vann_d's 4 x FicarIB318 build - Page 4 - Home Theater Forum and Systems -

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post #31 of 37 Old 06-12-13, 07:57 AM
Steve Bishop
Join Date: Mar 2013
Location: Louisville, Ky
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Re: vann_d's 4 x FicarIB318 build

vann_d wrote: View Post
Thanks a bunch!

Well, I guess for the reason that I didn't think to. Would the correct method be to invert one and also wire out of phase? (i.e. drivers firing out of phase but cone motion/vibration cancelling) I put them "opposed" to help cancel vibration. Inverting one would require the out-of-phase wiring to accomplish the same.

Now, I skimmed the thread you posted and it appears that yes, I should have them wired out-of-phase if I chose that alignment.

The difficulty for me would be related to installation. I would need to exchange my wood screws for threaded fasteners and inserts. Not sure if I have the real estate for that. Also, man-handling the sub into place would be difficult!

Edit: I guess I could still mount from the outside of the "plenum". Maybe I'll have to try it and see if I can measure differences...
The general IB consensus seems to be to wire them in phase and let the mechanical forces cancel. I don't think there is anything to really gain and I imagine you'll reduce your output. You could invert one and then wire it out of phase, but -(-1) = 1, I believe it'll equate to what you have now.

I don't know if you have an IB history or not, I certainly did not, and you're running them quite hot (I am running mine quite hot as well), I think this comes from years of hearing boxed subs and it's hard to not want to detect the LFE presence we are used to.

My biggest frustration is that there is big difference between a Bluray LFE channel and typical cable low frequency redirect that wants me to have different sub level settings between the sources.
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post #32 of 37 Old 06-12-13, 07:53 PM
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I completely agree, I have 3 different sun settings on my pro audio amps and have them labeled for blu-ray, TV, and Music. It's just a dial change but it is still annoying. My receiver does not have a way to adjust the LFE based in input.
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post #33 of 37 Old 06-14-13, 01:09 PM
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Re: vann_d's 4 x FicarIB318 build

A push-pull approach does possess measurable distortion lowering advantages in small sealed subs, and especially IB subwoofer systems.

As one can imagine, and similar to most all things subwoofer related ... there's much myth and misunderstanding about such techniques. Take any normal, double-driver, small sealed sub, ie., the monster JTR Captivator S2;

Obviously, both cones work together to create waves of bass. The cones are both mechanically in phase, and electrically in phase. To implement a push-pull approach, flip one driver around backwards, and flip it's polarity too. As one can see, the drivers are still working in concert with one another, and it's sensitivity and maximum output haven't changed at all.

What has changed is the manner in which the driver's acoustic energy sums together. The result is odd ordered harmonics are cancelled out. Magnetically, there exists a small asymmetry between the forward stroke, and the rearward stroke of the cone. Designers try to keep this as small as possible, but it's just a product of the magnetic motor/voice coil approach of dynamic drivers.

Essentially, any anomalies in the driver's cone, surround or spider, or magnetic properties through the stroke, are simply canceled out by the flipped driver's opposite characteristics.

Since the coil is moving, and the permanent magnetic element isn't, there's some non-linearities over the course of the stroke. The specifics are beyond the scope here, but combining the even ordered nonsymmetrical non-linearities (including the aerodynamic of the structure/basket, the spider, surround), then entirely nulling them by flipping one driver's orientation and polarity, is a distortion lowering technique that has merit.

The odd ordered harmonics remain, yet the even ordered are lowered. A small sealed, like the JTR CapS2, benefits, however the air volume loads the drivers, and although there's benefits, they're somewhat lessened. That said, conversely ... an IB subwoofer system utilizing a push pull approach fully benefits from this technique. The drivers need to be relatively close to one another, but given the sizable wavelengths being produced, typically this isn't an issue.

Now, why don't more mfrs make their subs this way? It's difficult to implement the reversed driver. Also, although THD is lowered, the remaining odd ordered harmonics are oftentimes the most objectionable subjectively, the even being somewhat more tolerable. THD is lowered in push pull, period. Some of the finest studio monitoring systems in the world, the TAD based Kinoshita systems (Rey Audio), can be upgraded with their sub system, which is push-pull. They've been offering 9hz extension playback since '91.

some Kinoshitas demoed, for sale. They use TAD drivers, if you've never had the pleasure to experience TAD, they're superb.

I hope this helps

btw ... found a push-pull pro audio, vented sub by EAW;

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post #34 of 37 Old 06-14-13, 03:10 PM
Steve Bishop
Join Date: Mar 2013
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Re: vann_d's 4 x FicarIB318 build


Good thing you're everywhere.

Even with those improvements, in real world practice, do you think it is more commonplace that said improvements would overshadowed by the increased mechanical transference? Maybe I just need to flip the phase on a couple of drivers and see what mechanical impact is has. Perhaps I'm assuming it to be more than it really is?
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post #35 of 37 Old 06-14-13, 04:09 PM
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Re: vann_d's 4 x FicarIB318 build

The advantages of the dual opposed mounting method are retained, that doesn't change.

It's as if the baskets flip,...and that's it.

Perhaps I misunderstand.
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post #36 of 37 Old 06-15-13, 02:09 AM Thread Starter
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Re: vann_d's 4 x FicarIB318 build

I understand the phenomenon now, I believe. My system is operating, in general, well below its mechanical or electrical limits. That is the path that I chose to low distortion. It is, however, an interesting experiment and I will see if I can measure differences at the LP. Now, just need to get time to do it.

Is it too selfish to ask for a measurement session on Father's Day?

Scuba: concept is flip driver and reverse polarity. Mechanical cancellation is retained. Non-linearity due to magnetic / electrical differences on either side of voice coil are somewhat cancelled. (My interpretation)
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post #37 of 37 Old 06-20-13, 08:47 AM
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Re: vann_d's 4 x FicarIB318 build

Absolutely fantastic looking room. I love it and now I want to go to denver and listen to an IB system.

Great work man. I am impressed
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