Let me start by saying that these are notes from a conversation I had with Ralph Morgan back around 2003.  His views were based on research and development which were conducted by him and others at the Selmer Company in the early 1960s.  If you are expecting mathematical formulas or proofs you will not find it here.   Through the course of the conversation, he convinced me that he was an authority on the subject and his findings made logical sense to me. Kind of like if I had gone to Carroll Shelby for tips on tuning a V8 engine…I would not have asked for mathematical proof, I would have just listened and assumed his research was sufficient.

     Around the year 2002 - 2003, I picked up an SML tenor which needed an overhaul.  Before starting the work, I thought about putting in an expensive resonator set.  I had talked to other repair techs about various resonator types…Noyak, metal dome, seamless dome, solid brass, sterling silver, flat, plastic etc.  The options were seemingly endless and so were the opinions.  Many of them had very short and general answers…brass resonators sound better, or large metal domes are more powerful, etc.

     The difficulty with resonators, is that it is virtually impossible to change just the resonators.  The horn has to be disassembled and reassembled.   At that point, too many variables have changed.  If pads were also changed, new pads may be stiffer or softer than older pads.  Key heights may have changed.  Leaks may have been corrected or created on reassembly.  Too much time passes…it’s not as if you can flip a switch to change resonators.  Hours, days, even weeks may pass.  Remembering how the horn sounded before the change in resonators can be difficult.  In the time that passed, the reed may have changed, etc.

     Knowing that Ralph retired as Chief Woodwind Designer at the Selmer Company, I asked him if he were re-padding this SML Tenor, what resonators would he use.

    He started the 50+ minute conversation by saying, back in the Fall of 1960 (or whatever year it was…he might have said 61 or 62), the engineers at Selmer researched resonators and decided to make the change from metal domes to nylon domes.  Ralph was one of the engineers who helped make this decision.

    They tested all types of materials…metals, synthetics, other natural materials and found that the material did not make a difference in the reflection of sound waves.  The material had to be a non-porous material with a solid surface.  They found that as long as the resonator was the same size and shape, the material it was made from made no acoustic difference.

     What did have a impact on the acoustics of the instrument was the size and shape of the resonator.  Ralph made clear there was nothing trivial about the dome shape of the resonators.  When the sound waves reflect off a resonator on an open key, an optimal dome shape helps reflect the sound waves out of the tone hole.  More importantly though is when sound waves reflect off a resonator on a CLOSED key, the dome shape helps reflect the sound down the body of the interior of the horn.  The arc or height of the dome of the resonator is critical and must do both functions with minimal turbulence of the airflow.  If all you are concerned about is reflecting sound out of a tone hole, then you would use a different shape and conversely, if you were just concerned about reflecting sound waves down the body of the horn, you would also use a different shape.  Because you need the resonator to perform both functions, you have to find a shape that will perform both functions well.  

     Ralph insisted that the low arc shape of the Selmer-engeneered dome resonator works for any saxophone…not just Selmers.  It will improve the acoustic efficiency of any saxophone.

    The other factor is the diameter size of the resonator.  Depending on the diameter AND height of the tone hole, the diameter of the resonator also makes a difference.  Again, the most efficient diameters of the resonators for each size tone hole were researched.  Unfortunately, I do not have any charts or exact size recommendations, but he said you DO NOT want the largest resonator possible (i.e. one the fills the tone hole), but you want some pad exposed between the interior rim of the tone hole and the edge of the resonator.  The height of the tone hole chimney can also be a factor here.

     While the resonator material made no difference in the Acoustic performance of a horn.  the material did make a difference in the life of the pads and a difference in the MECHANICAL performance of the horn.  Metal resonators oxidize and rust.  Brass and silver resonators can oxidize and tarnish.  Steel resonators can rust and corrode.  This oxidation and rust can impact the life of the pads.  Through the years, I have replaced a lot of pads long before their time because the resonators had rusted or oxidized.

     However, the main reason the Selmer engineers made the switch from metal to nylon was the nylon resonator was 1/6th the weight of the metal resonator (Ralph said a particular fraction and I do not remember what it was, but I believe he said 1/6th)  By having a lighter resonator, the overall weight of the key cup, pad, adhesive, and resonator is reduced.  With a lighter key, the springs do not have to work as hard…they can be set lighter or stiffer depending on player preference.  A lighter key also reduces “key bounce” in the lower stack and larger keys.

     After the Mark VI, Selmer went to center rivet metal dome resonators.  Ralph claimed that no research was done before making the change and it was just a case of making a change for the sake of making a change.  The metal dome resonators which followed the nylon resonators were a marketing ploy and not based on science.  They are prone to corrosion.  With a center rivet, they sometimes develop an annoying metallic buzz (resonator against rivet) as the pad becomes older or if the pad was not manufactured properly.

     Sadly, there was more information dumped on me during this conversation than I will ever be able to recall, but suffice it to say that after this conversation with Ralph, I always recommend Selmer style plastic dome resonators for just about any overhaul.  Some customers have a preference, and that is no problem, give the customer what they want.  I will not remove the original snap-ins from a Buescher or screw-ins for a Buffet.  Otherwise, if you ask my advice, I suggest what Ralph suggested.

     I used Selmer style plastic dome resonators on that SML and it turned out great, as most SML tenors do.  I saved myself and the eventual purchaser some money.   Would I have noticed any difference using an “inefficient” resonator?  Maybe. Maybe not.  Of all the resonator conversations I had with different technicians, none recommended Selmer-style plastic dome resonators.  Most recommended the expensive individual or custom sets.  None offered any fact-based reasons.  Ralph easily spoke 50+ minutes on the topic.  In the old days of saxophone and mouthpiece design, those old gray-haired craftsman put a lot of thought into every aspect of the instrument.  Nothing was trivial.