@vinylholicmusic,
There’s an aspect about vibration control (when we are talking about resonances in materials, not electrical connections) that often seems to escape universal recognition and that is just that the tighter the connecting fastener that joins two surfaces, the greater the tendency for both material parts to (vibrationally) act as one. IOW, the more rigid the structure is, the more it will tend to ring, like a bell. Rigid structures are, in our day-to-day experience anyway, good for stability and from that we tend to conclude that stable=damped. And in the lowest frequencies of motion that is demonstrably true (think of, say, the visible swaying back and forth in a tall, rickety gear rack), but in higher and higher frequencies of motion the wavelengths are very short and they do indeed begin to become more problematic for interfering with frequencies both in and above the audio band.
Backing off a fully tightened screw, as you’ve discovered, means that the two parts will now partially vibrate as two separate frequencies that are "blurred" or "smeared" together, no longer presenting a single, unified resonant frequency that would in fact be of higher amplitude than the reduced amalgam of frequencies now being spread out over a broader frequency range.
In the ongoing "isolation-vs-spiked" component/speaker debate, any attempt to make a truly rigid structure, must then make for a way to either damp or "drain away" the resulting tendency of the structure to ring at higher frequencies. We could of course make a totally rigid structure and then physically damp it by applying some absorbing material (sorbothane, blutac, dynamat, etc) to it, but (for the two-parts-joined-by-one-fastener analogy anyway), practically speaking, why bother - since it is sufficient to make a structure tight enough to be stable at lower frequencies, but also loosened just enough to be damped at higher ones. And, as you’ve discovered, tuning by ear is best.
Remember, don’t assume from that beautiful, expensive, factory-assembled amplifier you’ve seen that the manufacturer must have sonically had a good reason for making all the fasteners in it death-grip tight. They do not do that for reasons of sound quality. They do that solely for a durable product (certainly for shipping reasons) and to create in the mind of the buyer the impression of good (solid!) design. Although, I will say that, if you intend to take this idea further in the future, super-tight-fitting, CNC-machined parts with just about zero play or "slop" in their fit, even without fasteners in place, may be harder to adjust to a comfortable zone of blurred frequencies between parts than can be done with more usual tolerances. But, in any case you may come to find that there may be any number of things that manufacturers do for reasons that have in fact little to do with sound, but try not to let that throw you too much - you can never go too far wrong if you insist on asking the right questions - even if it’s true that the right questions are the ones that often have to be asked for a bit longer.
Regards,
John
