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Old 30th September 2013, 04:23 PM   #11
IG81 is offline IG81  Canada
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Here are a few FF225WK plots:

Yellow: WinISD recommended QB3
Blue: Fostex recommended
Green: Fostex recommended tuned to Fs
Pink: Vb=Vas + Fb=Fs

Click the image to open in full size.

The Vb=Vas/Fb=Fs box is indeed a sort of EBS, shelved by only 1dB though. I never built an EBS in any case. It might sound bassier and bigger, but probably will have lower power handling and compromised transient response? I like the WinISD recommendation, though I'd be tempted to re-tune to Fs once again and bring it somewhere in-between the Yellow and Green traces.

Giving each combination a bit of power, 8W, it's easy to see that the 28L@39Hz handles power better and breaks Xmax noticeably lower than any of the others. Pick your area of compromise, nothing new here.

Click the image to open in full size.

I conisdered the FF125WK for a good while before deciding to try the TB W4-1320SIF instead. I kept coming back to 9L@55Hz when simulating, very close to the factory recommendation.

IG
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File Type: jpg FF225WK_exc.jpg (296.7 KB, 170 views)

Last edited by IG81; 30th September 2013 at 04:29 PM.
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Old 30th September 2013, 06:22 PM   #12
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Pretty much as expected then; 28 litres to Fs with slightly less LF damping & Vb = Vas Fb = Fs quasi EBS with less of a shelf. Right, not much new in the world of vented boxes.

Yeah, EBS alignments work for v. low tuned subs, but for other duties / higher tunings where Fb is likely to be within or near (say) the average BW used in most musical genres & I'm less than convinced.
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Old 1st October 2013, 04:30 PM   #13
Greg B is offline Greg B  United States
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Quote:
Originally Posted by Scottmoose View Post
The 83 cabinet isn't up to much as far as I'm concerned, but it's spec. isn't ideal for BR loading in any case (the slow rise will help with step-loss, but the dip between 100Hz - 200Hz & peak at Fb aren't great);
I used to have a pair of the old FE83 in factory BR. Like you, I modeled them in WinISD and was somewhat aghast at the result. However, I had an empty pair of boxes of the correct volume just sitting around. At that point, I had not tried any of the Fostex suggested alignments, and I figured it was about time.

Actually, they were quite nice. The peak was lower Q than the sims indicated, and I didn't have a dip. The slight rise at the bottom subjectively made up for their limited Fc, and overall they sounded very balanced and listenable. I concluded that Fostex knew what they were doing, and the highish Q was intended to give these tiny speakers a semblance of full sound. In my view, it works. Sure, they could be put in something that looks better on paper, but who listens to graphs...
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Old 1st October 2013, 05:39 PM   #14
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Very few people I would imagine.

Alas, my experience does not match yours, because when I heard a pair with the En units they behaved pretty much as anticipated, notwithstanding room etc. influences. Let's just say I wasn't impressed & leave it at that.
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Old 10th October 2013, 04:08 PM   #15
IG81 is offline IG81  Canada
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I was screwing around in WinISD with FF225WK once more. I never much looked at the "Port Gain" plots before. It seems like the port output Q-factor (-3dB bandwidth to peak ratio) is decent at ~0.75 on the factory box. The tuning I prefered "on paper", at Fs=44Hz, has a higher Q at ~0.9.

One thing I noticed just now, when Fb=Fs, peak port output is at Fb, as I'd rightly expect. But, as Fb is shifted away from Fs, peak output then becomes correspondingly lower or higher than you'd think based on Fb alone. This is happening in WinISD simulation, which I assume gets it fairly correct, but is it so in real-life box measurements? Can't say I ever noticed much myself, as most BR I've built so far were tuned to Fs or very close. What is the reason behind this then?

Impedance minima does not seem to be such affected, usually landing pretty much on Fb, regardless of relation to Fs, maybe unless tuned ridiculously far from it... I also wonder exactly where excursion minima and cone null line-up with all this. Seems like it's be good for me to have a sit-down with my measurement gear and the deceptively "simple" BR enclosure... First-hand experience is how I learn best.

IG

Last edited by IG81; 10th October 2013 at 04:18 PM.
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Old 10th October 2013, 04:16 PM   #16
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Not that surprising but not often noticed. Traditionally (i.e. prior to Small and also Novak's unfortunately overlooked work which pre-dated it by some years) BRs would be tuned to Fs for maximum system efficiency. Of course, what Novak, Thiele & especially Small demonstrated in terms of mathematical filter equations (and what was regularly done via simpler formulas and / or empirical testing & tuning before that) is that you don't necessarily want maximum system efficiency at Fb. Certainly not in the large / efficient boxes that were used as a matter of course until the late '60s rather than the ducted types popular since the ready availability of cheap power.

Last edited by Scottmoose; 10th October 2013 at 04:21 PM.
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Old 10th October 2013, 04:55 PM   #17
IG81 is offline IG81  Canada
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I'm guessing maximum system efficiency at Fb might have been desirable when most amps had higher output impedance and matching the load was a concern. Not so much today indeed.

I'm tempted to build that 28L box. It looks like it'd have decent tuning flexibility depending on one's taste and might even work sealed if corner-loaded, Qt~0.63, f10 in the upper 40ies. I'd probably make a few people cringe though, were I to implement the BBC-slot I've wanted to try for a long time. I'm not supposed to be building more speakers for now anyway...

IG
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Old 10th October 2013, 05:01 PM   #18
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Pretty much, although it wasn't unknown for amps of the era to have an adjustable output impedance to better match the system.
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Old 11th October 2013, 12:52 AM   #19
GM is offline GM  United States
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Quote:
Originally Posted by Scottmoose View Post
Personally I don't much like EBS style alignments except for v. low tuned subs
Have you tried a real [D.B. Keele] EBS or just a large, low tuned alignment simmed in a program?

GM
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Old 11th October 2013, 12:56 AM   #20
GM is offline GM  United States
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Quote:
Originally Posted by Scottmoose View Post
Pretty much, although it wasn't unknown for amps of the era to have an adjustable output impedance to better match the system.
Yep, up to 20-30 ohms! Put a resistor that big in series to get an idea how much mid-bass 'boost' that is.

GM
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