Soft vs firm foam theories

[Bflat]

The discussion on the SKB 450 cases prompted me to start this thread. A music store salesperson and a couple of techs I've talked to have suggested that there are two "protection" theories that determine the use of soft vs firm foam inside horn cases.

Advocates of soft foam say that it affords protection by absorbing & cushioning the inevitable movement of the instrument when the case is dropped or receives a blow; believers in firmer foam (with a proper snug fit in all areas) argue that the more supportive material deters excessive movement and prevents damage caused by "acceleration" under impact.

Firmer foam is used by the makers of all approved motorcycle helmets (they also use softer materials in some areas, but this is primarily for comfort), which would seem to me to offer some support of the firm theory.

Any well-informed thoughts or fact-based opinions about this?

Bflat

[mark_m]

Don't know that I know more than anyone else about this, but I've been pondering the same question.

I think the firmer foam would do a better job of supporting the horn if it is taylored to the specific horn. On the other hand, the firmer foam is going to more directly transmit deflections of the case, so if you don't have a completely rigid case exterior, a denting or flexing of the case is going to transmit more directly to the horn.

My guess is ideal situation would be a firmer foam around and custom formed to the specific horn, with a softer foam against the shell of the case so that bending of the case would not be transmitted through to the horn. The case-within-a-case approach could certainly provide this.

Going with the motorcycle angle, there are some variable density foams used in seats, And I've built some seats with layers of differing densities of foam to optimize shock isolation and maximize form-fittingness.

The problem of comparing to motorcycle helmets is these are made to minimize the damage of very substantial impacts, and at lower impact forces they still transmit a lot of shock. The Snell rating requires a better protection at the higher impact levels, and the other (sorry I forget what it is) rating requires better performance at lower level impacts - they don't necessarily come together. I think most skulls will take more of an impact than a sax without bending, so the sax needs more protection at relatively low levels of impact, where a motorcycle helmet really doesn't do much. Put a helmet on and have someone punch it and you'll get the idea...

[danodownunder]

As A repair type I see lots of D# & C key guards broken off by styrofoam inners and the foam collapses quite quickly. dano.