So, on my 4 th build, and pretty happy with the evolution. Using a padron box, which is a bit thin ( inch and 3/4) and about 7 by 9.5 inches. Anyway... Sound holes. I found some info on here about size, and smaller helps bass tones, etc. planning on using .75 inch hole.... But placement?! I have always put them in quadrant on lid above the "bass" or deepest string and toward neck. This seems popular. Thoughts on other positions? Below this on high string side toward neck? Or even on side of box as opposed to lid or back? I will likely use a piezo of some sort but for this discussion lets assume we want max acoustic volume. Thanks.
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You want the sound hole at a nodal point, a point where the top is not vibrating. You can scatter salt across the top and vibrate it to identify the nodal points or simply guess as they will normally be in the center and corners.
Beyond that, I've read a corner on the bass side will emphasize bass and vice versa. Honestly I don't have enough building experience to agree or disagree but my gut feeling is that is any effect will be minor. I believe the size of the soundhole will have more influence on bass/treble than position.
The nodal points vary in position with pitch - they're not the same at all frequencies. To really oversimplify, consider the top as a string. Consider the lowest frequency component (a half-wave). In that case, the nodes are at the edges where the top meets the sides. Then, in the case of the first harmonic of that frequency, the nodes are at the middle and the two ends. Then there's the F3 mode, where the nodes are at the ends, and 1/3 of the way from the ends, and the middle is an anti-node. And so on. Depending on the frequency, the middle can be a node or an anti-node.
Complicate this further by the fact that the top is a plate, not a string, and generally not a uniform plate, so the modes of vibration are a lot more complex. As you said, the corners (or any place the top is not free to vibrate, so wherever it's attached to the sides) is a node. But nobody ever puts the soundhole there on an instrument. Similarly, I've never seen an instrument with a soundhole in the center of the top. So I'm having my doubts about the "put it at a node" concept...
I've been thinking about this stuff enough recently so that I'm just about motivated to put together a test setup to try to verify some of these urban legends once and for all... Or not. :)
You are taking "center" and "not vibrating" too literally, I suspect to make a point for argument. There may be no exact suitable point for a soundhole where there are zero vibrations. Compromises are made for both aesthetics and practicality.
No, I'm not looking for an argument, if that's what you mean - not at all. It's just that there are a lot of sort of half-truths and urban legends floating around, that get repeated until we've heard them enough times to consider them "true".
For example, placing the sound hole on a CBG in the upper bout. Why? I suspect the original reason was that, in through the body neck designs, putting it the center looked terrible because you could see the neck through the hole. So people found a convenient spot to put it where it would look ok, which had to be on one side or the other of the neck. When it was closer to the player, the instrument sounded louder to the player, so that became the sweet spot. After that, a whole bunch of extra stuff grew up around that placement.
Anyway, I'm really not trying to be argumentative. I just suspect that placement of the soundhole isn't all that critical. I do believe that having a soundhole is better than not having one, most of the time, for an instrument that's to be played acoustically. But even that's not always true - it really depends on the sound you're going for. I just completed a copy of an Anglo-Saxon lyre, that used a cedar top, no bracing, with no soundhole at all, and it sounds very sweet, and plenty loud, even with nylon strings. (I left the top thick near the bridge, and tapered it out to the edges...) Also, the Turkish saz is usually made with no soundhole at all, and it sounds ... well,... like a saz.
I've been trying to understand this all better myself - maybe a little obsessed. In any case, I apologize if I came off too strongly. I think questioning and challenging one another, as long as it's done with politeness and respect, is a great way for all of us to learn more than we came to the discussion with...
Urban myths aside, here is one you can reason through... The sound comes from the top and back vibrating, if you cut out the vibrating portion of the top, you'll have less mass vibrating. So on a CBG, generally a square box, there will be natural nodal points near the corners since it's supported on two sides and the diagonal will be in tension so that's where I cut sound holes. You can get into resonant frequencies and all that but it seems overkill for a box with only 100 or so cubic inches of volume.
I'm not following your reasoning. Of course there are nodal points where the top is fixed - the anchor points of a vibrating plate are always nodes - they're fixed and can't move. But the middle is not the same - it can be a node or an anti-node, (or neither), depending on the frequency of excitation. One thing that I've found when I've used the "tuning-fork test" for bridge placement, i.e. finding the spot that makes the loudest sound when I hold an A440 tuning fork against it, is that the middle is typically the spot that will allow the sound to be loudest, i.e. it's an anti-node for that frequency. I don't think I'd want to put a hole there.
Now, as far as mass is concerned, the thing that makes the sound coming off the top isn't the mass of the top, it's the surface area - the surface area moves air, which creates pressure waves in the air, which conduct the sound to your ears. Adding a hole removes some of that surface area, but it's compensated by the fact that the vibration of the top and back is also moving air through the hole. So, starting from no sound hole, the total sound volume increases as you increase the size of the sound hole - up to a certain point, at which point increasing the size of the sound hole starts to decrease the sound volume.
I believe you were right earlier, (I think it was you), when you said that ideally the hole would be at a place where there was no movement at all. Other than the place where the top attaches to the sides, there are no points like that on the top for all frequencies, so any placement is a compromise. This is why a lot of guitar makers have moved to the idea of putting the sound hole, or sound port, on the side of the instrument instead of on the top - usually on the side that faces up towards the player. In this way, they get the maximum energy transfer from the top, as well as getting the benefit of a sound hole ...
So maybe the real answer to the question that started this thread is to put the hole on the side that faces up when you play...
the thing that makes the sound coming off the top isn't the mass of the top, it's the surface area
Surface area is a measurement, mass vibrates.
I should clarify what I meant by center; I was referring to the upper center near the neck joint and where the fretboard overlaps the soundboard. That area will be less free to vibrate.
A sound hole facing up will benefit the player but not the listener. If the instrument is amplified then it doesn't matter. As I said, always compromises.
It's true that mass vibrates. But do this thought experiment. Imagine two objects with the same mass, but one of them is an extremely thin plate, and the other is a sphere. If you drive them with the same energy - like a vibrating string - which one do you think will transfer more of that energy to the air to create pressure waves that you hear as sound? There's a reason that fan blades are blades, and not fan balls.
Anyway, I think Sean response covered this. It would be cool to be able to get the benefit of a hole without reducing the area of the top, like when you put a sound port on the side facing the player, but to have it facing forward, towards the listener - maybe by using an elbow or a horn going from a sound port on the upper side, but facing forward. I think there was a fiddle made that way ...
Snip the thing that makes the sound coming off the top isn't the mass of the top, it's the surface area.
It is both, the energy from the strings has to drive the top, the lighter the top the more energy goes into vibrating it, in practice that means a thin top should vibrate more easily than a thick one. Once the top has begun to vibrate, it then moves the air inside the box and outside it, both are surface area effects. There will also be an effect at the base of the bridge as the sound runs through the saddle. That's how a skeleton instrument works when fitted with a bridge piezo
Sean Laffey > Michael RecchioneMay 29, 2013 at 5:44am
I did a quick and dirty empirical test on this theory. I took an old six string guitar and a Vintage brand ukulele. (Same basic shape,same cheapo wood).
Here how to repeat my test, you'll need a quiet room::
Strike a string and as the note resounds rub your finger over the sound board. For the guitar I could hear the note dying as my finger dampened the resonance in the plate, i could also get it to wow and flutter too, .With different strings I used this method to find the hot spots. The uke was dead before I ran my finger over it. So first conclusion the bigger top plate of a guitar does transmit a large proportion of its sounds as it vibrates.
OK we all know that.
So next up I took a very thin piece of clear plastic (from a CD stack.. the protective disc that comes with the CDs) and placed it over the sound holes of the uke and the guitar. This would add negligible mass to the top but prevent air escaping from the hole.
The results were: the uke was very much quieter with the plastic cover. The guitar was a bit more complex, hardly any change in volume but the treble was less complex, the top E string had less sparkle and gave a warmer sound. I then moved the disc around the sound hole of the guitar , partially covering it, and the result was with just a fraction of the air hole left open the top 3 treble strings brightened again. It seemed to have no noticeable affect on the 3 bass strings
Next I made a floating bridge from a scrap of wood and stuck it under the strings on the uke. Repeated the test with the sound hole cover and the sound was brighter (OK it wasn't in tune as the intonation was off, but I was only sampling the volume)r. So my conclusions are
1)small bodies instruments such a uke or CBG need the sound hole because the top is too stiff to project enough sound energy on their own.
2) a floating bridge will help drive the small stiff top.
3)) the bigger the instrument. the more of the top plate can flex, so the importance of the sound hole decreases.But as the higher tones comes from the smaller , narrower, stiffer upper bout of the guitar a sound hole helps to develop their character.
As a CBG is by definition box , there is no upper or lower bout*, so you should have far more choices for a sound hole size and position. Of course how and where you join the neck will affect the sound greatly.
*On the guitar I tested. I calculated the air volume in the upper bout to be about 2 litres , the lower at least 7 litres. I'd guess because the neck attachment is at the upper bout this would make that part t of the guitar much stiffer.The maximum width of the upper bout, ie side to to the finger board was only 10cm,again adding stiffness to that part of the guitar.
Replies
You want the sound hole at a nodal point, a point where the top is not vibrating. You can scatter salt across the top and vibrate it to identify the nodal points or simply guess as they will normally be in the center and corners.
Beyond that, I've read a corner on the bass side will emphasize bass and vice versa. Honestly I don't have enough building experience to agree or disagree but my gut feeling is that is any effect will be minor. I believe the size of the soundhole will have more influence on bass/treble than position.
The nodal points vary in position with pitch - they're not the same at all frequencies. To really oversimplify, consider the top as a string. Consider the lowest frequency component (a half-wave). In that case, the nodes are at the edges where the top meets the sides. Then, in the case of the first harmonic of that frequency, the nodes are at the middle and the two ends. Then there's the F3 mode, where the nodes are at the ends, and 1/3 of the way from the ends, and the middle is an anti-node. And so on. Depending on the frequency, the middle can be a node or an anti-node.
Complicate this further by the fact that the top is a plate, not a string, and generally not a uniform plate, so the modes of vibration are a lot more complex. As you said, the corners (or any place the top is not free to vibrate, so wherever it's attached to the sides) is a node. But nobody ever puts the soundhole there on an instrument. Similarly, I've never seen an instrument with a soundhole in the center of the top. So I'm having my doubts about the "put it at a node" concept...
I've been thinking about this stuff enough recently so that I'm just about motivated to put together a test setup to try to verify some of these urban legends once and for all... Or not. :)
You are taking "center" and "not vibrating" too literally, I suspect to make a point for argument. There may be no exact suitable point for a soundhole where there are zero vibrations. Compromises are made for both aesthetics and practicality.
No, I'm not looking for an argument, if that's what you mean - not at all. It's just that there are a lot of sort of half-truths and urban legends floating around, that get repeated until we've heard them enough times to consider them "true".
For example, placing the sound hole on a CBG in the upper bout. Why? I suspect the original reason was that, in through the body neck designs, putting it the center looked terrible because you could see the neck through the hole. So people found a convenient spot to put it where it would look ok, which had to be on one side or the other of the neck. When it was closer to the player, the instrument sounded louder to the player, so that became the sweet spot. After that, a whole bunch of extra stuff grew up around that placement.
Anyway, I'm really not trying to be argumentative. I just suspect that placement of the soundhole isn't all that critical. I do believe that having a soundhole is better than not having one, most of the time, for an instrument that's to be played acoustically. But even that's not always true - it really depends on the sound you're going for. I just completed a copy of an Anglo-Saxon lyre, that used a cedar top, no bracing, with no soundhole at all, and it sounds very sweet, and plenty loud, even with nylon strings. (I left the top thick near the bridge, and tapered it out to the edges...) Also, the Turkish saz is usually made with no soundhole at all, and it sounds ... well,... like a saz.
I've been trying to understand this all better myself - maybe a little obsessed. In any case, I apologize if I came off too strongly. I think questioning and challenging one another, as long as it's done with politeness and respect, is a great way for all of us to learn more than we came to the discussion with...
Urban myths aside, here is one you can reason through... The sound comes from the top and back vibrating, if you cut out the vibrating portion of the top, you'll have less mass vibrating. So on a CBG, generally a square box, there will be natural nodal points near the corners since it's supported on two sides and the diagonal will be in tension so that's where I cut sound holes. You can get into resonant frequencies and all that but it seems overkill for a box with only 100 or so cubic inches of volume.
I'm not following your reasoning. Of course there are nodal points where the top is fixed - the anchor points of a vibrating plate are always nodes - they're fixed and can't move. But the middle is not the same - it can be a node or an anti-node, (or neither), depending on the frequency of excitation. One thing that I've found when I've used the "tuning-fork test" for bridge placement, i.e. finding the spot that makes the loudest sound when I hold an A440 tuning fork against it, is that the middle is typically the spot that will allow the sound to be loudest, i.e. it's an anti-node for that frequency. I don't think I'd want to put a hole there.
Now, as far as mass is concerned, the thing that makes the sound coming off the top isn't the mass of the top, it's the surface area - the surface area moves air, which creates pressure waves in the air, which conduct the sound to your ears. Adding a hole removes some of that surface area, but it's compensated by the fact that the vibration of the top and back is also moving air through the hole. So, starting from no sound hole, the total sound volume increases as you increase the size of the sound hole - up to a certain point, at which point increasing the size of the sound hole starts to decrease the sound volume.
I believe you were right earlier, (I think it was you), when you said that ideally the hole would be at a place where there was no movement at all. Other than the place where the top attaches to the sides, there are no points like that on the top for all frequencies, so any placement is a compromise. This is why a lot of guitar makers have moved to the idea of putting the sound hole, or sound port, on the side of the instrument instead of on the top - usually on the side that faces up towards the player. In this way, they get the maximum energy transfer from the top, as well as getting the benefit of a sound hole ...
So maybe the real answer to the question that started this thread is to put the hole on the side that faces up when you play...
Surface area is a measurement, mass vibrates.
I should clarify what I meant by center; I was referring to the upper center near the neck joint and where the fretboard overlaps the soundboard. That area will be less free to vibrate.
A sound hole facing up will benefit the player but not the listener. If the instrument is amplified then it doesn't matter. As I said, always compromises.
It's true that mass vibrates. But do this thought experiment. Imagine two objects with the same mass, but one of them is an extremely thin plate, and the other is a sphere. If you drive them with the same energy - like a vibrating string - which one do you think will transfer more of that energy to the air to create pressure waves that you hear as sound? There's a reason that fan blades are blades, and not fan balls.
Anyway, I think Sean response covered this. It would be cool to be able to get the benefit of a hole without reducing the area of the top, like when you put a sound port on the side facing the player, but to have it facing forward, towards the listener - maybe by using an elbow or a horn going from a sound port on the upper side, but facing forward. I think there was a fiddle made that way ...
Snip the thing that makes the sound coming off the top isn't the mass of the top, it's the surface area.
It is both, the energy from the strings has to drive the top, the lighter the top the more energy goes into vibrating it, in practice that means a thin top should vibrate more easily than a thick one. Once the top has begun to vibrate, it then moves the air inside the box and outside it, both are surface area effects. There will also be an effect at the base of the bridge as the sound runs through the saddle. That's how a skeleton instrument works when fitted with a bridge piezo
I did a quick and dirty empirical test on this theory. I took an old six string guitar and a Vintage brand ukulele. (Same basic shape,same cheapo wood).
Here how to repeat my test, you'll need a quiet room::
Strike a string and as the note resounds rub your finger over the sound board. For the guitar I could hear the note dying as my finger dampened the resonance in the plate, i could also get it to wow and flutter too, .With different strings I used this method to find the hot spots. The uke was dead before I ran my finger over it. So first conclusion the bigger top plate of a guitar does transmit a large proportion of its sounds as it vibrates.
OK we all know that.
So next up I took a very thin piece of clear plastic (from a CD stack.. the protective disc that comes with the CDs) and placed it over the sound holes of the uke and the guitar. This would add negligible mass to the top but prevent air escaping from the hole.
The results were: the uke was very much quieter with the plastic cover. The guitar was a bit more complex, hardly any change in volume but the treble was less complex, the top E string had less sparkle and gave a warmer sound. I then moved the disc around the sound hole of the guitar , partially covering it, and the result was with just a fraction of the air hole left open the top 3 treble strings brightened again. It seemed to have no noticeable affect on the 3 bass strings
Next I made a floating bridge from a scrap of wood and stuck it under the strings on the uke. Repeated the test with the sound hole cover and the sound was brighter (OK it wasn't in tune as the intonation was off, but I was only sampling the volume)r. So my conclusions are
1)small bodies instruments such a uke or CBG need the sound hole because the top is too stiff to project enough sound energy on their own.
2) a floating bridge will help drive the small stiff top.
3)) the bigger the instrument. the more of the top plate can flex, so the importance of the sound hole decreases.But as the higher tones comes from the smaller , narrower, stiffer upper bout of the guitar a sound hole helps to develop their character.
As a CBG is by definition box , there is no upper or lower bout*, so you should have far more choices for a sound hole size and position. Of course how and where you join the neck will affect the sound greatly.
*On the guitar I tested. I calculated the air volume in the upper bout to be about 2 litres , the lower at least 7 litres. I'd guess because the neck attachment is at the upper bout this would make that part t of the guitar much stiffer.The maximum width of the upper bout, ie side to to the finger board was only 10cm,again adding stiffness to that part of the guitar.
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