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Anyone Want To Experiment?


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Boulder Creek Guitars has been getting a bit of press for their acoustic line with the soundhole located not on the top, but on the upper side, pointing to the player.

Daniel Sorbera's beautiful GOTM (October) acoustic also features a soundhole on the upper side, pointing to the player.

I have heard mixed reviews of the Boulder Creek guitars, but What I am wondering is how the top soundhole affects the sound of the Guitar. The GOTM description says that it makes it sound better.

I am wondering If anybody out there has an cheapish steel string acoustic they would be willing to drill a hole into. Unfortunately I do not, (my only acoustic right now is a nylon string). I think it would be a pretty cool experiment.

So yeah...Anybody want to give it a try???

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Are the boulder creek guitars the ones that have only a "player" soundhole doing away with the one on the front entirely?

If so than I've heard about them, and I heard that while they sound great for the player, and are nice plugged in, that they are lacking for any kind of acoustic audience in front of the guitar.

One the guitar I built I've played it while someone covers up and uncovers the "player" sound hole while your playing and you can hear the distinct difference. It's considerably better, both for the player, and for everyone out in front of the guitar with the extra sound hole there.

I've been playing it at gigs twice a week and I haven't noticed any drawbacks (ie feedback or anything like that).

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Yeah the boulder creek ones dont have a regular soundhole.

I am going to buy an acoustic guitar soon, as I just sold my old one. Im looking at a yamaha, which seems pretty nice. I am really interested in the upper soundhole thing not so much because I hate bending over a little to hear the guitar better, but also because I read the little caption about how the extra soundhole helps the guitar sound better. I dont just want to go cutting into a brand new guitar though, but if I knew it would make it sound a bit better, I would have no problem with doing it!

Thanks for the help!

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I wasn't aware people played semi hollow electrics without amplification?

If so than I guess it would help, to a very marginal degree, but if you always play through an amp I couldn't see it doing anything but causing more feedback.

But hey thats just conjecture seeing as I've never actually done it. :D

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I'm really glad you brought up this topic. I've been doing a bit of research on this topic for my next build, which I won't begin until 2009 (probably). The location of the sound hole is one thing that defines the sound you get on a Boulder Creek guitar, but I think the bracing system is even more innovative.

Behold.....

SBS1_01.gif

Linky

Daniel's player's hole differs from the Boulder Creek one in several ways. One is the location, which is self-evident. Another is size. Because Daniel also has a regular sound hole, he can get away with a small player's hole. The Boulder Creek guitar, on the other hand, needs a larger hole (almost 4" in diameter) because of something called Helmholz Resonance.

Click here for an excellent article on the subject.

I'm not going to try and explain it, but a significant part of the acoustic sound comes from the air inside the body. The sound hole is critical to that aspect.

Cutting an additional hole in a guitar will affect the air flow. I appreciated Daniel's description of how that worked in his guitar. I can also tell you that people have described larger sound holes (traditional ones) as producing brighter sounds.

Here I'm just getting into conjecture, but I'd be surprised if cutting an additional hole in every guitar would make it sound better. There are a lot of variables.

-Dave

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So how about this for an experiment (I'm sure I'll have time for this soon... :D )

Using a 1/4" thick piece of "pick your tonewood here" make a few templates that are routed to fit a maximum diameter of 2.5". Make the template 3" in diameter.

You would need to make a few of these so that you could drill holes of various size in them for example 1", 1.25" etc.

For basic experiments, use two-sided tape or whatever will hold and release that you like to "fill" the hole. This would allow you to experiment with different holes sizes in a given position and be able to go back to a smaller size. You could also make one to fill the top hole to see if that adds anything. You could then "repair" the holes by gluing in a solid template piece. The guitar may not be of much value, but that's the point. Each test is recorded and let several listen and opine. Thoughts?

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So how about this for an experiment (I'm sure I'll have time for this soon... :D )

Using a 1/4" thick piece of "pick your tonewood here" make a few templates that are routed to fit a maximum diameter of 2.5". Make the template 3" in diameter.

You would need to make a few of these so that you could drill holes of various size in them for example 1", 1.25" etc.

For basic experiments, use two-sided tape or whatever will hold and release that you like to "fill" the hole. This would allow you to experiment with different holes sizes in a given position and be able to go back to a smaller size. You could also make one to fill the top hole to see if that adds anything. You could then "repair" the holes by gluing in a solid template piece. The guitar may not be of much value, but that's the point. Each test is recorded and let several listen and opine. Thoughts?

Personally, I think that would be really cool. Another thing you could do... Boulder Creek makes the claim that because lows are omnidirectional, the sound hole is just as effective on the side of the guitar. You could also do some tests with a piece of scrap over the main sound hole to see what the effect might be.

Edited by dpm99
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I was thinking about how Daniel said that his guitar sounded "almost like there is a chorus on it." I think I know why.

Many subwoofers have what I believe is known as a "bass reflex port", or basically a hole which allows all of the speakers movement to be utilized to create a bigger sound. When a speaker moves, it pushes a compressional wave forward, out toward the audience. Then it must retract, or reflex, during which time it pushes another longitudinal wave (same as compressional) in the opposite direction. This sound can be harnessed by a bass reflex port, pushing sound out, and essentially making the speaker sound louder and fuller.

An interesting side effect of this, however, is that the wave created by the reflex comes slightly later than the original wave. The sound created by the reflex is actually 180 degrees out of phase.

A guitar operates on the same principle, but to a much more dirty effect. The top vibrates like the speaker, but the back and sides do too, so every sound played by a guitar naturally has a bit of reverb on it and much of the guitar's sound comes to the listener, out of phase (in varying degrees).

A chorus effect does just this. It splits up a signal, and pushes part of it slightly out of phase from the dry signal.

Having an extra soundhole in the guitar allows more of the sound from the reflex of the guitars top to exit the guitar rather than being absorbed, creating a chorus effect.

The effect would be maximized by placing a soundhole on the back of the guitar. However, since most people cover the back of the guitar while they play, it wouln't work.

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A guitar's not a 'simple' helmholtz resonator (it's not rigid; calculating the volume, the lowest the box itself can support as a frequency is something between an A and a G on the low E string, also depending on body size, bracing, etc.). Some feel there's a bass reflex couple going on between top and back, and build accordingly. Others build with a stiff, 'reflective' back. Almost everyone builds with pretty darn rigid (thanks to bending, sometimes lamination, sometimes side bracing) sides, so there's not a lot of flex in there. I do know that the tops/backs on my guitars are definitely 'coupled'. Damp the back in the middle, and the top resonance (on a 'loose' body, in this case) gets damped - doesn't sustain as long. Cover the side sound hole (1.5" diameter in a jumbo sized body) and the main air resonance (helmholtz resonance) drops, uncover it and it rises again by about half a step.

I don't think a significant part of the volume comes out of the soundhole. In terms of bass (psychoacoustically) and balance of tone, yes, the soundhole helps shape/define how things sound. But not in terms of loudness, and only some of it is 'pure' helmholtz resonance going on. Most of the sound gets made by the board, near and around the bridge. Ie, the bit that's vibrating most. The rest of the construction and overtones are shaped by the air resonance chamber, compliance of both top and back, and any coupling.

Re: size of hole, 4" is fairly standard, but anything from 3.5" to 4.5" is used fairly frequently. Most folks that do side ports/sound holes tend to make the main hole smaller by the surface area of the side port to balance out any helmholtz effects.

As far as the boulder creek bracing is concerned, it just looks really, really heavy to me. A wood soundboard will weigh roughly 200-250 grams without bracing, bracing another 60-100 grams, tops (depending on woods, guitar size, etc.). That setup up there looks like it'll weigh a lot more; aluminum is very, very heavy for its stiffness compared to spruce.

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I just noticed this thread (I'm a little new here), but it caught my attention.

The sound hole really isn't a sound hole. The wood on of the acoustic's top makes most of the sound. The hole is there mainly to let the guitar breath. Good airflow lets the instrument resonate easier.

Think about it. The violin family has very loud instruments and no "sound holes." The two f-holes let air flow through, while not removing much of the wood.

This is great example of what I mean:

http://destroyallguitars.com/tombills/102-...-genesis-series

Read his description. The second paragraph says exactly what I'm saying.

The sound hole under the strings has been a traditional way of doing it, but it's not the only way, or the best way. That's why acoustic arch tops usually have f-holes. The sound comes from the wood resonating.

If you really want the experiment to work well, try adding two holes on the sides, so the air can move easily through it. I bet the volume will be much louder and the sound will be a lot fuller.

Edited by NotYou
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Just to add a little something to this thread...

A fabulous book of guitar porn is "blue Guitar" by Ken Vose

It is a photo book about a challenge and exhibition of blue archtop guitars in appreciation of Jimmy d'aquisto whose last guitar was a blue archtop. 22 top luthiers made archtop guitars with the only proviso that they be blue. It is a beautiful book...

Anyway, John Monteleone did a great one with two side soundholes on the rim and an asymetrical soundhole in the top. All three have ebony outer rings for an "improved ported venturi surface". All three soundholes also have internal metal slides that can close or open them at will.

Robert Benedetto made a lovely guitar called "la Cremona Azzurra" that had soundholes in a kind of leaf motif on the top upper bout and lower back quarter...a similar one also on the top rim to match...a stunning guitar.

Linda Manzer also made one with f holes and a side soundhole that could be closed with a slide I see...she says that open "it could be compared to a flat-top sound. Closed it projects like an archtop"

Tom Ribbecke did one with ebony sound horn on the side that can be rotated...hmmm

Other makers include both the gibson and fender custom shops, Collings and many more...

Of interest is also the guitar that Jimmy d'aquisto las built 1995 Advance. This featured enlarged dual soundholes that had four segmented covers and unsual x bracing...this offered 18 variations in tonality and volume...hence a lot of the designs in tribute featured their own unusual and innovative variations.

They were commissioned by and for the Scott Chinery collection...

anyway...beautiful book of guitar "porn" and some interesting ideas from the top makers in the business...

pete

(ps...I used to be a bookseller, so I could get a hold of things like this, not even sure if it is still available)

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One thing to keep in mind is that archtops seem to be a lot more forgiving of 'non-standard' F hole shapes and locations than acoustic guitars because the sound is defined by the arch of the plate, and the bracing is more minimalist. Soundhole area matters, shape and position slightly less so. Acoustics, OTOH, sound like acoustics when their bracing is where we're used to them and their soundholes are in a normal position. Change things around, and the sound is different. That's likely why the 'off the wall' designs don't stick; the old designs simply work well, and the sound we've learned to associate with 'acoustic guitar' and the tone we like are associated with fairly traditional guitar sizes and shapes (major part of tone) and woods and bracing schemes.

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One thing to keep in mind is that archtops seem to be a lot more forgiving of 'non-standard' F hole shapes and locations than acoustic guitars because the sound is defined by the arch of the plate, and the bracing is more minimalist. Soundhole area matters, shape and position slightly less so. Acoustics, OTOH, sound like acoustics when their bracing is where we're used to them and their soundholes are in a normal position. Change things around, and the sound is different. That's likely why the 'off the wall' designs don't stick; the old designs simply work well, and the sound we've learned to associate with 'acoustic guitar' and the tone we like are associated with fairly traditional guitar sizes and shapes (major part of tone) and woods and bracing schemes.

I think it's worth experimenting with braces. A lot of builders put too much emphasis on easy structure and stability and it ruins the sound of the guitar. The old, pre-WWII Martins had X braces under the bridges, which sound amazing. Their position made the guitar a little unstable, though, and they stopped doing it. There might be a way out there that won't require a compromise, but we haven't found it yet.

Kasha bracing seems to be a great way to go. I haven't heard a guitar yet that uses it, but I've heard only good things. Has anyone tried one yet?

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Well...from my simplified understanding, arch-tops and flat-tops are completely different beasts mechanically.

A flat-top flexes in complex ways and the bracing plays a huge role in the way it does this and a lot of the sound comes from within the guitar so there are likely phase effects caused with the top soundwaves and internal sound waves mixing and bouncing off the back (something bridge piezos alone don't pickup btw and makes micing them to get the true sound an art).

An arch-top has a floating bridge and tailpiece and the top bounces, the sound being more immediate and coming straight off the top (hence their reputation for projection)...there is some internal sound of course, but the soundholes appear to be largely to avoid a vacuum inside the box that would inhibit this vibration.

Of course this is very simplified. It would be wrong to suggest that the more complex bracing in a flat-top means that the arch-top is less sophisticated though, the arched top itself provides the strength through the complex form and a real one involves a lot of artful carving not just to get the shape but the appropriate flexibility.

Possibly a wavering topic...it is interesting to note how Linda Manzer suggests that the side hole provided a more flat top effect, I kind of think this is because you would hear more of the internal sound and it's phasing effects perhaps. On an arch-top where the sound tends to be very directional, that may be a useful feature.

What was the subject again? Soundholes...maybe I am not too far off topic...

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