Opinions vary. Personally, I think most of the perceived change in tonal character achieved through changing the material the "sustain" block is made of is due largely to the power of suggestion. Spend $150 on a titanium block, and you're going to do your best to convince yourself that it's better somehow. Understand, I'm not saying that it
doesn't make a difference, only that its influence is probably overrated.
Having said that, there are some arguments that make sense, depending on the effect you're trying to achieve. Because different metals have different hardnesses and densities (among other characteristics), they respond differently to stress.
| Metal | Hardness | Density |
| Titanium | 334 | 4.43 |
| Steel | 130 | 7.75 |
| Brass | 60 | 8.5 |
| Aluminum | 160 | 2.7 |
| Zinc | 45 | 7.1 |
Disregarding the static tension a string imposes on its mounting points, the stress on those points is mainly vibration. The vibration of the string(s) is what we want to hear, so what effect is the mounting point's properties going to have on that?
Since the object of the exercise is to hear the strings vibrate, anything that absorbs those vibrations could be thought to be detrimental. So, you would want your mounting point to have a lot of mass so that inertia will tend to hold that point still. Going by that, the block materials that would make sense for increased sustain would fall in this order, from longest to shortest
Brass
Steel
Zinc
Titanium
Aluminum
For increased frequency response, you would want something harder. The block materials that would make sense for that would fall in this order, from highest to lowest
Titanium
Aluminum
Steel
Brass
Zinc
All things considered, steel is probably the best material overall for general purposes. Titanium will be brighter, but you'll lose sustain. Brass would have better sustain, but you'd lose frequency response. Aluminum and zinc don't appear to be particularly good at anything for our purposes, although from a manufacturing standpoint they're far and away the easiest/cheapest to produce.
It's telling that regardless of the numbers, aluminum and zinc are the most common materials used. Why? Cost is certainly a factor. Aluminum and zinc are fairly inexpensive just as raw materials, but so is steel. However, both the former are easily die cast, which eliminates a LOT of machining. That saves time and tools, which are both expensive.
Keeping in mind that all of the materials mentioned are going to be mounted to wood, which is considerably softer and less dense than metal, and that all the considerations have to do with vibration absorption, I think the reality is that when it comes to sustain blocks the difference the material makes is not prominent enough to justify anything exotic.
But, I could be wrong :laughing7:
