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Tim,

On your famous narrow bodied dread, did you put a soundport in and how did it sound?

I ask as I am in the middle of making a guitar that has had a similar dose of "serendipity" and is going to be a narrow bodied guitar with 16" wide lower bout. The side wood cracked off a piece when I was sanding the rim, so now instead of the planned 4 7/8" depth at the tail it will be just shy of 4". In fact the widest part of the body is the waist, and it then slopes down to the neck and tail.

The tap tone is really exciting, and I have the guitar all prepared for an egg-shaped soundport at the very top of the bass side upper bout. However, I'm now wondering how it will impact the sound with the shallower body. I suppose I could try it without first and put one in later - it will be French Polished so the finishing aspect should be OK.

The guitar is being made for Jim so has now become "Slim Jim". Anyway here are a few pics to give you the idea - the sides have only just begun being scraped hence the bitty look:




Dave White38672.644537037

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Looks like a beauty in the works Dave.
I like the shape/design.
Beautiful top too!!
What are you using for the top?

Thanks for the pictures!

Walter

Walter,

Thanks.

The top is European spruce from the same suppliers as in the Cocobolo guitar Russell posted recently.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Hi Dave:
No I did not port the "Skinny Slope-D". I was really surprised how much bass it had but then I did brace and graduate for it ;)

Mine is 3" deep at the lower bout and 2" at the neck.

I contemplated porting it but, like you, decided to try it first without a port. I really like the shape of yours by the way.

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tim...
http://www.mcknightguitars.com

I've done some work on sound ports, measuring what happens on a 'test mule' when I opened holes in various places. As usual, drawing parallels between the objective changes that one can measure and the subjective sound of the instrument is not simple or straightforward in all cases, but there are some general trends.

One thing that _will_ happen is that the pitch of the 'main air' resonance will rise when you open a port. The larger the port is, and the farther it is from the main soundhole, the more the pitch will go up. It's the same effect you'd get from making the main soundhole bigger, except the port will usually be more effective, area for area.

The main air' pitch is a function of the size and location of the main hole relative to the volume of air in the box, and also depends rather strongly on how much air the top can move. It's hard to predict, but on most Dreads and Jumbos it's around F# or G on the low E string. Surprisingly, making the body shallower (within reason) doesn't raise it much on a given guitar, but it does 'sharpen' it, in terms of the frequency response curve. With a shallow body and a farly large hole, you may find that you have one note that is noticably stronger than the ones around it. Adding a port is likely to make this effect stronger.

Whether the guitar will sound more or less 'bassy' with a port will depend on about thirty other things, like the way the top works, the location of Mars in the zodiac, and the wholesale price of coffee in Barundi. In other words, who can say?

A port will 'vent' other air resonances in the body, depending on it's location. This will reinforce certain notes. However, my experiment indicated that it will also cause a very small drop in output over the rest of the range. You don't tend to notice the small broadband drop, but you do notice the large gain at specific frequencies, so the guitar might sound 'louder' with the port than without. It is, but overall by only about 1%-2%.

A larger port does not yeild more overall power, but it does change the timbre and balance more. The narrow band gain of power is almost exactly balanced by the wide band loss, but you're 'venting' those high frequency air modes more, so they sing out louder.

I find a small (1") port somewhere near the wide part of the upper bout makes anice 'monitor'; shooting some high frequncy sound out to the player that would otherwise all be 'beamed' out in front. It's small enough and close enough to the 'main' hole not to change the balance and timbre too much, and it doesn't sound much different to the player than in does to the audience. That's the main use I've found for a 'port'.

What I found interesting on Tim's is how much LOUDER it got (both to the player and in front of the instrument). It was a significant change. You could really hear a difference when you closed off the port, vs let it play open.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Dave--is that Koa on Mahogany? It's a lovely combination.
That's a really pretty guitar.

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Tim - thanks for this. I think I will go ahead and put the port in. This will be the third ported guitar I will have made and so far I'm a big fan. Here's one I prepared earlier:



Alan - thanks also. I went ahead with porting after reading a lot of your fascinating stuff and experiments and also Tim's. I don't have an issue with loudness in my guitars (they are loud!) and so haven't noticed very much difference out fron with the port open or closed. The monitor description is the best for what I hear. I find I hear more depth to the guitar when playing and to my ears hear more fully the bass and mids with the sound port open. When you talk about one note maybe being stronger with the narrower depth body are you referring to the "so called" wolf notes? If so will a small soundport accentuate this?

Steve - thanks. Yes it's Cuban mahogany with Koa binding (plus a thin strip of snakewood in the endgraft). This was asked for by my last customer - I thought they would be to similar as the Cuban darkens up under finish and through time but they contrasted really nicely.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Thanks a heap Alan , That was excellent !
Now,, will I cut the whole ??

KiwiCraig

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CRAIG LAWRENCE of AUSTRALIA
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When I took the 'corker' to H'burg and passed it around, the most common reaction that people hade when they pulled out a pair of corks was: "Wow, that's louder!". Then they'd play for a while and say: "Wait a minute, I'm not so sure...". The measurements I made afterward made sense of that.

All of our senses are set up to detect changes. There are two things you can be pretty sure of with stuff, like rocks and trees, that don't change much: you can't eat them, and they won't eat you. So why would you be interested? Your brain devotes the processor time to the stuff that matters; picking out the little sound of the tiger in the bush.

The change in level at some frequencies can be quite large when you open a port. I found increases over a narrow frequency range of as much as 4dB; much more than double the output, and easily enough to hear as a difference in loudness. However, this was _only_ within a very narrow frequency band. Still, it was a change, and it stuck out.

The monitor function of the port has some bearing on this as well. The top and soundhole are the main sound producers. On a 'normal' guitar the low frequency sounds are being radiated in all directions, and the player can hear them. However, the high frequenciews tend to be 'beamed' off the top away from you, and all you get is the reflections from the walls or whatever. The port sends some of that in your direction. Since your ears are much more sensitive to the high frequency sounds that are coming out of the port, it sounds louder. For both of these reasons, then, the ported box does seem louder to the player.

Out in front it may or may not seem louder. My experiments suggest it _shouldn't_, but there is a lot of testimony that it does. Once again, it could be because most of the increases come in the higher frequency range: you've got just about the same power overall, but it's distributed in a more noticable way.

I tend to think of the idiot with the pepper shaker when it comes to this sort of thing. Just because little makes it better doesn't mean that a lot will make it wonderful.   

I suspect you are right, as usual...

but I do love lots of pepper on things.   

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Wow .. that has to be the cleanest work bench area I have ever seen !!! You must have a cleaning assistant or somehting. i like that corner spray booth tool, mine would look just like that if I tiled it !!! Nice looking work my friend.

I just put the ports in mine .. if someone likes it great, if not, buy a different guitar !!! TonyKarol38673.7267361111

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"