rebuilding speakers with different voicecoils, what changes?

[FE3T]

I have been playing with some speaker baskets and after market recone parts, and wonder if someone can help me predict the results of using different voice coil lengts.

All parts identical EXCEPT the voice coil.

If reconed with orginal parts:

Very ligth cone, accordian surround, and 14mm long coil
fs 85hz
Vas 14,2 L
sens 97 db/1w
qts 0,35
xmax 3mm (one way)


In my version i currently use a thick stiff cone with foam surround and a 19mm long coil
Here i belive that fs drops a lot, maybe as far as down to the high 30`s

Vas should rise to 30-50L

sensitivity should drop 6-9 db (mated with a 93 db tweeter they get slitghly overpovered by the tweet so my guess are 89-91 db/1w)

But what happens with qts? i know a heavier cone should rise qts but are unshure what a loser surround does and how does a longer coil change qts?
Here i have checked out a 10" with even heavier cone,and softer surround but the same voice coil and motor and these have a qts of 0,36. Am i totally wrong in assuming that my drivers are in the same ballpark?

So let me put together a guestimate for my drivers

This is with a 19mm long coil

fs 38hz
Vas 45L
sens 89 db/1W
qts 0.35
xmax 6mm (one way)

What if i build a version with a 16mm long coil?

Fs should rise a bit due to a ligther coil and former, but what other changes would the shorter coil give? will a shorter coil give greater force and even higher fs?

Vas shouldnt change should it?

What about sensitivity? shouldnt it be a tad higher?

Qts what about it? will it drop a bit like i belive?

xmax drops to 4,5mm

I can also build this drivers with a 14mm coil, but i guess that will only take the changes from gong from 19mm to 16mm a notch more in the same direction.

I know i should be getting a woofer tester, and plans to do so, but if you can enligthen me about basic driver understanding by answering my questions i would really appriciate it.

[sreten]

Hi,

If you shorten the coil but keep Re constant with the same wire :
(e.g. convert a long 2 layer to a shorter 3 layer)
- Fs, and Vas don't change
- Xmax drops (obviously)
- Qts drops, BL and sensitivity goes up

For all drivers a less stiff suspension causes Fs and Qts to drop. In most
boxes with Vbox < Vas the differences in Fbox and Qbox will be minor.

rgds, sreten.

[FE3T]

The Re will rise with the shorter coils i can chose from since they all will be 2 layer.

The raw baskets i have played with are JBL`s 2118
i even did a pair with 116H-2 aftermarket parts, (rather thin and ligth foam edged cone) but i found the midrange a bit intense.

its the version with 127H-1 aftermarket parts cut down in diameter and refoamed with 116H-2 foams i think are most suited for a planned XPL based center channel (using the 116H-3 woofer found in the XPL 140`s would require a sealed solution if an acceptable size are to be obtained, but i desire a ported center)