Search found 64 matches

by Jim watts
Tue Jan 29, 2019 3:55 pm
Forum: Instrument Builders Forum
Topic: Spectra question
Replies: 17
Views: 953

Re: Spectra question

Trevor, The amplitude difference between the t1,1 and t1,2 was my first thought too after rereading the section. With the set up in the original configuration, I held a book (your book BTW) 5-6" in front of the sound hole to know the amplitude of the t1,1 down. But I still had the deep trough, so I ...
by Jim watts
Sun Jan 27, 2019 4:24 pm
Forum: Instrument Builders Forum
Topic: Spectra question
Replies: 17
Views: 953

Re: Spectra question

Well, I spent part of the day trying figure this out and I believe I made some progress. Looking at Trevor's references of section 2.4.2 it appears that frequencies can interact with one another depending on their phase and strength. I won't bore you with a bunch of spectra plots unless you want, bu...
by Jim watts
Fri Jan 25, 2019 4:25 pm
Forum: Instrument Builders Forum
Topic: Spectra question
Replies: 17
Views: 953

Re: Spectra question

Trevor, Thanks for the references. I've been pretty tied up with some other work stuff, so I'm still chewing on this. I'll get closer to having this figured out in a few days, I think.
Jim
by Jim watts
Tue Jan 22, 2019 3:12 pm
Forum: Instrument Builders Forum
Topic: Spectra question
Replies: 17
Views: 953

Re: Spectra question

Ross, I just trashed my shop computer and my old amplifier a few months back, cleaning up the shop! Oh well :cry:
by Jim watts
Tue Jan 22, 2019 10:16 am
Forum: Instrument Builders Forum
Topic: Spectra question
Replies: 17
Views: 953

Re: Spectra question

Thanks Trent, I'm one of those very few anti smart phone guys.
As I was thinking about it a little more this seems more than likely a phase thing with the back. I'll check the black book for some more info.
I'll try retapping in the next day or two and see if I can get anything different.
Jim
by Jim watts
Tue Jan 22, 2019 5:09 am
Forum: Instrument Builders Forum
Topic: Spectra question
Replies: 17
Views: 953

Re: Spectra question

Thanks for the replies. This guitar is being built by a student over a long time period, a few years. I was just going over my notes, it appears we wanted to leave the top thick so we could bring down the resonances. The idea being he'd learn something from that exercise (me too of course) and he'd ...
by Jim watts
Sun Jan 20, 2019 5:15 pm
Forum: Instrument Builders Forum
Topic: Spectra question
Replies: 17
Views: 953

Re: Spectra question

Ross,
It looks we posted at the same time.
The uncoupled top is at 222 Hz. I had planed to do some top thinning on this one, but this is probably more than I wanted.
by Jim watts
Sun Jan 20, 2019 5:12 pm
Forum: Instrument Builders Forum
Topic: Spectra question
Replies: 17
Views: 953

Re: Spectra question

Hey martin, some addition information; - I used a Zoom h4 recorder for the mic. It actually has a pair of mics. - Recorded into Va, fft size of 16384 and sample rate of 11025. - The guitar was tapped with an eraser on a stick, lightly in the bridge area. - Averaged 10 samples. - The mic was little l...
by Jim watts
Sun Jan 20, 2019 6:47 am
Forum: Instrument Builders Forum
Topic: Spectra question
Replies: 17
Views: 953

Spectra question

I'm currently working on a guitar and have a questions concerning the dip in the spectrum at 201Hz. I was anticipating the top to be there. The guitar is nearing completion, It's a fan braced classical, without a bridge at this point. I'd like to pull everything down a bit. So, what is it and why do...
by Jim watts
Sun Jan 20, 2019 3:16 am
Forum: Instrument Builders Forum
Topic: Hollowbody electric
Replies: 10
Views: 832

Re: Hollowbody electric

She's a beauty!
by Jim watts
Sun Nov 11, 2018 4:26 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Predicting Panel Mass SS - Lookover
Replies: 4
Views: 538

Re: Predicting Panel Mass SS - Lookover

John, you lost me on your area calculation. Pause.... .00119 is in Kg/cm correct? Now that I've considered the area calculation, that's an interesting way to do it.
by Jim watts
Sun Oct 28, 2018 4:06 am
Forum: Instrument Builders Forum
Topic: Question re strength of different mahoganys
Replies: 16
Views: 1528

Re: Question re strength of different mahoganys

The only two true Mahoganies I'm aware of are Honduran and Cuban. There must be more, but there's lots of faux mahoganies which I assume the question concerns. I know Larrivee uses Khaya (African Mahogany?) with success for sometime now.
by Jim watts
Sun Jul 08, 2018 3:33 am
Forum: Instrument Builders Forum
Topic: 8 String bocote falcate braced nylon string crossover guitar
Replies: 17
Views: 2718

Re: 8 String bocote falcate braced nylon string crossover guitar

John, That looks great! How were you able to drop the main air that low? I'm primarily building with a Hauser plantilla and my air resonance is usually around 102 HZ and I would like to drop it some. Looking at Trevor's sensitivity analysis it looks like sound hole diameter and back stiffness are my...
by Jim watts
Mon May 14, 2018 11:27 am
Forum: Instrument Builders Forum
Topic: End of the week how to, how to fret skim
Replies: 12
Views: 2200

Re: End of the week how to, how to fret skim

OK, that makes sense. Usually I see the type of thing with a flat leveling device used under tension.
Thanks
by Jim watts
Mon May 14, 2018 7:51 am
Forum: Instrument Builders Forum
Topic: End of the week how to, how to fret skim
Replies: 12
Views: 2200

Re: End of the week how to, how to fret skim

I'm always confused when I see something like this. When we level frets under string tension aren't you removing any relief you had?
Thanks
by Jim watts
Wed May 02, 2018 1:37 pm
Forum: Instrument Builders Forum
Topic: Pinless Acoustic Bridge
Replies: 7
Views: 1583

Re: Pinless Acoustic Bridge

Mark,
I pattern routed using a 1/8" slotting style router bit with a guide bearing from my binding set to get the right depth.
The style of bit I used is shown on this web page.
https://www.mlcswoodworking.com/shopsit ... _slot.html
Hope this helps.
by Jim watts
Sun Apr 29, 2018 1:27 pm
Forum: Instrument Builders Forum
Topic: Pinless Acoustic Bridge
Replies: 7
Views: 1583

Re: Pinless Acoustic Bridge

Alan,
I just sent you a PM with an attached drawing.
Jim
by Jim watts
Sat Apr 28, 2018 9:52 am
Forum: Instrument Builders Forum
Topic: Pinless Acoustic Bridge
Replies: 7
Views: 1583

Re: Pinless Acoustic Bridge

Alan,
I think I have a drawing or model of a bridge I did a while back. See the photo below.
If you want, I can try to dig it up if you're interested.
2008_0124bridge0005.jpg
2008_0124bridge0005.jpg (114.05 KiB) Viewed 1530 times
by Jim watts
Thu Apr 26, 2018 1:46 pm
Forum: Instrument Builders Forum
Topic: RIP Jim Williams
Replies: 4
Views: 1554

Re: RIP Jim Williams

Seems like I've read many articles in the GAL by Jim. He contributed greatly to our craft and is a sad loss indeed.
by Jim watts
Thu Apr 26, 2018 12:46 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Measuring top and back frequencies while voicing
Replies: 21
Views: 9358

Re: Measuring top and back frequencies while voicing

Good to see this again and Brian's videos, thanks for posting that Trevor. I curious if there would be any use in adding a Q calculation to one of the taps as done in Trevor's book. If so which one. Or can we just compare the stiffness and weight and get a similar kind of thing (I think so) ? Seems ...
by Jim watts
Fri Sep 08, 2017 2:48 pm
Forum: Instrument Builders Forum
Topic: Completely traditional looking Hauser style classical guitar
Replies: 45
Views: 15931

Re: Completely traditional looking Hauser style classical guitar

Ouch, hopefully a new bridge is all that's required.
Sorry to see that John.
by Jim watts
Sat Sep 02, 2017 1:29 pm
Forum: Instrument Builders Forum
Topic: laminated plates
Replies: 12
Views: 3466

Re: laminated plates

Rod, you may have problem with the Nomex as it'll really only flex in one direction. An Archtop may have gentle enough curvature that you'll get away with it using 3mm thick core. But, there's a product called "flex core" which is designed to flex in both directions. It has a different cell geometry...
by Jim watts
Sat Jul 29, 2017 9:07 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: I lost the monopole...
Replies: 20
Views: 9580

Re: I lost the monopole...

Miguel,
Why is there not a strong peak for the main air frequency, does the paper rolled in the sound hole suppress it?
by Jim watts
Sat Jul 29, 2017 5:39 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: I lost the monopole...
Replies: 20
Views: 9580

Re: I lost the monopole...

Miguel, I should of noticed earlier but I see you back is only clamped on with a few clamps. I think every will change/be more defined when it's glued on.
by Jim watts
Thu Jul 27, 2017 2:51 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: I lost the monopole...
Replies: 20
Views: 9580

Re: I lost the monopole...

Miguel, While others are certainly better at deciphering this than me, I suspect if you were to take a tap spectrum you would see a very broad peak around the 202 mark, or perhaps a really narrow one that you just can't dial into with your frequency generator. I believe the first scenario is most li...