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DD
Oud Maniac
Posts: 91
Registered: 8-31-2005
Location: The same as yours, my friend.
Member Is Offline
Mood: one mirror reflecting another
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SOooo..
On account of the phenomenon known as the Helmholtz resonance, the bowl of the oud has its own specific note, a specific frequency at which the air
inside the bowl vibrates. The pitch or note of this resonance is determined by the size of the bowl relative to the size of the sound hole. As Elie
mentioned, if we increase the size of the bowl while keeping the size of the hole the same, this frequency will be lower; the same thing will be true
if we keep the bowl size the same but decrease the hole size: IOW, the larger the bowl and/or the smaller the hole, the lower the resonant
frequency (more bass). For a higher resonant frequency, we go in the opposite direction: the smaller the bowl and/or the larger the hole, the higher
the resonant frequency.
On a guitar, the bowl/hole size ratio is usually designed so that this resonant frequency falls somewhere between the notes of the quitar's two lowest
open strings (E2 and A2); usually if you sing F#2 into the sound hole, or even pluck the open A string, you can hear the air inside the guitar body
resonating. I don't know what the different ouds' resonant frequencie are usually intended to be; that is an important question. I guess we just have
to sing to them and see if they'll answer us!
Well, I just read the above to my wife, who was sitting next to my three-holed oud, and as I was about to comment, she picked it up and started
singing into the main sound hole—then she jumped in her seat when the oud suddenly sang back to her. D4. I could hear the resonance clearly from
where I was sitting at my computer across the room; actually, I think I felt it tactilely almost as much as I heard it. I asked her to try D3, which
is about the lowest pitch that she can hit, and the resonance was much stronger. I tried it, and I could feel the entire bowl vibrating strongly. D2
and D4 resonated about the same as each other and about half as much as D3, the strongest of any; next in line in strength of resonance was G3. There
were other definite resonances, too, but none of them as strong as those I've just mentioned. Now remember, this is a three-hole oud. We covered the
two smaller holes and tried again. A3. Same whole story as before, a 4th lower. (There are no strings to pluck just now, because I'm about to attempt
a touch-up job on the pitted line left from the break in the pegbox/neck joint.)
Now all of this brings me to the two main questions I have right now:
1. Exactly how does this resonant frequency effect the whole spectrum of notes that we play on the oud? It would seem to me that every single note we
play would be effected to some extent, since in a way that frequency is going on all the time we're playing, like a drone, to a greater and lesser
extent depending on how, and how closely, the notes we're playing are related to it—e.g. that note itself, its octaves, its third, fourth, or fifth
and their octaves, simultaneous notes whose combined overtones are any of these.... It makes me think of the instrument as having a sort of sonic
personality, expressing itself especially with certain tunings, maqamat, and so on.
It seems that in the case of the guitar, the main intention with the tuning of the resonant frequency is to enhance bass response. In an article
entitled Side Located Soundholes and Ports—Theory and Execution, a luthier named Ray Whitaker explains a lot about the effect of different sound hole
configurations on guitar sonics, especially in the context of describing his "adjustable port" design: a sound hole in the top side of the guitar (in
addition to the main hole–which is also in the side!), which has a little sliding door over it that the player can adjust to suit the music he
wishes to play, making the hole smaller to emphasize more bass, larger for more clarity and definition in the midrange, and so on. Now this brings me
to my second main current question:
2. How does having three sound holes, of two different sizes, change the nature and behavior of this resonant frequency? I know that, as Dr. Oud
mentioned, some sources indicated that having three holes nullified the Helmholtz effect, but I've read a number of descriptions of guitars with more
than one sound hole of different sizes, and these descriptions took it for granted that the Helmholtz effect was functioning normally with these
designs.
An interesting example, in addition to the one I mentioned above, is the Fleishman Instruments Harp Guitar (scroll down to the second one), which has two holes of two slightly different size. The luthier, Harry
Fleishman, says that the combined sizes of the two holes add up to a normal-hole size with an emphasis on bass response, but uniquely, that the bass
is very clear, not "boomy," and that because each hole has its own lower resonance than the combined holes' resonance, and each hole is a different
size, the bass emphasis levels off smoothly rather than having a sharp response peak.
It would seem that something of this nature might be true of the three-holed oud; though, at least with mine, it would seem to be the midrange, not
the base, that is being emphasized. I wonder if others' ouds "sing back" at lower frequencies?
OK, old wind bag here is going to quiet down for a while.
My very best to all,
Don
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DD
Oud Maniac
Posts: 91
Registered: 8-31-2005
Location: The same as yours, my friend.
Member Is Offline
Mood: one mirror reflecting another
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As I was just telling Samir(Canada), I've been wondering how singing into the oud would sound and feel if the strings were on, since I never did that
(I'll have my strings back on in a few days). With them off, the resonant frequency is really strong and obvious - it can't be missed; you just sing
sort of like a siren up and down, then suddenly the oud practically jumps in your hands and 'sings back' when you hit the resonant note.
After I found the resonant note, I tried its octaves, fifths, fourths, and thirds, and found some response with all of them, but with most notes other
than those, the bowl was more or less quiet and still. The fascinating thing is that once I had done that myself, I could hear it easily from across
the room when my wife did it; I new what I was hearing then, and it was easy to tell, from the quality as well as the strength of the tone, when the
pitch she was singing was at or near a resonance. The tone quality was richer in overtones and the timbre was more complex.
It would seem that in addition to the Helmholtz resonant frequency of the air inside the bowl, there would be two other main sources of resonance: the
bowl itself and the soundboard. AFAIK, each of these will also have a specific note or set of notes that will resonate with similar and related notes
being played on the strings, the resonance making the strings' notes louder, fuller, and more complex.
This phenomenon is considered a highly desirable and important element in musical instrument design (just the opposite of loudspeaker design for your
sound system, where the object is for the speaker to "sing along" as little as possible, preferably not at all, so that you get an accurate
reproduction of the original music). Violins especially, from what I've gathered so far, are constructed to produce powerful and refined resonance,
and diversity of resonance, from the face, back, and sides as well as from the air inside the body. The violin's resonances are so many and so varied
that when the musician plays vibrato, often the different pitches that the vibrato spans are also different resonances! Apparently this is one of the
main elements that gives the violin its special character among musical instruments.
The way that these different parts of an instrument vibrate makes a big difference in the sound, and that will definitely be one of the main
ways that our hypothetical three-holed oud differs from our hypothetical one-holed oud: The three-holed oud's soundboard ('all else being equal' in
this theoretical case) should vibrate more freely and on account of its lower mass, and coupled with the fact that the three holes provide less
resistance to the flow of air in and out of the bowl, this should result in more volume and projection of the sound.
So I think that we can be more or less certain at this point that the hypothetical three-holed oud will have 1) a higher-pitched resonant frequency
both of the air inside the bowl and of the soundboard (larger-area soundhole and smaller-area soundboard); and 2) more volume and projection (less
resistance and lighter mass providing both freer airflow and freer vibration). The hypothetical one-holed oud should be a more bassy, quieter
instrument.
It's quite possible also that the two instruments will differ in a third main way, but that so many other design elements figure in and overlap that
it's almost completely irrelevant. This third difference might be in timbre: It could be that the three-holed oud will provide more diversity of
resonant frequencies from the air inside the bowl. If what Dr. Oud's source said of the Helmholtz resonance applies to the oud, and/or if what the
luthier I mentioned earlier said about the harp guitar's two unequal holes apply's to the oud's unequal holes, then this difference would certainly be
a possibility: The three-holed oud might be richer in overtones, and the one-hole oud might be richer in fundamentals. I would think, though, that the
more important factors are the resonant pitch and the volume/projection.
BTW Elie, didn't you say in one of those earlier threads that you thought your oud might resonate at F? I wonder whether it resonates more strongly
(independently of the strings) at F3 than at the string's F2, as mine does at D3? Anyway...
Have you hugged your oud today and sung to it? :-) Anybody else?
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Dr. Oud
Oud Junkie
Posts: 1370
Registered: 12-18-2002
Location: Sacramento, CA, USA
Member Is Offline
Mood: better than before
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| Quote: | Originally posted by Elie Riachi
Doc, I do not know about DD, but I am a rocket scientist 
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Well, Mr. Science, if you're launching your rocket from that position, be sure to alert the local fire department first.
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Dr. Oud
Oud Junkie
Posts: 1370
Registered: 12-18-2002
Location: Sacramento, CA, USA
Member Is Offline
Mood: better than before
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| Quote: | | Originally posted by DD...Have you hugged your oud today and sung to it? :-) Anybody else? |
I hug
my ouds every day, and all of them equally so none get jealous. I will start singing into them as well as of singing with them and see what happens. I
have learned quite a bit from your explanation and appreciate the insight. I was laboring under the impression (mis-guided it seems) that the air pump
was interfering with the sound wave, while it is actually enhancing it at those resonant frequencies. duh! I shall endeavor to function more
competently in the future.
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Elie Riachi
Oud Junkie
Posts: 582
Registered: 4-9-2004
Location: Kansas
Member Is Offline
Mood: Gebran Tueni Lives For Ever, 12-12-05.
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| Quote: | Originally posted by Dr. Oud
| Quote: | Originally posted by Elie Riachi
Doc, I do not know about DD, but I am a rocket scientist
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Well, Mr. Science, if you're launching your rocket from that position, be sure to alert the local fire department first. |
Good one Doc. But joking aside, this is the prep position before launch. And
we actually have to inform the FAA before launching these little monsters. Unfortunately, sometimes they come down whistling in this position and in
that case they are called core samplers
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Elie Riachi
Oud Junkie
Posts: 582
Registered: 4-9-2004
Location: Kansas
Member Is Offline
Mood: Gebran Tueni Lives For Ever, 12-12-05.
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| Quote: | Originally posted by DD
BTW Elie, didn't you say in one of those earlier threads that you thought your oud might resonate at F? I wonder whether it resonates more strongly
(independently of the strings) at F3 than at the string's F2, as mine does at D3? Anyway...
Have you hugged your oud today and sung to it? :-) Anybody else? |
Don,
Thank you for bringing this topic up. It is very interesting and logical to me.
My singing voice is not the best way for me to check the biased resonance frequency of my oud. Here is what I did: I set the chromatic tuner on the
soundboard and near the bridge. Then I had the tuner GENERATE the different notes in the scale and found that the oud started to ring like a bell
when the tunner hit B. It did the same at F also but not as clear and loud as the B.
As for hugging my oud, unlike the Doc, I do not have a harem of them and I only have one and at the moment it is a love hate relationship with this
particular oud. I may have a different oud soon and this one will become a wall hanger.
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Elie Riachi
Oud Junkie
Posts: 582
Registered: 4-9-2004
Location: Kansas
Member Is Offline
Mood: Gebran Tueni Lives For Ever, 12-12-05.
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Doc, I am still laughing at your joke, good one.
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billkilpatrick
Oud Junkie
Posts: 563
Registered: 1-3-2004
Location: italy
Member Is Offline
Mood: what?
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ready? ...
i once saw an interview with a jazz percussionist from brazil who was said to be somewhat unconventional in his choice of instruments. when he was
asked if he could make music with anything, the musician asked the reporter to lean forward slightly, open his mouth while he proceeded to thump out a
hollow sounding rhythm on the reporter's back.
when he was finished he announced to the reporter that he was in the key of "e."
now perhaps ... i mean ... who knows ... but if all the reporter's orifices were open and resonating nicely, he could have ... you know ... he might
have produced a different note.
- bill
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