Are large underhung designs superior ro xbl^2? (1 Viewer)

[John E Janowitz]

Theoretically you can get a perfectly flat BL curve with XBL, but there are more factors involved that lead to variances. Tolerances in machining the notch in the gap plate and pole and tolerances within the windings of the VC can play a part. You also need perfectly symetric flux in the fringe field above and below the gap.

Out of curiosity, taking a 2" tall gap and a coil of .6" tall like the TC underhung design, how can you get more Xmax with XBL? You need to stick with a proper ratio of coil lenght vs gap height vs notch height to get a very flat curve. The only way to apparently get more Xmax if you don't stick to a useful ratio is to remove BL at the top of the curve by cutting the notches in the gap plate and pole. Xmax only increases because BL at rest is decreased.

The only time you will not have flux modulation is when the field is completely saturated. In the air gap you have much lower flux density than you do in the steel. Cutting a notch in the gap and pole gives more air, with less flux density.

As you said, the key to flux modulation is to keep as much of the VC in the highest flux regions. In an underhung, ALL of the coil is in the highest flux region. With XBL you have a low flux region in the middle of the gap where a large portion of the coil sits.

John

 

[DanWiggins]

John,

ALL drivers rely on symmetric fringe fields for performance. Simply extend or shorten the pole as needed. Real easy to do, and a very commonly done thing in overhungs and evenhungs. Those who have been doing driver design for several years do this as a matter-of-fact, checklist item when designing drivers. It's nothing new needed for XBL^2.

Alignment of the cuts isn't a problem at all - it's all in the machining of the parts which is a very simple task (vertical alignment of a few hundredths of an inch are all that's needed, and that's a MASSIVELY wide tolerance). Magnets, stampings, forgings are all easily controlled well within this tolerance range with no special effort at all. In fact, machinists are always shocked a just how LOOSE the tolerances can be (and in fact a tolerance study will show that XBL^2 is LESS sensitive to these tolerances than overhungs or underhungs).

Winding of the voice coil is also about the most consistent thing done in a driver - exact number of turns put on is VERY simple and highly repeatable. Coils get wound the same way, same length, thousands of times over. Large-volume testing of DCR of voice coils will show this is a VERY highly accurate, repeatable process. In fact, you get much more variance from the tinsel leads than you do from the voice coils.

Bottom line about assembly: XBL^2 really only needs tighter tolerances where it's easy to do - voice coil length. In the expensive/tough steps of tolerancing (voice coil centering and gap matching), it's much LESS sensitive than any other topology.

For the TC underhung, it's simple. Use multiple gaps. You know our technology can (and actually does in one driver) allow and use more than two gaps. In the case of the TC Sounds unit, four gaps would work well, and would allow around 1.2" one way of linear throw (about 70% more than the underhung). Many people really never read the patent, nor really understand how it works and so they overlook the fact that one can have two or MORE gaps for extended throw (we even have drawings showing a 3 gap driver).

You'll have flux modulation any time you put power through the voice coil. Saturation or no - it's about the magnetic field of the voice coil, not the magnet! ALL drivers - regardless of flux density in the gap - will have flux modulation.

The degree of modulation is inversely proportional to the flux in the gap, and this is where drivers with focused/shorter gaps (such as short gap overhungs, or XBL^2) excel - they increase the flux density of the system. Using the same magnets, you'll have a LOT lower flux density in the typical underhung driver, rather than an overhung or XBL^2.

Dan Wiggins
Adire Audio

 

[Greg Monfort]

Greets!

Playing the Devil's Advocate , this 'debate' begs the Q: how do these 'best of the best' point source motor designs compare performance wise with a servo driven system such as the SD Contrabass and the vastly more acoustically efficient, zero degree phase optimum basshorn?

GM

 

[DanWiggins]

Ask Mark Seaton what what he thinks... Put one of these flat BL, low THD, high excursion drivers in a bass horn and you can have a LOT of fun!

Dan Wiggins
Adire Audio

 

[Steven Kephart]

GrahamT

What's really funny is that we have a video on our site of the Brahma's literally doing this in Scottie Johnson's van.

Steven Kephart
Adire Audio

 

[Greg Monfort]

I have no doubt, but it side steps the Q. Not having auditioned any xbl^2 drivers, I'm inclined from just reading that they still have more audible distortion than the CB or horn since I haven't read any review of an xbl^2 system where they thought its output was 'dry' or 'sterile', which is a common remark from folks not familiar with what truly low distortion bass sounds like.

GM

 

[Kyle Richardson]

That surprises me because when the XBL drivers first came out it was a fairly common response. I still get similar remarks back from owners that are listening to them for the first time.

 

[Brian Tatnall]

I know the 'dry' comment is one often used to describe Brahmas.

 

[Rob Bird]

I'd like to see that video...where is it located? I didn't see it in the installs area.
Thanks,
Rob

 

[Brian Tatnall]

http://www.adireaudio.com/Files/Scot...akingDoors.wmv

 

[Paul Spencer]

Greg, I have seen a comparison of the Servodrive with a number of other subs including Adire Sadhara, Velodyne and Genelec. It's found here:

part one
part two
part three

The Servo drive wasn't as impressive as I thought it might be, although one interesting feature is its distortion has a sweet spot ... ie it gets lower as you turn it up to a point.

I asked Adire about the performance of their Sadhara, which was not as good as expected, and they commented that the unit they used was damaged and had a rattle, IIRC.

I think they didn't give fair consideration to Adire's sub.

The discussion here is a bit theoretical for most of us as the cost of these drivers is so high. Anything more expensive than the Tumult is a bit much!

I've heard a setup with the Tumult, well set up and calibrated with Behringer Ultracurve AND Ultradrive! The bass was very deep and powerful and clean. There were 5 subs in total (3 x M&K, 1x Focal 15" audiom) so they were all idling while producing high SPL down low. Best bass I have heard.

My system has a pair of AV12s (still in test boxes, one vented one sealed) and I'm calibrating with Ultracurve DEQ2496. I have had difficulty getting it calibrated correctly, but when I have got it sounding right, I find they are very clean. They reach 105db at my listening position while idling away - this is the practical limit of my main speakers, even though my subs can hit 118db (vented) within 70% of xmax at limit of power from my amp. At typical levels, I'm not so sure the difference between this and the Tumult is as much as many would think.

Still, when I'm ready to upgrade, I have my eyes on Tumult, Avalanche and in particular whatever John comes up with as everything from AE speakers is extremely competitive in terms of price and performance. And nothing is quite as stylish as a brushed aluminium cone with inverted dustcap!

 

[Robert_Gaither]

Personally I think Carlos is full of it since he states that his driver is too powerful for car audio (this is where most of the "just woofer" sales go for this market) as car audio will push the drivers to an extreme that no pro-audio would. He obviously never been to an Iasca event as not all car audio is about just being loud but clean as well. I would like someone to setup a little shoot out to see how his woofer really would fair from a "sound" perspective and not just "my woofer can take more power than yours". I believe he may have a product that most likely will sound great but he came off like a Bose commercial, all claims and no proof. If he intends to tell us we should wait for his product to come out before we judge then I'd like for him to have a product out that can be judged right next to a Tumult (is there anyone with a Tumult based sub in his area so a direct comparison can be made?), after all he made the claim it'd leave it in the dust...

 

[Paul Spencer]

The power handling of those subs is extremly high, I question if this is in fact necessary. There may be a "so what" factor here. It's great to have extra power handling, and to have low power compression, but the excursion is less than the tumult. What they wrote on their site tends to indicate they aren't designed for very small boxes. This would suggest they probably don't need all that power, but this comes down to a question of use as well. If you are using it for music and don't want to get down to 20 Hz, then all that extra power might come in handy.

 

[Robert_Gaither]

These are some of the things I'm wondering about as well I see more 1000w amps in cars than I've ever seen in the home environment. Higher power requirement, lower excursion, higher price (both woofer, amp, and electrician for the outlet), and larger box requirement makes me wonder why this should be purchased instead of one or more Tumults or multiple Avalanches, multiple Tempests, multiple Daytons, or multiple IB 15s from Stryke in an IB configuration. I want to know what is the advantage of going with this woofer vs the above (Bandpass sub? please...)?

 

[Paul Spencer]

One thing to keep in mind is that for music, very high end excursion drivers tend to run out of thermal power before they run out of excursion. The excursion is needed for first octave bass. Hence if you have extra thermal power, then the driver can handle the power that will get the cone moving in the midbass. Hence this sub with much less excursion than the Tumult *might* have more output for music if you look into it.

I learnt this when I hooked up my AV12s to a PA amp with 450w. The amp started clipping yet the driver had loads of excursion to spare. Yet I would have liked more output at the time.

 

[HowardLi]

The B-Hive motor seems like a copy of the Aurasound NRT motor. Hell, they even have 1808 in the name.

 

[John E Janowitz]

The B-hive does have similarities to the NRT. It has some significant differences as well though. That set it apart from the Aura patent. The 1808 name comes from the fact that it is an 18" woofer with an 8ohm impedance.

John

 

[Andrew S-]

Keep in mind that enclosure plays a huge role in excursion and output. All it takes is a larger enclosure to get you moving a bit more. Dont know why he talks about getting the cone moving in the midbass. It just isnt needed like the lower octave. For each octave you go up it takes 1/4 the throw to achieve the same ouput. Sure his sub might be louder than the tumult when you give it more power in the mid/high range of its bandwidth. But what happens when you hit a low note? Thwap!

What about the Le of that big coil? Remember, transient response relies on inductance. Good luck with such a huge coil.

 

[Jasen Chandler]

While I welcome yet another super-woofer choice, at the end of they day "bang for the buck" is what matters to most DIYers. The shiva was a perfect example of this. I pose this question:

Wouldn't you rather have 2 tumults as opposed to 1 acoupower?

I know I would.