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What about DB sound-box resonance?

Discussion in 'Setup & Repair [DB]' started by gbaker, Sep 10, 2008.


  1. I am new to posting in this forum but have been reading the archives and am impressed by the knowledge shared herein, so I am posing a question concerning the sound-box resonance of the typical DB.

    The question - why is the resonance frequency of the bass cavity not tuned lower?

    Background - I have built reflex ported-box bass speaker cabinets using Thiele's acoustic design parameters and I applied that method when I built two small upright acoustic basses. The basses were based on Music Kit's Baroque design. The first lacked loudness. I experimented and greatly improved version II by tuning the resonance of the sound box to low E (41 hz) with a port (hole) in the front. The hole also serves to reach in and set the sound post. There is a single f-hole on the base side. The improved model is about the size and loudness of a 2/4 bass but seems to have a better bottom register.

    I recently bought a '02 C1 Engelhart and was disappointed to find it resonated at about a C or D. I began to wonder why bass manufacturers do not lower the resonance to smooth the mid response and increase the loudness of the lower register.

    I researched forums and other links and found a research paper about what makes a good sounding double bass. About eight or ten different basses (cheap and expensive) were tested but not named. It was found that the best sounding (expensive) basses had a low box resonance (large) and a low top plate resonance (thin and flexible). It was also noted that the lower half octave rolled off severely for virtually all basses tested. I have since lost that link.

    In estimating the volume of my C1 I found it to be approximately 4 cu ft and that it would take about a 3" dia. hole to drop the cavity Fb resonance to 40 Hz. Judging from the experimentation with my home-made bass, this would greatly improve the low end and remove the peak boom from the C and D notes.

    So - if it is THAT simple to make a significant improvement why am I the first to notice? :eyebrow:

    I am not ready to take the hole-saw to my C1 but I cannot find any more info. Any thoughts or opinions would be most welcome.


    Thanks.
     
  2. wellp.... go ahead and drill that hole. and then tell us where you put the bridge. :)

    i don't know the answer to your question but i'm sure there's a very good reason why it is the way it is. i think lowering the resonant frequency would only make the bass BOOMIER, not necessarily louder, and I think boominess is already a problem for a lot of basses, especially when trying to amplify them. that might be part of it anyway.

    and I wouldn't think an entry level plywood bass would make the best control for such an experiment. not thumbing my nose at plys, it's what i play, but ya know...
     
  3. uprightben

    uprightben

    Nov 3, 2006
    Boone, NC
    I think your idea is very interesting, could you post some photos of your home made basses? Where do you put your sound port, and does its location matter?
     
  4. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    Therein lies the problem. As I see it, the two differ in many, many substantial ways in terms of physical acoustics. Just to mention a few, consider the differences in the driving forces and elements, the desired bandpass properties of the cavities, the fact that one is a resonant body while the other is not, and on and on and on and on...

    As I see it, what you assume to be an improvement, would actually not be at all!
     
  5. OK, uprightben, here is a link to a picture of my shop-made upright.

    http://home.att.net/~gary.baker/index.html

    Sorry, the little rubber string electric is kind of in the way. The upright has a 41" scale. The neck is removable and adjustable.

    The (half-hidded in the px) port is 4" with a insert reducer to 2.75". The port (reduced) tunes the box to E and provides reach-in accesss to the sound post should it fall out when the neck is removed. Since a lot of the sound of the lowest octive radiates from the port, it should be unobstructed in the front and not near an edge. The f-hole is to loosen the top on the bass-bar side to increase output (my opinion).

    The body construction is laminated - 2 sheets of 1/8" plywood, glued together in a form to hold the curves for plates and another form for the ribs.

    Most of the design credit goes to Musicmakers, www.harpkit.com, where full size plans for the Baroque bass are still available although they have discontinued the kit. I made my second version larger and changed to the front f-hole / port design.
     
  6. Gearhead43

    Gearhead43

    Nov 25, 2007
    NorCal
    So you're saying that in addition to the open area of both f-holes, the EC1 needs another roughly 3" hole to extend it's bass response? Interesting.

    Keep in mind, that the upright bass's tone has traditionally been a low-mid to midrange heavy sound, and the low end is only a part of the picture that makes a bass sound like a bass. You gotta start thinking more like a double bass player, and less like a bass guitarist to fully appreciate the tone. (or maybe you won't?)

    I enjoy the mid-range punch of my EC1, this is what helps it cut through and be heard in a band.

    If you plan to play amplified music, I would advise you to not cut that hole in your bass. Boominess (and the feedback it causes) is an ever-present problem in live music performances with a double bass. I get plenty of low-end when amplified, and I almost never need to boost the low end over what is already there when my EQ is flat on my amp. I just shape the mids.

    Wouldn't "tuning" the resonance of the bass to 41hz just cause the E to be the boomy note, instead of the D?
     
  7. ctregan

    ctregan

    Jun 25, 2007
    Syracuse N.Y.
  8. ctregan

    ctregan

    Jun 25, 2007
    Syracuse N.Y.
    Have you thought of using one of these to help push the sound?
     
  9. uprightben

    uprightben

    Nov 3, 2006
    Boone, NC
    Some baroque instruments, and some modern basses that hark back to the viol, have a rosette in the middle of the soundboard between the bridge and the neck in addition to ff holes. Why couldn't one put one of these sound ports, like the one pictured above, in the same place? If you made it removeable, you could have differnt lengths, which would give you the same effect of a parametric eq boost without any electronics. Let's not forget that the design of the double bass is one of the most maleable of all acoustic string instruments, and in that spirit I like to support crazy ideas like this one to see where it goes.:ninja:
     
  10. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    Yup!
     
  11. bassist14

    bassist14

    Oct 17, 2005
    Germany
    the pöllmann venezia-model has a rosette like that
    http://www.poellmann-contrabass.de/index.html
    you could ask them if they made it with the resonance-frequency in mind
     
  12. I hate to be shallow gbaker.... but after 400 years, bass makers have learned a thing or two about producing a bass sound from a box so I would doubt that it would be a "simple" to make a significant improvement.
    By all means experiment....and if you come up with something better that can be bowed with some musical resonance and still be deep I'm sure people will be interested.
     
  13. Gearhead43

    Gearhead43

    Nov 25, 2007
    NorCal
    I don't have any fundamental (no pun intended) aversion to the concept. I would just like to know more about what the extra porting would actually accomplish in terms of real world application.

    I would like to know more, please post your results when you complete your experiment.
     
  14. Thanks for the feedback. I will attempt to respond to your questions.

    To those several who feel evolution has produced the perfect bass. – You have a really good case. They have been building them about the same way for a long time. But if god had intended the bass to roll off at A he would have given it three strings. What's that . . just three? Well where did that E come from then? ;)

    However, I feel I have a working bass model that performed better after Helmholtz air resonance tuning which led me to post the question. Helmholtz is powerfull stuff - think pipe organ.

    I said first off it just couldn't be this simple and I wanted some discussion with folks that knew double bass. So here we are. . .

    Gearhead 43 –
    “So you're saying that in addition to the open area of both f-holes, the EC1 needs another roughly 3" hole to extend it's bass response? Interesting.”

    GB – Not sure how much the existing f-holes are affecting (tuning) resonance. On my shop-made bass the f-hole did not contribute to the venting (by design) – it was too narrow to allow an air column to form. I am not sure about the f-holes in the EC-1 – they are much wider, however I have some doubts they have much Helmholtz affect. I could not excite the openings with a compressed air stream as one can with a round port. The 3" was an estimate based on cavity sq ft and no other openings functioning as ports.

    “Keep in mind, that the upright bass's tone has traditionally been a low-mid to midrange heavy sound, and the low end is only a part of the picture that makes a bass sound like a bass. You gotta start thinking more like a double bass player, and less like a bass guitarist to fully appreciate the tone. (or maybe you won't?)”

    GB - Point well taken, and although I must admit to liking the low octave power of the bass guitar I am starting to like the big guy pretty well, they grow on you.

    GB - One of the papers I recently read indicated that low cavity resonance as well as low top plate resonance characterized a “full sounding” (and expensive) double bass. So low Fb seems like a good thing - like below 65 hz. If I can tune a smaller box to a lower Fb - 42 hz - well why is my big box resonating (in total) at like 75 hz? The same paper also noted the importance of the first and second harmonic – as I think you are pointing out. There can also be a problem with "roughness" that I don't understand.

    Here is the link (this paper can make your head hurt but there are conclusions therein):
    http://www.speech.kth.se/prod/publications/files/qpsr/1982/1982_23_4_149-174.pdf


    “I enjoy the mid-range punch of my EC1, this is what helps it cut through and be heard in a band.”

    GB – Yea, it can be useful. May be why Kays are so popular for dance work. Maybe if you could move the peak freq. around at will . . . more thoughts later.

    “If you plan to play amplified music, I would advise you to not cut that hole in your bass. Boominess (and the feedback it causes) is an ever-present problem in live music performances with a double bass."

    GB- I think you have a (typical) mid range peak now from what you said. I understand your point.

    “Wouldn't "tuning" the resonance of the bass to 41hz just cause the E to be the boomy note, instead of the D?”

    GB – Yes but it SEEMS flatter I think. Compensation - having the peak lower, where the human ear is less efficient was the main reason I dropped it. As the response rams up to the peak the ear fades . . .

    Ctregan –
    GB – Swiss cheese violin - interesting – demonstrated detuning the violin’s cavity resonance with holes it didn't need.

    GB – Vent ports - Yes - I did use a tube port to lower the resonance frequency from G (with the 4” hole) to E with a short tube reduced to a 2.75” hole. Too small of a vent hole can create unwanted sounds as air rushes through it. Port tubes are used to allow a larger hole diameter to perform equivalent to a smaller non-ported hole. Speaker building books often have charts that show port size for various cavity sizes for setting given resonance freq.

    Uprightben -
    GB - Tunable vent - I occasionally remove my reducer tube in my shop-made bass while playing in C or G just to get a stronger G that the 4" bare hole provides. I considered an adjustable opening with a graduated control rod up to the neck block area where the player could adjust the response curve “on the fly” but never followed through – seemed a bit hokey since only the root or maybe the fifth would be affected at a time.

    Bassist14-
    GB - I did send an inquiry to Pollmann as to the purpose of the center hole. If they answer I will post it. Great basses.

    Gearhead43
    GB - I am still just talking and not ready to cut yet. It is hard to undrill a hole. I considered buying an old bass to experiment with. But no, those old ones cost more, way more! :eek:

    New Question -
    GB - Does anyone have any experience with maybe a inadvertent hole punched in a bass? I indirectly heard of one that lost a chunk of the top plate and the owner partially filled the hole and left it. Liked the sound better that way I guess.

    Thanks for the replies.
     
  15. Gearhead43

    Gearhead43

    Nov 25, 2007
    NorCal
    Thanks for the answers. By the way, double basses used to only have 3 strings. Basses with the low E only became common shortly before or around the turn of the 20th century. (not positive on this, please correct me if needed guys)

    It could be one reason for your findings, and why the low E tends to be weak on alot of basses.

    Double bass "technology" has not progressed much in the last 100 years.
     
  16. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    It seems to me that what gbaker is really doing is designing another instrument with acoustic properties that he may find more desirable. Whatever the result, it will not be what we think of as a double bass. The acoustic characteristics of the instrument that have evolved over the centuries are precisely what define the instrument.

    gbaker said, "I began to wonder why bass manufacturers do not lower the resonance to smooth the mid response and increase the loudness of the lower register." The answer is simple. It is because to do so would produce an instrument that does not sound like a double bass.

    The goal is not at all to produce a "flat" or "smooth" response. The goal is not necessarily to produce an instrument that radiates more acoustic power in the "lower register." The double bass is a resonating body. The particular acoustic response, the spectral peaks and valleys, precisely how the overtone structure occurs, etc. are exactly what characterize the double bass.

    To be sure, there are differences in personal preference in terms of desired sound. Still, there is pretty good agreement on what are particularly good exemplars of different "classes" of the double bass sound (e.g., the French sound, Italian sound, powerful orchestral depth, more delicate solo sound).

    This is not to suggest that gbaker's project is folly. He may produce an interesting sounding instrument. I doubt, however, with the goals he has defined, that he will produce an instrument that has sonic characteristics that will be recognized as that of a fine double bass. Rather, he will likely produce an instrument with a different sound, however interesting it may be.
     
  17. Pentabass

    Pentabass

    Dec 11, 2007
    Winnipeg
    Ok, let's call this different instrument that he is designing, the Tripple-Bass !
     
  18. I wrote Pollmann:
    "Hello,
    Wonderful instruments!
    Can you tell me the purpose is of the center Rosette on the Venezia? Does it serve an acoustical function or is it just decoration?"


    The prompt reply was:
    "Thanks for the compliment.
    In that case we construct the Rosette together with the special f-hole. We want to use special f-holes and the top was to inflexible."


    I presume "top to [too] inflexible meant it was too stiff to have a low enough res freq without a larger vent. If you look at the bass, the f-holes are very thin or narrow. I guess the bass required more vent area than they provided so they added the center hole. :cool:

    Good info. thanks bassist14.
     
  19. Gearhead43

    Gearhead43

    Nov 25, 2007
    NorCal
    gbaker,

    Another interesting thing I have read is: In violin family instruments , the soundpost transfers vibration to the back of the instrument so that the instrument as a whole can vibrate much more than say a guitar - in which the top is the primary vibrating unit and the box functions as a simple heimholtz resonator.

    You can feel this vibration most when using the bow, the entire instrument moves. So you should also keep in mind the fact that the double bass was created primarily for using with a bow. They produce much greater volume and respond differently when bowed than when played pizzicato. Is your dissatisfaction with the acoustic resonance based on pizz-only testing?

    The use of the plucked (& slapped! :D) double bass in popular music could be viewed as an "unintended" use, considering the design of the instrument, and a compromise we are willing to make because we love the "unintended" sound. :eyebrow:
     
  20. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    This is yet another reason that the application of Thiele-Small alignments, etc. and physical acoustics as applied to ported non-resonating enclosures is not appropriate.

    Perhaps. The point is that the sound, "unintended" or not is the sound of the double bass. In a very real and practical sense, "it is what it is." Were today's knowledge available hundreds of years ago, perhaps, the instrument would sound different. Maybe not. The design is, after all, largely the result of what was the purpose of the instrument back then. I don't view the current state of the double bass as a failure to optimize its parameters.

    Considering the steady-state "response" of the double bass, I see no reason why one could not implement a substantial portion of gbaker's intended modifications via DSP (digital signal processing) in order to evaluate them before a saw is taken to wood. That is, one can take the sound of a real double bass and "smooth the mid response" and enhance the low end. In fact, alterations of that sort are what many tone-shaping accessories are about. We read over and over again here that, for many of us, amplification is a necessary evil with the holy grail most often being the acoustic sound of the double bass but "bigger." Once again, we return to the evolved sound of the instrument as being what is desired by DB players.

    Now, if we were discussing a new BG or new form of EUB that would be quite different. The makers of such instruments don't generally target the sound of the DB as a goal. They are very useful, different, and, to some, desirable instruments. Such may end up being the case for gbaker's new designs.
     

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