As handbell ringing has evolved and we are demanding more from the materials we use, the discussions on foam need to be addressed from three perspectives.
1. First is the PHYSICAL CONSTRUCTION OF THE FOAM. Foam has a universal language and I have discovered not all dealers speak the universal language. Foam is defined in two ways: IFD or ILD is the foam firmness - this is taken by measuring the force in pounds required to compress a foam sample. The most common compression used today is 25% of a 4" thick sample. Example, on a 28180, it would take 28 pounds of presssure, to compress it fromm 4" to 3" or 25% of the toal thickness. The higher the number, the more pressure it can take, and therefore the harder the foam feels. For bells, some choirs use foam as soft as a "12" and some like "30". Personally, I think the firnmess will correlate with the size of the bell and different firmnesses are probably a good idea for choirs with five or more octaves, as that is where the weight discrepencies widen their range. DENSITY is measured in pounds per cubic foot...the equation is: density = weight divided by lengthxwidthxheight. In a 28l80 foam sample, the l80 is actually a reading of 1.8 pcf. It is closely tied to foam performance and the higher the foam density, the better it is for seat cushions (and you should have at least a 180 for seat cushions)...not necessarily bells! However, the higher the density, the more durable the foam...and the more costly. I have heard of foam suppliers providing as soft as 12110 through 16120, 22150, and as hard as 30180.
2.Second is the correlation of the PHYSICS OF FOAM AND BELL...which raises
questions I cannot answer.
a) What gives the best quality sound or damping and is least traumatic to the
bell when table techniques are used?
b) Is there a significant difference in ensemble ringing requirements and
solo requirements?
c) Will handbell manufacturers put the time and money into research on the
firmness and densities of foam on the market to find which best matches the
different sizes of bells the the techniques ringers utilize for sound
production?
This is a difficult area to explore as many foam manufacturers guard their
formulas zealously and new products are always coming out. However, it may
be an area for further research as the instrument continues to evolve in it's
design and use.
3. The final area to consider when purchasing foam is the FOAM COVERINGS. The fabric selected will have a direct effect on the sound produced by table techniques and damping. If you are shopping for foam locally, take the fabric with you that you are planing to cover your foam with - the issue of fabric has been covered in previous L-digests...corduroy seems to be a favorite, but the issue is to look for the combination of foam firmness/density and fabric - giving yourself the options for expanding your handbell set to include larger and smaller bells.
Guess this is more than you ever wanted to know...but this is still an area which has not been explored from a physics angle and it would be nice to know what foam will cause the least trauma to the bell and still let us get the sound and use the techniques we want.
Written by:
Charm
PeteNCharm@aol.com
26 Jun 1997
Archived original can be found at: Re: FOAM