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Old 13th August 2012, 12:50 PM   #1621
NEO Dan is offline NEO Dan  United States
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Quote:
Originally Posted by AndrewT View Post
What are you calculating?
nothing of any use... lack of sleep I guess

At any rate djk has the scoop and so the coil length would need to be ~29.5mm long to get to 11mm x-max. The slice of magnet is 25mm thick, that driver better have a HUGE bump on the backplate... I doubt that it does, and I doubt that the coils is that long... It's probably like my bad math example above

The new Faital 15HP1030 can push itself to x-dammage, I gave one a good whack the other day, oops , it's alive and well though.
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Old 13th August 2012, 01:08 PM   #1622
djk is offline djk
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"Lies and damn lies seems little different from disreputable manufacturers' claims when it comes to audio product. "

Sure, if you say so.

You totally don't understand the 70% Bl specification.

The newer JBL models with the 12.7mm top plates have very low x-max by your method, but lay waste to the older models with the 8.1mm top plates.

The 70% Bl estimation with the the gap height/4 method also correlates well with how it sounds in practice.

Whatever.
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Last edited by djk; 13th August 2012 at 01:12 PM.
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Old 13th August 2012, 03:43 PM   #1623
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I wanted to thank jbell and jwmbro for great advice in adapting the ss15 into a 12" driver, slimmed down version:

~50 lb tapped horn, woofer under $100, high efficiency, low power?

I'm usually a big advocate of time correction of bass, but it looks like I won't have time correction in the system I'm currently thinking of for this, a portable PA using a class-d car amp. Can you get away without time correction here? I found the group delay sim earlier in the thread, see below. Figure that the mains are bass reflex with a high tuning (some group delay already), and active crossover at 80 to 100 hz which could be tuned for an overlap or gap, plus a parametric EQ. Do you think the integration will be pretty clean without time correction, assuming physical alignment? Thanks!

As a side note, has anyone run FIR room correction on a horn sub...?

TH-18 Flat to 35hz! (Xoc1's design)

Click the image to open in full size.
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Old 13th August 2012, 08:05 PM   #1624
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by djk View Post
You totally don't understand the 70% Bl specification.
Obviously I don't understand.
I didn't know it existed, nor did I see a need to corrupt the Xmax definition.
Your explanation has helped in drawing my attention to some new standard. Does someone want to take the time to refer me to a paper or other documentation that shows what the new dimension does for us and why we need to know it?

Now it looks like there is a new definition of stroke/travel that is bigger than Xmax but which lies within a tolerable limit.

What do you call that new stroke dimension?
It can't be Xmax. It must have some other non ambiguous title.
Does it incorporate the 70 that you have mentioned?
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Last edited by AndrewT; 13th August 2012 at 08:07 PM.
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Old 14th August 2012, 03:58 AM   #1625
Djim is offline Djim  Netherlands
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Hi Andrew,

I think what Djk meant is that the BL value drops as soon displacement starts.


However, Klippel proved there is no simple relation between BL and Xmax. He also showed there is no simple relation between harmonic distortion and Xmax either. In reality this means, even when Xmax is reached it does not guarantee that the excursion is really effective in 'usable' dB's. On the other hand there are also manufacturers that produce drivers with an Xmax that can be exceeded far beyond and still having large amounts of linear displacement in the right enclosures.


Xmax figures are usually food for misconceptions. Each driver has its own specific properties and each driver responds different to their load. Therefore is Xmax nothing more than an indication. Knowing the brand and its reputation and knowing the way they measure Xmax usually helps to expect what might happen. Measuring the real thing (in dB’s instead of mm) is the only guarantee.
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Old 15th August 2012, 03:47 AM   #1626
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For all you aus speaker builders, what do you think of building with form ply? I was planning to use 18mm form ply if i could get away with it. Its dense and laminated each side.
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Old 15th August 2012, 10:38 AM   #1627
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If you are referri.g to the fir plywood that has kraft paper bonded to two faces then go for it. It's good stuff. Used lots of it.
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Old 15th August 2012, 11:49 AM   #1628
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Quote:
Originally Posted by mwmkravchenko View Post
If you are referri.g to the fir plywood that has kraft paper bonded to two faces then go for it. It's good stuff. Used lots of it.
Im not sure If it is the same thing, but if it is then that's good news. Here in AUS its $80 for 2.4m X 1.2m sheet, compared to marine ply (next best aus thing to baltic birch) is $190+ for the same sized sheet. I thought the fact that its laminated may help reflecting sound through the box a bit better and may also help resonances due to probably being inferior to marine ply (maybe).
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Old 15th August 2012, 11:55 AM   #1629
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I'm guessing it is the same thing. Concrete is pretty much the same thing no matter where you work with it. The plywood is pretty much void free.

Keep in mind I have built with OSB (strand board) and cheaper poplar industrial plywoods with good effect. Keep your box well braced and you will do fine with most sheet goods.

The stiffer the box the higher the efficiency.
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Old 15th August 2012, 12:05 PM   #1630
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Well I figured being thicker at 18mm thick should help and will also do a lot of bracing too.
Four JB1500 drivers and a crown ITX4002 have been ordered :-)

Last edited by reminence; 15th August 2012 at 12:07 PM.
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