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I yanked the Altec 416Z drivers out of my valencia's and measured the t/s parameters using the WT3 Woofer Tester from Dayton Audio. The two measured relatively closely, but I didn't get the results I expected. Here they are:
f(s) 23.55
Q(ms) 5.191
V(as) 21.67 cubic ft (613.7 liters)
n(0) 3.21%
M(ms) 70.91 grams
R(e) 11.39
Q(es) 0.238
SPL 97.16dB SPL 1W/1m
C(ms) 0.64 mm/N
Piston Diameter 12.75
Zmax 259.4 Ohms
Q(ts) 0.228
L(e) 1.32 mH
BL 22.39
I expected a Vas quite a bit higher, based upon data posted on the net for other 416 drivers. This changes the optimum enclosure size from the 8 cubic feet or so I was expecting, down to around 4 or 5, which is about what the Valencia cabinets provide (surprise!).
Does anyone have similar results?
thanks
Les
Follow Ups:
I also measured my Altec 416a's recently with the Dayton WT3 and obtained similar results to what you have shown. The VAS predicted a cabinet between 4 and 5 cu. ft.
The custom cabinets that were built by the previous owner are that same size.
As you noted most of the Altec experts all recommend an 8 cu ft cabinet for these speakers. It would be interesting if someone could explain.
How did you measure the VAS with WT3?
Don M
Greets!
Historically, cabs were designed for passive XOs and high output impedance amps that increases the driver's effective Qts due to the added series resistance and since Qts dominates cab size it must be factored in for closest real world performance to T/S filter theory: Vb = 20*Vas*Qts^3.3
That said, while these vintage speakers were designed using the same driver Fs, compliance (Vas), etc., they were typically designed for a specific set of performance parameters to meet the varied needs of the app and of course for consumer apps, with rare exception the main goals were minimizing size and delivered cost to maximize profit margins, so almost all can be improved upon to a greater or lesser extent.
Bottom line, 'BIB' (bigger is better) rules when it comes to vented cab design for HIFI and 'full-range' HT speaker apps if for no other reason than it allows more in-room tuning flexibility.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
A follow up question, GM, if you don't mind.
For a system which will use subwoofers crossing over around 50hz at 24 db/oct, does the BIB suggestion still stand?
thanks
Les
Depends. Ideally you want at least an octave of ~flat BW on either side of the XO point for 2nd order (-12 dB), so two for 1st, 2/3 for 3rd and 1/2 for 4th.
At 50 Hz though, the room is dominating unless it's very large/open and the speakers are well away from any reflective boundaries, so absent any room gain curve data, a low tuned 'BIB' still rules since even more tuning flexibility is required.
With today's relatively inexpensive DSP though, you can use multiple subs spread around the room to increase sensitivity and even out room response as Dr. Geddes advocates. Once this is done you'll have a much better idea of what size/type alignment will blend best and a 50 Hz/4th order XO may not be the best choice, so just like when designing/building any vertically arrayed system be it a skyscraper or multiple driver speaker system, getting the foundation right is paramount to achieving a well integrated, high performance one since due to the way we hear, the more bass we experience, the more it affects the perceived SQ of its upper harmonics in the mids/HF.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Thanks, GM.
thanks GM.
Hi.
I used the added weight method. Yesterday I began construction of a 2 cubic foot box to try the standard box method. I'll report back later in the week.
Thanks for the replies.
Les
I had used 60 grams of weight on the cone to measure the VAS, which resulted in a VAS that was close to your results.
The instructions from Dayton did not provide guidance on the appropriate weights that should be used.
Don M
Greets!
Kind of late, I apparently didn't see your post at the time, but FWIW, you ideally want to add enough weight to lower Fs at least 1.56x [or 0.614x Fs].
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
currently don't have WT3 hooked up nor 416 Vas recorded but here's Q's of a 416-8 I tested
thanks
I built a 2 ft3 test box, and re-ran the measurements. The Vas measured between 24 and 26.8 on numerous tests in the box. The added weight number was around 21.67. So I will use 25 ft3 and get on with my box. It would appear that a 5 ft3 box tuned to 43hz is going to be my choice.
thanks for the input.
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