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Are large underhung designs superior ro xbl^2?


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#1 of 39 OFFLINE   Aaron Howell

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Posted December 30 2004 - 07:56 AM

First off let me say I did NOT create this post in the hopes of creating a conflict, but more so for a good debate. I made this a separate thread than Chad's so as to not junk up the thread I think Ascendant Audio deserves.

On another forum I frequent there was a statement made. There was a thread started about Chad's drivers, and this was one of the posts in that thread. This other forum does have many knowledgeable members, but the level of detail I have found on home audio forums is usually much more in depth.


This was the statement:

CBeltran
HOLD ON A MINUTE HERE BOYS!
Do not put our subs into the same category as XBL^2 subs. Our subs use a massive 6" V.C. TRUE underhung design, and leave XBL^2 drivers in the dust. They exhibit NO audible power compression for audio applications, and can handle 4kW "peak RMS" power. NO other driver in the workd can make that claim. We do not, however, have a 4 ohm version of the driver- only 8 ohms. These drivers were never indended to be put into a car, and we do NOT recommend that they be place in a car, as they would literally tear a car apart.

Visit http://www.acoupower.com for more information.

BTW, the t-s parameters are here:

15"
Sd = 0.068 m^2
Cms = 159 um/N
Vas = 103 liters
Re = 6.2 Ohms
Mms = 267.0 g
Fo = 24.4 Hz
BL = 23.3 t*m See Below
Qe = 0.469
Qm = 6.05
Qt = 0.44

18"
Sd = 108 m^2
Cms = 106.6 um/N
Vas = 174 liters
Re = 6.2 ohms
Mms = 305 g
Fo = 28.2 Hz
BL = 23.3 t*m See Below
Qe = 0.62
Qm = 8.90
Qt = 0.58

The numbers above were calculated by analysis of the impedance curve (as anyone else would do it). The actual BL is 25.0. Very large drivers do not follow the assumptions for accurate t-s data through electrical measurements.

What would make this underhung design "leave xbl^2 drivers in the dust"? Doesn't it still suffer from the same disadvantages that all underhung designs do? Does a large underhung design make the disadvantages of typical underhung motors less previlant?

#2 of 39 OFFLINE   Brian-K-Owens

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Posted December 30 2004 - 08:51 AM

This one has been fun on more than one forum!!!!

Who is to say it is not a great driver, but the claims they make as the best in the world and the $1000+ price tag just make it unreasonable to most people. . .
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#3 of 39 OFFLINE   ThomasW

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Posted December 30 2004 - 09:00 AM

For what they're charging for those drivers; I'll just take a 'few' Avalanche 18"s, and not be concerned about the XBL^2 vs underhung debate ....Posted Image

It would be interesting to see distortion plots on the acoupower drivers .... :wink:

#4 of 39 OFFLINE   Aaron Howell

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Posted December 30 2004 - 09:12 AM

This one has been fun on more than one forum!!!!


Really? Gotta link? Posted Image

I'm glued to my seat on this one. Posted Image

#5 of 39 OFFLINE   GrahamT

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Posted December 30 2004 - 09:16 AM

Quote:
For what they're charging for those drivers; I'll just take a 'few' Avalanche 18"s, and not be concerned about the XBL^2 vs underhung debate ....


Good point Thomas.

They come across as bombastic and I dont like the cut of their jib, but maybe that's just me. With statements like "they would literally tear a car apart." that is obviously not true for one, and they obviously meant that figuratively, not literally. I have read other statements by the company and they read the same, very rhetorical.

#6 of 39 OFFLINE   Allen Ross

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Posted December 30 2004 - 09:17 AM

if they can handle 4kw, i wonder what horrible SLP those things have.

also why is the Fs higher in the 18 then the 15?
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#7 of 39 OFFLINE   David_P

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Posted December 30 2004 - 09:30 AM

Quote:
also why is the Fs higher in the 18 then the 15?


stiffer, less compliant suspension, with stiffness increasing proportionally more than the moving mass, making Fs go up, not down... IIRC, the final design of the Tumult ended up with a stiffer suspension, due to concerns about the spider surviving under severe abuse, which raised Fs to 19hz just prior to the first production run.

That's my best guess...

#8 of 39 OFFLINE   MarkRoberts

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Posted December 30 2004 - 09:31 AM

They come across as full of s--- to me. The tear a car apart statement inparticular.I also think the drivers look weak.Posted Image

I think Thomas said it best.

#9 of 39 OFFLINE   Aaron Howell

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Posted December 30 2004 - 09:54 AM

My thoughts have been verified by this thread already.

I'm sure people would be a little more open to his products if he didn't make such outlandish statements. This guys needs to hire some PR soon...very soon!

#10 of 39 OFFLINE   Scott Simonian

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Posted December 30 2004 - 09:54 AM

Quote:
I think Thomas said it best.


Three or four eightteens is my kind of party!

Quote:
They exhibit NO audible power compression for audio applications, and can handle 4kW "peak RMS" power. NO other driver in the workd can make that claim.


What about the 2 year old Brahma Extreme?
Another supporter of 1080p and uncompressed multi-channel sound!

My Twin 18's. 50cuft of box, tuned to 11hz and with 2k watts on tap.

#11 of 39 OFFLINE   Shawn Solar

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Posted December 30 2004 - 10:03 AM

The term "peak rms" is enough to make me wonder. how can you have a peak AND rms is it one or the otherPosted Image

#12 of 39 OFFLINE   Scott Simonian

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Posted December 30 2004 - 10:13 AM

Hmmm. Maybe he meant that the highest the RMS is rated is 4kW? That is quite a number.
Another supporter of 1080p and uncompressed multi-channel sound!

My Twin 18's. 50cuft of box, tuned to 11hz and with 2k watts on tap.

#13 of 39 OFFLINE   Scott Simonian

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Posted December 30 2004 - 10:13 AM

Grrr. Double post. And I only hit the Submit once!
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#14 of 39 OFFLINE   DanWiggins

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Posted December 30 2004 - 04:54 PM

Few things to consider...

- Underhung motors require much longer gaps (read: more money) for the same stroke as an XBL^2 driver with the same voice coil length (same Re, Le, and mass). Typically twice as tall of a gap for the same voice coil.

- Underhungs are considerably less flux efficient (integrate less of the total flux of the system), meaning more magnet required to get a given BL (read: more money).

- Underhungs do not have as flat of a central passband.

The power handling Mr. Beltran gets from his drivers is because of the 6" diameter voice coil, not because it's an underhung.

I notice that Mr. Beltran claims 18mm one way with 100% linear BL. Assuming that means the BL doesn't drop at all over the center 36mm of stroke, there have been XBL^2 drivers on the market for 3 years with more clean, flat BL stroke than that.

And Scott, you're right - Scotty Johnson's run hundreds of 10kW bursts through each of his 9 Brahma Extremes and never burned a voice coil.

Dan Wiggins
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#15 of 39 OFFLINE   Aaron Howell

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Posted January 01 2005 - 12:46 PM

Thx for the info Dan. I know how hectic the holidays can be. Thanks for taking some time out of the holidays to respond.

I hate to link to another forum, but this debate has a much bigger thread at madisound forum.

http://www.madisound....gi?read=329657

And Happy New Year everyone. Posted Image

#16 of 39 OFFLINE   Brian-K-Owens

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Posted January 01 2005 - 02:32 PM

It is GREAT!!

I just wonder how many people who bash XBL high excursion units have ever listened to one???

I have 18 subwoofers in my house and car right now. . . 4 of them are XBL and are being used in the HT and suburban. The other 14 are in the garage in their shipping containers because I don't like listening to them after listening to the Tumults, RE XXX, and the new Avalanche. You can just listen to them and tell a differnce. . .

Brian
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#17 of 39 OFFLINE   John E Janowitz

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Posted January 02 2005 - 03:49 AM

Here is an interesting underhung design that someone I'm working with uses. www.bhivemotor.com

Like anything else it has advantages and disadvantages. The radially charged neo gives you nearly perfectly linear flux distribution throughout the gap with almost no stray flux above and below the gap. That means as long as the coil is fully within the gap, the BL curve is as close to ruler flat as possible. Yes, flatter than with XBL. With the neo being so strong, any modluation of the flux field is not an issue. With the short coil used in an underhung the inductance is kept to a minimum. The low inductance and ruler flat BL curve with virtually no modulation of the flux field means very low distortion.

The drawback is that you now have a short coil using only part of the gap. To get higher Bl product you need to increase your lenght of wire in the gap. The way to do this is increasing the VC diameter. The problem with that is the added cost of going up from a 3" to 4" coil, or even larger like the accoupower. More steel, more magnets, more expensive coil, etc. But if you want that ruler flat curve it does have it's advantages. The other problem is that power handling in the shorter coil is less than a longer coil, again giving the need for a larger diameter coil.

In an underhung design you do waste flux as you're only using a portion of the gap. However the B-hive design allows you to simply put in more magnets, making the gap taller. You are not distributing the same amount of flux over a larger gap plate. The taller the magnets, the longer the "gap" and the more Xmax. The flux always stays the same at any point in the gap because you are adding more magnets, not distributing the flux over a longer gap. That means you can take a .5" coil in a 1" gap to get about 7mm Xmax, or use the same coil, add magnets to get a 2" tall gap, and have 19mm Xmax. The BL stays the same in either application, but Xmax changes. The disadvantage is in the cost of additional magnets.

As with any other design, if you need more BL, you can also increase the magnet diameter, tighten the gap, change to different wire options, more layers, etc. It all depends on what you need for an end result.

What XBL does well is get you "close" to the flatness of an underhung design at much less cost. The B-hive motor alone will cost more than a Tumult would cost to produce. I can imagine the accoupower would be as expensive, especially with the single large piece of neo. Neither is the ultimate, "perfect" option. They are just two different ways to get to a certain result.

On a side note, the problem I see with the Acoupower is not really in the design, but in the presentation of the design by Carlos. When the coil is fully in the gap, the curve will be flatter than with a Tumult. The 6" coil will handle more power than the 3" coil in the Tumult. Their spider seems to be a nice alterntive to standard cloth spiders. Copper is great to lower inductance. Where there is room for debate is if any of these have a real world advantage over the Tumult. One thing for certain is that the Tumult, Acoupower, Bhive, some of my woofers, etc all have huge advantages over anything out there in the mainstream. That's the joy of DIY.

John

#18 of 39 OFFLINE   GrahamT

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Posted January 02 2005 - 04:25 AM

Quote:
What XBL does well is get you "close" to the flatness of an underhung design at much less cost.


Isn't that a huge plus? Say you have a underhung with 25mm Xmax (like the beehive) and a flat BL curve over that excursion. You could probably still make a XBL^2 driver with a flat BL curve over the same distance, but much more Xmax and it would still probably cost less.

I haven't seen your flat BL plans yet John but for all practical purposes (overall cost, low moving mass, cheaper smaller VC, lower inductance without copper, smallest motor depth) the XBL^2 designs seem to be the best so far.

As for power handling, that is not a big issue here in the HT area, maybe in car audio. Many of us have Tempests Shivas AV12s and 15s with 250w per. The ability of a single driver to take 4000w or whatever is not a big deal here, who has a 4000w plate amp?

I dont want to derail this thread, but have you released any details of your flat BL motors yet John?

#19 of 39 OFFLINE   John E Janowitz

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Posted January 02 2005 - 07:31 AM

Yes, that is definitely the advantage. There is no doubt a benefit to XBL as I said. Comparing a standard underhung to an XBL motor it can be seen. If you have a 1" tall gap with a short underhung coil, you can easily do an XBL type design and get more Xmax out of it. You will need a longer coil though to do this, meaning slightly higher inductance. You also have the notch giving more air gap and more flux modulation. It depends on your goals. Some people need higher Xmax, some people need the most linear they can get over that shorter distance. Just two different ways to look at things.


When you then compare something with a neo motor, you're no longer comparing apples to apples. Someone has a dual gap neo motor patented, possibly JBL, that would be a more likely comparison to the XBL. The same thing applys to having a ratio between VC length, gap thickness, and the space between the two gaps. Following the proper ratio gives you a very flat BL curve and all the other benefits of XBL. The added benefits are being fully sheilded, and a more stable flux field. Drawback is more cost.

I haven't released any details on my new motor yet. I'm waiting go get my small CNC lathe here to start production.

John

#20 of 39 OFFLINE   DanWiggins

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Posted January 02 2005 - 02:47 PM

Few corrections...

- XBL^2 motors can have ruler flat BL curves, flatter than any other out there. Look at the BL curve of the Extremis 6.8; we've done other motors with ruler-flat (less than 0.5% variance; basically at the limits of measurement resolution) BL curves. HOWEVER, you can make the tradeoff for a few percent of variance (which causes basically zero distortion) and gain excursion.

- You can use the same length voice coil and top plate as an underhung, and GAIN excursion. You do not need to use a longer voice coil. In fact, you can use a voice coil half as long as an underhung, and with the same size top plate gain excursion.

- Flux modulation isn't increased with XBL^2; in fact, it typically is reduced (and is why several pro-sound companies are either currently using or looking to use this technology). The key to flux modulation is to keep as much of the voice coil in the highest flux regions as possible; XBL^2 does just that.

- The approach used by JBL was actually patented by Hyperdynamics. It consists of two gaps with opposite-polarity flux, and two counter-wound voice coils. It's also implemented in many other drivers in the car and home audio field.

Dan Wiggins
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