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Old 11th October 2013, 03:02 AM   #21
IG81 is offline IG81  Canada
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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
I think I once tried ~100R in series with a 7" ADS woofer, Fs=22Hz, Qt=0.28, driver in free air, to see if it'd make decent desktop OB bass. Sure worked, but sensitivity was abysmal. As for the same on a fullrange driver, other than being effectively current drive and boosting HF as a function of VC inductance, it seems like it made the highs tizzier or something, in quality in addition to quantity.

IG
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Old 11th October 2013, 10:23 AM   #22
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Have you tried a real [D.B. Keele] EBS or just a large, low tuned alignment simmed in a program?
I've heard some decent examples (not sure if they were following a Keele alignment, but if not, likely similar), but I get wary when EBS is combined with a lot of modern low Vas / high[ish] Fs drivers. Certainly those following stock / near-stock software sims at any rate. I'm willing to be convinced otherwise though.

Last edited by Scottmoose; 11th October 2013 at 10:35 AM.
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Old 11th October 2013, 02:34 PM   #23
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Sure worked.......it seems like it made the highs tizzier or something, in quality in addition to quantity.
Yeah, you need a SET to keep efficiency and SQ acceptable.

GM
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Old 11th October 2013, 02:45 PM   #24
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Yeah, you need a SET to keep efficiency and SQ acceptable.

GM
Only have SEP, 6GW8 spud for now. I might make the GNFB resistor adjustable if it does not screw-up square-wave peformance too much within its range. It could be handy to tailor my FF125K in a simple bass reflex, which is fairly close to the Fostex recommend enclosure BTW. I can get about 2R to 8R output Z from a reasonable range of values IIRC. It can output a good 2.25W into 8ohm, the tiny OPTs being good to 100Hz at full power. Good enough for the low levels involved with the sensitive FF125K listened to nearfield.

IG
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Old 11th October 2013, 03:09 PM   #25
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I get wary when EBS is combined with a lot of modern low Vas / high[ish] Fs drivers.
Hmm, admittedly, I've not done any with any of the abysmal efficiency, low Qms drivers now popular, so his 0.625 Qts [Qts+any resistance required] and 2.6x Vas fixed specs may very well not work well with them.

Using the 12.2P with a ~8.35 ohm series resistor if Re is around 7 ohms: Vb = ~111.88 L/27.73 Hz Fb limited to ~9 W below ~45 Hz, so can get a low vent mach with a 3" dia. x 4" long tube.

Done as a MLTL with its greater vent damping reducing its length and near/at a wall, seems like it might be worth making a POC.

GM
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Old 11th October 2013, 04:19 PM   #26
IG81 is offline IG81  Canada
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Where is it most useful to look at group delay? If tuning the same Vb at various frequencies, it's obvious that the lower tunings (still around Fs) have the most GD down low, but the least within the f10 and up passband. Is it better this way, IOW, does high GD not matter as much below the passband?

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Old 11th October 2013, 04:33 PM   #27
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Hmm, admittedly, I've not done any with any of the abysmal efficiency, low Qms drivers now popular, so his 0.625 Qts [Qts+any resistance required] and 2.6x Vas fixed specs may very well not work well with them.

Using the 12.2P with a ~8.35 ohm series resistor if Re is around 7 ohms: Vb = ~111.88 L/27.73 Hz Fb limited to ~9 W below ~45 Hz, so can get a low vent mach with a 3" dia. x 4" long tube.

Done as a MLTL with its greater vent damping reducing its length and near/at a wall, seems like it might be worth making a POC.
Ah. Now I'm liking that, especially done as a QW (just taken a look in MJK). Definitely looks worth trying (sadly no space here )
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Old 11th October 2013, 04:39 PM   #28
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It varies depending on one's hearing acuity down low, but above ~35 Hz seems to be a common response and why I like EBS-like [bass shelf] alignments as it can have as good or better group delay than sealed up where we can perceive the difference along with a bit of LF boost down where our hearing has rolled off quite a bit, so can help make the reproduction sound just that little bit extra 'full'/life-like.

GM
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Old 11th October 2013, 04:52 PM   #29
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(sadly no space here)
I know the problem well, all my extra space is taken up with misc. broken vehicles, appliances, plus building materials, tools, etc. to the point where I have to do much of my wood, etc., working outdoors, so thanks to the wettest Spring, Summer on record, haven't gotten much done beyond some exterior repairs/replacements of the last few year's repairs/replacements.

Oh well, I've fared a lot better in recent years than many locally and around the country/world, so grateful for that.

GM
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Old 17th November 2013, 10:51 PM   #30
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Well waddyaknow, I built another set of speakers. I chose the factory alignment for FF225WK that were sitting on shelves, 28L@39Hz, so though I'd post here. I did not follow the enclosure or vent dimensions though.

Boxes are built out of 12"x0.75" jointed pine, please no comments, I just wanted quick boxes and am limited in workspace/time and weather this time of year. Before a bit of bracing and wall lining, these rang as if made of metal, you really gotta hear this. I was actually shooting for a 44Hz tuning, but it ended a bit lower and I kept it like that so far. I mostly wanted woofer boxes to use under the petal tractix horns I'm running on top. The info is still relevant for use for FR duty.

I quite like these boxes. First try was way more out in the room than shown below, FF225WK run fullrange, it sounded real thin. There was no BSC then. I'm using miniDSP crossover and set it for 800Hz for the Emilar driver on the 700Hz horn. I use (IIRC) 4dB of BSC and with better placement, bass is quite good IMO. It's really damped and dry, which works in my small room, I have something similar going on my larger TD15M boxes. The shallow roll-off digs deep, if in a tamed way. Sound very "hi-fi".

Click the image to open in full size.

Click the image to open in full size.

IG
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