Does Sd include the area of the dust cap? I would think so?
Okay, thanks for the info.
I’ll check for information on this so I can get clarity
Sd is the effective piston area which of course includes the dustcap cone. and around half of the surround
This is a bad analogy as per t/s. Engine displacement can be changed by altering stroke while keeping bore size. It's not so with speaker Sd however it should be, no?
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It is a perfect analogy - note the phrase 'For a given displacement...'.
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Oddly These two; Peavey 12" Black Widows and Fane 15" Colossus handled my Low and Medium frequencies in my tri-amped mobile sound system.
What marvelous experiences we had with them. Rarely have seen these two mentioned together in a post or anywhere. I got them out of studying driver specs online back at 1998-99 and availability in my rather distant country.
Any particular reason or "criteria" why you chose these two?
are those still in production ? (peavey and fane)
Peavey likes to change the TS parameters over the time
so i wonder if the 12" BW gave the same TS as in the 90's
Peavey likes to change the TS parameters over the time
so i wonder if the 12" BW gave the same TS as in the 90's
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I've asked driver designers about this and seen the results of measurements on drivers. The general rule of thumb that is supported by the measurements is that around 1/3 of the surround's area contributes to the Sd of the cone. At high excursions, some softer surround materials can be prone to moving out of phase (softer rubber-type materials and accordion fold fabric types are most prone) with the cone diminishing this, which is why material selection is important. Thick foam surrounds with either a hemispherical or a parabolic contour are surprisingly good at maintaining form so long as they're not operated near their mechanical limits. You can't really see what's going on with videos of car competitions and similar due to video artifacts caused by "rolling shutter", which makes everything look like it's rocking badly in a very non-linear manner.
The dust cap also contributes to the Sd for subwoofers. That only becomes an issue with "full-range" drivers and similar operated high enough for break-up to cause the cone to effectively decouple from the voice coil, operating in chaotic phase, leaving only the dust cap to behave pistonically. (Side point, this is why there's no such thing as a full-range driver. The decoupling behavior of the cone and dust cap can be modeled as a mechanical equivalent of an electrical crossover with all the same formulae involved.)
As for low sensitivity of small, high excursion drivers, that's an artifact of them having larger, more massive voice coils (higher Mms, lower sensitivity for the same motor), but also much taller flux gaps that reduces the strength of the field. Most high excursion VCs are also significantly overhung, which reduces the length of wire in the gap (lower BL), which also has an impact. However, this isn't necessarily a bad thing. A high excursion driver with a low standard sensitivity rating will have higher effective sensitivity at low frequencies due to the balance of the T/S parameters there. Its higher Mms, lower Fs and, typically, higher Qts will give it a flatter response than a high sensitivity driver that most always rolls-off much higher. Everything's a design trade-off.
Of course, high Xmax isn't everything. Air is squishy, especially so at low frequencies where the wavelengths are so much larger than the driver diaphragm.
You need something to compensate for that terrible resultant acoustic impedance matching and there are really only two effective options: a mechanical impedance matching transformer aka "horn" or a lot of surface area. It goes beyond mere displacement. A small driver beating its heart out will not match a large driver loafing (you can float a bubble in the cupped palm of your hand, but fail to move it by jabbing a finger at it wildly). But then those trade-offs come into play again because you can't get a driver large enough to always loaf. Every time you halve the frequency, you have to quadruple the displacement. So, you still need high linear Xmax to go with that large surface area to keep distortion down.