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Interchangeable Resonators

Discussion in 'General Acoustics Discussion' started by jbtsax, Oct 14, 2013.

  1. jbtsax

    jbtsax Distinguished Member Distinguished Member

    Dr. Pauline Eveno at McGill University in Montreal has already completed one study of the acoustic effects of different saxophone resonators. In an effort to continue her study she wrote to me asking where she could possibly get 4 identical saxophones. Finding that to be difficult, if not impossible, I suggested to her that she consider using one saxophone set up to allow the resonators to be changed without removing the pads. She really liked the idea.

    I posted the challenge on the Facebook Repair Techs site, and consulted with my repair mentor to gather ideas. The prototype that is the result of my investigation and the best of the suggestions is shown below. I am currently working on using a slightly larger neodymium magnet on the resonator and using a 1/32" thick magnet on the back of the pad instead of the steel disc to increase the pull strength. I am also working on a screw in design that would be the fall back position should the resonators held in place with magnets vibrate excessively and skew the measurements. One of the drawbacks to attaching a magnet to the pad or the keycup is that neodymium magnets begin to lose their strength when heated to the temperature require to melt shellac. :emoji_astonished:

    If anyone on this forum has any ideas or suggestions, please feel free to join in this fascinating work in progress.

    The first photo shows the components used: 1/8" x 1/8" cylinder magnets, small steel grommets, a metal disc made out of a razor blade.


    The second photo shows the magnets attached to the resonators using gap filling super glue.


    The third photo shows the grommet installed in the pad with and without the steel disc super glued over the opening.


    The last photo shows the resonators installed in the pads, held in place by the magnet's attraction to the steel sleeve it fits into and the backing disc.

  2. Helen

    Helen Content Expert Saxophones Staff Member Administrator

    What a fascinating idea. Besides the research applications that this obviously has, which I am very interested in, I'm wondering if this type of reso application might not have possibilities in real life?

    BTW, do you happen to know if Dr. Pauline Eveno has already published, or made public, her first study on the acoustic effects of saxophone resos? Perhaps maybe we will have some empirical prove that we can point to in this age old "Do these resos make my butt look fat?" ;-):-D Oops, I meant to to write, "Do different resos really change the sound of the horn?".
  3. jbtsax

    jbtsax Distinguished Member Distinguished Member

    It was by writing to Dr. Evino to ask when her study would be made public that I made her acquaintance. We have stayed in touch ever since. Her supervisor at McGill University is Dr. Gary Scavone. Antoine LeFebvre is another researcher there as well. It seems to be THE "happening place" as far as saxophone acoustics are concerned.
  4. Cool idea, John!

    Have you made up a jig to set the depth of the magnet relative to the plane of the back of the reso? I imagine that you want the reso flush to the pad but not so far away that the magnet loses strength in its attraction.

    You could adjust the effective height of the magnet by shimming between the reso and magnet.

    Are you planning to make various sizes of resos to test the effect of the ratio of reso area to pad area?

    The Buescher Snap-On for the 21st century? We don't need no stinkin' spuds!
  5. Hi, doc. Welcome to the forum. You'll note a paucity of white noise compared to the last place I saw your posts.
  6. saxhound

    saxhound Moderator Staff Member CE/Moderator

    Yes, this is the Switzerland of online forums. A friendly, neutral establishment with great scenery (pics!), and a fairly calm pace. We just don't have any banks!
  7. jbtsax

    jbtsax Distinguished Member Distinguished Member

    Sorry to take so long to respond. I have been working on a better method of attaching the magnets to the resonators. My concern with the small 1/8" diameter magnets was the small surface area to glue to the resonator. As the picture below shows, I have found a "tube" or "ring" magnet with a hole in the center that the shaft from the resonators fits inside. This has two advantages: 1) it helps to center the magnet, 2) it provides greater surface area to bond the magnet to the resonator.

    The small pads and resonators will be done in the manner shown in the previous pictures. I am sending these sample to Dr. Evino to consider for her project. She will determine the styles and sizes of resonators that she wishes to use for her study.

    Interestingly enough the length of the installed ring magnets come out very close and do not require shims. The best material for the back of the hole I have found is still the single edge razor blade made into a small disc. It has the strongest magnetic attraction of any metal that size and thickness that I have found. Maybe Dr. G can shed some light on why this is the case, and if it bears any relationship to that metals ability to be honed to a sharp edge.


    SOTSDO Old King Log Staff Member CE/Moderator

    A word of caution about the super-magnets that you are using. I don't know where your shop is set up, but if it is at all accessible to children (i.e., in the home with rug rats burrowing around on the floor), these have been shown to be "edible attractants" to toddlers. One of them eaten isn't all that bad, but if they ingest two of them, you can end up with serious internal injuries (perforated intestines being the worst of the lot).

    In short, keep them out of reach of children (particularly small children) at all times.

    Clever use of stock items (the ring magnets and the eyelets). I don't know that I'd want to bother with interchangeable resonators, but for a research project sort of horn, you've got it nailed.
  9. pete

    pete Brassica Oleracea Staff Member Administrator

    And pets.
  10. SOTSDO

    SOTSDO Old King Log Staff Member CE/Moderator

    That depends on whose pets are doing the munching. If it's the dog down the street that mauled my wife once...

    Incidentally, the same thing holds true for those little watch batteries and others of the "flat button" variety. For some reason. little ones (and pets) are drawn to shiny objects, and the ones who are too young (or too ignorant, in the case of the animals) to know any better like to put them in their mouth. Once the battery buttons are in the stomach, the acid attacks the layer of insulation between the terminals, unsealing the battery and letting all sorts of nasty crap leach out.
  11. jbtsax

    jbtsax Distinguished Member Distinguished Member

    No need to be concerned. The magnets are in my shop in back of the garage. My "rug rats" are in their 40's and the grand kids are in their teens. Yeah I know that makes me an "old fart" which also means I'm retired and have the time to play with magnets and other shiny things. :)
  12. Steve

    Steve Clarinet CE/Moderator Staff Member CE/Moderator

    I like the research.

    At one time I was researching this in a non-scientific way. But we all know resos don't change the tone. :)
    BUT ... anyways, I found that the resos up near the top had a major impact on tone across the horn versus ones further down the horn.

    But at that time I was on another forum in which I would have been eaten alive if I stated that.

    Alot to watch ... making sure it is perfectly sealed, pads are all the same height from different installs, etc. Too close a pad we know affects everything. But great research.

    Also make sure the Nowaks are tight, when they are loose they ring like christmas bells, which may be beneficial this time of year but mostly not.

    I also had an itching of analysis of airflow of various resos from flat, rounded to the pointed ones. But I'm insane anyways.
  13. jbtsax

    jbtsax Distinguished Member Distinguished Member

    I'm not sure I follow that reasoning. Dr. Eveno in her study found that the presence of "pad covers" as she calls them greatly reduces the sound energy that is lost with pads without a hard covering in the center. There was a very minor difference between the plastic and metal resonators themselves. It would seem that the energy loss of uncovered pads would be cumulative as more toneholes are closed making the effect of pads lacking resonators greater as one goes down the horn. Wouldn't the converse also be true, or is my thinking off?

    This study can be found by joining the Saxophone Acoustics Group and going to the files section.
  14. pete

    pete Brassica Oleracea Staff Member Administrator

    What's the definition of "greatly" in the context of this thread?

    Personally, the question I'd want answered is, "Do these make me sound better?" It doesn't matter how much sound energy I have if I sound like I'm playing a vuvuzela.
  15. jbtsax

    jbtsax Distinguished Member Distinguished Member

    A serious answer is that the study did not address the timbre of the notes with and without resonators present just the amount of energy dissipated by the uncovered leather pad. Essentially the musician has to put more energy into the system by blowing harder on a sax with plain pads to reach the same decibel level as a sax played that has resonators. It is hard to quantify "greatly" due to the fact that the losses are different at different frequencies.

    I have uploaded the study as a pdf. file for those who would like to investigate further.

    Attached Files:

  16. pete

    pete Brassica Oleracea Staff Member Administrator

    I'd call that addressed. Just not very satisfactorily :p.

    In other words, if you have resos it's easier to play louder. For some notes. The higher the note, the less the effect. In other words, an open C# on a baritone sax would have approximately as much effect caused by the resos as an open C# on a sopranino.

    True, but we get some nice graphs to look at.

    I think the biggest difference can be seen in Figure 3, which is the "absorption coefficient of the pads as a function of the frequency." Which is kinda logical: a spongy pad will absorb more than a metal or plastic disk. Figure 4, "radiation impedance of the cylinder," has the least differences. Figure 6 seems to indicate that a metal reso is better for "Mobility Amplitude," which I think means or implies that the seal is better.


    I'd like to find out if resos have any impact on intonation or perceived intonation; in other words, if you play a really low note, is the tone so bright that it sounds out of tune? Additionally, I'd like to find out what the differences are for a saxophone that was specifically designed without resos compared to one that was designed with. Just as a follow-up.

    Anyhow, I'd say that the real conclusion of the article is that, yes, resos do make a difference. It's not necessarily an outstanding difference, but it is a difference.
  17. jbtsax

    jbtsax Distinguished Member Distinguished Member

    I am grateful that someone is taking an academic look at the acoustical effects of resonators. There is a lot of anecdotal evidence about resonators in the world of saxophone playing that begs to be proven or disproven by careful scientific measurements.

    In my understanding the only time resonators would have an effect on intonation is when they protrude into the tonehole thereby decreasing the volume when the pad is closed. This would have the cumulative effect of raising the pitch of notes further down the tube. The question of whether the early Conns and Bueschers (before the snap ons) were designed differently because the pads did not have "covers" is an interesting one. It is quite well known that the "concept" of what a saxophone should sound like was quite different during that time as evidenced by the lower key heights and mouthpiece lays and tip openings. I personally don't think that the fact that the pads were without "covers" had any influence on the geometry of the interior of the horns.
  18. SOTSDO

    SOTSDO Old King Log Staff Member CE/Moderator

    I've always wondered about the sound quality of those Selmer horn made during the war, the ones with the rubber O-rings for the seal on the key. Was the key's interior solid metal? Inquiring minds want to know...
  19. pete

    pete Brassica Oleracea Staff Member Administrator

    The Selmer Padless. It was made by the good folks at Buescher. Pic galleries. The sound quality is fine ... provided you don't mind the clattering noise of the key hitting the ring.
  20. SOTSDO

    SOTSDO Old King Log Staff Member CE/Moderator

    That could be chalked up to not enough clearance for the cup and o-ring seat edges, I would guess.
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