What is Damping & How to Increase Damping Through Scraping

Robert Harter, Harter Reed Co.

 

Damping is one of the three main physical forces that determine how a reed will function.1 Damping is defined as “the loss of energy of an oscillating system by dissipation.” An object that possesses damping is referred to as damped. (Not dampened!) Damping in a bassoon reed primarily affects slower or low frequency vibrations by causing the vibrations to cut out before slowing down.

 

Some amount of damping is desirable in a reed because without much damping present, a reed can feel and sound wild, uncontrollable, and unstable in pitch. Damping helps focus the reed’s tone, stabilize pitch, and increase high note response. Too much damping can cause a reed to feel stuffy, dull, or unresponsive. Always strive for a good balance between the three forces!

 

The effect of damping on an oscillating wave

Image Credit: https://commons.wikimedia.org/wiki/User:Nicoguaro

 

How can we make our reeds more damped?

 

There are many adjustments we can make to a reed to affect damping. In this post, I will cover scraping (alteration of the reed blade profile by removing material) as the means of adjustment and will cover other methods in future posts.

 

You can damp your reed by creating steeper tapers from center-to-side, from back-to-front, or both. The center (spine) and back of the blade provide critical structural support to the reed and are responsible for the higher vibrational frequencies present when the reed is blown. By removing cane from the sides (rails) and front (tip) of the blade, we are weakening the scraped areas and relatively increasing the strength of those structural areas. Therefore, the area we want to focus on will be the corners which are where the sides of the blade meet the tip.

 

Suggested Method

 

This method takes advantage of the profound effect that creating steeper tapers to the corners has on damping. Multiple scraping patterns are layered on top of each other so that the corners will be scraped the most. It is crucial that only a little material is removed at a time and that the reed is tested between each step to avoid over-scraping.

 

You will need:

• Reed that needs to be damped

• Scraping tool(s) (Knife, File, or Sandpaper)

• Clean water for soaking the reed and cleaning files/sandpaper

• Plaque

• Holding Mandrel

• Optional Pencil

 

 

Prep. Mentally or with a pencil, divide the blades into thirds from front to back. I will refer to these as the back, middle and front thirds. Divide the blades in sixths lengthwise, I will label these as zones a-f from left to right. (This doesn’t have to be perfect, but try to keep it somewhat symmetrical.)

 

 

Step 1. Scrape zones a and f in the front third.

 

Step 2. Scrape zones a and f in the middle and front thirds, and zones b and e in the front third.

 

Step 3. Scrape zones a and f in the back, middle and front thirds. Then, scrape zones b and e in the middle and front thirds.

 

At this point, you will have scraped over zones a and f three times in the front third, twice in the middle third, and once in the back third. You will also have gone over zones b and e twice in the front third and once in the middle third. You will also have not touched any of the spine (zones c and d) and most of the back third, thus preserving the structural part of the blade while increasing the taper to the corners.

 

Step 4. Blend in work

Repeat all steps until the desired amount of damping is reached.

 

Pro tips

• Leaving out step 3 may lead to better damping results since the back will remain untouched. The purpose of step three is to ensure smooth tapers (avoiding bumps or sudden changes in thickness). Sudden changes in thickness can cause reeds to suddenly change modes of vibration in an undesirable way. Experience will help you determine when to skip this step.

• To add a bit more damping, it may be beneficial to continue the scrape into the c and d zones in the front third during step 3.

• For finer control, consider dividing the blade into smaller sections and following the same process in more incremental steps.

• The corners may start to collapse as a result of this process. Squeezing the 2nd wire from top and bottom will open the corners of the tip and undo some of the damping effect.

 

Happy Reeding!

 

1The other two being Compliance and Volume (Kopp)