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Question about the sound hole (Read 2707 times)
Acabooe
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Question about the sound hole
Feb 1st, 2008 at 2:04am
 
I was wondering....

What would happen if an Ukulele didn't have a sound hole?

Would it sound good?
Would it sound good, but very quiet?
Would it sound terrible?

I haven't learned enough about the science of sound yet to really understand how the sound hole placement and size effects the instrument, but I was just wondering what would happen with out a sound hole?

Mahalo to anyone who answers.
Bob 8)
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konacat
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Re: Question about the sound hole
Reply #1 - Feb 1st, 2008 at 9:28am
 
Bob,

If there was no sound hole then you would end up with a paddle. The strings impart their energy to the top generating sound but think of it as the sound being carried by focused air movement. The string energy moves the top creating air movement within the body. If there is no hole the air can’t escape the body thus little sound. If the sound hole is too large then there is no way to have pressure or air movement within the body. If the sound hole is too small then the air movement can’t exit the body easily and the sound is stifled. While I’m no expert, I hope this gives you what you are looking for.

Here is a link to a short article regarding sound holes.http://hal9000.ps.uci.edu/Weber%20H90%20Physics%20Paper.pdf

You should check out The Official Luthiers forum and http://www.luthiersforum.com/search the word “Helmholtz”. You should get quite a bit of information from these discussions. Pay particular attention to response from Alan Carruth. You can even search using his user name “Alan Carruth” and pull a mass of technical information on air/frequency movement and free plate tuning. Have fun!  Grin

Philip


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Don_Orgeman
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Re: Question about the sound hole
Reply #2 - Feb 1st, 2008 at 3:41pm
 
Bob:

On a uke or guitar about 25 percent of the sound comes from the vibration of the outside of the top and about 75 percent comes from the movement of air from the sound chamber.  With no sound hole you damp the volume to about 25 percent of the normal volume.  As you increase the size of the sound hole the volume increases.  Every instrument has an optimal size of sound hole where the volume will show a large increase (2-3 dB) compared to increses before the optimal size is reached.  When you get larger than the optimal size the volume begins to fall off instead of increasing.  This is hard to test because the striking force has to be the same for all tests.  I suspect that the correct value for a tenor uke is close to 2 1/2 inches since this is the standard most often seen.

If you're looking for more information on this topic, read Roger Siminoff's book The Art of Tap Tuning.  Siminoff not only tunes the sound box but also recommends tap tuning the tone bars and enharmonic braces plus the back braces.  This is an interesting book to read if you're into the technical theory stuff.

Has anyone building ukes played around with Siminoff's tap tuning methods for tuning braces and gotten any results they can share?

Don
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Acabooe
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Re: Question about the sound hole
Reply #3 - Feb 2nd, 2008 at 5:40am
 
Philip, and Don

Thank you both for your replys.
They helped me understand a little more about sound and vibration.

Mahalo
Bob 8)
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Jeff B
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Re: Question about the sound hole
Reply #4 - Feb 4th, 2008 at 5:48am
 
Remember the old riddle, "if a tree fell in the woods and there was no one there to hear it, would it still make a noise?"

The answer is yes since sound waves travel through all medium - air, water, earth, etc. Some media carry it better than others, but sound won't travel in a vacuum. Whether there's a receiver (your ear) there to detect it is immaterial. The sound is made anyway. By the way, sound travels faster the more dense the media. Temperature also affects the speed. The higher the temperature, the slower sound travels. You Hawai'i guys probably can't relate, but to those of us who live where it gets cold, did you ever notice how much better sound travels in the winter? For example, I live about 4 miles from a main railroad line. I can hear the train clearly in the winter, but it is barely discernable on a hot August day.

A ukulele is basically a wooden box with air in it. When the strings vibrate, they vibrate the air in the box and the box amplifies it out through the sound hole as the sound waves vibrate the air. Air needs to get in AND out to vibrate effectively.

So if you have no sound hole, only the wood of the box can vibrate and the sound will be very muffled as the more dense wood of the box won't vibrate the air around it nearly as much as the air that is inside it. You need to let that vibrating air out of the box so it can reach your ear better.

If you made a solid body uke and put on a humbucker pickup and fed it through an amplifier, you'd get sound. But that's because the pickup is detecting the string's vibration, converting it to an analog signal that is then amplified by the electronics in the amp. No air is involved until the amp's speakers begin to vibrate in accordance with the amplified signal.

Make sense?

Jeff
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Ukeman
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Re: Question about the sound hole
Reply #5 - Feb 4th, 2008 at 8:20am
 
Aloha all....In my uke building classes I always start the calss with the Hana Lima demo:

I bring out a stick with 4 strings, tuners and nut and saddled tune to GCEA. If you play the stick you can hear the notes but the majority of the sound is lost in space..very quiet and ineffective.

Place the stick over a workbench surface, strum and hey a bit louder...thats reflection

Place stick over a rubbish can..strum..fuller and low sound, place over a cigar box...fuller higher sound

End of stick...I now bring out a uke made with plexi back, koa sides all 1/8th thick with a spruce soundboard..play this and much louder, than reflection or enclosure but still not loud...no soundhole..no place for air captured in enclosure to escape.

Next uke is constructed to same dimensions with same materials...although has a center traditional soundhole..strum this puppy and we now have uke volumne...air inside enclosure pumped vial soundboard has place to escape.

Final demo: Retrieve Uke that had no soundhole...pull out a hidden sidehole plug to reveal a side port ...strum volumne very loud...more tham centersound hole    hmmmm  tells ya something..sound needs to be released from an enclosure but not necessarily through the center of the soundboard...if the uke box is likened to a bellows pumping air, then a hole in one surface would diminish the ability to effectively pump a greater amount of air than a surface with no hole..food for thought, but no doubt why there has been a major influx of sideported or multi ported instruments.

hopes this answers your question.....laters  ukeman

oh a ps.   you can close back up the secret plug in the sidehole uke...look to the tail of the instrument, remove another plug to reveal a 3/4 inch diameter puka...if ya insert a 7 foot plastic flexible tube into the puka and hold the other end of the tube to another persons ear 7 feet away, strum and sound comes from the uke to your ear much like the cup and string walkie talkie that we all made when we wuz jes small keed time...ha somethings never change
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Jeff B
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Re: Question about the sound hole
Reply #6 - Feb 5th, 2008 at 3:49am
 
Lots of good stuff in this thread. Triggered a question: Does anyone know of a good reference book/source that addresses the design of soundboard bracing? I have data on the typical layout as well as Kasha-Schneider. But what about X-bracing (as is done on many larger guitars) on a ukulele? Is there any reason to do so? It might be that an X-brace scheme would over-brace such a small instrument - unless the brace dimensions were significantly reduced, which could lead to reduced structural integrity. What value/advantage is there in the X-brace vs. traditional bracing both in terms of structure and tone?

I'd like to experiment with different bracing layouts but don't want to jump into it blind. A good reference on the subject would be appreciated. Does the "Art of Tap Tuning" book speak to it?

Mahalo!

Jeff

P.S. In case you haven't figured it out, I come from a highly technical background. I was educated extensively in underwater acoustics and electronics when I was a Navy Sonar Technician (homeported out of Pearl Harbor 1969-72) and have been a computer software engineer/manager for over 30 years. Sometimes I get more into the technology than the art. I hope that will change someday. The technology is beginning to bore me... Smiley
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Don_Orgeman
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Re: Question about the sound hole
Reply #7 - Feb 5th, 2008 at 12:37pm
 
Jeff:

No, the Art of Tap Tuning discusses the concept and how to tap tune but does not do anything for ukuleles on bracing layouts (except for the cheap double cross bars found on ABC versions of soprano ukes.  The book does show some guitar bracing patterns.  It also covers violin and mandolin bracing.  The book is based on the wonderful mandolins made by Gibson from 1920 to 1925 under the direction of Lloyd Loar, their acoustical engineer.

Jeff, with your background I think you would find this book of interest and worth the $35.  It gets really deep into the technical stuff and it deals most with the concept of being able to repeat building when you get an instrument with GREAT sound.  For the rest of us that may make a few instruments for our own enjoyment, is there any point to this fine tuning and measurement approach -- I doubt it.  Like you, I enjoy the technical stuff that can be applied to building a slightly better instrument.  I will probably tap tune the braces on the uke I am making as a fun exercise.  It can't hurt anything to try it.  I will be happy to share what I find with you when I finish.

Mike (Ukeman):

Great story!  You are a natural teacher of your craft.  I think it would be a blast to have an opportunity to attend your classes and watch, do, and learn.

Don
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Jeff B
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Aloha!

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Re: Question about the sound hole
Reply #8 - Feb 6th, 2008 at 10:26am
 
Thanks, Don.

I did find another book by the same author that appears to go more into the bracing design. It's called "The Luthier's Handbook". Amazon had it for $15. But I haven't made the buy yet.

Yes, I would really like to hear about your brace tuning efforts.

Agreed, sometimes you have to let the technical stuff go and build with your heart. I've done that with other kinds of projects and the results are usually positive. But I also want to build the best I can build. In my career I've had to deal with fixing too many projects that others have poorly designed, tested and executed - mostly because they weren't allowed the right tools, resources, knowledge, or time.

Also agree about Mike (ukeman). I teach, too, and there is nothing like it when you see the light bulb go on with one of your students and they get it. Mike has that ability to make the bulb come on.

Mahalo!

Jeff
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