Adjusting sound

[TallDad71]

Does anyone have a good source for texts to help analyse exactly what went wrong with a build?

I built a guitar with superb tone out of Sitka and walnut. Everything about it went well and the sound is balanced across all strings.

On the strength of this I built another of the same design except out of Engelmann Spruce and Sassafras. The sound it makes grits my teeth. The bass notes are great, the middles ok and the trebles sound like a banjo!

My first issue is that I don't have a vocabulary to describe the sound. I need a reference for this.

My second is even if I can describe the sound it makes I have no skills in determining what action to take inside the box. Suffice to say I have already tried different strings, nuts and saddles to no effect.

my first guess is that the monopole is sympathetic to the bass middle and the cross dipole is sympathetic to no one. However it could equally be the backboard conflicting with the soundboard.

I'm not seeking a solution so much as a methodology for identifying the source.

[johnparchem]

Yup Trevor Gore with Gerard Gilet Contemporary Acoustic Guitar Design and Build. The Design book covers everything you are asking about including a vocabulary on how to discuss it.

[TallDad71]

Both of my last two posts have ended in a recommendation to get this book.

Time has come me thinks!

[Steve.Toscano]

You wont be disappointed... get them and get them now !

[Fisherman]

Have you tried adding more weight to the bridge? I've noticed this can make a big difference. Just put a lump of blu tack on various spots and experiment a bit - if something works, add the weight to the inside in the corresponding spot. Heavier bridge pins would be another option if it needs more weight.

Is it a live back or dead back? Agree with all the others re The Books...

[peter.coombe]

For what it is worth, I made a flattop mandolin from Engelmann and Sassafras and did not like the treble sound. Built 2 more from European Spruce and Sassafras and the treble sounded great. Just finished a guitar from Adi and Sassafras and it sounds pretty special. I love the sound I get with Sassafras, but not with Engelmann Spruce. I am not using Engelmann and Sassafras again.

[Mark McLean]

Pete, you are making me think now. The nylon string OO that I recently built (and posted here in the Gallery) was also Sassafras and Engleman. It has amazing bass tone and sustain, pretty good mids, but weak treble. I didn't know any better as it is my first try at a nylon-string guitar, and I am planning to try different strings to see if it improves. It is also my first try of falcate bracing - and there are a hundred other variables that could make a difference to the treble tone/volume. Reading what you both say I am now also wondering if the pairing of sassafras and Engleman just doesn't work so well. But I can't think of a rational reason why that should be so.......

[TallDad71]

How curious that Engelmann and Sassafras have clashed for you guys. I tend to agree with your last sentence that I too can't think of a rational reason why that should be so.

I have got to the point where I am willing to deconstruct the guitar and swap the soundboard out for some Sitka and build a guitar that sounds great again. My biggest problem with this is that I still won't be any the wiser why this soundboard failed so miserably.

The guitar was designed for fingerpicking so the back is reasonably thin and active. That said it makes no difference to the quality of the treble if I suppress vibrations in the back when playing.

[Bob Connor]

I built this Sassafras and Engelmann 0-18 14 fret about 5 years ago.

Sounded nice and balanced with none of the symptoms previously described.

I'd be looking elsewhere for reasons other than wood combinations.

IMG_4752.jpg (174.62 KiB) Viewed 23901 times

Regards

[Mark McLean]

I'd be looking elsewhere for reasons other than wood combinations.

OK - I agree Bob. There are lots of potential reasons that are more plausible that the wood types. I need to do some frequency analysis, and maybe deflection testing, to understand how the top is working (TallDad - this stuff is all in those books.......).

[johnparchem]

Here is a start if you have a PC. Get visual analyser http://www.sillanumsoft.org/ Its free. Set up using Trevor's instructions http://www.goreguitars.com.au/attachmen ... ata_R1.pdf. Do a tap test of the top, strung up but with the strings muted. You can get a spectrum graph to tell you where the main resonances of your guitar are. You can post it for help reading the graph.

[Craig Bumgarner]

I used Visual Analyzer at first but switched to the FFT app by Andrew Smith a couple years. It is about $10. As far as I know, it works only on Apple iOS, iPhone and iPad. VA is kind of quirky to set up and use. FFT by Andrew Smith requires minimal set up, very intuitive to use, saves files for future interactive recall and overlays, saves screen shot images to camera roll. Drag a guideline in from the side of the screen for quantifying peaks. X & Y axis can be zoomed in/out and shifted left/right/up/down with smart phone gestures like pinch, spread, touch and drag. Because it is on my phone, it is always handy and ready to go. Accuracy seems every bit as good as VA. I use FFT on an iPhone 7+ now which is a big improvement over the smaller iPhone 5. Any of the iPads would be good too, but I like having it in my pocket.

[TallDad71]

A whole new world.

Will investigate options and post if you guys are willing to advise on the squiggles that would be great.

[TallDad71]

IGNORE THIS POST. SUSPECT THAT ONE OF THE GRAPHS IS CORRUOTED BY EXTERNAL SOUND.

Here is my first attempt at collecting FFT samples John Parchem.

Craig I used your advice and downloaded Andrew Smith's iPad app, it was quick to learn and seemed to record something useful.

I used Trevor Gore's guide to collecting stats, tapping 10 times near the bridge and near an antinode. Furthermore the App allowed background noise to be sampled and then subtracted from the recorded noise. The graphs are all results of average inputs.

The following two images show the results on two guitars side by side. The two guitars are made from the same mould, one labelled classic has a sound I am very satisfied with. The second 'sassafras' has a treble which seems to distort, almost like a wire on a snare drum, but much more subtle. Both guitars were fully tuned to EADGBE and strings were left open to resonate with the tapping. The taps were made by a fret hammer with layers of felt taped around the plastic hammer head.

If you do have five minutes to look at the graphs and suggest a root cause that would be very appreciated.

Strike on bridge
The sassafras (orange) guitar seems to be exciting a lot more partials than the classic (green). This, I guess, is due to stiff areas of the soundboard being excited that perhaps need bringing under control!

Strike at Anti Node, about 70mm in from bottom edge directly over the X Brace
Same fundamental tone with a markedly stronger overtone at 270Hz

RAW DATA

Sassafras Bridge Strike

Sassafras Anti Strike

Classic Bridge Strike

Classic Anti Strike

[kiwigeo]

Comments from me:

1. Dampen the strings when tap testing. I slip a large piece of foam rubber between the strings and upper fretboard....if the strings vibrate then your going to get peaks all over the place.

2. My hammer is an eraser stuck on the end of a piece of dowel. I do my tap tests sitting with the guitar in a playing position.

[Craig Bumgarner]

I'm not real good at looking at other builders Frequency Response Curves (FRC) because there is a fair amount of information picked in recording the curves that helps interpret. A couple things though. The big peak at 94hz seems too low to be T(1,1)2. More likely T(1,1)1, the air resonance. Are you pointing the sound hole right at the mic? Typically the air resonance is pitched below the main monopole and lower in amplitude. The other thing would be that I typically dampen the strings with my hand or some folded cloth under the strings. I tap with my index finger, give it a good wack. If the peaks are muddy looking (wide or split), I'll switch to a pencil tapping with an eraser end, but you have to careful not to bounce it on the top or you will get double peaks.

When you say the treble distorts, is it one string only? Or all the notes above a certain frequency no matter where they are played? Is it one note, a couple or many? What is the range? I'm thinking distortion is not a top tuning issue that will show up in an FRC, it is more likely a mechanical issue of some sort. Could the string(s) be buzzing on frets?

[TallDad71]

Brilliant

Will redo tests with damped strings.

Craig, it's a buzz that sounds like a fret problem that is heard on top two strings whether open or fretted, there is no fret issue as I have already looked into this replacing both saddle and nut with plenty of clearance.

The graphs had mic turned away from source.

[Craig Bumgarner]

....it's a buzz that sounds like a fret problem that is heard on top two strings whether open or fretted, there is no fret issue as I have already looked into this replacing both saddle and nut with plenty of clearance.

If the problem exists on the open B and E strings and every fret all the way up, this is a frequency range of 247 hz to over 1000hz. Not likely what you describe because a peak or two is out of place.

To me, it sounds like a mechanical problem as opposed to a top tuning problem. Have you tried dampening the other strings when you play the buzzy one(s)? Is the saddle a good tight fit? Any chance you have backbow in the neck? Even the slightest bit on the B & E will sound awful. What is the relief on treble side? Was is the string action at the 12th fret? If it was just the open strings, I'd be looking carefully at the nut, but if is also happening on fretted notes, not likely the nut.

If any of this fails to turn it up, I'd be dampening every part of the guitar with spare hands and fingers while playing the offending strings & frets. Sometimes it helps to have a third hand in the operation if you can recruit someone. A customer once brought me a guitar that had a peculiar sympathetic vibration. It was not all that loud to me, but he found it very annoying. By dampening parts of the guitar while he played, we traced it to a slightly loose screw on the tuner axle.

You might try tapping around the body in various places. Sometimes a loose part or piece will vibrate in sympathy with certain notes or strings. Loose brace(s)? Saddle not fully seated? Bridge not fully tight to the top? Loose truss rods will make some very annoying noises.

The graphs had mic turned away from source.

When taking FRC, I direct the top of the guitar toward the mic(s) in the phone, pointing the bridge area at mic, about 12" away. I don't think the distance is critical, but being consistent is probably important. It is just odd to see that much higher peak at 95hz, maybe it is the hammer somehow.

[scripsit]

... it's a buzz that sounds like a fret problem that is heard on top two strings whether open or fretted ...

Do you have an endpin or pickup endpin socket installed? I had a guitar with a rattle/buzz on some notes, open and fretted, which took ages to identify and turned out to be a slightly loose washer inside the guitar at the endpin.

Easier to find and fix, but a similar sound, came from a loose washer under a machine head on the headplate, on a different guitar. This developed a couple of years after purchase.

Kym

[TallDad71]

Wow this frequency reader app is ace!

I am still nowhere closer to finding the cause of the issue now but a spectrum analysis gives me some great insight.

My main issue is my top E-String. Most of my strings when plucked consistently play the fundamental note at around 70Db then a whole range of decaying overtones and reducing Db levels.

The offending E4 string only plays at around 55Db at the fundamental frequency 330Hz, however the overtones at E5, B5 and E6 are playing at around 65 Hz, louder than the fundamental and with less decay. I would hazard a guess that this is what I can hear when I said buzzing.

My thoughts is that something is causing the partials to get over busy on this string and that could be affected by its seating. I will strip it all down again and see what can be done.

Thanks for all of the help so far.

[Bob Connor]

What sort of wood is the fingerboard?

And are the frets securely seated?

I built an instrument a few years back that was destined to hang on the office wall of a sawmill so I made the fingerboard from highly figured Blackwood. The frets didn't seat securely in the relatively soft Blackwood and the trebles in this instrument sounded just as you describe.

The open strings were fine but fretted they sounded terrible.

I ended up running some super glue into each fret and it fixed the problem.

Might be worth a look at.

Regards

[kiwigeo]

The offending E4 string only plays at around 55Db at the fundamental frequency 330Hz, however the overtones at E5, B5 and E6 are playing at around 65 Hz, louder than the fundamental and with less decay. I would hazard a guess that this is what I can hear when I said buzzing.

My thoughts is that something is causing the partials to get over busy on this string and that could be affected by its seating. I will strip it all down again and see what can be done.

Thanks for all of the help so far.

Don't read too much into what you're seeing. Wound strings will often give a weak fundamental and louder partials...particularly common with the high tension Savarez nylon strings I use on my classicals and alot of the wound Daddario steel strings I ran on my test rig were giving similar results...Storobosoft was having great problems latching onto the fundamental frequency of the string being tested.

[kiwigeo]

Craig, it's a buzz that sounds like a fret problem that is heard on top two strings whether open or fretted, there is no fret issue as I have already looked into this replacing both saddle and nut with plenty of clearance.

The buzz is present when the string is fretted at the uppermost fret? If this is the case then I'd be focusing on the saddle end of the string. First thing I'd check is string break over the saddle.

[TallDad71]

What sort of wood is the fingerboard?

And are the frets securely seated?

I built an instrument a few years back that was destined to hang on the office wall of a sawmill so I made the fingerboard from highly figured Blackwood. The frets didn't seat securely in the relatively soft Blackwood and the trebles in this instrument sounded just as you describe.

The open strings were fine but fretted they sounded terrible.

I ended up running some super glue into each fret and it fixed the problem.

Might be worth a look at.

Regards

I use Ziricote mainly, beautiful pattern, high density and looks stunning.

Have checked all frets and they are firm.

[TallDad71]

The offending E4 string only plays at around 55Db at the fundamental frequency 330Hz, however the overtones at E5, B5 and E6 are playing at around 65 Hz, louder than the fundamental and with less decay. I would hazard a guess that this is what I can hear when I said buzzing.

My thoughts is that something is causing the partials to get over busy on this string and that could be affected by its seating. I will strip it all down again and see what can be done.

Thanks for all of the help so far.

Don't read too much into what you're seeing. Wound strings will often give a weak fundamental and louder partials...particularly common with the high tension Savarez nylon strings I use on my classicals and alot of the wound Daddario steel strings I ran on my test rig were giving similar results...Storobosoft was having great problems latching onto the fundamental frequency of the string being tested.

Boooooooooooo

Thought I found a smoking gun there for a moment, your comments suggests all is not so straightforward. Saying that, the good guitars I have built all have strong fundamentals that are followed by quieter overtones.

I'm no expert on what makes for great notes but this guitars E4 string has very loud and clear E6 and E7 partials ringing out.

The bracing is already very light I'm thinking that sanding down the soundboard on the treble side might quite down the partials.