Side sound port size?

Hello I am putting a side sound port in a tenor. I am looking for directions to proper sizing or how to size. I came across a thread awhile back concerning the method to making the hole. I have that down. I noticed that Chuck had installed an oval configuration and that is what I plan on. Can anyone help? Thank you, dannyb

Although it's extremely forward of me to speak for any of the others (many of whom who are much more experienced and talented luthiers), I think the straightest answer you'll get is "It depends."

What kind of wood are you using? Is there a soundhole on the top? I think if you add more details of your project, you'll get better answers.

I am far too green to even be considered a hobbyist. But I did put a side port in my second build. I went with the oval shape and actually didn't put too much thought into the size. I just wanted to ensure that it didn't creep too close to the edges. I glued a thin birch plate on the opposite of where I wanted to put the port and then bent the side.

Good luck!

On this subject, something I have wondered about is how the radius of the ports affects the effective size of the port, more squared, slightly eased edges vs. full radius vs. more rounded towards the face of the soundboard, more square towards the inside.

This may be totally unrelated, but I have seen a demonstration on a flow bench, a tool used for studying airflow ( in aspiration systems for combustion motors among other things) where the airflow is measured in cfm and mm/hg. When measuring the flow through a hole of any given size through a square edged hole in sheet metal (the flow bench top) , by placing a venturi ( a radiused flare) but with a smaller diameter hole then the first measurement with no venturi, the flow INCREASES. The squared edges do not flow nearly as well as the radiused edges. Granted this is at a higher airflow rate, but fluid mechanics is tricky business. Even at the micro air flow rate caused by the vibrating soundbox of a stringed instrument, I wonder how the radius at the edge of the ports affects the tuning of the port. The soundport is basically a venturi. When tuning loudspeakers, the effect of a flare on a soundport can definitely be heard. With speakers, the ports effect is mainly on the lower frequencies, as I believe it is in the instrument as well, the presence.

Does the radius of the port affect the tuning of the soundbox? The radius should affect airflow at the port. Will a very slight change in port diameter, or area, change the tuning of the instrument?

Another aspect of airflow through a port ( not necessarily an instrument but I do not know why not) is that majority of air movement happens at the edges of the port, not at the center of the port, this has something to do with gravity, and it is likely that (possibly very difficult to measure and maybe insignificant) the soundport on an instrument may perform differently when the instrument is excited with the port facing up, as opposed to the port in a vertical position like it is in normal use. Atmosphere is affected by gravity. A non round port, such as an f-hole, or the hibiscus port cutout used, I believe on one of the DeVine ukes, may perform differently than a circular port of the same surface area because of the larger edge area.

Does any of this even matter?

Sorry I should have said that this is a Koa tenor. I already have a 2 1/2" sound hole on normal top area. I do not know what else to tell you. I have an alternate plan if might side sound port doesn't make me happy. I am just not sure what it is! Ha!

dannyb said:

Hello I am putting a side sound port in a tenor. I am looking for directions to proper sizing or how to size. I came across a thread awhile back concerning the method to making the hole. I have that down. I noticed that Chuck had installed an oval configuration and that is what I plan on. Can anyone help? Thank you, dannyb

Click to expand...

On my soprano Moore Bettah, and the one i had previously,.....the sound port was round and about 1" in diameter. (maybe a hair under 1" from memory) I've had a ukulele with an oval sound port,.....but now much prefer the round variety. (especially on soprano and concert size bodies.)

The reason is on the smaller sizes, the soundport DOES affect the "C" string especially,.....reducing it's volumn noticably to the audience. The player does get the additional feedback a soundport offers, but if you're performing acoustically the audience suffers a bit.

The round sound port allows me to easily fit a cork or soft rubber plug to bring the "C" string back up to where it would be had it been built without a sound port. Just gives you an option to play it either way,........and i like that.

BTW, i make my soundport plugs thin,....maybe 1/4" thick. I got them off the internet from :

Rubber Stopper to fit almost 1" round sound port: http://www.widgetco.com/5-rubber-stoppers-plugs

Select Cork Stopper to fit almost 1" round sound port: http://www.widgetco.com/11-cork-stoppers-extra

(other sizes available of both)

They are cheap enough to order several at one time. (around $.60 each) This way you can do several, ond if you mess one up or lose one can have a spare. The shipping is reasonable, but makes more sense with a mutiple purchase. ($4.95 flat rate shipping with no minimum purchase, and free shipping if order is $40.00 or more)

I cut the bottoms off to reduce their length and not reduce the internal box volumn any more than necessary. The cork version is lighter, btw, and easier to cut and sand. Be sure to measure the diameter of your round soundport accurately, as you'll want about 1/8" extra diameter on the plug to give you something to grip onto to remove it when you want to. The stoppers come in many sizes, and the cork ones also have different grades. (amount of holes in cork vary). The highest grade cork stoppers are still very reasonable,....and that's what i ordered. The site is well done and the stopper measurements are listed once you pull an item up individually.

On a tenor ukulele,....the box is much larger so the "C" string affect of a soundport not likely to be as noticable, and a plug option probably not needed. An easy way to find out is place the ukulele on your lap with the main soundhole facing you and pluck each of the the stings one at a time, and then immediately cover the soundport with your palm and pluck the same string to compare the sound. If it's noticable different you might want to consider the plug "option".

cheers,
Joe T

With a 2 1/2 inch soundhole, then you're pretty much just doing a side port for the same reason I did, cuz it looks cool.

I'd go with joejeweler's suggestion of a small round one, so you have the option of corking it.