Banjo Hangout Logo
Banjo Hangout Logo

Premier Sponsors

Banjo Lovers Online

Irish Banjo Tone Brightner & Amp and Gibson Tone Enhancer & Amp

Posted by yellowdog on Monday, August 19, 2013

I recently replied to a post titled, "Minimizing Tubbiness", where I briefly described my solution for this problem on my modified Gold Tone CC Irish Tenor tuned GDAE.  I use this banjo to play Irish Traditional Music (ITM) using single-string style in weekly Irish sessions.  When I bought the banjo I wanted to improve the quality of the sound, so I  removed the resonator and some of the metal parts and in the process introduced an undesirable degree of "tubbiness" (excessive wooden timbre) to the sound.  I wanted to get a much brighter, metallic timbre so I recently added a "tone brightener and amplifier" of my own design inside the banjo.  In my reply to the "tubbiness" post I promised to take pictures of this new gadget and just did so.  You can see the pictures by clicking on the "Photos" tab above my picture on the left.

While I was at it I also took a couple of pictures of the heavy paper tone enhancer and amplifier which I have been using for the past year or two in my 1950's-era Gibson Mastertone ("Bow Tie" model) tenor which is tuned CGDA.  The Gibson is a very bright sounding banjo and certainly doesn't need a tone brightener but I thought that I could improve the quality of the sound.  My goal with this gadget was to improve the quality of the Gibson's sound by increasing the number and volume of harmonics - the high frequencies which are known to increase the quality of every note, including the bass notes but especially the highs.  Since I perform only solos with this banjo for small audiences the sound quality of all notes is very important.  As with the Irish tenor I don't use a resonator on the Gibson in order to get the best possible sound quality.  I am very pleased with the result of this very simple paper and tape amplifier which, unlike the Irish banjo gadget, does not require the presence of a rim bolt to work.  

I'll soon add drawings and specifications for both of these devices so that you can make them if you wish, and will be adding to this blog entry as I get more time.  But before then I thought I would describe why I think these two devices work so well.

Theory behind both devices (Background):

When any musical instrument is played vibrations cover all surfaces of the instrument.  These behave like waves on a lake except that the waves are initially very small (before they reflect on themselves and similar waves).  Just like waves on a lake, if waves encounter a wave of similar frequency coming from another direction, the waves will add (amplify).  This characteristic of waves is what enables the tiny waves on the musical instrument's surfaces to be amplified sufficiently to be heard after they are converted into waves in air.  Converting the waves to air (air pressure waves) is easily accomplished by routing the waves onto sheet materials such as paper or brass sheet.  Another characteristic of waves which move over surfaces or through materials that is useful is that waves pick up the timber characteristic of the materials that they move across or through.  This characteristic allows the timbre of the sound to be modified as desired.  For example, waves which move across wood, once made audible in air, will have the timbre of the type of wood that they move across; and waves which move across steel will eventually sound very bright and "steely"; waves which move across brass will sound "brassy", etc.  Paper seems to be timbre neutral since vibrating paper surfaces don't seem to change the timbre of the instrument even as volume and sound quality are increased.

Theory behind the Irish tone brightener and amplifier (See photo):

The desired metallic timbre characteristic described above is present in the banjo's sound chamber in the waves on the head of any rim bolt inside the sound chamber.  This is because the rim bolt is connected to the shoe and then the hook and the metal hoop touching the head.  These waves can also be assumed to be of very high quality because they are so directly connected to the source of the sound.  The goal is to capture and then amplify these waves by causing waves of similar frequencies to intersect repeatedly, and then be converted into air pressure waves inside the sound chamber of the banjo.  

The device which does this consists of a special cross shape of thin brass having four arms of equal length one of which has tapered sides, a center hole and two small holes at the ends of two opposite cross arms adjacent to the tapered arm.  All arms of the cross shape are curved upward in a smooth and gentle "cup saucer" curve.  There are also two steel eye screws the eyes (loops) of which have been opened to convert them to screw hooks which hook in the mentioned small holes at the two ends of the two cross arms.  The screw ends are screwed into the wood rim.  This device sits on top of a rim bolt head so that the rim bolt head touches the edge of the center hole of the brass cross at one or more places.  (It need not touch the entire hole edge.)

The modified cross shape of sheet brass (see drawing and photo) both amplifies the waves and converts them to air pressure waves.  This is because waves in the arms are reflected from the ends of the arms and then intersect similar waves near the center, amplifying them.  The center of the cross contains a punched hole of slightly smaller diameter than the diameter of the rim bold head so waves travel from the rim bolt head onto the brass cross wherever the edge of the hole touches the rim bolt head.  The arm that is tapered causes the waves on it to merge and so intersect (and amplify) even more than the straight edged arms.  The cross is secured in its position atop the rim bolt head by the two slightly opened steel eye screws, the ends of which pass through two small diameter drilled holes near the ends of the two opposite arms on either side of the tapered arm.   Because the brass cross shape is curved upward the ends of the brass arms having the two small holes rise upward until the end edge of the brass arms touch the eye screw.  This surface/edge contact is desirable for efficient transfer of the waves from the screw to the brass sheet.  This allows the rich, mostly lower frequencies on the surface of the wood rim to flow from the eye screw onto the brass cross, and after picking up the bright timbre characteristic of the steel from traveling over the steel eye screw.  These waves from the wood rim amplify on the cross in the same manner as the waves from the rim bolt head by intersecting themselves and waves of similar frequencies mostly near the center.  Amplification of the waves from both sources - the rim bolt head and the wood rim -  is sufficiently large to cause the brass cross to undulate and move the air to create audible sound.  This is new, bright, high quality audible sound that is now in the sound chamber and which was not in the banjo's sound chamber before.  This causes the banjo to sound not only brighter and better but louder - and very loud if needed.

Three important features of this Irish banjo tone brightener and amplifier should be mentioned:  (1) no sound absorbing materials, such as tape or paper, are used;  (2) metal-to-metal and metal-to-wood contacts are firm because the spring effect of the curved brass helps to insure that firm contacts are maintained; and, (3) motion of brass cross is minimally constrained which adds more harmonics to the air.

There are other elements of the Irish "banjo sound system" beyond this tone brightener which can be changed to increase brightness.  One of them that is often overlooked is the pick.  I almost overlooked this capability myself because I have used a .60 mm thick nylon Dunlop pick on both banjos for years and have been very happy with them.  Fortunately I remembered the importance of the pick to sound so I looked through my collection of old picks knowing that one in particular always creates a very bright sound - the Clayton brand "small teardrop pick number 12 (.50 mm) which is made by Steve Clayton, Inc. The material of this pick is "acetal polymer" which is stiffer than nylon and has a noticeably rougher surface.  The point of the small teardrop shape also seems more pointed than then the common teardrop shape which should create a quicker release and more definition to the sound.  The only downside to using the pick is that it is difficult to grasp because it is so small.  To make it easier to hold I attached a small rectangle of  double stick 1/32" thick foam tape (used for window insulation, etc.) folded over the upper end.  I was surprised that this addition of tape both improved the sound and gave me better pick control because the added thickness of the tape at the end essentially changed the cross section of the pick from a line to a "T" shape, allowing the tips of the fingers to touch the pick near the tip and the cross member of the "T" (the tape) to fill the air gap between the fingers and the pick, creating greater leverage on the pick.  The sound of the banjo using this Clayton pick, even without the foam tape, was noticeably brighter, very clear and of high quality, and this was even more true with the tape.  So the pick is certainly worth the effort to learn to use it.  

(This paragraph added on August 25, 2013 following a session with the banjo and pick on August 24.)  In preparing for our weekly Saturday afternoon session I found out that the brass cross had lost some of its "springiness" so I removed it from its mount above the rim bolt head and added more curvature to the brass cross arms which held it tight and gave a clearer sound.  I also found that the sound of the banjo was still not as clear as before and solved this problem by tilting the top of the bridge more toward the tailpiece.  (The tilt creates a point contact between the string and the bottom of the ebony notch in the bridge which sounded clearer than when the string lies along the full width of the bottom of the ebony notch that gives a short line contact between the two.  This small change in bridge angle with the head made a big difference in the quality and clarity of the sound.)  I was very impressed with both the sound of the banjo and speed of the new pick/double foam tape combination.  The pick was literally impossible to drop (and even stuck to a single finger!)  The pick provided a new ability to play very fast, clear and loud triplets which was highly noticeable and surprisingly easy.   Tremendous volume was easily obtained simply by pressing the tips of the fingers hard against both sides of the pick slightly to the rear of the point when extra volume was needed.  The thickness of the foam against the meat of the fingers at the same time locked the entire pick firmly in place.

The reason for this impressive difference in sound quality using the Clayton pick isn't understood but some of it probably lies in the microscopic roughness of its surface, which may pull on the banjo's strings in the manner that a rosined violin bow pulls on a violin's strings - pulling and releasing in very small increments.  This input motion is essentially a mechanical saw tooth wave input.  A saw tooth wave input to an electronic system, such as an amplifier, is known to generate all harmonics in the output of the amplifier when the amplifier itself is capable of producing such an output.  A mechanical saw tooth wave input to a banjo should do the same thing.

Theory behind the Gibson tone enhancer and amplifier (See photo):

This device is an improvement to the "business card" amplifier which I have described before on the hangout, in which a paper business card is taped to the wood rim in an arch using Scotch brand "Gloss Finish Transparent Tape" at both ends of the business card.  The improvements are in use of a larger piece of heavy paper (card stock) and cutting an arrow shape (see photos and drawing) so that the tip of the arrow shape is approximately 1/4" from the apex of the arch.  The improved sound that results is believed to be due to high frequency undulations of the arrow which creates similar high frequency distance changes between the edges of the arrow and the arch edge next to the arrow.  Since air flows between these shapes it is reasonable to assume that the motion between the two edges efficiently creates audible sound analogous to the motions on the arrow and the arch.

Notice that the tape is attached only at the centers of the ends of the arch so the corners of the arch are not constrained and can also move freely.  The tape carries the waves from the surface of the wood rim to both ends of the arch.  Just as with the business card amplifier audible sound is believed to be created between the inside surface of the arch and the wood rim since these two surfaces contain the same surface waves and the surfaces diverge.  The high frequency relative motion described above (between the arrow and the arch) is believed to create more high frequencies which add to the sound created between the diverging surfaces below the arch.  

This simple device works wonderfully well in the Gibson but the tape should be pressed against the wood rim before a gig to insure good contact between the two.  The amount of arch does change the sound, so one side of the arch should be moved about to find the best sound (and amount of arch) for a particular banjo.  It is unknown how well this device works in a banjo with a resonator.  


Be the first to comment on “Irish Banjo Tone Brightner & Amp and Gibson Tone Enhancer & Amp”

You must sign into your myHangout account before you can post comments.

More posts from yellowdog

Newest Posts

Click for Details 'Mikes Mute' 2 hrs

More >  

Hide these ads: join the Players Union!

Hangout Network Help

View All Topics  |  View Categories