Oh btw, how exactly do you tune BA drivers? The S8F/Pro are using the same drivers right but how come their tuning is different? Is it the design of the shell or tubes or is it in the electronics
from this
very in-depth source, it seems that BAs can be tuned by changing "membrane tuning holes", nozzle filters, in-tube damping filters, and effective internal volume, as well as properties of the armature itself like mass, stiffness, diaphragm placement, size, et c... but that's what distinguishes
drivers from each other, and your question is how they're tuned differently for a given model. for that, it says:
Just before a BA receiver is completely assembled, one last chance for fine tuning exists to make variants of that particular model. An acoustic filter can be placed within the nozzle, which generally reduces the the amplitude of the first peak. Very small holes can be punched into the diaphragm suspension membrane (with a laser), which reduces the second peak and bass response. Or a combination of both may be employed.
As if this subject isn't difficult enough, it gets worse when we consider actually using these devices in an IEM. The tubing that goes from the receiver nozzle to the exit port on the ear tip will have effects on the frequency response delivered. Overall length and diameter of the tube will change the sonic profile, as will a variety of acoustic tuning filters and their position within the tube.
Multiple drivers and cross-over networks can also be used to sculpt frequency response in ways not available to a single driver. Let's take a look.
They go into more detail that you can check out in the article. But the takeaway is:
Tubing length:
Tubing diameter (1.91mm dashed, 1.35mm solid, since it's hard to see. I'd also like to note that that's an area fraction of 2.00—
i.e., the air in the thick tube, while being pushed around by the drivers, has
twice as much area to move through, which is why the difference is so big. I assume that the diameter choices here are not arbitrary, given the very precise area fraction):
In-tube damping filters:
Damping receiver placement:
Multi-driver tuning (simplified picture; no electronic crossover is shown):
That's about it; I found it very informative! FWIW, the ACME8 has 8 drivers doing the above job, but introduces an
additional physical low-pass filter via the sharp-edged labyrinth, in addition to the standard "BAs roll off on their own" physical attenuation (shown above) and electronic lowpass/highpass frequency sorting. Fearless should send me one to take pics of
EDIT: You can see in this picture I found that the S8P has a different sound tube setup. I think the description somewhere stated it had 4, but HBB's looked like it had 3...
Compare to the more equilateral setup seen on mine:
if the bore arrangement is different, it's quite likely that the tubings have slightly different lengths and diameters, which could well account for the graph changes we see. what i'm personally more curious about is how that translates to a loss of microdetails—is it captured by the graph, or is it something to do with the bore arrangement or tubing differences? Either way, how? (I 100% trust HBB's ear on this, I'm just a neurotically curious person.)
edit again: yeugh, sorry to make this even longer, but maybe disregard that—looking at HBB's video, it has either the same or a very similar bore arrangement to the S8F:
perhaps the pic I found (from a Fearless product video) was a preproduction unit or something (and it's custom). I was curious whether it might have 4 tubes but
end in 3 bores, but that also doesn't seem to be the case:
the setup looks like the one in the S8F from what I can see. ¯\_(ツ)_/¯
