Gpa 416-8c

[Alien_Shore]

Hmm, typically Fs drops, Vas increases, Qts remains ~ the same, ditto measured efficiency, so something seems amiss. FWIW, the most accurate way to measure Vas [and the most tedious] is to find the sealed cab net Vb that raises Fs 1.56x, then divide it by 1.44.

Don?t currently have access to my collection of measured specs, but Le @ the 1 kHz reference is ~1.2-1.5 mH IIRC. A traditional 15? with 0.582 mH would need a shorting ring, which Altec never used AFAIK on any of its woofers, relying on its inductance rise to extend the driver?s HF response, especially when driven by a high output impedance.

You can check it though by working off an impedance plot:

Le = 1000*SQRT[[Zxo^2-Re^2]/[2pi*1000]] where Zxo is the resistance @ 1 kHz = 1.4954 mH Vs DATS?s 1.478 mH just ?eyeballing? Zxo = 12 ohms off your original plot, so it was accurate enough for me originally since it falls in line with my faded memory.

GM

Yep, you're right on, GM. John Murphy (DATS designer) let me know that DATS has selectable ranges and units for several of the t/s parms. My first Le readings for this driver (~1.5mH) were at 1kHz, while the second readings (~0.5mH) were at 10kHz. For others using DATS, you simply double-click on the units box to toggle (you can see which parms have selectable units because of the little box drawn around them).

I'll try to get that test box done this weekend. I'm not trusting my delta mass technique

FWIW, here are the T/S params in free-air, cone vertical, before and after break-in (sans Vas added mass that was skewing the data):

GPA 416-8C	new	after break-in
Re	7.77	7.59
Fs	23.55	22.88
Qts	0.294	0.293
Qes	0.308	0.309
Qms	6.638	5.931
Le (@1kHz)	1.51	1.47