Unibox numbers for SS 18W/8531

[xyrium]

Can someone else run the calcs on this driver (Scanspeak 18W/8531) using a 28.5l vented box? I want to use PE boxes of either .999 ft³ (28.29l), or 1.010 ft³ (28.6l). I'm getting the feeling that these results are off.

Here's what I get using 28.5l:

Design by Vb, Fb and Q
Physical Vb 28.5 l
Absorption, Qa 80
Leakage, Ql 15
Port, Qp 80
Alpha, a 2.035
Vb 29.0 l
Fb 40.28 Hz
F3 38.02 Hz
Response peak 2.89 dB
Peak at 58.08 Hz
Port min dia. 6.82 cm
Port length 43.01 cm
Port 1. resonance 358 Hz


The parameters I used for the driver are:

Fs 28.50 Hz
Re 5.80 Ohm
Qms 5.10
Qes 0.39
Sd 150.0 cm2
Vas 59.0 l
Xmax peak 6.50 mm
(Le) 0.35 mH
(Le2) 0.00 mH
(Re2) 0.00 Ohm
Nominal Power 70.0 W

[JonMarsh]

The 8531 requires a very large box to go ported. In 28L, you're better off sealed, unless you like the bump in the FR and the higher Q (ringing!).

Also, you should not take SS T/S parameters at face value, but measure yourself - Smith and Larsen Woofer tester 2 is a good tool for that, especially to get high accuracy measurements using a PC.

http://www.woofertester.com/

[Jonasz]

Here you go: http://www.htguide.com/forum/showthread.php4?t=23892

[xyrium]

Thanks Jon. I don't mind going higher than 35Hz (as the ported designs have been reported to achieve). In fact, if ported, I would accept 45Hz. I know these are truly novice questions, so please excuse my ignorance. I was under the impression that a driver needs a fairly high Qts (above 40) to be suited for sealed. The 8531 seems to maintain numbers below that, so I was concerned. This said, it appears the system Q target is 0.707, so I'll keep that as a constant in Unibox, I just don't know if the numbers it is spitting out are accurate since I'm simply taking all of the numbers from an existing DDBase entry, and editing just the driver info in the left corner.

The goal for this project is an F3 of 50Hz along with the ultimate in sound quality.

So, guys, do these numbers look right? I ask because Zaph used a 38l for his vented design, and Unibox wants a 56-58l, which seems ridiculous, and it's recommending a 22.9l for the sealed version. Maybe I can ask Madisound to test a pair of woofs before they ship 'em to me and give me the T/S info.

Closed Box
Standard Design
Vb 20.9 l
Fb 54.40 Hz
F3 54.41 Hz
Qtc 0.707
Response peak 0.00 dB
Max power input 12.3 W

Design by Vb and Q
Physical Vb 22.3 l
Absorption, Qa 20
Leakage, Ql 30
Alpha, a 2.574
Vb 23.7 l
Fb 51.95 Hz
F3 52.48 Hz
Qtc 0.706
Response peak 0.00 dB
Peak at none

The 8531 requires a very large box to go ported. In 28L, you're better off sealed, unless you like the bump in the FR and the higher Q (ringing!).

Also, you should not take SS T/S parameters at face value, but measure yourself - Smith and Larsen Woofer tester 2 is a good tool for that, especially to get high accuracy measurements using a PC.

http://www.woofertester.com/

[xyrium]

Thanks Jonas. I had those numbers, but for some reason, I think I may be missing something else since I'm getting some interesting results. I have to find a Unibox FAQ I suppose. Thanks again!

Here you go: http://www.htguide.com/forum/showthread.php4?t=23892

[JonMarsh]

Note Curt's comments- with a Qts of 0.5, you'd normally go sealed. Going ported without a peak in the response requires a large box and tuning below driver Fs to pull off a smooth response. Somewhere at home I've got a Unibox design I worked out for 2 8531 ported, and it was ginormous. Good driver Q for ported is 0.25 to 0.35. 0.5 just isn't a typical alignment. With that Q I'd go sealed with a series cap to tune the total woofer system Q; that way you can optimize response for room placement and get by with a smaller box, too- sometimes up to 50% smaller.

I've got a couple of designs in the works using this concept. IF the 8531's weren't so bloody expensive, I'd consider them for the treatment, too!

[xyrium]

I agree, that given their expense, they become difficult for the enthusiast to build multiple projects from. However, I don't plan on doing too many of these (I know, famous last words, and the same that was said when I did Zaph's L15). So, this could be the best two way standmount available. If they could hold me over for about 5 years, I'd be ecstatic!

If Madisound says they'll agree to measure before they ship, and the numbers look good for sealed, then I'll go sealed. I'll keep you guys posted if I move forward with it. I'll take measurements using REW, and post some waterfall plots. The cabinet is most likely going to be the PE 1cu ft straight cab (the curved models are nice, but I want to easily add braces and squares are easy )