore]

Hey Dom,

Did you get that USB mic.? How'd it go?

[Dominic]

Hi Trevor, I have the post office ticket for it so I'll pick it up today and give it a go. I'll let you know how it goes and put up a pic.
Cheers
Dom

[Clancy]

Sorry Dom, missed your question(s) somehow.

The plot I posted is of the Blackwood/Englemann OM I put in the forum earlier in the year.
The peak values are in the jpg name (so that I can always have an easy record)
ie. BW OM FS 105 189.jpg translates as "Blackwood Orchestra Model with peaks at 105Hz & 189Hz.
(In this case it was not a responsive back, so no third number)

Am I happy with it?
Well I was happy with it when it was built.
I'm happy that others have liked it and used it in recordings
I'm also happy to have gotten it back!

But I guess I am more critical of it having read the books and started applying some of the info.
The frequencies translate as G#+20 & F#+40, which seem fairly reasonable places to land.
Interestingly, I just finished another OM that's an identical build in everyway except the binding (blackwood cut from the same board, Hein's Englemann from the same order, African Mahogony from the same board, bracing from the same stock - cut and shaped to the same initial figures, etc)
The frequencies for that guitar, tapping again with my finger, came out at 104 & 180 - or G#+0 & F#-50.
This tells me, primarily, that I can build with fairly consistant results - not too bad since I use hand planes for thicknessing to my (previously) indeterminate "wobble board"/"yep, that feels about right" thickness for the plates
Of course, the results also indicate that I should give the soundhole size some consideration

Hope this answers your question(s)

[woodrat]

Sorry Dom, missed your question(s) somehow.

The plot I posted is of the Blackwood/Englemann OM I put in the forum earlier in the year.
The peak values are in the jpg name (so that I can always have an easy record)
ie. BW OM FS 105 189.jpg translates as "Blackwood Orchestra Model with peaks at 105Hz & 189Hz.
(In this case it was not a responsive back, so no third number)

Am I happy with it?
Well I was happy with it when it was built.
I'm happy that others have liked it and used it in recordings
I'm also happy to have gotten it back!

But I guess I am more critical of it having read the books and started applying some of the info.
The frequencies translate as G#+20 & F#+40, which seem fairly reasonable places to land.
Interestingly, I just finished another OM that's an identical build in everyway except the binding (blackwood cut from the same board, Hein's Englemann from the same order, African Mahogony from the same board, bracing from the same stock - cut and shaped to the same initial figures, etc)
The frequencies for that guitar, tapping again with my finger, came out at 104 & 180 - or G#+0 & F#-50.
This tells me, primarily, that I can build with fairly consistant results - not too bad since I use hand planes for thicknessing to my (previously) indeterminate "wobble board"/"yep, that feels about right" thickness for the plates
Of course, the results also indicate that I should give the soundhole size some consideration

Hope this answers your question(s)

Good post Craig....I was in the wobble board camp before Trevor and Gerard published their book....man am I glad they did...now I dont feel like I am shooting in the dark! More power to Everyone!

John