Voice coil height 604E

[martyh45]

Did Altec change the height of the voice coil on the E version? I?m trying to figure out xmax for a C with an E cone. Thanks

[bfish]

Hi Marty,

If it's not too late, just subtract the coil height from the front plate thickness and divide the result by two.

I'm guessing it's too late though, and that you already knew that anyway. Given the same thermal and electrical ratings, I think it's safe to assume the C and E would have the same xmax, though peak excursion before damage might differ due to the different suspension. Bill's the only one I know who could say for sure.

[martyh45]

Thanks Bfish,
Yep too late, already been built. I learned afterwards that the gap height was changed for the E and was wondering about the coil. The A,B & C have a pole piece that is 3/32? shorter than the E, the top plate was beveled near the gap on the older versions.

[bfish]

Interesting. Never been into any oldies.

Well, a deeper gap would suggest either more coil, more travel, or a little of both. And now you're wondering if your coil might be a little long...hmmm....

Still have the old coil?

[martyh45]

Nope, I don?t have the old coil anymore but? I called Bill at GPA and the newer versions have a slightly shorter coil. So the xmax should be slightly greater than the original C.
I?ve since searched the archives and found that Jim D mentioned the shorter coil in an earlier post but for some reason the non-beveled top plate is what stuck in my mind.
Assuming that the top plate thickness of the E and C are the same, xmax for the C frame-E cone hybrid should be .103? or 2.62mm as opposed to .15? or 3.81mm for the E. I?ve actually measured B and C top plates and know that they are the same so all should be the same for B frame-E cone hybrids.

[bfish]

Cool! All swell that end swell.

[bfish]

Took me awhile to remember where they were, but there are measured specs for the B, C, and E on member Wm. Eckles site;

http://www.wmeckle.com/ASHLEY/Ashley.htm

The data is close to your conclusion (if one assumes their decimal is misplaced).

[martyh45]

Thanks for the link bfish,

I would be willing to bet that the decimal is misplaced. 2/10th of a mm is about useless. If they were going to run it that close they might just as well have overhung the coil and lived with the distortion.

For the record, I measured one of mine. The pair is freshly rebuilt with GPA parts and re-magged. Strangely enough, the measurements look like a mix of the C and E as Ashley measured them. I haven?t really hit these with any serious LF yet so they might loosen up a bit from what I measured here.

604C with E cone.

f(s) = 27.59 Hz
Q(ms) = 2.263
Q(es) = 0.198
Q(ts) = 0.182
V(as) = 620.20 liters
n(0) = 6.28 %
M(ms) = 42.87 grams
R(e) = 14.14 Ohms
SPL = 100.10 dB SPL 1W/1m
C(ms) = 0.78 mm/N
Piston Diameter = 309.9 mm
Z(max) = 175.80 Ohms
L(e) = 2.49 mH
BL = 23.04

[bfish]

Thanks!

I think you'll get different results after you've "exercised" them. Doesn't take much, just to (or near) xmax for a couple minutes. At that point, they've settled in.

[bfish]

The old idiom of xmax strictly being a function of the physical dimensions of the components takes much for granted (depending on whose xmax def you follow). If you call it peak linear excursion, variables in compliance and fringe field usually make the actual knee of linearity something different than dimensions indicate.

Klippel has an interesting application note on that;

Performance-based measurement of peak displacement

that describes a dynamic, performance-based measurement technique. It's based on the observation that the knee of linearity and the knee of THD are related. A dual-tone IM pattern is applied, and the level is increased until the THD jumps, at which point you note the displacement. Therein lies the hitch for DIY...measuring the travel.

Once you're past the design stage, it's all moot anyway though, you'll hear it when it happens.

<font color="#FFFFFF" size="1">[ January 02, 2008 08:59 AM: Message edited by: bfish ]</font>